Method for predicting welding deformation of metal sandwich structure based on air layer

Abstract

The application provides a metal sandwich structure welding deformation prediction method based on an air layer, which is simulated in stages: firstly, heat and force coupling finite element calculation is performed on the basic unit of the metal sandwich structure, inherent strain parameters are calculated and extracted by accurately modeling, setting material parameters, boundary conditions and a laser heat source subroutine, and post-welding deformation is calculated; secondly, a metal sandwich structure model containing multiple welds is constructed, air layer units between the panel and the core plate are dynamically activated or killed by combining the birth and death element method, the overall stiffness cumulative effect of the component under different welding sequences is simulated, and inherent strain parameters are applied to perform deformation simulation calculation under different welding sequences; the contact calculation of the to-be-connected area is simplified through a virtual air layer, complex contact condition errors are avoided, and inherent strain parameters are loaded step by step to reflect the dynamic influence of the welding sequence on the deformation, so that the multi-weld deformation prediction precision is significantly improved, and the method has high efficiency and engineering practicability.

Description

Technical Field

[0001] This invention belongs to the field of finite element numerical simulation technology for welding processes, specifically, it relates to a method for predicting welding deformation of metal sandwich structures based on air layers. Background Technology

[0002] With the increasing demand for lightweight ships, metal sandwich structures are widely used due to their advantages such as high specific strength and low weight. Laser welding, as a key process in the manufacturing of metal sandwich structures, directly affects the assembly accuracy and service performance of the structure by controlling welding deformation.

[0003] Traditional methods for predicting welding deformation mainly include the thermo-elastic-plastic method and the inherent strain method. While the thermo-elastic-plastic method can accurately simulate the thermo-mechanical coupling effect of the welding process, its high computational complexity and long processing time make it difficult to apply to the deformation analysis of large and complex structures. The inherent strain method significantly improves efficiency by introducing equivalent plastic strain for elastic calculations, but it still has the following limitations: the inherent strain method typically assumes that the welding process is a one-time loading, failing to consider the dynamic changes in structural stiffness during step-by-step welding, resulting in insufficient accuracy in predicting deformation from the sequential superposition of multiple welds; when simulating multiple welds, the gap between the panel and core plate in the unwelded area is prone to introducing calculation errors due to complex contact conditions, affecting the realism of the deformation distribution.

[0004] Furthermore, existing research mostly focuses on single joints or simplified models, lacking a systematic analysis of the deformation caused by sequential welding of multiple welds in the overall metal sandwich structure. Therefore, developing a method capable of efficiently and accurately predicting structural deformation under complex welding sequences has become an urgent need for high-quality manufacturing of metal sandwich structures. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for predicting welding deformation of metal sandwich structures based on air layers.

[0006] The method for predicting welding deformation of metal sandwich structures based on air layers according to the present invention includes:

[0007] Step S1: Perform thermo-elastic-plastic finite element simulation calculations for the basic unit of the metal sandwich structure - the T-joint;

[0008] Step S2: Perform thermoelastic finite element simulation calculations based on the inherent strain method for the multi-weld metal sandwich structure.

[0009] Preferably, step S1 includes:

[0010] Step S11: For the T-joint in the metal sandwich structure, establish a three-dimensional finite element numerical model of the T-joint in the metal sandwich structure.

[0011] Step S12: Set the thermophysical and mechanical parameters of the material of the T-joint in the corresponding metal sandwich structure;

[0012] Step S13: Set the relevant analysis step parameters;

[0013] Step S14: Set relevant thermodynamic and mechanical boundary conditions based on the actual welding process;

[0014] Step S15: Write and embed the relevant laser welding moving heat source subroutine into the model of the T-joint in the metal sandwich structure;

[0015] Step S16: Calculate the welding deformation and extract the inherent strain parameters.

[0016] Preferably, step S2 includes:

[0017] Step S21: For the multi-weld-pass metal sandwich structure, establish the corresponding three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0018] Step S22: Set the material inherent strain parameters of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0019] Step S23: Set the step parameters for the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0020] Step S24: Set the boundary conditions for the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0021] Step S25: Apply thermal strain and perform calculations to obtain the deformation for different welding sequences.

[0022] The welding deformation prediction system for metal sandwich structures based on air layers provided by the present invention is characterized by comprising:

[0023] Module M1: Performs thermo-elastic-plastic finite element simulation calculations for the basic unit of metal sandwich structures - the T-joint;

[0024] Module M2: Performs thermoelastic finite element simulation calculations based on the inherent strain method for multi-weld metal sandwich structures.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention introduces an "air layer" and combines it with the birth and death element method to set up virtual air layer elements in the finite element model, dynamically activate or kill the elements to simulate the structural stiffness changes during the welding process; it can accurately reflect the cumulative effect of stiffness under different welding sequences and significantly improve the deformation prediction accuracy under the superimposed influence of multiple welding processes.

[0027] 2. The air layer unit of the present invention is in a "dead" state when not welded, avoiding complex contact calculations for the gap between the panel and the core board; the unit is activated and assigned material properties during welding, simplifying the contact condition settings and reducing calculation errors;

[0028] 3. This invention combines the inherent strain method with the birth and death element technology. While retaining the high efficiency of the inherent strain method, it achieves refined simulation of the welding sequence through step-by-step loading, making it suitable for engineering applications of various large and complex metal sandwich structures. Attached Figure Description

[0029] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 This is a schematic diagram of the process of the present invention.

[0031] Figure 2 This is a model and grid diagram of the T-type connector of the present invention.

[0032] Figure 3 This is a schematic diagram of the mesh boundary conditions for a T-joint.

[0033] Figure 4 This is a heat flux density distribution diagram for a laser heat source model.

[0034] Figure 5 This is a schematic diagram of the method for extracting inherent strain parameters.

[0035] Figure 6 This is a finite element model and mesh diagram of a metal sandwich structure.

[0036] Figure 7 This is a schematic diagram showing different welding sequences for a metal sandwich structure.

[0037] Figure 8 This is a schematic cloud diagram showing the longitudinal deformation of a metal sandwich structure under different welding sequences. Detailed Implementation

[0038] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0039] like Figures 1 to 8 As shown, the present invention provides a method for predicting welding deformation of metal sandwich structures based on air layers, comprising:

[0040] Step S1: Perform finite element simulation calculations for the thermo-mechanical coupling of the T-joint in the metal sandwich structure; specifically, perform thermo-elastic-plastic finite element simulation calculations for the basic unit of the metal sandwich structure - the T-joint - with thermo-mechanical sequential coupling.

[0041] Step S2: Perform finite element simulation calculations of the inherent strain of the overall metal sandwich structure, specifically thermoelastic finite element simulation calculations based on the inherent strain method for the multi-weld metal sandwich structure.

[0042] Further, step S1 includes:

[0043] Step S11: For the T-joint in the metal sandwich structure, establish a three-dimensional finite element numerical model of the T-joint in the metal sandwich structure.

[0044] Step S12: Set the thermophysical and mechanical parameters of the T-joint material in the corresponding metal sandwich structure;

[0045] Step S13: Set the relevant analysis step parameters;

[0046] Step S14: Set relevant thermodynamic and mechanical boundary conditions based on the actual welding process;

[0047] Step S15: Write and embed the relevant laser welding moving heat source subroutine into the model of the T-joint in the metal sandwich structure;

[0048] Step S16: Calculate the welding deformation and extract the inherent strain parameters.

[0049] Further, step S11 specifically involves: establishing the transverse cross-section of the T-joint in the simulation software, creating a solid using the stretching method, and applying a mesh of appropriate size to each side of the cross-section, generating the mesh using the sweeping method, and assigning mesh attributes according to the analysis mode.

[0050] Further, step S12 specifically involves: calculating the thermophysical and mechanical parameter variation curves of the material at different temperatures using material software; wherein the thermophysical parameters include: density, specific heat capacity, and thermal conductivity, and the mechanical parameters include Young's modulus, Poisson's ratio, coefficient of thermal expansion, and stress-strain curve.

[0051] Further, step S13 specifically involves setting different analysis steps and corresponding analysis times based on the actual welding conditions. The analysis steps generally include welding steps, cooling steps, and fixture release steps.

[0052] Further, step S14 specifically involves setting the thermal and mechanical boundary conditions of the model based on the actual heat dissipation of the welded sample and the constraint of the fixture; wherein, the thermal boundary conditions include convective heat transfer with the air and radiative heat transfer of the model itself, and the mechanical boundary conditions are to assign corresponding displacement constraints according to the actual position and direction of the fixture.

[0053] Further, step S15 specifically involves: using Dflux as a subroutine to load the heat source, and writing the heat source in Fortran language; the information included in the heat source subroutine includes: the total power of the heat source, the start / end point, the direction and speed of heat source movement, and the heat flux distribution function.

[0054] Further, step S16 specifically involves: loading a heat source, calculating the deformation after welding through heat-force sequential coupling, extracting the changes in lateral and longitudinal distances near the weld before and after welding as needed, and calculating the lateral and longitudinal shrinkage rates of the weld, i.e., the inherent strain parameters of the weld.

[0055] Further, step S2 includes:

[0056] Step S21: For the multi-weld-pass metal sandwich structure, establish the corresponding three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0057] Step S22: Set the material inherent strain parameters of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0058] Step S23: Set the step parameters for the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0059] Step S24: Set the boundary conditions for the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0060] Step S25: Apply thermal strain and calculate the deformation for different welding sequences;

[0061] The boundary conditions of the three-dimensional finite element numerical model of the multi-weld metal sandwich structure include constraints and the use of the birth and death element method.

[0062] Further, step S21 specifically involves: establishing a complete three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure, determining the range of inherent strain application, and performing corresponding mesh generation; the complete three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure includes the air layer structure at the connection between the weld and the core plate.

[0063] Further, step S22 specifically involves setting the inherent strain parameters of the material. For the material at the weld, the transverse and longitudinal thermal expansion coefficients per unit temperature are also applied according to the length and width of the weld. The inherent strain parameters specifically include the material's density, elasticity, and plasticity.

[0064] Further, step S23 specifically involves: the analysis step sequence of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure corresponds to the welding sequence of the multi-weld-pass sandwich structure, and the corresponding analysis steps are added and set sequentially according to the actual or planned welding sequence.

[0065] Further, step S24 specifically involves: setting the constraints of the model according to the actual fixture position; and, depending on the welding sequence, first deleting all air layer units, and then "activating" the corresponding air layers in sequence according to the weld sequence.

[0066] Further, step S25 specifically involves obtaining different simulation results based on different welding sequences, and using the change in the distance between the upper and lower plates as the standard to obtain the deformation value of the metal sandwich structure under different welding sequences.

[0067] The present invention also provides a welding deformation prediction system for metal sandwich structures based on air layers. The welding deformation prediction system for metal sandwich structures based on air layers can be implemented by executing the process steps of the welding deformation prediction method for metal sandwich structures based on air layers. That is, those skilled in the art can understand the welding deformation prediction method for metal sandwich structures based on air layers as a preferred embodiment of the welding deformation prediction system for metal sandwich structures based on air layers.

[0068] A welding deformation prediction system for metal sandwich structures based on an air layer, provided by the present invention, includes:

[0069] Module M1: Performs thermo-mechanical coupling finite element simulation calculations for T-joints in metal sandwich structures; specifically, it performs thermo-elastic-plastic finite element simulation calculations for the basic unit of metal sandwich structures—the T-joint—based on thermo-mechanical sequential coupling.

[0070] Module M2: Performs finite element simulation calculations of the inherent strain of the overall metal sandwich structure, specifically thermoelastic finite element simulation calculations based on the inherent strain method for metal sandwich structures with multiple weld passes.

[0071] Furthermore, the module M1 includes:

[0072] Module M11: For T-joints in metal sandwich structures, establish a corresponding three-dimensional finite element numerical model of the T-joints in the metal sandwich structure;

[0073] Module M12: Sets the thermophysical and mechanical parameters of the T-joint material in the corresponding metal sandwich structure;

[0074] Module M13: Sets the relevant analysis step parameters;

[0075] Module M14: Sets relevant thermodynamic boundary conditions based on the actual welding process;

[0076] Module M15: Write and embed the relevant laser welding moving heat source subroutine into the model of the T-joint in the metal sandwich structure;

[0077] Module M16: Calculates welding deformation and extracts inherent strain parameters.

[0078] Furthermore, module M11 specifically involves: establishing the transverse cross-section of the T-joint in the simulation software, creating a solid using the stretching method, and planting a mesh of appropriate size on each side of the cross-section, generating the mesh using the sweeping method, and assigning mesh attributes according to the analysis mode.

[0079] Furthermore, module M12 specifically calculates the thermophysical and mechanical parameter variation curves of the material at different temperatures using material software; wherein the thermophysical parameters include: density, specific heat capacity, and thermal conductivity, and the mechanical parameters include Young's modulus, Poisson's ratio, coefficient of thermal expansion, and stress-strain curve.

[0080] Furthermore, module M13 specifically sets different analysis steps and corresponding analysis step times according to the actual welding situation. The analysis steps generally include welding, cooling, and fixture release.

[0081] Furthermore, module M14 specifically sets the thermal and mechanical boundary conditions of the model based on the actual heat dissipation of the welded sample and the constraint of the fixture; wherein, the thermal boundary conditions include convective heat transfer with the air and radiative heat transfer of the sample itself, and the mechanical boundary conditions are to assign corresponding displacement constraints according to the actual position and direction of the fixture.

[0082] Furthermore, module M15 specifically uses Dflux as a subroutine to load the heat source, and the heat source is written in Fortran language; the information included in the heat source subroutine includes: the total power of the heat source, the start / end point, the direction and speed of heat source movement, and the heat flux distribution function.

[0083] Furthermore, the module M16 specifically involves: loading a heat source, calculating the deformation after welding through heat-force sequential coupling, extracting the changes in lateral and longitudinal distances near the weld before and after welding as needed, and calculating the lateral and longitudinal shrinkage rates of the weld, i.e., the inherent strain parameters of the weld.

[0084] Furthermore, the module M2 includes:

[0085] Module M21: For multi-weld-pass metal sandwich structures, establish a corresponding three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure;

[0086] Module M22: Sets the inherent strain parameters of the material in the three-dimensional finite element numerical model of a multi-weld metal sandwich structure;

[0087] Module M23: Sets the step parameters for the three-dimensional finite element numerical model of a multi-weld-pass metal sandwich structure;

[0088] Module M24: Sets the boundary conditions for the three-dimensional finite element numerical model of a multi-weld-pass metal sandwich structure;

[0089] Module M25: Apply thermal strain to calculate the deformation for different welding sequences;

[0090] The boundary conditions of the three-dimensional finite element numerical model of the multi-weld metal sandwich structure include constraints and the use of the birth and death element method.

[0091] Furthermore, module M21 specifically involves: establishing a complete three-dimensional finite element numerical model of a multi-weld-pass metal sandwich structure, determining the range of inherent strain application, and performing corresponding mesh generation; the complete three-dimensional finite element numerical model of the weld-pass metal sandwich structure includes the air layer structure at the connection between the weld and the core plate.

[0092] Furthermore, module M22 specifically sets the inherent strain parameters of the material. For the material at the weld, the transverse and longitudinal thermal expansion coefficients per unit temperature are also applied according to the length and width of the weld. The inherent strain parameters specifically include the material's density, elasticity, and plasticity.

[0093] Furthermore, module M23 specifically involves: the analysis step sequence of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure corresponds to the welding sequence of the multi-weld-pass sandwich structure, and the corresponding analysis steps are added and set sequentially according to the actual or planned welding sequence.

[0094] Furthermore, module M24 specifically sets the constraints of the model according to the actual fixture position; depending on the welding sequence, it first deletes all air layer units, and then "activates" the corresponding air layers in sequence according to the weld sequence.

[0095] Furthermore, module M25 specifically obtains different simulation results based on different welding sequences, and uses the change in the distance between the upper and lower plates as the standard to obtain the deformation value of the metal sandwich structure under different welding sequences.

[0096] The present invention will now be described in more detail. In a more specific embodiment, taking a metal sandwich structure with six core plates as an example, the present invention provides a method for predicting welding deformation of a metal sandwich structure based on an air layer, including:

[0097] Step S1: Perform finite element simulation calculations for the thermal coupling of the T-joint in the metal sandwich structure, specifically including the following steps:

[0098] Step S11: First, model the welded T-joint of the metal sandwich structure; based on the actual dimensions of the weldment, establish a model as follows: Figure 2 The finite element mesh model shown has a curved surface structure for the panel, with a width and height of 300mm and 5mm respectively, and a radius of curvature of 2m. The core plate has a width and height of 100mm and 4mm respectively, and the longitudinal length of the weld is 120mm. The panel and core plate are modeled separately and then assembled together. The mesh in the weld area and heat-affected zone is denser than that in the original weld location. The entire finite element model has 147,438 nodes and 100,416 elements. The DC3D8 element type is used for temperature field calculation, and the C3D8R element type is used for stress field calculation.

[0099] Step S12: Set the material parameters of the three-dimensional finite element numerical model of the T-joint in the metal sandwich structure, as shown in Tables 1, 2 and 3 below; the selected material is E36 steel, where the thermophysical parameters include density, specific heat capacity and thermal conductivity, and the thermodynamic parameters include Young's modulus, Poisson's ratio, coefficient of thermal expansion and equivalent plastic stress and strain.

[0100] Table 1. Thermophysical parameters of E36 (density, specific heat capacity, thermal conductivity)

[0101]

[0102] Table 2. Thermodynamic parameters of E36 (Young's modulus, Poisson's ratio, coefficient of thermal expansion)

[0103]

[0104] Table 3 Equivalent Plastic Stress-Strain of E36

[0105]

[0106] Step S13: Set the material parameters for the analysis step, mainly including the welding time, cooling time, and fixture release step. The welding time is 6 seconds, and the cooling time is 1200 seconds.

[0107] Step S14: Set the boundary conditions for the material; the boundary conditions include the heat dissipation and constraints of the three-dimensional finite element numerical model of the T-joint in the metal sandwich structure, such as... Figure 3 As shown

[0108] Heat dissipation considerations for convective heat transfer q in the three-dimensional finite element numerical model of the T-joint in a metal sandwich structure. c Heat exchange with radiation q r The calculations were performed using Newton's law and the Stefan-Boltzmann theorem, respectively.

[0109] qc =-h c (T-T0)

[0110] q r =-ε r σ r [(T+273.15) 4 -(T0+273.15) 4 ]

[0111] Among them, the material's convective heat transfer coefficient h c Set to 20W / (m 2 ℃), room temperature T0 is set to 25℃, and the material's radiative heat transfer coefficient ε r Set to 0.8, σ r is the Stefan-Boltzmann constant; the symmetry plane sets adiabatic thermal convection and thermal radiation boundary conditions; T is the temperature.

[0112] The model's constraints are divided into external constraints and 3.6 degrees of freedom constraints after the fixture is released. The red part is the loading part of the heat source subroutine.

[0113] Step S15: Set the subroutine code for the laser welding heat source, such as... Figure 4 The diagram shows the overall shape of the heat source. The upper part of the heat source uses a conical heat source with uniform energy distribution, and the lower part uses a cylindrical heat source with Gaussian energy distribution. The formulas are as follows:

[0114]

[0115] Where Q is the laser power, and the unit is J / s;

[0116] q1 and q2 are the heat flux distributions of the conical and cylindrical heat sources, respectively, in J / (s·m²). 3 );

[0117] η1 and η2 are the heat distribution coefficients for the conical and cylindrical heat sources, respectively;

[0118] r z r1 and r2 are the maximum and minimum radii of the cone, respectively, in meters.

[0119] r c Represents the radius of the heat source corresponding to the current calculation point.

[0120] r i Represents the minimum radius of the cone

[0121] r e Represents the maximum radius of the cone

[0122] Z i This represents the z-coordinate of the cone at its minimum radius.

[0123] Z e This represents the z-coordinate corresponding to the maximum radius of the cone.

[0124] Z d This represents the z-coordinate of the lowest point of the cylinder.

[0125] Z represents the z-axis coordinate of the current calculation point.

[0126] In addition to the formula, the heat source subroutine also contains information such as the power of the heat source, the starting point of the heat source, and the moving speed of the heat source.

[0127] Step S16: Run the simulation to obtain the results, and extract the corresponding inherent strain parameters based on the results. The specific range of the extraction is as follows: Figure 5 As shown; currently considering the transverse shrinkage ε of the weld. y and longitudinal contraction ε x .

[0128] Step S2: Perform finite element simulation calculations of the inherent strain of the overall metal sandwich structure under load; specifically including the following steps:

[0129] Step S21: Based on the dimensions of the actual metal sandwich curved surface structure, the following was established: Figure 6 The finite element model shown has 12 welds. The panel is a curved structure with a thickness of 5mm, a length of 1000mm, and a radius of curvature of 4m. The core plate has a thickness of 4mm, a height of 100mm, and a distance of 150mm between the two core plates. The weld length is 1000mm. The mesh is denser in the weld area and near the heat-affected zone, and gradually coarsens in areas farther from the weld. The entire finite element model has 263,718 nodes and 222,000 elements; the element type used is C3D8R. Step S22: Set the inherent strain parameters of the material, including density, elasticity, and plasticity. The material at the weld should be subjected to different transverse and longitudinal thermal expansion coefficients according to different layers, with specific values ​​of 0.0332 and 0.000339, respectively.

[0130] Step S23: The analysis sequence of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure corresponds to the welding sequence of the multi-weld-pass sandwich structure; such as... Figure 7 As shown, the welding sequence steps of the model are set, and two different welding sequences are set: from top to bottom and from the inside to the outside, and from top to bottom and from the outside to the inside.

[0131] Step S24: Boundary conditions for the three-dimensional finite element numerical model of the multi-weld metal sandwich structure include constraints and the use of the birth and death element method; set the constraints of the model according to the actual fixture position; according to the different welding sequences, first delete all air layer elements, and then "activate" the corresponding air layers in sequence according to the weld sequence. Figure 6 The red units in the diagram represent the application areas of the air layer corresponding to the dead and live units. When not welded, a layer of units between the panel and the core board is killed directly. When welding to this point, the units are reactivated, causing a change in the overall structural stiffness. The two ends of the weld are pre-spot welded, making the structure a whole before welding.

[0132] Step S25: Obtain longitudinal deformation value contour maps for two different welding sequences, such as... Figure 8 As shown, this method results in different changes in welding sequences after the application of inherent strain. Figure 8 As can be seen, the deformation at the corners is greater in sequence 1, with the distance between the upper and lower plates reaching 1.26mm, while in sequence 2 the distance between the upper and lower plates at the corners is 1.15mm. Further verification can be carried out based on the deformation under different welding sequences.

[0133] In summary, this invention provides a method for predicting welding deformation of metal sandwich structures based on air layers. Addressing the high computational cost of traditional thermo-elastic-plastic methods and the difficulty of considering the cumulative effects of multiple weld passes and contact condition errors in the inherent strain method, this invention proposes a phased simulation strategy: First, thermo-coupled finite element analysis is performed on the basic unit of the metal sandwich structure—the T-joint. Through precise modeling, setting material thermophysical / mechanical parameters, boundary conditions, and a moving laser heat source subroutine, post-weld deformation is calculated and inherent strain parameters are extracted. Second, a metal sandwich structure model with multiple weld passes is constructed. The air layer units between the panel and core are dynamically activated or destroyed using the birth-death element method to simulate the cumulative effect of overall component stiffness under different welding sequences. Inherent strain parameters are then applied to simulate deformation calculations under different welding sequences. This method simplifies contact calculations in the area to be connected by using a virtual air layer, avoiding errors from complex contact conditions. Simultaneously, the inherent strain parameters are applied step-by-step to reflect the dynamic influence of the welding sequence on deformation, significantly improving the accuracy of multi-weld pass deformation prediction. It combines high efficiency with engineering practicality and is suitable for welding process optimization and deformation control of large and complex metal sandwich structures such as ships.

[0134] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0135] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for predicting welding deformation of a metal sandwich structure based on an air layer, characterized in that, include: Step S1: Perform thermo-elastic-plastic finite element simulation calculations for the basic unit of the metal sandwich structure - the T-joint; Step S2: Perform thermoelastic finite element simulation calculations based on the inherent strain method for the multi-weld-pass metal sandwich structure; Step S2 includes: Step S21: For the multi-weld-pass metal sandwich structure, establish the corresponding three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure; Step S22: Set the material inherent strain parameters of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure; Step S23: Set the step parameters for the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure; Step S24: Set the boundary conditions for the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure; Step S25: Apply thermal strain and calculate the deformation for different welding sequences; In step S2: the boundary conditions of the three-dimensional finite element numerical model of the multi-weld metal sandwich structure include constraints and the use of the birth and death element method; In step S21: a complete three-dimensional finite element numerical model of the multi-weld metal sandwich structure is established, the range of inherent strain application is determined, and the corresponding mesh is generated; the complete three-dimensional finite element numerical model of the multi-weld metal sandwich structure includes the air layer structure at the connection between the weld and the core plate. In step S22: the inherent strain parameters of the material are set. For the material of the weld, the transverse and longitudinal thermal expansion coefficients per unit temperature are also applied according to the length and width of the weld. The inherent strain parameters specifically include the material's density, elasticity, and plasticity. In step S23: the analysis steps of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure correspond to the welding sequence of the multi-weld-pass sandwich structure. The corresponding analysis steps are added and set in sequence according to the actual or planned welding sequence. In step S25: different simulation results are obtained according to different welding sequences, and the deformation value of the metal sandwich structure under different welding sequences is obtained by taking the change in the distance between the upper and lower plates as the standard. In step S24: set the constraints of the model according to the actual fixture position; according to the different welding sequences, first delete all air layer units, and then "activate" the corresponding air layers in sequence according to the weld sequence; The calculation results of the thermo-elastic-plastic finite element simulation in step S1 include: inherent strain parameters; In step S2, inherent strain parameters are applied to perform deformation simulation calculations under different welding sequences.

2. The method for predicting welding deformation of metal sandwich structures based on air layers according to claim 1, characterized in that, Step S1 includes: Step S11: For the T-joint in the metal sandwich structure, establish a three-dimensional finite element numerical model of the T-joint in the metal sandwich structure. Step S12: Set the thermophysical and mechanical parameters of the T-joint material in the corresponding metal sandwich structure; Step S13: Set the relevant analysis step parameters; Step S14: Set relevant thermodynamic and mechanical boundary conditions based on the actual welding process; Step S15: Write and embed the relevant laser welding moving heat source subroutine into the model of the T-joint in the metal sandwich structure; Step S16: Calculate the welding deformation and extract the inherent strain parameters.

3. The method for predicting welding deformation of metal sandwich structures based on air layers according to claim 2, characterized in that, In step S11: the transverse cross section of the T-joint is established in the simulation software, the solid is created using the stretching method, and the mesh of appropriate size is applied to each side of the cross section. The mesh is generated using the sweeping method, and the mesh attributes are assigned according to the analysis mode. In step S12: the thermophysical and mechanical parameter variation curves of the material at different temperatures are calculated using material software; wherein, the thermophysical parameters include: density, specific heat capacity, and thermal conductivity, and the mechanical parameters include Young's modulus, Poisson's ratio, coefficient of thermal expansion, and stress-strain curve; In step S13: different analysis steps and corresponding analysis times are set according to the welding conditions; the analysis steps include welding steps, cooling steps, and fixture release steps. In step S14: the thermal and mechanical boundary conditions of the model are set according to the heat dissipation of the welded sample and the constraint of the fixture; The thermal boundary conditions include convective heat transfer with the air and radiative heat transfer within itself, while the mechanical boundary conditions are the corresponding displacement constraints imposed according to the actual position and orientation of the clamp.

4. The method for predicting welding deformation of metal sandwich structures based on air layers according to claim 2, characterized in that, In step S15: Dflux is used as a subroutine to load the heat source, and the heat source is written in Fortran language; the information included in the heat source subroutine includes: the total power of the heat source, the start and end points, the direction and speed of the heat source movement, and the heat flux distribution function; In step S16: a heat source is applied, and the deformation after welding is obtained through heat-force sequential coupling calculation. As needed, the changes in the transverse and longitudinal distances before and after welding near the weld are extracted, and the transverse and longitudinal shrinkage rates of the weld, i.e., the inherent strain parameters of the weld, are calculated.

5. A welding deformation prediction system for metal sandwich structures based on air layers, characterized in that, include: Module M1: Performs thermo-elastic-plastic finite element simulation calculations for the basic unit of metal sandwich structures - the T-joint; Module M2: Performs thermoelastic finite element simulation calculations based on the inherent strain method for multi-weld metal sandwich structures; The module M2 includes: Module M21: For multi-weld-pass metal sandwich structures, establish a corresponding three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure; Module M22: Sets the inherent strain parameters of the material in the three-dimensional finite element numerical model of a multi-weld metal sandwich structure; Module M23: Sets the step parameters for the three-dimensional finite element numerical model of a multi-weld-pass metal sandwich structure; Module M24: Sets the boundary conditions for the three-dimensional finite element numerical model of a multi-weld-pass metal sandwich structure; Module M25: Apply thermal strain to calculate the deformation for different welding sequences; In module M2: the boundary conditions of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure include constraints and the use of the birth and death element method; In module M21: a complete three-dimensional finite element numerical model of a multi-weld-pass metal sandwich structure is established, the range of inherent strain application is determined, and the corresponding mesh is generated; the complete three-dimensional finite element numerical model of the weld-pass metal sandwich structure includes the air layer structure at the connection between the weld and the core plate. In module M22: the inherent strain parameters of the material are set, and for the material of the weld area, the transverse and longitudinal thermal expansion coefficients per unit temperature are also applied according to the length and width of the weld; the inherent strain parameters specifically include the material's density, elasticity and plasticity; In module M23: the analysis step sequence of the three-dimensional finite element numerical model of the multi-weld-pass metal sandwich structure corresponds to the welding sequence of the multi-weld-pass sandwich structure. The corresponding analysis steps are added and set in sequence according to the actual or planned welding sequence. In module M25: different simulation results are obtained according to different welding sequences, and the deformation value of the metal sandwich structure under different welding sequences is obtained by taking the change in the distance between the upper and lower plates as the standard. In module M24: the constraints of the model are set according to the actual fixture position; depending on the welding sequence, all air layer units are deleted first, and then the corresponding air layers are "activated" in sequence according to the weld sequence. The calculation results of the thermo-elastic-plastic finite element simulation of module M1 include: inherent strain parameters; In module M2, inherent strain parameters are applied to perform deformation simulation calculations under different welding sequences.

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