Tool wear in drilling of composite/titanium stacks using carbide and polycrystalline diamond tools

This paper aims to establish the wear mechanisms of tungsten carbide (WC) and polycrystalline diamond (PCD) drills when drilling carbon fiber reinforced plastics (CFRP) stacked on top of titanium (Ti). During the drilling experiments, torque and thrust forces were measured using a dynamometer under the CFRP/Ti stacks. In addition, a Scanning Electron Microscope (SEM) and a Confocal Laser Scanning Microscope (CLSM) were periodically used to measure the wear progression of the tool surface and to analyze tool wear mechanisms. For the WC drills Ti adhesion was a predominant tool wear factor, covering the entire cutting edges. PCD drills on the other hand, showed less titanium adhesion, but had a significant amount of cutting edge chipping. Abrasion, by the carbon fiber and hard inclusions in Ti, and adhesion of titanium were found to be the dominant tool wear mechanisms. Higher torque and thrust values were observed at the higher spindle speeds which caused a significant increase in tool wear due to the higher temperature generated, especially when drilling the Ti plates.