A method for predicting residual stress of an alloy surface layer in powder bed fusion laser additive manufacturing

Abstract

The present application relates to a kind of powder bed fusion laser additive manufacturing alloy surface layer residual stress prediction method, comprising: S1: according to sample block to establish entity domain geometric model;S2: expansion is carried out in the periphery of entity domain, constructs the powder domain geometric model surrounding entity domain;S3: give entity domain dense alloy material attribute, give the equivalent thermal physical property of unmelted powder of powder domain, set thermal boundary condition;S4: apply moving heat source, activate material unit, execute thermal coupling transient simulation;S5: extract the surface layer residual stress of entity domain after cooling.The present application constructs powder area in the periphery of forming block, truly simulates the blocking, change effect of powder to heat convection and thermal radiation under powder laying environment, avoids the overcooling assumption that traditional model exposes entity surface directly to environment.Model is simple to realize, need not change original thermal coupling simulation process, is suitable for the residual stress prediction of powder bed fusion laser additive manufacturing of multiple alloy systems.

Description

Technical Field

[0001] This invention relates to the field of laser additive manufacturing technology, and specifically to a method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing. Background Technology

[0002] In powder bed fusion laser additive manufacturing (such as selective laser melting (SLM)), a high-energy laser scans and melts metal powder layer by layer, which then cools and solidifies to form a dense part. The inherent rapid heating and cooling process of this technology generates significant residual stress, which can lead to part deformation, cracking, or even printing failure. Therefore, accurately predicting the distribution of residual stress within the formed part, especially the surface residual stress, is crucial for process optimization and quality control.

[0003] Existing finite element method prediction methods generally adopt the "thermo-mechanical coupling method," which establishes a model based on the actual geometric dimensions of the formed block and uses the "birth and death element" technique to sequentially activate the cladding weld beads to simulate the layer-by-layer deposition process. In setting thermal boundary conditions, three heat dissipation methods are usually considered: thermal radiation (heat dissipation from the surface of the part to the environment), thermal convection (heat exchange between the surface of the part and the surrounding gas), and thermal conduction (heat conduction from the part to the equipment platform through the substrate), as shown in reference 1.

[0004] Reference 1: Chinese patent document with publication number CN115952723A Reference 1 discloses a method for predicting residual stress in laser cladding deposited parts, including the following steps: Step 1: Establishing a temperature field model, inputting the predicted material properties and setting temperature boundary conditions into the temperature field model; Step 2: Simulating the laser cladding deposition process using the birth and death element technique, calculating the temperature field, and introducing the change in latent heat of solid-liquid phase transition into the temperature field calculation; Step 3: Transforming the temperature field model into a stress field model, and then substituting the calculation results of the temperature field into the stress field model for phase calculation; Step 4: Calculating the average linear expansion coefficient and average yield strength of the mixed phase that affect the residual stress through the phase calculation results, thereby calculating the residual stress of the material after forming by introducing the solid-state phase transition effect.

[0005] However, the accuracy of predicting surface residual stress in alloy blocks manufactured using the aforementioned traditional methods is often insufficient. This is because traditional models neglect the actual physical environment of the powder-laying process: the formed block is always completely surrounded by unmelted alloy powder during manufacturing. Although solid metals have high thermal conductivity, the surrounding powder significantly alters the near-surface convection and radiation conditions—the powder layer obstructs airflow, reducing the efficiency of natural convection; simultaneously, the multiple reflections and shielding effects between powder particles also alter effective radiative heat transfer. Traditional methods directly expose the part surface to environmental convection and radiation, leading to a large deviation between the simulated surface cooling rate and the actual rate, ultimately resulting in inaccurate predictions of surface residual stress. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned technical problems existing in the prior art and to provide a method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing.

[0007] To address the shortcomings of the aforementioned technical problems, the present invention provides a method for predicting residual stress on the surface of alloys manufactured using powder bed fusion laser additive manufacturing, comprising the following steps: S1: Establish the geometric model of the solid domain based on the sample block size; S2: Expand the periphery of the solid domain to construct a powder domain geometric model that surrounds the solid domain; S3: Assign the properties of dense alloy material to the solid domain, and the equivalent thermophysical properties to the unmelted powder in the powder domain. Set thermal boundary conditions. Specifically, apply thermal radiation and thermal convection boundary conditions to the outer surface of the powder domain, and set the interface between the solid domain and the powder domain as only a thermal conduction boundary. S4: Apply a moving heat source to activate the material element, perform thermo-mechanical coupling transient simulation, and complete thermal and mechanical analysis; S5: Extract the residual stress on the surface of the solid domain after cooling.

[0008] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing according to the present invention: the material of the sample block in step S1 is titanium alloy, nickel-based alloy, stainless steel, aluminum alloy or cobalt-chromium alloy.

[0009] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing according to the present invention: in step S2, the outward expansion size of the powder domain is 0.1 to 1 times the size of the corresponding direction of the solid domain.

[0010] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing according to the present invention: the absolute thickness of the powder domain expanding outward in step S2 is 1~20mm.

[0011] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing according to the present invention: the equivalent thermal conductivity of the powder domain in step S3 is 1% to 20% of the thermal conductivity of the solid alloy.

[0012] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing of the present invention: the equivalent density of the powder domain is 40% to 60% of the density of the solid alloy.

[0013] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing of the present invention, the thermal boundary condition in step S3 further includes: setting an isothermal boundary or equivalent convective heat transfer coefficient at the bottom of the substrate or the contact surface of the fixture.

[0014] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing according to the present invention: the heat source in step S4 is a Gaussian surface heat source, a double ellipsoidal heat source, or a Gaussian body heat source.

[0015] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing according to the present invention: the thermo-mechanical coupling simulation in step S4 is either sequential thermo-mechanical coupling or complete thermo-mechanical coupling.

[0016] As a further optimization of the method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing of the present invention: in step S4, when performing force analysis, the powder domain is set as a viscoelastic material with an elastic modulus lower than 1 / 1000 of the solid elastic modulus.

[0017] The present invention has the following beneficial effects: 1. This invention simulates the blocking and alteration of thermal convection and radiation by powder in a powder-coated environment by constructing a powder region around the formed block, thus avoiding the over-cooling assumption of traditional models that directly expose the solid surface to the environment. During the prediction process, the surface temperature gradient and cooling rate are calibrated, resulting in a significant improvement in the accuracy of the simulated surface residual stress (especially the tensile stress parallel to the scanning direction) compared to experimental test values ​​(such as those obtained by X-ray diffraction).

[0018] 2. The prediction method of this invention has a simple model implementation, requiring no modification to the original thermo-mechanical coupling simulation process. Only a powder domain needs to be added in the geometric modeling and material property definition stages, resulting in a limited increase in computational resources. Furthermore, it is applicable to residual stress prediction in powder bed fusion laser additive manufacturing for various alloy systems (such as titanium alloys, nickel-based superalloys, stainless steel, aluminum alloys, etc.). Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the principle of the prediction method of the present invention; Figure 2This is a physical model drawing from Embodiment 1 of the present invention; Figure 3 This is a finite element model diagram from Embodiment 1 of the present invention; Figure 4 This is the residual stress cloud diagram calculated in Comparative Example 1 of the present invention; Figure 5 This is a residual stress cloud diagram calculated for Embodiment 1 of the present invention. Detailed Implementation

[0020] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the accompanying drawings in this application are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. Furthermore, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may not be implemented in sequence, and steps without logical contextual relationships may be reversed or implemented simultaneously. In addition, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts.

[0022] Furthermore, the described embodiments are merely some, not all, of the embodiments of this application. The components of the embodiments of this application described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0023] It should be noted that the term "comprising" will be used in the embodiments of this application to indicate the presence of the features declared thereafter, but does not exclude the addition of other features.

[0024] A method for simulating, modeling, and predicting residual stress in alloys used in powder bed fusion laser additive manufacturing includes the following steps: Step 1: Establish the geometric model of the formed block Based on the actual dimensions of the alloy block to be manufactured, a three-dimensional geometric model is established, denoted as the solid domain Ω_solid.

[0025] Step 2: Construct the outer powder region Around the solid domain Ω_solid, a certain size is extended outward along the normal direction of each of its outer surfaces to form a powder coating layer region surrounding the solid domain, denoted as the powder domain Ω_powder.

[0026] The expansion dimension is at least greater than the powder bed thickness and greater than the heat-affected zone depth. Optionally, the expansion dimension is 0.2 to 1 times the dimension in the corresponding direction of the solid domain, or the absolute thickness is 2 to 20 mm (determined based on the actual powder bed thickness and thermal diffusion length).

[0027] Step 3: Assign material properties to different areas Solid domain Ω_solid: Assigns material properties to dense alloys, including density, specific heat capacity, thermal conductivity as a function of temperature, elastic modulus, yield strength, Poisson's ratio, coefficient of thermal expansion, etc.

[0028] Powder domain Ω_powder: imparts equivalent thermophysical properties to unmelted alloy powders, including: The equivalent thermal conductivity k_powder is significantly lower than that of solid alloys (e.g., 1% to 20% of that of solid alloys) and can be expressed as a function of temperature. The equivalent density ρ_powder is determined based on the loose density of the powder (usually 40% to 60% of the bulk density). Equivalent specific heat capacity, similar to or slightly adjusted from the actual value; The emissivity ε_powder, due to multiple reflections between powder particles, can be higher than that of a solid surface, for example, it can be taken as 0.6~0.9.

[0029] Step 4: Set thermal boundary conditions On the outer surface of the powder domain Ω_powder, conventional thermal radiation and thermal convection boundary conditions (i.e., heat exchange with the external environment) are applied.

[0030] At the interface (inner surface) between the solid domain Ω_solid and the powder domain Ω_powder, a heat conduction boundary is set, without adding additional radiation or convection; the solid domain conducts heat to the powder domain, and then the powder domain dissipates heat to the environment from its outer surface.

[0031] A constant temperature boundary or equivalent convective heat transfer coefficient can be set on the bottom of the substrate or the contact surface of the clamp.

[0032] Step 5: Define the heat source model and scan path Laser energy input is simulated using a Gaussian surface heat source, a double ellipsoidal heat source, or a Gaussian body heat source. The cladding units in each layer are activated sequentially according to the actual process scanning strategy and interlayer rotation angle.

[0033] Step 6: Perform thermo-mechanical coupling transient simulation Thermo-mechanical sequential coupling or full coupling analysis is performed using finite element software (such as ANSYS, ABAQUS, COMSOL, etc.).

[0034] Thermal analysis: Solve for the temperature field T(x,y,z,t), considering latent heat of phase change, temperature-dependent material properties, effective heat conduction in the powder region, and heat dissipation at the boundary.

[0035] Force analysis: The temperature field is applied as a load, and the stress field and deformation are solved. In force analysis, the powder domain can be set as a virtual material with extremely low mechanical properties (such as an elastic modulus close to 0) to avoid it exerting non-physical constraints on the deformation of the solid; or only stress analysis can be performed on the solid domain, and the powder domain can only participate in the heat transfer calculation.

[0036] Step 7: Extract residual stress results After the simulation cooled to room temperature, the residual stress distribution on the surface of the solid domain was extracted.

[0037] Example 1

[0038] Residual stress prediction of 316L stainless steel blocks Geometric dimensions: The formed block is 10mm×10mm×5mm. A solid geometric model with the same dimensions as the actual formed block is created using 3D modeling software.

[0039] Powder domain expansion: Expand outward by 3mm around the perimeter and top of the bulk, and by 1mm at the bottom (the bottom can be appropriately reduced considering the influence of the substrate). The total outer dimensions of the powder domain are 16mm × 16mm × 9mm.

[0040] The model mesh was generated using eight-node hexahedral linear elements. The mesh size within the solid domain was set to 0.1-0.5 mm, and each layer in the thickness direction was divided into at least 2-3 layers of elements. The powder domain and the substrate used a coarser mesh, with a mesh size set to 0.6-1 mm.

[0041] Material properties: The thermophysical properties of solid 316L are as follows: density: ρ = 7980 kg / m³ 3(Constant); Thermal conductivity as a function of temperature (W / (m·K)): k(T) = 15.0 (20℃), 18.5 (200℃), 21.0 (500℃), 25.0 (1000℃); Specific heat capacity (J / (kg·K)): Cp(T) = 500 (20℃), 540 (200℃), 600 (600℃), 680 (1000℃); Elastic modulus (GPa): E(T) = 193 (20℃), 175 (200℃), 150 (500℃), 90 (1000℃), softening at high temperatures; Yield strength (MPa): σ_s(T) = 280 (20℃), 200 (200℃), 100 (500℃), 10 (1000℃); Poisson's ratio: ν = 0.3 (constant); coefficient of thermal expansion (×10) -6 / K): α(T) = 16.0 (20℃), 17.5 (200℃), 19.0(600℃).

[0042] The thermophysical properties of powdered 316L are as follows: the equivalent thermal conductivity is taken as 5% of the bulk density (i.e., 0.75 W / (m·K) at 20℃ and 1.25 W / (m·K) at 1000℃); the loose density is taken as 50% of the bulk density, i.e., 3990 kg / m³. 3 The radiation coefficient is set to 0.8. To avoid the powder domain exerting non-physical constraints on the deformation of the solid domain, the powder domain is given an extremely low elastic modulus of 1 × 10⁻⁶. -3 With MPa, Poisson's ratio 0.1, and thermal expansion coefficient set to 0, the powder domain only participates in heat transfer and does not affect stress calculation.

[0043] Heat source parameters: laser power 200W, scanning speed 800mm / s, spot diameter 0.1mm, layer thickness 0.05mm, using Gaussian surface heat source.

[0044] Boundary conditions: The substrate bottom surface is fixed at 25℃; the outer surface of the powder domain is set at an ambient temperature of 25℃, emissivity of 0.8, and natural convection coefficient of 15W / (m²). 2 ·K); The heat transfer mode of the solid domain, powder domain and substrate is heat conduction.

[0045] Simulation process: Sequential coupling analysis was performed using ABAQUS, and the results are as follows. Figure 5 As shown.

[0046] Comparative Example 1 Instead of establishing a powder domain, the outer surface of the solid domain is directly exposed to the environment, and a uniform convection (h=15 W / (m²)) is applied. 2 ·K)) and radiation (ε=0.6). All other parameters (heat source, material, mesh size) are exactly the same, and the results are as follows: Figure 4As shown.

[0047] contrast Figure 4 and Figure 5 It can be seen that the residual stress in the central region of the solid surface along the scanning direction was extracted, and the residual stress in the central region of the upper surface of the same size 316L block prepared by actual SLM was measured by X-ray diffraction. The average measured longitudinal residual stress was 310 MPa (tensile stress). The peak value of the longitudinal residual stress predicted by the traditional method reached 485 MPa. The peak value of the longitudinal residual stress predicted by the method of this invention was 328 MPa, and the error between the predicted value and the measured curve was less than 20 MPa.

[0048] Example 2

[0049] Simulation Prediction of Residual Stress on the Surface of TC4 Titanium Alloy Block Geometric modeling: The target dimensions of the formed block are set to 8 mm (length) × 8 mm (width) × 4 mm (height). The height direction corresponds to the deposition direction in additive manufacturing. The solid domain is pre-divided into 80 layers along the Y direction, each layer with a thickness of 0.05 mm (consistent with the actual powder layer thickness). The solid domain is extended outward by 3 mm along the normal direction of its length and width outer surface, with no extension at the bottom where it contacts the substrate. The final outer envelope dimensions of the powder domain are: 14 mm × 14 mm × 4 mm. The solid domain and powder domain are completely coplanar with no gaps at the interface. The substrate dimensions are set to 25 mm × 25 mm × 10 mm, and the material is TC4 forged alloy.

[0050] The solid domain uses hexahedral units with a grid size of 0.12 mm, and each layer is divided into 2 to 3 units in the thickness direction, totaling approximately 120,000 units; the powder domain uses tetrahedral units with a grid size of 0.5 mm, totaling approximately 25,000 units; the substrate uses hexahedral units with a grid size of 0.8 mm, totaling approximately 15,000 units.

[0051] Material properties: The thermophysical properties of solid TC4 are as follows: density: ρ = 4440 kg / m³ 3(Constant); Thermal conductivity as a function of temperature (W / (m·K)): k(T) = 6.8 (20℃), 7.4 (100℃), 8.7 (200℃), 9.8 (300℃), 10.3 (400℃), 15 (750℃); Specific heat capacity (J / (kg·K)): Cp(T) = 611 (20℃), 624 (100℃), 653 (200℃), 674 (300℃), 691 (400℃); Elastic modulus (GPa): E(T) = 114 (20℃), 105 (200℃), 90 (400℃), 60 (800℃), softening at high temperatures; Yield strength (MPa): σ(T) = 825 (20℃), 700 (200℃), 400 (400℃), 50 (800℃); Poisson's ratio: ν = 0.34 (constant); Coefficient of thermal expansion (×10) -6 / K): α(T) = 9.1 (20~100℃), 9.2 (200℃), 9.3 (300℃), 9.5 (400℃).

[0052] The thermophysical properties of TC4 powder are as follows: the thermal conductivity of TC4 powder is approximately 3.4% to 5.2% of that of solid TC4. In this embodiment, 4% of the solid value is used, i.e., k_powder = 0.04 × k_solid(T). At room temperature, it is approximately 0.27 W / (m·K); the loose bulk density is taken as 50% of the bulk density, i.e., 2220 kg / m³. 3 The radiation coefficient is set to 0.8. To avoid the powder domain exerting non-physical constraints on the deformation of the solid domain, the powder domain is given an extremely low elastic modulus of 1×10⁻⁶. -3 MPa, Poisson's ratio 0.1, thermal expansion coefficient set to 0, the powder domain only participates in heat transfer and does not affect stress calculation.

[0053] Heat source parameters: laser power 180W, scanning speed 600mm / s, spot diameter 0.1mm, layer thickness 0.05mm, Gaussian surface heat source is used, titanium alloy powder has high reflectivity, and energy absorption rate η is set to 0.30.

[0054] Boundary conditions: The substrate bottom surface is fixed at 25℃; the outer surface of the powder domain is set at an ambient temperature of 25℃, emissivity of 0.8, and natural convection coefficient of 15W / (m²). 2 ·K); The heat transfer mode of the solid domain, powder domain and substrate is heat conduction.

[0055] Simulation process: Thermo-sequential coupling analysis was performed using ABAQUS.

[0056] Example 3

[0057] Simulation Prediction of Residual Stress on the Surface Layer of AlSi10Mg Aluminum Alloy Bulk Geometric Modeling: Set the target size of the formed bulk as: 12 mm (length) × 12 mm (width) × 6 mm (height). It is pre-divided into 120 layers along the height direction, with each layer having a thickness of 0.05 mm. Expand 6 mm outward along the normal direction of the outer surfaces of the length and width of the solid domain (aluminum alloy has fast heat conduction and relatively large heat affected zone, so the thickness of the powder domain needs to be appropriately increased), and no expansion at the bottom. The final outer envelope size of the powder domain is: 24 mm × 24 mm × 6 mm.

[0058] The substrate size is set to 35 mm × 35 mm × 12 mm, and the material is forged AlSi10Mg alloy.

[0059] The solid domain adopts hexahedral elements with a mesh size of 0.15 mm, and 2 to 3 layers of elements are divided in the thickness direction, with a total of about 180,000 elements; the powder domain adopts tetrahedral elements with a mesh size of 0.7 mm, with a total of about 35,000 elements; the substrate adopts hexahedral elements with a mesh size of 1.0 mm, about 20,000 elements.

[0060] Material Properties: The thermophysical properties of solid AlSi10Mg are as follows, density (kg / m 3 ): ρ(T)=2750.05-0.244T; thermal conductivity (W / (m·K)): K(T)=161.3+0.0274T-0.64×10 -5 T 2 (300K<T<875K); specific heat capacity (J / (kg·K)): Cp(T)=757.9+0.4422T; elastic modulus (GPa): E(T)=70 (20℃), 60 (100℃), 40 (300℃), 10(500℃); yield strength (MPa): σ (T)=240 (20℃), 180 (100℃), 80 (300℃), 5 (500℃); Poisson's ratio: ν=0.33 (constant); thermal expansion coefficient (×10 -6 / K): α=20~21 (20~300℃).

[0061] The thermophysical properties of powdered AlSi10Mg are as follows. In this embodiment, 3% of the solid value is taken, which is about 4~6 W / (m·K) at room temperature. It is about 0.27 W / (m·K) at room temperature; the tap density is 50% of the solid density, that is 2220 kg / m 3 ; the radiation coefficient is 0.7. In order to prevent the powder domain from exerting non-physical constraints on the deformation of the solid domain, the powder domain is endowed with an extremely low elastic modulus of 1 × 10 -3With MPa, Poisson's ratio 0.1, and thermal expansion coefficient set to 0, the powder domain only participates in heat transfer and does not affect stress calculation.

[0062] Heat source parameters: laser power 250W, scanning speed 1000mm / s, spot diameter 0.1mm, layer thickness 0.05mm, using Gaussian surface heat source, energy absorption rate η = 0.25.

[0063] Boundary conditions: The substrate bottom surface is fixed at 25℃; the outer surface of the powder domain is set at an ambient temperature of 25℃, emissivity of 0.8, and natural convection coefficient of 15W / (m²). 2 ·K); The heat transfer mode of the solid domain, powder domain and substrate is heat conduction.

[0064] Simulation process: Thermo-sequential coupling analysis was performed using ABAQUS.

[0065] The 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 modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for predicting residual stress on the surface of alloys manufactured using powder bed fusion laser additive manufacturing, characterized in that, Includes the following steps: S1: Establish the geometric model of the solid domain based on the sample block size; S2: Expand the periphery of the solid domain to construct a powder domain geometric model that surrounds the solid domain; S3: Assign the properties of dense alloy material to the solid domain, and the equivalent thermophysical properties to the unmelted powder in the powder domain. Set thermal boundary conditions. Specifically, apply thermal radiation and thermal convection boundary conditions to the outer surface of the powder domain, and set the interface between the solid domain and the powder domain as only a thermal conduction boundary. S4: Apply a moving heat source to activate the material element, perform thermo-mechanical coupling transient simulation, and complete thermal and mechanical analysis; S5: Extract the residual stress on the surface of the solid domain after cooling.

2. The method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: The material of the sample block in step S1 is titanium alloy, nickel-based alloy, stainless steel, aluminum alloy or cobalt-chromium alloy.

3. The method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: In step S2, the outward expansion of the powder domain is 0.1 to 1 times the dimension of the corresponding direction of the solid domain.

4. The method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: In step S2, the absolute thickness of the powder domain expanding outward is 1~20mm.

5. The method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: In step S3, the equivalent thermal conductivity of the powder domain is 1% to 20% of that of the solid alloy.

6. The method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: The equivalent density of the powder domain is 40% to 60% of the density of the solid alloy.

7. The method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: The thermal boundary conditions in step S3 also include: setting a constant temperature boundary or equivalent convective heat transfer coefficient at the bottom of the substrate or the contact surface of the fixture.

8. The method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: In step S4, the heat source is a Gaussian surface heat source, a double ellipsoid heat source, or a Gaussian body heat source.

9. The method for predicting residual stress on the surface of alloys in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: In step S4, the thermo-coupling simulation can be either sequential thermo-coupling or complete thermo-coupling.

10. The method for predicting residual stress on the surface of an alloy in powder bed fusion laser additive manufacturing as described in claim 1, characterized in that: In step S4, when performing force analysis, the powder domain is set as a viscoelastic material with an elastic modulus lower than 1 / 1000 of the solid elastic modulus.

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