Continuous simulation method for bulging-pressure wave-arc welding stress deformation evolution of corrugated pipe

Abstract

The invention discloses a continuous simulation method for bulging-pressure wave-arc welding stress deformation evolution of a corrugated pipe, and belongs to the field of metal cold-hot processing continuous simulation. According to the method, a whole set of finite element modeling method for carrying out continuous simulation of a corrugated pipe manufacturing process chain is provided aiming at continuous processes of pipe bulging, end wave pressing and girth welding in a corrugated pipe machining process, so that simulation analysis of stress and deformation evolution processes in the corrugated pipe bulging and pressing processes is realized; and carrying out circular seam welding residual stress and post-welding deformation simulation analysis on the geometric model with the initial stress, so that the problems of poor simulation result precision and low credibility of a single-process finite element model are solved. By the adoption of the continuous simulation method, continuous simulation of pipe bulging, end wave pressing and girth welding is carried out on the U-shaped corrugated pipe with the wall thickness being 0.2 mm, the outer diameter being 20.4 mm, the inner diameter being 15 mm and the wave pitch being 3 mm, and simulation results and test verification data are both within the allowable error range.

Description

Technical Field

[0001] The present invention proposes a continuous simulation method for the stress and deformation evolution of bellows bulging-pressure wave-arc welding, which belongs to the field of continuous simulation of metal cold-hot processing. The method targets the continuous processing technology of tube bulging, end wave pressure wave and circumferential seam welding in the processing of bellows, and proposes a complete set of finite element modeling methods for continuous simulation of the bellows manufacturing process chain. The method can be used to predict the residual stress and deformation distribution of the bellows after undergoing different processes, and provide technical guidance and reference for the optimization and improvement of the actual processing and manufacturing process of the bellows and the analysis of the causes of failure during service. Background Art

[0002] Metal bellows is a cylindrical thin-walled elastic shell with transverse corrugations. With the comprehensive development of basic theory and manufacturing technology, metal bellows are widely used in elastic sensitive components of instruments and meters and connecting parts of various pipes. Metal bellows have good axial, angular and transverse deformation capabilities, force-deformation characteristics and geometric shape periodic change characteristics, and have functions such as displacement compensation, shock absorption and noise reduction, and sealing. It is widely used in oil pipelines, aerospace engines, sensitive components in instruments and other industries, and is used to manufacture various sensitive components, compensation components, flexible connectors, etc. Metal bellows are made of extremely thin-walled tube blanks, and the wall thickness is generally between 0.1 and 0.3 mm. With the development of science and technology, the performance indicators of metal bellows such as high and low temperature resistance, high pressure resistance, corrosion resistance, and long life are increasingly required.

[0003] Since the bellows undergo processes such as tube bulging, end wave pressure wave, and circumferential seam welding during the manufacturing process, unpredictable residual stress and deformation will be generated in the components, reducing the processing quality and the service life of the bellows. With the development of computing technology, numerical simulation technology is more and more widely used and recognized by the industry. The aerospace industry also regards numerical simulation technology as a very important part of advanced manufacturing technology. Through simulation analysis of the process, the stress distribution and deformation after processing can be predicted, which can be used for process optimization and reduce experimental costs.

[0004] Traditional finite element simulation is often based on zero initial stress and theoretical geometric models, and simulates the welding process alone without considering the residual stress and dimensional deviation of the previous process. The obtained stress and deformation results often deviate from reality and have little guiding value for actual engineering problems. Summary of the invention

[0005] In response to the existing problems described in the background technology, the present invention proposes a continuous simulation method for stress and deformation in the manufacturing and processing process of bellows, and conducts multi-process continuous simulation research on the pipe forming, end wave pressure wave and circumferential seam welding processes of the bellows components, so as to realize the transmission of stress and deformation data between the previous and subsequent processes, reproduce the stress, strain and deformation evolution process of the components in different process steps, and accurately predict the residual stress and deformation distribution after multiple processes, so as to guide the optimization of various processes, reduce the residual stress in key parts, and improve the service life of the bellows.

[0006] The specific process of the continuous simulation method proposed by the present invention is as follows: Figure 1 As shown, it includes the following steps:

[0007] Step 1: Establish geometric models of pipes, joints and various molds, and perform finite element meshing on pipes and joints. It is necessary to modify the coarse / fine mesh and transition meshing strategies according to the results of different process trials. The meshing results are as follows: Figure 2 As shown; According to the literature and material parameter calculation software, the material performance parameters are obtained, and some thermal physical parameters are as follows Figure 3 The stress-strain curve is shown in Figure 4 As shown;

[0008] Step 2: Establish a finite element simulation model for tube bulging process and divide the deformed body into sections. Figure 5 As shown; assemble the pipe and the mold, the assembly diagram is as shown Figure 6 As shown; according to the tube forming process, a reasonable hydraulic pressure-time curve and a die moving position-time curve are designed, such as Figure 7 , 8 As shown; structural simulation of tube bulging is carried out to obtain the stress and deformation results of the tube after hydroforming;

[0009] Step 3: According to the calculation results of the tube bulging simulation model, the bellows grid and the end wave pressure wave mold obtained after the bulging are assembled, as shown in Fig. 9 As shown in the figure, the calculated stress field result after bulging is used as the initial stress condition of the wave pressure wave model at the end of the bellows, and a reasonable mold movement position-time curve is set, as shown in the figure. Fig.10 As shown; structural simulation of the wave pressure wave at the end of the bellows is carried out to obtain the stress and deformation results after the wave pressure wave at the end of the bellows;

[0010] Step 4: According to the simulation calculation results of the pressure wave at the end of the bellows, the bellows deformation grid and the joint grid obtained after the pressure wave are axially aligned and assembled, and the stress field calculation results after the pressure wave are used as the initial stress conditions of the joint-bellows girth welding model. Reasonable thermal boundary conditions are set, and thermal / structural simulation of the joint-bellows girth welding is carried out to obtain the stress and deformation results after the joint-bellows girth welding;

[0011] Among them, the various types of molds in step 1 include corrugated molds during hydraulic forming, compression wave molds during compression wave, and limit clamps; the material performance parameters include density, Poisson's ratio, Young's modulus, thermal expansion coefficient, yield strength, thermal conductivity, and heat capacity, among which the yield strength is presented in the form of stress-strain curves at different strain rates and different temperatures.

[0012] Among them, the equilibrium equation solved by structural simulation in step 2 is:

[0013]

[0014] μ is the node displacement vector, M is the mass matrix, D is the damping matrix, K(T, μ, t) is the stiffness matrix, F is the externally applied force vector, and F th is the force caused by thermal strain.

[0015] Among them, the hydraulic level-time curve in step 2 requires multiple trial calculations and adjustments to ensure that the hydraulic process does not cause grid distortion due to excessive strain rate and that the rebound after the mold is unloaded is small.

[0016] Among them, when establishing the contact body in step 2, it is necessary to set the pipe segments as deformable bodies, and the contact relationship is a bonding relationship, which is convenient for mesh replacement when the circumferential seam welding simulation model is subsequently established without affecting the deformation data transmission.

[0017] Among them, the control equation solved in step 3 is the same as that in step 2; when assembling the compression mold, the limit fixture and the corrugated tube after hydraulic forming, it should be ensured that the grid position of the corrugated tube does not move, and the compression mold and the limit fixture are moved to achieve accurate assembly.

[0018] Among them, in step 3, when controlling the movement of the compression wave mold, a reasonable moving speed should be designed to ensure that the movement of the compression wave mold can make the component reach the size requirements after the compression wave is completed, and the rebound after the mold is unloaded is small.

[0019] The heat / structural analysis balance equation of the joint-bellows circumferential weld in step 4 is the same as that in step 2, and the heat conduction equation is as follows:

[0020]

[0021] In the equation, C th (T) and λ th (T) is the specific heat matrix and thermal conductivity matrix, Q is the internal heat, Q elec is the Joule heat, Q tedef is the heat caused by inelastic deformation, Q fric is the heat generated by friction, and T is the node temperature.

[0022] Among them, when adjusting the grid in step 4, remove the grid at the tip of the joint and the outer grid of the bellows, assemble them with the designed weld grid, and keep the grid position unchanged after the wave compression.

[0023] Among them, in step 4, when establishing the heat source model, a double ellipsoid heat source model suitable for TIG welding is selected. The double ellipsoid heat source model can well analyze the temperature field changes of deep penetration welds, shallow penetration welds and asymmetric welds, and can better reflect the morphological characteristics of the welding pool. The model uses the center position of the heat source loading as the boundary of the heat flux distribution before and after the model to divide the heat source into two parts with different heat flux distributions. The heat flux density distribution of these two parts is described by 1 / 4 sphere respectively, and the heat source model parameters can be adjusted according to the actual morphology of the weld.

[0024] The energy fraction of the first half of the ellipsoid is f f , the energy fraction of the ellipsoid in the second half is f r , and f f +f r =2, then the heat source distribution expression in the first half of the ellipsoid is as follows:

[0025]

[0026] Similarly, the heat source distribution in the second half of the ellipsoid is shown as follows:

[0027]

[0028] In the formula, a f is the length of the front semi-axis of the ellipsoid, a r is the length of the rear semi-axis of the ellipsoid, b is the half-width of the heat source, c is the depth of the heat source, and Q is the effective power of the welding heat source. The calculation expression is shown in the following formula:

[0029] Q=ηUI

[0030] Where η is the welding thermal efficiency, U is the welding voltage, and I is the welding current.

[0031] The beneficial effects of the present invention are as follows: the continuous simulation technology is applied to the plastic forming and hot working process of the bellows, and the three processes of tube bulging, end wave pressure wave and circumferential seam welding are formed into a process chain for continuous simulation, further improving the calculation accuracy of simulation of bellows processing and manufacturing. The process chain continuous simulation has obvious advantages over traditional finite element simulation: the stress, deformation and other results generated in the tube bulging process are transferred to the subsequent end wave pressure wave process, and the stress, deformation and other results generated in the end wave pressure wave process are transferred to the subsequent circumferential seam welding process, avoiding many problems existing in welding simulation based on theoretical components, facilitating the monitoring and analysis of the bellows manufacturing and processing process, timely discovering possible stress or deformation problems in each process, and having important guiding significance for the optimization and adjustment of the actual processing technology and failure analysis during service. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Flowchart of continuous simulation of bellows manufacturing and processing

[0033] Figure 2 Meshing of pipes, joints and welds

[0034] Figure 3 Some thermal physical parameters

[0035] Figure 4 Stress-strain curve

[0036] Figure 5 Segmented setting of the bellows deformation body before forming

[0037] Figure 6 Schematic diagram of bulging die assembly

[0038] Figure 7 Bulging die displacement-time curve

[0039] Figure 8 Bulging hydraulic pressure-time curve

[0040] Fig. 9 Schematic diagram of pressure wave mold assembly

[0041] Fig.10 Pressure wave die displacement-time curve

[0042] Fig.11 Bellows bulging results

[0043] Fig.12 Bellows end pressure wave results

[0044] Fig.13 Circumferential welding results of bellows and joints DETAILED DESCRIPTION

[0045] According to the continuous simulation method provided by the present invention, continuous simulation of the bellows manufacturing and processing process is carried out, as follows.

[0046] Step 1: The outer diameter of the tube is 15.4mm, the wall thickness is 0.2mm, and the tube length is 28mm. The first corrugation on the left end is divided into fine hexahedral grids, divided into 3 layers in thickness, 180 equal divisions in the annular direction, and the fine grid length in the axial direction is 0.0575mm; the grid transition in thickness is performed between the first and second corrugations, from 3 layers to 1 layer, the axial length is 0.115mm, and the annular direction remains unchanged; the grid transition in the annular direction is performed between the second and third corrugations, from 180 parts to 90 parts, and the thickness and axial direction remain unchanged. All grids to the right adopt this division method. The final number of grids is 89730. The joint is divided into fine grids near the weld area, and the number of circumferential grids is consistent with that of the pipe. Away from the weld area, transitions are made in the circumferential direction and thickness in turn, and the final number of grids is 15520. The weld geometric dimensions are obtained based on the test results, and the cross-sectional surface grid is divided according to the cross-sectional dimensions, and then stretched in the circumferential direction to obtain the weld hexahedral grid, with a grid number of 21960.

[0047] Step 2: Establish the mold geometry model. The cross section of the corrugated mold consists of a trough semicircle, a crest semicircle, and an end face straight line. The trough radius is 0.65mm, the crest radius is 0.85mm, and the end face straight line is 1mm long. After obtaining the cross-sectional curve, it is rotated and stretched around the axis in the ring direction to obtain a revolved surface. The compression wave mold is a cylinder with a bottom diameter of 47mm and a thickness of 1mm, and a cylindrical push rod with a diameter of 2mm and a length of 10mm is added to the back; the cross-sectional curve of the limit fixture is composed of the radial extension of the outer contour line of the trough and the outer contour line of the end face, and then rotated around the axis to obtain the main action surface of the limit fixture. This action surface and the external cylindrical contour surface constitute the three-dimensional structure of the limit fixture.

[0048] Step 3: Consult literature to obtain the various elemental components in the material; use material performance parameter calculation software to calculate various material performance parameters and eliminate individual data points that have undergone mutations due to phase changes.

[0049] Step 4: Establish the finite element model of tube bulging, including the following processes:

[0050] (1) Mold assembly: Import the pipe mesh model and the mold geometry model, and assemble the pipe mesh and the corrugated mold.

[0051] (2) Establish contact bodies and contact relationships: The pipe is divided into different deformation bodies, and the end trough of the first corrugation on the left, the left and right end faces and the crest, and the trough between the first and second corrugations are set as different contact bodies; the mold is set as a rigid body, and its position change curve is controlled by the displacement-time curve. The contact relationship between the deformation bodies is set to bonding; the contact relationship between the deformation body and the rigid body is set to a normal contact relationship, and the friction coefficient is set to 0.05. The displacement data of the mold relative to the starting position at different time nodes are shown in Table 1. During the movement, it moves at a uniform speed along the X-axis direction.

[0052] Table 1 Displacement data of bulging die at different time nodes

[0053]

[0054] (3) Establish material model: use mechanical property parameters at room temperature.

[0055] (4) Establish boundary conditions: Apply unit surface distributed force to the inner surface of the pipe to simulate the effect of liquid pressure, draw the hydraulic pressure-time curve, and control the hydraulic pressure level. The liquid pressure level data at different time nodes are shown in the following table. It changes at a uniform speed during the increase and decrease process.

[0056] Table 2 Hydraulic level data at different time nodes

[0057]

[0058] (5) Establish working conditions: Set the working time according to the hydraulic action time, which is 10s.

[0059] (6) Debug the model, complete the calculation, and carry out the structural analysis of the tube bulging process to obtain the forming morphology of the corrugated tube when it is bulged to half height and full height, such as Fig.11 As shown, the stress and strain distribution when bulging is completed can also be obtained.

[0060] Step 5: Import the bellows mesh model and stress data, and use the room temperature mechanical properties parameters again to build the end wave pressure wave simulation model. The modeling process includes the following:

[0061] (1) Mold assembly: Import the geometric model of the compression mold and the limit fixture, assemble the bellows grid and the corrugated mold, so that the compression mold is in a waiting state 20 mm away from the end wave, and the limit fixture fits the right side plane of the end wave of the bellows.

[0062] (2) Establish contact bodies and contact relationships: Maintain the settings of the deformation bodies in the tube bulging; set the mold as a rigid body, establish the position-time curve of the pressure wave mold, and control the speed and time of the pressure wave mold extrusion, pressure wave mold and limit fixture unloading. The contact relationship between different deformation bodies is set to bonding, and the contact relationship between the same deformation bodies is set to ordinary self-contact; the contact relationship between the deformation body and the rigid body is set to ordinary contact relationship, and the friction coefficient is set to 0.1. The displacement data of the pressure wave mold at each time node are shown in the following table. During the movement, it moves at a uniform speed along the positive direction of the X-axis.

[0063] Table 3 Displacement data of pressure wave mold at different time nodes

[0064]

[0065] (3) Establish material model: use mechanical property parameters at room temperature.

[0066] (4) Establishing initial conditions: Using the bulging process simulation results as initial conditions, the stress and strain data are transferred backward.

[0067] (5) Establish working conditions: Set the working time according to the extrusion action time to 0.5s.

[0068] (6) Carry out the structure analysis of the pressure wave at the end of the bellows to obtain the forming morphology when the pressure wave at the end of the bellows is completed, such as Fig.12 As shown, at the same time, the residual stress, strain and deformation after the pressure wave can be obtained.

[0069] Step 6: Import the bellows mesh model and stress data after pressure wave, and establish the joint-bellows circumferential weld finite element model, including the following processes:

[0070] (1) Grid adjustment: Remove the joint tip grid and the outer grid of the bellows end as the entire contact body and replace them with the designed weld grid.

[0071] (2) Establishing contact relationship: The joint and weld are defined as different deformation bodies, and the bellows contact body setting remains unchanged; the ambient temperature and heat dissipation parameters are defined in the contact body setting.

[0072] (3) Establishing initial conditions: Using the pressure wave process simulation results as initial conditions, the stress and strain data are transferred backward.

[0073] (4) Establish heat source model: Select the double ellipsoid heat source model, and the heat source model parameters need to be adjusted continuously according to the simulation results. The power is 240W, the welding speed is 1.58m / s, the efficiency is 0.6, and the welding path is set to the path formed by the outermost node of the weld.

[0074] (5) Establish boundary conditions: In welding and cooling conditions, simple constraints are imposed on the joint and the end of the bellows away from the weld, which is defined as constraint condition 1. In unloading conditions, only the end of the bellows away from the weld is simply fixed, which is defined as constraint condition 2.

[0075] (6) Establish working conditions: Establish three working conditions: welding, cooling, and unloading. In the welding working condition, select the heat source condition and constraint condition 1, and the working condition time is 39.5s; in the cooling working condition, only constraint condition 1 is selected, and the working condition time is 900s; in the unloading working condition, only constraint condition 2 is selected, and the working condition time is 10s.

[0076] (7) Conduct thermal / structural analysis of the joint-bellows circumferential weld to obtain the morphology of the bellows and joint after arc welding, such as Fig.13 As shown, at the same time, the residual stress and deformation distribution of the component after welding can be obtained.

[0077] The protection scope of the present invention includes but is not limited to the above embodiments. The protection scope of the present invention shall be based on the claims. Any replacement, deformation, and improvement of the present technology that can be easily thought of by those skilled in the art shall fall within the protection scope of the present invention.

Claims

1. A continuous simulation method for the evolution of stress and deformation of bellows bulging-pressure wave-arc welding, characterized in that The following steps are involved: Step 1: Establish geometric models of pipes, nozzles and various molds, and perform finite element meshing on pipes and nozzles. It is necessary to modify the coarse / fine mesh and transition meshing strategies according to the results of different process trials; Obtain material mechanical properties and thermophysical properties according to literature and material parameter calculation software; Step 2: Establish a finite element simulation model of the tube bulging process, assemble the tube and the die, design a reasonable hydraulic pressure-time curve and a die movement position-time curve according to the tube forming process, carry out structural simulation of the tube bulging, and obtain the stress and deformation results of the tube after hydraulic forming; Step 3: According to the calculation results of the tube bulging simulation model, the bellows grid and the end wave pressure wave mold obtained after the bulging are assembled, and the stress field calculation results after the bulging are used as the initial stress condition of the bellows end wave pressure wave model. A reasonable mold movement position-time curve is set, and the structural simulation of the bellows end wave pressure wave is carried out to obtain the stress and deformation results of the bellows end wave pressure wave; Step 4: According to the simulation calculation results of the pressure wave at the end of the bellows, axially align the bellows deformation grid and the connecting pipe grid obtained after the pressure wave ends, adjust the weld area grid, and use the stress field calculation results after the pressure wave ends as the initial stress condition of the connecting pipe-bellows circumferential seam welding model. Set reasonable thermal boundary conditions, carry out thermal / structural simulation of the connecting pipe-bellows circumferential seam welding, and obtain the stress and deformation results after the connecting pipe-bellows circumferential seam welding.

2. A continuous simulation method for the evolution of stress and deformation of bellows bulging-pressure wave-arc welding according to claim 1, characterized in that In step 1, the finite element mesh of the pipe should be applicable to all process simulations, and the three processes of pipe bulging, end wave pressure wave and circumferential seam welding have different requirements for the finite element mesh. Pipe bulging and end wave pressure wave need to be finely meshed in the large strain area, and circumferential seam welding needs to be finely meshed in the heat source action area. Therefore, different positions of the pipe and the connecting pipe need to be divided into fine meshes, coarse meshes and transition meshes to different degrees in thickness, circumferential direction and axial direction, so as to improve the calculation efficiency of the simulation model; it is also characterized in that in step 1, when obtaining the material parameters, the stress-strain curves of the material under different strain rates and different temperature conditions are obtained, so as to obtain more accurate stress and strain evolution processes and calculation results in different processes.

3. The continuous simulation method for the evolution of stress and deformation of bellows bulging-pressure wave-arc welding according to claim 1 is characterized in that In step 2, if the formed bellows mesh model is directly used for subsequent simulation, the stress field distribution data after bulging in the actual process cannot be obtained, and the subsequent simulation accuracy cannot be guaranteed. According to the actual bulging process, the hydraulic forming process of the pipe is simulated and analyzed, which can accurately reproduce the stress, strain and deformation evolution process of the pipe under the action of hydraulic pressure, and accurately obtain the stress field distribution data of the bellows after forming, that is, before the pressure wave, and use it as the initial stress condition of the end wave pressure wave simulation model to ensure the end wave pressure wave finite element simulation accuracy; it is also characterized in that in step 2, according to the actual process, the hydraulic level change curve is set, which is divided into three stages: wave starting, pressure holding, and pressure relief, which fully restores the actual process, ensures the forming accuracy, and reduces the metal rebound after forming; it is also characterized in that in step 2, according to the trial calculation results of the pressure wave process, the meshes of different parts of the pipe are set as different contact bodies, and preparations are made for adding weld meshes to the subsequent welding simulation model.

4. The method for continuous simulation of stress and deformation evolution of bellows bulging-pressure wave-arc welding according to claim 1 is characterized in that In step 3, an end wave pressure wave simulation model is established on the bellows grid after hydraulic forming, and the stress field distribution data of the bellows after bulging is used as the initial stress condition of the end wave pressure wave model, which can accurately reproduce the stress, strain and deformation evolution process of different parts of the bellows during the end wave pressure wave process, and accurately obtain the stress field distribution data of the bellows after forming, i.e. before the pressure wave, and use it as the initial stress condition of the end wave pressure wave simulation model to ensure the accuracy of the end wave pressure wave finite element simulation; it is also characterized in that in step 3, the mold position change curve is set according to the actual process, the actual process is reproduced, the dimensional requirements after the pressure wave are met, and the metal rebound after the pressure wave is reduced.

5. The method for continuous simulation of stress and deformation evolution of bellows bulging-pressure wave-arc welding according to claim 1 is characterized in that In step 4, a simulation model of the pipe-bellows girth welding is established on the deformed grid after the pressure wave ends. According to the actual weld morphology, a weld grid is drawn separately to replace the pipe and bellows grids at the same position, successfully solving the defect that the actual weld morphology cannot be obtained during thermal / structural analysis. It is also characterized in that in step 4, the stress field distribution data after the pressure wave is used as the initial stress condition of the girth welding model, fully considering the stress accumulation effect after different processes, and accurately reproducing the evolution process of the temperature field, stress field and deformation distribution during the girth welding process in the actual process, which plays a guiding role in further process optimization and failure analysis during service.

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