Laser welding temperature field simulation method and system

Abstract

The invention discloses a laser welding temperature field simulation method and system. The method comprises the following steps that a three-dimensional geometric model is established according to the geometric shape and the splicing state of a real welding part; performing grid division on the three-dimensional geometric model to obtain a finite element model; according to the material property of the real welding part, material property setting is conducted on the part, corresponding to the real welding part, in the finite element model; and applying a moving heat source on the finite element model to simulate laser welding, performing transient temperature field numerical calculation, and outputting a temperature field simulation result according to a transient temperature field numerical calculation result. According to the method, the equivalent heat conductivity is adopted as the heat conduction coefficient of the welding seam area in the finite element model, and the heat conduction coefficient fully considers multiple factors such as material attributes, the molten pool state and the abutted seam gaps, so that the temperature distribution condition at the welding seam can be effectively reflected when base metal with different abutted seam gaps is welded, and the welding quality is improved. And the welding quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of laser processing, and in particular to a laser welding temperature field simulation method and system. Background Art

[0002] In order to save experimental costs and shorten the research cycle in the welding process research process, the finite element method is often used to simulate the welding temperature field to predict welding parameters such as weld penetration and temperature. Due to the complex mechanism of laser welding, equivalent substitution methods are generally used when simulating the welding temperature field. The most common method is to use equivalent heat source parameters. For example, the paper "Simulation of welding plate based on equivalent heat source parameters and research on its bearing capacity" (Guo Zhenfei, 2018) uses equivalent heat source parameters to consider the influence of phase change, complex constitutive relations near the weld and other factors on the temperature field. However, when simulating the welding temperature field under constant laser process parameters, the equivalent heat source cannot effectively reflect the influence of different butt joint gaps on weld formation. Summary of the invention

[0003] To solve the above problems, the present invention proposes a laser welding temperature field simulation method and system, which adopts equivalent thermal conductivity as the thermal conductivity coefficient of the weld area in the finite element model, and the thermal conductivity coefficient fully considers many factors such as material properties, molten pool state and joint gap. Therefore, it can effectively reflect the temperature distribution at the weld when welding parent materials with different joint gaps, so as to improve the welding quality.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] On the one hand, a laser welding temperature field simulation method is provided, which comprises the following steps:

[0006] Establish a 3D geometric model based on the geometric shape and splicing status of the actual welded parts;

[0007] Meshing the three-dimensional geometric model to obtain a finite element model corresponding to the three-dimensional geometric model;

[0008] According to the material properties of the real welded parts, the material properties of the parts corresponding to the real welded parts in the finite element model are set respectively;

[0009] And, applying a mobile heat source to the finite element model to simulate laser welding, performing numerical calculation of transient temperature field during the simulated laser welding process, and outputting temperature field simulation results based on the numerical calculation results of the transient temperature field.

[0010] Preferably, the splicing state includes one or more of the joint form, weld type, splicing gap and groove angle.

[0011] Preferably, the grid is a hexahedral unit grid with a gradually changing size, and the grid size increases from small to large in a direction away from the seam gap.

[0012] Preferably, the material properties include one or more of density, thermal conductivity, and specific heat capacity.

[0013] Preferably, when the temperature is greater than or equal to the melting point of the actual weldment and a molten pool of liquid metal is generated, an equivalent thermal conductivity is used in the Z direction as the thermal conductivity coefficient of the weld area in the finite element model, and the expression of the equivalent thermal conductivity is as follows:

[0014]

[0015] Among them, λ z (δ) is the equivalent thermal conductivity in the Z direction; c is the specific heat capacity of the molten pool liquid metal, which is produced by the actual welded part absorbing the energy of the laser beam and then melting; ρ is the density of the molten pool liquid metal; ΔT is the difference between the melting point of the actual welded part and the room temperature; g is the gravitational acceleration; δ is the gap between the actual welded part; μ is the dynamic viscosity of the molten pool liquid metal at 1500°C; is the component of the temperature gradient T in the Z direction.

[0016] Preferably, the heat source is a Gaussian rotating surface heat source model, and its heat source distribution expression is:

[0017]

[0018] In the formula, is the heat source shape concentration coefficient, Q is the heat source power, R0 is the opening radius, H is the heat source height, x, y, z are the three-dimensional coordinate values ​​with the center of the heat source as the origin, and q is the heat flux density.

[0019] Preferably, the real welded part comprises two plates as base materials, and the two plates are butt-jointed, and the value range of the joint gap is 0-0.5 mm.

[0020] On the other hand, a laser welding temperature field simulation system is also provided, which includes:

[0021] A three-dimensional modeling unit, which is used to establish a three-dimensional geometric model according to the geometric shape and splicing state of the actual welded parts;

[0022] A finite element model acquisition unit, which is used to mesh the three-dimensional geometric model to obtain a finite element model corresponding to the three-dimensional geometric model;

[0023] A property setting unit, which is used to set material properties for the parts corresponding to the real welded parts in the finite element model according to the material properties of the real welded parts;

[0024] A heat source loading unit, which is used to apply a moving heat source on the finite element model to simulate laser welding;

[0025] And a simulation result output unit, which is used to perform transient temperature field numerical calculation in the process of simulating laser welding, and output temperature field simulation results according to the transient temperature field numerical calculation results.

[0026] The beneficial effects of using the present invention are:

[0027] The present invention adopts equivalent thermal conductivity as the thermal conductivity coefficient of the weld area in the finite element model, and the thermal conductivity coefficient fully considers many factors such as material properties, molten pool state and joint gap. Therefore, the temperature field simulation result finally obtained can effectively reflect the temperature distribution at the weld when welding parent materials with different joint gaps, and predict and evaluate the weld shape and size based on the temperature field simulation result, so as to accurately adjust the actual laser welding parameters and improve the welding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the steps of the laser welding temperature field simulation method of the present invention;

[0029] Figure 2 is a schematic diagram of a finite element model in the present invention;

[0030] Figure 3 It is a schematic diagram of force analysis of an imaginary metal block when the liquid metal in the molten pool flows downward along the gap of the joint in the present invention;

[0031] Figure 4 Schematic diagram of the Gaussian rotating curved surface heat source model in the present invention;

[0032] Figure 5 The simulation results of the temperature field in different areas of the weld cross section under different joint gaps δ in the present invention;

[0033] Figure 6 It is a structural schematic diagram of the laser welding temperature field simulation system in the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the technical solution more clear, the technical solution is further described in detail below in combination with specific implementation methods. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the technical solution.

[0035] Embodiment 1:

[0036] like Figure 1 As shown, this embodiment provides a laser welding temperature field simulation method, which includes the following steps:

[0037] S1. Establishing a three-dimensional geometric model according to the geometric shape and splicing state of the real welded parts, wherein the splicing state includes one or more of the joint form, weld type, splicing gap and groove angle;

[0038] For example, in this embodiment, Figure 2 As shown, the real weldment includes two plates B as base materials, and the two plates B are butt-jointed, the value range of the joint gap P is 0-0.5 mm, the sizes of the two plates B are 120 mm*50 mm*20 mm, and the material properties of the two plates B are exactly the same, such as both are EH40 steel plates;

[0039] S2. Meshing the three-dimensional geometric model to obtain a finite element model corresponding to the three-dimensional geometric model, such as Figure 2 As shown, the mesh is a hexahedral unit mesh with a gradual size change, and the mesh size changes from small to large along the direction away from the joint gap P. Since the temperature gradient is large at the joint gap P when the weld is subsequently formed by simulated welding, and the temperature gradient is small in the area away from the joint gap P, setting a smaller mesh size at the joint gap P is beneficial to improving the calculation accuracy, and setting a relatively larger mesh size at a distance from the joint gap P can improve the solution efficiency under limited computing resources;

[0040] S3. According to the material properties of the real welded parts, the material properties of the parts corresponding to the real welded parts in the finite element model (such as the two plates B) are set respectively, and the material properties set for different parts can be the same or different;

[0041] The material properties include parameters that can change with temperature, which may specifically include one or more of density, thermal conductivity, specific heat capacity, etc., and the corresponding material properties can be calculated by inputting the material chemical composition of the weldment in a program such as JMatPro software;

[0042] At the same time, after the material properties are set, the density changes and specific heat capacity changes of the finite element model and the real weld are the same; the thermal conductivity coefficients of the base material area and the real weld in the finite element model are the same; the thermal conductivity coefficients of the weld area and the real weld in the horizontal direction (i.e., the X direction and the Y direction) in the finite element model are the same; when the temperature is less than the melting point of the real weld, the thermal conductivity coefficients of the weld area and the real weld in the vertical direction (i.e., the Z direction) in the finite element model are the same, and when the temperature is greater than or equal to the melting point of the real weld and a molten pool of liquid metal is generated, the equivalent thermal conductivity is used in the vertical direction as the thermal conductivity coefficient of the weld area in the finite element model;

[0043] Furthermore, the expression of the equivalent thermal conductivity is as follows:

[0044]

[0045] Among them, λ z (δ) is the equivalent thermal conductivity in the Z direction; c is the specific heat capacity of the liquid metal in the molten pool, which is produced by the actual weldment absorbing the energy of the laser beam and then melting; ρ is the density of the liquid metal in the molten pool; ΔT is the difference between the melting point of the actual weldment and the room temperature (based on the measured welding environment temperature, when the welding environment is unknown, the room temperature = 25°C); g is the gravitational acceleration; δ is the gap between the actual weldment; μ is the dynamic viscosity of the liquid metal in the molten pool at 1500°C; is the component of the temperature gradient T in the Z direction, and the temperature gradient T can be obtained through the temperature field of two plates B with a joint gap P of 0;

[0046] Furthermore, the equivalent thermal conductivity λ in the Z direction is z (δ) is derived through force analysis and equivalent substitution method. The specific derivation process is as follows:

[0047] In the finite element model, there is an imaginary solid metal as a weldment in the gap before welding (the properties of the solid metal are exactly the same as those of the real weldment). The solid metal absorbs the heat of the laser beam L, causing its own temperature to rise until it melts above the liquidus temperature to produce a molten pool of liquid metal, thereby forming a molten pool. On this basis, a hexahedral imaginary metal block 100 (i.e., a part of the imaginary solid metal) located at the bottom of the molten pool and having lengths of dx, dy, and dz in the XYZ directions is taken as the research object. In this process, the heat dQ absorbed by the imaginary metal block 100 is in for:

[0048] dQ in =cΔTdm (1)

[0049] Among them, c is the specific heat capacity of the imaginary metal block 100 (that is, the specific heat capacity of the actual weld), ΔT is the difference between the melting point of the imaginary metal block 100 (that is, the melting point of the actual weld) and the room temperature, and dm is the mass of the imaginary metal block 100.

[0050] In the actual process, the liquid metal in the molten pool flows downward, and the heat conducted downward at the section where the gas-liquid interface of the imaginary metal block 100 is located is:

[0051]

[0052] Among them, λ z is the equivalent thermal conductivity in the Z direction; is the component of the temperature gradient T in the Z direction; dt is the time taken for heat conduction to occur on the imaginary metal block 100, and u is the velocity of the liquid metal in the molten pool flowing downward, and g is the acceleration of gravity; δ is the gap of the joint, ρ is the density of the imaginary metal block 100, μ is the dynamic viscosity of the liquid metal in the molten pool at 1500°C; dx is the length of the imaginary metal block 100 in the x direction;

[0053] The process of the liquid molten pool metal flowing downward along the gap includes the mass transfer process and the heat transfer process. In the temperature field simulation, the mass transfer process can be ignored, and only the process of the heat carried by the high-temperature liquid molten pool metal being transferred downward is considered. The laser energy absorbed by the melting of the imaginary metal block 100 can be equivalent to the heat conducted downward at the section where the gas-liquid interface of the research object is located. Therefore, we have:

[0054] dQ in =dQ out (3)

[0055] Substituting equations (1) and (2) into equation (3), we can obtain the equivalent thermal conductivity in the z direction:

[0056]

[0057] Furthermore, the speed u of the liquid metal in the molten pool flowing downward can be obtained by the following steps:

[0058] like Figure 3 As shown, the force analysis of the imaginary metal block 100 is performed according to formula (5):

[0059] F N =F G (5)

[0060] Among them, F N F is the force exerted by the unmelted solid parent material (i.e., the two plates B) on the imaginary metal block 100 in the Z direction; G is the gravity of the imaginary metal block 100; F N It is mainly the internal friction force of the side wall of the joint acting on the imaginary metal block 100;

[0061] When the gap between the joints is greater than zero, according to Newton's law of internal friction, the internal friction force per unit area exerted by the side wall of the joint on the imaginary metal block 100 is:

[0062]

[0063] Among them, u is the speed of the liquid metal in the molten pool flowing downward, dz is the length of the imaginary metal block 100 in the z direction, μ=μ(T) is the dynamic viscosity of the liquid metal in the molten pool, which is a function of the temperature T. Since the gap between the joints is much smaller than the plate thickness, the flow velocity of the liquid metal at each point in the molten pool can be regarded as distributed according to a linear law, and the internal friction force per unit area can be expressed as:

[0064]

[0065] When the gap between the joints is greater than zero, the force F exerted by the unmelted solid parent material (i.e., the two plates B) on the imaginary metal block 100 is N Size:

[0066] F N =2τdxdz(8)

[0067] The gravity acting on the imaginary metal block 100 is:

[0068] F G =ρgdV(9)

[0069] Wherein, ρ is the density of the imaginary metal block 100, g is the acceleration due to gravity, dV = dx × δ × dz, is the volume of the imaginary metal block 100, and the mass of the imaginary metal block 100 is dm = ρ × dV;

[0070] Substituting equations (7), (8) and (9) into equation (5), we can obtain the velocity u of the liquid metal flowing downward in the molten pool:

[0071]

[0072] In this embodiment, the values ​​of each parameter are shown in Table 1. It should be noted that the parameter value ranges in Table 1 are only used for illustration and do not constitute a specific limitation on the present invention. The actual values ​​can be specifically determined according to factors such as material properties and welding process parameter settings:

[0073] Table 1 Parameter value description

[0074]

[0075]

[0076] S4, applying a mobile heat source to the finite element model to simulate laser welding, performing transient temperature field numerical calculations during the simulated laser welding process, and outputting temperature field simulation results according to the transient temperature field numerical calculation results;

[0077] Specifically, Figure 4 As shown in the figure, the heat source is a Gaussian rotating surface heat source model, and its heat source distribution expression is:

[0078]

[0079] In the formula, is the heat source shape concentration coefficient, Q is the heat source power, R0 is the opening radius, H is the heat source height, x, y, z are the three-dimensional coordinate values ​​with the center of the heat source as the origin, and q is the heat flux density;

[0080] The finite element analysis software used in this embodiment is ANSYS, the power in the heat source is consistent with the actual laser power used for welding, such as 15kW, and the moving speed and moving direction of the heat source are consistent with the actual welding speed and welding moving direction, such as 10mm / s;

[0081] The temperature field simulation results are as follows Figure 5 As shown, it can be seen that the temperature field simulation results in this embodiment can clearly reflect the temperature distribution in different areas of the weld cross section under different joint gaps δ. Furthermore, the weld shape obtained according to the temperature field simulation results is basically consistent with the weld shape obtained by actual welding, and the weld size (such as penetration depth, penetration width, etc.) error is within 5%.

[0082] The reason is that, compared with the simulation method using an equivalent heat source in the prior art, this embodiment uses equivalent thermal conductivity as the thermal conductivity coefficient of the weld area in the finite element model, and the thermal conductivity coefficient fully considers many factors such as material properties, molten pool state, and joint gap. Therefore, the temperature field simulation results finally obtained can effectively reflect the temperature distribution at the weld when welding parent materials with different joint gaps, and predict and evaluate the weld shape and size based on the temperature field simulation results, so as to accurately adjust the actual laser welding parameters and improve the welding quality.

[0083] Embodiment 2:

[0084] This embodiment provides a temperature field simulation system for implementing the laser welding temperature field simulation method described in Embodiment 1. Figure 6 As shown, it includes:

[0085] A three-dimensional modeling unit 1, which is used to establish a three-dimensional geometric model according to the geometric shape and splicing state of the real welded parts;

[0086] A finite element model acquisition unit 2, which is used to mesh the three-dimensional geometric model to obtain a finite element model corresponding to the three-dimensional geometric model;

[0087] The property setting unit 3 is used to set the material properties of the parts corresponding to the real welded parts in the finite element model according to the material properties of the real welded parts;

[0088] A heat source loading unit 4, which is used to apply a moving heat source on the finite element model to simulate laser welding;

[0089] And a simulation result output unit 5, which is used to perform transient temperature field numerical calculation in the process of simulating laser welding, and output temperature field simulation results according to the transient temperature field numerical calculation results.

[0090] In summary, the present invention uses the equivalent thermal conductivity as the thermal conductivity coefficient of the weld area in the finite element model, so that the temperature field simulation results can clearly reflect the temperature distribution in different areas of the weld cross section under different joint gaps, and the weld shape obtained according to the temperature field simulation results is basically consistent with the weld shape obtained by actual welding, and the weld size (such as penetration depth, weld width, etc.) error is within 5%. This shows that the temperature field simulation method in the present invention can effectively reflect the temperature distribution at the weld when welding parent materials with different joint gaps, and predict and evaluate the weld shape and size based on the temperature field simulation results, so as to accurately adjust the actual laser welding parameters and improve the welding quality.

[0091] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, many changes can be made in the specific implementation methods and application scopes based on the ideas of the present technical content. As long as these changes do not deviate from the concept of the present invention, they all fall within the scope of protection of this patent.

Claims

1. A laser welding temperature field simulation method, characterized in that: The steps include: Establish a 3D geometric model based on the geometric shape and splicing status of the actual welded parts; Meshing the three-dimensional geometric model to obtain a finite element model corresponding to the three-dimensional geometric model; According to the material properties of the real welded parts, the material properties of the parts corresponding to the real welded parts in the finite element model are set respectively; And, applying a mobile heat source to the finite element model to simulate laser welding, performing numerical calculation of transient temperature field during the simulated laser welding process, and outputting temperature field simulation results based on the numerical calculation results of the transient temperature field.

2. The laser welding temperature field simulation method according to claim 1, characterized in that: The splicing state includes one or more of the joint form, weld type, splicing gap and groove angle.

3. The laser welding temperature field simulation method according to claim 1, characterized in that: The grid is a hexahedral unit grid with a gradually changing size, and the grid size increases from small to large in a direction away from the joint gap.

4. The laser welding temperature field simulation method according to claim 1, characterized in that: The material properties include one or more of density, thermal conductivity, and specific heat capacity.

5. The laser welding temperature field simulation method according to claim 1, characterized in that: When the temperature is greater than or equal to the actual melting point of the weld and a molten pool of liquid metal is generated, the equivalent thermal conductivity is used in the Z direction as the thermal conductivity coefficient of the weld area in the finite element model, and the expression of the equivalent thermal conductivity is as follows: Among them, λ z (δ) is the equivalent thermal conductivity in the Z direction; c is the specific heat capacity of the molten pool liquid metal, which is produced by the actual welded part absorbing the energy of the laser beam and then melting; ρ is the density of the molten pool liquid metal; ΔT is the difference between the melting point of the actual welded part and the room temperature; g is the gravitational acceleration; δ is the gap between the actual welded part; μ is the dynamic viscosity of the molten pool liquid metal at 1500°C; is the component of the temperature gradient T in the Z direction.

6. The laser welding temperature field simulation method according to claim 1, characterized in that: The heat source is a Gaussian rotating surface heat source model, and its heat source distribution expression is: In the formula, is the heat source shape concentration coefficient, Q is the heat source power, R0 is the opening radius, H is the heat source height, x, y, z are the three-dimensional coordinate values ​​with the center of the heat source as the origin, and q is the heat flux density.

7. The laser welding temperature field simulation method according to claim 1, characterized in that: The real welded part includes two plates as base materials, and the two plates are butt-jointed, and the value range of the joint gap is 0-0.5 mm.

8. A laser welding temperature field simulation system, characterized in that: include: A three-dimensional modeling unit, which is used to establish a three-dimensional geometric model according to the geometric shape and splicing state of the actual welded parts; A finite element model acquisition unit, which is used to mesh the three-dimensional geometric model to obtain a finite element model corresponding to the three-dimensional geometric model; A property setting unit, which is used to set material properties for the parts corresponding to the real welded parts in the finite element model according to the material properties of the real welded parts; A heat source loading unit, which is used to apply a moving heat source on the finite element model to simulate laser welding; And a simulation result output unit, which is used to perform transient temperature field numerical calculation in the process of simulating laser welding, and output temperature field simulation results according to the transient temperature field numerical calculation results.

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