Proposal of an evaluation method of variation in tool center points for ball-end milling of free-form surfaces

Though high surface quality is expected in die and mold machining, machined surfaces often need to be polished to improve their quality after machining. One of the main reasons for the deterioration of the machined surface is the tool paths generated for ball-end milling. Variation in tool center points in the feed direction may occur even in tool paths that are generated using a commercial computer-aided manufacturing (CAM) system. The variation often causes a lack of uniformity on the machined surface. However, it is difficult for unskilled operators to estimate the machined surface prior to machining. Therefore, there is a need for a method for evaluating variation in tool center points that does not depend on the skills of operators. In this study, to achieve high surface quality, a novel method for evaluating variation in tool center points is devised for the free-form surfaces of dies and mold. An appearance indicator is introduced to quantify the degree of non-uniformity of the machined surface and derive an evaluation index. The effectiveness of the proposed method is verified by conducting machining experiments using different tool paths. The tool radius and pick feed are changed to confirm correspondence between the obtained surface quality and the derived evaluation index. The machining experiments successfully demonstrate that the proposed evaluation method can be used to improve surface quality.