Improved stability predictions in milling through more realistic load conditions

Abstract

In this paper, the combined influence of the load condition and the spindle speed on the tooltip dynamics of a five-axis milling machine with dominant spindle modes is evaluated. A constant preload is applied through axially and radially arranged permanent magnets while the dynamic excitation of the rotating dummy tool takes place by a force impact. The structures response is measured with non-contact sensors and Frequency Response Functions (FRFs) are calculated. The required load levels are derived from time domain simulation of the process. The so-obtained stability charts are hence functions of the rotational speed and the load condition which in turn depends on the feed rate and depth of cut. For validation, cutting tests are performed in Aluminum 7075 and results are compared against the predicted lobes. The stability boundary resulting from this approach is capable to explain the shift of the stability pocket which is observed in the cutting experiments when comparing different feed rates.