Robust Control of High Speed End Milling with Unknown Process Parameter and CNC Delay

Abstract

Lack of complete knowledge of process characteristics, particularly uncertainties associated with milling processes and spindle behavior, severely limits the reliability of high speed spindles to support high speed machining. Attempts to regulate high speed milling processes based on sensing spindle power and controlling feed rate to prevent spindle stalls have not been successful, mainly due to the fact that power is often not the limiting factor. Instead, problems such as chatter, cutter and/or part deflection, milling forces, and its effects on the rapid wear of the taper of the tool holder and the spindle bearings can easily lead to scrapped parts and/or spindle breakdowns unless extreme care is taken. This paper addresses the stability analysis and design of a novel, robust, nonlinear milling controller implemented at Boeing Co. This controller is aimed at driving an end mill at the highest possible feedrate without damaging the cutter and the spindle. The successful implementation of this controller at Boeing has significantly reduced spindle failures in their extremely demanding high speed machining production lines.