Characterisation of friction at the tool-chip interface for orthogonal cutting of Ti-6Al-4V alloy

The main objective of this work is to characterise the frictional phenomena at the tool-chip interface and evaluate the contact pressure in the secondary deformation zone of machining. Due to the tool-chip-workpiece trio contact complexity in machining, there is a lack of fundamental understanding related to tribological parameters. During cutting, the coefficient of friction (CoF) and contact pressure along the rake face depend upon stresses, interface temperature, the velocity of the chip and tool-chip contact length. Under critical conditions, stresses and temperature are very high at the cutting edge which results in tool wear and sometimes premature failure of the tool. Existing pin-on-disc technique fails to reproduce the extreme contact conditions observed on the rake face while cutting. Accurate predictive models, considering separate sticking and sliding zones for the secondary deformation zone are yet to be developed. A new tribometer was designed to correlate the coefficient of friction and pressure distribution with variable chip velocities. Based on this tribometer design, pin-on-workpiece experiments were performed on Ti-6Al-4V with tungsten carbide spherical pins. It was observed that sliding velocity is one of the most influential parameters affecting the coefficient of friction. However, the variation in pressure distribution along the rake face was observed to be very less.