Research On Wide Strip Numerical Control Machining Theory And Its Application For Sculptured Surface

Numerical control (NC) technology is the foundation and core of advanced manufacturing technology, and has become a symbol of the national manufacturing development level. As an important part of NC technology, the NC machining programming technology has been always the focus and difficulty of research. Along with the development of aerospace, automobile, new energy, microelectronics and other fields, increasing products with sculptured surface have led to higher challenges for the NC machining programming technology. At present, the wide strip NC machining, which aims to realize the line contact, has shown its obvious advantage in the processing efficiency. However, there is a great deal of research on the theory and application to be carried out. For this reason, based on the toroidal cutter, the research mainly on tool positioning and tool path planning of the wide strip NC machining programming technology for sculptured surface was deeply implemented.After analyzing the existing theory of multi-point machining and classical multi-point tool positioning algorithms, the general mathematic model of the multi-point machining was established to provide an important theoretical basis for the subsequent research work. The optimization objective function was to maximize the machining strip width. And the three main constraint conditions were used to make tool and workpiece surface meet absolutely tangent in the two contact points, avoid the local gouge and control the maximum undercut error between the two contact points. For the convex sculptured surface machining with the toroidal cutter, the relational expression between the surface curvature and the tool's parameters without interference was deduced. In addition, the calculation method of tool position error distribution and machining strip width based on the circular curve of the toroidal cutter was also given.According to the drawback of Arc-intersect Method (AIM), the improved Arc-intersect Method (IAIM) was put forward. The relative location relationship between the toroidal cutter and the workpiece surface was firstly translated into that between the circular curve of the toroidal cutter and the offset surface of the workpiece surface. Then the parametric equation of the circular curve of tool determined by the backwards angle of tool was deduced. The final too positions were gotten after that the backwards angle of tool was to be optimized by the bisection method. Meanwhile, the improved algorithm for calculating the minimum distance between the circular curve of tool and the workpiece surface was also presented in order to avoid the local gouge. An example showed that the IAIM could not only be stable and efficient, but also produce the "W" shaped tool position error distribution like those multi-point tool positioning algorithms. Though there was only one contact point between the toroidal cutter and the workpiece surface, the IAIM was also considered to be an effective wide strip NC machining algorithm because it made the line contact machining become true under the given machining precision.Based on the IAIM, the Rotary Cntact Method (RCM) that contained two contact points and belonged to the wide strip NC machining algorithm was developed. The parametric equation of the circular curve of tool defined by the backwards and side tilt angle of tool was similarly deduced. As the optimization of the backwards and side tilt angle of tool was finished, there were two contact points between the toroidal cutter and the workpiece surface around the minimum direction of curvature without gouging. The RCM improved the workpiece surface quality and was verified by an example.In order to obtain the smooth tool paths and take full of the advantages brought by the wide strip NC machining algorithm, the definition of characteristic point, characteristic curve, characteristic parameter curve and characteristic parameter machining field was respectively given. Furthermore, the characteristic parameter curve tool path planning method was presented here. The basic idea was to determine the optimal tool positions by the RCM, and then make the left characteristic parameter curve of the next path being collinear with the right characteristic parameter curve of the current path under the given machining precision by the iterative calculation. Finally, the tool paths were completely arranged. An example showed that the characteristic parameter curve tool path planning method could not only generate the smooth and interfere-free tool paths, but also improve the actual machining efficiency by contrast with the iso-parametric method.The multi-point machining for the general convex sculptured surface was discussed through the example of cover car convex surface. The method to complete the model reconstruction of the cover car convex surface from the scattered points clouds was firstly described. Then the tool position error distribution for different path directions was deeply inspected. Results showed that the condition for multi-point contact was to make the tool feed along the maximum direction of curvature of the convex surface, which was completely opposite to the concave surface. At last, the relationship between the key parameters of the wide strip NC machining algorithm and the tool position error distribution was discussed. The non-interference tool paths for the cover car convex surface were gotten by the RCM and the characteristic parameter curve tool path planning method. Computational results and the machining experiment proved the proposed tool positioning and tool path planning method once again.