In order to satisfy high quality requirements of drilled holes on high strength carbon fiber reinforced plastics (CFRP) structural parts, one-shot drill bit is currently utilized in drilling CFRP. However, due to the special step-drilling (including pre-drilling, chambering and reaming) geometry of the one-shot drill bit, the wear status of secondary cutting edges determines the final hole surface quality. Also on account of high abrasiveness of carbon fibers, the drill bit suffers quick tool wear and the cutting edges usually encounter edge dulling, which leads to subsequent serious hole surface defects. By applying cutting edge rounding to characterize the dullness of the cutting edge, the results show the secondary cutting edge is prone to dulling at initial drilling stage, and then it is reground and re-sharpened. On the basis of tool wear analysis, the paper investigates the impacts of edge dulling on drilled hole surface defects under different fiber cutting angles. Finally by creatively designing internal coolant holes at specific position on the secondary cutting edge and applying minimum quantity lubrication (MQL), the dulling wear of secondary cutting edge is effectively reduced and hole surface quality is greatly improved. The study paves the way for the research on tools and processes of drilling CFRP with high quality.
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