Effect of cryogenic machining for titanium alloy based on indirect, internal and external spray system

Abstract

Due to the excellent properties of Ti-6Al-4V titanium alloy such as lightweight, high wear and corrosion resistance and able to maintain high strength at high elevated temperature, this material has been used mostly in aerospace and biomedical industries. However, titanium alloy being considered as a hard-to-cut material with poor machinability due to its low thermal conductivity which leads to the excessive tool wear during machining and requires high machining cost. To overcome these problems, cryogenic machining has been taken place as a promising method for machinability improvement in terms of tool wear reduction, lower energy consumption and low machining cost. Even though this method has been implemented for titanium alloy machining, it is difficult to handle the excessive extremely low-temperature coolant (up to -150) that exposed directly to the workpiece. As a result, the workpiece hardness will be increased, hence will increase the required cutting force for the machining process. In concern with the problem, this paper presents a novel cryogenic cooling mechanism (indirect cryogenic cooling) that will be used as one of the cooling and lubrication strategy. The performance of the indirect cryogenic cooling will be compared with flood cooling, Minimum Quantity Lubrication (MQL) and conventional cryogenic cooling method by using the external and internal spray system. Liquid nitrogen (LN2) being selected as the cooling medium in this work since its temperature can reach lower -196, odorless and more environmentally friendly. A specially designed tooling kit that able to supply the liquid nitrogen to the cutting tool internally is used in this method. The developed indirect cryogenic supply method able to improve the machinability of Ti-6Al-4V. The cutting force is reduced by 54% and the tool life is improved by 90% compared to the conventional flood coolant strategy.