A numerical simulation method for laser additive manufacturing using CFD-FEM coupled temperature and stress integrated modeling

Abstract

This invention discloses a numerical simulation method for laser additive manufacturing using CFD-FEM coupled temperature and stress integrated modeling, belonging to the field of additive manufacturing simulation technology. First, based on the calculation results of the CFD model, a mesh element geometric model in the FEM model is constructed. The temperature field calculated by the CFD model is then assigned to the mesh element geometric model. Simultaneously, the temperature field is coupled into the static calculations at the nodes. Gas nodes are identified by volume fraction, and liquid and solid nodes are distinguished by the thermal history of the temperature field. Gas stiffness attributes are assigned to gas nodes and unmelted powder particles, liquid stiffness attributes to liquid nodes, and solid stiffness attributes to solid nodes. This method utilizes the data information provided by the CFD calculation results, combining temperature and volume fraction data to complete FEM stress analysis modeling. This achieves efficient transmission of temperature information, ensuring both calculation accuracy and solution efficiency, while reducing programming difficulty and code maintenance costs.

Description

Technical Field

[0001] This invention belongs to the field of numerical simulation calculation for laser additive manufacturing, and relates to a numerical simulation method for laser additive manufacturing that integrates CFD-FEM coupled temperature and stress modeling. Background Technology

[0002] Laser additive manufacturing, due to its rapid non-equilibrium solidification and the technical characteristics of thermal cycling and accumulation, presents significant challenges to the rapid and high-precision forming of parts and the achievement of excellent mechanical properties. Traditional process optimization experiments and destructive part performance testing methods are expensive and time-consuming, while advanced numerical simulation methods have proven their strong reliability in predicting part manufacturing performance and optimizing processes. Numerical simulations can obtain physical parameters that are difficult to obtain experimentally during additive manufacturing, providing researchers with a scientific basis for understanding part deformation patterns and tracking defect evolution. Among these methods, the Finite Element Method (FEM) can couple the solution of temperature and stress fields, thus finding wide application in predicting the stress and strain of macroscopic parts manufactured by laser additive manufacturing. However, its temperature field calculation is limited by the simplicity of the underlying heat transfer formula, failing to consider the complex physical field information of the molten pool, thereby reducing the accuracy of FEM stress calculations. Computational Fluid Dynamics (CFD), however, can overcome this deficiency, more accurately calculating the morphology, velocity field, and temperature field information during the molten pool evolution process. However, the complexity of its calculations limits the model scale. Meanwhile, the Euler elements used in CFD calculations cannot perform structural mechanics calculations. Therefore, the CFD-FEM coupled temperature and stress integrated modeling numerical simulation method provides a new approach for high-precision prediction of macroscopic part performance. The key to realizing this technology lies in building a reliable bridge for transferring data from the Euler elements of CFD to the Lagrangian elements of FEM.

[0003] Based on the CFD-FEM coupled numerical simulation method, some scholars have carried out related research. The published paper "High-fidelity modelling of thermal stress for additive manufacturing by linking thermal-fluid and mechanical models" (Materials & Design, 2020, 11) uses the temperature field and morphology information of the molten pool obtained by CFD calculation to build a FEM molten pool numerical simulation model based on the static element method to solve the thermal stress evolution process of the cladding channel. Although the model accurately reflects the influence of the molten pool aggregate morphology on the evolution of thermal stress, it only uses temperature field information as the criterion to distinguish between gas and solid interfaces. This requires temperature differentiation processing for air elements and powder bed elements in the model, which introduces systematic errors. In addition, the interpolation algorithm for transferring data between CFD and FEM elements is inefficient and the algorithm programming is complicated, which seriously drags down the calculation efficiency and raises the threshold for using this method. The publicly published paper, "A thermal fluid mechanical model of stress evolution for wirefeeding-based laser additive manufacturing" (Journal of Manufacturing Processes, 2021, 9), utilizes CFD-calculated molten pool temperature field and volume fraction information to build a high-fidelity FEM molten pool numerical simulation model based on element activation technology to solve the thermal stress evolution process of the cladding channel. Although this model uses both CFD-calculated temperature field and volume fraction as criteria to accurately simulate the influence of cladding channel morphology on stress distribution, it performs an average interpolation based on nodal coordinates when mapping temperature data from Eulerian elements to Lagrangian elements. This method introduces the low-temperature values ​​of the surrounding air when processing data at the high-temperature boundary of the molten pool, resulting in distortion of the molten pool interface temperature.

[0004] In summary, existing CFD-FEM coupled numerical simulation models either fail to fully utilize CFD calculation results during data transfer, or the interpolation algorithm logic is not rigorous enough, resulting in the inability to reasonably transfer temperature information, causing significant systematic errors. At the same time, the complex data processing methods place higher demands on the reliability and ease of maintenance of the code, and this shortcoming will cause a large consumption of computing resources in subsequent solution calculations. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a numerical simulation method for laser additive manufacturing that integrates CFD-FEM coupled temperature and stress modeling, so as to solve the problems of complex data processing and distortion in the existing CFD-FEM coupled temperature and stress integrated modeling numerical simulation.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling includes the following steps:

[0008] Step 1: Obtain the CFD model calculation result file, which includes node coordinates, node temperature, and node volume fraction; Based on the node coordinates in the CFD model, generate the mesh element geometric model in the FEM model.

[0009] Step 2: Assign material temperature parameters to the nodes in the mesh element geometric model, set a predefined temperature field for the mesh element geometric model, and calculate the temperature field result file without valid data without applying a thermal load.

[0010] Step 3: Assign the nodal temperatures of the CFD model to the temperature field result file of the FEM model to obtain the FEM model temperature file sorted by time.

[0011] Step 4: Using the volume fraction in the CFD model calculation result file as the criterion, distinguish between solid nodes and gas nodes in the FEM model temperature file. Based on the temperature and volume fraction of the nodes, remove abnormal temperature data nodes in the solid nodes and gas nodes until the temperature field data meets the convergence requirements of thermal stress solution, and obtain the filtered FEM model temperature file.

[0012] Step 5: Assign thermo-coupling material parameters to the nodes in the geometric model of the mesh element in the FEM model in Step 1, and couple the filtered FEM model temperature file obtained in Step 4 to the FEM model with thermo-coupling material parameters to obtain the FEM thermo-coupling model.

[0013] Step 6: Determine the node type in the FEM thermo-coupling model through subroutines in the FEM thermo-coupling model. Differentiate between gaseous and solid nodes based on the node volume fraction in the CFD model calculation result file. Within solid nodes, further distinguish between solid, liquid, and gaseous nodes based on the node's thermal history. Assign gas stiffness attributes to gaseous nodes and unmelted powder particle units, liquid stiffness attributes to liquid nodes, and solid stiffness attributes to solid nodes. The solid stiffness attribute is a first order of magnitude multiple of the liquid stiffness attribute, and the liquid stiffness attribute is a second order of magnitude multiple of the gas stiffness attribute.

[0014] Step 7: Based on the subroutine's judgment result, perform thermal stress calculation on the FEM thermo-mechanical coupling model;

[0015] Step 8: Repeat steps 6 and 7 until the FEM thermo-coupling model calculations for all time periods are completed.

[0016] A further improvement of the present invention is that:

[0017] Preferably, in step 1, the process of generating the mesh element geometric model in the FEM model based on the node coordinates in the CFD model is as follows: based on the node coordinates of the Eulerian mesh element in the CFD model, establish the corresponding node coordinates of the Lagrange element in the FEM model, and number the nodes sequentially.

[0018] Preferably, in step 2, the temperature of the predefined temperature field is room temperature.

[0019] Preferably, in step 2, the material temperature parameters include density, specific heat capacity, and thermal conductivity.

[0020] Preferably, in step 4, the criteria for removing abnormal nodes are as follows: for nodes exceeding the material vaporization temperature, determine whether the node affects the convergence of the thermal stress calculation of the cladding channel model. If it does, remove it; remove unreasonable high temperature values ​​and modify them to the material vaporization temperature; modify nodes with solid node temperatures below room temperature to room temperature.

[0021] The process of eliminating abnormal nodes is repeated multiple times until the temperature field data meets the convergence requirements for solving the thermal stress.

[0022] Preferably, in step 5, the parameters of the thermo-coupling material include the coefficient of thermal expansion, Young's modulus, and Poisson's ratio.

[0023] Preferably, in step 6, the subroutine is written using the FEM model, and the subroutine and the FEM thermo-coupled model are connected through an interface.

[0024] Preferably, in step 6, the process of determining the node type in the FEM thermal coupling model through a subroutine in the FEM thermal coupling model is as follows:

[0025] 1) Differentiate between gaseous and solid nodes using the node volume fraction in the CFD model calculation results file.

[0026] 2) For solid nodes, if the node heats up and exceeds the melting point of the powder during the current FEM thermo-coupling model analysis and calculation process, then the node is a liquid node.

[0027] 3) For solid nodes, if the node heats up during the current FEM thermo-coupling model analysis and calculation process but does not exceed the melting point of the powder and its coordinates are located on the substrate, it is identified as a solid node; if the node heats up during the current FEM thermo-coupling model analysis and calculation process but does not exceed the melting point and is not located on the substrate, it is identified as a gaseous node.

[0028] 3) For solid nodes that are not on the substrate and are being cooled, if the node has experienced a melting heat history, it is considered a solid node; if the node has not experienced a melting heat history, it is considered a gaseous node.

[0029] Preferably, in step 6, the node numbers and corresponding volume fractions that have changed in the temperature field calculation results of each frame in the CFD model are selected. For the changed node numbers, the volume fractions are organized sequentially to refresh the node set file.

[0030] Preferably, in step 1, the coordinates of the Lagrange nodes in the FEM model are constructed based on the coordinates of the grid element nodes in the CFD model, and a hexahedral grid element is created through 6 adjacent nodes; in step 7, when the FEM thermo-coupling model performs thermal stress calculation, it is based on the hexahedral grid element.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] This invention discloses a CFD-FEM coupled temperature and stress integrated modeling method for numerical simulation of laser additive manufacturing. This method simultaneously couples CFD-calculated temperature and volume fraction information to the static element method for FEM stress calculation, achieving integrated temperature and stress modeling in laser additive manufacturing. By utilizing volume fraction to assist temperature information, it efficiently transmits the type of each node, ensuring both computational accuracy and solution efficiency. Furthermore, it reduces programming complexity and code maintenance costs. This method also offers the following advantages:

[0033] (1) Compared with the traditional CFD-FEM coupled temperature stress numerical simulation method, this invention makes full use of CFD calculation data information and uses temperature and volume fraction as criteria to more accurately replicate the irregular geometric shape of the cladding channel in the FEM software, so that the model can study the influence of small morphological defects of the cladding channel on the thermal stress distribution.

[0034] (2) Compared with the element birth and death technique, which cannot kill activated elements again during the material deposition process, the static element method creates independent groups for the elements that mainly participate in the thermal stress calculation by dynamically changing the element field variable properties based on time during the node type determination process. This satisfies the requirements of dynamic changes in element properties under laser action and keyhole effect, while reducing the requirements of numerical simulation convergence for repeated activation and killing of elements over time.

[0035] (3) Traditional integrated temperature and stress numerical simulation models generally involve writing complex time and space interpolation algorithms, which requires high coding skills from model developers. Furthermore, the efficiency of the interpolation algorithm is directly related to the developer's familiarity with the solver's underlying logic. Most developers' self-written code has low execution efficiency, significantly increasing the model's thermal stress calculation time. At the same time, the lengthy code adds to the burden of subsequent maintenance and optimization. This model utilizes the interpolation algorithm built into the FEM software to construct a subroutine for determining node types, simplifying the processing of thermally coupled temperature load data, reducing the difficulty of coding, and enhancing code stability while reducing the possibility of human-introduced system errors.

[0036] (4) Compared with existing models that use temperature data as a criterion to distinguish solid-gas boundaries, which requires setting a temperature difference between solid and gas nodes during CFD modeling, this model uses volume fraction criteria to supplement the shortcomings of temperature criteria, can effectively distinguish solid-gas interfaces, and does not require introducing a temperature difference during CFD modeling. The optimized criteria more accurately separate solid and gas units.

[0037] (5) Compared with the traditional static element method, which only gives the element classification based on the temperature data at the current time node and cannot distinguish the different weights of solid nodes in the cladding channel and unmelted powder solid nodes in the thermal stress calculation, this model separates the two by creating an array set based on the thermal history of the cladding nodes, and only retains the solid node attributes of the nodes in the cladding channel. This makes the model solution logic more rigorous and improves the accuracy of numerical calculation of thermal stress. Attached Figure Description

[0038] Figure 1 This is a flowchart of a numerical simulation method for laser additive manufacturing based on CFD-FEM coupled temperature and stress integrated modeling according to the present invention.

[0039] Figure 2 Set up a flowchart for field variables;

[0040] Figure 3 The temperature field cloud maps of the present invention are: (a) molten pool morphology, and (b) temperature distribution cloud map along the laser scanning direction.

[0041] Figure 4 Stress field cloud map: (a) cladding morphology, (b) stress distribution cloud map in the laser scanning direction. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings:

[0043] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0044] See Figure 1 This invention discloses a numerical simulation method for laser additive manufacturing using CFD-FEM coupled temperature and stress integrated modeling. The method includes the following steps:

[0045] Step 1: Generate FEM mesh element geometric model using CFD mesh element information;

[0046] The specific process is as follows: Analyze the CFD model calculation result file, which includes the coordinates of the grid cell nodes, the temperature of the grid cells, and the volume fraction of the grid cells. Construct an FEM mesh model file using the grid cell node coordinates from the CFD model. Establish the corresponding Lagrangian element node coordinates in the FEM based on the Eulerian grid cell node coordinates in the CFD model, and number the nodes sequentially. Use a lookup algorithm to construct the positional relationships between nodes based on spatial distance. Create a hexahedral mesh element for every six adjacent element nodes, and number the elements sequentially. Simultaneously, create an index relationship between element numbers and node numbers. Output the organized mesh model file in a format readable by the FEM software, completing the automated modeling of the FEM mesh element geometry.

[0047] Step 2: Use FEM software to generate a blank temperature calculation result file;

[0048] The specific process is as follows: Import the generated FEM mesh element geometric model into the FEM software, specify the element properties as heat transfer analysis elements, and input the material parameters required for FEM heat transfer analysis, such as density, specific heat capacity, and thermal conductivity. Create a heat transfer analysis step, set the initial temperature of the predefined temperature field to an arbitrary temperature, and apply normal convective heat transfer conditions. Do not apply thermal loads to the model. Submit the analysis to the solver for calculation, and obtain the temperature field result file without valid data.

[0049] Preferably, setting the initial temperature of the predefined field temperature to room temperature ensures that no heat transfer occurs in the model during the initial establishment of the temperature field, thus saving computation time.

[0050] Step 3: Map the temperature data in the CFD result file to the FEM temperature calculation result file to obtain the result file of the time-related FEM temperature field calculation data.

[0051] The specific process is as follows: the temperature data given by the node coordinates in the CFD calculation results are assigned to the corresponding node coordinates in the FEM result file, and the generated FEM result file is sorted frame by frame according to the time sequence given by the CFD calculation results, and organized into an FEM result file containing effective temperature data, which is the FEM model temperature file.

[0052] Step 4: Filter the temperature data to make it suitable for thermal load testing;

[0053] The specific process is as follows: The volume fraction corresponding to the node in the CFD calculation results is called. The volume fraction is used as a criterion to check the distribution of temperature field data in the substrate and powder bed. Grid cells with a volume fraction of 0 are gaseous, and grid cells with a volume fraction of 1 are solid. For nodes exceeding the material vaporization temperature, it is determined whether they affect the convergence of thermal stress calculation in the cladding model. Unreasonable high-temperature values ​​are removed and modified to the material vaporization temperature. For solid nodes with temperatures below room temperature, the temperature is modified to room temperature, and the temperature singularity values ​​of the unit nodes with a volume fraction of 0 are removed. This process continues until the temperature field data meets the convergence requirements for thermal stress solution, generating a temperature load and obtaining an FEM result file containing effective temperature data.

[0054] In the above process, the process is repeated multiple times to fully optimize the temperature load and reduce the impact of temperature singularities caused by numerical instability in CFD temperature field calculation results on the convergence of FEM thermal stress calculation.

[0055] Step 5: Set up the thermo-mechanical coupling analysis and couple the thermal load;

[0056] The specific process is as follows: import the geometric model file obtained in step 1 into the FEM software again, specify the element attribute as stress analysis element, input the thermo-mechanical coupling material parameters required for FEM thermo-mechanical coupling analysis, such as: coefficient of thermal expansion, Young's modulus, Poisson's ratio, and obtain the FEM model loaded with thermo-mechanical coupling material parameters.

[0057] Create a static general analysis step, set the FEM result file containing effective temperature data obtained in step 4 as a temperature field load, and couple it to the FEM model loaded with thermo-coupled material parameters in the form of a predefined field. Apply completely fixed constraints to the unit nodes on the bottom surface of the substrate in the model to complete the creation of the FEM thermo-coupled analysis and obtain the FEM thermo-coupled model.

[0058] Step 6: Set dynamically changing field variables for the elements in the FEM static analysis process;

[0059] The specific process is as follows: The static element method is used to solve for the stress and strain values ​​of the cladding channel. Different material stiffness properties are set for the nodes in the geometric model according to different field variables. A pre-defined subroutine determines the type of each element in the FEM thermo-coupling model: gaseous nodes are distinguished by volume fraction, liquid and solid nodes by temperature, and unmelted powder particles and solid nodes within the cladding channel by thermal history. For detailed procedures, please refer to [link to relevant documentation]. Figure 2 This includes the following steps:

[0060] 1) Create a global variable array to record solid nodes and nodes that have experienced melting heat history, and assign initial values ​​to the array. Begin thermo-coupling analysis for the FEM thermo-coupling model. 2) During the thermo-coupling analysis, refresh the solid node set when calling a new thermal load from the FEM result file containing effective temperature data. 3) Separate the nodes corresponding to gaseous nodes from the solid node set. The separation criteria are: in the created array of solid node cells, a Boolean value of 1 corresponds to a solid node, and a Boolean value of 0 corresponds to a gaseous node. Set gaseous field variables for the gaseous nodes. 4) Among the remaining solid nodes, determine whether the node is in the current analysis step. 5) For nodes in the heating nodes that exceed the melting point, set them as liquid nodes, assign them liquid field variables, and change the marker in the corresponding thermal history array. Conversely, for nodes in the cooling nodes that exceed the melting point, only set liquid field variables. 6) For nodes in the heating nodes that do not exceed the melting point, first determine whether they are located on the substrate, set solid field variables for the corresponding node units on the substrate, and then set gaseous field variables for the heating nodes that are not on the substrate. 7) For cooling nodes that are not on the substrate, determine whether the node has experienced melting heat history. Set solid field variables for the node units that have melted, and set gaseous field variables for the node units that have not melted.

[0061] Based on the different weights of different element types in the thermal stress calculation, solid nodes are assigned solid stiffness attributes, liquid nodes are assigned liquid stiffness attributes, and gaseous nodes are assigned gas stiffness attributes. Solid stiffness attributes are the highest, liquid stiffness attributes are in the middle, and gas stiffness attributes are the lowest. Unmelted powder particles play a similar role to gaseous nodes in the thermal stress calculation and are also assigned the lowest gas stiffness attribute. The principles for setting gas and liquid stiffness attributes should be as follows: there should be a significant order-of-magnitude difference from solid stiffness attributes; the numerical settings should ensure the overall convergence of the model and not have a major impact on the thermal stress calculation results; there should also be an order-of-magnitude difference between gas and liquid stiffness attributes, but this difference should be smaller than the order-of-magnitude difference between them and solid stiffness attributes.

[0062] In some embodiments of the present invention, the subroutine for determining the type of each unit in the thermo-coupling model is associated with the interface reserved for user subroutines in the FEM software. A field variable calling channel is created in the set analysis work, and the thermo-coupling analysis work is submitted to solve, so as to finally obtain the high-precision FEM thermal stress numerical simulation calculation results based on the CFD calculation results.

[0063] Step 7: Associate the subroutine with the analysis work and submit the solution to obtain the influence of the molten pool morphology on the thermal stress distribution. During the solution process, hexahedral mesh elements are used for the solution.

[0064] In some embodiments of the present invention, after step 5, a set of nodes whose volume fractions are updated at adjacent CFD time points is selected.

[0065] The specific process is as follows: Select the node number and corresponding volume fraction of the temperature field calculation result of each CFD frame that have changed, and organize the volume fraction to refresh the node set file in sequence at equal time intervals to reduce the amount of data read and written in subsequent thermo-coupling analysis and improve the calculation speed of the analysis.

[0066] If the volume fraction does not change during this process, it means that the state of the mesh remains unchanged throughout the additive manufacturing process. Therefore, there is no need to update the data, and the original data can be directly used for calculation to meet the requirements.

[0067] The implementation of the technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0068] Example 1

[0069] Step 1: Use the element node coordinate data in the CFD result file to automatically model and generate the FEM mesh element geometric model.

[0070] 1) Analyze the Eulerian mesh node coordinate information in the CFD calculation results data, write a search algorithm, record the maximum and minimum values ​​of the element node coordinates x, y, z respectively, and divide the FEM Lagrange mesh elements within this range using a seed length of 5μm consistent with the CFD mesh; 2) Number the obtained 384,000 FEM mesh nodes sequentially, organize the node numbers to the index of the node coordinates, and output them to the table starting with the keyword node in the geometric model file; 3) Construct the adjacent position relationship of nodes in space based on the distance between node coordinates, query the coordinates of the 8 nodes that make up a hexahedral element, and then obtain the relevant node numbers; 4) Use the 384,000 nodes to build 361,583 hexahedral elements, number the elements sequentially, organize the index of each element number and the corresponding 6 node numbers, and output them to the table starting with the keyword element in the geometric model file, finally completing the automated geometric modeling of the FEM element mesh.

[0071] Step 2: Based on the unit mesh geometric model, use FEM software to generate blank temperature field data result files.

[0072] 1) Import the established mesh element geometric model file into FEM software, set the heat transfer element properties for the mesh elements, and convert the component model into an assembly model; 2) Set the heat transfer material parameters for the assembly model, including: material density, specific heat capacity, and thermal conductivity. Here, the model material is set to aluminum alloy; 3) Create a heat transfer analysis step with a total analysis step duration of 1μs. Set a fixed analysis increment step size of 1μs, set the initial temperature of all element nodes to 26.85℃, skip the heat load setting step, set the ambient temperature to 26.85℃, and add conventional convection heat transfer conditions, without considering thermal radiation conditions; 4) Generate a heat transfer analysis job from the model with the set number and submit it to the FEM solver for solving. The result file without effective temperature field data can be obtained without calculation.

[0073] Step 3: Construct the FEM heat transfer analysis result file based on the temperature data and volume fraction data in the CFD calculation result file.

[0074] 1) Read the temperature data in column 4 and the volume fraction data in column 5 of the CFD calculation result file, which outputs one frame every 5μs, sequentially according to the node coordinate data provided in the first three columns, and save them to the computer memory; 2) Construct the result data of frames 2 to 22 in the FEM result file according to the same time interval; 3) Look up the node number of the temperature and volume fraction in memory according to the node coordinate index, and assign the result data to the temperature field variable and volume fraction field variable at the corresponding time of the node number; 4) Use the interpolation algorithm built into the FEM software to draw the temperature field distribution cloud map and the volume fraction field distribution cloud map, and view the rendered temperature and volume fraction evolution process animation in the software's visualization interface.

[0075] Step 4: Use volume fraction as a criterion to view the temperature field distribution cloud map of the powder bed, and filter the node temperature data that is not suitable for thermal coupling temperature load.

[0076] 1) In the FEM software visualization interface, select the element nodes with a volume fraction of 1, which correspond to the powder bed model elements. Observe the temperature field distribution cloud map under the geometry of this element and observe the distribution of nodes exceeding the material vaporization temperature. 2) Determine whether it affects the convergence of the thermal stress calculation of the cladding channel model. Remove unreasonable high-temperature values ​​and modify them to 1107℃, which is the vaporization temperature. 3) Modify the data of powder bed model element node temperatures below room temperature to room temperature 26.85℃, and remove the temperature singularity values ​​of element nodes with a volume fraction of 0, which correspond to independent temperature nodes in the air model caused by numerical calculation instability. 4) Reload the filtered temperature field result cloud map and check the filtering effect. If the result is not ideal, repeat the above operation; otherwise, proceed to the next step.

[0077] like Figure 3 As shown, the distribution of FEM temperature data generated based on CFD calculation results in the powder bed model is as follows. After multiple temperature filtering processes, isolated extreme temperatures that are not suitable for thermal stress analysis calculations are eliminated. At the same time, it is ensured that physical phenomena such as keyholes in the molten pool and remelting are not affected by the filtering process.

[0078] Step 5: Based on the generated FEM temperature load result file, set up the thermo-mechanical coupling analysis in the FEM software.

[0079] 1) Import the mesh element geometric model file into the FEM software again, set the stress analysis element properties for the mesh elements, and convert the component geometric model into an assembly geometric model; 2) Assign the material parameters required for thermo-mechanical coupling analysis to the assembly model, such as: coefficient of thermal expansion, Young's modulus, Poisson's ratio. Here, the model material is set to aluminum alloy; 3) Create a static general analysis step with a total analysis step duration of 100μs and set a fixed analysis increment step size of 1μs. Couple the generated temperature load result file to the model in the form of a predefined temperature field. Only read the effective temperature information increment step from the result file, i.e., the result data from frames 2 to 22; 4) Apply completely fixed constraints to the element nodes on the bottom surface of the substrate in the model to improve the efficiency of thermal stress solution.

[0080] Step 6: Filter out the set of nodes whose CFD unit node volume fraction changes between two adjacent frame result files.

[0081] 1) For the volume fraction file of the CFD calculation results at 0 μs, directly extract all node numbers and the corresponding volume fractions of the nodes, and save them to the corresponding node volume fraction update record file at 0 μs; 2) Compare the volume fractions of the same node numbers in the CFD calculation result files at 5 μs and 0 μs. If the difference between the two is greater than 0.001, it is considered that the node volume fraction has changed. Record the node number and the new volume fraction at 5 μs, and save it to the corresponding node volume fraction update record file at 5 μs; 3) Repeat the steps in 2) using a loop statement until all CFD data files are processed, and generate volume fraction update record files for each time from 5 to 100 μs in sequence; 4) Name the generated volume fraction update record files according to a unified naming format and save them to the FEM thermo-coupling analysis working directory to facilitate the FEM solver to call the data.

[0082] Step 7: Set different field variables for the elements in the FEM model to make the model adapt to the requirements of the static element method for solving thermal stress.

[0083] 1) Assign three field variables 1, 2, and 3 to all elements in the model, with the material stiffness increasing progressively. The solid nodes corresponding to field variable 3 mainly participate in thermal stress calculation and have the highest stiffness. Field variables 1 and 2 correspond to gaseous and liquid nodes, respectively. Their stiffness is orders of magnitude different from that of solid nodes and only plays a role in ensuring convergence in the calculation. 2) Using volume fraction as the criterion, set the field variable of the element composed of nodes with a volume fraction less than or equal to 0.5 to 1. 3) In the remaining elements, using temperature as the criterion, set the field variable of the element composed of nodes with a temperature higher than the material melting point of 780℃ to 2. 4) In the remaining elements, using thermal history as the criterion, record the nodes that have undergone melting in a separate table and set the field variable of the element corresponding to the node located on the substrate to 3. Set the field variable of the element composed of the node corresponding to the unmelted powder particles to 1.

[0084] Step 8: Associate the custom field variable subroutine with the FEM thermal stress solution main program, create a thermo-mechanical coupling analysis job, and view the calculation results.

[0085] 1) Create a subroutine interface of type "custom field" in the existing static general analysis step, and associate the subroutine containing the field variable classification criteria with this interface; 2) Create a thermo-coupling analysis job and submit it to the solver. Use an Intel(R) Xeon(R) W-2245 CPU (4 cores, 3.9GHz) to calculate for 5 hours to obtain the thermal stress calculation results; 3) View the thermal stress calculation results in the FEM software visualization interface, create a set of elements with field variable values ​​between 2 and 3 in the post-processing module, and view the evolution of the cladding channel morphology over time under this set; 4) By creating a cross-sectional view, view the evolution of the thermal stress of the cladding channel caused by the random movement of the heat source.

[0086] like Figure 4 As shown, the thermal stress result cloud map obtained by thermo-mechanical coupling calculation reflects the irregular aggregate morphology of the cladding channel edge, and the dynamic change process of the field variables also reflects the dynamic deposition process of powder material as the laser heat source moves.

[0087] This invention is based on a CFD-FEM coupled temperature and stress integrated modeling numerical simulation method. It fully utilizes CFD calculations of molten pool temperature and volume fraction data from laser additive manufacturing to build a high-precision FEM thermo-mechanical coupled numerical calculation model. Within the framework of the static element method, the influence of complex physical phenomena in laser additive manufacturing, such as remelting and keyhole features, on thermal stress distribution is reflected. Simultaneously, by leveraging the interpolation algorithms built into the FEM software, the code required for temperature data processing is simplified, the possibility of introducing systematic errors is reduced, and the overall execution efficiency and stability of the FEM solver are improved. This provides more possibilities for subsequent code maintenance and optimization, opening up a new path for integrated temperature and stress numerical simulation in laser additive manufacturing.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A numerical simulation method for laser additive manufacturing using CFD-FEM coupled temperature and stress integrated modeling, characterized in that, Includes the following steps: Step 1: Obtain the CFD model calculation result file, which includes node coordinates, node temperature, and node volume fraction. Based on the node coordinates in the CFD model, generate the mesh element geometry model in the FEM model; Step 2: Assign material temperature parameters to the nodes in the mesh element geometric model, set a predefined temperature field for the mesh element geometric model, and calculate the temperature field result file without valid data without applying a thermal load. Step 3: Assign the nodal temperatures of the CFD model to the temperature field result file of the FEM model to obtain the FEM model temperature file sorted by time. Step 4: Using the volume fraction in the CFD model calculation result file as the criterion, distinguish between solid nodes and gas nodes in the FEM model temperature file. Based on the temperature and volume fraction of the nodes, remove abnormal nodes from the solid nodes and gas nodes until the temperature field data meets the convergence requirements of the thermal stress solution, and obtain the filtered FEM model temperature file. Step 5: Assign thermo-coupling material parameters to the nodes in the geometric model of the mesh element in the FEM model in Step 1, and couple the filtered FEM model temperature file obtained in Step 4 to the FEM model with thermo-coupling material parameters to obtain the FEM thermo-coupling model. Step 6: Determine the node type in the FEM thermo-coupling model through subroutines in the FEM thermo-coupling model. Differentiate between gaseous and solid nodes based on the node volume fraction in the CFD model calculation result file. Within solid nodes, further distinguish between solid, liquid, and gaseous nodes based on the node's thermal history. Assign gas stiffness attributes to gaseous nodes and unmelted powder particle units, liquid stiffness attributes to liquid nodes, and solid stiffness attributes to solid nodes. The solid stiffness attribute is a first order of magnitude multiple of the liquid stiffness attribute, and the liquid stiffness attribute is a second order of magnitude multiple of the gas stiffness attribute. Step 7: Based on the subroutine's judgment result, perform thermal stress calculation on the FEM thermo-mechanical coupling model; Step 8: Repeat steps 6 and 7 until the FEM thermo-coupling model calculations for all time periods are completed.

2. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, In step 1, the process of generating the geometric model of the mesh element in the FEM model based on the node coordinates in the CFD model is as follows: Based on the node coordinates of the Eulerian mesh element in the CFD model, establish the corresponding node coordinates of the Lagrange element in the FEM model, and number the nodes sequentially.

3. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, In step 2, the temperature of the predefined temperature field is room temperature.

4. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, In step 2, the material temperature parameters include density, specific heat capacity, and thermal conductivity.

5. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, In step 4, the criteria for removing abnormal nodes are as follows: for nodes exceeding the material vaporization temperature, determine whether the node affects the convergence of the thermal stress calculation of the cladding channel model. If it does, remove it; remove unreasonable high temperature values ​​and modify them to the material vaporization temperature; modify the solid node temperature below room temperature to room temperature. The process of eliminating abnormal nodes is repeated multiple times until the temperature field data meets the convergence requirements for solving the thermal stress.

6. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, In step 5, the parameters of the thermo-coupling material include the coefficient of thermal expansion, Young's modulus, and Poisson's ratio.

7. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, In step 6, the subroutine is written using the FEM model, and the subroutine and the FEM thermo-coupling model are connected through an interface.

8. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, In step 6, the process of determining the node type in the FEM thermal coupling model through a subroutine is as follows: 1) Differentiate between gaseous and solid nodes using the node volume fraction in the CFD model calculation results file. 2) For solid nodes, if the node heats up and exceeds the melting point of the powder during the current FEM thermo-coupling model analysis and calculation process, then the node is a liquid node. 3) For solid nodes, if the node heats up during the current FEM thermo-coupling model analysis and calculation process but does not exceed the melting point of the powder and its coordinates are located on the substrate, it is considered a solid node; if the node heats up during the current FEM thermo-coupling model analysis and calculation process but does not exceed the melting point and is not located on the substrate, it is considered a gaseous node. 4) For solid nodes that are not on the substrate and are being cooled, if the node has experienced a melting heat history, it is considered a solid node; if the node has not experienced a melting heat history, it is considered a gaseous node.

9. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, After step 5, the node numbers and corresponding volume fractions that changed in the temperature field calculation results of each frame in the CFD model are selected. For the changed node numbers, the volume fractions are organized and the node set file is refreshed in chronological order.

10. The numerical simulation method for laser additive manufacturing with CFD-FEM coupled temperature and stress integrated modeling as described in claim 1, characterized in that, In step 1, the coordinates of the Lagrange nodes in the FEM model are constructed based on the coordinates of the mesh element nodes in the CFD model, and hexahedral mesh elements are created through 6 adjacent nodes; in step 7, the FEM thermo-coupling model calculates thermal stress based on hexahedral mesh elements.

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