NC tool path evaluator and generator for high speed milling

Milling is a most common type of material removal process by rotating tools to create a variety of features on a part. The material is removed in a controlled way by sweeping a rotating cylindrical tool along the specific trajectory known as milling tool path. For any specified shape and volume of material to be removed, there are a variety of possible tool paths and cutting conditions. These different possibilities can be evaluated based on various geometric as well as process related factors. Milling time is one of the most important factors in evaluating the process efficiency, which depends upon the tool path planning and the behavior of the physical machine tool. Tool path planning usually considers factors such as limitations of cutting tools, tolerance requirement and workpiece geometry etc., which directly influence the milling process time. Further, as milling process involves physical interaction between tool and workpiece, the wear and tear of milling tools is an important issue. As the breakdown of cutting tools is detrimental for productivity; the tool paths must be evaluated based on other important physical considerations like cutting forces and chatter. A number of cutting force models on the preselected cutting parameters with high reliable prediction capability are already available in the literature, however, a simplified category of constant engagement zones are usually assumed to exist. Engagement zone may vary along the tool path as it depends on instantaneous in-process workpiece geometry and hence imparting a change in the cutting forces also. Thus one of the objectives of this work is to present a system to verify a milling process plan to incorporate arbitrary tool paths and in-process changes in workpiece geometry. Among the available tool paths, contour parallel tool paths are the most widely used tool paths for 2D milling operations. A number of exact as well as approximate methods are available for offsetting a closed boundary in order to generate a contour parallel tool path; however, most of methods are inherently incapable of dealing with complex problems (change in topology and self intersecting feature) during offsetting and require highly efficient computational routines to identify and rectify these problems. In this work, a boundary value formulation of the offsetting problem is studied and a fast marching method based solution for tool path generation is presented. This method handles the topological changes during offsetting naturally and deals with the generation of discontinuities in the slopes by including an "entropy condition" in its numerical implementation. A number of examples are presented and computational issues are discussed for tool path generation. Although, the tool path generation methods discussed earlier guarantee to generate a geometrically feasible tool path the in-process engagement is still not constant or its variation is not minimized. This leads to variation of actual radial depth o