Piezoelectric Tool Actuator for Precision Turning of Turbine Shafts on Conventional CNC Lathes

A piezoelectric tool actuator system is presented for precision turning of turbine shafts on conventional CNC turning centers. The actuator system provides precise motion in the radial direction to accurately set the depth of cut in finish turning. The actuator allows for exchangeable turning tools and features a compact and self-contained design which can interface to standard turrets. Motion from the high voltage piezoelectric actuator is transmitted to the tool free of friction and backlash through the use of solid flexures. The overall stroke of the actuator is 36 μm, with a stiffness of 370 N/μm, and a natural frequency of 3200 Hz in the radial direction. A sliding mode control design provides positioning resolution of +/- 10 nm. The system was evaluated for turbine shaft machining. Tolerances on diameter of 1 μm were achieved, with an average surface roughness of 0.4 μm in machining AISI 4340 shafts (35-40 HRC). Overall the actuator demonstrated increased positioning accuracy compared with conventional turning centers.