Numerical control five-axis tool path generation method based on free-form surface model

Abstract

The invention discloses a numerical control five-axis tool path generation method based on a curved surface model, which comprises the following steps of: (1) carrying out discrete processing on the curved surface model to generate a discrete curved surface model consisting of triangular patches; (2) selecting an initial section based on the discrete curved surface model, and generating an initial polyline; (3) generating a pipeline model by taking the obtained polyline as a center line; (4) intersecting the pipeline model and the discrete curved surface model to obtain two new polylines, and selecting a single-side polyline as a new polyline to return to the step (3); (5) repeating the steps (3)-(4), and generating parallel polylines one by one until the whole curved surface is covered; and (6) sequentially connecting all the obtained parallel polylines to form a complete tool path. According to the method, efficient tool path generation is achieved in five-axis numerical control machining of the curved surface model, the tool path direction consistency is ensured, and the smoothness and continuity of the machining path are optimized.

Description

Technical Field

[0001] The present invention belongs to the technical field of numerical control machining and tool path planning, and particularly relates to a five-axis numerical control tool path generation method based on a free-form surface model. Background Art

[0002] In modern manufacturing, numerical control machining technology (CNC) plays a crucial role, especially in fields such as aerospace, automotive, and mold manufacturing that require high-precision machining of complex parts. As an advanced form of numerical control machining, five-axis numerical control machining technology has the advantages of high machining flexibility, excellent precision, and the ability to process complex surfaces, and is particularly suitable for the machining of shell parts in the aerospace field, such as aircraft wings, fuselage shells, engine shells, etc. These complex parts usually have large curvatures, free-form surfaces, and thin-wall structures, requiring high-precision and high-quality machining, and five-axis numerical control machining can perform cutting at multiple angles and directions to meet these requirements.

[0003] However, five-axis machining has extremely high requirements for the generation of tool paths, and it is necessary to accurately analyze and plan complex surface models to ensure machining efficiency and quality. Currently, the numerical control machining of complex surfaces mainly relies on tool path generation technology. The tool path generation method for free-form surfaces as the machining object is the research focus in the field of CAM (Computer-Aided Manufacturing). In the aerospace industry, the manufacturing of complex components such as aircraft wings, fuselage shells, and engine shells usually adopts free-form surface machining technology, which puts forward higher requirements for the accuracy and efficiency of tool path generation.

[0004] In the aerospace field, the manufacturing of complex components such as aircraft wings, fuselage shells, and engine shells requires that the tool path generation technology can handle the surface complexity, surface quality requirements, and machining accuracy of these parts. By discretizing the complex surfaces of these components into mesh models, the tool path generation process can be accelerated without sacrificing accuracy, thus improving machining efficiency. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention proposes a five-axis tool path generation method based on a surface model to solve the defects existing in the prior art.

[0006] To achieve the above object, the present invention adopts the following technical solution: A five-axis tool path generation method based on a surface model, comprising:

[0007] (1) Discretize the surface model to generate a discrete surface model composed of triangular patches;

[0008] (2) Select an initial section based on the discrete surface model to generate an initial polyline (the first polyline);

[0009] (3) Generate a pipeline model with the obtained polyline as the centerline;

[0010] (4) Intersect the pipeline model with the discrete surface model to obtain two new polylines, and select the unilateral polyline as the new polyline and return to step (3);

[0011] (5) Repeat steps (3) to (4) to generate parallel polylines one by one until the entire surface is covered;

[0012] (6) Connect all the obtained parallel polylines in sequence to form a complete tool path.

[0013] In step (1), the discrete surface model composed of triangular patches can be generated by using Delaunay triangulation.

[0014] Preferably, in step (1), when discretizing the surface model, the Delaunay triangulation method is usually used to generate uniform triangular patches; of course, any existing parametric surface discretization method can also be selected.

[0015] Preferably, in step (1), the surface model composed of triangular patches is usually saved in STL format; if there are special requirements for the format in the processing or application scenario, other custom formats can be used for saving.

[0016] In step (2), the method for obtaining the initial section is as follows:

[0017] (2-1) Obtain the boundary box (Boundary Box, generally a three-dimensional cuboid) of the discrete surface model and find the central position of the boundary box;

[0018] (2-2) Obtain the initial section according to the obtained central position;

[0019] (2-3) Find the intersection line of the initial section and the discrete surface model to obtain the initial polyline.

[0020] Preferably, in step (2), according to the central position of the boundary box of the discrete surface model, a plane passing through the central position of the boundary box and parallel to any plane of the boundary box is made, and this plane is used as the selected initial section.

[0021] Preferably, in step (2), the initial section intersects with the discrete free surface in STL format to obtain the initial polyline.

[0022] In step (3), according to the points on the polyline, calculate the lateral step distance of each point under the residual height constraint, and take the minimum value of the lateral step distances of all points as R. Further, in step (3), the method for obtaining the radius of the pipe model is as follows: use the classical residual height model to calculate the curvature of each point of the current polyline, calculate the lateral step distance of each point under the residual height constraint according to the curvature, and take the minimum lateral step distance of all points on the polyline, and this step distance is used as the radius of the pipe model.

[0023] Furthermore, the specific method is as follows:

[0024] According to the classical residual height model, as Figure 2 shown, taking the ball-end mill model as an example, the radius of the ball-end mill is r, and the relationship between the size d of the lateral step distance, the residual height h, and the curvature ρ is as follows:

[0025]

[0026] where: sign is the sign operator, 0 for a plane, 1 for a convex surface, and -1 for a concave surface.

[0027] For the average curvature of the points on the polyline, first solve it through Taubin approximation. On the edges or vertices of the triangular patches to which the points of the polyline belong, find one or more triangular patches corresponding to the edges or vertices of the triangular patch edges, and take the minimum value of the vertex curvatures of all triangular patches as the curvature of the corresponding points on the polyline.

[0028] In step (3), with the extension line of the initial polyline as the center, construct a pipe model, and the pipe radius of each point curvature of the polyline is the set value R. Further, in step (3), the method for obtaining the extension line of the polyline is as follows: for the two end points of the obtained polyline, respectively find the points on the boundary box that are the shortest distance from the end points, and use them as the extension points of the polyline for extension processing, and generate the pipe model with the extended polyline as the center line.

[0029] In step (4), the pipe model intersects with the discrete surface model to generate two new polylines, and select a single-sided polyline based on the surface normal vector and the position relationship.

[0030] More specifically, the method for selecting a single-sided polyline in step (4) is as follows: perform a geometric intersection operation using the pipe STL model and the discrete shell model to generate two new polylines; then,

[0031] (4-1) Take the start point and the end point of the central polyline corresponding to the center line of the pipe model, and form a direction vector of the central polyline from the start point to the end point

[0032] (4-2) Obtain the midpoint of the central polyline, denoted as point A. Traverse the points on the two side polylines to find the points closest to the midpoint. Denote the point on one side as point B and the point on the other side as point C, and obtain the direction vectors of AB and AC. and

[0033] (4-3) Obtain the normal vector of the triangular patch corresponding to the midpoint of the central polyline as the vertex vector of the midpoint.

[0034] (4-5) Calculate the direction vectors of AB and AC respectively. and The cross product results of the direction vectors and then dot multiply the two obtained vectors with the vertex vector of the midpoint respectively; if the result is greater than 0, it is one side; if it is less than 0, it is the other side. After selecting one side, use it as the direction for the subsequent steps.

[0035] Furthermore, in step (4), for the two new polylines (initial new polylines) obtained from the pipe model corresponding to the initial polyline, repeat steps (3) - (4) respectively to generate parallel polylines one by one until the entire surface is covered. After selecting one of the initial new polylines, first obtain all the parallel polylines corresponding to the direction of this side, and then for the other initial new polyline, obtain all the parallel polylines corresponding to the corresponding side of its corresponding direction, and obtain all the parallel polylines.

[0036] In step (5), use the selected polyline to repeat the steps of step (3) to generate a pipe model, and set the corresponding radius value and perform intersection processing with the discrete surface to generate parallel polylines one by one until the entire surface is covered.

[0037] Use the selected polyline to repeat generating the pipe model and intersection processing, and generate parallel polylines layer by layer until the entire surface is covered. The specific method is as follows: Based on the selected single-side polyline, extend both ends appropriately as the center line, and repeat steps (3) - (4) to generate parallel polylines one by one until the entire surface is covered.

[0038] After step (5) is completed, screen the short polylines generated for the surface boundary and connect them with the parallel polylines to form a complete tool path layer. The specific method is as follows:

[0039] The short polyline generated by extracting the boundary through detecting the boundary region of the surface model (formed by the intersection of the obtained parallel polyline and the boundary line of the surface model, and the endpoints of the short polyline are the intersection points of two adjacent parallel polylines) is used to sequentially find one endpoint of the polyline and connect it to the nearest boundary polyline, and then find the other endpoint in the same direction and connect it to the nearest boundary polyline, gradually traversing and connecting all parallel polylines and boundary polylines, so as to form a complete and continuous tool path layer.

[0040] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a tool path generation method based on a discrete surface model. Through Delaunay triangulation and the intersection strategy of the pipe model, it can efficiently handle complex surface structures, significantly improving the uniformity and machining accuracy of tool path generation. By screening the boundary short polylines and efficiently connecting the parallel polylines, the boundary processing strategy is optimized to ensure the consistency of the tool path direction, and at the same time, the continuity and integrity of the tool path are ensured. The present invention can generate five-axis machining tool paths for complex surfaces, is applicable to multi-axis machining scenarios such as aerospace and mold manufacturing, gives full play to the flexibility and high degree of freedom advantages of five-axis CNC equipment, effectively improves machining efficiency, surface quality and machining accuracy, and provides reliable technical support for the machining of complex parts. Brief Description of the Drawings

[0041] Figure 1 It is a flowchart of an embodiment of the present invention.

[0042] Figure 2 It is a schematic diagram of a classic residual height model of an embodiment of the present invention.

[0043] Figure 3 It is a schematic diagram of the surface model in an embodiment of the present invention.

[0044] Figure 4 It is a schematic diagram of the discretized surface model in an embodiment of the present invention.

[0045] Figure 5 It is a schematic diagram of the intersection of the initial plane and the discretized surface in an embodiment of the present invention.

[0046] Figure 6 It is a schematic diagram of generating a polyline by the intersection of the initial plane and the discretized surface in an embodiment of the present invention.

[0047] Figure 7 It is a schematic diagram of the intersection of the pipe model formed by the initial polyline and the discretized surface in an embodiment of the present invention.

[0048] Figure 8 It is a schematic diagram of generating a side offset line by traversing and generating a pipe in a certain direction in an embodiment of the present invention.

[0049] Figure 9Schematic diagram of the bilateral offset line in the embodiment of the present invention.

[0050] Figure 10 is Figure 9 Schematic diagram of the partial enlarged structure.

[0051] Figure 11 Schematic diagram of the complete tool path formed by connecting the short multi-segment lines generated by extracting the boundary and the offset line in the embodiment of the present invention. Detailed implementation manners

[0052] To make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings of the specification.

[0053] As Figures 1 to 9 shown, a method for generating a five-axis CNC surface machining tool path includes the following steps:

[0054] S10. Discretize the surface model to generate a surface model composed of triangular patches.

[0055] Among them, the processing of the surface model can use the Delaunay triangulation method to generate uniform triangular patches, and the generated discrete surface model can be exported as an STL format file.

[0056] In this step, read the surface model file, and the supported formats include IGES, STEP or other CAD file formats. Parse it into the form of surface parameters (such as control points, basis functions, and parameter ranges), parse the model file, and extract the control points, basis functions, and parameter range information of the surface.

[0057] Parse the model file, extract the control points, basis functions, and parameter range information of the surface model. According to the parameter form of the surface model, generate a sampling point set according to the set discrete density, perform Delaunay triangulation on the sampling point set to generate a uniform triangular grid, and map the triangulation result from the UV parameter space to the three-dimensional space to form a surface model composed of triangular patches;

[0058] Store the generated triangular patch model in the STL file format for subsequent tool path generation and CNC machining.

[0059] S20. Select an initial section based on the discrete surface model to generate the first multi-segment line (i.e., the initial multi-segment line). The specific method is as follows:

[0060] Obtain the boundary box of the discrete surface model and find the center position of the boundary box;

[0061] According to the central position of the bounding box, a plane passing through the central position of the bounding box and parallel to any plane of the bounding box is made, and this plane is used as the selected initial section;

[0062] The initial section is intersected with the discrete free-form surface in STL format to obtain an initial polyline.

[0063] S30. According to the points on the polyline, calculate the lateral step distance of each point under the residual height constraint, and take the minimum value of the lateral step distances of all points as R. With the extension line of the currently obtained polyline as the center, a pipeline area is constructed, and the pipeline radius is the set value R;

[0064] First, use the classical residual height model (such as Research on the Methods and Key Technologies of Computer Aided Manufacturing of T-Spline Surfaces (Gan Wenfeng), Zhejiang University, 2014, doctoral thesis) to calculate the curvature of each point on the initial polyline, calculate the lateral step distance of each point under the residual height constraint according to the curvature, and take the minimum lateral step distance of all points on the central polyline as R.

[0065] Then, obtain the extension line of the polyline. The method is to find the points on the bounding box that are closest to the two endpoints of the polyline (the initial polyline or the current polyline) as the endpoints of the extension line, and the extension line of the polyline.

[0066] Finally, after obtaining R and the center line: with the extension line of the polyline as the center and the obtained radius R as the pipeline radius of each point curvature of the polyline, construct a pipeline model, generate a pipeline model with a radius of R, and save it in STL format.

[0067] S40. The pipeline model intersects with the discrete surface model to generate two new polylines, and select the unilateral polyline based on the surface normal vector and the position relationship;

[0068] The specific method is as follows:

[0069] Perform a geometric intersection operation using the pipeline STL model and the discrete surface model to generate two new polylines;

[0070] Take the starting point and the ending point of the central polyline, and form a direction vector of the central polyline from the starting point to the ending point

[0071] Take the middle point of the central polyline, denoted as point A, traverse the points on both sides of the polyline, find the point closest to the middle point, the points on one side are denoted as point B, and the points on the other side are denoted as point C, and respectively set and as the direction vectors of the polylines on both sides;

[0072] Take the vector of the patch corresponding to the middle point of the central polyline as the vertex vector of the middle point

[0073] Calculate and respectively with the cross product result of the vectors, and then respectively dot-multiply the two obtained vectors with the vectors. If the result is greater than 0, it is on one side; if it is less than 0, it is on the other side. After selecting one side, use it as the direction for subsequent steps.

[0074] S50. Use the selected polyline to repeatedly generate the pipeline model and intersection processing, and generate parallel polylines layer by layer until the entire surface is covered; the specific method is as follows:

[0075] Based on the selected one-sided polyline, appropriately extend both ends as the center line, and repeat steps S30 - S50 to generate parallel polylines that meet the residual height constraint one by one until the entire surface is covered.

[0076] S60. Screen the short polylines generated for the surface boundary and connect them with the parallel polylines to form a complete tool path layer. The specific method is as follows:

[0077] Detect the intersection points of the boundary region of the surface model and the parallel polylines, and extract the short polylines generated by the boundary;

[0078] Successively find the boundary short polyline closest to one endpoint of the polyline and connect them. Then find the boundary short polyline closest to the other endpoint and in the same direction, and gradually traverse the entire parallel polyline until all parallel polylines are connected to form a complete tool path.

[0079] In this embodiment, in step S10, as Figure 3 、 Figure 4 shown, a surface model in STEP format ( Figure 3 shown) is generated into uniform triangular patches through the Delaunay triangulation method, and the generated surface model composed of triangular patches is usually saved in STL format.

[0080] In this embodiment, in step S20, as Figure 5 、 Figure 6 shown, according to the central position of the boundary box of the discrete surface model, make a plane passing through the central position of the boundary box and parallel to any plane of the boundary box, and this plane is used as the selected initial section; the initial section intersects with the discrete free surface in STL format to obtain the initial polyline.

[0081] In this embodiment, in step S30, at both ends of the initial or current polyline, respectively find the points on the boundary box that are the shortest distance from the endpoints, and use them as the extension points of the initial polyline to obtain the extended line of the initial or current polyline. Use the extended polyline as the center line to generate the pipeline model; as Figure 7As shown (in the figure, the radius of the pipe model is enlarged for clearer display), the pipe model intersects with the discrete surface model, generating two new poly-lines, and a unilateral poly-line is selected based on the surface normal vector and positional relationship. The specific method is as follows:

[0082] Perform a geometric intersection operation using the pipe STL model and the discrete shell model (surface model) to generate two new poly-lines;

[0083] Take the starting point and ending point of the central poly-line, and form the direction vector of the central poly-line from the starting point to the ending point

[0084] Take the midpoint of the central poly-line, denoted as point A. Traverse the points on both sides of the poly-line to find the point closest to the midpoint. The point on one side is denoted as point B, and the point on the other side is denoted as point C. Let and be the direction vectors of the poly-lines on both sides;

[0085] Take the vector of the patch corresponding to the midpoint of the central poly-line as the vertex vector of the midpoint

[0086] Calculate and The cross product results with vector respectively, and then dot product the two obtained vectors with vector respectively. If the result is greater than 0, it is one side; if it is less than 0, it is the other side. After selecting one side, it is used as the direction for subsequent steps.

[0087] In this embodiment, in step S50, as shown in Figure 8 、 Figure 9 , use the selected poly-line to repeat generating the pipe model and intersection processing, and generate parallel poly-lines layer by layer until the entire surface is covered. The specific method is as follows:

[0088] Based on the selected unilateral poly-line, extend both ends appropriately as the center line, and repeat steps S30 and S40 to generate parallel poly-lines one by one until the entire surface is covered.

[0089] For the two poly-lines (poly-line Ia and poly-line Ib) obtained by intersecting the pipe model corresponding to the initial poly-line (or the first poly-line), select the poly-line in one direction (such as poly-line Ia), extend it, and repeat S30 and S40 until the generation of the poly-lines on the corresponding side of this direction is completed, as shown in Figure 8 . Then perform the same operation for the poly-line in the other direction (such as poly-line Ib), and repeat S30 and S40 until the generation of the poly-lines on the corresponding side of this direction is completed. Finally, obtain the parallel poly-lines covering the entire surface, as shown in Figure 9as shown

[0090] In this embodiment, in step S60, as Figure 10 and Figure 11 shown, the short polylines generated for the curved surface boundary are screened and connected to the parallel polylines to form a complete tool path layer. The specific method is as follows:

[0091] The short polylines 101 generated by extracting the boundary by detecting the boundary region of the surface model (i.e., formed by the intersection of the surface model boundary and the parallel polylines) are found. Starting from one side of the parallel polylines, the endpoints of the parallel polylines 102 are sequentially connected to the nearest boundary short polylines, and then the other endpoints are found and connected to the nearest boundary short polylines in the same direction, gradually traversing and connecting all the parallel polylines and the boundary short polylines, so as to form a complete and continuous tool path layer.

Claims

1. A numerical control five-axis tool path generation method based on a surface model, characterized in that Including: (1) Discretize the surface model to generate a discrete surface model composed of triangular patches; (2) Select an initial section based on the discrete surface model to generate an initial polyline; (3) Generate a pipe model with the obtained polyline as the centerline; (4) Intersect the pipe model with the discrete surface model to obtain two new polylines, and select one-sided polyline as the new polyline and return to step (3); (5) Repeat steps (3) to (4) to generate parallel polylines one by one until the entire surface is covered; (6) Connect all the obtained parallel polylines in sequence to form a complete tool path.

2. The method for generating a numerically controlled five-axis tool path based on a surface model according to claim 1, characterized in that, In step (2), the method for obtaining the initial section is as follows: (2-1) Obtain the bounding box of the discrete surface model and find the center position of the bounding box; (2-2) Obtain the initial section according to the obtained center position; (2-3) Obtain the intersection line of the initial section and the discrete surface model to obtain the initial polyline.

3. The method for generating a numerically controlled five-axis tool path based on a surface model according to claim 2, wherein, In step (2-2), the initial section is a plane passing through the center position and parallel to any plane of the bounding box.

4. The method for generating a numerically controlled five-axis tool path based on a surface model according to claim 1, wherein In step (3), the method for obtaining the radius of the pipe model is: use the classical residual height model, calculate the curvature of each point of the current polyline, calculate the lateral step distance of each point under the residual height constraint according to the curvature, take the minimum lateral step distance of all points on the polyline, and this step distance is used as the radius of the pipe model.

5. The method for generating a numerically controlled five-axis tool path based on a surface model according to claim 1, wherein In step (3), for the two end points of the obtained polyline, find the points on the bounding box that are closest to the end points respectively, and use them as the extension points of the polyline for extension processing. Generate the pipe model with the extended polyline as the centerline.

6. The method for generating a numerically controlled five-axis tool path based on a surface model according to claim 1, wherein In step (4), for the two new polylines obtained from the pipe model corresponding to the initial polyline, repeat steps (3) to (4) respectively to generate parallel polylines one by one until the entire surface is covered.

7. The method for generating a CNC five-axis tool path based on a surface model according to claim 1, wherein The method for selecting one-sided polyline in step (4) is as follows: (4-1) Use the starting point and ending point of the central polyline corresponding to the centerline of the pipe model, and form the direction vector of the central polyline from the starting point to the ending point; (4-2) Obtain the middle point of the central polyline, denoted as point A, traverse the points on the polylines obtained by intersecting both sides, find the point closest to the middle point, the points on one side are denoted as point B, and the points on the other side are denoted as point C, and obtain the direction vectors of AB and AC; (4-3) Obtain the normal vector of the triangular patch corresponding to the middle point of the central polyline as the vertex vector of the middle point; (4-5) Calculate the cross product results of the direction vectors of AB and AC with the direction vector of the central polyline respectively, and then perform dot product of the two obtained vectors with the vertex vector of the middle point respectively; if the result is greater than 0, it is one side; if it is less than 0, it is the other side, and select one of the sides as the one-sided polyline.

8. The method for generating a numerically controlled five-axis tool path based on a surface model according to claim 1, wherein Generate the discrete surface model composed of triangular patches using Delaunay triangulation.

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