Method for creating a two-dimensional intrinsic strain library for an electric arc welding process

Abstract

The application discloses a kind of electric arc welding process two-dimensional inherent strain library creation method, comprising: determining electric arc welding process parameters and two-dimensional molten droplet weld on the cross-sectional dimension of welding part, calculate molten pool length;According to the heat space distribution of arc heat source, temperature-dependent material density and specific heat, iterative calculation to heat balance, obtain the temperature distribution of two-dimensional molten droplet weld and heat affected zone when arc heating;Establish two-dimensional grid model, carry out heat transfer and solid-liquid phase change calculation, obtain solid-liquid distribution at different time;For the two-dimensional grid model of weld and local welding part, carry out residual solid thermal expansion calculation and welding part shrinkage calculation, obtain the expansion deformation and shrinkage deformation of each microelement;Finally, for each microelement in welding area, superimpose expansion deformation and shrinkage deformation, as plastic strain index, store in inherent strain library.The application can more accurately describe the size and distribution of inherent strain, greatly improve the solving precision of inherent strain method.

Description

Technical Field

[0001] This invention belongs to the field of welding mechanics analysis, specifically a high-precision calculation method for two-dimensional inherent strain data under arc welding process. Background Technology

[0002] Arc welding is a process that first utilizes the heat and melting of the material caused by the approach of an electric arc, and then utilizes the cooling and solidification of the material after the arc is removed to achieve material bonding. It is one of the most widely used, efficient, and important fusion welding processes. The stress and deformation laws of arc welding of complex components are complex, and the main analysis and prediction methods include: thermo-elastic-plastic simulation methods and inherent strain methods.

[0003] Mesh-based finite volume methods and finite element methods are the most effective methods for fluid-thermal-mechanical coupling analysis of deformation and stress, providing highly accurate deformation and stress calculation results for complex components. However, to obtain highly accurate calculation results, a massive number of mesh elements and time load steps that match the mesh density and conform to the welding path and sequence are required. This results in high computational costs, which is not conducive to large-scale numerical sampling, process planning, and engineering application promotion.

[0004] The inherent strain method primarily uses the coefficient of linear expansion as a process parameter, applied to the weld location of complex components, and then obtains the overall deformation and stress of the weldment through the finite element method. Compared with the thermo-elastic-plastic simulation method, it has higher computational efficiency and shorter cycle time. Its drawback is that it sets the strain distribution in the weld zone as a uniform value—the coefficient of linear expansion—which cannot accurately represent the residual strain state at various locations in the fusion weld zone, thus limiting the calculation accuracy of two-dimensional inherent strain data for arc-welded structural components. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for creating a two-dimensional inherent strain library for arc welding processes. This method, from the perspective of structural stress, superimposes the deformation corresponding to the plastic strain generated by each micro-element in the welding zone during the welding process, and finally obtains the two-dimensional deformation components of each micro-element in the transverse and longitudinal directions. By accurately solving the magnitude and distribution of inherent strain in the welding zone, the calculation accuracy of the inherent strain method is effectively improved.

[0006] The technical solution to achieve the purpose of this invention is as follows:

[0007] Step 1: Determine the arc welding process parameters, including the workpiece material, welding speed v (the speed at which the welding electrode moves relative to the workpiece), arc length r, energy proportionality constant C, arc voltage U, welding current I, and welding electrode thermal efficiency η.

[0008] Step 2: Determine the distance between the welding electrode and the workpiece, and determine the cross-sectional area A' of the molten pool on the surface of the workpiece.w and the width of the molten pool W;

[0009] Step 3: Calculate the molten pool length L. Based on the spatial distribution of heat from the electric arc heat source, establish the relationship between the arc heat q, the arc center distance r, the initial temperature T0, and the current temperature T. Then, based on the above relationship, the temperature-related material density ρ and specific heat C... p The temperature of the electrode droplet weld seam is obtained by continuously adding a certain increment to the current temperature based on its initial value and iterating until heat equilibrium is reached. d Temperature T of the heat-affected zone c ;

[0010] Step 4: Establish a two-dimensional mesh model of the electrode droplet weld, the heat-affected zone of the weldment, the remaining areas of the weldment, and the air. Use the temperature distribution T obtained in Step 3. d and T c As boundary conditions, heat transfer and solid-liquid phase transformation calculations are performed to obtain the solid and liquid distribution at multiple key moments during the expansion, contraction and solidification of the molten pool.

[0011] Step 5: Establish a two-dimensional mesh model of the droplet weld and the local arc weld. For the solid part at the moment of molten pool expansion in Step 4, perform solid thermal expansion deformation calculation to obtain the maximum expansion deformation of each micro-element in the droplet zone and the heat-affected zone. Based on the temperature distribution at the solidification moment in Step 4, perform structural shrinkage calculation on the weldment to obtain the shrinkage deformation of each micro-element in the droplet zone and the heat-affected zone.

[0012] Step 6: For each micro-element in the droplet zone and the heat-affected zone, the expansion deformation and contraction deformation are superimposed to form the two-dimensional inherent strain data under the current arc welding process, and stored in the two-dimensional inherent strain library.

[0013] Compared with the prior art, the present invention has the following significant advantages:

[0014] The anisotropic inherent strain of this weld cross-section was obtained through calculations of temperature distribution, heat transfer and phase transformation, and thermal expansion and contraction. Compared with traditional methods that unify inherent strain into a mean value, the created two-dimensional inherent strain data can effectively describe the plane strain state, thus achieving higher calculation accuracy. Attached Figure Description

[0015] Figure 1 This is a flowchart of the method proposed in this invention.

[0016] Figure 2 In this embodiment, the two-dimensional molten pool area is formed when the molten electrode drips onto the surface of the workpiece.

[0017] Figure 3In the embodiment, the grid represents the electrode droplet weld, the heat-affected zone, the remaining areas of the weldment, and the air.

[0018] Figure 4 The data format of the two-dimensional intrinsic strain library in this embodiment is shown. Detailed Implementation

[0019] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 This is a flowchart of the method for creating a two-dimensional inherent strain library for arc welded parts according to the present invention, which specifically includes the following steps.

[0021] Step 1: The welding method used in this embodiment is shielded metal arc welding (SMAW), the material is 304L stainless steel, and the process parameters include: electrode thermal efficiency η is 0.80, electrode diameter is 2mm, average circuit voltage U and average welding current I are 27V and 65A respectively, and the electrode moving speed v relative to the workpiece is 12mm / s. For SMAW, the energy proportionality constant C is 3.2~5.5mm / KW. The ambient temperature is 298.15K and the ambient pressure is 1atm.

[0022] Step 2: The arc length is 5.6 mm, which is the straight-line distance from the electrode tip to the workpiece. This is twice the droplet radius r0. Figure 2 The width W of the molten pool cross-section is 6.35 mm, and the area A' is... w It is 8.63mm 2 .

[0023] Step 3: Calculate the length of the molten pool L based on the relationship between the electrical energy ratio constant C and the length of the molten pool L = CUI. Taking an electric arc heat source with a Gaussian heat distribution as an example, establish the relationship between the electric arc heat q, the distance r from the center of the arc, the initial temperature T0, and the current temperature T, as shown in equation (1).

[0024]

[0025] Where ρ and C p These are the density and specific heat of the weldment material at the current temperature T, respectively. e is the natural constant, ρ' is the resistivity, and r0 can be taken as half the arc length, which is 2.8 mm. When r ≤ r0, T is the temperature at the location of the molten electrode droplet; when r > r0, T is the temperature at the location of the heat-affected zone. c To obtain the temperature distribution of the heat-affected zone, it is divided into n regions based on different distances from the electric arc, and the temperatures of these regions are T. c1 ,…,T cn ,and Figure 3 There are 12 sub-regions.

[0026] Density ρ and specific heat C of 304L stainless steel at different temperatures T p They satisfy equations (2) and (3) respectively.

[0027] C p = 4182 × 0.1122 + 4182 × 3.222 × 10 -5 T Unit: J / (kg·K) (2)

[0028]

[0029] Substituting equations (2) and (3) into equation (1), and setting the initial temperature value T0 to 298.15 K, continuously increment the current temperature T based on the initial temperature value T0, and calculate the left and right sides of equation (1). Continue until the left and right sides of the equation are equal, i.e., heat balance is achieved, and the temperature T of the molten electrode droplet is obtained. d The temperature T of the heat-affected zone is 2944.2 K. c1 ,T c2 ,…,T c12 The corresponding values ​​are 2944.2K, 2311.1K, 1779.5K, 1377.7K, 1070.7K, 838.8K, 667.5K, 544.3K, 458.4K, 400.1K, 361.7K, and 321.4K.

[0030] Step 4, Establish Figure 3 The model shown is a two-dimensional mesh model including air 1, electrode droplet weld 2, and weldment 3. Among them, 3-1 is the heat-affected zone of the weldment, and 3-2 is the weldment area adjacent to the heat-affected zone of the weldment. The mesh of heat-affected zone 3-1 has 12 sub-regions.

[0031] In the heat transfer and solid-liquid phase transition calculations, the boundary conditions are set as follows: air and electrode droplets are defined as liquids, and the workpiece as a solid; the air pressure and air temperature are defined as 101325 Pa and 298.15 K, respectively, and the initial temperature of the workpiece is the same as the air temperature; the initial temperature of the droplets and the heat-affected zone is T. d ,T c1 ,…,T c12 The phase transition process is the process of heat transfer, melting, and solidification between the molten droplet and the weldment. In Fluent software, this process is calculated in transient mode by solving the governing equations stepwise based on pressure. The governing equations include the Navier-Stokes equations, the energy equation, the k-ωShear Stress Transport turbulence model, and the melting and solidification model. The total length of the calculation time step is set to 1 second.

[0032] After calculation, the temperature distribution and solid-liquid phase ratio of the molten droplet weld and the weldment were obtained as a function of time. The complete solidification time of the heat-affected zone was 0.4178 s, and the complete solidification time of the molten droplet was 0.7922 s. From 0.0001 s to 0.11 s, the weld pool expanded at different locations in the weld zone, and 15 sets of solid regions and temperature distributions of the weld pool were obtained.

[0033] Step 5, Figure 3 The mesh shown, which includes the electrode droplet weld 2, the heat-affected zone 3-1, and the nearby weldment area 3-2, is converted into a structural mesh for thermal deformation calculation.

[0034] First, for each moment in the molten pool expansion stage, based on the shape of the molten pool, nodes and elements located in the liquid phase region of the molten droplets and heat-affected zone are deleted, and the thermal expansion deformation of the remaining solid region at that moment is calculated, outputting the deformation of each node. The deformation corresponding to the plastic strain at different moments is calculated using equation (4).

[0035]

[0036] Where x is the deformation of the structural element along any coordinate axis, and ε e 、ε' p ε p These are, respectively, the elastic strain, the plastic strain equal to the elastic strain, and the residual plastic strain, where ε e =ε' p .

[0037] The process iterates through 15 time points, saving only the thermal expansion deformation corresponding to the maximum plastic strain for each node. Based on the molten pool size at each of these 15 time points, some elements in the weldment structure mesh are deleted at each time point. Then, thermal deformation calculations are performed on the solid regions of these 15 weldments to obtain the structural strain under temperature loads at 15 different time points. For each solid micro-element in the model, the deformation corresponding to the plastic strain at these 15 time points is calculated according to equation (4), and the thermal expansion deformation corresponding to the maximum plastic strain is saved.

[0038] For welds and weldments, the temperature distribution at 0.418 s of complete solidification is used as the boundary condition. Corresponding material parameters are defined, and the strain generated when the temperature drops to room temperature is calculated. For convenience, the structural expansion process from room temperature to this temperature distribution is calculated. The expansion deformation of all infinitesimal elements is negatively represented as contraction deformation.

[0039] Step 6: For each micro-element of the electrode droplet and heat-affected zone, superimpose expansion and contraction deformations to obtain the two-dimensional inherent strain data under the current arc welding process, and store it in a two-dimensional inherent strain library. The two-dimensional inherent strain library includes the coordinates of the positioning points, the numbers, coordinates, and plastic strain indices of the discrete nodes of the droplet and heat-affected zone. For example... Figure 4 As shown, -9.488,0,0 represents the coordinates of the positioning point. The main fields are the discrete point number, two-dimensional coordinates, and its two-dimensional plastic strain index.

Claims

1. A method for creating a two-dimensional inherent strain library for arc welding process, characterized in that, Includes the following steps: Step 1: Determine the arc welding process parameters, including welding speed, arc length, arc voltage, welding current, workpiece and electrode materials, electrode thermal efficiency, and the electrical energy ratio constant related to the molten pool length. Step 2: Determine the structural dimensions of the part, determine the distance between the welding rod and the workpiece, and determine the cross-sectional dimensions of the molten pool formed by the welding rod droplets on the workpiece, including the width and cross-sectional area of ​​the molten pool; Step 3: Calculate the length of the molten pool. Based on the spatial distribution of heat from the electric arc heat source, the temperature-related material density and specific heat, continuously add a certain increment to the current temperature on its initial value, iterate the calculation until heat balance is achieved, and obtain the temperature distribution of the two-dimensional droplet weld and heat-affected zone during electric arc heating. Step 4: Using the temperature distribution of the molten droplet weld and the heat-affected zone during arc heating as boundary conditions, establish a two-dimensional mesh model of the electrode molten droplet weld, the heat-affected zone of the workpiece, the remaining areas of the workpiece, and the air. Perform heat transfer and solid-liquid phase transformation calculations to obtain the solid and liquid distribution at multiple key moments during the welding process. Step 5: Establish a two-dimensional mesh model of the droplet weld and the local arc weld. Based on the solid part at the moment of molten pool expansion in Step 4, perform solid thermal expansion deformation calculation to obtain the maximum expansion deformation of each micro-element in the droplet zone and the heat-affected zone. Based on the solidification moment in Step 4, perform structural shrinkage calculation on the two-dimensional weld to obtain the shrinkage deformation of each micro-element in the droplet zone and the heat-affected zone. Step 6: For each micro-element in the droplet region and the heat-affected zone, superimpose the maximum expansion deformation and contraction deformation, calculate the plastic strain index, and store it in the two-dimensional intrinsic strain library.

2. The method for creating a two-dimensional inherent strain library for arc welding process according to claim 1, characterized in that, In step 3, the temperature distribution of the two-dimensional droplet weld and heat-affected zone during arc heating is obtained by setting the initial temperature increment and calculating until the heat balance is achieved by considering the relationship between the distance of each position from the arc center, arc voltage, welding current, welding speed, droplet cross-sectional area, material temperature-related density and specific heat and other parameters.

3. The method for creating a two-dimensional inherent strain library for arc welding process according to claim 1, characterized in that, In step 4, the heat transfer and solid-liquid phase change calculation is performed using the droplet temperature and the temperature distribution of the heat-affected zone as boundary conditions. A certain time step is set to perform heat transfer and phase change calculations on a two-dimensional grid, and the shape of the molten pool at each moment during the expansion stage of the molten pool is recorded until the molten pool no longer invades the solid region of the weldment.

4. The method for creating a two-dimensional inherent strain library for arc welding process according to claim 3, characterized in that, In step 4, the critical moment refers to the moment when the molten pool invades a new solid region in the recorded molten pool shape.

5. The method for creating a two-dimensional inherent strain library for arc welding process according to claim 1, characterized in that, In step 5, the solid thermal expansion calculation is performed at each moment during the molten pool expansion stage. Based on the shape of the molten pool, nodes and elements located inside the molten pool in the mesh are deleted, and then the thermal expansion calculation of the solid region of the weldment at that moment is performed. The displacement of each node is output. Then, based on the values ​​and positive and negative directions of elastic strain and plastic strain, the displacement is decomposed proportionally to obtain the displacement corresponding to plastic strain. This process is repeated for all moments, and only the displacement corresponding to the maximum plastic strain is saved for each node.

6. The method for creating a two-dimensional inherent strain library for arc welding process according to claim 1, characterized in that, In step 5, the shrinkage calculation of the weldment is based on the temperature distribution at the moment when the weld zone is completely solidified, and the strain and displacement caused by this temperature distribution dropping to room temperature are obtained.

7. The method for creating a two-dimensional inherent strain library for arc welding process according to claim 1, characterized in that, In step 5, the shrinkage of the weldment can be obtained by a reverse process, that is, by expanding the structure from room temperature to the temperature distribution, outputting the displacement of all nodes, and taking the negative of the displacement of all nodes as the shrinkage displacement.

8. The method for creating a two-dimensional inherent strain library for arc welding process according to claim 1, characterized in that, In steps 5 and 6, the plastic strain index calculation is a linear superposition of the displacement and shrinkage displacement corresponding to the maximum plastic strain of each node of the molten droplet and the heat-affected zone.

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