Research On Freeform Surface Tool-Path Planning Algorithms Of Human-Simulated Polishing

In modern industry, NURBS surfaces are widely used in CAD/CAM systems to express the shape of work-piece. So how to manufacture a NURBS surface precisely and efficiently causes great concern. Because of the machine finishing and hand polishing period is about 75% of the total machining time in die manufacturing, it is an important and urgent work to develop versatile polishing machine tool and to build up effective algorithms for tool-path generation. Moreover, it is always a dream to mimic human polish behavior by a machine.In the end of 2004, a virtual-axis polishing machine tool with five degrees of freedom was produced in our laboratory. The machine has several peculiarities. First, through catering the curvature of each machined point, the actuators mounted on the polishing head can control the polishing pressure. Second, by applying corresponding algorithm of partitioning tool-path planning, we can make up the coupling and the nonlinear nature of long distance movement. That is to say a large work-piece should be subdivided into patches first. After subdivision, it is easy to keep the polishing intensity of pressure continuously in a convex or a concave surface patch by the actuator.In this case, it is necessary to develop new tool-path generating methods for this machine tool. And because of the available open CNC systems are not open in their core techniques, it is difficult to change their interpolation method and to modify their control algorithms. In order to fully utilize the faculties of this machine and to fulfill the aim of NURBS direct interpolation, the research group decides to make our own CNC system. Anyway, the main target of this dissertation is to discuss the algorithms of the polishing tool-path planning that can simulate human elastic lapping and dressing behavior.The most commonly used methods for tool-path generation are contour-parallel, iso-parametric, iso-planer, iso-scallop. In these methods, a unique standard is introduced to ensure the preciseness of a work-piece, which is the scallop height h. But all of them produce non-continuous tool path and need many tool retractions during machining. Newly developed...