Study On The Modeling And Multi-axis NC Machining Technology For Freeform Surface Blade

With the rapid development of aerospace industry and automobile manufacturing, freeform surfaces have been widely used to represent the complex mechanical parts. In order to obtain higher machining efficiency and better machining quality, multi-axis numerical control (NC) machine tools should be applied to the machining process of these mechanical parts. So freeform surface modeling and multi-axis machining has become an important research branch of CAD/CAM technology.In this dissertation, the geometry modeling and NC machining technology for blade surface of centrifugal compressor impeller is studied deeply and systematically. The main research consists of non-uniform B-spline modeling method and tool-path generation method of multi-axis NC machining for blade surface. The main contents are described as follows:Firstly, through the study of relative algorithms of non-uniform B-spline curve and surface, C++ programming language and object-oriented programming method are adopted to realize these core algorithms. By embedding OpenGL in Visual C++/MFC integrated development environment, the blade surface is demonstrated.Secondly, on the basis of analysis for the tool-path generation method of multi-axis NC machining, iso-parametric method and iso-scallop method are adopted to generate the machining tool paths for the blade surface. Through the calculating of the path interval, step length, cutter contact point, cutter location data and tool axis vector, then, the tool paths are generated according to iso-parametric method. This method is easy to be realized, but the drawback is its low efficiency with respect to iso-scallop method. On the basis of differential geometry properties of surface and calculating of the adjacent cutter contact paths, iso-scallop method is proposed to generate the tool paths for the blade surface. The scallop height generated between adjacent tool paths remains constant. This makes no tool-path redundancy in machining process, and leads to a higher machining efficiency. Tool paths are demonstrated in the Visual C++/OpenGL environment by tool-path generation methods with ball cutter. It is shown that the tool paths distribute orderly on the offset surface of the original blade surface.Thirdly, the properties of multi-axis post-processing are also analyzed in the dissertation. Different four-axis post-processing algorithms are involved considering the different configuration of NC machine tools.Finally, based on the NC program which is generated through post-processing, the proposed methods and algorithms are verified by computer machining simulation with SL-EXSLWIN software. Eventually, an experiment is implemented on three-axis machine tool. The results indicate that the proposed algorithms are correct.