A 3D printing direction optimization method based on thermal deformation

Abstract

The present invention belongs to the field of three-dimensional printing of computer-aided design, and relates to a three-dimensional printing direction optimization method based on thermal deformation. The present invention takes into account the support factor. Since the support volume generated in different directions is different, it is taken as one of the research contents. The present invention takes into account the thermal deformation factor, uses ISM (Inherent Strain Method) to simulate the printing process, and calculates the model deformation. The present invention takes into account the printing quality problem based on the step effect. The present invention takes into account the printing time problem. The present invention selects the NSGA‑2 algorithm improved based on the genetic algorithm to solve the above-mentioned multi-objective optimization problem and finds the optimal printing direction. At present, there has been no research that simultaneously considers the above factors to optimize the printing direction. The present invention combines printing direction optimization with process simulation, which can effectively reduce structural deformation and improve the strength and quality of the printed structure.

Description

Technical Field

[0001] The invention belongs to the field of computer-aided design three-dimensional printing and relates to a three-dimensional printing direction optimization method based on thermal deformation. Background Art

[0002] 3D printing is a manufacturing technology that creates objects by stacking materials layer by layer. During the 3D printing process, molten material is extruded and deposited layer by layer onto a build platform to form the desired object shape. While 3D printing has become widely adopted in the manufacturing industry, several challenges remain. One of these is determining the printing orientation of the material to achieve optimal build quality and structural strength.

[0003] Currently, much research has focused on the impact of different printing orientations on the required support volume, print quality, and printing time of printed models, while ignoring the thermal deformation behavior of materials in high-temperature environments. Layer-by-layer printing causes the printed material to repeatedly undergo a melting-solidification process, resulting in significant residual stress between layers. Ignoring thermal deformation behavior can reduce the mechanical properties and structural strength of the printed structure, ultimately leading to shape and dimensional distortion of the component. Summary of the Invention

[0004] The present invention aims to find the best printing direction by comprehensively considering the following factors. First, the present invention takes the support factor into consideration. Since the support volume generated in different directions is different, it is taken as one of the research contents. Second, the present invention takes the thermal deformation factor into consideration, uses ISM (Inherent Strain Method) to simulate the printing process, and calculates the model deformation. Third, the present invention considers the printing quality problem based on the step effect. Fourth, the present invention considers the printing time problem. Finally, the present invention selects the NSGA-2 algorithm improved based on the genetic algorithm to solve the above-mentioned multi-objective optimization problem and finds the best printing direction. At present, there has been no research that considers the above factors at the same time to optimize the printing direction. The present invention combines the printing direction optimization with process simulation, which can effectively reduce structural deformation and improve the strength and quality of the printed structure.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for optimizing the direction of 3D printing based on thermal deformation, comprising the following steps:

[0007] Step S1: Pre-processing stage: Input the 3D model M, obtain the triangular faces f and vertices v of the 3D model, and voxelize the model using a hexahedral mesh.

[0008] Furthermore, the specific implementation steps of S1 are:

[0009] Step S1.1: Input the triangular mesh structure into the system and read the coordinates of the triangular faces and vertices of the three-dimensional structure;

[0010] Step S1.2: voxelize the 3D model using a hexahedral mesh;

[0011] Step S2: Calculate the support volume required for the model;

[0012] Furthermore, the specific implementation steps of S2 are:

[0013] Step S2.1: Check whether the triangular mesh faces are suspended in the air.

[0014] Step S2.2: Add support structures for the triangular overhanging surfaces;

[0015] Step S2.3: Calculate the support volume value;

[0016] Step S3: Calculate the maximum thermal deformation generated during the model printing process.

[0017] Furthermore, the specific implementation steps of S3 are:

[0018] Step S3.1: coupling support voxels with model voxels;

[0019] Step S3.2: Calculate the displacement of all mesh vertices of the 3D model using the ISM method;

[0020] Step S3.3: Finite element analysis module;

[0021] Step S3.4: Calculate the maximum deformation size of all vertices of the model.

[0022] Step S4: Calculate the printing quality of the model.

[0023] Furthermore, the specific implementation steps of S4 are:

[0024] Step S4.1: Calculate the tip height;

[0025] Step S4.2: Calculate the error caused by the staircase effect;

[0026] Step S5: Calculate the printing time of the model.

[0027] Step S6: Use the NSGA-2 algorithm to optimize and obtain a Pareto optimal solution set that does not dominate each other.

[0028] Furthermore, the specific implementation steps of S6 are:

[0029] Step S6.1: constructing a printing frame;

[0030] Step S6.2: Optimize using the NSGA-2 algorithm;

[0031] Furthermore, the specific implementation steps of S6.2 are as follows:

[0032] Step S6.2.1: Initialize the population; each individual in the population represents a printing direction;

[0033] Step S6.2.2: Calculate the non-dominated order of each individual in the population and the crowding degree between individuals;

[0034] Step S6.2.3: Generate parent individuals;

[0035] Step S6.2.4: Obtain offspring through genetic operators such as crossover, mutation, and selection, and mix the offspring with the parent generation;

[0036] Step S6.2.5: Select the next generation parent individuals from the mixed population;

[0037] Step S6.2.6: Repeat the above steps until the iteration termination condition is reached.

[0038] Beneficial effects of the present invention:

[0039] The present invention comprehensively considers various influencing factors in the printing process and the thermal strain generated in the printing process, and can effectively enhance the strength of the printing structure and improve the printing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the overall optimization flow chart;

[0041] Figure 2 It is a schematic diagram of overhang structure detection;

[0042] Figure 3(a) is a diagram of the input instance model;

[0043] Figure 3(b) shows the model voxelization and overhang area detection;

[0044] Figure 3(c) shows the support voxels added to the overhanging area;

[0045] Figure 4 It is a schematic diagram of the ISM method;

[0046] Figure 5 It is a schematic diagram of the step effect;

[0047] Figure 6 It is a schematic diagram of the optimization algorithm generating new offspring;

[0048] Figure 7(a) shows the four-dimensional optimization results, where the three-dimensional coordinate axes are the maximum deformation, support volume, and printing time;

[0049] Figure 7(b) shows the four-dimensional optimization results, where the three-dimensional coordinate axes are support volume, printing time, and printing quality;

[0050] Figure 7(c) shows the four-dimensional optimization results of the maximum deformation, support volume, and printing quality in three-dimensional coordinate axes;

[0051] Figure 7(d) shows the height of the model at each point in Figure 7(a). DETAILED DESCRIPTION

[0052] The present invention is further described in detail below with reference to the accompanying drawings and specific implementation examples.

[0053] Part 1: Pre-processing stage, the steps are as follows:

[0054] Step S1.1: Figure 1 As shown, the triangular mesh structure is input into the system, and the triangular faces and vertex coordinates of the three-dimensional structure are read;

[0055] Step S1.2: Voxelize the 3D model using a hexahedral mesh. The result is Figure 1 Bone models in the optimization framework;

[0056] Part 2: Calculate the support volume required for the model. The steps are as follows:

[0057] Step S2.1: Check whether the triangular mesh faces are dangling. The detection criteria are as follows:

[0058]

[0059] If δ i If θ is 1, it means that the triangle face is suspended in the air and a support structure needs to be added; otherwise, no support structure is needed. i Represents the angle between the outer normal vector of the i-th triangle face and the triangle printing direction, z i Represents the average height of the three vertices of the triangle face. Figure 2 As shown, surface f2 is suspended and requires additional support structure, while f1 does not.

[0060] Step S2.2: Add support structures for triangular overhanging surfaces; as shown in Figure 3(a), the bone model is input and voxelized in (b). The overhanging areas of the model need to be detected and marked in black; in (c), for the overhanging areas, support structures need to be added to their lower sides, namely gray hexahedral mesh blocks.

[0061] Step S2.3: Calculate the support volume value;

[0062]

[0063] Among them, δi This is the δ in step S1 above. i .

[0064] Part 3: Calculate the maximum thermal deformation during the model printing process. The main steps are as follows:

[0065] Step S3.1: Support voxels are coupled with model voxels; due to the influence of model deformation, the model may fail to print. In order to ensure successful printing, it is necessary to add supports to the overhanging areas. Figure 3(a) to Figure 3(c) As shown in the figure, the support voxels and the model voxels need to be coupled with each other, and the simulation system includes the model voxels and the support voxels in the figure.

[0066] Step S3.2: Use the ISM method to calculate the displacement of all mesh vertices of the 3D model; Figure 6 As shown, the bottom block represents the printing substrate, and the block above represents the printed object. To simulate the printing process, the object first needs to be sliced ​​and each layer is activated from bottom to top. The left side of the figure shows that L1 is activated, where L1 includes four printing layers, and the inherent strain ∈ is added to this part. inh After the first printing stage is activated, the right side shows that L1 is deposited and L2 is activated. The above process is repeated until all printing layers are traversed.

[0067] Step S3.3: Finite element analysis module;

[0068] f(∈ inh )=D T C T ∈ inh ,

[0069] Where C is the elastic matrix and D is the strain-displacement matrix.

[0070] Solve the stiffness equation:

[0071] K i U i =f i

[0072] K i is the global stiffness matrix composed of the elements of the first i-1 printing stages, i.e. f i By L i Stress caused by activation; U i It's L i The amount of displacement produced at the vertex when activated.

[0073]

[0074] Finally, L iThe total deformation of the model at this time can be obtained by adding the displacements generated when it is activated.

[0075] Step S3.4: Calculate the maximum deformation size of all vertices of the model.

[0076]

[0077] MD=max(D 1 ,D 2 ,...,D N )

[0078] Part 4: Calculate the print quality of the model.

[0079] Step S4.1: Calculate the tip height;

[0080] CH=tcos(θ)

[0081] The smaller the CH is, the less obvious the step effect is. Figure 4 As shown by the lines in .

[0082] Step S4.2: Calculate the error caused by the staircase effect;

[0083]

[0084] in, θ i As described in Part II, step S1.

[0085] Part 5: Calculate the printing time of the model.

[0086]

[0087] In the sixth part, the NSGA-2 algorithm is used for optimization to obtain a set of non-dominated Pareto optimal solutions. Step S6.1: Construct the printing framework;

[0088] min (α,β,γ) g=(g1(α,β,γ),g2(α,β,γ),g3(α,β,γ),g4(α,β,γ)),

[0089] stα∈[0,2π],β∈[0,2π],γ∈[0,2π].

[0090] Among them, g i (α, β, γ) are the optimization objectives proposed in the second, third, fourth and fifth parts, namely SV, MD, SE and BT, and α, β and γ represent the rotation angles of the model along the x-axis, y-axis and z-axis respectively.

[0091] Step S6.2: Optimize using the NSGA-2 algorithm;

[0092] Furthermore, the detailed steps of step S6.2 are:

[0093] Step S6.2.1: Initialize the population; each individual in the population represents a printing direction;

[0094] Step S6.2.2: Calculate the non-dominated order of each individual in the population and the crowding degree between individuals;

[0095] Step S6.2.3: Generate parent individuals;

[0096] Step S6.2.4: Obtain offspring through genetic operators such as crossover, mutation, and selection, and mix the offspring with the parent generation;

[0097] Step S6.2.5: Select the next generation parent individuals from the mixed population, using the following method: Figure 5 First, we need to perform Pareto sorting on the mixed group, and then select individuals that meet the group size based on the crowding degree.

[0098] Step S6.2.6: Repeat the above steps until the iteration termination condition is reached.

[0099] like Figure 7(a) to Figure 7(d) As shown in Figure 7(d), when optimizing the above model, we used three 3D Pareto charts to display the optimization results. To demonstrate the correctness of the results, we used the print height target for intuitive display. Figure 7(d) shows the model height in various directions in Figure 7(a) to verify the effectiveness of the algorithm for multi-objective optimization problems.

Claims

1. A three-dimensional printing direction optimization method based on thermal deformation, characterized in that: Here are the steps: Step S1: Pre-processing stage: input the 3D model M, obtain the triangular faces f and vertices v of the 3D model, and voxelize the model using a hexahedral mesh; Step S1.1: Input the triangular mesh structure into the system and read the coordinates of the triangular faces and vertices of the three-dimensional structure; Step S1.2: voxelize the 3D model using a hexahedral mesh; Step S2: Calculate the support volume required for the model; Step S2.1: Check whether the triangular mesh faces are suspended in the air. Step S2.2: Add support structures for the triangular overhanging surfaces; Step S2.3: Calculate the support volume value; Step S3: Calculating the maximum thermal deformation generated during the model printing process; Step S3.1: coupling support voxels with model voxels; Step S3.2: Calculate the displacement of all mesh vertices of the 3D model using the ISM method; Step S3.3: Finite element analysis module; Finite element analysis module; f(∈ inh )=D T C T ∈ inh , Where C is the elastic matrix and D is the strain-displacement matrix; Solve the stiffness equation: K i U i =f i K i is the global stiffness matrix composed of the elements of the first i-1 printing stages, i.e. f i By L i Stress caused by activation; U i It's L i The displacement amount generated at the vertex when activated; Finally, L i The total deformation of the model at this time can be obtained by adding the displacements generated when it is activated; Step S3.4: Calculate the maximum deformation size of all vertices of the model MD=max(D 1 ,D 2 ,...,D N ); Step S4: calculating the printing quality of the model; Step S4.1: Calculate the tip height; Step S4.2: Calculate the error caused by the staircase effect; Step S5: Calculate the printing time of the model; Step S6: Use the NSGA-2 algorithm to optimize and obtain a Pareto optimal solution set that does not dominate each other; Step S6.1: constructing a printing frame; Step S6.2: Optimize using the NSGA-2 algorithm.

2. The method for optimizing the direction of three-dimensional printing based on thermal deformation according to claim 1, wherein: The specific operation of step S2.1 is as follows: check whether the triangular mesh faces are suspended in the air in sequence, and the detection criteria are as follows: If δ i If it is 1, it means that the triangle face is suspended in the air and a supporting structure needs to be added; Otherwise, no support structure is needed; where θ i Represents the angle between the outer normal vector of the i-th triangle face and the triangle printing direction, z i Represents the average height of the three vertices of a triangle face.

3. A method for optimizing the direction of three-dimensional printing based on thermal deformation according to claim 1 or 2, characterized in that: The specific operations of step S4 are as follows: Step S4.1: Calculate the tip height; CH=tcos(θ) The smaller the CH is, the less obvious the step effect is; Step S4.2: Calculate the error caused by the staircase effect; in, θ i Represents the angle between the outer normal vector of the i-th triangle face and the triangle printing direction.

4. A method for optimizing the direction of three-dimensional printing based on thermal deformation according to claim 1 or 2, characterized in that: The specific operations of step S6.2 are as follows: Step S6.2.1: Initialize the population; each individual in the population represents a printing direction; Step S6.2.2: Calculate the non-dominated order of each individual in the population and the crowding degree between individuals; Step S6.2.3: Generate parent individuals; Step S6.2.4: Obtain offspring through crossover, mutation, and selection of genetic operators, and mix the offspring with the parent generation; Step S6.2.5: Select the next generation parent individuals from the mixed population; Step S6.2.6: Repeat the above steps until the iteration termination condition is reached.

5. The method for optimizing the direction of three-dimensional printing based on thermal deformation according to claim 3, wherein: The specific operations of step S6.2 are as follows: Step S6.2.1: Initialize the population; each individual in the population represents a printing direction; Step S6.2.2: Calculate the non-dominated order of each individual in the population and the crowding degree between individuals; Step S6.2.3: Generate parent individuals; Step S6.2.4: Obtain offspring through crossover, mutation, and selection of genetic operators, and mix the offspring with the parent generation; Step S6.2.5: Select the next generation parent individuals from the mixed population; Step S6.2.6: Repeat the above steps until the iteration termination condition is reached.

6. A method for optimizing the direction of three-dimensional printing based on thermal deformation according to claim 1, 2 or 5, characterized in that: The specific operations of step S5 are as follows:

7. The method for optimizing the direction of three-dimensional printing based on thermal deformation according to claim 3, wherein: The specific operations of step S5 are as follows:

8. The method for optimizing the direction of three-dimensional printing based on thermal deformation according to claim 4, wherein: The specific operations of step S5 are as follows:

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