Batch Mode Microultrasonic Machining ( $\boldsymbol \mu $ USM) Using Workpiece Vibration

This letter reports on the evaluation of an unconventional approach to microultrasonic machining in which the workpiece is vibrated while the tool remains static. The vibration of the workpiece, and not the tool, alleviates the accumulation and the agglomeration of the slurry particles and debris between the machined features. This approach is appealing for batch mode pattern transfer of closely packed features into ceramics and glass. However, the question of how the workpiece vibration will cause selective machining of features on the opposing tool surface has not been addressed. In this effort, fluidic modeling is performed to study slurry flow due to workpiece vibration. The modeling reveals a higher slurry velocity (2.20-2.46 m/s) in the target machining regions confined by the proximity of the tool tips and a lower velocity (0.16-0.50 m/s) elsewhere. To demonstrate and characterize the resulting machining ability, arrayed tools made from stainless steel #304 with feature sizes ranging from 5-50 μm were used on flat workpieces of fused silica. At 20-kHz vibration frequency and 12-μm tool-to-workpiece separation, the average machining rates ranged from 6-90 nm/s for workpiece vibration amplitudes ranging from 1-5 μm. The average surface roughness, S
_a
, was 40-65 nm. The tool wear, i.e., the ratio of the tool height worn to the machined depth, was <;4%.