Research On Free Form Surface Mold Machining Technology Based On Surface Subdivision

The beautiful and complex appearance of the product result in more product with complex surfaces and higher requirement in the machining accuracy of the curved surface accordingly.The selection of NC milling parameters and the rationality of tool path planning determine the machining efficiency and the quality of the machined surface.In order to improve machining efficiency and machining quality,the theory and practical application of high efficiency and high quality machining of die free surface are studied in this thesis.On the basis of analyzing the advantages and disadvantages of the surface description methods,the NURBS surface is selected to describe the free surface of the mold and the intrinsic geometric parameters of the surface are analyzed.The free surface is constructed by using Matlab and the curvatures of discrete points are calculated.According to the attributes of the points on the surface,the surface is initially divided into convex elliptical surface,concave elliptical surface,convex paraboloid,concave paraboloid and hyperboloid.The K-means clustering algorithm is used to further subdivide the surface to get the surface patches with the same or similar curvatures,then determine the boundary of the curved surface and finish the zoning plan of the surface.The tool path planning for free surface with ball-end mill is completed.The method of Iso-scallop height is used to calculate and analyze the tool path length,the machining distance,the CC points and the CL points of the milling tool path planning with the ball-end mill.The CC points are different when selecting different initial tool path.In order to improve machining efficiency and make the average distance of all tool paths largest,the initial path corresponding to the tool path of the maximum mean curvature radius in all feed directions are selected.The example shows that the total length of the tool path corresponding to the initial tool path is the minimum,and the corresponding cutting time is the shortest.The effect of multi axis ball-end milling parameters on the surface integrity of hardened die steel was studied by multi factor orthogonal test.Different machining parameters such as spindle speed,feed per tooth,radial depth of cut,tilt angle and lead angle are selected as the influencing factors.The surface roughness Ra,micro-hardness HV and surface residual stress were taken as evaluation indexes.According to the test results,the influences of the machining parameters on the surface integrity are analyzed,providing a theoretical basis for the prediction of surface integrity and providing the basis for the selection of reasonable cutting parameters for high efficiency and high quality machining of the mold.The simulation and experimental research on the UG NC machining of the automotive front floor punch are completed.The machining efficiency and surface quality under the surface subdivision machining and the single tool path are compared and analyzed.The research shows that in the precision machining stage,the machining efficiency of the mold can be improved obviously by surface subdivision while the machining quality is guaranteed.