The geometrical effect between stages in step drilling of composite materials

The delamination-induced of step drill with step angle, stage ratio, feed rate and spindle speed in drilling Carbon Fibre Reinforced Plastic (CFRP) laminate was experimentally investigated in this study. Delamination can be minimised by changing the drill geometry of step drill. A 0.6 stage ratio of step drill with a larger step angle of 120? produced a smaller thrust force than the one with an 80? step angle during exit of the step drill. However, the effect of stage ratio on the delamination is more critical when the step angle is small.