The 5-axis machining of sculptured surfaces offers many advantages over 3-axis machining, including faster material-removal rates, reduced machining time, better tool accessibility, and improved surface finish. In practice, 5-axis machining suffers from a number of drawbacks, such as difficulty in tool path planning, vulnerability of cutter interference, and instability of inverse-kinematic solution. As a result, 5-axis machining has mainly been used in special mass-production applications such as marine propellers, turbine blades, and impellers. In recent years, however, there are increasing demands for 5-axis machining of die and mold, especially car body stamping dies. This thesis is intended to contribute to the development of a CAM software system (or NC module) for 5-axis machining of die and mold.
Described in the thesis are overall procedures of generating 5-axis NC tool paths for the machining of sculptured surfaces represented in three different forms: parametric surface model, Z-map model, and triangular facet model. The generation of 5-axis NC tool paths in general consists of the following five steps: 1)preparation of machined surface models and raw stock shape model, 2)modeling of 5-axis machine structure and tooling systems, 3)planning and generation of CC(cutter contact) paths, 4)generation of interference free CL-data (cutter location data), 5)tool path smoothing (linearization in joint space) and post-processing.
For a machined surface represented as a parametric surface model, CC paths are generated along iso-parametric lines and a method of generating 'optimal' 5-axis CL-data is presented. In order to prevent cutter interference in parametric surface machining, a secondary Z-map model is constructed from the parametric surface model and a heuristic scheme of interference avoidance is applied. The proposed optimization scheme has been successfully applied in the five-axis face milling of large marine propellers.
When the machined surface is in a Z-map form, CC-paths are planned on the x,y-plane and interference-free CL-data are generated from the Z-map model. As it is very time consuming to check possible interferences between the cutter and the Z-map model, the concept of bucketing and majorizing is utilized to speed up the computation. Then the machined surfaces is in a triangular facet model, CC-paths are generated by intersecting the facet model with a series of vertical (and parallel) plane and interference-free CL-data are generated by checking the possibility of interference between the cutter and each of the triangles in the facet model. As with the Z-map case, the concept of bucketing and majorizing is utilized to speed up the computation.
