Laser percussion micro-drilling on PBF-LB/M-manufactured CoCrMo alloy plates: process characterisation and comparison with additively manufactured holes

The paper deals with the laser micro-drilling of CoCrMo superalloy sheets, 1.5 mm in thickness, manufactured via powder bed fusion by laser beam melting (PBF-LB/M) technology, by percussion drilling techniques. Laser drilling tests were carried out using a 450/4500 QCW pulsed fiber laser with a pulse power of up to 4.5 kW. The experimental tests were performed adopting a Box-Behnken design. During the tests, the pulse power, pulse duration, assistant gas pressure, focus position, and total released energy were varied. Hole geometries were characterised at the beam entrance and exit by adopting a 3D digital microscope. The entrance and exit diameters, roundness, taper angle, spatter area, and maximum dross height were analysed. ANalysis Of VAriance (ANOVA) and Response Surface Methodology (RSM) were adopted to investigate the influence of the process parameters and model the process. The geometrical characteristics of the laser-drilled holes were compared to additively manufactured ones. Multi-Objective-Optimization (MRO) was adopted to identify optimal process conditions to produce micro-holes with an imposed diameter and minimal taper angle. Then, the RSM model was experimentally validated, showing a strong correlation with predicted values up to 600 µm. Moreover, the geometry of additively manufactured holes was characterised too, and the mechanisms of defect generation were discussed. From the result, comparing the geometry of the laser-drilled holes to the ones obtained by additive manufacturing, the former technique is particularly competitive in the diameter range of 300–600 μm.