Investigating tool wear mechanisms in machining of Ti-6Al-4V in flood coolant, dry and MQL conditions

Abstract

The objective of this study is to identify and explain tool wear mechanisms that dominate during machining of titanium alloy Ti-6Al-4V in dry, flood coolant, and minimum quantity lubrication (MQL) conditions. A series of experiments were conducted using end milling of Ti-6Al-4V by varying feed rate and depth of cut, while the cutting speed was kept constant at comparatively higher cutting speed. Both uncoated and titanium aluminum nitride (TiAlN)-coated carbide tools were used for machining Ti-6Al-4V at the same settings of parameters. It was observed that abrasion was the most dominant tool wear mechanism for all dry, flood coolant and MQL machining conditions. Edge chipping and tool nose wear were the next dominating tool wear mechanisms in conventional flood coolant machining, which may be associated with the thermal fatigue caused by the periodic cooling of tool tip from the high temperature generated during machining. On the other hand, adhesion was the second most dominant tool wear mechanism in the dry machining. Both the edge chipping and adhesion of chips to the cutting tools were reduced significantly in MQL machining. The delamination of coating film was observed when TiAlN-coated carbide tools were used for machining Ti-6Al-4V. The delamination was more significant in wet and MQL machining compared to dry machining, indicating the effectiveness of coated tools in dry machining condition compared to wet and MQL machining conditions. Among three conditions, MQL provided the least occurrences of tool wear, indicating suitability of MQL in productive machining of titanium alloys.