Cutter/Workpiece Engagement Feature Extraction from Solid Models for End Milling

Abstract

Accurate process modeling requires the calculation of cutter/workpiece engagement (CWE) geometry. This is challenging when the geometry of the workpiece is changing unpredictably as is the case for most machined components of moderate complexity. Solid modelers are increasingly being considered as a computational engine for performing these calculations. This is largely due to increased robustness and computing efficiency that is evolving within this technology. The vast majority of reported research using solid modelers focuses on the domain of 212D machining with flat end mills. While significant there remain restrictions in the types of in-process workpiece geometry that can be processed with these approaches. In particular, they assume a constant axial engagement for a connected set of tool paths. This assumption cannot be made when the initial workpiece geometry is nonrectangular prismatic stock, when multiple setups are machined and when tool changes introduce tools of different diameters. In these cases the depth of engagement can vary over a single rotation of the cutter even though there is no axial feed motion. In this paper a solid modeling based solution is presented for calculating CWE geometry when multiple setups and tool changes are considered. Orthogonal setups and flat end mills are assumed so as to preclude cutter engagement on inclined workpiece faces. Intersections between a semi-cylinder representing the cutting tool and the workpiece are performed so as to generate the CWE geometry. Cutter Engagement Features (ceF) are used to characterize this geometry. Several classes of ceFs are defined to support this approach. The process of identifying ceFs is presented as a feature extraction problem. Algorithms for ceF extraction and parametrization are provided in this paper and validated using a test part. This is a new application for features which have traditionally been used to define final part geometry or in-process geometry between material removal steps. The results obtained validate the extraction algorithms presented. This work also extends the capabilities of solid modeling techniques for calculating CWE geometry.