The Effect of Flexible-Tool Rotation on Regenerative Instability in Machining

Abstract

For rotating-tool machining, such as milling, line boring, and cylinder boring, the tool rotation causes the machining force on each tooth to rotate repetitively relative to the inertial coordinate frame. This is quite different than stationary-tool machining, such as turning or boring with a stationary boring bar, in which the force directions are fixed relative to the inertial frame. Although the subject of stability analysis for rotating tools has been studied extensively in milling, the process is intermittent and hence time varying, which leads to analysis methods that are either analytically approximate or employ time-domain simulation. In this paper nonintermittent machining processes that employ a rotating tool are modeled and analyzed in the rotational coordinates both to simplify the stability analysis and to permit an exact solution. Using rotating-bar boring to illustrate, the analytical results show that the stability limits for boring with a rotating boring bar are quite different from those for boring with a stationary boring bar, and the experimental validation is also provided. Furthermore, the results show a discrepancy to exist between the predicted stability limits for the exact and approximate solutions, especially at low spindle speeds. In both cases an explanation is provided based on the analysis presented.