Comparative tool wear and hole quality investigation in drilling of aerospace grade T800 CFRP using different external cooling lubricants

The T800 Carbon fiber reinforced polymer/plastic (CFRP) has been increasingly used for its considerable specific strength/modules to manufacture the primary load-carrying structures in aerospace industry. The abrasive carbon fibers can cause rapid tool wear in CFRP drilling, which deteriorate the quality of hole wall and result in unpredictable decrease of bearing capacity. In order to effectively reduce the tool wear, a cooling method namely external cooling lubrication (ECL) is applied in this study by using two different lubricants (Boelube 70104 and Castrol Syntilo 9828). The results show that Boelube 70104 lubricant exhibits the maximum flank wear (VB) reduction (34.5%) as compared to dry drilling after drilling 30 holes. And, the maximum CER reduction (57.4%) is obtained by using Castrol Syntilo 9828 lubricant. Different from previous researches, the maximum thrust force of drilling process using ECL presents obvious decrease as compared to dry drilling. And, the value of surface roughness (Ra) exhibits an obvious decrease when using Boelube 70104 lubricant. Two main different mechanisms for Ra decrease namely reducing surface cavity at FCA of 90° < θ < 180° and reducing saw-tooth surfaces at FCA of 0° < θ < 90° are separately observed for Boelube 70104 and Castrol Syntilo 9828 separately.