Improving the Machinability when Milling Ti-6Al-4V Using a Sub-Zero Metalworking Fluid

Abstract

Because of its excellent ratio of high strength to low density, Ti-6Al-4V is widely used in industrial applications. However, the titanium alloy is also a hard-to-cut material, which is mainly attributed to its low thermal conductivity and high chemical reactivity. Machining Ti-6Al-4V results in high cutting temperatures which promote a rapidly progressing, thermo-chemically induced tool wear. To improve the machinability, suitable cooling strategies are a necessity to reduce the thermal load and consequently tool wear. A novel, highly efficient approach is the usage of sub-zero metalworking fluids (MWF) which are applied at liquid state but at temperatures well below 0 °C. Therefore, sub-zero cooling approaches can combine very low supply temperatures and a beneficial wetting behavior, resulting in very high cooling capacities. In this paper, the influence of a sub-zero cooling strategy on the resulting tool wear when milling Ti-6Al-4V is investigated. The performance of the sub-zero cooling approach is compared to a conventional flood cooling strategy. In addition, the influence of a cutting edge preparation is investigated. The results show that no significant influence on the tool life is observed for conventional and sub-zero milling at a cutting edge radius of rβ = 5 μm. However, applying the sub-zero cooling promotes a more stable milling process and reduces the progression of tool wear. Increasing the cutting edge radius to rβ = 25 μm significantly reduces tool life under conventional flood cooling conditions, whereas tool life only slightly decreases for sub-zero milling. As a result, tool life is almost doubled when substituting a conventional flood cooling with a sub-zero cooling approach.

Keywords: Ti-6Al-4V, Tool wear, sub-zero MWF, Milling, Machinability