Pulsed Laser Micro Polishing of Microfabricated Nickel and Ti6Al4V Samples

The objective of this work is to improve our understanding of pulsed laser micro polishing (PLμP) by studying the effects of laser pulse length, pulses per mm, and workpiece material on surface roughness. PLμP experiments are conducted with a multi-mode Nd:YAG laser (1064 nm wavelength) that is focused down to approximately 50 μm diameter and scanned over the stationary workpiece surface. Simulation results presented here and previous work suggest that longer laser pulses are better for polishing. Results on microfabricated nickel samples using laser pulse lengths of 300 ns and 650 ns test this hypothesis. Additionally, a surface artifact introduced by the PLμP process will be investigated. Results on the microfabricated nickel sample prove that longer laser pulses yield a higher reduction in surface roughness; 300 ns and 650 ns pulses reduce the R_a of the sample by 30% and 50%, respectively. The artifact introduced by the PLμP is found to be directly related to the number of laser pulses per mm. Successful polishing is achieved on Ti6Al4V and the surface roughness (R_a) of the sample is reduced from 0.250 μm to 0.058 μm. It is also shown that the presence of argon shielding gas is necessary to avoid surface cracks. The results presented here further validate the simplified thermal and fluid flow modeling of the PLμP process and demonstrate the effectiveness of PLμP on a broadly used titanium alloy, Ti6Al4V.