Evaluation of an Adhesive Friction Coefficient under Extreme Contact Conditions and Its Application to the Machining Process

Abstract

The premature failure of cutting tools during machining of titanium alloys is primarily attributed to their low thermal conductivity and strain hardening. The coefficient of friction (CoF) at the tool –chip contact depends on the high stress–strain values, interface temperatures, and the velocity of the chip. In this work, a new tribometer is developed to overcome the drawbacks of the existing tribometer and evaluate the adhesive CoF, the heat partition ratio (HPR), and contact pressure. The experiments were conducted on Ti-6Al-4V alloy to estimate the variable CoF and HPR along the rake face. The extent of heat accumulation at the tool–chip interface was quantified using an infrared thermal imaging camera, and the approach successfully mimicked machining conditions, where the tangential force measured up to 900 N and contact pressure was up to 3 GPa. The experiments showed a clear indication of the adhesion of Ti alloy on the tool, strongly suggesting the existence of distinct CoF values for sliding and sticking. The results were further used to develop and validate a finite element model to predict the adhesive CoF, by taking into account the heat partitioning. The results showed considerable dependence of the CoF and HPR on the sliding velocity when implemented in a machining model where 13% maximum error was found in the cutting forces.

Keywords:

• Adhesive coefficient of friction
• heat partition ratio
• machining
• Ti6Al4V
• finite element method