A study on the effects of machining variables in drilling and surface grinding of Zerodur glass ceramic using rotary ultrasonic machining

Zerodur® glass ceramic, featured by its near-zero thermal expansion coefficient and exceptional thermal homogeneity, is a preferred substrate material in ultra-precision optical systems such as photolithography equipment and astronomical telescopes. However, its inherent brittleness and low fracture toughness pose significant challenges for conventional machining processes, often resulting in subsurface damage and accelerated tool wear. This study investigates the viability of rotary ultrasonic machining (RUM) for machining Zerodur glass ceramic through drilling and surface grinding. The effects of ultrasonic power, spindle speed and feed rate on cutting force, surface roughness and edge chipping were studied. Surfaces produced by grinding with ultrasonic vibration and without ultrasonic vibration were systematically compared. Residual stress within machined components was characterized and compared using Raman spectroscopy. Cutting tool wear was studied. Material removal mechanisms were investigated through nanoindentation and scanning electron microscopy. The experimental results demonstrated that drilling thrust force decreased by up to 55% as ultrasonic power increased from 0% to 50% at fixed machining conditions (7000 rpm, 0.01 mm/s). Improved surface finish and minimal edge chipping were achieved at high spindle speed and moderate feed rate. Additionally, RUM was able to facilitate reduction in residual stress generation and promoted material removal via ductile deformation with minimal tool wear.