An investigation into the surface integrity and cutting force characteristics in titanium alloy end milling using soluble oil and MQL as coolants

Ti–6Al–4V, a titanium alloy, is a lightweight material characterized by a relatively high strength-to-weight ratio. Due to its exceptional resistance to corrosion, this material is extensively used in the aerospace and automotive sectors. Additionally, its biocompatibility has enabled its use in the medical field. An inherent difficulty in end milling titanium alloy is its modest thermal conductivity and covalent reactivity with other compounds. The low thermal conductivity of the alloy results in elevated tool temperatures, which expedites tool wear and diminishes tool longevity. To address these issues, end milling is performed using lubricants such as minimum quantity lubrication (MQL) and soluble oil. A variety of cutting speed, feed, and depths of cut were employed during the end milling process to analyze their influence on surface integrity and tool life. Optimization of the cutting parameters was achieved using ANOVA and Taguchi methods. The cutting speed influenced the cutting force in both soluble oil and MQL as coolants. Minor tool burning was observed when using soluble oil, whereas this issue was not encountered with MQL. Additionally, MQL demonstrated a faster heat removal rate compared to soluble oil during the milling process.