Surface integrity and tool wear in minimum quantity lubrication-assisted micro-milling of additively manufactured NiTi alloys

NiTi alloys possess excellent shape memory properties and superelasticity, demonstrating significant value in applications such as aerospace and medical devices. To address the problems of poor surface quality, pronounced work hardening, and severe tool wear in the micro-milling of additively manufactured NiTi alloys, specimens were fabricated by laser powder bed fusion (LPBF), and comparative micro-milling experiments were conducted under dry and minimum quantity lubrication (MQL) conditions. The effects of cutting parameters on surface integrity and tool wear were investigated, and the improvement mechanism of MQL was analyzed in combination with machined surface characterization. The results show that, under dry micro-milling conditions, the combined effects of ploughing and adhesive tool wear tend to cause defects such as surface tearing and deep grooves on the machined surface. Compared with dry cutting, MQL reduced the average surface roughness by approximately 30.1% and the average surface microhardness by approximately 8.9%, while burr height and burr width decreased by 34.4% and 50.2%, respectively. In addition, tool wear changed from severe edge chipping and rake/flank wear to slight cutting-edge blunting. By reducing friction at the tool-workpiece interface, suppressing heat accumulation, and improving chip evacuation, MQL promotes a transition in the material removal mechanism from ploughing-dominated removal to stable shear-dominated removal, thereby significantly improving surface integrity and reducing tool wear in the micro-milling of additively manufactured NiTi alloys.