Simulation method for fused deposition modeling process of composite material based on interlayer variable path strategy

Abstract

The invention relates to a composite material fused deposition modeling process simulation method based on an interlayer variable path strategy, and the method comprises the following steps: carrying out APDL parameterized language programming according to ANSYS finite element software, and building a finite element model module; adding corresponding attributes including specific heat capacity, thermal conductivity, density, elasticity modulus and the like according to composition materials in the composite material; grid division is conducted on a forming part module, variable-layer-height grid division is conducted on the module according to the proportion of composition materials in the composite material, and the forming process of the composite material is simulated; performing birth and death unit processing on a formed part, activating different interlayer units according to a selection sequence and a formulated printing path in a control unit numbering manner, and simulating an interlayer variable-path forming process; the temperature field obtained after transient thermal analysis serves as a thermal load to be imported into a structure field to be solved, and a temperature field cloud picture, a thermal stress field cloud picture and a strain field cloud picture of the interlayer variable-path printing composite material are obtained; a printing simulation result is analyzed and compared with an actual printing result, errors are reduced, actual printing is guided through the optimized interlayer path and other technological parameters, and the overall forming precision is improved.

Description

Technical Field

[0001] The present invention relates to the field of parametric simulation of ANSYS software used in the process of forming different paths between layers using 3D printing technology. This falls within the intersection of FDM 3D composite material printing with different paths between layers, thermodynamics, and ANSYS APDL parametric simulation. Specifically, a simulation method for the composite material fused deposition molding process based on a layer-by-layer variable path strategy is designed. Background Art

[0002] 3D printing technology forms physical objects by solidifying fusible materials layer by layer. With technological advancements, precision and efficiency in molded parts are gaining increasing attention. Simulation allows for rapid research into the 3D printing process, capturing relevant data and reducing the need for consumables and repeated testing. Parametric simulation facilitates rapid modification and adaptability to different models, facilitating the modification of printing parameters. The impact of varying parameters on printing accuracy can then be compared, ultimately leading to optimal parameters through simulation.

[0003] At present, some scholars have conducted simulation research on the 3D printing molding process, using different simulation schemes. They mainly studied the influence of factors such as nozzle temperature during the printing molding process, heat transfer, heat convection during the material molding process, and printing speed on the printing quality under the same material and the same path. Studies have shown that the molding accuracy and printing efficiency of 3D printing, especially in the field of composite material printing, are closely related to the printing path. At present, the simulation of the 3D printing molding process generally adopts the same material and the same interlayer path. Using the same material and the same interlayer path can simplify the command flow (APDL), but there are limitations of a single printing material and the problem of ignoring the influence of the printing path in the consideration of process parameters; different interlayer paths are adjusted according to the appropriate printing path of the component materials in the interlayer composite material, which has obvious advantages. Therefore, the layer height is set according to the proportion of the components in the composite material to achieve finite element analysis of the composite material printing process. During the composite material molding process, the control unit activation sequence is used to control the printing molding path. This method can realize different paths between layers in the molding process and quickly plan the optimal printing path for each layer of material in the composite material. Parametric simulation can quickly achieve a molding process that is consistent with the actual printing path. At the same time, parametric simulation can adjust the properties of the material to achieve the purpose of studying various composite materials. In addition, parametric simulation can study the effects of factors such as printing speed, layer thickness, and printing path on molding accuracy. By analyzing the simulation results and adjusting the actual printing parameters, a reference is provided for selecting the optimal interlayer molding path for 3D printing of composite materials, which is conducive to improving overall molding accuracy.

[0004] The present invention uses ANSYS finite element software to simulate the effects of different interlayer printing paths, layer thickness, printing speed, and other process parameters on the molding accuracy during the composite material printing process. During the use of birth-and-death cell technology, cell numbers are determined and selected through grid division. The cell numbering controls the activation sequence of the cells, thereby simulating the printing path. Finally, transient thermodynamic analysis is used to obtain cloud maps of the temperature, stress, and strain fields of the molded part, as well as a graph showing the temperature change over time at different locations. The molding accuracy is determined based on the overall deformation of the molded part in the simulation results, and the printing path and other process parameters of the composite material components are adjusted to obtain a more optimal interlayer printing path and other process parameters. Summary of the Invention

[0005] This paper proposes a simulation method for composite material fused deposition modeling (FDM) based on a layer-by-layer variable path strategy, using ANSYS APDL to perform finite element analysis of the process. This method addresses the problem of determining the optimal printing path for the composite material during printing, analyzing the temperature and stress of the molded part using simulation cloud maps, and analyzing the molding accuracy based on the overall deformation and regional maximum deformation of the molded part. By adjusting the interlayer path and process parameters, optimal simulation results are obtained, thereby optimizing the actual molding accuracy.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a composite material fused deposition modeling process simulation method based on a variable path strategy, comprising the following steps:

[0007] S1. Construct a 3D printing part model by programming the APDL parametric language in ANSYS;

[0008] S2. Add corresponding properties according to the components of the composite materials used in the printing process. The model material properties can be dynamically adjusted to adapt to most composite materials;

[0009] S3. Meshing the finite element module of the molded part and determining the layer height according to the proportion of the component materials in the composite material to simulate the molding process of the composite material;

[0010] S4. Use the life and death unit technology to simulate the printing process, so that the unit has two states: "kill unit" and "activate unit";

[0011] S5. Control the activation state of the specified unit by selecting the unit number and simulate the molding process of different paths between layers;

[0012] S6. Apply loads and unit boundary conditions to the molded part, calculate the temperature change during the printing process, and obtain a temperature cloud map and a curve showing the temperature change over time at different positions of the molded part;

[0013] S7. Perform temperature field simulation and import the simulation results as thermal loads into the stress field. Simulate and generate stress and strain contours. Analyze molding accuracy issues during composite material printing using a variable path strategy. Adjust parameters and continue simulation. Compare multiple sets of simulation results, then perform actual printing and compare the actual printing and simulation errors. If the errors are within the allowable range, the simulation results are validated. Adjust the actual interlayer path and other process parameters to achieve better molding accuracy.

[0014] In transient thermal analysis and structural field analysis, the APDL parametric language is used to define the element type of the molded part as solid70 and solid185 respectively, and the actual model size is set to build a three-dimensional model.

[0015] Set the material parameters of the molded part module. Based on the parameters of the composite materials used in the actual printing, assign the properties of the printed material at different temperatures to the molded part model. Material-related properties include specific heat capacity, thermal conductivity, density, coefficient of expansion, elastic modulus, Poisson's ratio, etc. Use the three-dimensional transient heat transfer differential equation as the heat transfer expression to iterate the heat conduction and heat of each unit in contact during the printing process.

[0016] The unit cells of the molded part are meshed, and the unit size of the molded part is divided into units with the same length and width but different heights in each layer. The layer height is determined by the proportion of each material in the composite material, so as to simulate the composite material printing process;

[0017] Using the birth and death unit technology, all the molding unit modules are first killed, and the printing filament melt accumulation process is simulated by controlling the activation and killing states of the unit;

[0018] After meshing the molded part, a certain number of cells are obtained. Each cell has a different number. By selecting the cell number, the corresponding cell in the molded part module is activated. By adjusting the order of the activated cells, different paths between layers can be printed during the molding process.

[0019] During the simulation of printing, the nozzle temperature is applied to the selected activated unit, and the time of temperature application is controlled to control the printing speed. Air convection conditions are applied to the activated units. The ambient temperature of the first layer of printing units is defined as 50°C to simulate the base temperature, and the ambient temperature of other layers is 25°C. Heat exchange is carried out between the activated units, and the nozzle temperature applied to the activating unit exchanges heat with the temperature of the surrounding already formed units.

[0020] Start the nonlinear solution, specify the analysis type as transient, calculate the temperature field of the molded part, and obtain the temperature field cloud map of the composite material at different times under different inter-layer printing paths. Draw the temperature change curve of different positions in the molded part with printing time.

[0021] The temperature field results of the molded part are read, and the temperature of each unit node is imported into the structural field analysis as a thermal load. The thermal stress field and strain field cloud diagrams are obtained by solving. The printing quality is judged according to the overall deformation of the molded part, and the printing parameters are adjusted to obtain better printing results.

[0022] Compared with the existing technology, the present invention provides a method for simulating the composite material fused deposition modeling process based on an interlayer variable path strategy, which has the following beneficial effects: The present invention sets the layer thickness according to the proportion of the constituent materials in the composite material, and then simulates the composite material molding process. By using the life and death unit technology, the interlayer printing path is changed by selecting the unit number. Then, the influence of the interlayer path and other process parameters on the printing effect is analyzed. The simulation results can show the temperature field, stress field, and strain cloud map at different times, which is convenient for comparison and analysis with actual experiments, and then adjust the interlayer molding path and other process parameters to improve the accuracy of the printed parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the present invention;

[0024] Figure 2 This is a schematic diagram of a printed molded part model of the present invention;

[0025] Figure 3 This is a schematic diagram of the molded part of the present invention after mesh division according to the proportion of materials;

[0026] Figure 4 Schematic diagram of different paths between layers of the present invention;

[0027] Figure 5 It is the temperature field cloud map of the simulation result of the present invention;

[0028] Figure 6 Schematic diagram of the change of node temperature over time on the molded part of the present invention;

[0029] Figure 7 This is a cloud diagram of the equivalent stress variation of the molded part of the present invention;

[0030] Figure 8 This is the total strain cloud diagram of the molded part of the present invention. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] See also Figure 1 The present invention provides a technical solution: a composite material fused deposition modeling process simulation method based on an interlayer variable path strategy, comprising the following steps:

[0033] S1: Use ANSYS finite element software to program APDL parametric language to build a finite element model of the 3D printed parts. Figure 2 shown.

[0034] Open the MechanicalAPDL Product Launcher of ANSYS software and use the APDL function block command to create a cube model with a length, width and height of 20mm, 20mm and 0.7mm respectively. Figure 2 shown.

[0035] S2: Add the properties of the components of the composite material and dynamically adjust them according to the actual printed composite material.

[0036] The APDL functions mptemp and mpdata are used to define the thermal properties of the printed material. The thermal properties of the printed material in this embodiment of the patent are shown in the table:

[0037] Table of thermal properties parameters of composite materials

[0038] In order to more accurately simulate the thermal transformation of the printing unit during the fused additive manufacturing process, transient thermal analysis is used. The thermal control equation used in transient thermal analysis is shown below: Where: ρ is the material density; c is the specific heat capacity of the material; k x ,k y ,k z Represent the thermal conductivity coefficients along the x, y, and z directions respectively; T is temperature; t is time; Q=Q(x, y, z, t) represents the distribution of heat source intensity inside the object.

[0039] S3: Divide the model into grid layers according to the proportion of the composite materials to model the composite material forming process;

[0040] Use the ESIZE function to set the length and width of the grid to 2mm, and the height to 0.5mm and 0.2mm according to the proportion of the composite material. The grid division results are as follows: Figure 3 shown.

[0041] APDL program that assigns different material properties to different layers esize,2 mat,1 esize,2 mat,2

[0042] S4: Apply the life and death unit technology in the molding path simulation process, and the unit contains two states: "kill" and "activate";

[0043] Use the esel function to select all units of the entire molded part, and then use ekill to select all units and "kill" them.

[0044] "Kill Cell" APDL Procedure esel,s,mat,,1 esel,a,mat,,2 eplot ekill,all

[0045] Use the esel function again to select the cell with the specified number, and the ealive function will activate the selected cell.

[0046] "Activate Unit" APDL procedure eseln,s,all ealive,all

[0047] S5: By selecting the unit number, the activation state of the specified unit is controlled to simulate the molding process of different paths between layers;

[0048] Overly large models and overly small meshes can result in numerous cell numbers. To avoid repeated cell activation commands and facilitate print path planning, *do and *enddo loop functions are used to control the cell activation sequence and load application. To distinguish between layer paths, this example uses a "Z"-shaped print path for the first layer of material, and a spiral offset print path for the second layer.

[0049] S6: Apply loads and unit boundary conditions to the molded part, calculate the temperature field during the printing process, and obtain a temperature cloud map and a temperature curve at different positions of the molded part over time;

[0050] For the activated unit, the nozzle temperature is applied using the d function. Air convection is applied to the specified activated unit through the sf function, and the heat convection is 72W / (m 2 ℃), the room temperature of the first layer is set to 50℃, and the other layers are set to 25℃. The deltim function is used to control the time when the load is applied to each element. The ddele function is used to remove the load after the load is applied.

[0051] In the ANSYS classic interface, select Main Menu→PostProc→Plot Result→Cont ourPlot→Nodel Solution to display the node temperature and observe the overall temperature distribution. In Main Menu→TimeHist Postpro, select any node in the molded part to view the curve of the node temperature changing with the printing time. Figure 5 Shown is the temperature nephogram at the end of printing for a Z-shaped printing path for the first layer of material and a spiral offset printing path for the second layer of material at a printing speed of 40 mm / s. Figure 6 The temperature variation curve of two adjacent nodes at different layer heights from the first layer to the second layer directly above the origin of the molded part over time shows that the heat dissipation efficiency of the nodes is different under different printing path conditions. The constituent materials in the composite material have corresponding melting temperatures. During the second layer printing process, the solidified node should be selected as the starting point of the second layer spiral offset printing according to the node temperature distribution, and the appropriate printing path should be selected according to the actual printing material properties.

[0052] S7: Perform solid structure field simulation and solve the problem. The temperature field is imported into the stress field as a thermal load. Through the cloud map obtained by simulation, the quality problems in the composite material molding process of printing different interlayer printing paths are analyzed. The interlayer path and other process parameters are adjusted to simulate and improve the overall molding accuracy.

[0053] When solving the stress field, use the etchg function to change the unit for structural solution, use the esel function to select the unit, use the ldread command to read the temperature of this unit, and use this temperature as the imported thermal load to solve the thermal stress and strain of the molded part.

[0054] In the ANSYS Classic interface, select Main Menu → PostProc → Plot Result → ContourPlot → Nodel Solution → Displacement vector sum to display the overall deformation. You can then select X, Y, Z—Component of displacement to display the deformation in the X, Y, and Z directions. You can display the average Mises stress in Nodel Solution → Stress → von Mises stress. You can then select X, Y, Z—Component of stress to display the stress in the X, Y, and Z directions. You can also display shear stress and tension between surfaces.

[0055] Depend on Figure 7 The equivalent stress can be checked and it can be seen that the equivalent stress value in the center area of ​​the model with the highest printing speed is relatively small. Figure 8 The total strain contour is shown. By observing the overall model variables, we can see that the main deformation areas of the printed model are concentrated at the edges, with the deformation of the second layer being more pronounced. This is because the second layer of the composite material used in the example is fiber-reinforced, and the material has anisotropic shrinkage. Therefore, by adjusting the interlayer printing path and other process parameters and comparing the simulation results, the overall molding accuracy of the composite material printed using different interlayer paths can be improved.

[0056] In summary, the composite material fused deposition modeling simulation method based on the interlayer variable path strategy of the present invention can simulate actual dual-nozzle composite material interlayer variable path printing. Transient thermal analysis and solid structure field analysis can be used to examine the distribution of the temperature, stress, and strain fields of the molded part at different times. By adjusting the interlayer printing path and other process parameters, optimal simulation results can be obtained and applied to actual printing. Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. A method for simulating a composite material fused deposition modeling process based on a layer-by-layer variable path strategy, comprising the following steps: S1. Construct a 3D printing part model by programming the APDL parametric language in ANSYS; S2. Add corresponding properties according to the components of the composite materials used in the printing process. The model material properties can be dynamically adjusted to adapt to most composite materials; S3. Meshing the finite element module of the molded part and determining the layer height according to the proportion of the component materials in the composite material to simulate the molding process of the composite material; S4. Use the life and death unit technology to simulate the printing process, so that the unit has two states: "kill unit" and "activate unit"; S5. Control the activation state of the specified unit by selecting the unit number and simulate the molding process of different paths between layers; S6. Apply loads and unit boundary conditions to the molded part, calculate the temperature change during the printing process, and obtain a temperature cloud map and a curve showing the temperature change over time at different positions of the molded part; S7. Perform temperature field simulation and import the simulation results as thermal loads into the stress field. Simulate and generate stress and strain contours. Analyze molding accuracy issues during composite material printing using a variable path strategy. Adjust parameters and continue simulation. Compare multiple sets of simulation results, then perform actual printing and compare the actual printing and simulation errors. If the errors are within the allowable range, the simulation results are validated. Adjust the actual interlayer path and other process parameters to achieve better molding accuracy.

2. The method according to claim 1, wherein: Use APDL parametric language programming to define the model, determine the model size, and add air convection conditions.

3. The method according to claim 2, wherein: Use APDL parametric language to define the properties of composite materials and assign dynamic properties to the model.

4. The method according to claim 3, wherein: The model is divided into variable layer thickness grids according to the proportion of each component material in the composite material.

5. The method according to claim 4, characterized in that: The life and death process of the unit is realized by modifying the stiffness of the unit body. When the stiffness of the unit is multiplied by a very small reduction coefficient, the output of the unit is approximately 0, and the unit is regarded as killed. When the reduction coefficient value of the unit stiffness is changed to 1, its output returns to the initial setting value of the system, and the unit is regarded as activated. The activation and killing states of the unit are controlled to simulate the printing wire melting deposition process.

6. The method according to claim 5, characterized in that: After meshing the molded part, a certain number of cells are obtained. Each cell has a corresponding number. By selecting the cell number, the corresponding cell in the molded part module is activated. Then, by controlling the order of activated cells, different printing paths between layers during the composite material molding process are simulated.

7. The method according to claim 6, characterized in that: Apply a heat load based on the nozzle temperature to the selected active cells, and simulate the printing speed by controlling the temperature application time. Apply 50°C air convection to the first layer of cells to simulate the base temperature, and apply 25°C room temperature convection conditions to the remaining layers. Finally, perform transient thermal analysis to obtain the overall temperature field of the molded part and the curves of node temperature changes over time at different times.

8. The method according to claim 7, wherein: Obtain the temperature field results of the molded part, import the node temperature as a thermal load into the structural field for analysis, and obtain the thermal stress field and strain field distribution cloud map of the molded part.

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