Fiber pull-out damage formations and their effect on hole quality when drilling carbon fiber reinforced plastic (CFRP) composites using various tool geometries

This paper investigates how tool geometries and process conditions influence fiber pull-out formations, drilling forces, and hole quality parameters during the drilling process of quasi-isotropic CFRP laminates. The dry drilling experiments with the tools having three different point angles (two single point angles of 166° and 118°, and one double point angle of 100°/60°) were conducted with the feed conditions of 0.08 mm/rev to 0.2 mm/rev and the spindle speed conditions of 1500 rpm to 5000 rpm. A destructive method was used to quantify the fiber pull-out area and depth concerning the interaction angle of the cutting tool edge and fiber directions. The feed condition and the drill point angle affect the drilling forces and undeformed chip thickness, which influence the fiber pull-out formation mechanisms. The drill with the higher point angle produced less fiber pull-out area; however, it resulted in deeper fiber pull-outs, causing higher surface roughness.