CN104331555A - Slicing processing method aiming at non-closed STL model with boundaries - Google Patents

Abstract

The invention discloses a 3D printing-oriented slice processing method for a non-closed STL model with boundaries. The method includes the following steps: extracting point, edge and surface information of triangles in the STL model and establishing the topological relationship among them; extracting all boundary edges according to the boundary edge judgment rules; performing layered slice processing on the non-closed grid to obtain the non-closed grid Two-dimensional polygon; path optimization is performed on the printable inner and outer contour lines after polygon offset processing to reduce empty travel; the general Gcode file is output from the slice file for 3D printers to read and print. The invention proposes a slicing method for non-closed STL models from the perspective of boundary extraction for the first time, breaking the shackles of only closed STL models in traditional 3D printing, and realizing non-closed STL models with boundaries Slicing processing enables non-closed STL models to be printed directly.

Description

A slice processing method for non-closed STL models with boundaries

technical field

The invention relates to the field of computer integrated manufacturing, in particular to a slice processing method for non-closed STL models with boundaries.

Background technique

3D printing technology is a cutting-edge and leading emerging technology, especially suitable for small batch, personalized, complex structure and expensive raw material manufacturing. With the development of 3D printing technology, traditional production methods and production processes will undergo profound changes, and industries such as design, architecture, aerospace, medicine, and education will also be profoundly affected. "The Economist" magazine called 3D printing technology "an important symbol of the third industrial revolution" in 2012, and believed that it is an important opportunity to promote a new round of industrial revolution, which has attracted widespread attention from all over the world.

Fused Deposition Modeling (Fused Deposition Modeling) 3D printing technology is a kind of 3D printing technology, which adopts the principle of discrete/accumulation, and directly manufactures a 3D model into a 3D entity under the control of a computer. The basic principle is that the heating nozzle heats and melts the thermoplastic polymer material under the control of the computer, so that it is extruded from the nozzle in a molten state, and is formed layer by layer by the self-bonding of the high-temperature extruded wire. Among them, the tasks processed by the computer are: slice processing and instruction transmission. The slicing process is to intersect the STL grid model in layers to obtain a 2D outline that can be printed, and then plan the printing path reasonably. Command transmission is to transmit this series of actions to the hardware and provide a control interface to control other functions. Mainstream commercial 3D printing client software, such as Slic3r and Makeware, have integrated these two functional modules, the core of which is the slicing processing module (slicing engine), and the slicing algorithm for STL models is the key to slicing processing.

Existing slicing algorithms require that the input model must be a closed triangular mesh, and cannot directly slice a non-closed triangular mesh. However, in practical applications, some models that have been scanned, modeled, edited and modified, such as cloth, leaves, and segmented local models, are a class of non-closed STL (STereo Lithography) models with boundaries. The input is an unclosed STL model, which is directly sliced, and the generated slice files can be actually printed, which is of great significance for promoting the popularization and application of 3D printing.

Contents of the invention

In order to solve the problem that the existing slice processing algorithm restricts the input model to be a closed triangular mesh, the present invention provides a slice processing method for non-closed STL models with boundaries, which enables slice processing to generate non-closed STL models through boundary extraction. Closed two-dimensional polygon, and according to the forming characteristics of the non-closed STL model, the path optimization of the inner and outer contour lines of the two-dimensional polygon after offset processing is carried out to improve the forming efficiency.

The technical scheme that the present invention takes is as follows:

A slice processing method for non-closed STL models with boundaries, comprising the following steps:

Step 1, extracting the point, edge and surface information of the triangular patch in the STL model, and establishing the topological relationship between the point, edge and surface information;

The data structures of the points, edges and faces of the topological relationship are as follows:

The point data structure includes the point coordinates and the index value of the surface adjacent to the point;

The surface data structure includes the index value of the adjacent point and the index value of the adjacent surface;

The edge data structure includes the index value of the edge, the index value of the adjacent surface of the edge and the index value of two adjacent points.

Step 2. Using the topological relationship, extract all the boundary edges of the STL model according to the boundary edge judgment rules;

①Traverse all the edges of the triangular facets, according to the judgment rules of the boundary edge, if the number of adjoining triangular faces of an edge is 1, it is the boundary edge;

②Restore all the extracted boundary edges according to the data structure of boundary edges, so as to facilitate search and access.

The boundary extraction rules are:

Let the triangular mesh surface be M=(v _i ,v _j ,…v _n ), any vertex in M is v _i =( _xi ,y _i , _zi ), if two of the triangular mesh surface M The edge edge(v _i , v _j ) connected by vertices is the edge of a triangular patch Δv _i v _j v _k , then the edge edge(v _i , v _j ) is called the adjacent edge of Δv _i v _j v _k . Let L(v _i ,v _j ) represent the set of all triangular faces containing edge(v _i ,v _j ). For an edge edge(v _i , v _j ), the number of its adjacent triangular faces is represented by |L(v _i , v _j )|. An edge is a boundary edge if the number of adjacent triangles associated with it is 1. If the number of adjacent triangles associated with an edge is 2, it is called an inner edge. At the same time, the two vertices of the boundary edge are boundary points, and a triangle with one or two boundary points is called a boundary triangle.

The expression of the boundary extraction rule is:

BoundaryEdge: {edge(v _i ,v _j )|if:|L(v _i ,v _j )|=1},

Among them, x _i , y _i , z _i are the coordinates of vertex v _i ; v _i , v _j ,...v _n represent points on the triangular mesh model in space;

Edge(v _i ,v _j ) is the adjacent edge of Δv _i v _j v _k , L(v _i ,v _j ) represents the set of all triangular patches containing edge(v _i ,v _j ), |L( v _i , v _j )|indicates the number of adjacent triangular faces, if the number of adjacent triangular faces of an edge is 1, it is a boundary edge.

Step 3. Perform layered slice processing on the non-closed grid to obtain a non-closed two-dimensional polygon, which specifically includes the following steps:

①According to the slicing accuracy, obtain the total number of slicing layers n and all slicing planes z _i (i=1,2...n) of the model;

②Read a triangle surface of the STL model, according to the maximum value z _max , the minimum value z _min and the slice precision of the z coordinates of each point of the triangle, inversely calculate the K slice planes z _j that intersect the triangle, 1≤j≤n ;

③ Obtain the slice segment where the slice plane intersects the triangle surface, and add indication information for the slice segment to indicate whether the vertex of the slice segment is on the boundary edge: read an intersecting slice plane z _j and calculate the intersection point, and obtain a For slice fragments (the line segment where the slice plane intersects the triangle surface, a fragment data structure needs to be established), add the instruction information BorderFlag for the slice fragment. According to the patch index of the triangle, find out whether there is a boundary edge belonging to the triangle patch in the boundary edge set. If it exists, calculate whether there is a fragment vertex on the border edge, and set BorderFlag to True if it is on the border edge, or set it to False if it is not. If it does not exist, BorderFlag is directly set to False;

Among them, obtaining slice fragments includes the following steps:

(a) The direction D of the slice segment is determined by the vector product of the layer direction Z and the normal vector N of the triangle:

D=Z×N

Among them, Z is the layering direction, and N is the normal vector of the triangle patch;

The vertices of the slice segments are sequentially connected to form a two-dimensional polygon, and the two-dimensional polygon (two-dimensional polygon outline) is a polygon outline formed after the intersection of the slice plane and the triangular mesh model in space.

(b) Calculation of the intersection point of the layered plane (slicing plane) and the triangular patch:

P(t)=p+t(q-p), t∈[0,1]

$\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}$

Among them, Z=h is the layered plane height, p=(x _p ,y _p ,z _p ), q=(x _q ,y _q ,z _q ) are the two vertices of one side of the triangle, z _q means Cartesian The Z coordinate of point p=(x _p , y _p , z _p ) in the space coordinate system; z _p represents the Z coordinate of point q=(x _q , y _q , z _q ) in the Cartesian space coordinate system.

The intersection points of the layering plane and the triangle patches are the intersection points of the slice plane and each triangle patch.

(c) The data structure of the slice segment obtained after triangle intersection is:

The data structure of a slice segment includes the segment start point, face index, whether the segment has been added to a polygon, and the boundary segment flag.

④ Recording step ③ The index information of the triangle patch to which the slice segment belongs, traverse to obtain all the slice segments of K slice planes and triangle faces: if the calculation of the intersection between K slice planes and the triangle face is completed, go to the next step ;Otherwise go to ②, read the next plane that intersects with the triangle;

⑤ Store all intersecting slice fragments between the slice plane and the triangle facet by layer: store all the intersecting slice fragments of the triangle facet by layer, and turn to ①; if all the triangle facets have been intersected and processed, go to the next step;

⑥Traverse the indication information of all slices and obtain the initial connection point of the two-dimensional polygon: read all the slices of the i=i+1 layer (starting from i=0), and judge whether there is a BorderFlag in this layer whose BorderFlag is True fragment. If it exists, take out the segment whose BorderFlag is True in the direction of the contour line, and set the triangle patch to which the segment belongs as the current patch; if not, it means that the layer is closed, and take out any slice segment in the direction of the contour line , and set the triangular patch to which the fragment belongs as the current patch;

⑦ Judging whether there is a slice fragment on the adjacent surface: read an adjacent surface of the current patch, and judge whether there is a fragment of the i-th layer on the adjacent surface. If it does not exist, go directly to ⑧; if it exists, judge whether the segment has been added to the polygon. If it has been added to the polygon, turn to ⑧; if it has not been added to the polygon, add the segment to the polygon, and set the patch as the current patch, turn to ⑨;

⑧Traverse all the adjacent faces to see if there are slices; judge whether the adjacent faces have been traversed, if not, go to ⑦; if traversed, go to the next step;

⑨When multiple vertices of a layer slice segment appear in pairs on the boundary edge, use the triangular face where the slice segment is located as the indication information is true as the starting face to connect the two-dimensional polygon: judge the segment indication in the adjacent face Information whether BorderFlag is True. If it is not True, execute the next step; if it is True, judge whether there is a next segment with BorderFlag=True in the direction of the contour line. If it exists, set the segment as the current patch, and go to ⑦; if it does not exist, perform the next step;

⑩ Traversing all slice layers, each layer forms a two-dimensional polygon: judge whether to traverse all segments of this layer. If the traversal is not completed, go to ⑦; if the traversal is completed, store all non-closed polygons or closed polygons of this layer. Determine whether i≤n, if so, go to ⑥, otherwise the algorithm ends.

Step 4. Perform path optimization on the printable inner and outer contour lines after polygon offset processing to reduce empty travel. The method includes the following steps:

① Use the polygon offset processing library to perform polygon offset processing (Offset) on the generated two-dimensional polygons to generate printable inner and outer contours;

② Perform path optimization on the generated printable inner and outer contours, where the path optimization strategy is:

A. The scanning directions of adjacent contour lines in the same layer are opposite;

B. The order of scanning the contour lines of adjacent layers is reversed;

C. The scanning directions of the same contour of adjacent layers are opposite.

Step 5. Output the general Gcode file from the slice file for reading and printing by the 3D printer.

Preferably, in step 2, the data structure of the boundary edge is composed of: the data structure of the boundary edge includes: the index value of the vertex at one end of the boundary edge, the index value of the vertex at the other end of the boundary edge, and the index of the patch to which it belongs.

Preferably, the data structure of intersecting slice fragments stored by layer in Step 5 of Step 3 includes a collection of fragments and fragments and corresponding face indexes of each layer.

The present invention adopts a slicing method based on topological information, solves the problem of slicing processing of a non-closed STL model with boundaries from the perspective of boundary information extraction, and breaks the existing slicing processing algorithm that can only be processed for closed STL model slices limited. From the perspective of improving the molding efficiency, the present invention adopts a contour scanning strategy different from the closed STL model, and optimizes the contour scanning path according to the molding characteristics of the non-closed STL model with boundaries. The invention not only solves the problem of slice processing of non-closed STL models, but also improves the molding efficiency from the perspective of practical application, which is of great value in promoting the popularization and application of three-dimensional printing.

According to the boundary edge information of the STL model, the present invention combines the slicing method based on topological relationship information to perform hierarchical slicing processing on non-closed grids to obtain non-closed two-dimensional polygons; through layered slicing of the STL model, all Layer slice fragments, and connect the slice fragments of each layer in the direction of the outline

Description of drawings

Fig. 1 is a schematic flow chart of a slice processing method for a non-closed STL model with boundaries according to the present invention;

Figure 2 (a) Schematic diagram of the point data structure of the topological relationship;

Fig. 2 (b) schematic diagram of surface data structure of topological relationship;

Figure 2(c) schematic diagram of the edge data structure of the topological relationship;

Fig. 3 is an illustration of a data structure describing a border edge;

Fig. 4 is a schematic diagram of a boundary point and a boundary edge;

Fig. 5 is the flowchart of layered slicing algorithm;

Fig. 6 is a demonstration diagram of a two-dimensional polygon generation process in a layered slice;

Figure 7(a) Demonstration diagram of the contour line where the slice plane intersects with the triangle patch;

Figure 7(b) Schematic diagram of the direction of the contour line where the slice plane intersects with the triangle patch;

Fig. 8(a) is a demonstration diagram of alternate combination of sequence and reverse order in the same layer of path optimization strategy;

Fig. 8 (b) is a demonstration diagram of the scanning result of the adjacent layer of the path optimization strategy;

Fig. 9 is the display diagram of actual printing test results after slicing processing: (a) is the front display diagram based on the closed model printing, (b) is the reverse display diagram based on the closed model printing, (c) is the present invention for printing with boundaries The front display diagram of the slicing processing of the non-closed STL model; (d) is the reverse display diagram of the slicing processing of the non-closed STL model with boundaries in the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figure 1, a slice processing method for non-closed STL models with boundaries includes the following steps:

Step 1, input the STL model, extract the point, edge and surface information of the triangle in the STL model and establish the topological relationship among them, the data structure describing the topological information is shown in Figure 2(a), 2(b), 2(c); The data structures of the points, edges and faces of the topological relationship are as follows: the point data structure includes the point coordinate vertice and the index value faceIndexList of the face adjacent to the point; the face data structure includes the index values index[0], index[ 1], index[2], and the index values of the adjacent faces touching[0], touching[1], touching[2]; the edge data structure includes the edge index value Edgeindex, the edge adjacent face index value AdjacentFace[0], AdjacentFace[1] and the index values AdjacentVertice[0] and AdjacentVertice[1] of two adjacent points.

The data structure of the points, edges and faces of the topological relationship is

Step 2: Extract all the boundary edges of the model according to the boundary judgment rules. The data structure describing the boundary edges is shown in Figure 3. The method of boundary extraction is as follows:

①Traverse all the edges of the triangular facets, according to the judgment rules of the boundary edge, if the number of adjoining triangular faces of an edge is 1, it is the boundary edge;

②Restore all the extracted boundary edges according to the data structure of boundary edges, so as to facilitate search and access.

As shown in Figure 4, the relationship between boundary points and boundary edges, connecting boundary points to form boundary edges, the boundary extraction rules are:

Let the triangular mesh surface be M=(v _i ,v _j ,…v _n ), any vertex in M is v _i =( _xi ,y _i , _zi ), if two of the triangular mesh surface M The edge edge(v _i , v _j ) connected by vertices is the edge of a triangular patch Δv _i v _j v _k , then the edge edge(v _i , v _j ) is called the adjacent edge of Δv _i v _j v _k . Let L(v _i ,v _j ) represent the set of all triangular faces containing edge(v _i ,v _j ). For an edge edge(v _i , v _j ), the number of its adjacent triangular faces is represented by |L(v _i , v _j )|. An edge is a boundary edge if the number of adjacent triangles associated with it is 1. If the number of adjacent triangles associated with an edge is 2, it is called an inner edge. At the same time, the two vertices of the boundary edge are boundary points, and a triangle with one or two boundary points is called a boundary triangle.

The boundary extraction rule expression is:

BoundaryEdge: {edge(v _i ,v _j )|if:|L(v _i ,v _j )|=1},

Among them, x _i , y _i , z _i are the coordinates of vertex v _i ; v _i , v _j ,...v _n represent points on the triangular mesh model in space;

Edge(v _i ,v _j ) is the adjacent edge of Δv _i v _j v _k , L(v _i ,v _j ) represents the set of all triangular patches containing edge(v _i ,v _j ), |L( v _i , v _j )|indicates the number of adjacent triangles.

The data structure of the boundary edge is:

Step 3, according to the information of the boundary edge of the STL model, combined with the slicing method based on topological relationship information, perform hierarchical slicing processing on the non-closed grid to obtain a non-closed two-dimensional polygon, as shown in Figure 5. Hierarchical slicing processing to obtain non-closed two-dimensional polygons, the process of generating two-dimensional polygons is shown in Figure 6; specifically includes the following steps:

①According to the slicing accuracy, obtain the total number of slicing layers n and all slicing planes z _i (i=1,2...n) of the model;

②Read a triangle surface of the STL model, according to the maximum value z _max , the minimum value z _min and the slice precision of the z coordinates of each point of the triangle, inversely calculate the K slice planes z _j that intersect the triangle, 1≤j≤n ;

③ Obtain the slice segment where the slice plane intersects the triangle surface, and add indication information for the slice segment to indicate whether the vertex of the slice segment is on the boundary edge: read an intersecting slice plane z _j and calculate the intersection point, and obtain a Fragment (the fragment data structure needs to be established), and the instruction information BorderFlag is added for the fragment. According to the patch index of the triangle, find out whether there is a boundary edge belonging to the triangle patch in the boundary edge set. If it exists, calculate whether there is a fragment vertex on the border edge, and set BorderFlag to True if it is on the border edge, or set it to False if it is not. If it does not exist, BorderFlag is directly set to False;

Among them, obtaining slice fragments includes the following steps:

(a) The direction D of the slice segment is determined by the vector product of the layer direction Z and the normal vector N of the triangle:

D=Z×N

Among them, Z is the layering direction, and N is the normal vector of the triangle patch;

The vertices of the slice segments are sequentially connected to form a two-dimensional polygon, and the two-dimensional polygon (two-dimensional polygon outline) is a polygon outline formed after the intersection of the slice plane and the triangular mesh model in space.

(b) Calculation of the intersection point of the layered plane (slicing plane) and the triangular patch:

P(t)=p+t(q-p), t∈[0,1]

$\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}$

Wherein, Z=h is the layered plane height, p=(x _p , y _p , z _p ), q=(x _q , y _q , z _q ) are the two vertices of one side of the triangle.

As shown in Figures 7a and 7b, the intersection points of the layer plane and the triangle patches are the intersection points of the slice plane and each triangle patch.

(c) The data structure of the slice segment obtained after triangle intersection is:

The data structure of the slice segment includes a segment start point, a face index, whether the segment has been added to a polygon, and a boundary segment flag.

That is, the data structure of the segment obtained after triangle intersection:

④Recording step ③The triangle facet index information to which the slice segment belongs, traverse to obtain all slice segments of the K slice planes and the triangle facet: if the calculation of the intersection between the K slice planes and the triangle facet is completed, Then execute the next step; otherwise, turn to ② to read the next plane that intersects with the triangle;

⑤ Store all intersecting slices of the triangular facets by layer: store all intersecting slices of the triangular facets by layer, and go to ①; if all the triangular faces are intersected and processed, go to the next step;

The data structure of intersecting fragments stored by layer includes a collection of fragments and fragments and corresponding face indices for each layer. That is, the data structure stored by layer is:

⑥Traverse the indication information of all slices and obtain the initial connection point of the two-dimensional polygon: read all the slices of the i=i+1 layer (starting from i=0), and judge whether there is a BorderFlag in this layer whose BorderFlag is True fragment. If it exists, take out the segment whose BorderFlag is True in the direction of the contour line, and set the triangle patch to which the segment belongs as the current patch; if not, it means that the layer is closed, and take out any segment in the direction of the contour line, And set the triangle patch to which the fragment belongs as the current patch;

⑦ Judging whether there is a slice fragment on the adjacent surface: read an adjacent surface of the current patch, and judge whether there is a fragment of the i-th layer on the adjacent surface. If it does not exist, go directly to ⑧; if it exists, judge whether the segment has been added to the polygon. If it has been added to the polygon, turn to ⑧; if it has not been added to the polygon, add the segment to the polygon, and set the patch as the current patch, turn to ⑨;

⑧Traverse all the adjacent faces to see if there are slices; judge whether the adjacent faces have been traversed, if not, go to ⑦; if traversed, go to the next step;

⑨When multiple vertices of a layer slice segment appear in pairs on the boundary edge, use the triangular face where the slice segment is located as the indication information is true as the starting face to connect the two-dimensional polygon: judge the segment indication in the adjacent face Information whether BorderFlag is True. If it is not True, execute the next step; if it is True, judge whether there is a next segment with BorderFlag=True in the direction of the contour line. If it exists, set the segment as the current patch, and go to ⑦; if it does not exist, perform the next step;

⑩ Traversing all slice layers, each layer forms a two-dimensional polygon: judge whether to traverse all segments of this layer. If the traversal is not completed, go to ⑦; if the traversal is completed, store all non-closed polygons or closed polygons of this layer. Determine whether i≤n, if so, go to ⑥, otherwise the algorithm ends.

Step 4, path optimization is performed on the printable inner and outer contour lines after polygon offset processing to reduce empty travel, as shown in Figure 8(a) and 8(b), the path optimization method is as follows:

① The scanning directions of adjacent contour lines in the same layer are opposite;

② The order of scanning the contour lines of adjacent layers is reversed

③ The scanning direction of the same contour of adjacent layers is opposite.

Step 5, output Gcode and print, as shown in Figure 9 is the display of the actual printing test results after slice processing: (a) is the front display based on the closed model printing, (b) is the reverse display based on the closed model printing , (c) is the front display diagram of the present invention for the slice processing of the non-closed STL model with border; (d) is the reverse display diagram of the slice processing of the non-closed STL model with border in the present invention, as can be seen, Figures (a) and (b) are printed in a closed manner, which takes a long time to print and has low efficiency. The front and back sides of Figures (c) and (d) printed by the present invention are non-closed printing, which has high printing efficiency and saves materials.

The method of the present invention is based on the slicing processing method based on topological information, and solves the problem of direct slicing processing for non-closed STL models with boundaries as input from the perspective of boundary extraction, so that many non-closed STL models in practical applications can be directly processed. Slices are processed and actually printed to form efficiently.

Those skilled in the art can make changes or modifications to the present invention without departing from the spirit and scope of the present invention. Therefore, if these modifications and variations of the present invention fall within the technical scope of the claims of the present invention and equivalents thereof, the present invention is also intended to include these modifications and variations.

Claims (9)

1. A slice processing method for the non-closed STL model with boundary, it is characterized in that, comprising the following steps, Step A1, extracting the point, edge and surface information of the triangular patch in the STL model, and establishing the topological relationship between the point, edge and surface information; Step A2, using the topological relationship to extract all boundary edges of the STL model according to the boundary edge judgment rules; Step A3, according to the boundary edge information of the STL model, combined with the slicing method based on topological relationship information, perform hierarchical slicing processing on the non-closed grid to obtain a non-closed two-dimensional polygon; Step A4, performing polygon offset processing on the non-closed two-dimensional polygon to obtain inner contour lines and outer contour lines, and performing path optimization on the inner contour lines and outer contour lines to reduce empty travel; In step A5, a common print file is output from the slice file for reading and printing by the 3D printer. 2. A kind of slicing processing method for the non-closed STL model with boundary according to claim 1, it is characterized in that, the data structure composition of the point, edge and face of topological relationship described in step A1 is respectively: The point data structure includes point coordinates and an index value of a surface adjacent to the point; The surface data structure includes the index value of the adjacent point and the index value of the adjacent surface; The edge data structure includes the index value of the edge, the index value of the adjacent surface of the edge and the index value of two adjacent points. 3. A kind of slice processing method for the non-closed STL model with boundary according to claim 1, it is characterized in that, the boundary extraction rule described in step A2 is: Let the triangular mesh surface be M=(v _i ,v _j ,…v _n ), any vertex in M is v _i =( _xi ,y _i , _zi ), if two of the triangular mesh surface M The edge edge(v _i , v _j ) connected by vertices is the edge of the triangular patch Δv _i v _j v _k , then the edge edge(v _i , v _j ) is the adjacent edge of Δv _i v _j v _k ; (v _i , v _j ) represents the set of all triangular faces _including edge ₍ v _i , v _{j )} ; v _j )| means; if the number of adjacent triangles associated with an edge is 1, the displayed edge is a boundary edge; if the number of adjacent triangles associated with an edge is 2, it is an inner edge, and the two border edges Vertices are boundary points, and triangle patches with one or two boundary points are boundary triangles; The expression of the boundary judgment rule is: BoundaryEdge: {edge(v _i ,v _j )|if:|L(v _i ,v _j )|＝1}; Among them, x _i , y _i , z _i are the coordinates of vertex v _i ; v _i , v _j ,...v _n represent points on the triangular mesh model in space. 4. A kind of slice processing method for the non-closed STL model with boundary according to claim 1, it is characterized in that, step A2 specifically comprises the following steps: Step A21, traversing each edge of all the triangle faces, according to the judgment rule of the boundary edge, if the number of adjacent triangle faces of an edge is 1, the edge is a boundary edge; Step A22, re-store all the extracted boundary edges in the data structure form of boundary edges, so as to facilitate search and access. 5. according to a kind of slicing processing method for the non-closed STL model with boundary according to right 4, it is characterized in that, the data structure of the boundary edge described in step A22 consists of: The data structure of the boundary edge includes: the index value of the vertex at one end of the boundary edge, the index value of the vertex at the other end of the boundary edge, and the index of the triangle patch to which it belongs. 6. A kind of slice processing method for the non-closed STL model with border according to claim 4, it is characterized in that, step A3 specifically comprises the following steps: Step A31, obtain the total number of slice layers n and all slice planes z _i (i=1,2...n) of the STL model according to the slice accuracy; Step A32, read a triangle surface of the STL model, according to the maximum value z _max , the minimum value z _min and the slice precision of the z coordinates of each point of the triangle surface, inversely calculate the K slice planes z _j intersecting the triangle, 1≤j≤n; Step A33, obtain the slice segment where the slice plane intersects the triangle face, and add indication information for the slice segment to indicate whether the vertex of the slice segment is on the boundary edge: read a slice plane z _j and calculate the relationship between the slice plane and the triangle face Intersection, to obtain a slice segment belonging to the triangle facet, add indication information BorderFlag for the slice segment; according to the facet index of the triangle facet, find whether there is a border edge belonging to the triangle facet in the border edge set; if If it exists, calculate whether there is a slice fragment vertex on the border edge, and set the indication information BorderFlag to True if there is no slice fragment vertex on the border edge, then set it to False; if there is no border edge in the border edge set Belongs to a triangular patch, then BorderFlag is directly set to False; Step A34, recording the index information of the triangle patch to which the slice segment described in step A33 belongs, traversing to obtain all slice segments of the K slice planes and the triangle patch: if the intersection of the K slice planes and the triangle patch is After the calculation is completed, then execute step A35; otherwise, turn to step A32, and read the next plane intersecting with the triangular surface successively; Step A35, storing all intersecting slice segments of the slice plane and the triangle facet by layer; Step A36, traversing the instruction information of all the slice fragments to obtain the starting connection point of the two-dimensional polygon: For all the slice fragments in each slice layer, judge whether there is a slice fragment with BorderFlag as True in each layer; if it exists, take the first slice fragment with BorderFlag as True in the contour line direction, and set the triangular surface to which the slice fragment belongs If not, it means that the layer is closed, take out any segment in the direction of the contour line, and set the triangular patch to which the segment belongs as the current patch, which is used to process closed surface graphics; Step A37, judging whether there is a slice segment on the adjacent surface; Step A38, traversing all adjoining faces to see if there are slices; Step A39, when a plurality of vertices of a slice segment of a certain layer appear in pairs on the boundary edge, the triangular patch where the slice segment is located where the indication information is true is used as the starting patch to connect into a two-dimensional polygon; Step A310, traversing all slice layers, each layer forming a two-dimensional polygon. 7. According to a kind of slice processing method for the non-closed STL model with boundary according to claim 6, the acquisition of the slice segment described in step A33 includes the following content: ① The direction D of the slice segment is determined by the vector product of the layer direction Z and the normal vector N of the triangle: D=Z×N Among them, Z is the layering direction, and N is the normal vector of the triangle patch; ② Calculation of the intersection point of the slice plane and the triangle surface: P(t)=p+t(q-p), t∈[0,1] $\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}$ Among them, Z=h is the layered plane height, p=(x _p ,y _p ,z _p ), q=(x _q ,y _q ,z _q ) are the two vertices of one side of the triangle; z _q means Cartesian The Z coordinate of point p=(x _p , y _p , z _p ) in the space coordinate system; z _p represents the Z coordinate of point q=(x _q , y _q , z _q ) in the Cartesian space coordinate system; ③The data structure of the segment obtained after triangle intersection: The data structure of the segment includes a segment start point, a face index, whether the segment has been added to a polygon, and a boundary segment flag. 8. According to a kind of slice processing method for the non-closed STL model with boundary according to claim 6, the data structure of the slice fragment intersected by the slice plane and the triangular surface described in step A35 includes the fragment collection and fragment of each layer with the corresponding face index. 9. A kind of slice processing method for the non-closed STL model with boundary according to claim 1, the strategy of path optimization described in the step A4 comprises: The scanning directions of adjacent contour lines in the same layer are opposite; The order of scanning adjacent layer contour lines is reversed; The scanning directions of the same contour in adjacent layers are opposite.