Design And Smoothing Of NC Trajectory Based On Cubic Trigonometric Interpolation Spline

High speed NC machining with basic characteristics of high efficiency, high precision and high surface quality is an advanced technology of the21st century, and it has been more and more widely used in automotive, aerospace, mold manufacturing and other industries with enormous economic benefits have been achieved. It is the development trend of the contemporary advanced manufacturing technology. However, the current NC motion path is not smooth enough, and the mathematical description of complex motion path is also not concise enough, which hinders the further development of high speed NC machining. The mathematical description of NC motion path needs to be further simplified and unified, in order to get a smoother path.To meet the needs of researching and developing high speed NC machining technology and explore a smoother NC motion path which is more suitable for high speed machining, the paper presented and defined a new spline curve called Cubic Trigonometric Cardinal Interpolation Spline with shape adjustable, which realized the unification to accurately represent some common engineering curves such as straight line, arc and free curve. Then respectively to have research on the optimization of tool motion path in planar and hook face NC machining, and using the spline to describe and smoothing on the tool motion path to realize the continuity of tool feed speed in the whole machining process, so as to explore smooth machining method with high speed and high precision.In the tool motion path planning research of planar NC machining, the paper explored to use Cubic Trigonometric Cardinal Interpolation Spline Curve to describe the common tool motion path curves, such as straight line, arc, free curve, etc. Besides, the paper researched on the smooth transition method of corners, and proposed to use the spline to structure the smooth transition path curve of the corner, so as to realize the continuity of tool feed speed in the whole NC machining. In addition, by choosing appropriate shape adjustable parameter can effectively reduce the acceleration mutation at the start and end locations in the smooth transition process of corners, so it can keep the numerical control system with good dynamic characteristics and reduce the impact on machine tools in the machining process, which can better meet the requirements of high speed and high precision NC machining.In the tool motion path planning research of hook face NC machining; the paper put forward a kind of "3D spiral form" tool smooth motion path planning strategy, which is geared to the high speed NC machining. Using Cubic Trigonometric Cardinal Spline to orderly interpolate the discrete tool location points obtained by certain path planning algorithm, then fitting to generate the continuous and smooth "3D spiral form" machining path curves. Due to the spline satisfies C1continuity, it can guarantee the feed speed with high continuous when the tool goes along the "3D spiral form" path curve during the machining process, which can realize the whole machining process with a smooth tool motion path and well meet the demands of modern NC machining for high speed, stability and flexibility.Based on the above theoretical analysis and algorithms, the paper firstly developed an NC automatic programming software of "3D spiral form" machining path by using Visual FoxPor; then respectively realized the dynamic simulation of tool motion path and entity machining process through secondary development on AutoCAD and SolidWorks; finally the paper carried on a comparative machining experimental test with the tool motion paths which are differently obtained from "3D spiral form" machining path and the Mastercam contour layered milling path. By comparing, it can be found that the after planning tool motion path makes the whole NC machining process smoother and the surface quality is relatively better. It also shows that the planning strategy of "3D spiral form" tool smooth motion path is correct and reasonable, which has the good practicability and superiority to meet the demands of free surfaces NC machining, and lay the foundation for curved surfaces NC machining to develop in the direction of high speed and high precision.