Columnar part four-axis rough machining method based on discrete subdivision slicing

Abstract

The invention provides a columnar part four-axis rough machining method based on discrete subdivision slicing, which comprises the following steps of: constructing a slicing plane by taking a cutter line spacing as a spacing, and slicing a blank and a workpiece by adopting a discrete subdivision slicing method to obtain machining areas on different slicing planes; a cylindrical surface is constructed with the cutting depth as the interval, intersection calculation is conducted on the cylindrical surface and the machining areas on the different slice layers, and a tool machining path line is obtained; and the machining tracks of the same cutting layer are correspondingly connected end to end, and a feeding path is obtained. According to the numerical control rough machining layer cutting method based on discrete subdivision slicing, a universal layer cutting method is provided for cylindrical blank parts, a workpiece and a blank are sliced at first, and then cutter machining tracks under different cutting depths are obtained through a method of intersection calculation of a biased cylindrical surface and a machining area obtained through slicing.

Description

Technical Field

[0001] The present invention belongs to the technical field of computer aided manufacturing (CAM), and in particular relates to a four-axis rough machining method for columnar parts based on discrete subdivision slicing. Background Art

[0002] Cylindrical blank workpieces are widely used in the field of mechanical manufacturing, such as molecular pump rotors, aircraft engine impellers, vacuum pump impellers, etc. These parts often have high surface accuracy and dynamic balance requirements, complex curved surface modeling, high processing difficulty, and require the use of four-axis or above CNC machining centers to complete milling.

[0003] The machining characteristics of these workpieces are narrow machining channels and deep cutting depths. The bottom of the machining channel is the outer cylindrical surface of the hub. Therefore, during rough machining, it is often necessary to feed in a direction close to perpendicular to the axial direction to remove the material layer by layer along the radial direction of the workpiece. How to quickly and efficiently calculate the machining area of ​​each cutting layer is a crucial issue when machining such parts.

[0004] Among the patents on rough machining methods for parts milling that have been disclosed so far, most of them are rough machining methods for a specific workpiece. There are very few discussions on general rough machining methods for cylindrical workpieces. For complex workpieces, the generation of machining trajectories is usually obtained by solving the intersection of offset surfaces, which has the problems of large amount of calculation, long time consumption, and unsatisfactory calculation accuracy. These factors limit the processing and manufacturing of complex impeller parts. Summary of the invention

[0005] To solve the existing problems, this paper proposes a four-axis rough machining method for cylindrical parts based on discrete subdivision slicing. This method realizes the gradual subdivision of the slicing space based on the interval tree, realizes the rapid division of the triangular facets, and obtains the plane slicing results of the model; based on the offset function of OpenCascade, the slicing results of the workpiece and the blank are offset outward and inward respectively to obtain the area to be processed in the slicing plane; a set of coaxial cylindrical surfaces are constructed, and multiple tool paths are obtained by calculating the intersection with the plane processing area; the intersection results of the same cylindrical surface and the plane processing area are organized to plan the tool processing trajectory of a certain cutting layer.

[0006] A four-axis rough machining method for a cylindrical part based on discrete subdivision slicing comprises: constructing a slicing plane with a tool line spacing as a spacing, slicing a blank and a workpiece by a discrete subdivision slicing method, and obtaining machining areas on different slicing planes; constructing a cylindrical surface with a cutting depth as a spacing, and performing intersection calculation with machining areas on different slicing layers to obtain a tool machining trajectory line; and correspondingly connecting the beginning and the end of the machining trajectory of the same cutting layer to obtain a tool path.

[0007] A four-axis rough machining method for a columnar part based on discrete subdivision slicing comprises the following steps:

[0008] (1) Constructing a slicing plane in the height direction of the workpiece, using the slicing plane to subdivide and discretely slice the blank and the workpiece, and obtaining the slicing results of all slicing planes;

[0009] (2) For any slicing plane, the slicing results of the blank and the workpiece are offset inward and outward respectively to obtain the processing area of ​​all slicing planes;

[0010] (3) With the workpiece axis as the axis, a set of coaxial cylindrical surfaces is constructed. For any cylindrical surface, the machining area of ​​each slice plane is traversed, the intersection line between the cylindrical surface and the machining area is calculated, and each line of tool trajectory on the cutting layer is obtained;

[0011] (4) The beginning and the end of each row of trajectory lines on all cylindrical surfaces are connected respectively to obtain the tool trajectory of all cutting layers.

[0012] In step (1), the thickness of the discrete slices of the workpiece and the blank is the tool processing line spacing. More specifically, the blank and the workpiece are subdivided into discrete slices in the height direction of the workpiece. In actual processing, a cylindrical end mill is generally used for processing. The appropriate tool diameter d is manually selected according to the workpiece to be processed. The tool spacing h is determined by a percentage a of the manually selected tool diameter, h = da. Adjust the model posture angle so that the XOY plane in the spatial coordinate system of the bottom surface of the model fits. Traverse all the vertices of the triangular face of the model to determine the maximum height H of the model max , the construction height range is 0~H max A set of slice planes parallel to the XOY plane, with the distance between adjacent planes being h, which can be chosen to be equidistant.

[0013] The specific steps in step (1) are as follows:

[0014] (1-1) constructing multiple slice intervals according to the height value of the slice plane;

[0015] (1-2) According to the height range of the triangles and the constructed slice interval, all triangles are divided into intervals using a tree structure;

[0016] (1-3) For any slicing plane, the intersection calculation is performed on the triangular facets in its corresponding adjacent slicing interval, and the obtained contour is the slicing result of the layer, and finally the slicing results of all slicing planes are obtained.

[0017] Furthermore, in step (1-1), the height values ​​of two slice planes at adjacent heights constitute a single interval; in step (1-2), the interval is divided using the maximum height value point in the triangular face.

[0018] Furthermore, in step (1-3), the intersection of the slice plane slice and the triangle patch obtains a set of scattered line segments, and the line segments are spliced ​​by finding line segments with common endpoints to obtain one or more contours; if there are multiple contours, the inner contour and the outer contour are judged.

[0019] More specifically, the slicing method for the blank or workpiece adopts a fast slicing method of discrete subdivision slicing planes, and the specific steps are as follows:

[0020] 1) According to the height value h of the slice plane 0 ,h 1 ,h 2 ,……,h N Construct a set of intervals Intervals: {[h 0 ,h 1 ],[h 1 ,h 2 ],……[h N-1 ,h N ]};

[0021] 2) The slice interval is stored in a tree structure. First, the initial root node root is created to represent [h 0 ,h N ], interval, add all the triangles of the model to be sliced ​​to the root node interval;

[0022] 3) Create a subnode interval. Traverse the triangles in the root node interval. If the height range of the triangles overlaps with the subnode interval, add it to the current subnode, thus completing the subdivision of the triangles in the root node interval.

[0023] 4) Continue to subdivide the triangular face until the interval of the child node is a single interval that cannot be divided any further, completing the interval division of all triangular face;

[0024] 5) For a slice plane with a slice height of hi, select the triangles in the interval [hi-1,hi] and [hi,hi+1] (when i=0 or N, only select a single existing interval) to complete the intersection calculation, and the resulting contour is the slice result of this layer.

[0025] 6) According to step 5), all slicing planes are traversed to complete the discrete subdivision fast slicing of the model to be sliced.

[0026] Preferably, in step 2) or step (1-2), a binary interval tree structure is selected, and the correspondence between nodes and triangular facets is realized through a dictionary data structure. When the initial root node is created, a dictionary T_map associating nodes and triangular facets is created, wherein the key is the node number of each node, and the value is the number of the triangular facet within the range.

[0027] As a preference, in step 3), according to the root node T i , create two child nodes T in the interval tree 2i+1 and T 2i+2 , the interval T contained in the root node i .Interval is divided into two parts to get the interval T contained in the two child nodes 2i+1 .Interval and T 2i+ 2 .Interval. Sort the triangles T_map[i] associated with the root node in ascending order by the maximum height value of the triangle.Zmax, and find the triangles with the maximum height value in T 2i+1 All triangles within the .Interval interval are added to T_map[2i+1]; the remaining triangles in T_map[i] are added to T_map[2i+2].

[0028] In step 4), the single interval that cannot be divided any further refers to the interval in Intervals that is formed by the heights of two adjacent slices.

[0029] Preferably, in step 5), the intersection of the slice plane slice and the triangular facet obtains a set of scattered line segments, and the line segments are spliced ​​by finding line segments with common endpoints to obtain one or more contours. If there are multiple contours, a point on the contour is selected to construct a ray, and the intersection of the ray and the line segment is calculated:

[0030] If the number of intersection points is an odd number, the contour is judged to be an inner contour;

[0031] If the number of intersection points is even, the contour is judged to be an outer contour.

[0032] Step (2): For any plane, the slicing results of the blank and the workpiece are offset respectively. The processing area on each slicing plane is constructed by the contour obtained by offsetting the blank slicing result inward and the contour obtained by offsetting the workpiece slicing result outward; the slicing results of all slicing layers are traversed, and the processing areas of all slicing planes are offset.

[0033] In step (2), the offset and Boolean difference operation of the slicing contours of the blank and the workpiece are implemented based on the OpenCascade library. Specifically, the slicing contours of the blank and the workpiece respectively use the contour offset function BRepOffsetAPI_MakeOffset of the OpenCascade library to implement the inward offset of the blank and the outward offset of the workpiece, and the contour of the area to be processed is constructed with the contour of the blank after offset as the outer contour and the contour of the workpiece after offset as the inner contour.

[0034] Preferably, the specific steps of calculating the processing area on any slice plane are as follows:

[0035] (2-1) For the rough slice contour RoughPoly, based on the contour offset function BRepOffsetAPI_MakeOffset of the OpenCascade library, RoughPoly is offset inward along the contour curvature, and the offset distance is d offset1 , get the offset contour RoughOffsetPoly;

[0036] (2-2) For the workpiece slice contour WorkPoly, based on the contour offset function BRepOffsetAPI_MakeOffset of OpenCascade, WorkPoly is offset outward along the curvature, and the offset distance is d offset2 , get the offset contour WorkOffsetPoly;

[0037] (2-3) Use RoughOffsetPoly as the outer contour and WorkOffsetPoly as the inner contour to construct the contour of the area to be processed.

[0038] Step (3): With the workpiece axis as the axis, construct a set of coaxial cylindrical surfaces. For any cylindrical surface, traverse the processing area of ​​each plane slice and calculate the intersection line between the cylindrical surface and the processing area, which is the tool trajectory line of each row on the processing layer. In step (3), the intersection calculation between the cylindrical surface and the processing area is implemented based on the Section intersection function of the OpenCascade library.

[0039] As a preferred method, the intersection calculation between the cylindrical surface and the processing area is implemented based on the Section intersection function of the OpenCascade library. Based on the surface construction function MakeSurface of OpenCascade, a plane ToolSurface with holes and boundaries is constructed through the contour ToolPoly, and the curve aToolPath in three-dimensional space is obtained by intersecting with the cylindrical surface.

[0040] Step (4): Connect the beginning and the end of each row of trajectory lines to obtain the final machining tool trajectory. Finally, traverse all cylindrical surfaces to obtain the tool trajectory for cutting all cutting layers. Furthermore, in step (4), the connection method of each row of trajectory lines is that the trajectory line starts from the starting point and ends at the end point in a counterclockwise direction. The end point of the current trajectory line is connected to the end point of the adjacent previous row of trajectory lines by a straight line segment, and the starting point is connected to the starting point of the adjacent next row of trajectory lines by a straight line segment.

[0041] In step (4), the steps for obtaining the machining trajectory of any cutting layer are as follows:

[0042] (4-1) For each tool machining trajectory line on any cutting layer, determine whether the tool machining trajectory is a closed contour:

[0043] If the tool machining path is closed, the first and last points of the tool machining path are the same, select any point on the closed contour;

[0044] If the tool machining trajectory is not closed, the first and last points of the tool machining trajectory are the starting and ending points of the trajectory line;

[0045] (4-2) The connection method of each row of trajectory lines is that the trajectory line starts from the starting point and ends at the end point in the counterclockwise direction. For a certain tool processing trajectory line, the end point of the current trajectory line is connected to the end point of the adjacent previous trajectory line by a straight line segment, and the starting point is connected to the starting point of the adjacent next trajectory line by a straight line segment;

[0046] (4-3) Traverse all processing trajectory lines to obtain the tool processing trajectory of this layer.

[0047] Compared with the prior art, the advantages of this method are:

[0048] (1) The present invention is a CNC rough machining layer cutting method based on discrete subdivision slicing, and provides a general layer cutting method for cylindrical blank parts. The workpiece and the blank are first sliced, and then the tool machining trajectory at different cutting depths is obtained by calculating the intersection of the offset cylindrical surface and the machining area obtained by slicing.

[0049] (2) The slicing method proposed in this method is efficient. It avoids judging the intersection of the cut surface and the triangle patch by enumeration traversal method by discrete slicing space step by step, thus reducing the amount of calculation and improving the efficiency of slicing calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a flow chart of a method according to an embodiment of the present invention;

[0051] Figure 2 It is a schematic diagram of the cutting plane for slicing the workpiece in the height direction;

[0052] Figure 3 A flow chart of a method for discrete segmentation of a model;

[0053] Figure 4 A schematic diagram of a method for constructing a processing area;

[0054] Figure 5 It is a schematic diagram of the intersection calculation between the cylindrical surface and the processing area;

[0055] Figure 6 To obtain a schematic diagram of the machining trajectory of any cutting layer;

[0056] Figure 7 It is the STL model of the blank in Application Example 1;

[0057] Figure 8 is the STL model of the workpiece in Application Example 1;

[0058] Fig. 9 This is the visualization result of the tool machining trajectory generated in Application Example 1. DETAILED DESCRIPTION

[0059] like Figure 1 As shown, an algorithm flow chart of a four-axis rough machining method for a columnar part based on discrete subdivision slicing of the present invention is shown, and the specific steps are as follows:

[0060] Step 1: Subdivide and discretely slice the blank and the workpiece in the height direction of the workpiece.

[0061] like Figure 2 As shown, a cylindrical end mill is used for machining. The appropriate tool diameter d is manually selected according to the workpiece being machined. The tool spacing h is determined by the percentage a of the manually selected tool diameter, h = da. Adjust the model posture angle to make the XOY plane in the spatial coordinate system of the model bottom surface fit. Traverse all the triangular face vertices of the (blank and workpiece) model to determine the maximum height H of the model max , the construction height range is 0~H max A set of slicing planes parallel to the XOY plane, the distance between adjacent planes is h (equidistant slicing is used in this embodiment, of course, unequal distance slicing can also be used).

[0062] like Figure 3 As shown, the slicing method for the blank or workpiece adopts a fast slicing method of discrete subdivision slicing plane, and the specific steps are as follows:

[0063] (1) According to the height value h of the slice plane 0 ,h 1 ,h 2 ,…,h i ,…,h N Construct a set of intervals Intervals: {[h 0 ,h 1 ],[h 1 ,h 2 ],…,[h i ,h i+1 ],…[h N-1 ,h N ]}; where h 0 is the height of the slice plane closest to the XOY plane; [h i ,h i+1 ] is the i+1th single interval;

[0064] (2) The slice interval is stored in a tree structure. First, the initial root node root is created to represent [h 0 ,h N] interval, add all the triangles of the model to be sliced ​​to the root node interval;

[0065] (3) Create a subnode interval. Traverse the triangles in the root node interval. If the height range of the triangles overlaps with the subnode interval, add it to the current subnode, thus completing the subdivision of the triangles in the root node interval.

[0066] (4) Continue to subdivide the triangular face until the interval of the child node is a single interval that cannot be divided any further, thus completing the interval division of all triangular facets;

[0067] (5) For a slice height h i The slice plane is selected in the interval [h i-1 ,h i ] and [h i ,h i+1 ](when i=0 or N, only a single existing interval is selected) to complete the intersection calculation, and the obtained outline is the slicing result of this layer.

[0068] (6) According to step (5), all slicing planes are traversed to complete the discrete subdivision fast slicing of the model to be sliced.

[0069] The tree structure used in this embodiment is a binary interval tree structure, and the correspondence between nodes and triangular facets is realized through a dictionary data structure. When creating the initial root node, a dictionary T_map associating nodes and triangular facets is created, whose key is the node number of each node, and the value is the number of the triangular facet within the range.

[0070] The specific steps for subdividing the triangle patches in the root node interval are as follows:

[0071] ① According to the root node T i , create two child nodes T in the interval tree 2i+1 and T 2i+2 ;

[0072] ②The interval T contained in the root node i .Interval is divided into two parts to get the interval contained by the two child nodes

[0073] T 2i+1 .Interval and T 2i+2 .Interval;

[0074] ③ Sort the triangles T_map[i] associated with the root node in ascending order according to the maximum height value of the triangle Triangle.Zmax

[0075] ④ Find the maximum height of the patch at T 2i+1All triangles within the .Interval interval are added to T_map[2i+1];

[0076] ⑤Add the remaining triangles in T_map[i] to T_map[2i+2].

[0077] The intersection of the slice plane slice and the triangle patch results in a set of scattered line segments, which are spliced ​​by finding line segments with common endpoints to obtain one or more contours. If there are multiple contours, a point on the contour is selected to construct a ray, and the intersection of the ray and the line segment is calculated:

[0078] If the number of intersection points is an odd number, the contour is judged to be an inner contour;

[0079] If the number of intersection points is even, the contour is judged to be an outer contour.

[0080] Step 2: For any plane, the slicing results of the blank and the workpiece are offset respectively. The machining area on each slicing plane is constructed by the contour obtained by offsetting the blank slicing result outward and the contour obtained by offsetting the workpiece slicing result outward.

[0081] like Figure 4 As shown in the figure, the specific steps to construct the processing area on any slice plane are as follows:

[0082] 1) For the rough slice contour RoughPoly, based on the contour offset function BRepOffsetAPI_MakeOffset of the OpenCascade library, RoughPoly is offset inward along the contour curvature, and the offset distance is d offset1 , get the offset contour RoughOffsetPoly;

[0083] 2) For the workpiece slice contour WorkPoly, based on the contour offset function BRepOffsetAPI_MakeOffset of OpenCascade, WorkPoly is offset outward along the curvature, and the offset distance is d offset2 , get the offset contour WorkOffsetPoly;

[0084] 3) Use RoughOffsetPoly as the outer contour and WorkOffsetPoly as the inner contour to construct the contour of the area to be processed.

[0085] According to step 2, traverse the slicing results of all slice layers and offset to obtain the processing area of ​​each layer. Step 3: With the workpiece axis as the axis and the cutting depth as the spacing, construct a set of coaxial cylindrical surfaces. For any cylindrical surface, traverse the processing area of ​​each plane slice, calculate the intersection line between the cylindrical surface and the processing area, and obtain the tool trajectory lines of each row on the processing layer.

[0086] like Figure 5 As shown in the figure, the intersection calculation between the cylindrical surface and the processing area is realized by the Section intersection function of OpenCascade. Based on the surface construction function MakeSurface of OpenCascade, a plane ToolSurface with a hole and an outer boundary is constructed through the contour ToolPoly, and the curve aToolPath in three-dimensional space is obtained by intersecting with the cylindrical surface.

[0087] Step 4: Connect the beginning and the end of each row of trajectory lines respectively to obtain the final machining tool trajectory;

[0088] like Figure 6 As shown, the steps to obtain the machining trajectory of any cutting layer are as follows:

[0089] 1) The intersection of the cylindrical surface and all processing areas is the tool processing trajectory line on the cutting layer, and it is judged whether the tool trajectory is a closed contour:

[0090] If the tool path is closed, the first and last points of the tool path are the same, select any point on the closed contour;

[0091] If the tool path is not closed, the start and end points of the tool path are the start and end points of the trajectory line.

[0092] 2) For a certain tool trajectory line, the starting point of the tool trajectory line is connected to the starting point of the previous tool trajectory line by a straight line segment, and the ending point of the tool trajectory line is connected to the ending point of the next tool trajectory line by a straight line segment.

[0093] According to step 4, traverse all cylindrical surfaces to obtain the tool path for cutting all cutting layers.

[0094] Application Example 1:

[0095] 1. Input the model of the blank such as Figure 7 As shown, the blank size is 80mm×80mm×55mm; the input workpiece model is as follows Figure 8 As shown, the workpiece size is 80mm×80mm×50mm;

[0096] 2. Set the tool radius to 5mm, the machining line spacing to 5mm, the tool cutting depth to 5mm, and the offset distance d offset1 is 2.5mm, the offset distance d offset2 It should be noted that the above parameter settings are for the purpose of illustrating the effectiveness of the algorithm and may not necessarily conform to the actual process parameters;

[0097] 3. Use the above judgment method to Figure 8 The workpiece shown generates the machining tool path. Fig. 9The tool path result is generated.

Claims

1. A four-axis rough machining method for columnar parts based on discrete subdivision slicing, characterized in that: include: The slicing plane is constructed with the tool spacing as the interval, and the blank and workpiece are sliced ​​using the discrete subdivision slicing method to obtain the processing areas on different slicing planes; The cylindrical surface is constructed with the cutting depth as the spacing, and the intersection calculation is performed with the processing area on different slice layers to obtain the tool processing trajectory line; the beginning and end of the processing trajectory of the same cutting layer are connected respectively to obtain the tool path.

2. The four-axis rough machining method for columnar parts in discrete subdivision slices according to claim 1 is characterized in that: The following steps are involved: (1) In the height direction of the workpiece, a slicing plane is constructed with the tool spacing as the spacing, and the blank and the workpiece are subdivided and discretely sliced ​​using the slicing plane to obtain the slicing results of all slicing planes; (2) For any slicing plane, the slicing results of the blank and the workpiece are offset inward and outward respectively to obtain the processing area of ​​all slicing planes; (3) A set of coaxial cylindrical surfaces are constructed with the workpiece axis as the axis and the cutting depth as the spacing. For any cylindrical surface, the processing area of ​​each slice plane is traversed, the intersection line between the cylindrical surface and the processing area is calculated, and each line of tool trajectory lines on the cutting layer is obtained; (4) The beginning and the end of each row of trajectory lines on all cylindrical surfaces are connected respectively to obtain the tool trajectory of all cutting layers.

3. The four-axis rough machining method for columnar parts in discrete subdivision slices according to claim 2 is characterized in that: The specific steps in step (1) are as follows: (1-1) constructing multiple slice intervals according to the height value of the slice plane; (1-2) According to the height range of the triangles and the constructed slice interval, all triangles are divided into intervals using a tree structure; (1-3) For any slicing plane, the intersection calculation is performed on the triangular facets in its corresponding adjacent slicing interval, and the obtained contour is the slicing result of the layer, and finally the slicing results of all slicing planes are obtained.

4. The four-axis rough machining method for columnar parts in discrete subdivision slices according to claim 3 is characterized in that: In step (1-1), the height values ​​of two slice planes at adjacent heights constitute a single interval; in step (1-2), the interval is divided using the maximum height value point in the triangular face.

5. The four-axis rough machining method for columnar parts in discrete subdivision slices according to claim 3, characterized in that: In step (1-3), the intersection of the slice plane slice and the triangle patch obtains a set of scattered line segments, and the line segments are spliced ​​by finding line segments with common endpoints to obtain one or more contours; if there are multiple contours, the inner contour and the outer contour are judged.

6. The four-axis rough machining method for columnar parts in discrete subdivision slices according to claim 2, characterized in that: In step (2), the slicing contours of the blank and the workpiece are respectively offset inward for the blank and outward for the workpiece using the contour offset function of the OpenCascade library, and the contour of the area to be processed is constructed with the offset contour of the blank as the outer contour and the offset contour of the workpiece as the inner contour.

7. The four-axis rough machining method for columnar parts in discrete subdivision slices according to claim 2, characterized in that: In step (3), the intersection calculation between the cylindrical surface and the processing area is implemented based on the Section intersection function of the OpenCascade library.

8. The four-axis rough machining method for columnar parts in discrete subdivision slices according to claim 2, characterized in that: In step (4), the steps for obtaining the machining trajectory of any cutting layer are as follows: (4-1) For each tool machining trajectory line on any cutting layer, determine whether the tool machining trajectory is a closed contour: If the tool machining path is closed, the first and last points of the tool machining path are the same, select any point on the closed contour; If the tool machining trajectory is not closed, the first and last points of the tool machining trajectory are the starting and ending points of the trajectory line; (4-2) The connection method of each row of trajectory lines is that the trajectory line starts from the starting point and ends at the end point in the counterclockwise direction. For a certain tool processing trajectory line, the end point of the current trajectory line is connected to the end point of the adjacent previous trajectory line by a straight line segment, and the starting point is connected to the starting point of the adjacent next trajectory line by a straight line segment; (4-3) Traverse all processing trajectory lines to obtain the tool processing trajectory of this layer.

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