Surface finishing on IN625 additively manufactured surfaces by combined ultrasonic cavitation and abrasion

Abstract

The poor and non-uniform surface quality of parts produced by powder bed fusion (PBF) processes remains a huge limitation in additive manufacturing. Here we show that ultrasonic cavitation abrasive finishing (UCAF) could improve the surface integrity of PBF surfaces built at various orientations –0°, 45° and 90°. Average surface roughness, Ra, was reduced from as high as 6.5 μm on side surfaces (90°) to 3.8 μm. Surface morphological observations showed extensive removals of surface irregularities and peak reduction on sloping (45°) and side surfaces. The micro-hardness of the first 100 μm of the surface layer was enhanced up to 15 % post-UCAF. Dimensional changes were minimal and uniquely dependent on the initial surface characteristics. A parametric study further showed the effect of abrasive size, abrasive concentration, ultrasonic amplitude and working gap on UCAF's performance. A moderate abrasive size at 12.5 μm and concentration level at 5 wt% resulted in the lowest final Ra; as the two dominant material removal mechanisms – direct cavitation erosion and micro-abrasive impacts – were balanced. Finally, UCAF was demonstrated to result in 20 % Ra improvement of internal surfaces of a 3 mm diameter channel.