Additive manufacturing processing path generation method based on implicit function

Abstract

The invention relates to an implicit function-based additive manufacturing processing path generation method, which comprises the following steps of: pre-processing a filling area according to the process characteristics of an LPBF, and determining the boundary of a processing area; converting a generation problem of a filling pattern into a solving problem of an implicit function contour line, and constructing a track construction function based on curve evolution; a Marking Square algorithm is utilized to solve and extract a track construction function in the preprocessed filling domain, and a processing track is generated; corresponding machining process parameters are given to the machining track, a single machining path capable of being recognized by LPBF equipment is formed, a complete machining path file is combined to be used by additive manufacturing equipment, the traditional CAD modeling, STL conversion and slicing processes are omitted, multiple discrete errors caused by STL format conversion and slicing are avoided, the machining path is directly driven by a design function, and the machining efficiency is improved. High consistency of a manufacturing result and a design model can be ensured, and data processing time and computing resource consumption can be greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of additive manufacturing, in particular to an additive manufacturing processing path generation method based on implicit functions. BACKGROUND

[0002] At present, the mainstream processing path generation of LPBF process depends on STL file format; the process is a "top-down" mode, which first needs to complete the three-dimensional geometric modeling of the part (such as generating a CAD model containing a large number of point cells), then converts the model into an STL triangular mesh file, then slices the STL model to obtain a two-dimensional contour, and finally fills the two-dimensional contour with paths (such as parallel lines, zigzag lines, etc.), to generate the final processing path. Among them, the top-down AM process data processing is inefficient, and for a point array structure containing a large number of small and complex cells, the calculation amount of generating its complete CAD and STL model is huge, and the subsequent slicing and path filling process is also time-consuming and long, which is difficult to meet the demand of efficient data processing. Secondly, from the CAD model to the STL model (triangularization discretization), to the slicing contour (polygonization), and finally to the processing path, there are multiple geometric discretization and format conversion in the process, which will cause multiple precision loss, and the final generated processing path is difficult to keep consistent with the original design model. For complex patterns such as TPMS patterns, the traditional LPBF method based on explicit filling is difficult to directly generate, which limits the manufacturing of high-performance point array structures. SUMMARY

[0003] The purpose of the present application is to provide an additive manufacturing processing path generation method based on implicit functions, which constructs a trajectory construction function and solves its contour to generate a path, and discards the traditional model discretization and slicing process, thereby improving the manufacturing precision and data processing efficiency of complex structures (such as TPMS point arrays) from the root.

[0004] To solve the above technical problems, the present application adopts the following technical scheme: an additive manufacturing processing path generation method based on implicit functions, comprising the following steps: S1, according to the process characteristics of LPBF, pre-processing the filling area to determine the boundary of the processing area; S2, converting the generation problem of the filling pattern into the solving problem of the contour of the implicit function, and constructing a trajectory construction function based on curve evolution; S3, using the Marching Squares algorithm to solve and extract the trajectory construction function in the pre-processed filling domain to generate the processing trajectory; S4, assigning corresponding processing parameters to the processing trajectory to form a single processing path recognizable by the LPBF device, and combining into a complete processing path file for use by the additive manufacturing device.

[0005] Preferably, the preprocessing includes surface transformation and contour offset.

[0006] Preferably, the trajectory constructor is: ; ; ; in, The largest fill line number. , , Indicates the evolved first The level set function of the filled line, To fill the baseline, Let L be the level set function of the baseline. Let x be the spacing of the fill lines, and x be the physical coordinates in Euclidean space. , This is the area for graphic design.

[0007] Preferably, the arctangent function is used to construct the trajectory. After normalization, the optimized trajectory constructor is obtained as follows: ; in, Construct a trajectory constructor by solving... To obtain the processing trajectory of the lattice structure.

[0008] Preferably, in S3, the Marching Squares algorithm is used to perform implicit functions within the preprocessed filled domain. The zero contour lines are solved and extracted, including: S31. Mesh the planar design domain D of the trajectory constructor; S32. Calculate the function value for each grid node using the trajectory constructor, and binarize it using the contour line values. For the 0 contour line, use the Heaviside function, i.e.: ; in, , For the Heaviside function; S33. Create approximate contour lines for the trajectory constructor in the grid, i.e., the outline of the designed graphic. S34. Referencing the original nodal function values, calculate the intersection coordinates using linear interpolation, and then connect them to form the final approximate contour lines.

[0009] Preferably, in S4, the processing technology includes laser power P and scanning speed v, and based on the processing parameters, a single processing path recognizable by the LPBF device is formed.

[0010] Beneficial effects: (1) This invention transforms the problem of generating filling patterns into the problem of solving implicit function contour lines, constructs a trajectory constructor based on curve evolution, and directly defines the geometry of the processing path using the trajectory constructor based on implicit functions. It skips the traditional CAD modeling, STL conversion and slicing process, avoids multiple discrete errors caused by STL format conversion and slicing, and the processing path is directly driven by the design function, which can ensure a high degree of consistency between the manufacturing result and the design model. It is especially suitable for precision structures such as micro-lattice, saves the process of building complex three-dimensional models and large STL files, and can directly generate processing paths, greatly reducing data processing time and computing resource consumption.

[0011] (2) The present invention introduces the Marching Squares algorithm in the trajectory constructor to solve the contour lines of the implicit function, transforming the complex pattern filling problem into a reliable numerical calculation problem, thereby generating complex curve paths. It can handle complex filling patterns defined by implicit functions that are difficult to generate by traditional methods, thus expanding the range of lattice structures that can be manufactured.

[0012] (3) The present invention forms a complete “bottom-up” processing path driven data processing paradigm, realizing direct and seamless connection from design to manufacturing path, and is especially suitable for additive manufacturing preprocessing of complex graphics such as micro-matrix and TPMS structure. Attached Figure Description

[0013] Figure 1 This is a flowchart of the additive manufacturing process path generation method based on implicit functions according to the present invention; Figure 2 This is a graph of the level set function in an embodiment of the present invention; Figure 3 This is a diagram of the MS algorithm lookup table in an embodiment of the present invention; Figure 4 This is a diagram illustrating the evolution of the trajectory constructor function for the filling line in an embodiment of the present invention. Figure 5 This is a contour plot of the constructor function 0 for the filled line trajectory at different times in an embodiment of the present invention; Figure 6 The Schwarz-P surface in this embodiment of the invention ( Evolution diagram of the planar trajectory constructor function; Figure 7 The Schwarz-P surface in this embodiment of the invention ( Evolution diagram of the planar trajectory constructor function; Figure 8 This is a diagram showing the evolution of the plane filling lines at different heights on the Schwarz P surface in an embodiment of the present invention. Detailed Implementation

[0014] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0015] Example: Figure 1 As shown, an additive manufacturing process path generation method based on implicit functions includes the following steps: First, the filling area is preprocessed according to the process characteristics of LPBF, with the goal of determining the boundary of the processing area. This step is consistent with the LPBF processing path generation method based on explicit filling, and mainly includes two parts: plane transformation and contour offset. Then, an implicit function construction method based on curve evolution is adopted. This function transforms the problem of generating the filling pattern into solving the problem of implicit function contour lines, thus constructing a trajectory constructor. refer to Figure 2 As shown, for the level set function in high-dimensional Euclidean space Different level set parameters You can extract a set of boundary curves or surfaces on a function. ,Right now: ; Where x is the physical coordinate in Euclidean space. , It is a curve containing (or curved surface) space; taking a two-dimensional plane as an example, the curve divides the two-dimensional plane into three parts: the curve The inner region enclosed by the curve and the outer region of the curve. Its geometric model satisfies the formula: ; For closed curves and the structural domains they enclose , level set function It can be represented by the Signed Distance Function (SDF), and its expression is as follows: ; in, , For the boundary The point on, For a planar design domain; for a non-closed curve L, the structural domain. It does not exist, that is Therefore, the above formula can be modified as follows: ; in, For the fill baseline; for the fill lines, to ensure print density, equidistant lines are used, therefore the level set function of a single fill trajectory can be described as: ; in, . Indicates the evolved first The level set function of the filled line, Let L be the level set function of the baseline. Hatching space is the spacing between the fill lines. In the domain The evolution result is a closed curve, but in the planar design domain D, because D is a finite domain, The evolution result may be divided into multiple curve segments by this domain; therefore, the level set function of the overall filled line That is, the trajectory constructor is: ; in The largest fill line number. ; In another embodiment, the arctangent function is used to construct the trajectory. After normalization, the optimized trajectory constructor is obtained as follows: ; in, Construct a trajectory constructor by solving... To obtain the machining trajectory of the lattice structure; while the parameters such as fill angle and fill type used in the STL-based data processing method are converted into the construction of the baseline L; Next, using the Marching Squares algorithm, implicit functions are processed within the preprocessed filled domain. zero contour lines ( The solution and extraction are performed; the calculation steps are as follows: Mesh the planar design domain D of the trajectory constructor; The function value for each grid node is calculated using the trajectory constructor, and then binarized using the contour values. For the 0 contour, the Heaviside function is used, i.e.: ; in, , For the Heaviside function; Utilize Figure 3 The MS algorithm lookup table creates implicit functions in the grid. The approximate contour lines, i.e., the outlines of the designed graphic. Figure 3 A solid point represents the function value at that point. Hollow points represent the function values ​​at those points. ; Referencing the original nodal function values, the coordinates of the intersection points are calculated using linear interpolation, and then connected to form the final approximate contour lines; Taking the 0 contour line as an example, if the square side Intersects the 0 contour line at Point, then The interpolation formula for a point is shown below: ; Finally, corresponding processing parameters are assigned to the processing trajectory to form a single processing path recognizable by the LPBF equipment, and these paths are combined into a complete processing path file for use by the additive manufacturing equipment. In this embodiment, the processing technology includes laser power... P Based on the scanning speed v and the processing parameters, a single processing path recognizable by the LPBF device is formed. .

[0016] In a specific case study: taking parallel lines and the Schwarz P structure in TPMS as examples, the trajectory construction function and the evolution results of the filled line are illustrated respectively; taking parallel lines with an interval of 0.5mm as an example, Figure 4 The evolution of the level set function for the parallel line filling type is given, when At this point, the zero contour lines of the level set function no longer change; the filled lines can be obtained by solving for the zero contour lines of the final level set function using the MS algorithm. The results of the filled lines at different times are as follows: Figure 5 As shown. For a given Schwarz P surface: ; In this case, Select respectively and The trajectory lines on two planes undergo horizontal set function evolution; through Figures 4-5 As shown, the zero contour lines extracted by the level set function evolution and Marching-Squares algorithm have precise and controllable trajectory spacing and good continuity. The manufacturing results are strictly consistent with the design parameters (such as h=0.5mm), avoiding the distortion breakpoint problem caused by STL mesh or slicing algorithm in traditional methods.

[0017] Its evolution process is as follows Figure 6 and Figure 7 As shown, the 0 contour line at the final moment, i.e., the filled line, is as follows: Figure 8 As shown, Figure 8 (a) is flat, Figure 8 (b) is The planar structure successfully generated complex periodic trajectories of the Schwarz P type, breaking through the limitation of traditional explicit filling that can only handle straight / zigzag lines. It transformed the difficult-to-manufacture TPMS structure into an implicit function that can be directly solved, expanding the boundaries of the topology that can be manufactured by lattice structures, and ensuring the conformal accuracy required for mechanical properties.

[0018] The embodiments of the present invention have been described in detail above with reference to the examples. However, the present invention is not limited to the above embodiments. For those skilled in the art, after learning the contents described in the present invention, several equivalent changes and substitutions can be made without departing from the principle of the present invention. These equivalent changes and substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A method for additive manufacturing process path generation based on implicit functions, characterized by: The method comprises the following steps: S1, preprocessing the filling area according to the process characteristics of LPBF, and determining the boundary of the processing area; S2, converting the generation problem of the filling pattern into the solving problem of the implicit function contour, and constructing a trajectory construction function based on curve evolution; S3, using the Marching Squares algorithm to solve and extract the trajectory construction function in the preprocessed filling area to generate the processing trajectory; S4, assigning corresponding processing parameters to the processing trajectory to form a single processing path recognizable by the LPBF device, and combining into a complete processing path file for use by the additive manufacturing device.

2. The method of claim 1, wherein: The preprocessing includes face transformation and contour offset.

3. The method of claim 1, wherein: The trajectory construction function is: ； ； ； wherein, is the largest filling line index, , , denotes the level set function of the th filling line after evolution, is the filling base line, is the level set function of the base line L, is the distance of the filling line, x is the physical coordinate in the Euclidean space, , is the design domain.

4. The method of claim 3, wherein: Using an arctangent function for the trajectory constructor The normalized trajectory constructor is obtained as follows: ； wherein is the trajectory constructor, the processing trajectory of the dot matrix structure is obtained by solving .

5. The method of any of claims 1-4, wherein: In S3, the zero level set of the implicit function is solved and extracted in the preprocessed filled domain by using the Marching Squares algorithm, including: S31, meshing the plane design domain D of the trajectory construction function; S32, calculating the function value of each grid node using the trajectory construction function, and binarizing it using the contour value, for the 0 contour, using the Heaviside function, that is: ； wherein , H is the Heaviside function; S33, creating an approximate contour line of the trajectory construction function in the grid, that is, the contour line of the design graph; S34, referring to the original node function value, and calculating the intersection coordinates using linear interpolation, and then connecting to the final approximate contour line.

6. The method of claim 1, wherein: In S4, the machining process includes laser power P and scanning speed v, and based on the machining process parameters, a single machining path recognizable by the LPBF device is formed .

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