An investigation of stainless steel 316L parts produced by powder bed fusion submitted to micro-endmilling operations

Additive manufacturing (AM) technologies associated with metal cutting, as in hybrid manufacturing, are able to produce parts of complex shapes, which could hardly be fabricated by other conventional processes. Stainless steel parts made by AM in layer-by-layer deposition can be used in microdevices intended to several applications in many fields. The possibility of achieving a very high level of details and surface finishing control by micromachining could introduce a relevant approach to produce microdevices with low roughness and less geometrical deviations. However, material response during microcutting has been pointed as a relevant issue when dealing with AM processes. The present work aims at investigating important aspects when micro-endmilling of stainless steel AISI 316L produced by AM. Workpieces were produced by powder bed fusion (PBF) process and micro-endmilled with different ball nose micromills (600 and 800 μm diameters). Spindle rotation was 32,000 rpm, depth of cut was 100 μm, and feed per tooth was from 0.5 to 3 μm performing full slot in all trials. The machining was carried out changing the toolpath direction in specific angles (60°, 90°, 120° and 180°) along the slot length. Roughness parameters were measured in different surfaces inside the slot, in an attempt to assess geometrical deviations, surface finishing and any material anisotropy. Analysis of variance (ANOVA) and post hoc comparisons using the Tukey test showed the effect of two main parameters (cutting direction and cutting parameters) on surface roughness. The results indicate that R_z parameter is sensitive to anisotropy effects when reducing endmill diameter. Better groove formation is noticed when using higher tool size and a better microchannel quality was found when both values, feed per tooth and cutting edge radius, are close to each other.