Residual stress prediction method for die casting, and computer and storage medium

Abstract

The present application relates to a residual stress prediction method for a die casting and based on a finite volume method, and a computer and a storage medium. The residual stress prediction method for a die casting and based on a finite volume method comprises: constructing a model of a workpiece to be die-cast; on the basis of a solidification process simulated by the model, obtaining a solidification temperature gradient; on the basis of the solidification temperature gradient, calculating a residual temperature; and on the basis of the residual temperature, calculating a corresponding residual stress. In the present application, a model of a large casting is constructed, and the model is controlled to simulate the solidification of the casting and the shrinkage resulting therefrom, so as to obtain the residual stress and shrinkage generated by the large casting during a casting process; moreover, simulated material properties and boundary conditions can yield faster and more accurate results for engineering applications, and the provided solution is easy to use and has low computational cost.

Description

Methods, computers, and storage media for predicting residual stress in die castings Technical Field

[0001] This application relates to the field of casting technology, and in particular to a method for predicting residual stress in die castings, a computer, and a storage medium. Background Technology

[0002] In practical engineering applications, various commercial simulation tools have been developed in the field of casting technology to calculate filling, solidification, and residual stresses in the manufacturing of metal castings, molds, and plastics. These tools employ complex numerical methods from fluid and solid mechanics to calculate these problems. In most cases, the calculation at each step involves the coupling of fluid and solid. Commercial software such as Flow3D has been developed to simplify this simulation process. While this development uses the finite element method to provide fully coupled fluid-solid interactions and thermal stress evolution, stress modeling in the casting process often results in a coupled three-dimensional thermophysical problem, including solidification with time-varying boundary conditions. However, these commercial software simulations are computationally intensive, time-consuming, and prone to errors in accuracy.

[0003] The residual stress during the casting process of large aluminum alloy die-cast parts is simulated and evaluated. During mold filling, partially solidified regions and semi-solid regions containing both liquid and solid phases are formed. Under current technology, the filling calculations handle the resulting stresses using fluid dynamics and solid mechanics changes during solidification. The solid phase expands into a moving interface, which can be numerically represented using coupled and moving field equations, but this leads to a high computational workload. The formation of mixed regions with unknown material properties due to the coupling process further complicates the process, as these mixed regions cannot be calculated as easily as elastoplastic regions.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a method, computer, and storage medium for predicting residual stress in die castings based on the finite volume method. By simulating the solidification of the casting and the resulting shrinkage, the residual stress and shrinkage generated in large castings during the casting process can be obtained. At the same time, the simulated material properties and boundary conditions can produce faster and more accurate results for engineering applications. The proposed solution is easy to use and has low computational cost.

[0006] To achieve the above objectives, this application provides the following solution:

[0007] In a first aspect, this application provides a method for predicting residual stress in die-cast parts based on the finite volume method, including:

[0008] Construct a model of the part to be die-cast;

[0009] The solidification temperature gradient is obtained based on the solidification process simulated by the model.

[0010] The residual temperature is calculated based on the curing temperature gradient.

[0011] The residual stress is calculated based on the residual temperature.

[0012] Preferably, the step of constructing the model of the die-cast part includes:

[0013] Construct a three-dimensional model of the die-cast part;

[0014] Set boundary conditions and material properties for the three-dimensional model.

[0015] Preferably, the boundary conditions include at least: temperature, displacement, and residual temperature.

[0016] Preferably, the material properties include at least the mechanical properties and thermal properties of the material.

[0017] Preferably, the step of calculating the residual stress of the die casting based on the solidification process includes:

[0018] The solidification process is simulated by controlling the model through solidification process field calculation and processing software.

[0019] When the temperature is detected to have reached the solidification temperature, record the temperature gradient and solidification time of the solidification cell.

[0020] The curing temperature gradient is constructed based on the temperature gradient and curing time of each recorded solidification cell.

[0021] Preferably, the step of calculating the residual temperature based on the curing temperature gradient includes:

[0022] The curing temperature gradient is interpolated from the center of the cell to the surface of the cell;

[0023] Obtain the cell with the longest curing time and set the residual temperature of that cell to zero;

[0024] Create a priority list based on curing time;

[0025] The cell with the shortest solidification time is selected as the current cell based on the priority list;

[0026] Search for adjacent cells of the current cell;

[0027] When the adjacent cells meet the preset conditions, the adjacent cells and their corresponding solidification times are added to the priority list;

[0028] Continue executing the step of selecting the cell with the shortest solidification time as the current cell based on the priority list. If the priority list is empty, stop executing.

[0029] The residual temperature is obtained by integrating the solidification temperature gradient along the solidification path of the model.

[0030] Preferably, the adjacent cells satisfy the following preset conditions:

[0031] If the residual temperature of the adjacent cell has already been set, then skip the adjacent cell;

[0032] If the residual temperature of the adjacent cell is not set, the residual temperature of the adjacent cell is updated based on the residual temperature of the current cell, and the residual temperature is applied as an increment.

[0033] If the solidification time of the adjacent cell is less than the solidification time of the current cell, then the updated value is subtracted.

[0034] Preferably, the step of calculating the residual stress based on the residual temperature includes:

[0035] The residual stress is obtained by calculating the residual temperature using residual stress field calculation and processing software.

[0036] Secondly, this application provides a computer, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor executing the computer program to implement the steps of the above-described method for predicting residual stress in die castings based on finite volume.

[0037] Thirdly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for predicting residual stress in die castings based on finite volume as described above.

[0038] According to the specific embodiments provided in this application, the following technical effects are disclosed:

[0039] This application provides a method, computer, and storage medium for predicting residual stress in die castings based on the finite volume method. By constructing a model of a large casting and controlling the model to simulate the solidification and resulting shrinkage of the casting, the residual stress and shrinkage generated in the large casting during the casting process can be obtained. At the same time, the simulated material properties and boundary conditions can produce faster and more accurate results for engineering applications. The proposed solution is easy to use and has low computational cost. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 is a schematic flowchart of the residual stress prediction method for die castings based on the finite volume method provided in the embodiments of this application.

[0042] Figure 2 is a schematic flowchart of the calculation of residual stress of the die casting based on the solidification process provided in the embodiment of this application;

[0043] Figure 3 is a schematic diagram of the solidification process effect provided in the embodiment of this application;

[0044] Figure 4 is a schematic diagram of the process for calculating the residual temperature based on the curing temperature gradient provided in an embodiment of this application. Detailed Implementation

[0045] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] The casting filling process is a typical multiphase flow problem, involving the liquid-solid transformation of the metallic phase and the interaction between air and the metallic phase. For example, gas can impede the flow of the metallic phase or be entrained in the molten metal. In die casting, residual stress during filling and solidification causes deformation and displacement, which is a serious defect. Excessive residual stress and deformation can lead to casting failure. To improve the casting yield, residual stress and deformation during the casting process can be predicted first, improving the accuracy of numerical simulation calculations before mass production, thus reducing R&D costs. This invention establishes a gas-liquid-solid multiphase mathematical model based on OpenFOAM, and then performs numerical simulation of the casting filling process, simulating the filling and solidification processes to predict the possible strain and displacement of the casting.

[0047] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] Example 1

[0049] Referring to Figure 1, this application provides a method for predicting residual stress in die-cast parts based on the finite volume method, comprising:

[0050] Construct a model of the part to be die-cast;

[0051] The solidification temperature gradient is obtained based on the solidification process simulated by the model.

[0052] The residual temperature is calculated based on the curing temperature gradient.

[0053] The residual stress is calculated based on the residual temperature.

[0054] In the embodiments of this application, before predicting the residual stress of large castings, a three-dimensional model of the die casting is first constructed using modeling software, such as CAD software, SolidWorks software, UG software, and Pro / E software, to construct the three-dimensional model corresponding to the casting whose residual stress is to be predicted. Further, the mesh tool snappyHexMesh within the computational fluid dynamics (CFD) library openFoam is used to generate a mesh model from the three-dimensional model, and edge length information is set. The boundary conditions of the three-dimensional model, such as temperature, displacement, and residual temperature, are further set using the computational fluid dynamics (CFD) library openFoam. In this embodiment, the model can also use boundary conditions with fixed outer surface values ​​to avoid the introduction of heat transfer coefficients. Material properties, such as the mechanical and thermal properties of the material, are input into the model to simulate and evaluate the residual stress during the casting process of large aluminum alloy die castings.

[0055] In the embodiments of this application, the relationship between the mechanical properties and thermal properties of the material is expressed as follows:

[0056] Mechanical properties: E is Young's modulus, ρ is density, ν is Poisson's ratio, and α is the coefficient of thermal expansion. Young's modulus is obtained from the bending strength test of the rod. Table 1 shows the mechanical properties used for simulation.

[0057] Table 1

[0058] Thermal properties: where s and l represent the solid and liquid phases, respectively, c is the isobaric heat capacity, T is the phase transition temperature, λ is the thermal conductivity, and L is the latent heat of fusion, as shown in Table 2 for the thermal properties used in the simulation.

[0059] Table 2

[0060] After constructing the casting model, the model is further controlled to simulate the solidification process of the casting. The solidification temperature gradient of the model is obtained based on the simulated solidification process using the solidification process field calculation and processing software Solidification Foam. This gradient is then further processed by the temperature integrator T... resIntegrator calculates the residual temperature based on the curing temperature gradient of the obtained model, and further processes it using residual stress field calculation and software T... res StressFoam calculates the residual stress of the model based on the obtained residual temperature and confirms that the residual stress is a prediction of the residual stress generated in the casting during the casting process.

[0061] Referring to Figure 2, the steps for calculating the residual stress of the die-casting based on the solidification process provided in this application include:

[0062] The solidification process is simulated by controlling the model through solidification process field calculation and processing software.

[0063] When the temperature is detected to have reached the solidification temperature, record the temperature gradient and solidification time of the solidification cell.

[0064] The curing temperature gradient is constructed based on the temperature gradient and curing time of each recorded solidification cell.

[0065] In the embodiments of this application, when simulating the solidification process based on the constructed model, the following assumptions are made first: a. At the start of the solidification process, the mold is completely filled with liquid salt at a given temperature. Liquid shrinkage has no effect on later deformation and is not considered; b. The solidified salt is demolded early enough that its deformation can be considered perfectly elastic. Furthermore, the solidification process is simulated using the solidification process field calculation and processing software Solidification Foam. In the simulated solidification configuration, when the solidification temperature reaches the solidification temperature T... s At this point, strain occurs at the solidification front of the material, and the expression for calculating the strain force at that cell in the model is as follows: Δε f r=α(T s )ΔT where, Δε fr For the volumetric increase of the freezing strain, α(T) s ) is the coefficient of thermal expansion, and ΔT is the temperature difference between the two layers on both sides of the interface;

[0066] Further expanding the temperature difference using Taylor series, we obtain: Δε fr =αT res (r)

[0067] Where Tres represents the residual temperature field, which is defined as the profile integral of the temperature gradient at the time of solidification. Tres is the gradient field representing the intensity of solidification shrinkage, as shown in the schematic diagram of the solidification process in Figure 3.

[0068] Furthermore, during the simulated solidification process, the temperature gradient and solidification time of each cell in the model are recorded. The solidification temperature gradient of the model is formed by the temperature gradient and solidification time of all cells. Referring to Figure 3, for solidification, the simplified boundary conditions assume that the material properties of each phase are constant. The latent heat of fusion is considered in the phase transition from liquid to solid.

[0069] Referring to Figure 4, the steps for calculating the residual temperature based on the curing temperature gradient provided in this application include:

[0070] The curing temperature gradient is interpolated from the center of the cell to the surface of the cell;

[0071] Obtain the cell with the longest curing time and set the residual temperature of that cell to zero;

[0072] Create a priority list based on curing time;

[0073] The cell with the shortest solidification time is selected as the current cell based on the priority list;

[0074] Search for adjacent cells of the current cell;

[0075] When the adjacent cells meet the preset conditions, the adjacent cells and their corresponding solidification times are added to the priority list;

[0076] Continue executing the step of selecting the cell with the shortest solidification time as the current cell based on the priority list. If the priority list is empty, stop executing.

[0077] The residual temperature is obtained by integrating the solidification temperature gradient along the solidification path of the model.

[0078] In the embodiments of this application, the temperature integrator T res The Integrator calculates the residual temperature of the model and passes the result of the first calculation to the next step of calculating the residual temperature. In this step, the solidification temperature gradient is integrated along the solidification path using the following formula:

[0079] In the specific calculation process, the curing temperature gradient is first considered. Interpolating from the cell center to the cell face, the system further searches for the cell with the longest curing time and sets its residual temperature to zero. Further, a priority list based on curing time is created to determine the order in which cells are processed. From the created priority list or its top entry, the cell with the shortest curing time is selected and set as the current cell. The system then searches all adjacent cells. In this embodiment, if the residual temperature of an adjacent cell has already been set, that cell is skipped; otherwise, the residual temperature in the adjacent cells is updated using the value in the current cell, and the residual temperature increment is applied. The calculation expression for this increment is as follows: Here, Δr represents the distance between the current cell and its neighboring cells. When the solidification time of a neighboring cell is less than the solidification time of the current cell, the updated value is subtracted. Further, the neighboring cells, along with their corresponding solidification times, are added to the priority list of the component. The process continues, selecting the cell with the shortest solidification time from the created priority list or its top entry, until the priority list is empty. The solidification temperature gradient is then integrated along the solidification path of the model; that is, the residual temperature is calculated by integrating the temperature gradient recorded by each cell during the solidification process.

[0080] In the embodiments of this application, after calculating the residual temperature of the model, further calculating the corresponding residual stress based on the residual temperature specifically includes: using the residual stress field calculation and processing software T res StressFoam calculates the residual stress based on the residual temperature, specifically using the following formula to solve thermoelastic problems and calculate the residual stress:

[0081] Example 2

[0082] This application provides a computer, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor executing the computer program to implement the steps of the above-described method for predicting residual stress in die castings based on finite volume.

[0083] Example 3

[0084] This application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the residual stress prediction method for die castings based on finite volume as described in Embodiment 1 above.

[0085] In summary, the method of this application can greatly reduce the computational workload. When calculating the residual temperature, if the local maximum values ​​of the curing time are inconsistent, a simplified integrated method will be used to solve this problem, thereby avoiding common problems in the inspection of complex weld lines.

[0086] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0087] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for predicting residual stress in die-cast parts, wherein, include: Construct a model of the part to be die-cast; The solidification temperature gradient is obtained based on the solidification process simulated by the model. The residual temperature is calculated based on the curing temperature gradient. The residual stress is calculated based on the residual temperature.

2. The method according to claim 1, wherein, The steps for constructing the model of the die-cast part include: Construct a three-dimensional model of the die-cast part; Set boundary conditions and material properties for the three-dimensional model.

3. The method according to claim 2, wherein, The boundary conditions include at least: temperature, displacement, and residual temperature.

4. The method according to claim 2, wherein, The material properties include at least the mechanical and thermal properties of the material.

5. The method according to any one of claims 1 to 4, wherein, The step of calculating the residual stress of the die casting based on the solidification process includes: The solidification process is simulated by controlling the model through solidification process field calculation and processing software. When the temperature is detected to have reached the solidification temperature, record the temperature gradient and solidification time of the solidification cell. The curing temperature gradient is constructed based on the temperature gradient and curing time of each recorded solidification cell.

6. The method according to claim 5, wherein, The steps for calculating the residual temperature based on the curing temperature gradient include: The curing temperature gradient is interpolated from the center of the cell to the surface of the cell; Obtain the cell with the longest curing time and set the residual temperature of that cell to zero; Create a priority list based on curing time; The cell with the shortest solidification time is selected as the current cell based on the priority list; Search for adjacent cells of the current cell; When the adjacent cells meet the preset conditions, the adjacent cells and their corresponding solidification times are added to the priority list; Continue executing the step of selecting the cell with the shortest solidification time as the current cell based on the priority list. If the priority list is empty, stop executing. The residual temperature is obtained by integrating the solidification temperature gradient along the solidification path of the model.

7. The method according to claim 6, wherein, The adjacent cells satisfy the preset conditions including: If the residual temperature of the adjacent cell has already been set, then skip the adjacent cell; If the residual temperature of the adjacent cell is not set, the residual temperature of the adjacent cell is updated based on the residual temperature of the current cell, and the residual temperature is applied as an increment. If the solidification time of the adjacent cell is less than the solidification time of the current cell, then the updated value is subtracted.

8. The method according to claim 6, wherein, The step of calculating the residual stress based on the residual temperature includes: The residual stress is obtained by calculating the residual temperature using residual stress field calculation and processing software.

9. A computer, comprising: The memory and processor are computer programs stored in the memory and executable on the processor, wherein the processor performs the method as described in any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, wherein, The computer program causes the computer to perform the method as described in any one of claims 1-8.

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