Tool life improvement in cryogenic cooled milling of the preheated Ti-6Al-4V

Abstract

Cryogenic-based machining has been drawing attention for machining hard metals and super alloys such as the titanium alloys due to environmental concerns and growing regulations over pollution. In this study, cryogenic-assisted milling of Ti-6Al-4V has been performed with the preheated workpiece methods to avoid the cryogenic hardening by liquid nitrogen (LN2). Preliminary experiments show an increase in the cutting force due to cooling of the workpiece; therefore, workpiece preheating was adopted to increase the workpiece temperature. Three cutting speeds and three machining environments (dry, cryogenic, and cryogenic plus preheated) were considered in the analysis of tool wear, cutting forces, tool wear morphology, and chip morphology. Soft (Si coating) and hard (CrTiAlN)-coated tools were used in this study. It was observed that the tool life was increased by 50 to 90 % for Si-coated tools and 50 to 55 % for CrTiAlN-coated tools. The tool wear morphology showed that rubbing and chipping were the primary tool wear mechanisms. It is expected that the present work will be useful for improving tool life and reducing the cost of hard metal products. It may also be useful for reducing the ecological problems by conventional cutting fluids.