Cutting torque feedback control for thin-wall conical workpieces

An innovative approach of online cutting torque estimation and real-time feedback control for thin-wall tubular geometry workpieces is proposed and verified by experiments. This research is focused on how to formulate the appropriate applied cutting torque estimated by the feedback of current to spindle motor during milling process so that the milling cycle can be greatly reduced. On the other hand, a few suitable cutting conditions to prevent potential break/crack of thin-wall workpieces that enhance productivity but almost retain the same cutting quality are addressed as well. To achieve these goals, the milling dynamics of the thin-wall tubular geometry workpieces, including milling vibration and static deflection, is constructed at first. Based on the dynamic model, a fuzzy adaptive torque tuning (FATT) control strategy is synthesized to adaptively maximize the vertical feed rate under the constraint of preset upper limit of surface profile error on workpieces. Finally, the milling experiments and surface profile error measurements for the thin-wall tubular geometry workpiece have been undertaken to examine the effectiveness of proposed FATT strategy. Compared with constant cutting torque policy, it is observed that the vertical feed rate can be increased by 230 % under FATT. It implies that the required milling cycle is greatly shortened more than 70 % while the corresponding cutting accuracy upon finish of workpiece can be almost retained.