Impact of process variables on surface finish and burr development during NiTinol micro-milling

Abstract

Micro-milling of NiTinol shape memory alloys presents significant challenges due to their unique mechanical properties, including superelasticity and work-hardening behavior. This study focuses on optimizing key machining parameters—spindle speed, feed rate, and axial depth of cut—to improve surface integrity. Experiments were designed using an L₉ Taguchi orthogonal array, with spindle speeds ranging from 35,000 to 45,000 r/min, feed rates from 1.0 to 1.4 mm/min, and axial depths of cut between 100 and 300 µm. Surface roughness, burr formation, and material removal rate (MRR) were evaluated using advanced metrology techniques (Alicona Micro CMM). Statistical analysis, including analysis of variance, was employed to determine the significance of input parameters. The optimal surface roughness (R_a = 0.326 µm) was achieved at 40,000 r/min, 1.2 mm/min feed rate, and 300 µm depth of cut. A nominal MRR of 0.010 mm³/min was maintained, ensuring effective machining with minimal thermal impact. Burr formation was significantly reduced, with the lowest burr width recorded at 65.27 µm under optimized conditions. These results contribute to establishing a reliable machining strategy for NiTinol, particularly in biomedical and aerospace micro-manufacturing applications.