Table of contents

Metal forming is a crucial and irreplaceable manufacturing technology, since it can efficiently produce components with micro-nano size, large size, complex structure and excellent performances used in the fields of aerospace, automotive, nuclear, ocean engineering, etc. Metal forming involves in the variation of geometrical shape and microstructure under the interactions of force, thermal, electric and magnetic, and the realization of coordinated control of shape and property is the widespread goal of metal forming. With the rapid development of modern society, light-weight, short process, extreme forming, green forming, and intelligent control have become the primary keywords of metal forming. Hence, developing new forming processes or innovating the traditional processes always attract the interests of scientists, academics and engineers. The International Conference on Metal Forming exactly provides a very good academic platform for the researchers throughout the world to share and communicate their latest findings in metal forming.

The International Conference on Metal Forming was founded by AGH University of Science and Technology, Poland, in 1974. From 1994 to 2010, the Conference was organized every two years, jointly with University of Birmingham, UK. In 2010, University of Birmingham was replaced by Toyohashi University of Technology, Japan, and the Conference went to Japan for the first time. Metal forming 2012 was organized by AGH University of Science and Technology, together with Toyohashi University of Technology and University of Palermo, Italy. Metal forming 2014 and 2016 were respectively held by University of Palermo and AGH University of Science and Technology, whereas the Conference was organized by Toyohashi University of Technology in 2018 and came back to AGH University of Science and Technology in 2020. This year, the 19^th International Conference on Metal Forming (Metal Forming 2022) was held online through a combination of live and video streaming due to the impact of global COVID-19 on September 11-14 by the China Society for Technology of Plasticity, CMES, P.R. China.

The conference papers of the 19^th International Conference on Metal Forming are collected in this issue. During the conference, 293 papers (including abstracts) were submitted by authors representing universities, research institutes and industry from 16 countries, and 124 papers are included in the issue of IOP Conference Series: Materials Science and Engineering. In terms of the research objects, materials such as steel, aluminium alloys and titanium alloys are still the focus, while materials such as high-temperature alloys and hard-to-deform alloys have received significantly more attention as well, and the theoretical research on material property, microstructure evolution, mechanical analysis of deformation processes and constitutive modeling have been continuously improved. In terms of forming processes, traditional forming processes such as forging, extrusion, stamping, rolling, etc. have been further developed in terms of deformation theory and process optimization, and the research on special forming technologies such as electromagnetic forming, ultrasonic vibration-assisted forming, flexible incremental forming, micro-forming, and laser forming, etc. have become more mature. With the continuous optimization and innovation of materials and forming processes, as well as the accuracy, reliability, and automation & intelligent development of forming equipment, the forming of many complex components with demanding requirements on precision, performance, and service environment has become increasingly possible.

List of Steering Committee, Scientific Committee, Conference Chairs, Local Organizing Committee, Chief Editors are available in this Pdf.

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• Number of submissions received:166

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• Number of submissions accepted:124

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In situ EBSD investigations were conducted to polycrystalline NiTi alloy during tensile deformation to study the variation selection of martensitic transformation and its effect on pseudoelasticity. Experiments show that more than one martensite variants are formed in most grains, and the directions of traces for some variants are close to the direction of macroscopic Lüders band. Then the Schmid factors of activated variants in each grain were calculated, the results show that Schmid factors of activated shear systems can be divided into three categories, I: maximum Schmid factor; II: sub-maximum Schmid; III: small Schmid factor. The appearance of the latter two categories is mainly influenced by constraints of neighboring grains and variety of local stress state caused by Lüders band. And the Schmid factors of residual martensites belong to the third category. It is mainly because dislocations are easily introduced at the front of the Lüders band during the transformation process, which decrease the order degree of B2 phase and increase the difficulty of reverse phase transformation, and the sample shows poor pseudoelasticity.

Multi-stage sheet forming is an encouraging technique to obtain complex geometries by change of the design of intermediate stages. Due to the occurrence of stepped feature during multi-stage forming, the final geometry shape is affected and the formability is deteriorated. To eliminate fracture and enhance formability, ultrasonic assistance is integrated with the multi-stage sheet forming process. The present work aims to investigate the effect of ultrasonic-vibrations (UV) on formability and thickness evolution using two multi-stage strategies through experiments. A frequency of 29 kHz and an amplitude of 10 μm are taken for the ultrasonic-assisted incremental forming process. Firstly, two distinct strategies are compared by experiments. Secondly, thorough investigation of formability experiments is performed by applying the UV at only one or two stages instead of the complete multi-stage forming process. The results show that formability of the part is increased while applying UV at intermediate stages. Similarly, it is confirmed that UV is more advantageous during latter stage of experiment. This work provides an effective strategy to improve the formability of the incremental sheet forming process by using the ultrasonic vibrations in a smart way.

Alloy structural steels with good fatigue and mechanical properties are widely used in transmission parts of industrial fields. However, alloy structural steels are difficult to deform at room temperature due to the low ductility and large deformation resistance. Current-assisted flow spinning (CAFS) is one of the most promising methods for manufacturing cup-shaped parts made of difficult-to-deform metals. The current assisted plane strain compression (CAPSC) test was proposed as the physical simulation test for CAFS, and the air cooling method was used to eliminate the effect of Joule heat. The CAPSC tests and the FE simulations of 30CrMnSiA were carried out, and the influences of peak current density and duty ratio on flow behavior were analysed. The results show that the constructed CAPSC test setup can be used to avoid the generation of the Joule heat effectively. The flow stress under pulse current is lower than that of without pulse current, and decreases gradually with the increasing of duty ratio and peak current density; the strain hardening exponent under pulse current is higher than that of without pulse current, and increases with the increasing of duty ratio and peak current density.

Solution treatment was carried on a post-deformed GH4586 superalloy in the solution temperature range of 1020°C to 1100°C and solution time of 2 h and 4 h. The results showed that the static recrystallization (SRX) occurred due to the residual distortion energy caused by high temperature deformation. With increasing solution temperature from 1020°C to 1100°C, the average grain size of γ matrix firstly decreased and then increased. With increasing solution time from 2 h to 4 h, the average grain size of γ matrix gradually increased from 24.2±3.2 μm to 30.9±3.8 μm. Grain boundaries and twinning boundaries are the main nucleated site for SRX. And when solution treated at 1020°C for 2 h, carbides can also become the preferential nucleation position. In addition, by analysing the relative deviation (v/v_m) distributions of Σ3 boundaries, it could be found that the higher solution temperature would lead to the increasing fraction of coherent Σ3 boundaries and the decreasing fraction of incoherent ones. Besides, the annealing twins nucleated and grew gradually during the migration of recrystallized grain boundaries, and their length fraction increased from 10.0% to 54.9% with increasing solution temperature.

Aluminum alloy double-wall gap tube is prone to wrinke in the rotary draw bending because the rigidity of the inner and outer tubes of the thin-walled structure is low, the mechanical properties between the tubes and the polymer filling medium are different greatly, and the bending forming is a complex nonlinear process of multi-mold coordination and multifactor coupling. While the process parameters are the main factors that affect the wrinkling of inner and outer tube, there are many process parameters and there are interactions among them. Therefore, based on the platform of ABAQUS/Explicit, elastic-plastic 3D-FE model of double-wall gap tube's bending is established to study the influence mechanism of process parameters on the wrinkling aluminum alloy double-wall gap tube in rotary draw bending. The results show that the clearance between mandrel and inner tube, clearance between pressure die and outer tube, the anti-wrinkle die and the outer tube have significant effects on the wrinkling of the inner tube. The clearance between inner tube and core die, filling medium and inner tube and clearance between anti-wrinkle die and outer tube have significant effects on the wrinkling of inner tube. The wrinkling of the outer tube is more obvious than that of the inner tube. The results can provide a theoretical basis for optimizing the process parameters to suppress the wrinkling of aluminum alloy double-wall gap tube in the rotary-draw bending.

The neck development for bore expansion problem is analyzed. Static implicit calculations are carried out for the A2219 Aluminium alloy sheet using ABAQUS/Standard. The equations to give the conditions of the onset of the localized necking of sheet metal based on the general bifurcation theory are presented for plane stress. Since accurate calculation of stresses and strains are the basis for the necking prediction, both associated and non-associated flow rule are adopted in the material model in which Hill's quadratic functions are used. User defined subroutine UMAT is developed using a fully implicit integration scheme. The results of necking prediction show that necking occurrence delays for the Hill solid using both AFR and NAFR based model compared with Mises solid and necking occurrence slightly delays for the Hill solid using AFR based model compared with Hill solid using NAFR based model. Initial necking occurs when equivalent plastic strain is respectively 0.33, 0.39 and 0.348 for the Mises solid and Hill solids using AFR and NAFR based models. Theses indicate that the material model has significant influence on the accuracy of necking prediction.

The wrinkling behavior of the ultra-thin components during the tube hydro-pressing process was investigated by finite element analysis and confirmed by hydro-pressing experiment and the causes of various typical defects were explored. There are three typical wrinkle defects appearing on the part during the tube hydro-pressing process: transverse wrinkles, longitudinal wrinkles and oblique wrinkles. The transverse wrinkles are mainly caused by compressive stress perpendicular to wrinkles. The longitudinal wrinkles are mainly caused by tensile stress parallel to wrinkles. While, the oblique wrinkles are mainly due to shear stress.

Unified constitutive equations have been developed in recent years to predict viscoplastic flow and microstructural evolution of metal alloys for metal forming applications. These equations can be implemented into commercial FE code, such as ABAQUS and PAMSTAMP, to predict mechanical and physical properties of materials in a wide range of metal forming processes. These equations are normally stiff and need significant computer CPU time to solve. In this research, a series of numerical analyses are performed to investigate the difficulties within MATLAB of solving these stiff unified constitutive equations. A metric is introduced to allow evaluation of the numerical stiffness to assess the most appropriate numerical integration method. This metric is based on the ratio of maximum to minimum eigenvalue. This metric allows for an appropriate numerical method to be chosen giving more effective modelling of deformation and plasticity processes. Based on the theoretical work described above, a user-friendly system, based on MATLAB, is then developed for numerically integrating these types of stiff constitutive equations. This is particularly useful for metal forming engineers and researchers who need an effective computational tool to determine constitutive properties well based on numerical integration theories.

Given the significant difference in the properties of the two metals, the rolled composite has a severe problem of uncoordinated deformation and low bond strength. The effect of the same diameter and different diameters of the rolls and single roll drive on the composite plate's coordinated deformation and bond strength is investigated. Simulation modeling employs finite element (FE) secondary development, and the plate warpage mechanism is analyzed by combining synchronous and asynchronous rolling experiments. The aluminum side is subjected to compressive stresses in the rolling direction during the rolling process. The steel side is subjected to tensile stresses in the rolling direction. The roll diameter in contact with the aluminum plate is reduced, the rolling pressure is distributed more evenly along the vertical plate section direction, improving deformation coordination. The side of the roll that touches the aluminum is driven, and the bimetal starts to bond closer to the exit of the roll. The frictional stresses and bending moments between the bimetallic interface are smaller, resulting in better deformation coordination and higher bond strength.

With the rapid development of metaverse and intelligent manufacturing, the requirement for the digitization of the traditional manufacturing process is a challenging task for industries. Roll forming is a highly efficient sheet metal forming process which can be widely been applied in a wide range of sectors, such as automotive, transportation, building other key sectors. However, this forming process is highly dependent on the experience of the on-site engineers. This paper presents a highly intelligent, flexible and self-adaption roll forming machine co-developed by the University of Electronic Science and Technology of China and data M. The machine consists of several flexible moving units controlled by codded stepper motors with a decent control system. Moreover, a high-performing artificial intelligence algorithm achieved from a systematic machine learning training process is integrated into this machine. The algorithm has already been use to predict and control the forming process to achieve a high-quality product. Data collection on a large scale and integrated sensors lead to an increased understanding of the process and provide the basis to develop self-optimizing roll forming machines, increasing the productivity, quality and predictability of the roll forming process. The application of digital twin and machine learning techniques is used to predict and reduce the amount of springback in the product. The first high-strength steel parts successfully manufactured with this new forming concept are presented.

The conical rotary part with variable wall thickness is a typical aircraft engine sheet metal casing, which requires high forming quality. In this paper, the hot power spinning process of conical rotary part with continuously variable wall thickness of superalloy GH4169 was simulated by DEFORM-3D FE (finite element) software. The equivalent stress, equivalent strain and temperature distribution characteristics were analysed to explore the forming mechanism. The single factor variable method was used to explore the influence of three process parameters, namely, the mandrel speed, the roller feed ratio and the spinning temperature, on the forming quality. The wall thickness deviation and the roundness error of the cone outer surface were taken as the evaluation indexes. Excessive thinning rate will produce large equivalent strain, which may lead to work piece fracture. Therefore, appropriate roller feed ratio should be selected to reduce the generation of defects. The results provide a theoretical basis for improving the service life of aero-engine sheet metal casing.

Shaft and pipe parts are an important steel product. Due to various factors, their straightness often exceeds the standard, which seriously affects their performance and life. In view of the limitations of the existing straightening processes, this paper proposes a rotating bending straightening process. The two ends of the workpiece are clamped by the fixtures, and the bending and rotation are realized by controlling the movement of the fixtures. In the process, the workpieces undergo multiple reciprocating bending and is finally straightened. The feasibility of the process is verified by numerical simulation and experiments. The deflection of the shaft with an initial deflection of 1 mm is less than 0.1 mm after straightening. This process can improve the straightening efficiency and accuracy, and is suitable for mass straightening.

The B-pillar is one critical structural component pertinent to automobile safety under side impact. Local reinforcement is an effective approach to enhance the energy absorption capability of the B-pillar without causing excessive deformation. In this paper, impact simulation of a B-pillar part was carried out with five different strength distribution schemes, including all low strength, all high strength, upper 1/3 reinforced, upper 2/3 reinforced, and rounded corners reinforced. The amount of deformation, the absorbed energy, and the stress distribution over the B-pillar were analyzed. It is observed that local reinforcement effectively reduced the deformation of B-pillar under impact while maintaining sufficient energy absorption ability.

Laser peen forming technology LPF is proposed on the basis of laser peen strengthening technology and mechanical peen forming technology. It is an advanced high-efficiency and long-life manufacturing technology for panels. This forming technology has a wide application prospect in the field of aerospace manufacturing. In the forming process, there are many factors affecting the forming process, such as laser pulse energy, shot peening times, shot peening path, material, structure and so on. At present, there are few studies on the influence of laser peen forming process parameters on the shape of parts, which can not meet the technical requirements of forming process. In this paper, based on the single curvature bending forming of al2024-T351 aluminum alloy, the elastic-plastic deformation of metal surface formed by laser shot peening is investigated. The spot morphology formed by laser shot peening is analyzed. The influence law of different forming process parameters on the forming shape of parts is established. The results show that the thickness is the main influencing factor for the curvature radius of the impact area. The radius of curvature increases with the increase of thickness, and decreases with the increase of pulse energy and coverage. Using the regression analysis method, the mathematical model of laser peen forming curvature radius is established. The predicted results are consistent with the experimental results, and the maximum relative deviation is 2.6%.

This paper introduces a new forming method of railway axles: the square bloom is forged into a round axle billet by fast forging machine, then the round billet is rolled into the rough axle by the cross-wedge rolling machine. In order to prove the feasibility of this method, we have done an experimental trial of the technology on making scale-down Chinese railway freight axles with the scale ratio 1:1.4. The test result shows that the new method can double the productivity compared with the single forging method, save about 9% materials and improve shape accuracy of rough axle. Microstructure and mechanical properties of the axles formed by the new method have been tested and the test results show that the yield strength is greater than 345Mpa, the tensile strength is greater than 610Mpa, and the grain size reaches grade 8, which meets the standard requirements; The transverse and longitudinal impact toughness is greater than 21J, and the cross-sectional hardness distribution is uniform; The fatigue toughness test shows that the KQ value of the journal and shaft body in the deformation area of cross wedge rolling is slightly larger than that of the wheel seat, which indicates that the CWR process has no negative effect on fracture toughness of axles.

The surface of steel/aluminum clad plate was treated by 0. 3 mm steel wire brush and #180 sandpaper grinding before rolling, steel plate and aluminum plate adopt the same surface treatment. Then, it was rolled at 45% reduction rate and 450 °C rolling temperature. The rolled steel/aluminum clad plates were annealed at different times, and the steel/aluminum clad plates subjected to different surface treatments were compared for differences in bonding strength and microstructure after rolling and annealing. The surface treatment of steel wire brush formed a continuous hardened layer, and the hardened layer fragment into independent pieces during rolling. The exposed fresh steel matrix was combined with aluminum matrix to form high-strength metallurgical bonding. The surface polished with sandpaper had no obvious hardening layer, and the bonding strength after rolling was lower than that treated with wire brush. After annealing, the diffusion degree of elements at the bonding interface of clad plates subjected to different surface treatment methods increased significantly, and the bonding strength increased significantly. However, due to the oxygen concentration gradient between the steel surface hardening layer and the matrix, a new kind of iron oxide was formed between the hardening layer and the steel matrix during annealing, which connected the steel matrix and the independent hardening layer pieces, and the bonding strength increased rapidly. The research results can provide reference for the surface treatment of the hot-rolled steel/aluminum clad plate.

The manufacturing process of double wall brazed tube (DWBT) consists of the multi-pass roll forming from the flat strip to double wall structure and brazing process. And the poor roundness of cross section for DWBT in the multi-pass roll forming not only affects the forming accuracy and quality, but also restricts the subsequent brazing process of DWBT. Thus, the parameters of Hill'48 yield criterion for the steel strip were firstly determined in this paper, and the reliable 3D finite element model of the multi-pass roll forming of DWBT was established based on ABAQUS/Explicit platform. Then the cross-sectional dimension of DWBT after each roll forming was analyzed. The results show that the multi-pass roll forming of DWBT requires the cooperation of the forming roller, horizontal roller and vertical roller, and the radius of the horizontal roller profile becomes larger with the increasing roll pass. The evolution of cross section is accompanied by the accumulation of equivalent strain, following the forming sequence of two arms on both sides, inner wall, outer wall and sizing process. An expression representing roundness is proposed, and it is concluded that the roundness of the outer tube is better than that of inner tube. Moreover, the cross-sectional distribution of the outer tube is more uniform along the circumferential direction.

The seizure resistance in the ironing process of stainless steel cups was improved with lubricants containing Al₂O₃ particles, and the ironing limit of the cups was increased. The effects of suspending different concentrations of Al₂O₃ particles in paraffin based oils on increasing the ironing limit of SUS430 cylindrical cups before seizure were investigated using a lapped tungsten carbide die. By containing c = 2vol% of Al₂O₃ particles having nominal diameter d between 0.02 to 4 micrometres in an oil with a kinematic viscosity of 500 mm²/s, the ironing limit of the cup was 8% under a punch speed of 100 mm²/s. The limit was similar to the limit using a commercial low-viscosity oil with chlorine additive. The kinematic viscosity of the base oil was reduced. In d = 0.2 μm and c = 0.5vol%, the limit of the oil more than kinematic viscosity of 180 mm²/s was similar to the limit by the commercial oil. In d = 4 μm and c = 1vol%, the limit of the oil having more than kinematic viscosity of 100 mm²/s was effective. It was found that the seizure resistance in the ironing process was improved by the proper ironing conditions with lubricants containing particles.

In this paper, the electromagnetic deformation combined with heat treatment (ET) process was studied, which was meaningful for the forming of high performance Al-Li alloy sheet metal parts. In the ET process, the annealed sheet was firstly subjected to solution treatment, electromagnetic deformation. and artificial age until it reaches the peak aging state. Compared with the traditional T6 heat treatment, the time efficiency of the ET process is significantly improved, and the mechanical properties of the specimen are enhanced. The ET process only takes 6 hours to reach the peak aging, and the time efficiency of precipitate strengthening is reached up to 4 times compared with the T6 process. At the same time, the mechanical properties of the ET specimen are higher than the T6 one, an increase of 17.6% in Vickers hardness. Moreover, the mechanism of higher time efficiency and mechanical properties of the ET process is revealed. It is found that a high density of cellular dislocations and sub-grain were introduced during the electromagnetic deformation process, which is conducive to the nucleation and growth of the T₁ precipitate during artificial aging. The T₁ precipitates of the ET specimen are more dispersed and finer.

Measurement of the Bauschinger effect of ultra-thin metallic sheet by the conventional tension-compression (TC) test is challenging due to the premature buckling during compression. In this study, a test method based on a multi-layered sandwich specimen is newly introduced to suppress the buckling in the uniaxial compression. Theoretical calibration is conducted for obtaining accurate flow stress under compression by correcting the effects of adhesive and friction induced by supporting side plates. Also, strains during the TC tests are measured by the digital image correlation (DIC) technique. From the proposed TC test with the sandwich specimen, plastic deformation of 0.1-mm-thick ultra-thin pure titanium sheet was investigated under reverse loading. Finally, the constitutive model based on the distortional hardening concept is newly developed and calibrated to reproduce the Bauschinger effect of the investigated ultra-thin sheet subject to TC loadings.

The realization of metal physical objects by localized laser fusion techniques requires the building under specified and predictable conditions in order to reduce errors in that phase. The stratification and the dimension got by solidified melt bath pools determine the geometry and the surface micro-characteristics appearing on the manufactured component. The relationship between internal microstructure and external characteristics are proposed by a analytical modeling in which internal variables such as the melt pool surfaces detected in the sectioned part of the specimen are given as input to describe the surface roughness at given positions of the surface of the object. The proposed method is based on the use of melt pool areas directly as obtained by the building history and on the use of an interpolating equation able to approximate their trend in order to reduce the variability got by real process. The obtained analytical models are able not only to correlate but to describe in detail the surface roughness as a function of internal bath areas. The modeling approach proposed is based on the regression analysis in which different variables affecting the geometry and the surface roughness are considered and their significance evaluated. An improvement in the predictive ability of the model using the interpolated melt pool areas is obtained.

Investigation of the ductile damage in single point incremental forming (SPIF) is necessary for improving the formability during the manufacturing process. In this paper, an enhanced Continuum Damage Mechanics (CDM) model was applied for ductile damage prediction in SPIF process. In particular, the stress state dependence was considered in the damage evolution to improve fracture prediction capability at various loading paths. The enhanced CDM model was implemented into finite element code ABAQUS/Explicit through user subroutine VUMAT. The accuracy of the finite element model to predict the failure during SPIF process was investigated, good agreements were found between the simulation results and the experimental observations.

In order to satisfy the requirement of the engine heat exchangers, ultra-thin tubes with higher dimensional accuracy and better performance are required. Inconel 718, as the basic material of ultra-thin tube, is one of the materials that can meet the requirements of the engine heat exchanger. In this study, ultra-thin tubes with diameters and thicknesses of 1.50mm and 0.050mm were prepared by floating plug drawing process. The results showed that the yield strength increased and the corresponding elongation decreased with the increase of drawing passes. The wall thickness of the ultra-thin tube can be controlled by floating plug drawing. And the inner surface quality was greatly improved compared with the initial tube. The inner surface roughness can be controlled below 1.7μm. The average grain size after drawing can be reduced from 4.9μm to 2.1μm.

Additive manufacturing (AM) has been developing into a revolutionary technique, in which parts are created by additive processing as opposed to the conventional subtractive manners. AM components possess the characterization of special microstructure and porosity. In this paper, a computational method is developed to investigate the mechanical property of selectively laser melted (SLM) AlSi10Mg alloy. The DREAM.3D software is utilized to generate a polycrystal model based on electron backscatter diffraction (EBSD) results. The investigated alloy shows a weak texture that the grain preferential grows along the <100> orientation. The real defect geometries are reconstructed from X-ray Computed Tomography (XCT) experimental slices and embedded into a representative volume element (RVE) model. Furthermore, a crystal plasticity (CP) model integrated fast Fourier transform method (FFT) in Düsseldorf Advanced Material Simulation Kit (DAMASK) package is implemented to simulate the mechanical response for the RVE model. The effect of porosity on tensile strength is studied, and result shows the defects degrade tensile strength.

Aluminum tube with single row of small channels used in frequency conversion module of air-conditioner for heat radiation is manufactured by porthole extrusion, which has the characteristics of thin wall and large wall thickness difference. Due to the tiny dimension and offset distribution of channels, the design of process and die faces great challenges. In this study, a porthole extrusion die for aluminum flat tube with offset small channel was designed, and the offset porthole was used to balance the force on the both sides of the die core. The numerical simulation model of porthole extrusion process was established, and then, the structure of the extrusion die was optimized by taking the uniformity of metal flow velocity on the cross-section of the profile at the exit of the die. The effects of extrusion temperature, extrusion speed and die temperature on the displacement of the core, extrusion load, flow velocity and temperature of the metal at the exit of the die were studied. The optimal parameter combination of extrusion speed and temperature was obtained. The result showed that the dimensional accuracy of profile meets requirements. This study can provide guidance for the die design and process optimization of aluminum flat tube profile with offset small channel.

The dimensional instability caused by irreversible micro-plastic deformation can be evaluated with the micro-yield strength. Cf/Mg composite material prepared by liquid-solid extrusion following vacuum infiltration(LSEVI) process was taken as testing material and its dimensional stability was evaluated. The load-unload cycle test method is used to explore the stress range for the Cf/Mg composite to generate residuals plastic strain in static conditions. The results show that micro-plastic deformation for Cf/Mg composite material occurred in the stress range between 35 and 45 MPa. When the micro-plastic strain reaches 10⁻⁵, the micro-yield strength of the Cf/Mg composite material is evaluated as 79MPa. Compared with matrix alloy, the micro-yield strength has increased by more than 89%, which is the same level as beryllium alloy. This paper provides an effective strategy for characterize the dimensional stability of continuous fibre reinforced metal matrix composites.

The constructive forming process is a new plastic forming process of manufacturing heavy forgings from small blank units. In this process, first, the surfaces of the blank units are cleaned, and then the blank units are packaged into a whole blank, finally, the whole blank is deformed into a heavy forging by thermal deformation in a vacuum. In order to solve the key problem of constructive forming which is bonding interface healing, electric pulse treatment was introduced to regulate and control bonding interface healing. Through the electric pulse treatment experiments of stainless steel blanks before and after high temperature deformation, the effects of electric pulse treatment on the geometric morphology, microstructure and chemical composition of stainless steel bonding interface were revealed. The results indicate that using electrical pulse treatment before high temperature deformation can pre-connect the bonding interface and promote the thermal deformation healing of the bonding interface, using electrical pulse treatment after high temperature deformation can promote the healing of micro-voids in the bonding interface area and further improve the healing effect of the bonding interface. The research results provide a new idea for solving the problem of interfacial traceless bonding technology in metal constructive forming.

For the problems that the stability problem that affects the fully automated production of precision extrusion of cylindrical parts, the cooling and lubrication of the die under high temperature and high pressure is the key technology that affects the production stability. During the hot extrusion process, the punch die has a short life under high temperature and high pressure, and cannot be Achieving continuous production and maintaining the life of the punch is the key technology to realize high-efficiency unmanned production of hot extrusion automation. First, the temperature rising and cooling formula for die especially for punch was obtained by theoretical calculation. The convective heat transfer coefficient on the surface of the internal cooling pipe was calculated and punch cooling device was made based on the forced convection heat transfer of cooling water. The changing law of the temperature field after punch extrusion was obtained by the infrared temperature measuring device and the test results were consistent with the theoretical calculation results.

Laser shock peening (LSP) is a promising surface strengthening process in the field of aircraft maintenance. However, unreasonable residual stress distribution often exists at the edge of the damaged aircraft component strengthened by LSP, which results in a significant decrease in strengthening effect of LSP. To explore the residual stress distribution after LSP in the edge region of components and reveal the influence of edge effects on deformation and inducing residual stress, the finite element (FE) models of LSP on 7075 aluminum alloy was established based on ABAQUS. The reliability of the FE model was verified by comparing the experiment and simulation results. The residual stress distribution in the edge and center region after LSP were analyzed. The results show that the edge effect enhances the flow of material to the edge and introduces tensile stress in this direction, thereby reducing the overall residual compressive stress level in the edge region. The influence range of edge effect on residual stress distribution is about 70% of the laser spot diameter. Besides, edge effects reinforce the phenomenon of residual stress holes, which results in a reduction of the maximum value by 109.2MPa. The influence of edge effect can be solved by multi surfaces LSP.

Stainless steel foils are extensively used in the manufacture of micro-metallic products for their excellent corrosion resistance, high mechanical strength and superior ductility. In the present work, stainless steel foils with 50 μm thickness were annealed at temperatures ranging from 750 to 1150 °C for 5 min and then cupped at drawing speeds ranging from 0.1 to 2 mm/min. The formability of metal foils was systematically investigated and the quality of drawn cups via micro deep drawing (MDD) was discussed. The results show that the total elongation of metal foils appears a gradual increase when annealing temperature rises from 750 to 950 °C. With a further increase of annealing temperature from 950 to 1150 °C, both the ultimate tensile strength and the total elongation decline sharply, while the scatter of stress increases. The results of MDD tests show that wrinkling problem becomes increasingly significant on the drawn cups whilst thickness distribution on the drawn cup mouth become quite nonuniform with the increase of drawing speed from 0.1 to 2 mm/min. Overall, optimal annealing temperature and drawing speed are obtained with the purpose of manufacturing high quality micro circular cups.

With the development of lightweight technology, advanced high strength steel (AHSS) had been widely used in automotive and construction industry. However, twist defect restricts the application of thin-walled components with asymmetric section. In this work, AHSS MS1500 was taken to investigate the complex non-linear elastoplastic behaviors and twist defect in roll forming process. Finite element analysis (FEA) model was established by COPRA software and the material model considered Young's modulus variation with plastic deformation and material anisotropy was selected. With the developed model, the mechanism of twist defect was discussed and the effect of forming strategy on twist defect was analyzed. For asymmetric hat channel steel, the asymmetric residual longitudinal stress is the principal reason for twist defect. Loading patterns have a significant effect on twist defect and the developed UDT-type (USTB-Durable-type) method can control twist defect effectively. This study has provided theoretical and technical support on large-scale application of AHSS.

Hot-stamped products are widely used for the body in white of an automobile to enable lightweight design and improve crashworthiness. Al-Si coated 22MnB5 steel sheets are applied to prevent oxide scale and adhere to a painting in hot stamping. To strengthen the bent member, corner thickening by planar compression in hot stamping was applied. However, the Al-Si coating layer peels off by large deformation due to corner thickening. The effect of corner thickening on the peeling of the Al-Si coating layer was investigated in hat-shaped bending. The coating layer on the outer corner was cracked by tensile deformation and the peel of the coating layer was observed above 5% in the thickening ratio. Deformability of the coating layer without crack was investigated in V-shaped bending. The sidewall angle was changed to taper to prevent peeling failure. In addition, to improve the elongation of the coating layer during hot stamping, the heating temperature was increased. The peeling and crack of the coating layer were reduced by heating at 1050 °C for 4 min.

The fabrication of functional micro-structures at sheet surface has a wide range of applications in noise reduction, friction reduction, heat and mass transfer, etc. By integrating the conventional rolling forming and the incremental sheet forming process, a flexible and widely applicable incremental rolling forming process was proposed in the present work to fabricate surface micro-grooves. First, a rolling tool which has hemispherical ring convex on the roller and the convex height is much higher than the height of forming groove was designed and manufactured. Then, a series of incremental rolling tests on titanium alloy (TA1) were carried out by using self-designed rolling tools, with varying roller size, rolling depth and feed rate. The results show that continuous micro-grooves with good dimensional consistency were prepared on the surface of the plate. Furthermore, by investigating rolling force and groove size after rolling, it was found that the rolling depth have significant effects on the micro-groove formation and only localized material flow is occurred at the grooved region. Compared with the traditional rolling process, the incremental rolling process has the advantages of low rolling force and adjustable groove spacing, which is conducive to the subsequent processing of the sheet.

Anti-barrel shape is a typical phenomenon for a cylinder deformed in the upsetting process superimposed with sufficiently high intensity of ultrasound. In this paper, the cylindrical specimens of aluminum 6061, ϕ 4.08mm×4.8mm, were performed as the experimental object. With the different temperatures of 350°C, 400°C and 500°C and the longitudinal vibration amplitudes of 6μm and 10μm, the anti-barrel forming law of cylindrical specimens was studied, as well as the material flow law in the forming process. Results show that, the anti-barrel profiles may show up elliptic and hyperbolic curves, as well as the circular arc. The forming process of anti-barrel profile consists of multiple processes of high-speed collision, low-speed collision, high-speed compression and low-speed compression. The formation of anti-barrel profile may effectively promote the uniform flow of the end material and avoid upward-moving of the lateral material which is inevitable in conventional upsetting. The barrel and anti-barrel profiles perform almost opposite types of hot-working streamline, of which the layout of arcs opening inward and outward respectively.

By means of numerical simulation and experimental, the liquid filling forming process of an aluminum alloy double concave and convex curved sheet part was studied. The quality of forming parts, especially the thinning rate, is compared and studied during different hydroforming process. The results show that the thinning rate of the product is more than 25% regardless of the passive or active liquid filling drawing. However, the maximum thinning rate of the product is less than 20% when the hybrid hydroforming is carried out in a set of die with passive liquid filling in sequence, followed by pulsating reverse liquid filling. The method has reference significance for improving the forming quality of the parts with concave and convex surface of thin plate.

The densification mechanism of the electric field-assisted sintering (E-FAST) for Inconel 718 alloy miniature gears was studied using the Bernard-Granger model. Under the conditions of sintering temperature of 950 °C, 1000 °C and 1050 °C and dwelling time of 240 s, 300 s and 360 s, the Inconel 718 powders were subjected to E-FAST using the Gleeble thermal simulator, and the densification rate was up to 10⁻³ s⁻¹. With the increase of the sintering temperature, the peak of the densification rate of the sintered sample was enlarged, and the time for the peak to appear became shorter. The densification of Inconel 718 alloy miniature gears was mainly concentrated in the dwelling stage. When the dwelling time reached 300 s, the densification rates of the samples under different temperature conditions were similar, indicating that the gear samples were close to full density at this time. Simulation and sintering test results show that the densification stages of the gear samples can be divided into low sintering stress stage with stress index n = 0.4 and high sintering stress stage with stress index n = 3.5. The apparent activation energy of the densification changes with the variation of the sintering stress stage.

The 6061 aluminum alloy wires with diameters of 0.15 mm and 0.20 mm were cut into different structural sizes of 5 × 10 mm and 10 × 15 mm by a spring machine to bend the aluminum alloy fibers, one is 5 mm short side, 10 mm long side, and 1 mm arc radius, and the other is 10 mm short side, 15 mm long side, and 1 mm arc radius. Special cylindrical molds are used to prepare folding sheets with different porosities using vacuum hot pressing sintering technology. Bent aluminum fiber porous material. The gas displacement method was used to detect the pore size and pore size distribution, and the Plastic Deformation Behavior were analyzed by quasi-static uniaxial compression test. Research shows that the material presents a three-stage stress-strain curve, from the initial nonlinear elastic deformation stage to the pseudo-platform stage and the densification stage, the wire diameter and structure of the material The smaller the size, the more conducive to the densification of the silk skeleton, and the smaller the average pore size formed, the higher the compressive strength.

This paper focuses on the deformation mechanism of aluminum alloy cylinder with multi-level stiffeners in flow spinning. A flow spinning finite element model is established based on ABAQUS software, and the material flowing and damage behavior between different width stiffeners were analyzed. The research results can provide guidance for spinning process of aluminum alloy cylinder with multi-level stiffeners.

A new dieless forming method is proposed to produce metal bellows induced by local thermal buckling. The thermal buckling forming process is realized according to the local deformation behavior of metal tubes under the action of high temperature softening and axial pressure. In this paper, a forming device is designed and it is capable to produce metal bellows in two forming modes of a discontinuous bellow forming process and a continuous bellow forming process. FEM simulations are used to analyze this thermal buckling forming process and its product performance. The results show that the presented process can increase wall thickness and improve the energy absorption performance of metal bellows. Meanwhile, some thermal buckling forming cases of metal bellows of different materials and different sizes are presented.

In order to obtain the pure shear deformation characteristics along the circumferential direction of tubes, a circumferential shear test for thin-walled tubes is proposed in this paper. The experimental device consists of a tubular sample and two cylindrical mandrels with shear plates. The torque along the circumferential direction was applied to the tubular sample by the two shear plates to make the pre-set shearing zone of the sample under a circumferential pure shear stress state. The two cylindrical mandrels support the inner wall of the tube to avoid buckling so that the pure shear stress state can be maintained during the whole deformation process. A 5052 aluminum alloy tube with an outer diameter of 50 mm and a wall thickness of 1.2 mm was used in the test. It is shown through simulation and experiment that shear deformation is concentrated in the pre-set shearing zone. This test can be used to obtain the circumferential pure shear stress-strain relationship.

Additive forging technology is an innovative method for manufacturing heavy forgings by using multi-layer hot-compression bonding. To achieve better bonding performance, the surface of the metal substrate needs to be ground and cleaned before hot-compression bonding. However, the process is less automated in factory production which tremendously hinders the increase of productivity. This paper presents an automatic grinding scheme and the experimental device were designed to verify the feasibility of the scheme. The effects of contact pressure, spindle speed and feed speed on the grinding effect of 316H stainless steel were studied. The results show that the best grinding effect can be obtained when the contact pressure is 25 N, the spindle speed is 8000 rpm, and the feed rate is 30 mm/s, which can significantly improve the product quality and production efficiency.

Experiments of repetitive uniaxial tension are performed for DP590, TRIP590, TRIP780, and BH220 steels. Variation of chord modulus of the four materials with accumulated plastic strain is discussed. Large specimens of uniaxial tension, wide plate tension and cruciform tension are prestrained in different plastic strain. Uniaxial tension of sub-size samples which are machined from the prestrained large specimens is performed. Dependence of the normalized chord modulus of the four metals on strain path is discussed in detail. The results show that elastic modulus degradation is dependent on the material strength, accumulated plastic strain and strain path. At the same equivalent strain, the chord modulus degradation of TRIP780, TRIP590, DP590, BH220 steels decreases in turn. The chord modulus of TRIP780 steel at 0.24 equivalent strain reaches 20.5%. The chord modulus of DP590 steel is more sensitive to strain path change than the other three metals. The path of biaxial stretching combined with uniaxial tension provides the greatest chord modulus degradation among the six loading paths. Each material should have the most suitable loading path under which the elastic modulus variation can be minimized so springback can be easily controlled.

FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube is firstly put forward and it can be fabricated by means of isothermal extrusion. Based on Arrhenius constitutive model of FeMnSiCrNi and NiTiNb shape memory alloys, isothermal extrusion of FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube is simulated by rigid viscoplastic finite element method. It can be found that the deformation zone of the dissimilar shape memory alloy composite tube is always in a three-dimensional compressive stress state during extrusion, and the deformation of the inner tube is obviously higher than that of the outer tube. It is necessary to guarantee the interface compatibility between the inner tube and the outer tube during isothermal extrusion of FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube. The relationship between macroscopic process variables and microscopic variables during plastic deformation of FeMnSiCrNi shape memory alloy tube at high temperature is established by coupling finite element simulation and cellular automaton simulation. The microstructural evolution of FeMnSiCrNi shape memory alloy in different deformation zones during isothermal extrusion of dissimilar shape memory alloy composite tube is simulated. It can be concluded that the grain size of dynamic recrystallization is reduced with the increase of plastic strain in the deformation zone.

As the increase in demand for microparts of metal foil, the micro-blanking process with many advantages of plastic deformation has been widely applied on microparts manufacturing area. But the fracture zone of shearing surface is always present and affects the service life of the part. This paper proposes a new micro-blanking die based on fine blanking technology. In this die, the rubber as the power transmission device is selected to provide a blank holder force and counter force. In the FEM simulation, the influence of a few key die parameters is considered such as punching clearance and fillet radius of female die and punch. And the fine micro-blanking experiments for superalloy foils were conducted to evaluate the feasibility of the die designs. The results had shown the fine micro-blanking die proposed was able to be used for micro-blanking and obtain metal microparts.

Columnar grain structures (CCS) often distinct in steel ingots, which have to be refined and homogenized during forging. In this investigation, simulation of deformation and dynamic recrystallization of austenitic stainless steels with CCSs were carried out by macroscopic, mesoscopic (microscopic) and nanoscale simulation techniques. (1) Using molecular dynamics simulation method, the nano-CGSs model with different loading directions was simulated. The results show that the deformation stresses are anisotropic with variation of angles between the loading direction and the columnar crystal growth direction. The higher stresses present at the 0° and 90° angles due to higher dislocation density; However, the lower stresses present at the angles from 30° to 60° due to higher stacking faults and twins. (2) The cellular automata (CA) fractal rules were proposed to simulate nucleation and grain growth of dynamic recrystallization by introducing weighted variables considering Σ3 twin nucleation rate for the twinning-promoted recrystallization. The CA method of nucleation at primary columnar crystal boundaries, secondary dendrites and deformation bands was proposed to simulate the joint nucleation. (3) The coupling simulation of macroscopic thermal parameters by finite element method, solidification of columnar structures and hot deformation dynamic recrystallization by CA was realized.

Stainless steel single sink with countertop (SC) has the characteristics of large depth and asymmetric countertop. Its traditional stamping process is mainly realized by the combination of multi-stage deep drawing and annealing process, which leads to the complex manufacturing process, long production chain and poor consistency of products. Based on finite element analysis software (Dynaform) with nonlinear dynamic display algorithm, numerical simulation analysis and research are carried out on the parameters of hydrodynamic deep drawing. First, the sink and the part of countertop are preformed into a cylinder shell, and then the excess of the cylinder shell is drawn back to the countertop. The research results show that the hydrodynamic deep drawing process can effectively improve the flow uniformity of stainless steel sheet, increase the forming of stainless steel tank, drawing a more uniform wall thickness, thus effectively improve the quality of single tank with countertop by setting up reasonable preform structure, controlling the liquid pressure and its loading paths and blank-holder force.

Based on the electromagnetic hole-flanging (EMHF) experiment and numerical simulation, the inverse identifications of Johnson-Cook (J-C), Huh-Kang (H-K), Allen-Rule-Jones (A-R-J) and Cowper-Symonds (C-S) constitutive models were performed for AA5182-O aluminium alloy sheet at high strain rates. The accuracy of constitutive models was inspected by comparing the simulated height and thickness with experimental ones. The flow stress curves of AA5182-O aluminium alloy sheet at high strain rates were investigated. Based on the Marciniak-Kuczynski (M-K) model and constitutive models, the electromagnetic forming limit curves (EMFLC) of AA5182-O aluminium alloy sheet were predicted. The results show that the constitutive models at high strain rates can be determined by inverse identification on basis of EMHF. The flow stress curves at high strain rates predicted by different constitutive models are significantly distinguished. The constitutive model directly affects the numerical prediction of EMFLC. The EMFLC with J-C and A-R-J models shows little strain rate sensitivity, the EMFLC with H-K model shows positive strain rate sensitivity at a certain range of strain rate, and the EMFLC with C-S model shows significantly positive strain rate sensitivity.

The plastic forming of titanium alloy tubes at room temperature exhibits strong anisotropy, low elongation, and large deformation resistance. Numerical control warm bending assisted forming technology can improve the stability of the titanium alloy tube bending process, increase the bending limit and reduce the springback angle. This technology promotes the wide application of high-precision titanium alloy bent tubes in many high-end fields such as aerospace, shipbuilding, chemical industry, and military industry. However, the titanium alloy tube bending at high temperatures involves complex material rheological behavior and microstructure characteristics. The coupling relationship between the stress-strain properties of the material and the temperature field makes it difficult to predict the springback behavior of titanium alloy tubes after warm bending. In this paper, based on the mechanical behavior of titanium alloy tubes at high temperatures, a constitutive model of titanium alloy suitable for local heating is improved. The theoretical model of springback for warm rotary draw bending of titanium alloy tube is established. The influence of warm bending strategies on the springback of bending is studied. The theoretical model is verified by establishing a thermal-mechanical coupling finite element model for the whole process of warm bending under the state of heat balance. The results show that the bending springback theory based on the modified John-Cook model can accurately simulate the temperature change of titanium alloy tube section, adapt to local heating strategies and provide high prediction accuracy of bending springback.

Ni-based superalloy components with complex shape, such as conical-cylindrical parts, are one of the most important structural components widely used in aviation and aerospace fields. Composite spinning process, consisting of shear spinning and deep drawing spinning, is the most effective method to manufacture this complex component. However, the fracture and wrinkling defects usually occur due to the severe work hardening and complex strain path. Therefore, in order to evaluate the forming limit of Ni-based superalloy during spinning under complex strain path at room temperature, the finite element model of the shear-deep drawing composite spinning was established. The strain path during the shear-deep drawing composite spinning was analysed. The forming limit of Ni-based superalloy was also studied. Then the forming limit diagram of Ni-based superalloy during the shear-deep drawing composite spinning was established. The results show that the limit half cone angle of Ni-based superalloy for shear spinning is 30°; and the limit deep drawing spinning coefficient is 0.63. The strain path can be approximately the superposition of two linear strain paths during shear-deep drawing composite spinning. The safety zone is "wing shaped" in tension-compression strain zone during the shear-deep drawing composite spinning. The experimental results show that the limit diagram can accurately predict the forming defects.

Die face design of automotive panel is a tedious repeated process and depends heavily on experience of engineers, which leads to increase of lead time and production costs. An intelligent template based die face design method is presented for process reuse of automotive panel. In this method, the new part is extracted as feature parameters to match the existing process in the template library automatically and the similar process model is applied to the new part adaptively. Finally, a process reuse system for die face is developed and a typical automotive panel is employed to verify the effectiveness of the proposed method. The results show a favourable effectiveness and practicability in reducing design period and reliance on experience.

Titanium offers exceptional corrosion resistance both in organic & inorganic acid media. Thus, it is a preferred material by various industries such as Oil and Gas refining, Petrochemical (PTA Plant) including Nickel refining by Hydrometallurgy. These equipment are operated at high temperature and pressure, necessitating the use of higher thickness for safety and efficient functioning. Therefore, use of solid titanium is not economical, and often substituted with explosion bonded Ti-Clad steel. Fabrication of certain components of this equipment like Dished heads are required to be made by forming with options of cold, warm or hot forming. Selection of forming method for Ti-clad steel component is often governed by its effect on Clad-Base metal bond integrity and reduction shear strength unlike other commonly used Stainless steel or Ni-based alloy clad material, wherein thickness of the base metal is major deciding factor. In case of Ti-Clad steels both cladding and base metal are not metallurgically compatible as well as differs significantly in their physical properties, forming temperature plays a crucial role. This paper describes the effect of various Dished heads forming methodology on integrity of clad plate. Also, it brings out how the Ti-clad steel forming is critical than the forming of solid Titanium.

High velocity forming technologies are widely used in manufacturing industries to improve the formability of the aluminum alloy sheets. In order to better control the high velocity forming technologies through numerical simulation, the dynamic compression properties of the thin 6000-series aluminum alloy sheet were investigated by SHPB experiments. The influence of strain rate on the mechanical properties is analyzed in detail. Results show the elastic modulus is independent of the strain rate. However, under high strain rate condition, the yield stress, ultimate compression strength and ductility enhance with the increased high strain rate. So this 6000-series aluminum alloy sheet has significant strain rate sensitivity. As a reference, the quasi-static uniaxial tension test is also carried out and the uniaxial compressive stress-strain data in the literature is also listed. However, it is found the quasi-static uniaxial tensile yield stress is larger than the uniaxial compressive yield stress, and the quasi-static uniaxial compressive yield stress is lower than that under dynamic compressive condition. Results prove the aluminum alloy has obvious tension-compression anisotropy. For the high velocity forming technologies that take stretching as the main deformation mode, the dynamic tensile behaviour, instead of the dynamic compressive behaviour, should be used for accurate simulation.

Roping is a severe surface defect in aluminium alloy sheets that can affect the product's surface quality. However, quantitative prediction of roping is still a challenge. This paper introduces an approach combining experiment and simulation to analyse the roping phenomenon quantitatively in aluminium alloy sheets. A white light interferometer is employed to acquire large-area surface morphology with a detailed description of the corresponding morphological image preprocessing method. The electron backscatter diffraction (EBSD) mapping is conducted on the surface of the two sheets with different roping intensities to acquire orientation maps, and the crystal plasticity framework is developed to predict thickness strain after uniaxial tension. To obtain the quantitative roping prediction, a scaling parameter is proposed to map the predicted thickness strain to the actually measured height variance in depth.

GGG70L is a kind of cold-working die steel widely used in large automobile cover parts die. In order to ensure the life of the die, laser quenching process is usually used to form a certain hardened layer at a specific part of the die. In this paper, the changes of microstructure and hardness of ductile iron GGG70L after laser quenching were studied through a large number of process experiments, and the influence of quenching process parameters on the microstructure and properties of GGG70L was obtained. The relationship between the depth of hardened layer and the laser energy density is established and a quadratic function relationship was found between the two. It is found that both higher hardness and deeper hardening depth can be obtained when the energy density is 24-28 (J/mm²). The finite element model of the laser quenching process of GGG70L was established, and the temperature of the hardened zone and its evolution law during the laser quenching process were studied numerically.

Press hardening steels (PHS) with very high strength are current key materials for lightweight engineering solutions and corresponding CO₂ savings. In the present study, the microstructure and mechanical properties of a 2000 MPa grade ultrahigh strength boron steel for hot stamping were reported. Microstructure evolution experiment revealed that the microstructure of the 2000 MPa grade PHS only consisted of martensite when the cooling rate increased to 20 °C/s. The prior austenite grain size was about 6.8 μm when the sample was austenitized at 900 °C for 300 seconds. The appropriate isothermal quenching process should be austenitized between 900 °C and 950 °C during hot stamping because there is an abnormal grain growth of austenite grains at 950 °C. Following the optimal hot stamping condition, the 2000 MPa grade PHS alloy demonstrated yield strength in excess of 1300 MPa and ultimate tensile strength in excess of 2000 MPa together with a total elongation of about 7%.

To explore the variation law of workpiece temperature in the process of three roll skew rolling (TRSR) hollow axle, the process of TRSR hollow axle is tested and simulated in this paper. Firstly, the working principle of TRSR hollow axle is described; Then the blank and rolling process parameters are selected according to the actual performance of TRSR mill; Next, the finite element model is established, and the changes of workpiece temperature are studied; Finally, the simulation results are verified by experiments. The results show that the simulation results are basically consistent with the experimental results. The temperature change of workpiece in the rolling process is very small as a whole, and the temperature drop will be greater only at the place in contact with the die.

The following paper addresses the large demand for further comprehension of the ferritic AISI 430 steels owing to deep drawing processes and accompanying forming technologies, such as rolling. Their good corrosion resistance and relative low cost, make them reasonably well competitors in a great deal of applications. There has been thus evaluated in a pilot mill the influence of three different cold rolling passes with 76% thickness reduction to the drawability and mechanical properties of stainless steel plates. Erichsen, Nakazima and tensile tests were complemented with ODF, pole figure, SEM-FEG observations. It was believed that changes on the cold rolling passes, which alters the anisotropy of materials, would favorably influence deep drawing applications. Experiments revealed, however, that changes defining the deep drawing parameters from 15, 20 and 24 passes, were not statistically significant after rolling. Notwithstanding, texture gradients are reported.

Thin-wide aluminium rib stiffened plate structure reduces the weight and provides high stiffness, which makes it in high demand in transportation vehicles, marine, and structural applications for energy saving and CO2 emission reduction. In this study, the applicability of rolling in manufacturing an integral rib stiffened plate is reviewed through analysis of different rolling processes. The effect of rolling parameters and rib geometry on the formation and quality of ribs are analysed. The analysis provides an important basis to advance the understanding of metal flow, viscoplastic deformation and roll shape design during rolling, significantly helping the design of an innovative rolling process for rib stiffened plate. In addition, geometry and rolling parameters, plate curvature, and roll pass design (RPD), that highly affect the rolling process design are discussed. This paper presents the limitations and improvements of specific shape rolling processes and preliminarily concludes that rolling could be a potential method to produce high quality thin-wide panels with high stiffeners.

In tube bending processes, accurate control of springback is of crucial importance as this affects the dimensional accuracy of the final product and overall equipment efficiency. The distribution of stress and strain during bending is one of the most fundamental issues determining the springback magnitude of the product. In conventional analyses of rotary draw bending, the deformation behaviour along the bending direction is normally assumed to be uniform for constant-radius bends, following the contour of the die configuration. In practice, however, the stress-strain distribution is non-uniform, particularly at the transition between the bent and unbent regions of the formed component. The distribution makes a significant contribution to springback and its variations, especially for low bend-angle components. This research focuses on exploring the strain distribution at the end transition of the bend of aluminium tubes in rotary draw bending. An experimental test setup for strain measurements with a strain gauge glued to the unbent area has been designed and conducted to measure the strain distribution during bending. The characteristics of non-uniform strain distribution during tube bending, including the evolving transition behaviour at the transition between bent and unbent areas, are studied. The results enhance the understanding of deformation characteristics of bent tubes, and contribute to improved physically-based models and springback control routines in industrial practice.

Digitalization is becoming increasingly common in the steel industry. Formerly developed models of individual phenomenon or separate sub-processes are being further developed into wider complexes where multiple models are coupled together. Virtual rolling automation, which can be used to control a finite-element rolling model, is a new element in these complexes. The automation enables to model the variations caused by the process adjustment. It must be taken in the account that neither the model nor the industrial process are ideal, but there are limitations in the attainable accuracy in both cases. Inclusion of the new automation control in the FE-model introduces new requirements: the setup calculations for all six rolling stands and the automation logic adjustments must perform within the model. The focus of the current article is prediction of the roll force and the virtual rolling automation of six stand finishing mill.

Extrusion of wide plates and sheets of light alloys has been studied over a long period of time, yet the extrudable width of the material is still limited due to high extrusion force requirement. To overcome this drawback, a new multi-container extrusion process is proposed in the research, which allows the production of lightweight plates and sheets with less force compared to that of existing extrusion methods. A lab scale feasibility study system with three containers has been designed and built and tested for AA1060 billets. Experimental work has been carried out with the extrusion temperature of 450°C and extrusion speed of 0.5 mm/s. Optical microscopy observation and tensile tests have been performed for the extruded materials at different positions to investigate the extrusion welding quality between the three extrusion billets. The test results show that the welding quality improves as extrusion progresses and the overall welding quality is stable. This study demonstrates the feasibility of the new multi-container extrusion method.

At present, hollow axles are mostly manufactured by precision forging and then deep processing, which has long technological process and high cost. In order to realize the integrated forming of hollow axles with short process and low cost piercing and skew rolling, a method of piercing billet by two-roll skew rolling is proposed in this paper, and the finite element model of the forming process is established by using SimufactForming software. The effects of roll feed angle, roll speed and plug advance on the wall thickness uniformity of piercing tube billet are explored, and the process parameters with the best wall thickness uniformity are obtained. It lays a technical foundation for the blank guarantee and the realization of the integrated forming process of hollow axle.

In this paper, the grain deformation of SUS304 stainless steel foil under small fillet bending was studied. First, bending experiments were performed on 50 and 100μm thick foils, and the results showed that when the bending radius was close to the thickness of the foil, the surface grains in the bending zone collapsed and extruded, resulting in a rough surface. Then, Crystal Plastic Finite Element Method (CPFEM) was used to simulate the bending of different thickness foil (20, 50 and 100μm), in which the grains are hexagonal and the opposite edge distance is 20μm. Simulation results showed that when the relative fillet radius (the ratio of fillet radius to thickness) is similar, the surface layer of fillet becomes coarser with the increase of the foil thickness-grain size ratio. In addition, the uncoordinated intergranular deformation is caused by orientation difference, which leads to high density Geometric Necessary Dislocation (GND) in grain boundary region. Electron Backs-Scattered Diffraction (EBSD) experiments on recrystallized annealed foils with a thickness of 100μm showed that the GND density of the grain boundary after bending is significantly higher than that of the intragranular, which has the same distribution characteristics as the simulation results.

Copper/aluminum (Cu/Al) laminated composite has been extensively applied in the fields of batteries, electronics and electrochemistry owing to its cost reduction, light weight, good conductivity and resistance to corrosion. The Cu/Al composite strips produced by micro flexible rolling consist of three regions based on different thickness, i.e. the thicker, the transition and the thinner zones, and have a broad application prospect, especially in micro-electromechanical systems (MEMS). In this study, the effect of rolling reduction on the coordinated deformation of the Cu/Al interface and the microstructure of Cu/Al matrixes at three regions were investigated. The microstructure of the specimens was characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and the thickness of thin strips with varying thickness (TSVT) were measured by laser scanning microscope to explore the mechanism of microstructural evolution. The results show that the increase of rolling reduction gives a rise to the proportion of deformation occurred in the Al matrix, and the fracture of the intermetallic compounds (IMCs) is observed at the interface, which plays a significant role of transmitting and releasing stress during plastic deformation.

Electrically assisted compression experiments were conducted on Ti6554 titanium alloy to investigate the electroplasticity behavior under different process parameters (current density, duty cycle) and to analyze the effect of pulsed current on flow stress and temperature. An electroplasticity constitutive model based on dislocation density theory was developed and using ABAQUS subroutine secondary development for electrically assisted compression simulation. The results show that the established electroplasticity constitutive model can better predict the true stress-strain curves under different process parameters, and the average error is controlled at 6%. The evolution law of dislocation density reveals that α, which characterizes the dislocation strength, is smaller with the increase of current density, n and K2, which characterize the dynamic recovery mechanism of the material, increase with the increase of current density, and the dislocation density ρ decreases with the increase of deformation temperature.

A new testing method, Biaxial Tension under Bending and Compression (BTBC), is developed to investigate the effect of different deformation modes on material formability in Incremental Sheet Forming (ISF). A cruciform specimen is designed by simulating the material deformation under biaxial tension using Finite Element (FE) method. In the BTBC experimental testing, the cruciform specimen can be stretched in biaxial directions and the strain ratio of the two perpendicular directions can be varied. Furthermore, the superimposed effect of compression, bending and cyclic loading can be investigated. Material formability of aluminium alloy AA5251-H22 under plane strain path is tested. True strains of the specimen under different deformation modes are obtained by measuring distortions of circular grids inscribed onto the surface of the specimen. The experimental results show that the introduction of bending and compression contributes to localised material deformation. Material formability is improved by the introduction of bending, which is further enhanced by applying compression and cyclic loading. The BTBC test overcomes the limitation of commonly used testing methods in ISF formability studies, providing a fundamental explanation of the effect of strain path and loading conditions on the material deformation and fracture behaviour in ISF.

Thinning rate is a crucial factor in forming quality of the thin-walled seal ring with complex features. To control the excessive thinning by altering the stress state during the material deformation, a new multi-stage three-dimensional (3D) hydroforming technology was proposed in this work. Based on the characteristics of the seal ring and the used superalloy strip, a multi-stage internal pressure forming process was established through finite element analysis (FEA) and forming experiment verification. In addition, the distribution of wall thickness in every stage was discussed. And the influence of the width of deformation zone and the pressure loading path in the cavity on the wall thickness of the part in each step was studied. Finally, the optimal forming parameters of each step that can achieve a stable state of metal flow were obtained. The experimental results demonstrated that the developed 3D hydroforming technology can accurately control the material flow in the multi-stage forming of the multi-wave seal ring with small-diameter and ultrathin wall thickness. For the optimized parameter combination, the blank dimensions of deformation zone are 8 mm in the first step and 18 mm in the second step, while the pre-bulging pressure is 9 ~ 12 MPa and the maximum pressure is 100 MPa in the two steps.

In this work, three eleven-layered composite plates based on Cu (six layers) and one of the reactive metals such as Ta, Nb or Fe (five layers) fabricated using a single-shot explosive welding process were studied. The morphology and phase composition of the interfacial layers were thoroughly investigated using scanning (SEM) and transmission (TEM) electron microscopy. The microstructural and chemical composition analyses were then correlated with micro-hardness measurements to evaluate the mechanical properties of the interfacial layers. It was found that layers near the interfaces exhibited a complex and hierarchical microstructure on various levels. Optical microscopy characterization confirmed the high quality of the composites, without voids or layers delamination. SEM analyses showed that the solidified melt regions unveiled different morphologies but always consisted of a mixture of pure Cu and Ta, Nb or Fe elements. Quantitative nano-scale analysis using TEM revealed that nanoparticles and small dendrites dominated the reaction regions. Although no brittle intermetallics were observed near all interfaces of all composites, the microhardness of the solidified melts was 2-3 times higher than those of the sheets in the annealed state.

Molecular dynamics simulations are performed to reveal the underlying deformation mechanisms of gradient nano-grained materials with different-sized twins. The results indicate that the critical twin boundary spacing where the strength begins to soften decreases and the maximum strength of the material increases with the declining of the gradient. Below the critical value, the plastic deformation mechanism is dominated by the partial dislocations paralleling to the twin boundary, but when the twin boundary spacing exceed the critical value, the dislocation moved by the way of intersecting to the twin boundary.

This paper investigates the application of Laser beam prewelding/superplastic forming/diffusion bonding (LBW/SPF/DB) process in cylindrical parts. The forming die design and the processing process have been researched. A numerical simulation was carried out to determine the parameters of the superplastic forming/diffusion bonding process. The causes of defects are analysed and effective optimization methods are presented. In this paper, the main research contents are as follows, (1) Considering the characteristics of the structure and process of the workpiece, a design idea using a flapping tool and wedge fastening is presented. The process scheme for forming the core barrel step is described. (2) A laser welding power of 1300W and a welding rate of 1000mm/min were determined as the welding parameters for the SPF/DB process. The weld depth and weld width were considered suitable for parameters for laser welding. (3) The results of high temperature material performance indicate that 900 °C and a strain rate of 0.1s-1 strain rate were selected to simulate the forming process. (4) Verify the workpiece in accordance with the simulation parameters and evaluate defects, such as grooves on the surface of the workpiece and triangular areas between vertical bars. All the cylinders' indexes can meet the requirements, and the process quality is stable and controllable.

This study investigated the effect of Al–Si coating and its service condition on hydrogen embrittlement (HE) of hot-stamped ultra-high strength martensitic steels (22MnB5) through electrochemical hydrogen charging. The HE behaviour of coated and uncoated specimens under different charging conditions was investigated. The deterioration degree of mechanical properties of charged specimens with charging current is monotonous. At low-current charging, the more severe deterioration of coated specimens due to the excess hydrogen which was provided by corroded coatings. Contrary, with high-current charging, the integral coatings provided effective protection and retarded HE behaviour. Furthermore, the scanning electron microscopy revealed a similar transition of fractography, i.e., from ductile (uncharged) to quasi-cleavage (0.001A-2h) and a mixture of quasi-cleavage and intergranular fracture (0.1A-2h). Additionally, the coated tailor rolled blank steel was selected to investigate the effect of coating condition on HE. It revealed that the deformation-induced defects on coatings would impair the resistance to HE. Thus, we demonstrated that the Al–Si coating which effectively alleviate HE, was dependent on its integrality.

TB15 titanium alloy has shown a good application prospect in aviation large-scale structural parts. In this paper, the dynamic recrystallization (DRX) mechanism and model of TB15 titanium alloy were studied by thermal simulation compression experiment in temperature range of 810-930°C and strain rate range of 0.001s⁻¹-10s⁻¹. The microstructures under different deformation conditions were analyzed by optical microscopy (OM) and electron back scatter diffraction (EBSD). The results show that the degree of dynamic recrystallization decreased significantly with the increase of strain rate, and the nucleation position of dynamic recrystallization tended to migrate from the interior of grain to grain boundary. At low strain rate, the continuous dynamic recrystallization (CDRX) mechanism of subgrain merging and rotation was dominant. When the strain rate was 10s⁻¹, the rare geometric dynamic recrystallization (GDRX) occurred due to strong strain concentration effect, and the dynamic recrystallization grains showed fine chain distribution. Finally, the DRX critical strain, volume fraction and grain size models of the studied alloy were established, and the DRX volume fraction model was modified by quantitative microstructure.

In this work, a variable thickness tube blank geometry is proposed to be used in T-shaped tube hydroforming. The dimensions of the tube blank are optimized by the response surface method (RSM) linked with finite element simulation during T-shaped tube hydroforming. The influence of the wall thickness, angle and length of the tube blank are discussed on the thinning ratio and branch height. Multi-objective functions that relate objectives and design variables are formulated. Furthermore, the design variables having greatest impact on the objectives are obtained by sensitivity analysis. The optimal the geometric dimensions are determined within the given criterion by RSW and desirability approach. The optimized results have good agreement with the obtained results by finite element simulation and experiment.

Edge cracks are a more prominent problem during the rolling process of magnesium alloy sheets. The hexagonal structure of magnesium alloys and the product defects caused by the second phase impurities mixed in the sheets are the main causes of edge cracking. Conventional hot-rolled edge cracking simulations can only characterize the edge damage of the sheets numerically, however, the actual crack morphology is ignored. In this paper, the Gurson-Tvergaard-Needleman (GTN) damage model coupled with a continuous medium shear damage model was developed for improving the applicability of the model at low-stress triaxiality. Powell's "Dogleg" method was used in the numerical solution of the damage model instead of the traditional Newton-Raphson method and the Vumat subroutine was written for the finite element simulation by the stress return algorithm. The damage model parameters were calibrated by a shear specimen. The results showed a good agreement between the simulated crack morphology and the experiment.

Torsion extrusion (TE) method as a severe plastic deformation (SPD) process can effectively refine the microstructures and improve the mechanical properties of materials. Accurate and rapid prediction of the extrusion force in the process of TE is an important problem in industry. This paper proposed an analytical model using upper bound method (UBM) for predicting the extrusion force in the TE process. The kinematically admissible velocity field is established based on a continuous spherical extrusion velocity field coupled with a torsional velocity field constrained in a conical die. The torsional angular velocities along the radial and axial directions are assumed with quadratic and cubic function, respectively, due to the radial and axial nonlinearity of torsional velocity in the deformation zone. In addition, considering its complexity, the shape of the deformation zone is mapped to a rectangular zone. By establishing the torsional velocity field in the mapped zone, the torsional velocity field of the deformation zone is obtained according to the mapping relation. The UBM model is validated by comparing the predicted extrusion force with the simulation results obtained from the finite-element method (FEM). Moreover, the influences of the friction factor, reduction ratio and die angle on the extrusion force were investigated as well.

During numerical simulation of sheet metal forming, the accurate models to describe material yielding and hardening behavior by considering the anisotropy, non-uniform evolution of the yield surface and strength differential effect are vital to predict complicated deformation and forming defects such as fracture and springback. In the present work, a novel yield model with non-associated flow rule is proposed based on the frame of S-Y2009 criterion and coupled with normal stress components and the second deviatoric stress invariants, where the former is used to describe the anisotropy and non-uniform evolution of yield loci, and the later enables the description of SD effect. Different from some other models which identify the parameters via optimization algorithms, the proposed model adopts an analytical identification method from the stress-strain curve in various loading conditions, including uniaxial tension and compression along 0°, 45°, 90° to the rolling direction, and equi-biaxial tension and compression. The flexibility of the proposed model is validated for high strength steels, aluminum alloys and titanium alloys.

Controlling the hot rolling process requires a deep understanding of the underlying metallurgical phenomena. Quantitative methods are of paramount importance for achieving the capability of controlling microstructural evolution. Since the final mechanical properties of steel result from microstructural evolution in the whole process, analysis of the microstructure provides an important input for numerical simulations that can be used for tailoring the mechanical properties of steel. The evolution of grain size distribution of a low-carbon CrNiMnB ultrahigh-steel in austenitic state is studied in hot forming and annealing using experimental data obtained with the Gleeble 3800 thermo-mechanical simulator. A general method is described that can be utilized to systematically compare the grain size distributions obtained from the experimental studies. The experimental data has been obtained from laser scanning confocal microscopy images using the mean linear intercept method. A custom-made semi-automatic software has been utilized to process the data rapidly and reliably.

Cross wedge rolling (CWR) process is expected as an efficient and innovative preforming process for the forged aero-engine blades. But it is still a grand challenge to control the process defects and the performance of the rolled parts. According to the requirements of an aero-engine Ti-6Al-4V (TC4) blade billet with heavy section reduction up to 83%, flat CWR tools were designed and optimized by the thermal-mechanical coupling finite element (FE) method. The metal flow, damage evolution, and the distribution of stress and strain during the forming process were analysed. Then, the CWR experiments were carried out on IM500 flat CWR mill under different technological conditions. The obtained rolled parts were subjected to non-destructive testing (NDT), tension tests and microstructure analysis. The results showed that the central defects, such as micropores and voids, which seriously reduce mechanical properties, occurred in some of the rolled parts more or less. The volume of central defects was closely related to the initial rolling temperature of the billets. When the heated temperature of the TC4 billet was higher than 850°C, the target rolled part without central defects can be obtained. This research work can be a reference for the single-wedge CWR forming of titanium alloy with heavy section reduction, promoting the application of CWR in the aero-engine blade preforming process.

The lightweight of structural materials was an important research focus for reduced energy consumption and transport efficiency. Aluminium matrix composites (AMCs) had the advantages of high specific strength and good wear resistance, so they were widely used in automobile, aerospace and other fields. At present, the deformation mechanism of AMCs reinforced by high-entropy alloy particles (HEAp) in asymmetric rolling was not clear. In this work, AMCs ingot reinforced with 6 wt% HEAp was prepared by stir casting process. Then the mechanical properties of HEAp/AMCs under different rolling processes were studied by asymmetric rolling (AR) and asymmetric cryorolling (ACR) processes. High-entropy alloy (HEA) had excellent strength and toughness, which imparted good deformation ability when added to AMCs as reinforcement. The microstructure of AMCs reinforced by HEAp was refined by ACR. At the same time, the HEAp/AMCs obtained by ACR displayed a higher ultimate tensile strength (UTS) than that obtained by AR. The study of ACR shows that AMCs reinforced with HEAp have good toughness. ACR can reduce the thickness of HEAp/AMCs to a greater extent so as to produce AMCs strip with excellent mechanical properties.

The limited formability of ultra-high strength steels (UHSS) poses some challenges for the bending process in the form of strain localisation, surface defects and pseudo-polygonal "nut-like" shape of the bend. Bendability is well known to be affected by surface quality, and especially shot blasting. Therefore, in this study, the effect of surface roughness on bendability of UHSS grade is investigated with 3-point bending tests, utilising Digital Image Correlation (DIC) for measuring the strain distributions on the outer curvature. Investigated bending samples of 4 mm thick commercial martensitic were tested in different surface conditions: As-rolled (with scale), "lightly" shot blasted (SB I), "roughly" shot blasted (SB II), dry electropolished (As-rolled P) and a combination of "rough" shot blasting and dry electropolishing (SB II P). Shot blasting increased the surface roughness and subsurface hardness. Utilizing a commercial dry electropolishing process reduced the surface roughness, although this also had major effect on the hardness. Bending results showed that coarser surface roughness decreased the bending capacity, i.e. reduced maximum bending angle and critical strain. A strong correlation between surface roughness (with R_v: the maximum valley depth below the mean surface) and critical bending angle was found, likewise with the subsurface hardness and critical bending angle.

Grasping the mechanism of texture evolution during hot power spinning of magnesium alloy cylindrical parts with inner ribs, which have the dual lightweight advantages of material and structure, can provide a theoretical basis for texture regulation in the preparation of high-performance magnesium alloys. Based on the crystal plastic finite element method, the macro-meso coupled model was constructed and the simulation study of magnesium alloy cylindrical parts with inner ribs during hot power spinning was carried out. The texture evolution mechanism at the position of cylindrical wall (CW) and inner rib (IR) was revealed by tracking the change of grain orientation and the analysis of Schmid factor (SF). The results show that the c-axis of grains of magnesium alloy extruded blank gradually deflects from parallel to tangential direction (TD) to parallel to radial direction (RD). Under the action of radial compressive stress, the formation of texture at CW is attributed to the orientation deflection of grains which have larger SF of basal slip system and locate in the region of the maximum texture strength of blank, while the origin of the texture at IR mainly comes from the orientation deflection of grains with a smaller (0.1~0.2) SF of basal slip system.

This paper presents a new method in axles manufacturing called flexible skew rolling (FSR) process and its application exploration was conducted in laboratory by producing a rail car axle. The FSR rolling path for rail car axle was designed and calculated and then programmed into the FSR mill. The material of the rolled shafts was LZ50 steel and its diameter is 60 mm. By conducting experiments, a rail car axle with multistep was rolled successfully. There is no central crack in the rolled piece, and the outer grain is refined into 22.23μm from 76.45μm and the inner grain is refined into 38.94 μm from 83.47 μm. This study results verified that the FSR process is positive and the rail car axle can be rolled by FSR process.

This paper focused on the forming limit curves (FLC) of the AZ31B magnesium alloy sheet metal under different complex loading paths in-plane. Compared with simple loading paths, the study of forming limit of sheet metal under complex loading paths was more practical. In this study, biaxial tensile test of the cruciform specimen was utilized to acquire the FLC after the cruciform specimen was subjected to uniaxial pre-tensile process along rolling direction, which experimentally characterize the forming limits under different pre-strain values of 1.15%, 2.34%, 4.0%, and 5.4%. Subsequently, based on the constitutive model, Hill48 yield criterion and shear failure criterion, the theoretical FLCs of AZ31B magnesium alloy sheet metal was be calculated. Meanwhile, the normal biaxial tensile tests were also simulated by Abaqus to obtain the limit strains by Finite Element Analysis (FEA). Extracting limit strains from the fracture region in FEA model when the first derivative of the strain difference with respect to time reached the maximum value between the first principal strain of necked element and the first principal strain of the element adjacent to the necked zone. As a result, the experimental FLCs was qualitatively consistent with the result of theoretical model and FEA model. In addition, the FLCs of AZ31B magnesium alloy sheet moved to the upper left of forming limit diagram with the increase of the pre-strain, which indicated that the pre-strain process along the rolling direction could significantly improve the formability of the sheet metal.

The heat transfer behavior during wire arc additive manufacturing is closely related to the dimensional accuracy and performance of the formed part. To investigate the thermal behavior of stainless steel 316L straight wall part fabricated by the wire arc additive manufacturing process, a three-dimensional transient finite element model is established based on the double elliptic heat source model. At the same time, the temperature measurement experiment on the characteristic position of the substrate is carried out. The thermal cycle curve obtained by the finite element model is in good agreement with the measured result. By analyzing the simulation results, the finite element model established can effectively reveal the thermal behaviors such as melting, solidification, heat accumulation and remelting during the forming process of the straight wall part. In addition, the solidification parameters obtained by the model are correlated with the microstructure. High G/R induces the production of cellular crystals and columnar dendrites, on the contrary, the formation of equiaxial crystals, which provide guidance for the prediction of the morphology of the microstructure.

Magnesium alloys are an important structural material to many global industries. Their high specific physical properties are useful in the design of lightweight engineering systems. In this study, the development of a numerical model for the prediction of high-temperature extrusion of an Mg-Zn-Ce alloy (ZE20) is presented. A novel design of an I-shaped profile for extrusion processing was created as part of this effort. This design was used to produce extrudates with large strain gradients across a single profile. In parallel, new numerical tools were developed to predict the extrusion behaviour of the ZE20 alloy. Finite element simulation of the indirect extrusion laboratory trials was used to calibrate the numerical model. Microstructural measurements of experimental samples through EBSD analysis were compared with simulation calculations, and insights into the relationship between extrusion temperature, strain, and resulting microstructure were gained. A fully recrystallised, bimodally distributed grain microstructure was observed throughout the samples. Proportions of grain refinement within the bimodal distribution were shown to correspond with localised strain gradients for a profile with nearly uniform temperature. Ultimately, extrusion press load calculations using the numerical model were shown to be within 5% of experimental trial values.

Titanium alloy sheet metal shows promising applicability in the aerospace industry with excellent mechanical properties, while its limited room-temperature formability is essential to be improved by thermal-assisted methods, with expensive equipment and much energy consumption. In this work, the flexible free incremental sheet forming process is adopted to manufacture Ti6Al4V free-form surface panel at room temperature. The strain evolution and thickness distribution during this new process are also analysed through finite element methods to reveal the deformation mechanism. Experimental and simulated results show that this process has potential advantages in rapidly fabricating low-ductility sheet metal with complex shapes at room temperature by improving strain and thickness distributions.

Ti45nb is a commonly used titanium alloy with high strength for aviation. However, it is mainly cold formed under conventional conditions and cracks often occur when deformation is large. Ultrasonic vibration-assisted compression test of Ti45Nb titanium alloy was carried out on a universal testing machine equipped with an ultrasonic vibration system. The influence of ultrasonic vibration on the deformation behavior of Ti45Nb was investigated. The results showed that ultrasonic vibration can significantly reduce the flow stress in the deformation process, and the reduction amplitude increases with the continuation of the compression process. The decrease in flow stress is caused by the stress superposition and acoustic softening effect. Compared to the conventional compression test, the grain in the center of the ultrasonic vibration-assisted compressed sample is finer, and the thickness of the lamellar substructure in the shear band is thinner. Therefore, ultrasonic vibration has a promoting effect on the deformation of Ti45Nb alloy.

A multi-scale numerical investigation of local heterogeneities in the strain and stress fields occurring during forming of explosively welded layered metallic sheets is the main goal of the research. Explosive welding is a complex process involving various phenomena occurring in materials during an impact at high velocities and pressures, especially at the interfaces of colliding metals. As a result, the interface of the layered metallic sheets is often highly heterogeneous at the microscale level, what directly affects the sheet behaviour under subsequent forming conditions. To investigate this issue, the mesh-free numerical model of the explosive welding process is used first to recreate the characteristic features of the interface morphology. Various detonation velocities are used to provide diversified morphological features at the interface. Obtained results are then used as input data to develop the concurrent multi-scale finite element model of material behaviour under deformation conditions. The multi-scale modelling concept with explicit representation of the interface region is used. The highly refined heterogeneous FE mesh was generated in the interface region to capture local heterogeneities occurring at the microscale. Particular attention is put on numerical investigation of an influence of interface morphology in the welding zone on the development of the stress localisation that may directly lead to fracture initiation during forming.

In this work, the static softening behaviour of GH4500 superalloy during the two-pass thermal deformation was investigated via thermal-simulation compression experiments at the temperature range of 1293 K to 1373 K, strain rate range of 0.01 s⁻¹ to 1 s⁻¹ and interval time range of 0 s to 180 s. The metallographic structure acquired from optical microscope (OM) indicated that both static recovery (SRV) and post dynamic recrystallization (PDRX) would occur during the holding stage. Meanwhile, the influence of interval time, deformation temperatures and strain rates on static softening behaviour were revealed. The results showed that the softening effects principally induced by PDRX strengthened with the increase of the interval time, deformation temperatures and strain rates. To quantitatively describe the PDRX kinetic process of GH4500 superalloy, a model on grounds of Avrami kinetics was established to predict the PDRX softening fraction via eliminating the effect of static recovery. The predicted data of the PDRX softening fraction were well consistent with the experimental data, manifesting that the model could precisely evaluate the PDRX softening behaviour in the stage of inter-pass holding.

The effect of the negative clearances between punch and die of a flange with different fine blanking half-cutting depths was investigated for two low carbon steels with various elongation rates, C18E (0.18%C) and 20MnB5 steels (0.2%C, with upper mechanical properties than the carbon steel), industrially used for forming car seat parts. A specific tool adaptable on a tensile machine was built to determine the force needed to fine blank a simple geometry, in the objective to further transpose the obtained results to the complex geometry of industrial parts. Heat treatment was carried out to optimize the microstructure, hardness and dimensional modifications for the combination material/clearance/half-cutting height tested. Increasing the elongation rate of the raw material allows to reach a better formability and reduces the force needed to create a given geometry, but cracks were detected for the extreme deformation rate. Moreover, after fine blanking and heat treatment operations, different microstructures were observed according to the material grade, stable for low alloy 20MnB5 steels (martensitic microstructure) while non reproducible for the low carbon steel (mix of ferrite, bainite and martensite).

Differential velocity sideways extrusion (DVSE) is a novel process for fabricating curved profiles; welding quality during extrusion is an important issue for its industrial application. In this study, solid bars of aluminium alloy AA1070 were extruded from multiple billets at 500 °C using the novel process and the microstructure and mechanical properties of the extrudate were investigated. The weld formed between the billets includes longitudinal and transverse solid-state weld regions formed as the metal was extruded. The longitudinal welds have better mechanical properties than the transverse welds. Dynamic recrystallisation (DRX) occurred in areas with high dislocation density during the extrusion process and as a result, grains across the bonding interfaces of longitudinal welds have been formed, which improves the weld quality. In the areas with the transverse welds, macro weld defects can be observed at the weld front. With further progress of sideways extrusion, the defect density reduced and new grains formed at the bonding surface.

With the advantages of high utilization of raw materials, high precision and low cost, micro metallic parts produced by micro deep drawing (MDD) have been tremendously used in a variety of fields such as micro-electromechanical systems (MEMS), vehicle engineering and chemical engineering. In order to study the deformation behavior of two-layer stainless steel-copper composite foils during MDD, a series of MDD tests were performed with specimens annealed at temperatures ranging from 600 to 1000 °C. The results show that complete circular cups cannot be formed using the as-received material due to its poor formability. For the specimens annealed at 600 and 700 °C, significant wrinkling is observed on the drawn cups. Differently, few wrinkles are characterized on the drawn cups when the composite foils are annealed at temperatures ranging from 800 to 1000 °C. An optimal annealing temperature of 800 °C is obtained for the MDD of stainless steel-copper composite cups with high surface quality.

The control of workpiece properties enables an application-oriented and time-efficient production of components. In reverse flow forming, e.g., the control of the microstructure profile, in contrast to the adjustment of the geometry, is not yet part of the state of the art. This is particularly challenging when forming seamless tubes made of metastable austenitic stainless AISI 304L steel. In this steel, a phase transformation from austenite to martensite can occur due to mechanically and/or thermally induced energy. The α'-martensite has different mechanical and micromagnetic properties, which can be advantageous depending on the application. For the purpose of local property control, the resulting α'-martensite content should be measured and controlled online during the forming process. In this paper, results from an empirical correlation model of process parameter combinations and resulting α'-martensite content as well as geometry will be presented. Based on this, the focus of the paper will be on process modeling by means of FEM in order to create the transition to a numerically supported process model. Furthermore, it will be specified how the numerical process model can be used in a predictive manner for an online closed-loop process control.

In many industries, there is a trend towards miniaturization of technical components, such as drive systems, which enable the solution of high-precision positioning tasks because of their low volume and high dynamics. Geared micro parts are currently mainly produced by cutting and LIGA processes, but in mass production cold forming offers ecological and economic benefits. However, the cold forming of micro gears is restricted to a lower module limit of m = 0.2 mm due to high tool stresses, size effects and handling difficulties. To solve these challenges, in this contribution a three-stage forming process chain for the manufacturing micro gears (m = 0.1 mm) is investigated. In the first stage, a pin as wheel blank is extruded from sheet metal, which is geared subsequently by lateral extrusion. Finally, the micro gear is separated from sheet by shear cutting. The aim of this study is to demonstrate the applicability of the process chain for the materials Cu-OFE and CuZn30. In addition, the influence of the sheet thickness, which has a major impact on the forming process and the material efficiency, is analyzed. The geometrical and mechanical component properties as well as the machine data are evaluated to assess the variables.

To improve the productivity of automated forging production units, reasonable layout is very important. In this paper, the layout optimization method of the robot working unit was studied to improve the production efficiency of forged crankshaft products, the bottleneck production unit is taken as the research object to find a satisfactory solution to the layout planning. Based on a mathematical model, a hierarchical description method of robot workspace and a prediction method of transition points were proposed. The robot running time and operability were used as evaluation indexes of the layout. The NSGA-II algorithm was used to optimize the layout scheme to obtain a better solution, and the optimized solution has better operability and runtime performance. The simulation results of professional software showed that the proposed layout optimization method and layout scheme were reasonable and significantly improved.

Solid state recycling allows direct recycling of metal chips into semi-finished products. This process category proved to lower the environmental impact of metals recycling. Friction stir consolidation (FSC) is a new solid-state technique taking advantage of friction heat generation and severe plastic deformation to consolidate chips into billets. The new frontier of FSC process could be its evolution from recycling techniques towards the concept of upcycling technique: reuse (discarded objects or material) in such a way as to create a product of higher quality or value than the original. The authors have recently successfully applied FSC for producing multi-material based functionally graded materials (FGM). In this paper, the forgeability of the billet consolidated out of two dissimilar aluminium alloys AA 7075 and AA 2011-T3 chips, was analyzed. A proper forging test was designed, and mechanical and metallurgical properties of the forged parts were assessed through Vickers hardness measurements.

Friction stir processing (FSP) is a method to produce severe plastic deformation (SPD) of materials, which can well improve and optimize the microstructure and mechanical properties of Mg-Li alloy. In this paper, the FSP experiment of LA103Z Mg-Li alloy was conducted, and the influence of process parameters on the microstructure, tensile strength, elongation after fracture and fracture morphology of the material was studied. The microstructure of the Mg-Li alloy after FSP was significantly refined. With the increasing rotational speed of the stirring head, the grain boundaries became clearer and more distinguishable, and the low angle grain boundaries transformed into the high angle grain boundaries. With the increasing feed speed of the stirring head, the grain refinement became more pronounced, and the dispersion of α-Mg phase in the stir zone became more uniform and distributed at the grain boundaries. When the rotational speed and the feed speed of the stirring head were 800-1000 r/min and 100-200 mm/min respectively, the comprehensive performance of the Mg-Li alloy plate after FSP was expected to be optimal.

Isothermal hot stamping process, which is composed of stamping and subsequent stress-relaxation steps, is an important technology to form complex thin-walled titanium components in the aerospace industry. It is a key issue to enable the accurate simulations of these two steps simultaneously for the process design and optimization. In this study, a unified constitutive model connecting both the plastic flow behaviour in stamping and the stress-relaxation behaviour in subsequent step is developed by considering the continuous evolution of key microstructures, i.e., dislocation density, in the whole process. A series of basic mechanical tests, including tensile and stress-relaxation tests, of a typical titanium alloy Ti-6Al-4V at 750°C was performed to calibrate the developed model. The unified model was then implemented into the commercial software ABAQUS via the VUMAT subroutine, and simulations of the complete hot stamping process were done, including stamping, stress-relaxation and final springback. In addition, a typical curve-shape component was hot-stamped at 750°C and stress-relaxation for 5 minutes was performed. The predicted result from the developed constitutive model and FE model shows a good agreement of the springback with the corresponding experimental result, verifying the effectiveness of the developed model for the further applications in hot stamping process design and optimization in the industry.

In this paper results on shear bands developed in pure iron are presented. The main focus was put on microstructural characterization and crystal lattice rotation in sheared regions. The hat-shaped samples were deformed at a high strain rate of 560 s⁻¹ using a drop-hammer. The microstructure of deformed specimen was investigated by optical microscopy and scanning electron microscopy equipped with a high-resolution electron backscattered diffraction facility. The changes of mechanical properties in the band area and neighbouring matrix were investigated using nano-indentation test. This paper clearly shows that initial stages of shear bands formation are associated with the formation of kink-type bands. The orientation maps revealed the crystallographic determination of the shear band formation. During deformation in each grain located within the sheared region, one of the {110}-type planes situate along the macro-shear band plane and <111> direction situates along the shear direction. In consequence, the formation of specific texture components within the shear band region was observed, different from texture observed in deformed matrix. In micro-scale no effects of dynamic recrystallization were observed. Nano-hardness tests indicated that notable increase of strain hardening is related to the strain localization in narrow shear band' regions, while the matrix undergoes almost no deformation.

The honeycomb sandwich structure reflector panel is a multilayer structure formed by three-layer aluminum plate and two-layer honeycomb bonded by epoxy resin adhesive, and its thermal deformation behavior is complicated. In this study, the thermal deformation behavior of the reflector panel is studied by a combination of experiment and finite element simulation.

Firstly, the thermal deformation analysis finite element model of reflector panels with honeycomb sandwich structure is established. The three-layer aluminum plate is modeled according to actual geometric parameters and adopts shell element model. The honeycomb core is equivalent to a homogeneous orthotropic layer with a constant thickness. The elastic modulus of the equivalent model of the honeycomb core with adhesive are obtained through the tensile and compressive mechanical performance tests. Then, the temperature deformation experiment of the honeycomb sandwich structure panel is carried out. Combined with the experimental results and the thermal deformation simulation analysis model, the multi-island genetic algorithm is used to modify the thermal expansion coefficient of the honeycomb core layer.

Finally, the thermal deformation behavior of the reflector is verified by finite element simulation and experiment. The results show that the profile error distribution caused by the panel thermal deformation has continuous symmetry. From the error distribution trend and numerical deviation, the established simulation model can be used to predict the thermal deformation of sandwich panels.

Tribological developments including lubricant and die material etc. contribute to improvement of die life and product quality in forging. They have used several tribological tests in laboratories. A container-less tapered-plug penetration test was proposed to estimate tribological properties of lubricants with prevention galling and reducing friction. This simple test uses a thick and hollow specimen so that pressure can be higher even without the container. Not to use the container can limit the frictional interface between a tapered-plug and a specimen. Consequently, the friction directly affects the forming load, and it is more simply and precise to estimate the frictional coefficient. In this paper, the frictional coefficient between the tapered-plug and the specimen is estimated using a perturbation method with both FEM analytical and experimental data on the forming load. A change in the frictional coefficient is also indicated during the test.

In order to modify heat and mass transfer, alter crystal orientation and suppress elemental segregation of the molten pool by electromagnetic stirring effect, a new in-situ transverse magnetic field generated by clamp-type electromagnet integrated with a 6-axis robot was firstly applied to real-time control the arc characteristic and fluid flow when welding 316L stainless steel by GMAW-CMT. As the magnetic field intensity at the end point of the wire increases from 0 mT to 14.6 mT and then 20.7 mT, the 316L welding bead morphology becomes flatter, and their cross sections clearly exhibit a lower welding reinforcement, a wider welding width and a smaller welding penetration. Microstructure observations show that the application of in-situ transverse magnetic field in GMAW-CMT process can contribute to the lower inner porosity, the smaller stress concentration, the more dispersed austenite grain orientation and the elimination of residual skeletal ferrite distributed in the austenite matrix. CPP and EIS tests indicate that 14.6 mT molten pool exhibits the highest pitting corrosion resistance and the most compact passive film, which is related with the finer cellular γ grain with dispersed orientation and less Cr-Mo atomic segregation on the boundary. The deflection of arc column and the fragmentation of dendritic tips induced by the Lorentz force under the appropriate transverse magnetic field are verified, which provides great potential for optimizing weldment performance.

Wire arc additive manufacturing (WAAM) technology offers a material-saving and efficient method of manufacturing the 300M steel components, but the obtained microstructure and properties hardly reach the level of wrought materials. By combining WAAM technology with forging process, a novel forming process is proposed. The preferred shape pre-forgings are easily prepared, and the number of forging steps significantly decreases. The WAAMed as-cast microstructure also can be transformed into the wrought state by the proposed forming process. The aim of this study is to investigate the hot deformation behavior and microstructure evolution of WAAMed 300M steel under various deformation temperatures and strain rates. The results show that the WAAMed 300M steel exhibits a higher plastic deformation resistance than the wrought 300M steel. With the increase of deformation temperature and strain rate, the difference of flow stress between the WAAMed and wrought 300M steel decreases. The hot deformation activation energy of WAAMed 300M steel is calculated as 374.1 kJ/mol, which is much higher than that of wrought 300M steel (332.3 kJ/mol). The possible processing windows obtained from the hot deformation activation energy maps are 1040-1120 °C/0.01-10 s⁻¹ for the WAAMed 300M steel and 1010-1130 °C/ 0.1-10 s⁻¹ for the wrought 300M steel. The constitutive model considering strain compensation is established to describe the hot deformation behaviors of WAAMed and wrought 300M steel. The high correlation coefficient and low average absolute relative error confirm the suitability of the developed constitutive models for predicting the flow stresses of WAAMed and wrought 300M steel.

The surface micro groove structure on metallic components has received extensive attention for its role in improving the heat transfer coefficient. Limited by the size effect, it is difficult to manufacture μ-scale micro groove structure with large depth-to-width ratio through conventional extrusion or rolling processes. A novel UV assisted ploughing-extrusion process was proposed to manufacture μ-scale micro grooves. A series of UV assisted compression tests were conducted to study the acoustic deformation behavior of α-Ti, and a modified Ludwik model were established., The influence of deformation parameters was investigated, and the optimized deformation parameters are the leading angle is 60°, the extruded angle is 40°, and the ultrasonic amplitude is 10.30 μm. The results indicate that the novel ultrasonic vibration assisted ploughing-extrusion is able to continuously form large-sized micro-grooves parts with high quality.

Ti₂AlNb-based intermetallic alloy has a great potential application in the manufacturing of aeronautical structures. However, the casted ingots of this alloy often consist of very coarse grains even as large as in centimetre level. The refinement of the coarse grain by hot deformation is essential for prompting this material to the engineering applications. In this work, multi-directional isothermal forging (MDIF) was conducted on Ti-20Al-24Nb at 1200°C and 1050°C with 2, 4, 6, 8 and 10 cycles, and a comparative study was emphasized on the grain refinement by two different reductions (30% and 40%) in each compression. The microstructure evolution has been systematically investigated. Results show that dynamic recrystallization (DRX) occurred preferentially near grain boundary, and very large strains were required to refine B2 grains. For 40% reduction per compression, the recrystallization volume fraction after four cycles was more than 95%, and the grain size was evenly refined from centimetre level to ~250μm. However, for 30% reduction per compression, the original coarse grains still exist after 10 cycles, and the recrystallization is far from complete, although the total strain is much greater than the process by using 40% reduction but with fewer cycles. The results demonstrate that the grain refinement of this material depends mainly upon the height reduction per compression and the deformation temperature and the magnitude of deformation or strain is not the critical factor to determine the recrystallization.

During hot rolling process, an oxide scale grows at the surface of steel slabs. To avoid surface defects such as embedded scale at the end of the finishing mill, descaling stands are added in the production line to remove it using high-pressure water jets. Different steel grades show different descaling capacities and final surface qualities, which may depend on composition through oxide and interface toughness. The idea of this study is to measure the latter using micro-indentation to feed thermomechanical models of the descaling process. After indentation, Focused Ion Beam (FIB) is employed to observe cracking and delamination of oxidized specimen and to calculate adhesion of oxide thanks to an analytical formula. The experimental study confirms that alloying elements have a strong influence on the adhesion of oxide film and suggests that difficult-to-descale grades are those showing a large scatter of interfacial toughness. In parallel, numerical finite element (FEM) simulations of indentation are carried out using Abaqus® to have a better understanding of cracking mechanism and delamination of oxide.

The size of aluminum alloy fiber wire with a short side of 5mm, a long side of 10mm and an arc radius of 1mm were prepared from the raw material of 6061 aluminum alloy fiber with diameter of 0.15mm by Spring machine cutting, namely the structure size of 5×10mm bending aluminum alloy fiber. The aluminum alloy fiber porous body with different porosity were prepared by vacuum hot pressing sintering furnace, and it was sleeved with 6063 aluminum alloy round tube to prepare aluminum alloy fiber porous body filled tube. The impact test was carried out with drop hammer impact testing machine, The plastic deformation behavior of aluminum alloy fiber porous body and its filled tube under impact loading with different porosity was studied. The results show that the impact process of aluminum alloy fiber porous body can be divided into three stages: plastic platform stage, densification stage and unloading stage, the filled tube with aluminum alloy fiber porous body can be divided into four stages: elastic deformation stage, progressive buckling stage, densification stage and unloading stage. Low porosity will make more fibers, and more benefit the generation of the sintering necks, the plastic deformation strength increases with the porosity decrease. The coupling effect of the aluminum alloy tube and the aluminum alloy fiber porous body makes the filled tube absorb the same energy with shorter impact displacement, and has stronger impact resistance and better mechanical properties.

The rapid drop of peak flow stress in the initial stage of hot compression experiment was found to be related to the occurrence of dynamic transformation from alpha phase (hcp) into beta phase (bcc) of a near α high-temperature titanium alloy. In order to predict the flow stress at all strain, the dynamic recovery (DRV) model and the Back-Error Propagation (BP) neural network architecture were established and comprehensively utilized to characterize the flow stress, which exhibited high accuracy in tracking the flow behavior at different deformation parameters. The variation of peak flow stress at initial stage of hot compression indicated that the rapid drop extent of peak value increased with the rise of deformation temperature, the decrease of strain rate and the increase of strain. It was worth noting that the dynamic transformation evolution in the microstructure exhibited the consistent variation of peak flow stress with different deformation parameters. The high-magnification microstructure analysis indicated that the dynamic transformation was accomplished by the immigration of α/β interface and the penetration of beta phase into alpha phase from edge to inside, all of which were related to the dislocation motion. The experimental result proved that the dynamic transformation was the dominant factor resulting in the rapid drop of peak flow stress at the initial stage of hot deformation.

True fracture strains obtained from the fracture surface area measurement of tensile test specimens allow for gauge-length independent characterization of the local formability. It is difficult and error prone to use the norm method (ASTM-E8) for fracture area measurement on modern advanced high strength steels (AHSS) owing to the irregular fracture surface and excessive necking, as this makes the accurate identification/measurement difficult and leads to high scattering. The presented work aims to solve this problem in local formability measurement and make the measurement process more robust. The results of the proposed approach, which involves specimen masking and image binarization show that through this method it is possible to improve the repeatability of the measurements, reduce the scattering due to operator influence and significantly reduce the time required for the measurements.

In bending process of sheet materials, a springback is remarkable due to the residual stress generated inside of the material, which greatly affects the product accuracy. In order to suppress the springback, the rubber-assisted stretch bending method, which bending process is performed with applying a tensile force in the longitudinal direction of a sheet material has been proposed. We propose the optimum arrangement of the two kinds of rubbers for the "rubber-assisted stretch bending method" for the uniform bending with a constant curvature radius. The optimum tensile stress is realized by each frictional force between the individual rubber and specimen. And since the rubber is partially affixed to the dies, the bending deformation is carried out by the metal surface of the die material, improvement of shape accuracy can be expected. The upper and lower dies are divided into three division on the surface, and the two elastic rubbers are placed on each part on the bending surface of the die. The springback was decreased to 17% in comparison with simple bending using ordinary metal dies by the optimum arrangement of rubber layout.

Metallic bipolar plates (BPPs) are key components of the proton exchange membrane fuel cell (PEMFC). To lower the fabrication cost of metallic BPPs, precoated BPPs have attracted much attention due to the high efficiency of precoating-stamping process. However, precoatings on metallic substrate tend to crack during the forming process, leading to deterioration or even complete loss of corrosion resistance. Therefore, to avoid micro cracks of formed precoated BPPs, development of coatings with high ductility is necessary. In this study, Niobium coatings with different thicknesses on SS316L substrate are prepared with magnetron sputtering process, and uniaxial tensile tests are then conducted for the precoated specimens to evaluate their ductility. The microstructure and fracture behaviour of the Niobium precoatings are characterized by XRD, SEM, TEM, laser confocal microscope analysis. It is found that with the increase of coating thickness, the number of micro cracks at the same strain decreases significantly, and the strain for the first crack to appear also increases. Furthermore, a brittle-to-ductile transition of fracture mechanism is observed. The grain size of Niobium nanocrystalline coating increases with the thickness, which leads to the improvement of plasticity and failure strain. Therefore, the application of precoated metallic BPPs is further advanced.

Carbon neutrality and carbon peaking are one of the key tasks of our country in the future. As a major carbon producer, the steel industry played an important role in achieving energy conservation. The feasibility and benefits of rapidly heating (over 100 °C/s) has been proven to be effective for producing press hardening steel, which can also shorten the hot forming process. In this work, we studied the application of short hot forming process in a medium manganese steel. Results shown that the new process can greatly reduce the austenitizing time while ensuring the strength of the materials. In addition, the short-term heating of the material in a non-equilibrium state exacerbated the uneven distribution of alloying elements. Thus, the content of retained austenite in the final microstructure doubled (increased from 8.7% to 18.5%) through the new process, thereby further improving the toughness of the material. The microstructure evolution and mechanical properties of the material under the short process hot forming process was analysed, together with the feasibility of the new process in the future industrialization.

Canning extrusion is an effective way to refine grains, eliminate defects from hot isostatic pressing consolidation and enhance mechanical properties of P/M nickel-based superalloy. The present research constructed the optimized extrusion processing window for superalloy in consideration of extrusion speed, initial billet temperature, and extrusion ratio to provide guidelines for the choice of extrusion parameters. The processing window was built by integrating the results of finite element (FE) simulations, extrusion experiments, and deep neural network (DNN). The peak extrusion load and temperature under different extrusion parameters were collected as input datasets by FE simulations. The DNN was trained by optimizing the learning parameters and then predicting the load and temperature over various extrusion conditions. Finally, the extrusion processing window was established, including an optimized processing zone and two instability zones. The extrusion experiments were performed to verify the reliability of the processing window, which could be able to promote the extrusion production of nickel-based superalloys with high efficiency and quality.

In the automotive industry, hot stamping has been established as a key technology for manufacturing safety-related car body components with high strength-to-weight ratio. During the forming operation, however, hot stamping tools are highly stressed by cyclic thermo-mechanical loads, which encourage the formation of severe wear and high friction at the blank-die interface. Against this background, an innovative surface engineering technology named laser implantation has been investigated for improving the formability of the parts and the efficiency of the hot stamping process. The laser implantation process is based on the generation of highly wear resistant microfeatures on tool surfaces by embedding hard ceramic particles via pulsed laser radiation. As a consequence, the contact area of the tool and thus the tribological and thermal interactions at the blank-die interface are locally influenced. In previous studies, the improved tribological performance of the modified tool surfaces has already been proven. However, the thermal interactions between tool and workpiece have not been analyzed, which in turn have a significant impact on the resulting part properties. In this regard, quenching tests have been carried out under hot stamping conditions by using conventional as well as laser-implanted tooling systems. Based on these results, Vickers hardness test and optical measurements have been performed on the quenched blanks, to qualify the mechanical properties and clarify the cause-effect relations.

A unified viscoplastic constitutive model based on continuum damage mechanics (CDM) has been recently developed for the prediction of forming limit curves (FLCs) and fracture forming limit curves (FFLCs). In this CDM model, two damage variables which are strain path dependent (so called strain-based model) have been introduced to model the necking and fracture limits in sheet metal forming. In this study, the two damage variables have been modified by replacing the strain components with stress components to model stress path dependence (so called stress-based model). Then the two sets of CDM models have been analysed and compared in respect to their computational accuracy and efficiency. For this purpose, all the material constants in the models have been calibrated using the recently published data of 22MnB5 boron steel sheet under hot stamping conditions. Subsequently, the two models together with the calibrated material constants have been implemented into the commercial software ABAQUS using a user subroutine VUMAT, and applied to biaxial tests for the computation of both the necking and the fracture limit strains at hot stamping temperatures. Computational results show that there is little difference between the two CDM models with respect to the computed limit strain values, but the strain-based CDM model is more time-efficient.

Formability is an essential material property that needs to be considered when selecting materials for hot stamping applications. Due to the difficulties of achieving rapid cooling before deformation and the failure of lubricant systems, however, it is challenging to use conventional Nakajima and Marciniak tests to evaluate the formability of materials under hot stamping conditions. Recently, biaxial test methods have shown great potential to overcome this challenge. In this paper, recent developments of the biaxial test methods for formability evaluation are reviewed, including testing machines, specimen designs, specimen heating methods, testing procedures, and limit strain determination methods. Compared to the Nakajima or the Marciniak tests, the biaxial test method can provide better simulation for hot stamping conditions and it can be a promising method for evaluating the formability of sheet metals under hot stamping conditions. However, more developments such as the standardisation of the specimen designs and the limit strain determination methods, are still needed for the wide use of the biaxial test method.

Microstructure evolution and interface characteristics of dissimilar TC4/TB8 titanium alloys subjected to diffusion bonding and aging treatment are investigated. TC4/TB8 alloys plates can be metallurgically bonded at 830°C for 2h under 18MPa. The microstructure of TC4 alloy is composed of fine intergranular β grains and equiaxed α grains due to recrystallization. The α grains characterized by lath-like, granular, and continuous layer morphology are precipitated from β matrix in the TB8 alloy during furnace cooling and aging treatment. Element distribution mapping and line-profile data indicate that Mo atoms diffuse from the enrichment area (TB8) to the depleted area (TC4), while a small amount of Al and V atoms diffuse along an opposite direction. In addition, the behavior of grain growth across the bonded interface is not obvious under the current parameters.

Functionally gradient materials (FGMs) with continuous variation in composition or microstructure can realize gradient properties in different positions of the same component. The layer-by-layer laser deposition additive manufacturing is one of the most promising technologies that prepare FGMs with gradient properties. The present study is focused on the preparation of gradient titanium alloy by laser depositing Ti₂AlNb powders on the substrate of a near-α high temperature titanium alloy. The microstructure, composition, and micro-hardness of prepared gradient titanium alloy with and without transition layer were compared and analyzed. Results show that an obvious bonding interface with variant microstructure morphology and element contents formed during directly deposited Ti₂AlNb powders on near-α titanium alloy substrate and the bonding interface exhibits higher micro-hardness than the substrate and the deposited zone. However, the microstructure and the element exhibit gradient distribution characteristics along the deposition direction after adding the mixed powders of both two alloys as intermediate transition layers between the near-α titanium alloy and the Ti₂AlNb alloy. The gradient distributed micro-hardness from the substrate to the top deposited zone sufficiently demonstrates the feasibility of obtaining gradient properties of gradient titanium alloy with composition transition layer during laser depositing.

Local amorphous phases often appear in NiTi shape memory alloys (SMAs) which undergo a large degree of cold plastic deformation. Fracture damage is a common failure mode of NiTi SMAs in engineering application and it is usually caused by the crack initiation and propagation. The crack initiation and propagation behaviours in NiTi SMA parts containing amorphous phases have not been reported so far. In the present study, extended finite elements method (XFEM) was applied to investigate the influence of amorphous phase on crack initiation and propagation behaviours in a notched NiTi SMA specimen processed by cold plastic deformation. The results show that the amorphous zone has a significant influence on both the crack initiation and the crack propagation. Crack is easier induced if there exists amorphous phase in the NiTi SMA but it is difficult for the crack to pass through the amorphous zone.

This research aims to characterize the anisotropic hardening behaviour AA3003-O under uniaxial tension by experiments and analytical modelling. Experiments are conducted with dogbone specimens along different loading directions under quasi-static conditions to characterize the strain hardening behavior of the alloy under different loading conditions. Experimental results show the strong anisotropic hardening behaviour of the alloy under uniaxial tension along different directions. The anisotropic hardening behaviour is analytically characterized by the Yld2000-2d, Stoughton-Yoon2009 and a newly proposed anisotropic hardening models. The analytical predicted yield surfaces are compared with experiments and other constitutive models. It demonstrates that the proposed functions provide the best accuracy for the modelling of anisotropic hardening behaviour of uniaxial tension along different directions.

Regarding to the impact of temperature on springback in hot stretch bending (HSB) process, this work proposed an investigation on temperature uniformity control of titanium extrusion in HSB process based on the mould which can be elevated by resistance heating. Prior to the HSB test, mould structure was designed to fit for resistance heating. Coupled thermal electrical structural finite element model of HSB process was created in ABAQUS. Resistance heating and HSB tests were performed using displacement control electrically assisted stretch bending machine. The results of simulation indicate that the temperature uniformity of titanium extrusion and the forming accuracy of curved part can be effectively improved by increasing the initial temperature of mould. At last, the curved part of titanium extrusion with L-section was achieved, and the forming accuracy of which was measured and evaluated.

Wide aluminium panels with stiffeners are extensively applied in aviation, bridge and marine structures due to their high stiffness and light-weighting. Many efforts and contributions have been made to overcome the manufacturing difficulties of wide aluminium stiffened panels over years. The aim of this study is to analyse and compare current methods for producing wide stiffened panels for different applications. The manufacturing techniques for stiffened panels such as riveting, welding, machining, additive manufacturing, extrusion, are discussed. Thereinto, extrusion is a very promising technology in the production of wide aluminium stiffened panels as it can efficiently obtain extruded products with high material utilisation, good mechanical properties and structure integrity. Therefore, the methods of widening the stiffened panels in extrusion technology such as spread extrusion and postproduction flattening after extrusion are analysed emphatically. The present study is an attempt to analyse these efforts in order to guide future work in the area of producing much wider aluminium stiffened panels.

The latest hot stamping processes can enable efficient production of complex shaped panel components with high stiffness-to-weight ratios. However, structural redesign for these intricate processes can be challenging, because compared to cold forming, the non-isothermal and dynamic nature of these processes introduces complexity and unfamiliarity among industrial designers. In industrial practice, trial-and-error approaches are currently used to update non-feasible designs where complicated forming simulations are needed each time a design change is made. A superior approach to structural redesign for hot stamping processes is demonstrated in this paper which applies a novel deep-learning-based optimisation platform. The platform consists of the interaction between two neural networks: a generator that creates 3D panel component geometries and an evaluator that predicts their post-stamping thinning distributions. Guided by these distributions the geometry is iteratively updated by a gradient-based optimisation technique. In the application presented in this paper, panel component geometries are optimised to meet imposed constraints that are derived from post-stamping thinning distributions. In addition, a new methodology is applied to select arbitrary geometric regions that are to be fixed during the optimisation. Overall, it is demonstrated that the platform is capable of optimising selective regions of panel component subject to imposed post-stamped thinning distribution constraints.

Increasing requirements on lightweight construction to preserve resources necessitate new processes and methods in the production of weight-optimised multi-material-systems. Common joining processes such as the conventional semi-tubular self-piercing riveting are reaching their limits because of the rigid process designs. To extend this process, the linear punch movement is superimposed by an orbital forming process with a tumbling kinematic and provides new possibilities to influence the joining process. The configuration of the tumbling strategy consisting of the parameters tumbling angle and tumbling kinematics enables a targeted control of the material flow for the production of tailored joints. Within the scope of the investigations, the influence of the two parameters is examined both for the joining process and for the resulting joint formation. Force-displacement diagrams, micrographs and rivet head geometries are analysed to determine the influence on the process itself. Further, shear tensile tests and cross section tests are carried out to characterise the load-bearing capacities of tumbled joints and to identify the effects of the tumbling strategy on the mechanical properties. The tested materials in form of a dual-phase steel HCT590X+Z and a precipitation-hardening aluminium alloy EN AW-6014 have widely varying mechanical properties to represent multi-material-systems.