Characterization of anti-abrasion and anti-friction coatings on micromachining response in high speed micromilling of Ti-6Al-4V

Micromilling process finds applications in biomedical and aerospace industries to produce complex 3D micro-scale features and components. One of the key limitations of micromachining is the low flexural stiffness of the micro-tool due to small diameter. For machining of difficult-to-cut materials like Ti alloys, high rotational speeds are typically used to reduce the chip load and cutting forces. High speed micromilling of Ti alloys generates high temperature in cutting zone due to low thermal conductivity which can lead to a variation in the cutting forces and excessive tool wear. The friction at the tool-chip interface between the workpiece and the cutting tool also affects the cutting forces. It may be noted that abrasion resistant coatings on cutting tool can play important role in reduction of the tool wear and friction. In addition, the solid lubricant coatings over the abrasion resistant coating can further reduce the friction and heat generation between the surface and the cutting tool. This study is focused on investigating the effect of coatings on micro-tool in high speed micromilling of Ti-6Al-4 V. Experiments were carried out at a rotational speed of 50,000 rpm and different depth of cut using uncoated, anti-abrasion coating of TiAlN and TiAlSiN and anti-friction coating of solid lubricant WS2. The cutting forces and specific cutting pressures were compared for machining with different coated tools and uncoated tools. A significant reduction in the cutting forces was found if dry lubricant coating of WS2 is used with TiAlN. The machined surface finish shows an improvement if the solid lubricant coatings are used. A comprehensive assessment of the tool damage was done to understand the progression of wear with different coatings. Stability limits have been predicted and compared for diiferent tool coatings. Dry lubricant coating over TiAlN coated tool shows a maximum increase of ∼47% in stability limits.