Impact of Dry and Cryogenic Cutting Medium on Shear Angle and Chip Morphology in High-speed Machining of Titanium Alloy (Ti-6Al-4V)

Abstract

Ti-6Al-4V, a titanium alloy, is widely employed in various engineering sectors due to its attractive combination of strong corrosion resistance and specific strength. However, titanium alloys frequently result in serrated chips, which present considerable machinability issues compared to other materials. The cutting medium plays a vital role in the chip formation mechanism, further affecting the machined part integrity and thermo-mechanical properties. Chip morphological parameters such as shear angle, compression ratio, and segmentation degree are essential aspects of estimating machined part surface roughness, tool wear, cutting forces, and energy consumption. Therefore, it is important to understand the entire mechanism of chip formation in terms of chip morphology in high-speed cutting. This fundamental research aims to analyze and compare the shear angle model and chip formation of titanium alloy Ti-6Al-4V for cutting speeds ranging from 50 m/min to 150 m/min and feed rates ranging from 0.12 mm/rev to 0.24 mm/rev under dry and cryogenic cutting environments. Single-point turning experiments were conducted on Ti-6Al-4V workpieces with uncoated tungsten carbide inserts (without chip breakers), which are advantageous for heat transfer. After the chip analysis, it was observed that the shear angle obtained practically with model-4 is the most appropriate model for shear angle calculation, and the cryogenic cutting medium is suitable for Ti-6Al-4V machining. At the feed rate of 0.12-0.24 mm/rev and cutting speed of 50-150 m/min, the shear angle in dry-medium machining ranges from 32° to 42°, while in cryogenic medium machining, it ranges from 34.6° to 44.6°. Overall, a larger shear angle has been observed in cryogenic turning compared to dry turning, which is advantageous for reduced cutting forces owing to a lesser shear plane. The tool-chip contact length, which is the intimate contact between the tool face and chip surface, significantly decreases under cryogenic media. A smaller tool-chip contact length results in an elevated shear angle, which improves process sustainability and economy during cryogenic turning, as described.