Effects of cooling position on tool wear reduction of secondary cutting edge corner of one-shot drill bit in drilling CFRP

Drilled hole surface quality of carbon fiber reinforced polymer (CFRP) deteriorates quickly with rapid tool wear, which ultimately influences service performance of CFRP parts. For one-shot drill bit, it is the secondary cutting edge, especially its end part close to tertiary cutting edges (secondary cutting edge corner) that mainly determines drilled hole surface quality. In order to effectively reduce tool wear of the secondary cutting edge corner, minimum quantity lubrication (MQL) coolants are applied and delivered to the desired location on secondary cutting edges. And coolant supply outlets of the drill bits are specially designed at two different locations at the secondary cutting edges of separate drill bits to verify the effects of cooling position on tool wear reduction of secondary cutting edge corner. The results show that delivering MQL mist out from the end of secondary cutting edges contributes to better wear reduction than that from the front of secondary cutting edges. In addition, by compared with dry drilling, the effects of cooling supply position on tool wear reduction of desired secondary cutting edge corners are further validated. Holes drilled by the drill bit ejecting MQL mists from the end of secondary cutting edges also exhibit superior quality. The results are valuable for further research on drill bit design and process development in drilling CFRP.