A method for flash forming and multi-physical field prediction of dissimilar stainless steel inertia friction welding

Abstract

The present application relates to a kind of heterogeneous stainless steel inertia friction welding flash forming and multi-physical field prediction method, comprising the following steps: S1, establishing inertia friction welding model;S2, setting material attribute parameter;S3, grid division;S4, setting fixture action;S5, setting boundary condition;S6, setting the interaction and friction behavior between contact surface;S7, construct inertia friction welding process thermal-mechanical coupling model, calculate the temperature change data of feature point, obtain simulated welding flash morphology;Then let iteration i=1, and start to carry out iterative simulation calculation: according to the temperature change data of feature point, then update model parameter, then judge the temperature of feature point, whether simulated flash morphology reaches termination condition, yes, stop iteration, obtain simulation prediction result, otherwise read the temperature change data of feature point in the i th iteration, and let i=i+1.The method is conducive to efficiently and accurately predict flash forming and multi-physical field.

Description

Technical Field

[0001] This invention relates to the field of friction welding process simulation technology, specifically to a method for predicting flash formation and multiphysics field inertial friction welding of dissimilar stainless steels based on numerical simulation. Background Technology

[0002] In existing technologies, the inertial friction welding process is as follows: Figure 1 As shown, welding is a complex thermo-mechanical coupling dynamic process, typically completed within 3-6 seconds. This makes it difficult to experimentally measure real-time temperature changes, stress changes, and the flow of the plastic layer in different regions of the weld material. The finite element method (FEM) is not constrained by experimental conditions and can study the influence of various physical forces during welding based on simulation processes and results data, thus saving research costs. Furthermore, in actual production, the removal of weld flash increases forming costs. Effective control of the weld flash morphology can correspondingly reduce costs. Achieving flash control requires a certain predictive ability of the physical field changes. Therefore, predicting the temperature, stress, and plastic fields of inertial friction welding is essential.

[0003] Current simulations of inertial friction welding either fail to consider heat generation from plastic deformation, treat friction behavior as simple Coulomb friction, or treat material parameters as constants, leading to inaccurate simulation results. Therefore, establishing a numerical simulation-based method for flash forming and multiphysics prediction is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting flash formation and multiphysics field in inertial friction welding of dissimilar stainless steels. This method is beneficial for efficiently and accurately predicting flash formation and multiphysics field.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for flash forming and multiphysics prediction of dissimilar stainless steel inertial friction welding, comprising the following steps:

[0006] S1. Establish an inertial friction welding model;

[0007] S2. Set material property parameters;

[0008] S3. Divide the grid;

[0009] S4. Set the fixture action;

[0010] S5. Set boundary conditions;

[0011] S6. Set the interaction and friction behavior between contact surfaces;

[0012] S7. Construct a thermo-mechanical coupling model of the inertial friction welding process, calculate and obtain the temperature change data of the feature points, and obtain the simulated welding flash morphology; then set the iteration number i = 1 and start the iterative simulation calculation: update the model parameters according to the temperature change data of the feature points, and then determine whether the temperature of the feature points and the simulated flash morphology have reached the termination condition. If yes, stop the iteration and obtain the simulation prediction result; otherwise, read the temperature change data of the feature points in the i-th iteration and set i = i + 1.

[0013] Furthermore, in step S1, considering the complexity of model establishment as well as computational efficiency and accuracy, the following assumptions are made for the inertial friction welding model to be established: (1) the welding material is isotropic; (2) the initial temperature of the material is constant and the same as the ambient temperature; (3) the heat-work conversion coefficient is constant during friction welding; (4) the physical parameters of the material change with temperature; (5) the yield strength of the material follows the Mises yield criterion.

[0014] Furthermore, based on the established assumptions, a two-dimensional axisymmetric geometric model of inertial friction welding is established using AutoCAD software. The geometric model includes: a rotating end fixture, a moving end fixture, bar A, and bar B.

[0015] Further, in step S2, the established geometric model is imported into the preprocessing module of the DEFORM simulation software, the fixture is set as a rigid material that will not deform, and the rods A and B are set as plastic materials that can undergo torsional deformation.

[0016] The elemental content of the material is simulated in JMAtpro software to obtain physical parameters that change with temperature; relevant physical parameters of the material as a function of temperature are then assigned.

[0017] Considering the severe deformation of the welding materials during inertial friction welding, a hyperbolic sine constitutive equation is used to describe the relationship between the flow stress, strain, and temperature of bars A and B respectively:

[0018]

[0019] In the formula, A, α, and n are set constants, ΔH is the thermal activation energy of heat deformation, R = 8.314 J / (mol·K) is the gas constant, T is the temperature during the welding process, ε is the strain, and σ is the flow stress.

[0020] Further, in step S3, the mesh partitioning adopts the mesh window method, the temperature distribution weight of the mesh window is set to 0.2 considering the influence of temperature on the welding process, and the rest is the window weight; the mesh module of DEFORM simulation software is entered, the four-node tetrahedral element is selected to perform local partitioning of the imported geometric model; the mesh re-partitioning condition is set to the maximum growth step number 50, the distorted element is re-partitioned to obtain the final mesh model; the mesh window away from the welding surface is in turn: the mesh dense area, the mesh relatively dense area, and the mesh sparse area; the thermal-mechanical coupling field of the material at the weld is changed dramatically, the mesh size of the mesh window at the weld is set to the mesh dense area, considering the calculation accuracy and efficiency, the mesh size at the weld is set to 0.01; the mesh size of the mesh relatively dense area close to the weld is set to 0.1, and the mesh size of the mesh sparse area at the base material is set to 1;

[0021] The model is re-meshed by DEFORM subroutine to eliminate distortion, and the mapping technology is used to assign the data contained in each node element before re-partitioning to the new mesh node element.

[0022] Further, in step S4, the tool movement module of DEFORM simulation software is entered, and the rotating speed of the rotating end clamp and the welding pressure of the moving end clamp are set respectively; the rotating speed of the rotating end clamp and the pressure of the moving end clamp change with time, in order to ensure the accuracy of the simulation parameters, the real parameters under the corresponding working condition of welding are obtained through the inertia friction welding monitoring platform.

[0023] Further, in step S5, the BoundAry conditions module of DEFORM simulation software is entered, and the displacement conditions and thermal boundary conditions of the finite element model are set:

[0024] The thermal boundary condition is calculated by the following formula:

[0025]

[0026] The heat generated by friction and plastic deformation is conducted to the inside of the workpiece; the heat loss includes the convective heat transfer between the surface of the workpiece and the environment and the heat conduction between the workpiece and the clamp; the influence of thermal radiation on heat loss is ignored; wherein, h c is the heat convection coefficient, λ (w,c) is the heat conduction coefficient between the workpiece and the clamp, T w , T a and T c are the temperatures of the workpiece, the surrounding environment and the clamp respectively, q fr is the heat generated by friction, q pl is the heat generated by plastic deformation;

[0027] The boundary conditions of the rotary end clamp are composed of three displacement constraints u (x,0,0) = 0, u (0,y,0) = 0, u (0,0,z) = 0 and two rotation constraints θ (x，0，0) = 0, θ (0,0,z) = 0; the boundary conditions of the moving end clamp are composed of two displacement constraints u (x,0,0) = 0, u (0,0,z) = 0 and three rotation constraints θ (x，0，0) = 0, θ (0,y,0) = 0, θ (0,0,z) = 0.

[0028] Further, in step S6, the inter-object relationship is set in DEFORM, including the master-slave relationship between the geometric models, the friction type when the bar A and the bar B are in inertia friction welding contact, so as to ensure that the simulation process can be completed smoothly and effectively;

[0029] In the DEFORM master-slave relationship setting, three pairs of contacts are set: the rotary end clamp-bar A, the bar A-bar B, and the bar B-moving end clamp; wherein the rotary end clamp and the moving end clamp are set as the main components; the friction coefficients of the rotary end clamp-bar A and the bar B-moving end clamp are set as 1; the bar A-bar B is set as a face-to-face contact, and the friction coefficient is set as two parts of coulomb friction and shear friction;

[0030] The friction behavior changes in the welding process, which is equivalent to being divided into two stages of coulomb friction model and shear friction model; in the initial friction stage, the welding interface temperature is low, and the workpiece does not appear plastic deformation, so the main friction between the two sides of the workpiece is dry friction, and therefore the coulomb friction model is adopted to represent the friction type; and the corresponding stress formula is:

[0031]

[0032] In the formula, τ a is the friction stress, σ a is the normal stress, V a is the relative friction rotational speed, and μ is the friction coefficient;

[0033] In the stable friction stage, a large amount of heat is generated by the friction of the two workpieces, so that the end face bonding place will have severe plastic deformation and plastic flow, and therefore the shear friction model is adopted to represent the friction type, and the corresponding stress formula is:

[0034]

[0035] In the formula, τ f is the friction stress, m is the shear friction coefficient, the value range is 0-1, v s is the relative linear velocity, and k is the shear yield strength of the metal material.

[0036] Further, in step S7, in the simulation control module of the DEFORM simulation software, the simulation termination condition is set, the time sub-step increment is set, and then the simulation calculation is performed, the grid distortion is controlled through the remeshing technology; the flash shape after welding, the temperature field, the stress and strain field, the interface temperature change and the axial shortening change are analyzed.

[0037] Further, after the simulation calculation is completed, the inertia friction welding test is performed, the temperature at the characteristic point is measured by using the thermocouple, and the test verification is performed.

[0038] Compared with the prior art, the present application has the following beneficial effects: the present application provides a heterogeneous stainless steel inertia friction welding flash forming and multi-physical field prediction method based on numerical simulation, which establishes a complete thermal-mechanical coupling model of inertia friction welding based on DEFORM, and when applied, can simultaneously calculate the temperature, fluid, stress and strain of friction welding, and further realize the direct coupling numerical simulation calculation of the multi-physical field of the friction welding process. The present application can efficiently and accurately obtain the simulation calculation result when used for inertia friction welding process simulation, and can improve the consistency with the actual friction welding process. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a schematic diagram of inertia friction welding in the prior art;

[0040] Figure 2 It is a method implementation flowchart of the embodiment of the present application;

[0041] Figure 3 It is a finite element model of inertia friction welding in the embodiment of the present application;

[0042] Figure 4 It is a material parameter curve of two kinds of materials in the embodiment of the present application; wherein, (a) is the thermal conductivity coefficient and Young's modulus curve of 2205 stainless steel, and (b) is the thermal conductivity coefficient and Young's modulus curve of 316L stainless steel;

[0043] Figure 5 It is the action curve of the displacement end clamp and the rotary end clamp in the embodiment of the present application;

[0044] Figure 6 It is a comparison curve diagram of the simulation and actual measurement data of the workpiece surface measurement point temperature in the welding process in the embodiment of the present application;

[0045] Figure 7 It is a comparison diagram of the flash forming after welding and the flash forming after test in the embodiment of the present application. DETAILED DESCRIPTION

[0046] The present application will be further described below in combination with the drawings and embodiments.

[0047] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0048] It is also important to note that the terms "example" and / or "exemplary" as used herein illustrate certain embodiments of the application and should not be construed to limit the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0049] The present embodiment provides a numerical simulation-based method for predicting flash formation and multi-physical field in heterogeneous stainless steel inertia friction welding. The method uses friction and plastic deformation heat flux as the model heat source, uses a hyperbolic sine constitutive equation model to describe the plastic deformation law of the material, and introduces a temperature-dependent friction coefficient equation to describe the coupling effect of temperature and friction. The method is illustrated by taking 2205 / 316L stainless steel inertia friction welding as an example. Figure 2 As shown in the flowchart, the specific implementation steps are as follows.

[0050] S1, establish an inertia friction welding model

[0051] First, considering the complexity of model establishment and the calculation efficiency and accuracy, the following assumptions are made for the inertia friction welding model to be established:

[0052] (1) The welding material is isotropic; (2) The initial temperature of the material is constant and the same as the ambient temperature (20℃); (3) The heat conversion coefficient is constant during friction welding; (4) The physical parameters (specific heat, thermal conductivity, Young's modulus) of the material change with temperature; (5) The yield strength of the material obeys the Mises yield criterion.

[0053] Then, based on the established assumptions, a two-dimensional axisymmetric geometric model of inertia friction welding is established by AutoCAD software, including: rotating end fixture, moving end fixture, rod A and rod B.

[0054] Since the welding material has axial symmetry, and the temperature field, stress field and plastic field are also distributed in axial symmetry, only half of the welding rod is taken. In this embodiment, the geometric model includes: rotating end clamp, moving end clamp, rod 2205, rod 316L. According to the actual measured material size, the geometric model of the rod 2205 and the rod 316L is a rectangle with a length of 120 mm and a width of 17.5 mm. The size of the rotating end clamp and the moving end clamp has no effect on the simulation process, and the specific size can not be limited. The finite element model is as shown in Figure 3 .

[0055] S2, setting material attribute parameters

[0056] The established geometric model is imported into the pre-processing module of the DEFORM simulation software, the clamp is set as a rigid material that will not deform, and the rod 2205 and the rod 316L are set as plastic materials that can deform.

[0057] The element content of the material is simulated by JMAtpro software, and the physical parameters varying with temperature are obtained. The material is given the relevant physical parameters varying with temperature as described in step 1. In this embodiment, the material parameter attribute parameters are as shown in Figure 4 .

[0058] Considering that the welding material will deform seriously in the inertia friction welding process, the hyperbolic sine constitutive equation is used to describe the relationship between the flow stress, strain and temperature of the rod 2205 and the rod 316L:

[0059]

[0060] In the formula, A, α and n are constants, ΔH is the thermal deformation thermal activation energy, R=8.314 J / (mol·K) is the gas constant, T is the temperature in the welding process, ε is the strain, and σ is the flow stress.

[0061] S3, dividing the grid

[0062] The grid division adopts the grid window method, considering the influence of temperature on the welding process, the temperature distribution weight of the grid window is set to 0.2, and the rest is the window weight.

[0063] Enter the mesh module of DEFORM simulation software, select four-node tetrahedral element to import the geometry model for local mesh partitioning. The mesh re-partitioning condition is set to the maximum growth step 50 steps, the distorted unit is re-divided into mesh to obtain the final mesh model. The mesh window away from the welding surface is: mesh dense area, mesh relatively dense area, mesh sparse area. The heat-force coupling field of the material at the weld is changed dramatically, the mesh size of the mesh window at the weld needs to be set smaller, so it is set to mesh dense area, considering the calculation accuracy and efficiency, the mesh size at the weld is set to 0.01. The mesh size of the mesh relatively dense area near the weld is set to 0.1, and the mesh size of the mesh sparse area of the base material is set to 1.

[0064] The model is re-meshed by DEFORM subroutine to eliminate distortion, and the data contained in each node element before re-partitioning is assigned to the new mesh node element by mapping technology.

[0065] S4, setting the action of the clamp

[0066] Enter the tool movement module of DEFORM simulation software, set the rotating speed of the rotating end clamp and the welding pressure of the moving end clamp respectively. The rotating speed of the rotating end clamp and the pressure of the moving end clamp change with time, in order to ensure the accuracy of the simulation parameters, the real parameters under the corresponding working condition of welding are obtained through the inertia friction welding monitoring platform, as shown in Figure 5 .

[0067] S5, setting the boundary condition

[0068] Enter the BoundAry conditions module of DEFORM simulation software, set the displacement condition and thermal boundary condition of the finite element model:

[0069] The thermal boundary condition is calculated by the following formula:

[0070]

[0071] The heat generated by friction and plastic deformation is conducted to the inside of the workpiece. The heat loss includes the convective heat transfer between the surface of the workpiece and the environment and the heat conduction between the workpiece and the clamp. The influence of thermal radiation on heat loss is ignored. Wherein, h c is the heat convection coefficient, λ (w,c) is the heat conduction coefficient between the workpiece and the clamp, T w , T a and T c are the temperatures of the workpiece, the surrounding environment and the clamp respectively, q fr is the heat generated by friction, q pl is the heat generated by plastic deformation.

[0072] The boundary conditions of the rotary end clamp are composed of three displacement constraints u (x,0,0) = 0, u (0,y,0) = 0, u (0,0,z) = 0 and two rotation constraints θ (x，0，0) = 0, θ (0,0,z) = 0. The boundary conditions of the moving end clamp are composed of two displacement constraints u (x,0,0) = 0, u (0,0,z) = 0 and three rotation constraints θ (x，0，0) = 0, θ (0,y,0) = 0, θ (0,0,z) = 0.

[0073] S6, setting the interaction between the contact surfaces and the friction behavior

[0074] In DEFORM, the relationship between objects is set, including the master-slave relationship between geometric models, the friction type when the bar 2205 and the bar 316L inertia friction welds contact, to ensure that the simulation process can be completed smoothly and effectively.

[0075] In the DEFORM master-slave relationship setting, three pairs of contacts are set: the rotary end clamp-bar 2205, the bar 2205-bar 316L, and the bar 316L-moving end clamp. Among them, the rotary end clamp and the moving end clamp are set as the main components. The rotary end clamp-bar 2205 and the bar 316L-moving end clamp are set as fixed connections, and the friction coefficient is set to 1. The bar 2205-bar 316L is set as a face-to-face contact, and the friction coefficient is set as two parts of Coulomb friction and shear friction.

[0076] The friction behavior will change during the welding process, which is equivalent to being divided into two stages of Coulomb friction model and shear friction model. In the initial friction stage, the welding interface temperature is low, and the workpiece does not appear plastic deformation, and the main friction between the two workpieces is dry friction, so the friction type adopts the Coulomb friction model; the corresponding stress formula is:

[0077]

[0078] In the formula, τ a is the friction stress, σ a is the normal stress, V a is the relative friction speed, and μ is the friction coefficient.

[0079] In the stable friction stage, a large amount of heat is generated by the friction between the two workpieces, which causes severe plastic deformation and plastic flow at the end face bonding site, so the friction type adopts the shear friction model, and the corresponding stress formula is:

[0080]

[0081] In the formula, τ fis the friction stress, m is the shear friction coefficient, which is in the range of 0~1, and is taken as 0.3 in this paper, v is the relative linear velocity, k is the shear yield strength of the metal material. s is the relative linear velocity, k is the shear yield strength of the metal material.

[0082] The energy of the inertia friction welding mainly comes from the high-speed rotating flywheel. Under the action of inertia, the two workpieces are subjected to intense friction, and the stored kinetic energy is converted into heat required in the welding process. The heat flow at the welding interface can be expressed as

[0083] q(r,t)=2π·r·μ·p(r,t)·ω(t)·η

[0084] In the formula, q(r,t) is the heat flux density, r is the radius of the calculation node, μ is the friction coefficient, p(r,t) is the friction pressure, ω(t) is the angular velocity, and η is the conversion efficiency.

[0085] S7, a thermal-mechanical coupling model of the inertia friction welding process is constructed, temperature change data of the characteristic points are calculated, and a simulated flash morphology is obtained; then the iteration number i is set to 1, and iterative simulation calculation is started: the model parameters are updated according to the temperature change data of the characteristic points, and then it is judged whether the temperature of the characteristic points and the simulated flash morphology reach the termination condition, if yes, the iteration is stopped, and the simulation prediction result is obtained, otherwise the temperature change data of the characteristic points in the i-th iteration is read, and i is set to i+1.

[0086] In the simulation control module of the DEFORM simulation software, the simulation termination condition is set as the welding time measured by the friction welding monitoring platform, the time sub-step increment is set to 0.01 steps / s, then the simulation calculation is performed, and the grid distortion is controlled through the re-meshing technology; the flash morphology after welding, the temperature field, the stress and strain field, the interface temperature change and the axial shortening change are analyzed.

[0087] After the simulation calculation is completed, the inertia friction welding test is performed to compare the flash morphology, the temperature at the characteristic points is measured by using the thermocouple, the model parameters such as the friction coefficient are adjusted according to the difference between the simulated temperature and the measured temperature, so that the difference between the experimental temperature and the simulated temperature is within 10%, as shown in Figure 6 and Figure 7 .

[0088] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the above disclosed technical content to obtain equivalent embodiments. However, any simple modification, equivalent change and modification made on the basis of the technical essence of the present application to the above embodiments still belongs to the protection scope of the present application.

Claims

1. A heterogeneous stainless steel inertia friction welding flash forming and multi-physical field prediction method, characterized in that, The method comprises the following steps: S1, establishing an inertia friction welding model; S2, setting material attribute parameters; S3, dividing a grid; S4, setting a clamp action; S5, setting a boundary condition; S6, setting interaction and friction behavior between contact surfaces; S7, constructing a heat-force coupling model of the inertia friction welding process, calculating temperature change data of characteristic points, and obtaining a simulated flash morphology; then setting an iteration number i=1 and starting iteration simulation calculation: updating model parameters according to the temperature change data of the characteristic points, and then judging whether the temperature of the characteristic points and the simulated flash morphology reach a termination condition, yes, stopping iteration, obtaining a simulation prediction result, or no, reading the temperature change data of the characteristic points in the i-th iteration, and setting i=i+1; In step S1, considering the complexity of model establishment and the calculation efficiency and accuracy, the following assumptions are made for the inertia friction welding model to be established: (1) the welding material is isotropic; (2) the initial temperature of the material is constant and the same as the ambient temperature; (3) the heat work conversion coefficient is constant during the friction welding process; (4) the physical parameters of the material change with temperature; (5) the yield strength of the material obeys the Mises yield criterion; Based on the assumptions, a two-dimensional axisymmetric geometric model of inertia friction welding is established by using AutoCAD software, and the geometric model comprises a rotating end clamp, a moving end clamp, a rod A and a rod B; In step S2, the established geometric model is imported into the pre-processing module of DEFORM simulation software, the clamp is set as a rigid material that will not deform, and the rod A and the rod B are set as plastic materials that can deform in torsion; In the JMAtpro software, the element content of the material is simulated to obtain the physical parameters that change with temperature; the material is given the relevant physical parameters that change with temperature; Considering that the welding material will deform seriously during the inertia friction welding process, the hyperbolic sine constitutive equation is used to describe the relationship between the flow stress, strain and temperature of the rod A and the rod B: In the formula, A, α and n are constants, ΔH is the heat deformation heat activation energy, R=8.314 J / (mol·K) is the gas constant, T is the temperature during the welding process, ε is the strain, and σ is the flow stress.

2. The method of flash forming and multi-physical field prediction of dissimilar stainless steel inertia friction welding of claim 1, wherein In step S3, the grid division adopts the grid window method, the temperature distribution weight of the grid window is set to 0.2 considering the influence of temperature on the welding process, and the remaining window weights are set; the mesh module of DEFORM simulation software is entered, the imported geometric model is locally divided into a four-node tetrahedral element, the grid re-division condition is set to a maximum growth step of 50 steps, the distorted element is re-divided into a grid to obtain a final grid model, and the grid windows far from the welding surface are a grid dense area, a grid relatively dense area and a grid sparse area in turn; The grid size of the welding seam area is set to the grid dense area considering that the heat-force coupling field of the material in the welding seam area changes dramatically, and the grid size of the welding seam area is set to 0.01 considering the calculation accuracy and efficiency; the grid size of the grid relatively dense area close to the welding seam is set to 0.1, and the grid size of the grid sparse area of the base material is set to 1. The model is re-meshed by DEFORM subprogram to eliminate distortion, and the data contained in each node unit before re-division is correspondingly assigned to the new mesh node unit by mapping technology.

3. The method of flash formation and multi-physical field prediction of dissimilar stainless steel inertia friction welding of claim 2, wherein, In step S4, the tool movement module of DEFORM simulation software is entered, and the rotating end clamp rotation speed and the moving end clamp welding pressure are set respectively; the rotating end clamp rotation speed and the moving end clamp pressure change with time, in order to ensure the accuracy of simulation parameters, the real parameters under the corresponding working condition of welding are obtained through the inertia friction welding monitoring platform.

4. The method of flash formation and multi-physical field prediction of dissimilar stainless steel inertia friction welding according to claim 3, characterized in that, In step S5, the Boundary conditions module of DEFORM simulation software is entered, and the displacement conditions and thermal boundary conditions of the finite element model are set: The thermal boundary condition is calculated by the following formula: The heat generated by friction and plastic deformation is conducted to the inside of the workpiece; the heat loss includes the convective heat exchange between the surface of the workpiece and the environment and the heat conduction between the workpiece and the clamp; the influence of thermal radiation on heat loss is ignored; wherein h c is the heat convection coefficient, λ (w,c) is the heat conduction coefficient between the workpiece and the clamp, T w , T a and T c are the temperatures of the workpiece, the surrounding environment and the clamp respectively, q fr is the heat generated by friction, q pl is the heat generated by plastic deformation; The boundary conditions of the rotary end fixture are composed of three displacement constraints u (x,0,0) = 0, u (0,y,0) = 0, u (0,0,z) = 0 and two rotation constraints θ (x，0，0) = 0, θ (0,0,z) = 0; the boundary conditions of the moving end fixture are composed of two displacement constraints u (x,0,0) = 0, u (0,0,z) = 0 and three rotation constraints θ (x，0，0) = 0, θ (0,y,0) = 0, θ (0,0,z) = 0.

5. The method of flash formation and multi-physical field prediction of dissimilar stainless steel inertia friction welding of claim 4, wherein, In step S6, the relationship between objects is set in DEFORM, including the master-slave relationship between geometric models, the friction type when bar A and bar B are in inertia friction welding contact, so as to ensure that the simulation process can be completed smoothly and effectively; In the DEFORM master-slave relationship setting, three pairs of contacts are set: rotating end clamp-bar A, bar A-bar B, and bar B-moving end clamp; among them, the rotating end clamp and the moving end clamp are set as the main components; the friction coefficients of rotating end clamp-bar A and bar B-moving end clamp are set to 1; bar A-bar B is set as face-to-face contact, and the friction coefficient is set as two parts of coulomb friction and shear friction; The friction behavior will change during the welding process, which is equivalent to be divided into two stages of coulomb friction model and shear friction model; in the initial friction stage, the welding interface temperature is low, and the workpiece does not appear plastic deformation, so the main friction between the two workpieces is dry friction, and the friction type adopts coulomb friction model; the corresponding stress formula is: where τ is the shear stress, σ is the normal stress, V is the relative rotational speed, and μ is the coefficient of friction. a where τ is the shear stress, σ is the normal stress, V is the relative rotational speed, and μ is the coefficient of friction. a where τ is the shear stress, σ is the normal stress, V is the relative rotational speed, and μ is the coefficient of friction. a where τ is In the stable friction stage, a large amount of heat is generated by the friction of the two workpieces, which causes severe plastic deformation and plastic flow at the end face joint, so the friction type adopts shear friction model, and the corresponding stress formula is: where τ is the friction stress, m is the coefficient of shear friction, which has a value ranging from 0 to 1, v is the relative linear velocity, and k is the shear yield strength of the metal material. f where τ is the friction stress, m is the coefficient of shear friction, which has a value ranging from 0 to 1, v is the relative linear velocity, and k is the shear yield strength of the metal material. s where τ is the friction stress, m is the coefficient of shear friction, which has a value ranging from 6. The method of flash formation and multi-physical field prediction of dissimilar stainless steel inertia friction welding of claim 5, wherein, In step S7, in the simulation control module of DEFORM simulation software, the simulation termination condition is set, the time sub-step increment is set, and then the simulation calculation is carried out, and the grid distortion is controlled by the re-meshing technology; the flash shape after welding, temperature field, stress and strain field, interface temperature change and axial shortening change are analyzed.

7. The method of flash formation and multi-physical field prediction of dissimilar stainless steel inertia friction welding of claim 6, wherein, After completing the simulation calculation, inertia friction welding test is carried out, and thermocouple is used to measure the temperature at the characteristic point to verify the test.

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