Freeform surface fabrication on hardened steel by double frequency vibration cutting

Hardened steel is a typical hard-to-cut material and is widely used in mechanical components and molds. It is still challenging to precisely and efficiently fabricate freeform surfaces on hardened steel using conventional slow slide servo (SSS) and fast tool servo (FTS) diamond turning. Ever since the double frequency vibration cutting method has been proposed, its advantages have been demonstrated in machining microstructures on steels. Nevertheless, the surface quality and the depth of the machined microstructures by this method remains limited due to limitations imposed by existing double frequency vibration cutting systems. Therefore, an improved double frequency vibration cutting process and the corresponding cutting system were developed. The system consists of a 1D non-resonant compliant vibrator, a 2D resonant ultrasonic vibrator, a three-axis translational stage and a control system. In this system, the low frequency vibration generated by the 1D non-resonant compliant vibrator is used to generate the freeform surface, while the ultrasonic elliptical vibrations generated by the 2D resonant ultrasonic vibrator are responsible for improving the machinability of the hard-to-cut material. In addition, benefiting from the newly proposed configuration, the developed double frequency vibration cutting system overcomes some inherent drawbacks of the conventional SSS/FTS. Based on the working principle of this double frequency vibration cutting method, a tool vibration path generation strategy is proposed. To ascertain the feasibility of the developed double frequency vibration cutting system, experiments were conducted on hardened steel. The machined freeform surfaces show high consistency with the simulation results.