Comparative study of drilling super austenitic stainless steel with external applications of reduced quantity nanofluid and flooded bio-lubricant

Abstract

AISI 904L is a super austenitic stainless steel (SASS) with excellent corrosion resistance and good mechanical strength at high temperatures that can be applied in extreme operational conditions. Consequently, it has low machinability. Research involving SASS drilling is scarce in the literature. Thus, this work aims to evaluate the TiAlN-coated carbide drill life associated with thrust force and torque in the full-hole drilling of the Ultra® 904L under external lubrication with a 100-mm/min feed rate. Nanofluid-based reduced quantity lubricant (2.0 L/h) at 840-rpm spindle speed and flood bio-lubricant conditions (540 L/h) at 840- and 1260-rpm spindle speeds were applied, totaling three tool-life tests. Digital image analysis showed that the failures in the main cutting edges occurred due to chipping resulting from the rupture of the built-up edge. The drill wear did not reach expressive values. Low tool life was observed with nanofluid in reduced quantity (E1 test, 0.67 min) and flood condition with 1260 rpm (E3 test, 1.34 min). The longest drill life was registered for 840 rpm with flood biofluid (E2 test, 8.04 min). Lastly, a growth of 11% in thrust force and 9% in torque were noted when increasing the lubricooling flow from the E1 to E2 test; however, there was a reduction of 31% and 42% when raising the spindle speed from E2 to E3 test. The flood condition resulted in a longer drill life and smaller thrust force and torque values (at least 20% lower), which are associated with chip deformation, hardness, and friction coefficient reductions due to increased cutting speed and temperature. Moreover, built-up edges were formed during the drilling of all the holes.