Tool selection and path planning in 3 - axis rough machining

We present a novel approach to CAD/CAM integration for 3-axis machining. Instead of redefining the workpiece in terms of machining features, we generate tool paths directly by using the accessibility of the surface of the part as the central and the over-arching constraint. This eliminates the problem of feature extraction. We envision this as the core strategy of a new direct and seamless CAD/CAM system. We perform our analysis in two steps: global roughing and face-based finishing. In this thesis, we present algorithms to select optimal roughing tools and to generate roughing tool paths directly from the shape of the model using geometric volume filling algorithms for a given setup. Assuming that the part is already oriented in a given setup direction, our approach to global roughing is based on slicing, clipping and filling. We slice the component into a number of layers, clip lower layers to the vertical shadows created for upper layers (because shadowed regions cannot be reached by a non-overhung tool), and generate tool paths to fill each slab. In this way, we can generate interference free tool paths directly from the boundary representation. The clipping approach permits us to account for the shapes of tool holders and spindle while computing the accessibility of a tool-assembly. Our approach to tool selection is based on a comprehensive computation of the area the tool can access at each slab. In the process of selecting an optimal tool sequence, we develop methods to rank the material removal rates achievable by using metal cutting theory. The search space for optimal tool sequence selection, is drastically reduced by using cluster-ordering techniques and then pruning the ineffective tools from the sequence using a greedy algorithm. Once the tools and sequence have been selected, a contour-shrinking tool path is generated using a Voronoi Diagram. The output of this system is a numerical control(NC) tool-path code. This information is generated directly from the CAD representation with no operator assistance.