Research On Tool Path Planning Of Free-form Surface In Five Axis Linkage Machining

Free-form surface is widely used in automobile,aerospace,shipbuilding,energy,mold and other industries.In recent years,with the development and progress of numerical control machining technology,especially the universal application of five axis linkage machining technology,how to realize free-form surface machining with high efficiency and quality has become a key research.Tool path planning technology is an important technology of free-form surface machining.The quality of path planning directly affects the machining accuracy and efficiency of free-form surface.Under the same processing conditions,a shorter tool path can save the time required for free-form surface processing and prolong the service life of the tool.Meanwhile,the volume of the tool position file recording the tool contact coordinates and tool axis vector information will also be reduced,thus reducing the dependence on the calculation and the large storage function of the machine tool controller.Therefore,it is of great practical significance to study a free-form surface machining method that meets the error requirements and has a short tool path.This paper utilizes the idea of equal residual height method for path planning,and makes an in-depth study from the perspective of two parameters: step size and row spacing.The main research contents are as follows:(1)In order to solve the problems of error overrun and over conservative step size when encountering the sharp fluctuation of curvature in the free curve interpolation calculation of equal bow height error method,an equal bow height error interpolation algorithm based on curvature partition is proposed.According to the geometric relationship between the tool and the curve,the initial reference step size is derived.Taking the constant maximum bow height error in each interpolation section as the constraint condition,the curvature zoning strategy is introduced,and the automatic step size adjustment mechanism is proposed to realize the rapid calculation of the optimal step size while ensuring that the maximum bow height error in the interpolation step size is constant as the set value.The experimental results show that the improved method can well avoid the problem that the accuracy of the traditional equal bow height error method is not up to standard,the number of interpolation points calculated is small,and the machining efficiency is effectively improved.(2)In order to solve the problem of tool path redundancy in machining hyperbolic paraboloid and other special geometric surfaces by equal residual height method,an improved equal residual height algorithm is proposed.On the premise that the residual height of the free-form surface is uniform and consistent after machining,the auxiliary coordinate system is constructed respectively according to the different local concave convex properties of the surface,the calculation formula of line spacing corresponding to various cases is deduced,and an optimization scheme for determining the initial machining path along the direction of maximum principal curvature is proposed to skillfully avoid the problem of tool path redundancy.The experimental results show that compared with the equal residual height method,the optimized method can ensure that the residual height meets the machining requirements,reduce the total length of tool path,and have better adaptability and machining efficiency of special geometric surface.(3)In order to ensure the correctness of the path planning method of free-form surface in five axis linkage machining,the tool path generated by the improved equal residual height method is converted into a tool position file through UG NX secondary development,and then the post-processing corresponding to the five axis double turntable machine tool is realized by UG/post builder,so as to obtain the G code recognized by the NC system.The simulation machining of virtual five axis machine tool is realized in VERICUT software,and the residual error of free-form surface parts after machining is analyzed by using the built-in error detection and comparison function,which verifies the effectiveness of the tool path planning model for surface machining.