Improvement of micro-hole precision by ultrasound-assisted drilling of laser powder bed fused Ti6Al4V titanium alloy

Ti6Al4V alloy can be successfully used to fabricate complex near-net-shape industrial products and prosthetic components with enhanced biocompatibility by means of additive manufacturing (AM) technologies. Post-processing machining of such components are still necessary steps; however, the different machinability that characterizes AM products affect the manufacturing process in a great extent. To this aim, Ti6Al4V cylindrical samples were produced by laser powder bed fusion (LPBF) and micro-holes were machined on their surfaces by varying the cutting speed and feed per tooth, using both vibration-assisted drilling (VAD) and conventional drilling (CD). The drilled holes were comprehensively characterized in terms of geometrical, dimensional and outer edge quality, surface roughness, surface defects and microstructure. In general, VAD was found to improve the overall quality of the holes, regardless the cutting parameters applied thanks easier evacuation of the chips as well as enhanced material flow. To find the optimize process parameters conditions, all the characterization outcomes were combined in a global quality index (Qi). The highest cutting speed, the lowest feed per tooth and the use of VAD undoubtedly leads to the formation of the holes characterized by the best surface quality. The improvement given by VAD with the respect of the corresponding CD operation is found equal to 65%. These findings confirm the effectiveness of using VAD when approaching difficult to cut materials such as titanium alloys produced by LPBF.