A method and system for additive manufacturing model reconstruction based on forming error

Abstract

The present invention discloses a method and system for rebuilding an additive manufacturing model based on forming errors. The method comprises the following steps: constructing an error model based on principle errors, mechanical errors, forming process errors and random errors; quantitatively calculating each error in the model, using each error as compensation data to compensate the original three-dimensional model data, establishing deviation data of each layer of contour data, dividing the deviation data of each layer of contour data equally, connecting corresponding segmentation points in adjacent layers from top to bottom to establish triangular facets, and traversing all coordinate points to complete the reconstruction of the three-dimensional deviation model; predicting the final deformation of the model, correcting the three-dimensional data according to the error model before forming, improving the shape and position accuracy of the final formed part, and realizing deformation control; quantitatively calculating the minimum slice thickness according to the surface roughness and volume error requirements, providing a threshold reference for process parameter setting, and establishing an error model in the forming process.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to a method and system for rebuilding an additive manufacturing model based on forming errors. Background Art

[0002] The additive manufacturing process forms three-dimensional parts by stacking them layer by layer. During the forming process, the continuous free surface data is discretized into two-dimensional contour data for printing, such as Figure 1 As shown in the figure, due to the melting and solidification of materials, the thermal stress generated by the expansion and contraction of the materials in this process will cause obvious deformation of the parts, so there will always be geometric errors between the formed parts and the original models. Through theoretical analysis and experimental testing, it is found that the errors of the formed parts can be divided into four categories, namely: principle error, mechanical error, forming process error and random error. Among them, the principle error mainly comes from the conversion error of the model, that is, the use of triangular mesh instead of the original free-form surface. Since each layer in the forming process is a polyhedral prism, an obvious step-like texture will be formed on the surface of the model, so the forming process error is mainly caused by 3D layer-by-layer stacking. Mechanical system errors and random errors are inherent properties of the equipment, and the statistical laws can be found through a large number of experiments. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a method for rebuilding an additive manufacturing model based on forming errors. An error model in the forming process is established, and the model is compensated and reversely reconstructed before printing to improve the shape and position accuracy of the printed parts.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: a method for rebuilding an additive manufacturing model based on forming errors, comprising the following steps:

[0005] The experimental data of CT scanning or the theoretical data of finite element simulation are used as the error data in the forming process, and the error model is constructed based on the principle error, mechanical error and random error combined with the error data;

[0006] Quantitatively calculate each error in the model, use each error as compensation data to compensate the original 3D model data, and establish the deviation data of each layer of contour data.

[0007] The deviation data of each layer of contour data is equally divided, and the corresponding segmentation points in adjacent layers are connected from top to bottom to establish triangular facets, and all coordinate points are traversed to complete the reconstruction of the three-dimensional deviation model.

[0008] The error model is specifically:

[0009] ε(θ)=ε M (θ)+εp1 (θ)+ε p2 (θ)+ε E (θ)=Δρ(θ)+ε E (θ)+ε p2 (θ) (1)

[0010] Among them, ε M is the principle error, ε p1 is the mechanical system error, ε p2 is the forming process error, ε E is the random error, ρ is the polar diameter with the contour centroid as the pole, and θ is the polar angle.

[0011] Principle error E p for:

[0012]

[0013]

[0014] In formulas (2)-(4), H is the total height of the model, n is the number of slices, i is the layer number, j is the sequence number of the coordinate point in the closed contour, k is the number of coordinate points in the closed contour, θ is the angle between the normal vector of the triangular mesh and the slice direction, S i is the area of ​​the i-th slice contour. When the angle between the triangle and the slice direction is acute, the volume error is positive, otherwise it is negative.

[0015] The mechanical system error comes from the coordinate movement during the forming process. Saddle-shaped or pillow-shaped errors will appear in the position far away from the center of the substrate in the XOY plane. The scanning error compensation model is established by double chessboard calibration. The error in the z direction of the mechanical system error mainly comes from the lifting movement of the forming cylinder. The error in the z direction is used as the size compensation data in the z direction.

[0016] In the forming process error, for the contour without accurate function expression, parametric equation is used to model the error data. The source data in the error model establishment process comes from CT scanning and finite element simulation, and the corresponding theoretical contour data comes from model slices; the change of the theoretical polar diameter and the polar diameter after deformation at different angles is:

[0017]

[0018] Where n is the number of coordinate points, A i , c, w and Obtained from the source data, it is used to control the deformation of the contour, and ε represents the random error.

[0019] In the forming process error, for the contour curve with an accurate expression, its deformed contour can be decomposed into rotation around the centroid and translation along the coordinate axis. The process of establishing its error model is to solve the transformation matrix.

[0020] (x,y,z) T =D S D R D T (x',y',z) T +ε (6)

[0021] Where x, y, z are the transformed contour coordinates, x', y' are the original coordinates before transformation, and D S is the scaling matrix, D T is the translation matrix, D R is the rotation matrix, which is solved from the source data, and ε represents the random error; the random error comes from uncontrollable factors such as process fluctuations, changes in oxygen content and changes in forming chamber pressure.

[0022] On the other hand, the present invention also provides a system for model reconstruction of additive manufacturing based on forming errors, including an error model building module, an error calculation module and a three-dimensional deviation model building module;

[0023] The error model building module uses the experimental data of CT scanning or the theoretical data of finite element simulation as the error data in the forming process, and builds an error model based on the principle error, mechanical error and random error combined with the error data;

[0024] The error calculation module is used to quantitatively calculate each error in the model;

[0025] The three-dimensional deviation model building module is used to divide the deviation data of each layer of contour data into equal parts, connect the corresponding segmentation points in adjacent layers from top to bottom to build triangular facets, and traverse all coordinate points to complete the establishment of the three-dimensional deviation model.

[0026] In addition, a computer device may be provided, including a processor and a memory, wherein the memory is used to store a computer executable program, and the processor reads and executes the computer executable program from the memory. When the processor executes the computer executable program, the method for reconstructing an additive manufacturing model based on forming errors described in the present invention can be implemented.

[0027] A computer-readable storage medium is also provided, in which a computer program is stored. When the computer program is executed by a processor, the method for additive manufacturing model reconstruction based on forming errors described in the present invention can be implemented.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects: predicting the final deformation of the model, correcting the three-dimensional data according to the error model before forming, improving the shape and position accuracy of the final formed part, and realizing deformation control; quantitatively calculating the minimum slice thickness according to the surface roughness and volume error requirements, and providing a threshold reference for process parameter setting. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of slicing of a three-dimensional model.

[0030] Figure 2 Schematic diagram of stack-up manufacturing errors.

[0031] Figure 3 It is a line graph of the forming cylinder lifting error.

[0032] Figure 4 Schematic diagram of the torsion of the model along the forming direction and the translation of the forming plane. DETAILED DESCRIPTION

[0033] Since each link in the forming process is affected by the hardware and software systems and environmental factors, the dimensional error generated from the original three-dimensional model to the finished product can be divided into four categories: principle error, mechanical error, forming process error and random error. The present invention reconstructs the original model according to a series of shape changes experienced by the model from data to product to improve the shape and position accuracy of the final formed part. This method can greatly improve the yield of the additive manufacturing process and realize deformation control based on experimental data.

[0034] Random errors are caused by fluctuations in some unknown variables. The other three types of errors are caused by certain factors and can be quantitatively evaluated.

[0035] ε(θ)=ε M (θ)+ε p1 (θ)+ε p2 (θ)+ε E (θ)=Δρ(θ)+ε E (θ)+ε p2 (θ) (1)

[0036] Additive manufacturing technology discretizes continuous polysurfaces or triangular mesh data into a finite number of prisms with layer thickness as height by accumulating them layer by layer. In this way, complex parts of arbitrary shapes can be quickly manufactured within given error requirements without being restricted by molds. Due to the characteristics of layer-by-layer manufacturing, the manufactured parts inevitably have principle errors E p ,like Figure 2 shown.

[0037]

[0038]

[0039]

[0040] In formulas (2)-(4), H is the total height of the model, n is the number of slices, i is the layer number, j is the sequence number of the coordinate point in the closed contour, k is the number of coordinate points in the closed contour, θ is the angle between the normal vector of the triangular mesh and the slice direction, S i is the area of ​​the i-th slice contour. When the angle between the triangle and the slice direction is acute, the volume error is positive, otherwise it is negative.

[0041] The mechanical system error mainly comes from the coordinate movement during the forming process. Since the laser is directly above the center of the substrate, a saddle-shaped or pillow-shaped error will appear in the XOY plane away from the center of the substrate. This part of the error can be used to establish a scanning error compensation model through double chessboard calibration. Therefore, the mechanical system error in the XOY plane can be ignored. The error in the z direction mainly comes from the lifting movement of the forming cylinder. The experimental statistical results of the positioning error are as follows: Figure 3 As shown in the figure, it can be seen that the error fluctuation range in the z direction is -2μm-6μm, the average error is 2μm, and the cumulative error in the z direction after 50 layers is maintained at about 50μm. Therefore, when high precision requirements are required, this part of the error can be used as size compensation data in the z direction.

[0042] The error in the forming process is mainly caused by the inconsistent expansion and contraction rates of materials in different regions under different temperature gradients, which manifests as twisting along the forming direction and translation of the forming plane, such as Figure 4 As shown. For contours without accurate functional expressions, the present invention uses parametric equations to model the error data, where the source data in the error model establishment process comes from CT scanning and finite element simulation, and the corresponding theoretical contour data comes from model slices. The change △ρ of the theoretical polar diameter and the polar diameter after deformation at different angles is:

[0043]

[0044] Where n is the number of coordinate points, A i , c, w and Solved from source data to control the deformation amount of the contour.

[0045] For a contour curve with an accurate expression, its deformed contour can be decomposed into a rotation around the centroid and a translation along the coordinate axis. The process of establishing its error model is to solve the transformation matrix.

[0046] (x,y,z) T =D S D R DT (x',y',z) T +ε (6)

[0047] Where x, y, z are the transformed contour coordinates, x', y' are the original coordinates before transformation, and D S is the scaling matrix, D T is the translation matrix, D R is the rotation matrix, D R Solve from source data.

[0048] Random errors mainly come from uncontrollable factors such as process fluctuations, changes in oxygen content and changes in forming chamber pressure. Therefore, a noise signal ε is introduced into the deviation model, as shown in equations (5) and (6).

[0049] According to equations (1)-(6), the deviation data of each layer of contour data is established and divided equally. The corresponding segmentation points in adjacent layers are connected from top to bottom to establish triangular facets, and all coordinate points are traversed to complete the establishment of the three-dimensional deviation model.

[0050] On the other hand, the present invention also provides a system for model reconstruction of additive manufacturing based on forming errors, including an error model building module, an error calculation module and a three-dimensional deviation model building module;

[0051] The error model building module is used to build an error model based on principle error, mechanical error and random error according to the experimental data of CT scanning or the theoretical data of finite element simulation as the error data in the forming process;

[0052] The error calculation module is used to quantitatively calculate each error in the model, and use each error as compensation data to compensate the original 3D model data, and establish the deviation data of each layer of contour data;

[0053] The three-dimensional deviation model building module is used to divide the deviation data of each layer of contour data into equal parts, connect the corresponding segmentation points in adjacent layers from top to bottom to build triangular facets, and traverse all coordinate points to complete the reconstruction of the three-dimensional deviation model.

[0054] In addition, the present invention can also provide a computer device, including a processor and a memory, the memory is used to store a computer executable program, the processor reads part or all of the computer executable program from the memory and executes it, and when the processor executes part or all of the computer executable program, it can implement the method of additive manufacturing model reconstruction based on forming error based on compressed sensing and center frequency described in the present invention.

[0055] On the other hand, the present invention provides a computer-readable storage medium, in which a computer program is stored. When the computer program is executed by a processor, the method for additive manufacturing model reconstruction based on forming error based on compressed sensing and center frequency described in the present invention can be implemented.

[0056] The computer device may be a laptop computer, a desktop computer or a workstation.

[0057] The processor may be a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), or an off-the-shelf field programmable gate array (FPGA).

[0058] The memory of the present invention may be an internal storage unit of a laptop computer, a desktop computer or a workstation, such as a memory or a hard disk; or an external storage unit, such as a mobile hard disk or a flash memory card.

[0059] Computer-readable storage media may include computer storage media and communication media. Computer storage media include volatile and non-volatile, removable and non-removable media implemented by any method or technology for storing information such as computer-readable instructions, data structures, program modules or other data. Computer-readable storage media may include: read-only memory (ROM), random access memory (RAM), solid-state drive (SSD) or optical disk, etc. Among them, random access memory may include resistance random access memory (ReRAM) and dynamic random access memory (DRAM).

Claims

1. A method for model reconstruction of additive manufacturing based on forming error, characterized in that: The following steps are involved: The experimental data of CT scanning or the theoretical data of finite element simulation are used as the error data in the forming process, and the error model is constructed based on the principle error, mechanical error and random error combined with the error data; Quantitatively calculate each error in the model, use each error as compensation data to compensate the original 3D model data, and establish the deviation data of each layer of contour data. The deviation data of each layer of contour data is equally divided, and the corresponding segmentation points in adjacent layers are connected from top to bottom to establish triangular facets, and all coordinate points are traversed to complete the reconstruction of the three-dimensional deviation model; the error model is specifically: (1) in, ε M is the principle error, ε p1 is the mechanical system error, ε p2 is the molding process error, ε E is a random error, ρ is the polar diameter with the contour centroid as the pole, θ is the polar angle; Principle error E p for: , i =1,2,..., n (2) , j =1,2,..., k (3) (4) In formulas (2)-(4), H is the total height of the model, n is the number of slices, i is the layer number, j is the sequence number of the coordinate point in the closed contour, k is the number of coordinate points in the closed contour, θ is the angle between the normal vector of the triangle mesh and the slice direction, S i For the i The area of ​​the slice contour. When the angle between the triangle and the slice direction is acute, the volume error is positive, otherwise it is negative. In the forming process error, for the contour without accurate function expression, parametric equation is used to model the error data. The source data in the error model establishment process comes from CT scanning and finite element simulation, and the corresponding theoretical contour data comes from model slices; the change of theoretical polar diameter and polar diameter after deformation at different angles is △ ρ for: , i =1,2,..., n (5) In the formula n is the number of coordinate points, A i , c , w and φ i Obtained from the source data, used to control the deformation of the contour. Represents random error; in the forming process error, for the contour curve with an accurate expression, its deformed contour can be decomposed into a rotation around the centroid and a translation along the coordinate axis, and the process of establishing its error model is to solve the transformation matrix; (6) In the formula x , y , z is the transformed contour coordinate, x’ , y’ is the original coordinate before transformation, D S is the scaling matrix, D T is the translation matrix, D R is the rotation matrix, solved from the source data, Represents random error; random error comes from uncontrollable factors such as process fluctuations, changes in oxygen content and changes in forming chamber pressure.

2. The method for additive manufacturing model reconstruction based on forming error according to claim 1, characterized in that: The mechanical system error comes from the coordinate movement during the forming process. Saddle-shaped or pillow-shaped errors will appear in the position far away from the center of the substrate in the XOY plane. The scanning error compensation model is established by double chessboard calibration. The error in the z direction of the mechanical system error mainly comes from the lifting movement of the forming cylinder. The error in the z direction is used as the size compensation data in the z direction.

3. A system for model reconstruction of additive manufacturing based on forming errors, characterized in that: It includes an error model building module, an error calculation module and a three-dimensional deviation model building module; The error model building module uses the experimental data of CT scanning or the theoretical data of finite element simulation as the error data in the forming process, and builds an error model based on the principle error, mechanical error and random error combined with the error data; the error model is specifically: (1) in, ε M is the principle error, ε p1 is the mechanical system error, ε p2 is the molding process error, ε E is a random error, ρ is the polar diameter with the contour centroid as the pole, θ is the polar angle; principle error E p for: , i =1,2,..., n (2) , j =1,2,..., k (3) (4) In formulas (2)-(4), H is the total height of the model, n is the number of slices, i is the layer number, j is the sequence number of the coordinate point in the closed contour, k is the number of coordinate points in the closed contour, θ is the angle between the normal vector of the triangle mesh and the slice direction, S i For the i The area of ​​the layer slice contour, when the angle between the triangle patch and the slice direction is acute, the volume error is positive, otherwise it is negative; in the forming process error, for the contour without an accurate function expression, the parametric equation is used to model the error data, where the source data in the error model establishment process comes from CT scanning and finite element simulation, and the corresponding theoretical contour data comes from the model slice; the change of the theoretical polar diameter and the polar diameter after deformation at different angles ρ for: , i =1,2,..., n (5) In the formula n is the number of coordinate points, A i , c , w and φ i Obtained from the source data, used to control the deformation of the contour. Represents random error; in the forming process error, for the contour curve with an accurate expression, its deformed contour can be decomposed into a rotation around the centroid and a translation along the coordinate axis, and the process of establishing its error model is to solve the transformation matrix; (6) In the formula x , y , z is the transformed contour coordinate, x’ , y’ is the original coordinate before transformation, D S is the scaling matrix, D T is the translation matrix, D R is the rotation matrix, solved from the source data, Indicates random error; random error comes from uncontrollable factors such as process fluctuations, changes in oxygen content and changes in forming chamber pressure; The error calculation module is used to quantitatively calculate each error in the model, and use each error as compensation data to compensate the original 3D model data, and establish the deviation data of each layer of contour data; The three-dimensional deviation model building module is used to divide the deviation data of each layer of contour data into equal parts, connect the corresponding segmentation points in adjacent layers from top to bottom to build triangular facets, and traverse all coordinate points to complete the reconstruction of the three-dimensional deviation model.

4. A computer device, characterized in that: It includes a processor and a memory, the memory is used to store a computer executable program, the processor reads the computer executable program from the memory and executes it, and when the processor executes the computer executable program, it can implement the method for additive manufacturing model reconstruction based on forming errors as described in claim 1 or 2.

5. A computer-readable storage medium, characterized in that: A computer program is stored in the computer-readable storage medium, and when the computer program is executed by a processor, the method for additive manufacturing model reconstruction based on forming errors as described in claim 1 or 2 can be implemented.

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