Research On Tool Path Generation Technology For High-Performance NC Machining Of Sculptured Surface

With the rapid development of automotive industry in China, more sculptured parts are used in automobiles for aesthetic and mechanical functions. In CNC machining of these sculptured surfaces, tool paths are crucial to high performance machining: high surface accuracy and finish, high machining efficiency, and long tool life. Especially, in surface finish machining, tool paths planned with high speed and high accuracy can produce quality surfaces without much machining time and manual polish. However, due to the complexity of the sculptured parts and limits of CNC machine tools, generating tool paths for high performance machining is quite difficult.In the conventional approach for CNC machines to perform a sculptured surface machining, the cutter location (CL) path generated by CAM system are usually divided into a set of line or circular segments (also called NC codes). These segments will approximate the original CL path to a desired accuracy if sufficient numbers of segments are used. To obtain a more accurate approximation and to reduce the contour error, the size of the NC code should be increased, but this approach could lead to the following drawbacks. Firstly, too many short segments will slow down the cutting speed. In addition, the CNC machining task may never achieve the desired feedrate due to the automatic acceleration and deceleration applied at the beginning and end of each segment. As a result, the feedrate is not constant along the CL path and thus the smoothness of the cutting surface will be affected. Second, a large number of segments will increase the federate variations and the machining time, which will reduce the averaged feedrate. Finally, the CNC's memory capacity is relatively small compared with the number of segments to be stored for a machining part with complex surfaces.Based on the above observation and analysis, it is evident that accurate high-speed manufacturing is hard to achieve if the conventional line and circular command generators are used. To solve this problem, smooth tool paths with G1 continuity are necessary to guide the CNC machine to perform the cutting work.This thesis focuses on the research about tool path generation for high-performance NC machining and involves the tool path generation of arc spline, non-gouging biarc and Non-Uniform Rational B-Spline (NURBS) with G 1 continuity.1) A new algorithm is proposed to fit a 2D NURBS profile with an arc spline, and then the arc spline tool path with G1 continuity is generated. The main contribution of...