Improved inherent strain loading method based on partition thought

Abstract

The invention relates to an improved inherent strain loading method based on a partition thought, which comprises the following steps of: performing clustering partition processing on extracted inherent strain values which are non-uniformly distributed along a scanning path to obtain a set of different inherent strain classes of components of a small-scale thermal structure standard model under specific process parameters; the result is an inherent strain clustering analysis result of the scale model; partitioning the to-be-printed structure on the basis of the inherent strain clustering analysis result of the small-scale model; grid division is carried out on the to-be-printed structure, the center-of-mass coordinates of all units are obtained, and partitions to which the units belong are judged according to the center-of-mass coordinates of the Changing the thermal expansion coefficient of each characteristic region unit of the to-be-printed structure according to the partitioning result of the to-be-printed structure so as to complete the endowing of different inherent strain classes; and according to an actual layer-by-layer printing strategy, calculation of a layer-by-layer partition inherent strain method is completed, deformation and stress distribution of the to-be-printed structure is obtained, and prediction of residual deformation and stress of the to-be-printed structure is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of advanced additive manufacturing technology, and more specifically relates to a method for efficiently predicting residual stress and deformation in additive manufacturing, including an inherent strain distribution clustering method and a loading method based on a partitioning concept. Background Art

[0002] Additive Manufacturing (AM), commonly known as 3D printing, is a technology that manufactures objects based on adding materials layer by layer. This is a revolutionary manufacturing technology. Additive manufacturing has greatly changed the production methods of traditional manufacturing by providing design freedom, improving material utilization, flexible production, reducing supply chain links, reducing assembly steps and lightweight design. Due to its unique molding characteristics, it has broad application prospects and research value in the fields of prototype manufacturing, consumer electronics, biomedicine, automobiles, aerospace, etc. GE Aviation uses additive manufacturing technology to produce fuel nozzles for gas turbine engines, which reduces weight by 25% compared to traditional manufacturing methods, and improves part strength and performance.

[0003] However, additive manufacturing also faces some challenges, such as product consistency, molding accuracy and quality control. During the accumulation process of each layer, due to inconsistent printing parameters, uneven powder distribution, and different thermal expansion coefficients and cooling shrinkage rates of different materials during heating and cooling, uneven thermal stress distribution leads to a series of molding quality problems. These uneven stress distribution and molding quality problems will cause the dimensional accuracy of the parts to not meet the design requirements, reduce the mechanical properties of the parts such as fatigue strength and toughness, and increase the risk of failure during use.

[0004] Since the above problems hinder the rapid and sustainable development of additive manufacturing, studying the evolution and mechanism of thermal behavior in the additive process is of great significance to improving the precision and quality of the final product. However, due to the high cost of advanced additive technology materials, equipment, and processes, experimental research is not widespread. Through simulation, the manufacturing process can be simulated in a virtual environment, the deformation and residual stress of parts during the manufacturing process can be predicted, and a basis for the optimization of the manufacturing process can be provided.

[0005] There are currently two types of methods for simulating the macroscopic thermal problems of additive manufacturing. The first is the transient thermal-mechanical coupling method, which requires the establishment of a unit-by-unit or layer-by-layer thermal-mechanical sequential coupling finite element model for the entire process, and then predicts the stress-strain distribution through transient thermal-mechanical coupling analysis. This transient thermal-mechanical coupling method for the entire process needs to consider heat conduction, material phase change, and mechanical response at the same time, and its highly nonlinear problems produce unacceptable computational costs. The second is the inherent strain method, which converts the thermal problem into a pure mechanical problem, and only requires layer-by-layer quasi-static analysis to achieve the residual stress and deformation prediction of the structure printing process. The concept of inherent strain first appeared in the field of metal welding, and then expanded to the field of additive manufacturing to solve the problem of residual stress and deformation prediction in the additive manufacturing process. The inherent strain calculated by a small-scale model under a certain process is used as the inherent property of the material, and is loaded into the large-scale model in the form of pre-strain. Only layer-by-layer static analysis can obtain the structural residual stress and deformation field, saving a lot of computational costs. However, the current inherent strain analysis method lacks consideration of the true distribution of the inherent strain, and the inherent strain averaged at each point is used to load the entire model, which fails to achieve good accuracy. Therefore, in order to efficiently predict the residual stress and deformation of additive manufacturing, the method of the present invention is improved on the basis of the second method mentioned above to take into account the actual inherent strain distribution to achieve accurate prediction of stress and deformation. Summary of the invention

[0006] The present invention solves the problem that the existing inherent strain analysis method lacks consideration of the real distribution of inherent strain, and uses the averaged inherent strain of each point to load the whole model, which fails to achieve good accuracy. Therefore, in order to efficiently predict the residual stress and deformation of additive manufacturing, the inherent strain calculation process needs to be improved to consider the real distribution of inherent strain to improve the calculation accuracy and the shortcomings of the inherent strain loading model with low accuracy; the present invention discloses an improved inherent strain loading method based on the partitioning concept, comprising the following steps: An improved inherent strain loading method based on the partitioning concept, comprising the following steps:

[0007] S1: Design a small-scale thermal structure standard model of the structure to be printed, extract the inherent strain value of each node of the small-scale thermal structure model along the scanning path under specific process parameters and determine its distribution law;

[0008] S2: For the extracted inherent strain values ​​that are non-uniformly distributed along the scanning path, clustering and partitioning processing is performed to obtain a set of different inherent strain classes of components of the small-scale thermal structure standard model under specific process parameters, that is, the inherent strain clustering analysis result of the scale model;

[0009] S3: partitioning the structure to be printed based on the cluster analysis results of the inherent strain of the small-scale model; meshing the structure to be printed and obtaining the centroid coordinates of each unit, and determining the partition to which the unit belongs based on the centroid coordinates of the unit;

[0010] S4: changing the thermal expansion coefficient of each characteristic area unit of the structure to be printed according to the partition result of the structure to be printed, so as to complete the assignment of different inherent strain types;

[0011] S5: According to the actual layer-by-layer printing strategy, the calculation of the layer-by-layer partition inherent strain method is completed to obtain the deformation and stress distribution of the structure to be printed, and the residual deformation and stress of the structure to be printed are predicted.

[0012] Furthermore: the small-scale thermal structure standard model is a three-layer deposition layer finite element model with a substrate.

[0013] Furthermore: the extraction of the inherent strain value of each node of the small-scale thermal structure model along the scanning path direction under specific process parameters is obtained by calculating the transient thermal-mechanical coupling of each unit to obtain the inherent strain value of each node of the model along the scanning direction.

[0014] Furthermore: the cluster partitioning adopts K-means method to perform cluster analysis, and the specific process is as follows:

[0015] Based on the value of inherent strain, the appropriate number of class centers is selected to classify the inherent strains extracted at each point along the scanning direction, and the inherent strain values ​​of different characteristic areas are obtained. The classification result is that the inherent strain class of each unit within 6mm on both sides of the scanning direction path is the contour inherent strain; the inherent strain class of each unit in the middle area of ​​the scanning direction path is the center inherent strain.

[0016] Further: the process of partitioning the structure to be printed based on the cluster analysis results of the inherent strain of the small-scale model is as follows:

[0017] First, the structure to be printed is divided into grid cells, and then the distance between the centroid coordinates of the cell and the boundary of the structure to be printed is calculated. If the distance is ≤6mm, it belongs to the contour cell, otherwise it is the center cell.

[0018] Further: the thermal expansion coefficient of each characteristic area unit of the structure to be printed is changed according to the partition result of the structure to be printed to complete the process of assigning different inherent strain types as follows:

[0019] Different inherent strain types are equivalent to the inherent properties of the material under specific process parameters, and the inherent strain is introduced in the form of changing the thermal expansion coefficient of the material.

[0020] Further: the method of calculating the inherent strain method of layer-by-layer partitioning is completed according to the actual layer-by-layer printing strategy to obtain the deformation and stress distribution of the structure to be printed, and the prediction process of the residual deformation and stress of the structure to be printed is as follows:

[0021] First, after the inherent strain is imparted, all units of the structure to be printed are deactivated to simulate the state where the material does not exist at the beginning of actual additive manufacturing. Then, the units of the structure to be printed are activated layer by layer, and a quasi-static mechanical analysis is performed until the printing process is completed to obtain the residual stress and deformation field distribution of the structure to be printed.

[0022] The present invention improves the loading of inherent strain based on a partitioning concept. It considers the real inherent strain distribution of additively manufactured structural parts, clusters and partitions the inherent strains that are non-uniformly distributed along the laser scanning path in the small-scale standard model according to the numerical value, and obtains the inherent strain class set of the characteristic area on the scanning path; then, the structural units to be printed are partitioned according to the small-scale characteristic area standard, and the corresponding inherent strains are assigned to the characteristic area units after partitioning. The prediction accuracy of the inherent strain model is improved without significantly increasing the calculation cost. Because it is a method based on the migration and application of the clustering partitioning concept in the field of data processing, it is called an improved inherent strain loading method based on the partitioning concept.

[0023] The beneficial effects of the present invention are:

[0024] (1) The invention describes a small-scale thermal structure model designed to observe the inherent strain distribution characteristics and extract data to be applied to the structure to be printed, which takes into account a more realistic inherent strain distribution. In order to simplify the calculation process and reduce the calculation cost, the traditional structural model usually simply assumes that each node of the small-scale thermal structure model experiences the same thermal history, and then considers the inherent strain to be a uniform single fixed value. Although this assumption is simple to implement, it greatly reduces the accuracy of the calculation. The method of the invention makes improvements on this and improves the accuracy of residual stress and deformation prediction in additive manufacturing.

[0025] (2) The present invention clusters and partitions the non-uniform inherent strain data instead of directly applying the extracted data to the structure to be printed, which avoids the problem that the method of the present invention is not applicable to other different structural models. Although loading completely according to the extracted inherent strain distribution can improve the accuracy to a certain extent, it is only applicable to a specific model designed.

[0026] (3) The data clustering method described in the present invention can classify a large amount of disordered data according to the characteristics of interest so as to achieve a specific need. After data clustering, the characteristics of the real inherent strain distribution can be well restored and the calculation program can be simplified to make its function universal.

[0027] (4) The present invention partitions the structural units to be printed based on the above data clustering results by calculating the distance between the coordinates of the center of mass of the current unit and the structural contour, and determining which inherent strain type the current unit specifically belongs to. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0029] Figure 1 is a flow chart of an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of the three-layer small-scale standard model grid;

[0031] Figure 3 It is the inherent strain distribution diagram on the laser scanning path of the small-scale model;

[0032] Figure 4 Schematic diagram of the structure to be printed;

[0033] Figure 5 This is the deformation distribution result of the ten-layer thin-walled structure;

[0034] Figure 6 This is the stress distribution result of the ten-layer thin-walled structure;

[0035] Figure 7 Comparison of residual deformation between transient thermal-mechanical coupling model and partitioned inherent strain model; DETAILED DESCRIPTION

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] As described in the background technology, the inherent strain method converts thermal problems into pure mechanical problems. Only layer-by-layer quasi-static analysis is required to predict residual stress and deformation during the structure printing process, saving a lot of computational costs. It uses the inherent strain calculated by a small-scale model under a specific process as the inherent property of the material and loads it into the large-scale model in the form of pre-strain. In order to achieve the technical effect, this application designs a new inherent strain loading mode and summarizes its partition loading method.

[0039] Figure 1 This is a flow chart of an improved inherent strain loading method based on the partitioning concept of the present invention.

[0040] S1: Design a small-scale thermal structure standard model of the structure to be printed, extract the inherent strain value of each node of the small-scale thermal structure model along the scanning path under specific process parameters and determine its distribution law;

[0041] S2: For the extracted inherent strain values ​​that are non-uniformly distributed along the scanning path, clustering and partitioning processing is performed to obtain a set of different inherent strain classes of the components of the small-scale thermal structure standard model under specific process parameters, that is, the inherent strain clustering analysis result of the scale model;

[0042] S3: partitioning the structure to be printed based on the cluster analysis results of the inherent strain of the small-scale model; meshing the structure to be printed and obtaining the centroid coordinates of each unit, and determining the partition to which the unit belongs based on the centroid coordinates of the unit;

[0043] S4: changing the thermal expansion coefficient of each characteristic area unit of the structure to be printed according to the partition result of the structure to be printed, so as to complete the assignment of different inherent strain types;

[0044] S5: According to the actual layer-by-layer printing strategy, the calculation of the layer-by-layer partition inherent strain method is completed to obtain the deformation and stress distribution of the structure to be printed, and the residual deformation and stress of the structure to be printed are predicted.

[0045] The steps S1 / S2 / S3 / S4 / S5 are executed sequentially; the inherent strain method analysis process is to obtain the inherent strain under the node-specific process parameters from the small-scale standard model, and then introduce the inherent strain into the structure to be printed by equivalent to the inherent property of the material (thermal expansion coefficient), and calculate the residual stress and deformation field in the form of thermal strain by applying temperature load.

[0046] Introduce a collection of different inherent strain classes into the structure to be printed to achieve stress and deformation prediction. Introducing inherent strain is achieved by changing the thermal expansion coefficient of the material. The specific process is as follows:

[0047] First, the structure to be printed is divided into grid cells, and the cells are traversed to calculate the distance between the centroid coordinates of the cells and the boundary to determine the partition to which the cells belong.

[0048] Secondly, the cells within 6mm from the boundary of the structure to be printed are given contour inherent strain, otherwise the center inherent strain is given. Here, giving inherent strain means changing the thermal expansion coefficient of the material in each characteristic area.

[0049] Finally, the units are activated layer by layer and unit temperature load is applied. The thermal strain generated is the equivalent inherent strain. After the inherent strain is introduced, quasi-static analysis is performed to complete the prediction of structural residual stress and deformation.

[0050] Further, for S1: the small-scale standard model is a typical three-layer deposition structure containing a substrate, such as Figure 2 This transient thermal-mechanical coupling calculation is generally performed element by element, activating and completing the coupling calculation of the temperature field and the stress field element by element until the printing simulation is completed.

[0051] Furthermore, the extraction of the inherent strain value of each node of the small-scale thermal structure model along the scanning path direction under specific process parameters is obtained by calculating the transient thermal-mechanical coupling of each unit to obtain the inherent strain value of each node of the model along the scanning direction.

[0052] After obtaining the residual strain field, the inherent strain is calculated. After completing the thermal-mechanical coupling analysis of the standard model, the residual strain field obtained is not the final strain value, but the elastic strain that cannot be fully recovered due to the mutual constraints between layers. Therefore, the calculation formula for the inherent strain value is as follows:

[0053]

[0054] Where t1 and t2 represent the time corresponding to the intermediate state and steady state of the point of interest in the additive manufacturing process, respectively. They represent the plastic strain and elastic strain of the position of interest in the intermediate state, represents the elastic strain at the location of interest in steady state. The intermediate state is the state when the temperature of the point first reaches the peak, and the steady state is the state when the point cools to the ambient temperature.

[0055] Further, for S3: extract the data of each node along the scanning path and calculate the inherent strain to obtain the following Figure 3 The distribution shown is given by Figure 3It can be seen that the distribution of the inherent strain along the scanning path is not uniform. For this non-uniform distribution of inherent strain values, the K-means method is used for cluster analysis to obtain the distribution characteristics of the node inherent strain along the scanning path and the set of inherent strain classes under the characteristic area. The K-means cluster analysis process is as follows: based on the value of the inherent strain as the classification basis, the appropriate number of class centers is selected to classify the extracted inherent strains at each point along the scanning direction, and the inherent strain values ​​of different characteristic areas are obtained. The classification results are that the inherent strain class of each unit within 6mm on both sides of the scanning direction path is the contour inherent strain; the inherent strain class of each unit in the middle area of ​​the scanning direction path is the center inherent strain.

[0056] The purpose of K-means clustering is to make each sample closer to the center point of the class to which it belongs than to the center points of other classes. The following is the objective function of the program:

[0057]

[0058] Here: k is the number of cluster centers, C i is the set of data belonging to each class, x represents a data point, μ i is the center of each class, ‖x-μ i ‖ is the point x and point μ i The Euclidean distance between .

[0059] Initially, we select K points in the sample and use them as the initial cluster centers. Then we calculate the distance between each sample and each cluster center, and take the class center with the smallest distance as the class center of this data. Repeat this step until all data points are classified. The classification effect is easily affected by the value of the initial cluster center. Therefore, we take the mean of each class as the new class center and repeat the above steps for classification to reduce the impact of the initial value selection.

[0060] In K-means clustering, determining the appropriate number of clusters k is an important issue. The commonly used method is the "elbow rule".

[0061] The elbow rule plots the total sum of squared errors (SSE) of clustering as a function of k and finds the point where the rate of SSE reduction slows down significantly, which is a reasonable k.

[0062] The formula for calculating the total sum of squared errors (SSE) is:

[0063]

[0064] Here: k is the number of cluster centers, x j is the jth data point, C i is the set of data belonging to each class. i‖ is the point x and point μ i The Euclidean distance between .

[0065] The process of partitioning the structure to be printed based on the cluster analysis results of the inherent strain of the small-scale model is as follows:

[0066] First, the structure to be printed is divided into grid cells, and then the distance between the centroid coordinates of the cell and the boundary of the structure to be printed is calculated. If the distance is ≤6mm, it belongs to the contour cell, otherwise it is the center cell.

[0067] Furthermore: For the data that have been clustered, we can obtain the classification results of the inherent strain values: the inherent strain class of each unit in the area within 6mm on both sides of the scanning direction path is the contour inherent strain, which is generally a positive value; the inherent strain class of each unit in the middle area of ​​the scanning direction path is the center inherent strain.

[0068] Further: the structure to be printed is divided into grid cells, the distance between the centroid coordinates of the cell and the boundary is calculated by traversing the cells, and the partition to which the cell belongs is determined. The cells within 6 mm from the boundary of the structure to be printed are given contour inherent strain, otherwise the center inherent strain is given.

[0069] The process of changing the thermal expansion coefficient of each characteristic area unit of the structure to be printed according to the partition result of the structure to be printed to complete the assignment of different inherent strain types is as follows:

[0070] Different inherent strain types are equivalent to the inherent properties of the material under specific process parameters, and the inherent strain is introduced in the form of changing the thermal expansion coefficient of the material. Furthermore: the inherent strain value is equivalent to the thermal expansion coefficient of the material to increase the unit temperature of each unit to introduce this inherent strain field. The units are activated layer by layer and unit heat loads are applied, and quasi-static calculations are performed layer by layer to obtain the final residual stress and deformation field.

[0071] For pre-strain loading, in actual operation, the inherent strain value is generally set to the thermal expansion coefficient of the material, and a unit temperature load is applied to the active unit to generate thermal strain to achieve the inherent strain application:

[0072] ε I =ε

[0073] ε=αΔT

[0074] Where ε I is the inherent strain, α is the equivalent thermal expansion coefficient, ε is the equivalent thermal strain, and ΔT is the temperature change.

[0075] The method of calculating the inherent strain method of layer-by-layer partitioning is completed according to the actual layer-by-layer printing strategy to obtain the deformation and stress distribution of the structure to be printed, and the prediction process of the residual deformation and stress of the structure to be printed is as follows:

[0076] First, after the inherent strain is imparted, all units of the structure to be printed are deactivated to simulate the state where the material does not exist at the beginning of actual additive manufacturing. Then, the units of the structure to be printed are activated layer by layer, and a quasi-static mechanical analysis is performed until the printing process is completed to obtain the residual stress and deformation field distribution of the structure to be printed.

[0077] Further: In order to make this application more convincing, a specific case is provided here, and the calculation results of the case applying the method of the present invention are explained and compared with the detailed thermal structure method.

[0078] Embodiment 1:

[0079] In the embodiment of the present invention, the model to be printed using this method is a ten-layer thin-walled structure with a size of 100mm*6.4mm*10mm, and the mesh unit size in the finite element model is 2mm*3.2mm*1mm. The small-scale standard model is a three-layer sedimentary layer structure, and the finite element mesh model is as follows Figure 2 The grid unit size is also 2mm*3.2mm*1mm.

[0080] First, the inherent strain value of each point needs to be obtained through the small-scale transient thermal-mechanical coupling calculation of each unit. The distribution of the inherent strain along the scanning path is as follows: Figure 3 shown.

[0081] For this non-uniformly distributed inherent strain value, the K-means method is used for cluster analysis. The inherent strain value is used as the classification basis, and the appropriate number of class centers is selected to classify the extracted inherent strains at each point along the scanning direction, and the inherent strain values ​​of different characteristic areas are obtained. The classification results are that the inherent strain class of each unit within 6mm on both sides of the scanning direction path is the contour inherent strain, which is generally positive; the inherent strain class of each unit in the middle area of ​​the scanning direction path is the central inherent strain.

[0082] After obtaining the inherent strain of the partition, it is loaded into the structure to be printed to achieve stress deformation prediction. Figure 4 As shown. The structure to be printed is divided into grid cells, and the distance between the centroid coordinates of the cell and the boundary is calculated by traversing the cells to determine the partition to which the cell belongs. The cells within 6 mm from the boundary of the structure to be printed are given contour inherent strain, otherwise the center inherent strain is given.

[0083] Finally, the inherent strain value is equivalent to the thermal expansion coefficient of the material to increase the unit temperature of each unit to introduce this inherent strain field. The units are activated layer by layer and unit thermal loads are applied, and quasi-static calculations are performed layer by layer to obtain the residual stress and deformation field of the structure to be printed.

[0084] The deformation and stress of the structure to be printed are as follows: Figure 3 , Figure 4 As shown in the figure, the maximum deformation occurs in the top area of ​​the side of the structure and is symmetrically distributed on the left and right ends of the structure. In this case, the scanning direction is the X direction, and the results show that the stress in the X direction is a large compressive stress on both sides and a large tensile stress in the top and middle areas.

[0085] Figure 5 This is the deformation distribution result of the ten-layer thin-walled structure;

[0086] Figure 6 This is the stress distribution result of the ten-layer thin-walled structure;

[0087] In order to compare and illustrate the effectiveness of the improved inherent strain loading method, the transient thermal-mechanical coupling method and the traditional inherent strain method are used to analyze the printed structure. Figure 4 The path extracts the X-direction deformation value of each point under the three calculation methods of thermal-mechanical coupling and inherent strain, such as Figure 7 As shown in the figure, the deformation obtained by the two methods is basically the same. However, the calculation results of the traditional inherent strain method are quite different from the calculation results of the whole process transient thermal-mechanical coupling. The improved inherent strain loading method improves the calculation accuracy by 20.15% compared with the traditional calculation method. Moreover, the calculation time of the improved inherent strain method is much shorter than the calculation time of the whole process transient thermal-mechanical coupling. This shows that the method of the present invention has the effect of good accuracy and low calculation cost.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the embodiments describe the present invention in detail, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An improved inherent strain loading method based on the partitioning concept, characterized in that: The following steps are involved: S1: Design a small-scale thermal structure standard model of the structure to be printed, extract the inherent strain value of each node of the small-scale thermal structure model along the scanning path under specific process parameters and determine its distribution law; S2: For the extracted inherent strain values ​​that are non-uniformly distributed along the scanning path, clustering and partitioning processing is performed to obtain a set of different inherent strain classes of components of the small-scale thermal structure standard model under specific process parameters, that is, the inherent strain clustering analysis result of the scale model; S3: partition the structure to be printed based on the cluster analysis results of the inherent strain of the small-scale model; Divide the structure to be printed into a grid and obtain the coordinates of the centroid of each unit, and determine the partition to which the unit belongs based on the coordinates of the centroid of the unit; S4: changing the thermal expansion coefficient of each characteristic area unit of the structure to be printed according to the partition result of the structure to be printed, so as to complete the assignment of different inherent strain types; S5: According to the actual layer-by-layer printing strategy, the calculation of the layer-by-layer partition inherent strain method is completed to obtain the deformation and stress distribution of the structure to be printed, and the residual deformation and stress of the structure to be printed are predicted.

2. An improved inherent strain loading method based on the partition concept according to claim 1, characterized in that: The small-scale thermal structure standard model is a three-layer deposition layer finite element model with a substrate.

3. An improved inherent strain loading method based on the partition concept according to claim 1, characterized in that: The method for extracting the inherent strain value of each node of the small-scale thermal structure model along the scanning path direction under specific process parameters is obtained by calculating the inherent strain value of each node of the model along the scanning direction through transient thermal-mechanical coupling calculation unit by unit.

4. The improved inherent strain loading method based on the partition concept according to claim 1 is characterized in that: The cluster partitioning adopts the K-means method to perform cluster analysis, and the specific process is as follows: Based on the value of inherent strain, the appropriate number of class centers is selected to classify the inherent strains extracted at each point along the scanning direction, and the inherent strain values ​​of different characteristic areas are obtained. The classification result is that the inherent strain class of each unit within 6mm on both sides of the scanning direction path is the contour inherent strain; the inherent strain class of each unit in the middle area of ​​the scanning direction path is the center inherent strain.

5. The improved inherent strain loading method based on the partitioning concept described in claim 1 is characterized in that: The process of partitioning the structure to be printed based on the cluster analysis results of the inherent strain of the small-scale model is as follows: First, the structure to be printed is divided into grid cells, and then the distance between the centroid coordinates of the cell and the boundary of the structure to be printed is calculated. If the distance is ≤6mm, it belongs to the contour cell, otherwise it is the center cell.

6. The improved inherent strain loading method based on the partitioning concept described in claim 1 is characterized in that: The process of changing the thermal expansion coefficient of each characteristic area unit of the structure to be printed according to the partition result of the structure to be printed to complete the assignment of different inherent strain types is as follows: Different inherent strain types are equivalent to the inherent properties of the material under specific process parameters, and the inherent strain is introduced in the form of changing the thermal expansion coefficient of the material.

7. The improved inherent strain loading method based on the partitioning concept described in claim 1 is characterized in that: The method of calculating the inherent strain method of layer-by-layer partitioning is completed according to the actual layer-by-layer printing strategy to obtain the deformation and stress distribution of the structure to be printed, and the prediction process of the residual deformation and stress of the structure to be printed is as follows: First, after the inherent strain is imparted, all units of the structure to be printed are deactivated to simulate the state where the material does not exist at the beginning of actual additive manufacturing. Then, the units of the structure to be printed are activated layer by layer, and a quasi-static mechanical analysis is performed until the printing process is completed to obtain the residual stress and deformation field distribution of the structure to be printed.

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