Electro-Discharge Drilling on DMLS parts in Co-Cr-Mo alloy

Cobalt-base alloys are generally used in applications that require wear, corrosion and heat resistance. In particular, Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloy is adopted in the aerospace and medical field. These applications are characterized by low volumes and high personalization, so they could take advantage by the employment of additive technologies, such as Direct Metal Laser Sintering (DMLS). This technology still has limitations for the manufacture of small cavities, such as holes with diameters below 0.6 mm and high aspect ratio, which require drilling of the additive manufactured part. Scope of this research is to investigate the effects of Electro-Dicharge Drilling (EDD) on surface and subsurface features of CoCrMo samples built by DMLS. High aspect ratio holes are produced with diameter of 0.6 mm and depth fifteen times higher. The attractiveness of ED machining for thin deep geometries stems from then absence of physical contact between tool and workpiece, which makes machining forces negligible and minimizes tool deformation. Micro features can be produced with a high accuracy irrespective of the material hardness and strength. Material Removal Rate (MRR), Electrode Wear (EW) and surface roughness are investigated versus the process parameters. Results are supported by the study of material removal mechanisms and surface morphology in the microscale, to account for the macroscopic trends.