Experimental analysis on the effect of build directions during microdrilling of SLM fabricated maraging steel (18-Ni-300)

This paper aims to study the effect of different build directions (BD) during micro-drilling process of Selective Laser Melting (SLM) fabricated maraging steel. It includes analysis of thrust force, cutting torque, surface roughness, tool wear, and chip morphology. The study was also extended to conventional hot forged maraging steel for comparison purposes. Along with these, three post treatments i.e., aging, solution annealing with hardening heat treatment and deep cryogenic treatment were carried out on both SLM fabricated as well as hot forged components. This was to analyse the effect of post treatment on directional anisotropy. From the set of experiments conducted, a higher requirement of thrust force as well as engagement torque was observed in the case of components fabricated parallel to the BD of the additively manufactured (AM) part. Also, the maximum thrust force is identified in the aged specimens due to its increased hardness. In the surface roughness analysis of the drilled surface, perpendicular to the BD specimen displayed less roughness than that along the BD and a significant reduction is observed in the difference of surface roughness between parallel and perpendicular to BD after aging and cryogenic treatment. Directional anisotropy was also observed in chip width and thickness and it was found that the average thickness of chips produced in micro-drilling parallel to BD was 11.843 & mu;m, which reduced to 6.330 & mu;m in perpendicular to BD at 3000 rpm. Similarly, chip width in parallel to BD was 134.0 & mu;m, which reduced to 38.641 & mu;m in perpendicular to BD. This directly indicates that the energy requirement in machining of parallel to BD was higher than perpendicular to BD. Thus utilizing the post-processing operations the directional anisotropy can be controlled and hence the functionality in applications such as micro dies, moulds, fuel injection nozzles, micro-electro components, etc. can be improved.