Experimental characterization of the inner surface in microdrilling of stainless steel: a comparison between EDM and ultrashort laser pulses

The inner surface morphology of micro-drilled hole is analyzed, at nano-scale, by Shear Force Microscopy (SHFM). A difference in morphology of the drilled surfaces is evident for the two examined drilling techniques: EDM and fs-pulses laser. Surface topography is acquired in three specific areas along the hole axis (entrance, centre and exit) and filtered to remove the hole curvature. Acquired maps confirm that surfaces obtained by electroerosion are less regular and characterized by a random distribution of craters. Laser ablated surfaces offer a better uniformity and a smoother texture with a peculiar periodic structure. The mean-squared surface roughness (RQ) derived from the scanned maps ranges between 250-500 nm for EDM and 80-125 nm for fs-pulses laser drilling. Laser ablated surfaces are found to be more regular in diameter along the thickness of the material with an extremely sharp edge at the exit side.