Calculation method of thermal stress in casting based on multi-scale modeling

Abstract

The present invention relates to the technical field of thermal stress calculation of castings, and specifically discloses a method for calculating thermal stress of castings based on multi-scale modeling by using molecular dynamics, first principles and finite element simulation to analyze the thermal stress generated by castings during the casting process, including S1: calculating the relationship between the thermophysical properties and mechanical properties of the melt casting material and the temperature change through a molecular dynamics method based on a microscale; S2: calculating the relationship between the thermophysical properties and mechanical properties of other solid phase materials in the casting system and the temperature change through a first principle method based on a microscale; S3: performing thermal stress simulation calculation on the casting process of the casting based on a macroscale finite element simulation. The present invention accurately obtains the temperature field and thermal stress of the casting during solidification through multi-scale calculation, obtains the thermal stress of the casting during the casting process intuitively, clearly, conveniently and economically, and solves the problem of difficult casting thermal stress testing.

Description

Technical Field

[0001] The invention relates to the technical field of casting thermal stress calculation, and in particular to a casting thermal stress calculation method based on multi-scale modeling. Background Art

[0002] In casting production, the casting transfers heat to the surrounding molding materials, which changes the temperature distribution of the entire system. Due to the different solidification and cooling rates of the casting and the uneven temperature distribution of each part, thermal stress is generated in the casting. Casting thermal stress is the main reason for deformation and cracking of castings during production, processing and use. It not only reduces the dimensional accuracy and performance of the casting, but also directly leads to the scrapping of the casting. Casting thermal stress can be measured by thermal stress test, but only the average thermal stress value is displayed for a specific casting, and the thermal stress of each part of the casting cannot be obtained. The deformation and cracking of the casting caused by excessive local thermal stress cannot be discovered and solved in time. Summary of the invention

[0003] The present invention aims to provide a method for calculating the thermal stress of castings based on multi-scale modeling, which utilizes molecular dynamics, first principles and finite element simulation to analyze the thermal stress generated by castings during the casting process.

[0004] The method for calculating thermal stress of castings based on multi-scale modeling of the present invention comprises S1: calculating the data of the thermophysical properties and mechanical properties of the molten casting material as a function of temperature by a molecular dynamics method based on microscopic scale;

[0005] S2: Using the first-principles method based on microscopic scale, the temperature-dependent changes in the thermophysical and mechanical properties of each solid material in the casting system are calculated respectively;

[0006] S3: Based on macro-scale finite element simulation, thermal stress simulation calculation of casting process is performed.

[0007] The preferred implementation of the present invention is that S1 specifically includes the following contents:

[0008] S101: Establish supercell of casting material;

[0009] S102: setting simulation conditions, temperature range, and time step, firstly simulating the system to run at the highest temperature for a set time to obtain a balanced liquid structure, then cooling at a set cooling rate, and performing a first set number of ion steps to obtain a balanced liquid structure each time the temperature drops by a set temperature;

[0010] S103: After the temperature is lowered by a set temperature and a set number of ion steps are performed to obtain a balanced liquid structure, a second set number of ion steps are run to perform thermodynamic and kinetic analysis to obtain thermophysical properties and mechanical properties of the melt casting material.

[0011] The preferred implementation of the present invention is that S2 specifically includes the following contents:

[0012] S201: Relaxing the crystal structure of each solid material in the casting system until it is fully converged;

[0013] S202: for each solid material in the casting system, calculating the mechanical properties of the crystal structure at different volumes, performing polynomial fitting on the mechanical properties and the volumes, and obtaining analytical expressions of the mechanical properties and the volumes;

[0014] S203: For each solid material in the casting system, the thermophysical properties of the crystal structure at different volumes are calculated to obtain data on volume versus temperature, and then the volume is used as an intermediate quantity to obtain data on mechanical properties versus temperature.

[0015] Among them, S203 specifically uses the quasi-harmonic approximation (QHA method) to calculate the relationship between the thermophysical properties of each solid material in the casting system and the temperature (including volume, thermal expansion coefficient, heat capacity), obtains the relationship between the thermal expansion coefficient, heat capacity and temperature, and the data of volume and temperature, and then uses the volume as an intermediate quantity to obtain the data of mechanical properties and temperature.

[0016] The preferred implementation of the present invention is that S3 specifically includes the following contents:

[0017] S301: constructing a casting model according to a real casting system or a target casting system;

[0018] S302: assigning the data of the thermophysical properties and mechanical properties of the melt casting material and the temperature to the liquid casting metal material, assigning the data of the thermophysical properties and mechanical properties of each solid material in the casting system and the temperature to the solid casting metal material, and constructing a finite element parameter model of the casting system;

[0019] S303: meshing the casting model obtained in S301 to form a network model;

[0020] S304: Setting initial conditions and boundary conditions;

[0021] S305: Simulate and calculate the thermal stress of castings during the casting process.

[0022] The preferred implementation mode of the present invention is: in S201, the crystal structure of each solid material in the casting system is fully optimized and relaxed until it is fully converged to obtain the most stable crystal structure, and then the atomic position of the fixed volume of this most stable crystal structure is relaxed until it is fully converged.

[0023] The first step is full relaxation to obtain the most stable crystal structure (the most stable structure that is not affected by volume changes), and the second step is fixed volume relaxation after changing the volume to obtain the most stable structure at different volumes (the most stable structure at a fixed volume).

[0024] The preferred embodiment of the present invention is that: in S202, the analytical expression obtained by fitting the mechanical properties and the volume polynomial is in the form of y=a+bx+cx 2 +dx 3 +…, where a, b, c, d… are fitting parameters, y is the corresponding mechanical property, and x is the volume.

[0025] The purpose of polynomial fitting of mechanical properties and volume is: 1) to conveniently use volume to represent mechanical properties, so as to conveniently use volume as an intermediate quantity to obtain data on mechanical properties with temperature; 2) in order to extend to higher or lower temperatures and generate continuous data, the form of numerical fitting is changed to analytical fitting, and unknown data can be predicted according to the analytical formula to expand the data range.

[0026] The preferred embodiment of the present invention is that: in S304, for the initial condition setting of the temperature field, the unstable temperature field when the casting begins to solidify after the filling is completed is used as the initial temperature field, and the temperature drop is set to 1.0*10 13 K / s; the stress field boundary condition is to impose a fixed constraint on the bottom of the mold.

[0027] A preferred embodiment of the present invention is that the casting is a high-chromium cast iron reinforced with an alumina ceramic particle preform.

[0028] In the case where the casting is alumina ceramic particle preform reinforced high chromium cast iron, the solid materials in the casting system refer to solid phase high chromium cast iron, alumina preform and molding sand. The casting system includes castings, pouring gates, risers and sand boxes.

[0029] In the present invention, the thermophysical properties and mechanical properties (density, Poisson's ratio, thermal conductivity, heat capacity, thermal expansion coefficient, Young's modulus) are used as inputs for finite element simulation.

[0030] The preferred embodiment of the present invention is that in S202, the relationship between the mechanical property Young's modulus E and the volume is: high chromium casting: y = 3536.721-14.178x + 0.0142x 2 ;Al2O3: y=1035.90-5.690x-0.0263x2 ; Sodium silicate: y = -4929.392 + 34.649x - 0.060x 2 ).

[0031] The present invention has the following technical advantages:

[0032] The invention discloses a casting thermal stress calculation method based on multi-scale modeling, which is applicable to metal-based ceramic reinforced composite castings, heterogeneous metal composite castings and single metal complex configuration castings.

[0033] The present invention uses molecular dynamics based on micro scale to obtain the thermophysical properties and mechanical properties of the melt casting material, uses the first principle based on micro scale to calculate the thermophysical properties and mechanical properties of each solid phase material in the casting system, and uses the above thermophysical properties and mechanical properties as the input of finite element simulation, and obtains the temperature field distribution in the casting process of the casting and the temperature field and thermal stress field distribution in the solidification process through finite element simulation based on macro scale, so that it can be used to predict shrinkage, shrinkage, pores, cracks, incomplete composite defects, optimize the casting process parameters, optimize the structure of the preform, and obtain high-quality castings. Compared with the traditional "trial and error" repetitive experiment, it greatly saves production costs, shortens the production cycle of products, provides guidance and technical support for industrial production, and accelerates the development of castings.

[0034] First principles: First principles calculation method is ab initio calculation, which is widely used in chemistry, physics, life sciences and materials science. Its basic idea is to regard the system composed of multiple atoms as a system composed of multiple electrons and atomic nuclei, and to handle the problem as "non-empirical" as possible according to the basic principles of quantum mechanics. It only needs 5 basic constants (m0 (electron mass), e (original charge), h (Planck constant), c (speed of light), k B (Boltzmann constant) can be used to calculate the energy and electronic structure of the system. First-principles calculations can determine the structure and basic properties of known materials and achieve precise control at the atomic level. They are a powerful tool for solving experimental theoretical problems and predicting the structural properties of new materials. In addition, first-principles calculations do not require real experiments, which greatly saves experimental costs.

[0035] Finite element simulation: Finite element simulation refers to the use of mathematical approximation methods to simulate real physical systems. It also uses simple but interacting elements, namely units, to approximate real systems with infinite unknown quantities with a finite number of unknown quantities. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a flow chart of the method for calculating thermal stress of castings based on multi-scale modeling of the present invention;

[0037] Figure 2 It is a casting model diagram in an embodiment of a casting thermal stress calculation method based on multi-scale modeling of the present invention;

[0038] Figure 3 A surface stress distribution diagram of a model during the solidification process of a hexagonal hole preform obtained in an embodiment of a method for calculating thermal stress of a casting based on multi-scale modeling of the present invention;

[0039] Figure 4 It is a unit cell diagram of high chromium cast iron established by SQS in an embodiment of the method for calculating thermal stress of castings based on multi-scale modeling of the present invention. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described below are only used to explain the present invention and will not limit the protection scope of the present invention.

[0041] As attached Figure 1 As shown, the method for calculating thermal stress of castings based on multi-scale modeling disclosed in this embodiment includes S1: calculating the thermophysical properties and mechanical properties of the molten casting material by a molecular dynamics method based on a microscopic scale.

[0042] S1 specifically includes the following:

[0043] S101: Establish supercell of casting material;

[0044] S102: setting simulation conditions, temperature range, and time step, firstly simulating the system to run at the highest temperature for a set time to obtain a balanced liquid structure, then cooling at a set cooling rate, and performing a first set number of ion steps to obtain a balanced liquid structure each time the temperature drops by a set temperature;

[0045] S103: After the temperature is lowered by a set temperature and a set number of ion steps are performed to obtain a balanced liquid structure, a second set number of ion steps are run to perform thermodynamic and kinetic analysis to obtain thermophysical properties and mechanical properties of the melt casting material.

[0046] S2: Using the first-principles method based on the microscopic scale, the relationship between the temperature changes of various thermophysical properties and mechanical properties of each solid phase material in the casting system is calculated separately.

[0047] S2 specifically includes the following:

[0048] S201: Perform full optimization relaxation on the crystal structure of each solid phase material in the casting system until it is fully converged to obtain the most stable crystal structure, and then relax the atomic positions of the fixed volume of the most stable crystal structure until it is fully converged;

[0049] S202: For each solid phase material in the casting system, the mechanical properties of the crystal structure at different volumes are calculated, and the mechanical properties and the volume are fitted by polynomials to obtain analytical expressions of the mechanical properties and the volume; specifically, the analytical expression obtained by the polynomial fitting of the mechanical properties and the volume is in the form of y=a+bx+cx 2 +dx 3 +…, where a, b, c, d… are fitting parameters, y is the corresponding mechanical property, and x is the volume. The purpose of polynomial fitting of mechanical properties and volume is: 1) It is convenient to use volume to represent mechanical properties, so as to conveniently use volume as an intermediate quantity to obtain data of mechanical properties with temperature; 2) In order to extend to higher or lower temperatures and generate continuous data, the form of changing from numerical fitting to analytical fitting is adopted, and unknown data can be predicted according to the analytical formula to expand the data range.

[0050] S203: For each solid phase material in the casting system, the quasi-harmonic approximation (QHA method) is used to calculate the relationship between its thermophysical properties and temperature (including volume, thermal expansion coefficient, heat capacity), and the data of thermal expansion coefficient, heat capacity and temperature as well as the data of volume and temperature are obtained. The volume is then used as an intermediate quantity to obtain the data of mechanical properties and temperature.

[0051] S3: Based on macro-scale finite element simulation, thermal stress simulation calculation of casting process is performed.

[0052] S3 specifically includes the following:

[0053] S301: constructing a casting model, and constructing a casting model according to a real casting system or a target casting system, wherein the casting system includes a casting, a preform, a pouring gate, a riser, a sand box, and molding sand;

[0054] S302: assigning the data of the thermophysical properties and mechanical properties of the melt casting material and the temperature to the liquid casting metal material, assigning the data of the thermophysical properties and mechanical properties of each solid material in the casting system and the temperature to the solid casting metal material, and constructing a finite element parameter model of the casting system;

[0055] S303: meshing the casting model obtained in S301 to form a network model;

[0056] S304: Set initial conditions and boundary conditions. For the temperature field setting, the unstable temperature field when the casting begins to solidify after the filling is completed is used as the initial temperature field, and the temperature drop is set to 1.0*10 13 K / s; the stress field boundary condition is to impose a fixed constraint on the bottom of the mold;

[0057] S305: Simulate and calculate the thermal stress of castings during the casting process.

[0058] More specifically, this embodiment uses the finite element software COMSOL to simulate the thermal stress of casting alumina ceramic particle preforms to reinforce high chromium cast iron as an example. Other metal-based ceramic reinforced composite castings, heterogeneous metal composite castings and single metal complex configuration castings are also protected by the present invention.

[0059] S1: The thermophysical and mechanical properties of molten high-chromium cast iron are calculated by molecular dynamics based on microscopic scale, including the following contents:

[0060] S101: The EAM embedded atom method developed by Pun et al. was selected as the potential function, and the Materials Studios software was used to establish a high chromium cast iron supercell, 5a0×5a0×5a0, where a0 is the lattice constant. Periodic boundary conditions were used in all three directions when establishing the supercell.

[0061] S102: Simulation condition setting, temperature range is 1300K-2000K, time step is set to 5×10 -15 s, the initial velocity of the atoms is randomly assigned by Gaussian distribution. The system is first simulated at 2000K for 30ps to obtain a balanced liquid structure, and then the system is simulated at 1.0*10 13 The temperature was cooled at a cooling rate of 100 K / s, and 5000 ion steps were performed for every 100 K drop in temperature to obtain a balanced liquid structure.

[0062] S103: An isothermal and isobaric NPT ensemble (indicating a system with a certain number of particles N, pressure P, and temperature T) is selected, and calculations are performed with constant pressure, number of particles (i.e., the number of atoms in the system remains unchanged) and temperature. After 5000 ion steps are performed for each 100K drop in temperature to obtain a balanced liquid structure, 3000 ion steps are run to perform thermodynamic and kinetic analysis to obtain the thermophysical and mechanical properties of the molten high chromium cast iron. The thermophysical properties of the molten high chromium cast iron include density, thermal expansion coefficient, and heat capacity. The calculation formulas for the density, thermal expansion coefficient, and heat capacity of the melt are:

[0063]

[0064] ρ L is the density at the melting point, T Lis the melting point,

[0065]

[0066] Where β represents the thermal expansion coefficient, β L is the thermal expansion coefficient at the melting point,

[0067]

[0068] C is the isobaric heat capacity and H is the enthalpy.

[0069] S2: The data of the thermophysical properties and mechanical properties of each solid material in the casting system (specifically solid phase high chromium cast iron, alumina preform, and molding sand) changing with temperature are calculated by the first principle method based on microscopic scale, including the following:

[0070] S201: Relax the crystal structure of each solid material in the casting system until it is fully converged:

[0071] The crystal structures of Al2O3 (preform) and sodium silicate (main component of water glass molding sand) were obtained from the ICSD crystallographic database, the structure of high chromium cast iron was simplified and a crystal structure model was established using the SQS method. The crystal structures of each material were fully optimized and relaxed until fully converged, and then the atomic positions of the fixed volume were relaxed until fully converged. Specifically, the crystal structure of Al2O3 was downloaded from the crystallographic database ICSD; water glass sand was selected as the molding sand, and its component was sodium silicate, and its crystal structure was downloaded from ICSD; the structure of high chromium cast iron was simplified and a crystal structure model was established using the SQS method. The unit cell of high chromium cast iron established by SQS is as follows: Figure 4 As shown in the figure, the crystal structures of Al2O3, sodium silicate and high chromium cast iron were fully optimized and relaxed to complete convergence by using the first-principles software VASP, and then the atomic positions of the fixed volumes of the crystal structures of Al2O3, sodium silicate and high chromium cast iron were relaxed to complete convergence. Some parameters in the VASP calculation were selected as follows: the projector-augmented wave method (PAW) was used to describe the interaction between ionic real and valence electrons; the PerdewBurke Ernzerhof (PBE) functional in the generalized gradient approximation (GGA) was used to deal with the interaction between electrons; the plane wave cutoff energy in the reciprocal space was set to 400-520 eV; the k-point Monkorst-Park grid was used in all calculations; the energy convergence (EDIFF) and interatomic interaction force (EDIFFG) convergence criteria that met the calculation accuracy requirements were set to EDIFF=1*10 -6~1*10 -8 ,EDIFFG=-0.01~-0.001.

[0072] S202: For each solid material in the casting system, the mechanical properties of the crystal structure at different volumes are calculated, and the mechanical properties and the volume are fitted by polynomials to obtain analytical expressions of the mechanical properties and the volume: the mechanical properties of the crystal structure at different volumes are calculated using the stress-strain method, including Young's modulus E and Poisson's ratio. The formulas for Young's modulus E and Poisson's ratio ν are respectively formula (4) and formula (5), where B represents the bulk modulus and G represents the shear modulus.

[0073]

[0074]

[0075] The relationship between the mechanical properties of Young's modulus E and volume is: High chromium cast iron: y = 3536.721-14.178x + 0.0142x 2 ;Al2O3: y=1035.90-5.690x-0.0263x 2 ; Sodium silicate: y = -4929.392 + 34.649x - 0.060x 2 .

[0076] S203: For each solid material in the casting system, the quasi-harmonic approximation QHA method is used to calculate the data of its thermophysical properties as a function of temperature (including volume, thermal expansion coefficient, heat capacity), and the data of thermal expansion coefficient, heat capacity and temperature as well as the data of volume as a function of temperature are obtained. The volume is then used as an intermediate quantity to obtain the data of mechanical properties as a function of temperature. This embodiment specifically uses phonopy software in combination with VASP to perform QHA calculations.

[0077] Furthermore, the slack model was used to obtain the thermal conductivities of Al2O3, sodium silicate and high chromium cast iron in the casting system.

[0078] The formula of the slack model is as follows:

[0079]

[0080] in is the average atomic mass, δ 3 is the average volume of each atom, θ D is the Debye temperature, n is the number of atoms in the unit cell, γ is the Grieneisen constant, and A is a coefficient related to γ. D The formulas for and γ are as follows:

[0081]

[0082] h is Planck's constant, k is B is the Boltzmann constant, ν m is the speed of sound, which is related to the elastic modulus,

[0083]

[0084] ν is Poisson's ratio.

[0085] S3: Calculate the thermal stress of the casting process, including the following:

[0086] S301: The prefabricated structure in the casting adopts the most commonly used hexagonal prefabricated structure. The gate, riser and sand box are modeled according to the pouring system structure and size of the casting in the actual pouring process to build a casting model, as shown in the attached figure. Figure 2 As shown. The specific modeling process is: use the geometry module of COMSOL Multiphysics to establish the geometric model of two groups of hexagonal preforms. First, establish a single hexagonal model with a hole diameter of 1.8 cm and a hole wall of 2.2 cm. Then, form the approximate shape of the preform through array and movement. Then, delete the unnecessary entities by splitting and deleting entities. Finally, through Boolean operations and union selection in the splitting, combine the independent hexagons into a whole to complete the establishment of the geometric model of the hexagonal preform. After the preform is drawn, start drawing other components, including gates, risers and sand boxes (the dimensions are given in the figure, and the specific dimensions can be referred to the dimension grid). The sand box and other parts are simplified, and smaller parts such as bolts on the sand box are ignored. These small parts have little effect on the final calculation results. Omitting the drawing of this part can also shorten the calculation process and save simulation time.

[0087] S302: assign the data of the thermophysical properties and mechanical properties of the molten casting material and the temperature to the liquid casting metal material, assign the data of the thermophysical properties and mechanical properties of each solid material in the casting system and the temperature to the solid casting metal material, and construct a finite element parameter model of the casting system; assign the data of the thermophysical properties and mechanical properties of the alumina preform and the molding sand with the temperature to the alumina preform and the molding sand, and construct a finite element parameter model of the casting system; wherein the melting point of high chromium cast iron is set to 1473K, and the thermophysical properties of the molten high chromium cast iron liquid phase are used above 1473K, and the thermophysical properties of the high chromium cast iron solid phase are used below 1473K.

[0088] S303: meshing the casting model obtained in S301 to form a network model, using a denser mesh for the casting and the smaller parts such as the internal particle preform, gate, and riser, and using a coarser mesh for the larger parts such as the molding sand and sand box.

[0089] S304: Set initial conditions and boundary conditions. For the temperature field setting (i.e., the metal liquid solidification process), the unstable temperature field when the casting begins to solidify after the filling is completed is input into the model as the initial temperature field, and the temperature drop is set to 1.0*10 13 K / s; Stress field boundary conditions: apply fixed constraints at the bottom of the mold.

[0090] S305: Simulate and calculate the thermal stress during the casting process, and draw a thermal stress cloud map based on the simulation calculation results, as shown in the attached figure. Figure 3 As shown in Figure 2, the temperature field and stress field of the casting system model are simulated using finite element method based on the thermophysical and mechanical properties.

[0091] The preferred implementation modes of the present application are described in detail above in conjunction with the accompanying drawings. Typical known structures and common knowledge technologies in the preferred implementation modes are not described in detail here. Ordinary technicians in the relevant field can improve and implement the technical solutions of the present invention based on their own abilities under the inspiration given by the present implementation modes. Some typical known structures, known methods or common knowledge technologies should not become obstacles for ordinary technicians in the relevant field to implement the present application.

[0092] The scope of protection required by this application shall be based on the contents of its claims, and the contents recorded in the invention content, specific implementation methods and drawings of the specification shall be used to interpret the claims.

[0093] Within the technical concept of the present application, several modifications may be made to the specific implementation methods of the present application, and these modified specific implementation methods should also be regarded as within the protection scope of the present application.

Claims

1. A method for calculating thermal stress of castings based on multi-scale modeling, characterized in that: Including S1: Calculate the temperature-dependent data of the thermophysical and mechanical properties of the melt casting material by molecular dynamics method based on microscopic scale; S2: Using a first-principle method based on microscopic scale, the relationship between the temperature change of various thermophysical properties and mechanical properties of each solid material in the casting system is calculated respectively, and the various solid materials include casting materials, preforms, and molding sands; S2 specifically includes the following: S201: Relaxing the crystal structure of each solid material in the casting system until it is fully converged; S202: for each solid material in the casting system, calculating the mechanical properties of the crystal structure at different volumes, performing polynomial fitting on the mechanical properties and the volumes, and obtaining analytical expressions of the mechanical properties and the volumes; S203: For each solid material in the casting system, the thermophysical properties of the crystal structure at different volumes are calculated to obtain data on volume versus temperature, and then the volume is used as an intermediate quantity to obtain data on mechanical properties versus temperature; In S202, the analytical form of volume and mechanical properties is y=a+bx+cx 2 +dx 3 +…, where a, b, c, d… are fitting parameters, y is the corresponding mechanical property, and x is the volume; S3: Based on the macro-scale finite element simulation method, thermal stress simulation calculation of casting process is performed.

2. The method for calculating thermal stress of castings based on multi-scale modeling according to claim 1, characterized in that: S1 specifically includes the following: S101: Establish supercell of casting material; S102: setting simulation conditions, temperature range, and time step, firstly simulating the system to run at the highest temperature for a set time to obtain a balanced liquid structure, then cooling at a set cooling rate, and performing a first set number of ion steps to obtain a balanced liquid structure each time the temperature drops by a set temperature; S103: After the temperature is lowered by a set temperature and a set number of ion steps are performed to obtain a balanced liquid structure, a second set number of ion steps are run to perform thermodynamic and kinetic analysis to obtain thermophysical properties and mechanical properties of the melt casting material.

3. The method for calculating thermal stress of castings based on multi-scale modeling according to claim 1, characterized in that: S3 specifically includes the following: S301: constructing a casting model according to a real casting system or a target casting system; S302: assigning the data of the thermophysical properties and mechanical properties of the melt casting material and the temperature to the liquid casting metal material, assigning the data of the thermophysical properties and mechanical properties of each solid material in the casting system and the temperature to the solid casting metal material, and constructing a finite element parameter model of the casting system; S303: meshing the casting model obtained in S301 to form a network model; S304: Setting initial conditions and boundary conditions; S305: Simulate and calculate the thermal stress of castings during the casting process.

4. The method for calculating thermal stress of castings based on multi-scale modeling according to claim 1, characterized in that: First, the crystal structure of each solid phase material in the casting system is fully optimized and relaxed until it is fully converged. Then, the atomic position of the fixed volume is relaxed until it is fully converged for the variable volume of the crystal structure of each solid phase material in the casting system.

5. The method for calculating thermal stress of castings based on multi-scale modeling according to claim 3, characterized in that: In S304, for the setting of temperature field, the unstable temperature field when the casting begins to solidify after filling is completed is used as the initial temperature field, and the temperature drop is set to 1.0*10 13 K / s; the stress field boundary condition is to impose a fixed constraint on the bottom of the mold.

6. The method for calculating thermal stress of castings based on multi-scale modeling according to claim 1, characterized in that: The casting is high-chromium cast iron reinforced with an alumina ceramic particle preform.

7. The method for calculating thermal stress of castings based on multi-scale modeling according to claim 6, characterized in that: In S202, the relationship between the mechanical property Young's modulus E and volume is: High chromium casting: y=3536.721-14.178x+0.0142x 2 ;Al2O3: y=1035.90-5.690x-0.0263x 2 ; Sodium silicate: y=-4929.392+34.649x-0.060x 2 .

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