Experimental study of drilling composite materials with step-core drill

In conventional machining, drilling is the most applied method accounting for as much as 40% for all material removal processes. However, problems in drilling, particularly the heterogeneity and anisotropy of composite materials, increase delamination. Several studies have proved that delamination is related to the thrust force in drilling composite materials. The thrust force of step-core drill with drilling parameters (diameter ratio, feed rate and spindle speed) in drilling carbon fiber reinforced plastics (CFRP) laminates were experimentally investigated in this study. The results indicate that diameter ratio and feed rate have the most significant influence on the overall performance of step-core drills and step-core-saw drill produces the highest drilling thrust force. The advantages of the step-core drill design are that the thrust force exerted is distributed toward the drill periphery in drilling. The diameter ratio may be a viable alternative for the step-core drill in terms of drilling thrust.