Experimental investigation into optimal conditions for ultrasonic-assisted microhole grinding using PCD tools

Ultrasonic-assisted microhole grinding using wear-resistant polycrystalline diamond (PCD) tools effectively mitigates grinding forces in hard, brittle materials. This study investigated the ultrasonic-assisted microhole grinding of single-crystal silicon using PCD tools fabricated via electrical discharge machining (EDM). Optimal conditions for minimizing grinding force and improving hole quality were identified: tool feed speed of 0.20 µm/s or less, tool rotation speed of 1000–2000 min⁻¹, and ultrasonic oscillation amplitude of 0.50–1.25 µm. Although conventional square tools achieved sub-5 µm grinding, the hole entry exhibited elliptical morphology and poor circularity. To resolve this issue, corner-radius tools were developed by leveraging EDM electrode wear to round the peripheral edges. This geometry stabilized tool engagement and suppressed entry chipping. Comparative experiments demonstrated that the corner-radius tool effectively eliminated elliptical morphology while minimizing chipping, successfully achieving an ultrasmall hole with a diameter of 4.5 µm with high circularity.