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Electrodischarge 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 0.6 mm and high aspect ratio, which require drilling of the additive manufactured part. This research aims at investigating the effects of electrodischarge 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 15 times higher. Due to the absence of physical contact between tool and workpiece in EDD, machining forces are negligible and microfeatures 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, Electrode wear rate (EW rate), and surface roughness are measured as responses. S/N ratios and analysis of variance analysis lead to identify the significant process parameters and the optimal combination level of machining parameters. From the responses can be determined which ensures high productivity and smooth surface finish, even if tool wear is medium high. All the analyses are supported by the study of material removal mechanisms and surface morphology in the microscale, to account for the macroscopic trends.
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