Research On Tool Path Planning Algorithm Based On Five-axis Machining For Subdivision Surface

Complex surface machining has always been a difficult problem in NC machining and manufacturing industry,in which the differential geometry information of the surface,the NC machining path interval,and the step length are hot topics and studied by many scholars.Tool path generation capability machining complex surfaces by five-axis CNC has direct influence on the surface quality and processing efficiency.The discrete triangular mesh and mesh model reconstruction of the point cloud data model is carried out,then the triangular mesh surface model is subdivided adaptively and the topological and regular triangular mesh subdivision model is obtained,which is the premise of generating the tool path.The proposal of "Made in China 2025" puts forward higher requirements for manufacturing industry.Therefore,the study on five-axis machining tool path generation of mesh subdivision surface model has practical significance for the development of NC technology.In this thesis,the principle of data storage,topology reconstruction of surface mesh model,and the differential geometric characteristics of surface are analyzed.The information of point cloud data model is introduced.After processing,point cloud data can be stored as STL files with triangular information.Triangular unit information is stored in the form of mesh half structure,then triangular mesh STL model file is reconstructed into mesh model,which achieved the calculation of vector and curvature of vertex of the triangular mesh surface model.According to the Loop subdivision rule and vertex coordinate information,the distance formula between the mesh vertex position and the vertex limit position is deduced.When the arbitrary precision threshold ? is given,the k value is calculated to determine the subdivision depth,an adaptive subdivision surface algorithm for error control is proposed,thereby which solved the problem of complex surface model subdivision.The results of cases simulation and theoretical analysis show that when different precision thresholds are taken,the smoothness of the subdivided mode surface and subdivision time are different.The too small threshold affected the subdivision time,and the too large threshold affected the smoothness of the surface.Within the allowed accuracy range,the subdivision depth of the surface model is determined used by the adaptive subdivision algorithm,the problem of infinite growth of triangular slices is solved,the time complexity limited is controlled effectively,and the relationship between the subdivision depth k and the precision threshold ? is obtained.The method by using equal scallop-height and section plane of ball-end cutter to machine subdivision surface mesh model is studied.Firstly,the triangular mesh subdivision surface model is equidistance offset,the offset algorithm proposed can effectively avoid the self-intersection of offset surfaces.Then the intersection method of cutter position generation in offset subdivision mesh model is studied,and the position relation between the section plane and the mesh surface is discussed,and the method of calculating the cross section point is given.According to the actual machine performance,the tool position are interpolated by spline curve interpolation and the trajectory obtained by fitting is the tool path.The saddle surface model is simulated according to the improved algorithm of intersection plane,the results of the cases simulation show that the generated tool path have better smoothness and the optimal length path,and ensures the consistency of scallop-height on the surface,which prove that the algorithm is feasible,and the theoretical basis for the generation of NC machining tool path on subdivision mesh surface is provided.