The way of numerically rough roughing knife path generation
Roughing tool path generation Roughing is mainly to remove a large amount of material, generally using a flat milling cutter to cut one layer at a time, called layering cutting. The thickness of the layered cut is determined by the tool parameters and the shape of the surface. Roughing the surface requires enveloping the subdivision surface within a certain gap (cutting tolerance) and facilitating fast calculations. Generally, the best way is to use an intermediate inaccurate mesh surface as the roughing surface, but this coarse mesh surface may not meet the conditions of the cutting, so it needs to be transformed into the mesh surface closest to the cutting condition. , called the overlay surface. The overlay surface is generated as an example of the basic concept of overlay surface generation in a two-dimensional plane. You can solve the problem of overcutting by moving the nodes under the surface to the node position as shown. The position of these new nodes can be determined by offsetting their extreme positions within the cutting tolerances so that an overlay surface of the envelope limit surface can be generated. However, this method is not easy to implement in 3D space, because even if all control nodes are above the surface, the extreme surface portion may exceed the surface, as shown. The excess needs to be partially checked out of the mesh and then judged whether the vertices fall on the triangular patch. Z-map model of rough-machined surfaces For the overlay surface of rough-machined surfaces, a Z-map model can be built. In order to sample the surface data, the sampling interval can be calculated by the following formula:), 2/min (Rηγ=where the cutting tolerance of η roughing, R is the tool radius. When roughing the tool position to calculate the layered cutting, the roughing needs to be calculated The position of each layer of the tool. Using the Z-map model that generates the overlay surface, for each X (or Y) constant grid line, a polyline can be defined by the Z-map model. Then in the vertical direction (Z Direction) Cut one by one to find the intersection of the slice and the polyline. These intersections are defined as CC (tool contact) points, then CL (tool position) points are calculated by offset tool radius R, by connecting these CLs Point, you can get a tool path. By repeating (sampling interval), you can get the roughing tool path of all the patches. Inspection and Correction of Machining Interference During machining, the area where the selected tool is not machined or machined is the interference area. The inspection and avoidance of the interference area is very important. In the study of this paper, we mainly deal with unprocessed interference, especially in the concave area, when the tool is too large to be processed. In order to check the uncut area, the curvature of each CC point needs to be calculated. The radius of curvature can be calculated according to the G. Taubin method. If the CC point is within a triangle in the triangular mesh plane, the radius of curvature of the triangle vertex of the subdivision surface is first calculated, and then the radius of curvature of the CC point is calculated according to the center of gravity coordinate of the CC point of the triangle. When performing interference check, first compare the radius of curvature of the tool contact point and the radius of curvature of the tool in the tool magazine, and then select the tool whose tool radius is smaller than the radius of curvature of all contact points to meet the non-interference during machining. If no tool is available in the magazine, add a small radius tool to calculate the new tool path. Simulation results and conclusions According to the above Z-map model and tool path generation method, this paper develops a simulation program based on OpenGL subdivision surface machining with VC++6.0 as the tool. The program has the functions of iterative generation of subdivision surface, generation of subdivision surface of subdivision mesh, tool path generation and machining simulation. The resulting machining simulation results are shown. The simulation results of the simulation machining results show that the three-axis NC roughing tool path generation of the Loop subdivision surface proposed in this paper is feasible. This set of methods can also be used on mesh surfaces other than Loop subdivision surfaces. Considering the practicability of the method in this paper, it is necessary to further improve the calculation method of the covered surface and the automatic intersection of the covered surface in the future research process. 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