Wear mechanisms and tool life management of WC–Co drills during dry high speed drilling of woven carbon fibre composites

Woven carbon fibre composites are extensively used in aerospace, automotive and civil applications. Optimization of high speed drilling of composites is an issue of great economical impact. Tool wear and part quality are central to the definition of the objective function and constraints of the optimization scheme. This paper presents an experimental investigation of the wear mechanisms of tungsten carbide (WC) drills during dry high speed drilling of quasi-isotropic woven graphite fibre epoxy composites. Tool wear was evaluated at spindle speeds of up to 15,000 rpm using a standard two flute drill. The paper examines the nonlinear behavior of this tribo-system and the interdependence of the wear process and cutting forces in relation to surface damage of the system components. It was found that chipping and abrasion were the main mechanisms controlling the deterioration of WC drill. The two friction regimes, the lightly and heavily loaded, were found to dictate the increase in forces, delamination of composite and surface roughness. The aggressive rubbing by fractured graphite fibres and WC grains against the soft epoxy matrix caused high temperature rise and consequently enhanced flank wear. During the primary and secondary wear stages, wear on the flank face of main cutting edges was found to be dominant, while adhesion of carbon was found to occur along with abrasion in the tertiary zone. Tool life results revealed the increase in the delamination and surface roughness with transition from the primary to tertiary wear regime. The correlation between tool wear, delamination damage and surface roughness was established. Finally it was concluded that a tool replacement strategy could be devised by monitoring the cutting forces.