Dynamics and chatter stability of crest-cut end mills

Abstract

Chatter is a major problem reducing part quality and productivity in milling operations. In order to improve productivity with standard end mills, higher cutting speeds must be employed to reach deeper stability lobes. However, due to machine tool and machinability limitations in cutting hard-to-cut materials, higher cutting speeds are not feasible. For those cases, special milling tools such as variable pitch and crest-cut cutters offer an alternative method to increase productivity. Due to their special geometry crest-cut tools introduce large stable regions at low-speed ranges where variable pitch tools provide narrow stability lobes. This advantage is caused by the wavy edge shape along the cutting edges of the crest-cut tools. In this study, stability of crest-cut tools is studied using the semi-discretization method by implementing a novel geometrical modeling approach enabling accurate cutting force predictions verified experimentally for the first time in literature. Based on the proposed model, the effect of edge wave geometry on stability is analyzed and compared with standard and variable pitch tools. Results show that the crest-cut tools introduce significant advantages in terms of stability limit and stable zones compared to other types of end mills. This superiority results in higher productivity as well as higher robustness at a different cutting speed zones. Finally, a guideline is presented for selection of the best crest-cut tool geometry for desired operating conditions.