Simulation of frame beam additive Connection Process based on ABAQUS

In order to determine the optimal process parameters in the process of frame beam additive connection, Reduce thermal deformation caused by high temperature in the process of additive connection as much as possible, In this paper, ABAQUS finite element analysis software was used to conduct finite element analysis on the process of frame beam additive connection. By analyzing the temperature field and deformation amount under different connection currents in the process of additive connection, The optimal process parameters were determined as connection voltage 16V, connection current 80A, connection speed 5mm/s. The experimental results show that the heat generated in the process of frame beam additive connection is the least and the deformation is the least.


Introduction
Plane frame beam in the process of increasing material connection will produce large amounts of heat, it is easy to produce hot deformation, so we need before the material of the box beam increases connection for the connection of process parameters and process design, reasonable process parameters can add material as far as possible to reduce heat in the process, as far as possible control gain material produced during deformation, improve the accuracy of connection box Liang Zeng material.In this chapter, ABAQUS finite element analysis software is used to analyze the temperature field and deformation under different connection parameters, and the most reasonable process parameters of additive connection are selected according to the analysis.

Finite element analysis theory A. Temperature field energy control equation
Add material in the process of the connection, due to the movement of the laser beam in the connection process connection area started to melt and rapid temperature rise, in the heat transfer, the first law of heat conduction equation is mainly controlled by thermal and get energy by more equation is derived, in Descartes three-dimensional rectangular coordinate system, the change of the transient temperature field should satisfy the control equation.Qv is the density of the internal heat source.Where ρ is material density;C p s the specific constant pressure heat capacity of the material;K is the thermal conductivity of the material;T is the material temperature;qv is the density of the internal heat source.

B. The heat source model
When carries on the finite element analysis of temperature field, we must establish the corresponding heat source model, heat source model is to add material connection source of energy in the process of finite element analysis, the heat source model, the more precise the analysis result is more accurate, when connected by finite element method (fem) simulation process, the heat source has to be used to describe the distribution of heat input of the linking process.There are two commonly used heat source models: gaussian function heat source distribution and double ellipsoid heat source distribution [1,2] .The heat flow distribution model of Gaussian function is shown in Figure 1, and its general form is: Where q(r) is surface heat flow at the radius(W/m 2 )；qmax is the maximum heat flux at the center of the reservoir；r is he distance from the center of the reservoir；K is energy concentration coefficient Double ellipsoid heat source distribution model, namely volume heat source.As shown in Figure .2, it is assumed that the heat flux distribution on the body conforms to the double ellipsoid distribution, which can be expressed by the following formula: Where a1,a2,b,c is heat source shape parameter model; In the welding simulation analysis, for manual arc welding, TIG welding and other welding methods, using gaussian distribution function simulation can get accurate simulation results in engineering application.For welding methods with large arc impulse effect, such as MIG welding and laser welding, gaussian heat source function model is used to simulate the welding heat source load.The calculated results cannot reflect the influence of arc stiffness, so double ellipsoidal heat source distribution function is often used as heat source load [3,4] .

ABAQUS frame beam connection simulation modeling A. Selection of material properties
The material of frame beam of a certain type of aircraft this time is TA15.Its specific heat capacity, expansion coefficient and specific heat parameters at different temperatures are shown in Table 1.

B. Parameter setting of double ellipsoid heat source
According to the melting point and material thickness of the base material in the process of connection and combined with the weld pool morphology in the welding process, the shape parameters of the connection heat source model were defined.When the double ellipsoid heat source distribution function was used to simulate the connection of 3mm thick aluminum alloy, the shape parameters of the double ellipsoid heat source were finally determined as follows: a1 =0.002m, a2=0.003m,b=0.002m, c=0.003m; The proportion of heat source between the front and back parts f1=1.2.

C. Meshing
Due to the integral design of the plane frame beam size is larger, if speak two import simulation box beam as a whole size, then the subsequent simulation process will be quite tedious, therefore, after fully considering the heat in the process of welding condition, regional orientation determine the box beam welding simulation model for positioning to work overtime on both sides of the box beam, 3 d modeling of box beam joint.Then, the simulation model of frame and beam connection is imported into ABAQUS simulation software [5] .
In the process of grid division, different geometry simulation, the method of grid division is not completely the same, the size of grid size is not completely the same.The number of grids directly determines the time of welding simulation with ABAQUS.A larger number of grids means a larger amount of calculation, a longer time is needed, and the accuracy of calculation and solution will be more.In general, by gradually increasing the number of grid cells divided in the simulation process, the solution accuracy of welding simulation deformation is constantly improved, and finally the final simulation deformation solution is obtained.According to the theory related to finite element analysis, with the continuous increase and refinement of grid cells, the results of simulation analysis and solution will also increase, but the calculation time of simulation analysis will also increase [6].D. Contact and ambient temperature setting When ABAQUS conducts welding heat source simulation, setting environmental temperature is a necessary operation.When dividing frame beam connection plate type plate and weld mesh in Hypermesh, common node is adopted for dividing frame beam connection plate type plate and weld due to simple mesh division, so contact does not need to be established during ABAQUS analysis and calculation.Since the welding of aircraft frame beam is carried out at room temperature this time, the temperature can be set at room temperature when setting the ambient temperature, that is, the ambient temperature is 20℃.In addition to the ambient temperature, the absolute zero and Boltzmann constant need to be assigned to determine the zero is -273.15℃,and the Boltzmann constant is 5.67×10 -8 .E. Setting of arc additive connection process parameters The main parameters affecting the deformation of arc additive manufacturing are connection voltage, connection current and connection speed.This time, the setting of welding parameters was analyzed by comparative experiment, and the ABAQUS finite element analysis simulation was carried out by changing the connection speed and the connection current respectively.The process parameters in the simulation process are shown in Table 2

Simulation deformation analysis of frame beam connection based on ABAQUS
The process of box beam in connect will produce a lot of heat, heat of box beam temperature changes, thermal stress, and thus, box beam under the effect of thermal stress will generate deformation, as much as possible in order to reduce the connection process of deformation, it need to control the thermal stress in the process of connecting, Therefore, it is necessary to analyze the deformation of frame beam connection under different technological parameters.

A. Influence of welding current on temperature field
According to arc additive connection parameters, three connection speeds were designed for v=5mm/s, V =6mm/s, V =8mm/s, and two connection currents were I=80A, I=90A.Control variable method was used to analyze.According to arc additive connection parameters, three connection speeds were designed for v=5mm/s, V =6mm/s, V =8mm/s, and two connection currents were I=80A, I=90A.Control variable method was used to analyze.The connection voltage U=16V and connection speed V =5mm/s in the connection process remain unchanged.The connection current in the connection process is changed for analysis, and the connection current is I=80A and I=90A respectively.ABAQUS analysis was conducted for the process of frame beam additive connection.According to the analysis results, temperature fields of 10s, 125s and 250s were selected for analysis, and the temperature cloud map was shown in Fig 3.In the process of arc additive connection, the electrode of the welding machine used has heat source input.So in the connection of weld location, can produce a highly concentrated area, temperature of the box beam in the process of simulation, the simulation of the highest temperature area concentrated in the position of the welding joint, as shown in fig 3 (a) it can be seen in the connection for 80 a current, the temperature is about 2290 ℃ , when connecting current is 90 a, the temperature is about 2479 ℃, This is mainly because as the connection current increases, the heat generated instantly increases, and the temperature in the highly concentrated area increases.However, in the process of heat source simulation, arc closing was not simulated in the welding process, so the temperature in this part was relatively high.In reality, the temperature stability stage should occur in the connection stability stage, as shown in Fig. 3(b) and 3(e).The temperature is about 1200℃, and the temperature of 1280℃ when the connection current is 90A is slightly higher than that of 1218℃ when the connection current is 80A, but both are higher than the melting point of TA15.Due to the increase of material in the process of connecting the highest temperature is much higher than the melting point of TA15 and so on material in the process of the connection, as the link in the process of the movement of the welding gun, welding torch near the parent metal quickly achieve melting state, and rapid cooling after the torch left the mobile location, the electrode with the parent metal rapidly solidified into a whole, realize the arc added material connection.In the process of welding, material around the temperature gradient is great, lead to the expansion of the weld around the needs to connect the expansion of the distal parent metal and weld size there is a certain difference, so the welding stress and as time goes on, the position of the welding torch changes gradually, has been a part of the welding temperature falling rapidly cooling, Residual temperature will transfer from the weld area gradually to the base area, the temperature of the parent metal will pass into the surrounding environment, the greater the temperature gradient, the transmission speed will be faster, so in the 250 s, the overall connection process has been completed, the temperature began to gradually reduce, and then continue  , as the connection has just started, although the temperature is high and the heat accumulates in large quantities, the overall frame beam does not generate too much heat, so the stress generated at this time is small.The frame beam additive connection fixture can play a constant role in the resulting stress deformation.At this time, the deformation is shown in Fig. 4(a) and 4(d) respectively.When the connection current I=90A, the deformation is 0.16mm, and when the connection current I=90A, the deformation is 0.14mm.With the gradual progress of the connection process, the heat generated by the additive connection cannot be dispersed at the first time, because the heat generated by the additive connection begins to accumulate gradually, which leads to the deformation of the connection area of the frame beam.Although the deformation control device of the frame beam additive connection fixture has a certain inhibitory effect on the deformation of the frame beam connection area, the overall size of the frame beam is large, so the deformation will still occur in the process of connection.When the connection current I=90A, the deformation is 0.82mm; when the connection current I=90A, the deformation is 0.74mm.At this time, the additive connection process is coming to an end.With the end of the connection process, the heat gradually decreases and the thermal stress becomes smaller.At this time, the deformation is the deformation generated in the process of frame beam additive connection.When the connection current I=90A, the deformation is 0.46mm, and when the connection current I=90A, the deformation is 0.42mm.As the connection current increases, the heat generated will increase, and the deformation will also increase accordingly.

Conclusions
Integrated the above for the analysis of the temperature field and the deformation can be found that connect current changes will lead to temperature field, stress field generated in the process of the connection and the deformation of change, the fundamental factors affecting thickening of material deformation of the connection process is connected to generate heat in the process of how many, the smaller the connection of the electric current in a reasonable scope, the heat generated by the smaller, the smaller the deformation, Therefore, by comprehensive comparison, the process parameters of

Figure 2 .
Figure 2. Double ellipsoid heat source distribution In the welding simulation analysis, for manual arc welding, TIG welding and other welding methods, using gaussian distribution function simulation can get accurate simulation results in engineering application.For welding methods with large arc impulse effect, such as MIG welding and laser welding, gaussian heat source function model is used to simulate the welding heat source load.The calculated Fig 3(a), 3(b) and 3(c) are temperature cloud diagrams of 10s, 125s and 250s when connection voltage U=16V, connection speed V =5mm/s and connection current I=80A, respectively.Fig 3(d), 3(e) and 3(f) are temperature cloud diagrams of 10s, 125s and 250s when connection voltage U=16V, connection speed V =5mm/s and connection current I=90A respectively.

Figure 4 .
Figure 4. Deformation cloud picture with V=5mm/s At 10s, as the connection has just started, although the temperature is high and the heat accumulates in large quantities, the overall frame beam does not generate too much heat, so the stress generated at this time is small.The frame beam additive connection fixture can play a constant role in the resulting stress deformation.At this time, the deformation is shown in Fig.4(a) and 4(d) respectively.When the connection current I=90A, the deformation is 0.16mm, and when the connection current I=90A, the deformation is 0.14mm.With the gradual progress of the connection process, the heat generated by the additive connection cannot be dispersed at the first time, because the heat generated by the additive connection begins to accumulate gradually, which leads to the deformation of the connection area of the frame beam.Although the deformation control device of the frame beam additive connection fixture has a certain inhibitory effect on the deformation of the frame beam connection area, the overall size of the frame beam is large, so the deformation will still occur in the process of connection.When the connection current I=90A, the deformation is 0.82mm; when the connection current I=90A, the deformation is 0.74mm.At this time, the additive connection process is coming to an end.With the end of the connection process, the heat gradually decreases and the thermal stress becomes smaller.At this time, the deformation is the deformation generated in the process of frame beam additive connection.When the connection current I=90A, the deformation is 0.46mm, and when the connection current I=90A, the deformation is 0.42mm.As the connection current increases, the heat generated will increase, and the deformation will also increase accordingly.

Table 2 .
. Arc additive connection process parameter setting