Generic solid modelling based machining process simulation

Abstract

<p>In machining, the ability to automatically generate an optimum process plan is an essential step toward achieving automation, higher productivity, and better accuracy. These requirements are particularly emphasized in die and mold manufacturing, where complex tool and workpiece geometries involved make generation of the process plan a difficult task. High die production costs, narrow tolerance requirements, and the continuous demand for new components make process planning and NC code generation very complex and error-prone tasks. The current research need is to develop a system that is based on a simulation of the actual machining process, rather than simple geometric verification. Such a machining process simulator is needed to respond to the current need to enhance CAD/CAM technology with a machining process simulation that accounts for process mechanics and dynamics. A major impediment to implementing these systems is the lack of a general and accurate method for extracting the required geometric information. In this thesis, a novel approach to perform this task is presented. It uses general and accurate representations of the part shape, removed material, cutting edge and rake face. Solid models are used to represent the part and removed volume, B-spline curves are used for the cutting edge representation and B-spline surfaces for the rake face. Next, a generic solid modeler based milling process simulation system for 3-axis machining of complex parts using flat and ball end mills is implemented. It consists of geometric and physical simulators. In the geometric simulation, the tool swept volume is generated for every completed tool path (one NC block) and intersected with the part, yielding the corresponding removed material volume. The tool cutting edges are then intersected with that volume to produce the tool-part immersion geometry in the form of in-cut segments. These and an expression for the chip thickness are used to determine the chip load distribution along the cutting edge. The updated part can be used instead of the removed volume in the intersection step to generate the in-cut segments. The physical simulator models the mechanics and dynamics of the cutting process and uses the chip load to compute instantaneous cutting forces and predict other process parameters. The milling process simulation is demonstrated and verified experimentally for 2 1/2- and 3-axis ball end milling. In addition, it is shown that geometric modelling of 4- and 5-axis milling using different tool shapes as well as other machining processes such as turning and drilling can be performed using the same approach.</p>