Electro-Discharge Drilling performance on parts produced by DMLS

Cobalt-base alloys are generally adopted in applications that require wear-, corrosion- and heat resistance. In particular, Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloy is currently being used in the aerospace and medical field. Both applications require product personalization and take advantage by parts manufacturing through 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 0.6mm, which require drilling of the additive manufactured part. This research aims at investigating 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. Due to the absence of physical contact between tool and workpiece in EDD, machining forces are negligible and micro features can be produced with a high accuracy irrespective of the material hardness and strength. In this study, peak current, pulse-on-time and duty ratio are adopted as control factors using the Taguchi method. Material Removal Rate (MRR), Electrode Wear (EW) and surface roughness are measured as responses. Signal to noise ratios and ANOVA analysis lead to identify the significant process parameters, the levels that optimize each response and regression models for the performance criteria. From an overall evaluation of the responses an optimum process set-up can be determined which ensures high productivity and smooth surface finish, even if tool wear is medium-high. All the analysis is supported by the study of material removal mechanisms and surface morphology in the microscale, to account for the macroscopic trends.