Experimental study of thrust force and surface quality when drilling hybrid stacks

Abstract : Increasing aircrafts’ productivity and reducing their riveting time have created the need of one-shot drilling of dissimilar materials. The present work had followed this strategy on 4 shaft satin weave carbon fiber and epoxy matrix (AS-4 woven CFRP) and aluminum alloy (AA 2189) in order to study the effect of drilling direction on Al and carbon fiber reinforced polymer thrust force evolution and holes’ quality. It presents a comparison between CFRP, CFRP/Al, and Al/CFRP results using the same drilling tool and cutting parameters to understand the influence of adding metal layers on CFRP drilling defects. It was observed that the increase of the thrust force is related to cutting parameters. It causes thermal degradation of composite matrix when drilling CFRP/Al, and it impacts the aluminum surface roughness. One-shot drilling strategy does not affect thrust force evolution whenever the layers’ position in the stack. Drilling defects exist especially in the composite part such as uncut fibers, chipping, and spalling. It was found that the cutting speed had the dominant influence on surface damage. Holes’ quality differs from one configuration to another. Adding Al layer on the top reduces seriously the composite drilling defects and causes groove in the Al holes. Composite matrix smearing was observed when drilling CFRP/Al. It seems that drilling CFRP sheet between to supports improves composite holes’ quality.