Review on Multi-pass Rolling Forming of Thin-walled Ring with Complex Section

Superalloy thin-walled ring with complex cross section plays an important role in aerospace, energy and chemical industry, and it has excellent mechanical properties and oxidation resistance in high temperature and pressure environment. However, multi-pass rolling forming of thin-walled ring with complex cross-section of superalloy is a complex forming process that needs to undergo complex uneven plastic deformation under the coupling of multiple fields and factors. The research progress of multi-pass rolling forming of superalloy thin-walled ring with complex cross section is summarized from three aspects: deformation behavior and stress analysis, defect behavior analysis, process optimization and simulation, and several directions that need further research in the future are put forward.


Introduction
Superalloy thin-walled rings are widely used in aerospace, weapons and petrochemical industries because of their high temperature resistance, light weight, simple structure and good vibration tracking [1].With the rapid development of aerospace industry, the demand for thin-walled rings (aero engine sealing rings, receivers and compressor cones [2]) with complex cross-section of superalloys is increasing.Therefore, it is essential to develop precision forming technology for such parts.Multi-pass roll forming technology [3] is a chip-free, continuous progressive forming processing method, which can meet the requirements of high-precision and digital manufacturing of thin-walled parts, and has occupied an important position in aerospace, nuclear industry and petrochemical industry [4].
The forming process of thin-walled rings with complex interfaces of superalloys is generally rolled and welded into a ring blank by thin plates, and then rolled into the required parts through multiple passes as shown in Figure .1.However, the material undergoes complex plastic deformation under the action of multi-field and multi-factor coupling during the multi-pass rolling forming process of a thin-walled ring with a complex cross-section, which usually leads to very uneven plastic deformation during the forming process, and the rolling parts are prone to wrinkles, non-roundness, springback, cracking, and dimensional and shape accuracy that are not up to standard.This paper mainly introduces the research progress of thin-walled ring multi-pass rolling forming of complex sections of superalloys from three aspects: deformation behavior and stress analysis, defect behavior analysis of parts, process optimization and simulation.

Rolling Deformation Behavior and Law
Ring rolling forming is a nonlinear and unstable forming process that is influenced by a number of elements.It has strong synergistic limitations that must be met in order for the roller forming molds to cooperate with one another.The rolling forming process of thin-walled ring sections has been the subject of much experimental research and numerical simulation by numerous academics both domestically and internationally.
Figure .1.Schematic diagram of the roll forming of ring [5] The influence of process parameters such as bending radius, roller speed, wall thickness and other process parameters on the rebound of the profile during the process of profile bending were discussed by Elkins [6] and Wang [7], and optimized the rolling process parameters based on these laws.In addition, compensation measures are proposed to reduce the springback effect of the profile after bending.Hansen et al. [8] studied the variation of strain and stress during the rolling forming process of the plate by using a simplified model of the plate processed by the roller bending machine.The equations for calculating the deflection angle and bending radius are derived.The research of Hansen et al. is of great significance for understanding the mechanical behavior of sheet machined by roller bending and designing the rolling process.They provide a feasible calculation method for the processing of sheet metal by roller bending machines and provide the basis for further research.Xiao et al. [9] selected symmetrical grooved thin-walled annular parts, used copper sheet, analyzed the mechanical characteristics, main forming defects and forming limits of roll-forming thin-walled annular parts through finite element simulation and forming test, and gave the stress-strain distribution in the deformation zone of the specimen.Li et al. [10] studied the rolling forming process of stepped annular sheet metal parts, and designed a roller to meet the rolling needs, which solved the problems of distortion of the profile and uncertain material deformation of the rolling forming process.
In terms of rolling experimental research, Ma et al. [11] conducted experimental research on tubeless rim rolling forming, analyzed the root cause of lateral force, and found that in the rolling forming deformation, the amount of deformation distribution in each pass was different, and the lateral force was also different.The influence of relevant forming parameters on the quality index of U-shaped steel roll bending were studied by Bui [12],this search used numerical simulation method to establish a model of multi-pass progressive forming U-shaped steel roll bending, the results showed that there were two material properties for the more obvious parameters of U-shaped steel roll bending and forming, namely the yield limit and hardening index of the material, while the friction coefficient between the mold and the U-shaped steel had no obvious effect on the forming result.Li et al. [13] used finite element simulation software to simulate the process of roll forming of aluminum alloy spherical curved sheet material, and found that with the increase of spherical curved surface roll forming passes, the plasticity of aluminum alloy and the wall thickness of curved surface became larger.Guo et al. [14] established a simulation model of U-ring rolling forming based on numerical simulation, which effectively solved the key technologies in the modeling process, such as the design of rolling mold, material properties and meshing and other key steps, and verified the feasibility of U-ring rolling forming simulation through experiments.Guo [15] established a three-dimensional finite element model of multi-pass rolling forming based on ABAQUS/Explicit, studied the stress-strain variation law of W-ring rolling forming process, and found that the peak value of the ring increased rapidly during the feed loading forming stage of the driven roll, and the peak value of the equivalent force of the ring part remained basically unchanged after entering the rolling stage.
The above results show that the finite element simulation software can not only make up for the shortcomings of multi-pass rolling row research of thin-walled rings with complex sections, but also can be more comprehensive and accurate than theory and experiments.The combination of numerical simulation and experiment can conduct a comprehensive and efficient study on the multi-pass rolling forming of thin-walled rings of complex sections of superalloys, it is an effective method for studying the rolling forming of thin-walled rings of complex sections.

Analysis of Rolling Defect Behavior
Multi-pass rolling forming of complex cross-section toroids of superalloys is an uneven plastic deformation process under the coupling of multiple factors, which usually leads to the rolling parts being prone to wrinkles, non-roundness, springback, cracking and other defects.These defects seriously affect the forming quality of thin-walled rings of complex sections of superalloys, and are difficult problems that researchers have been trying to solve.
Peng [16] based on the finite element model of radial axial ring rolling established by DEFORM-3D software platform, it is found that with the increase of drive roll speed and drive roll diameter, the smaller the roundness error and the closer the final diameter is to the ideal diameter.In order to solve the problems of ellipse and irregular circle, Chen [17] adopted the method of combining theory modeling and finite element simulation, the effect of rolling process parameters (feed speed and rotation speed of lower roll) on the roundness of the cylinder pitch was studied, it is found that the roundness of the cylinder can be improved by reducing the feed speed of the upper roller and the rotational speed of the roller.Jian [18] established a reliable finite element model of multi-pass rolling forming process of complex cross-section torus based on ABAQUS finite element platform, and systematically studied the influence of forming parameters such as drive roll speed, driven roll feed speed, friction coefficient between drive roller and ring parts, and friction coefficient between driven roller and ring on roundness in the process of multi-pass rolling forming of ring parts, and combined with theoretical analysis, the causes of ellipses are explained in detail.Xiao et al. [9] used finite element simulation and experimental research to study the defect analysis of the rolling forming of thin-walled rings with copper strip groove, and the results showed that the size of the thickness to width ratio is an important influencing factor determining wrinkling or cracking, and increasing the rolling coefficient can improve the forming limit.Hu [19] used LS-DYNA's Element-Free Galerkin Method to analyze the rolling forming of U-shaped sections, studied the displacement law and strain distribution of edge nodes of U-shaped plate metal rolling, and compared the EFG numerical simulation results with finite element simulation and experimental results, which verified its effectiveness and superiority.The springback angle prediction model established by the hybrid response surface method is used to realize the prediction and optimization of the springback angle of typical U-section roll forming.Chen et al. [20] used numerical simulation methods to study the effects of maximum compression ratio and plate thickness on wrinkling defects during continuous rolling.The results show that when the maximum compression ratio is too large, the middle part of the convex surface and the edge of the saddle part are prone to wrinkle defects, and the degree of wrinkling increases with the increase of the maximum compression ratio.Increase the thickness of the plate and have an inhibitory effect on wrinkle.
It can be seen that the current research on cracking, wrinkling, non-roundness and springback defects in the process of multi-pass rolling forming of thin-walled rings of complex cross-sections is mainly carried out from two aspects: the factors affecting the defects and the process methods for eliminating defects.The research results effectively reduce and eliminate defects and improve the forming quality of formed parts.

Rolling process Optimization and Simulation
Multi-pass rolling forming of complex cross-section toroids of superalloys is a complex plastic deformation process under the coupling of multiple fields and multi-factors, which requires very harsh process parameters.If the process parameters are slightly unreasonable, it is extremely easy to cause defects or even scrap of the workpiece.Therefore, studying the influence of process parameters on the multi-pass rolling process of thin-walled rings of complex sections of superalloys and determining the selection criteria of reasonable process parameters are still the focus of current research on thin-walled rings of complex sections.
Lv et al. [21] conducted experimental research on the rolling forming of steel rims, and the results showed that increasing the friction factor was conducive to the forming of the workpiece, and when the friction factor increased to 0.3, the effect on the forming wall thickness was not obvious.Ma Yao and Ran Jing [22] aimed at the problem of uneven deformation during processing, taking the W-shaped metal sealing ring as the research object, and studied the deformation law and process parameters of ring blanks on the forming accuracy during processing.When it is found that the diameter of the main roller is 1/3 of the diameter of the workpiece, the rolling processing accuracy is the highest; with the increase of feed speed, the machining accuracy gradually decreases; the rotational speed has little effect on the machining accuracy.Zhao et al. [23] systematically analyzed the multi-pass rolling forming of high-temperature alloy GH4169 thin-walled W-shaped ring based on finite element simulation and combined with experimental and theoretical methods.By proposing a characterization method for the degree of uneven deformation, the influence of friction on the uneven deformation of multi-pass rolling forming of thin-walled rings with complex sections of superalloys is studied.The friction control principle is obtained: that is, the friction between the drive roller and the ring is controlled at about 0.2, the friction coefficient between the driven roller and the ring is controlled at about 0.2, and the guide roller is dry friction.Li et al. [24] established a three-dimensional elastoplastic finite element model of GH4169 thin-walled W section sealing ring multi-pass rolling forming based on ABAQUS/Explicit platform, analyzed the influence of process parameters on the change of wall thickness of ring parts, and obtained suitable multi-pass roll forming process parameters, among which: the speed of the drive roller was 2 rad/s, the feed roller feed speed was 0.2mm/s, and the friction number between the feed roller and the ring was 0.1.
The above results show that the optimization research on multi-pass rolling forming of thin-walled parts with complex cross-section of superalloy is mainly based on simulation and simulation.The method has a short design cycle, rapid and accurate experimental results, and meets the needs of process digitalization and high-tech development, and has become a feasible and reliable way to optimize the design of multi-pass roll forming process.

Conclusion
In the process of rolling forming complicated cross-section thin-walled superalloy parts, the forming quality can be predicted and controlled by integrating computer modeling simulation optimization with theoretical analysis and experimental investigation.Therefore, this is an effective way to study such complex plastic forming processes.Scholars mainly use experiments combined with finite element simulation methods to study the multi-pass rolling forming of thin-walled rings of complex sections, mainly focusing on the thickness of billet, roller parameters and speed, feed speed, friction coefficient between billet and roller, and then obtain the corresponding forming law.However, in multi-pass roll forming, there are still some shortcomings in the current research, such as the stability of forming accuracy, the influence of grain behavior and rebound amount control on forming quality during deformation, etc., which need to be further studied.It is of great significance to develop multi-pass roll forming technology and comprehensively improve the technical level and ability of high-quality, low-cost, short-cycle manufacturing of thin-walled rings with complex sections.

Acknowledgements
The authors would like to thank the National Natural Science Foundation of China (No. 52165051 and 51665041), the Key Program of Jiangxi Natural Science Foundation (20232ACB204021) for the support given to this research.

Author Contribution
Keliang Lu constructed the framework of the paper and wrote it; Gangyao Zhao provided guidance and revisions to the paper; Zhenghua Guo processed and analyzed the data of the paper; Ranyang Zhang collected and summarized literature; Dongliang Yu adjusted the format and layout of the paper.