Secondary cutting edge wear of one-shot drill bit in drilling CFRP and its impact on hole quality

Drilled hole quality of carbon fiber reinforced polymer (CFRP) deteriorates quickly with rapid tool wear, which ultimately influences service performance of CFRP parts. And for one-shot drill bit, it is the secondary cutting edge that directly determines hole surface quality. This work first carries out an investigation on wear evolution of secondary cutting edge of one-shot drill bit in drilling CFRP. The tool wear is characterized by the cutting edge rounding (CER) and the flank wear (VB), and the tool wear measurement interval is shrunk down to every two holes to obtain detailed wear mechanisms. The secondary cutting edge is found prone to dulling according to CER and cutting edge profile. However, flank wear has regrinding effects on the cutting edge, which in turn decreases CER. Then combined with chip formation mechanisms, tool wear impacts on cutting capabilities of secondary cutting edge under various fiber cutting angles are investigated. And CER is proved to determine cutting capabilities under acute fiber cutting angles. Based on above analyses, initiation of hole surface damages and damage formation mechanisms are further discussed. Damages induced by degradation of cutting capabilities are of great difference within and across prepreg laminates under various fiber cutting angles. (C) 2017 Elsevier Ltd. All rights reserved.