Reducing the cutting tool wear in diamond turning of Zerodur glass-ceramic by the mechanical cleaning effect of ultrasonic vibration assistance

The effects and mechanisms of using ultrasonic vibration assistance (U.V.-assisted machining) combined with straight-nosed cutting tools on reducing the cutting tool wear in single-point diamond turning (SPDT) of Zerodur glass-ceramic are analysed and experimentally investigated. Aiming at the predominant abrasive wear in machining hard and brittle materials, analyses have shown that applying appropriate ultrasonic vibration to the cutting tool can induce considerable inertial acceleration to the wear particles residing on the tool-work interface for promoting their ejection from the contact area to reduce the abrasion. Meanwhile, the high thermal conductivity of diamond can prevent the possible excessive temperature elevation of the cutting tool surface that may result from the in-plane vibration components. To verify these, a longitudinal ultrasonic vibrator that works together with the Poisson's effect was designed for the SPDT processes with straight-nosed cutting tools. Machining tests on Zerodur optics have shown that the assistant ultrasonic vibration is able to decrease the tool flank wearland width by about 30 %, and the groove-like scratches on the tool flank wearland surface were reduced, which is consistent with the analytical deductions. Besides, no significant traces of structural change, element diffusion, and oxidation were found on the worn cutting tool surfaces under either the assisted or un-assisted cutting conditions. The experiments have also shown that the enhanced durability of cutting tools has extended the cutting tool life for maintaining good machined surface quality, which is particularly beneficial to the ultra-precision machining of large-size optical parts.