Cycle time prediction in high-speed milling operations for sculptured surface finishing

Abstract

This work studies the cycle time prediction of high-speed milling for sculptured surfaces with high feed rates. Experiments and predictions were focused on representative surfaces of dies and molds, whose geometric complexity and complexity distribution were modified parametrically. CNC programs for machining these surfaces were executed in a HURON KX-10 machining center with a SIEMENS 840D controller, with different levels of programmed feed rate. Discrepancies between programmed and actual feed rates were evaluated. A mechanistic approach for cycle time evaluation in high-speed milling of sculptured surfaces is proposed. The mechanistic model construction is based on: (a) the frequency distribution (histogram) of linear interpolation path lengths in the CNC program and (b) a characterization of the machine tool for brisk (large changes in tool path direction) and smooth movements (small changes in tool path direction). Two case studies were used to demonstrate the effectiveness of the proposed approach (a set of representative sculptured surfaces with spherical caps and a forging die surface). Comparing the actual cycle time versus ideal cycle time under programmed feed rates up to 16 m/min, discrepancies of 300–800% were found. The proposed model is capable of predicting cycle time with a maximum error of 5–22%.