Role of porosity in machinability of additively manufactured Ti-6Al-4V

Despite numerous benefits, the additively manufactured (AM) parts present poor surface quality and dimensional errors, requiring semi-finishing or finishing operations. Machining of AM metals presents multiple challenges due to porosity, anisotropy, microcracks, and uneven layer thickness. This paper studies the role of porosity in the machinability of AM porous Titanium alloy (Ti6Al4V). Microendmilling experiments are conducted using the AM Ti6Al4V with four porosity levels. The machining response is analyzed in terms of machining force, chip morphology, tool wear, and machined surface finish; and compared with that of solid/continuous Ti6Al4V. A new metric has been proposed to quantify and statistically correlate the random variations in the machining force with AM part porosity. At higher porosities, tool chipping increases due to thermo-mechanical shocks as the tool encounters random pore-material boundaries. This results in microburrs and an increase in surface roughness (R-a). The chip and surface morphology show pore closure phenomenon at lower porosity levels, while chip segmentation is observed at higher porosities. Overall, the findings of this research provide valuable insights into the cutting mechanism of AM porous metals. Moreover, the correlation between the machining response and the porosity-driven part quality could be instrumental in in-situ process monitoring/control of hybrid additive-subtractive processes.