Experimental study on drilling machinability of CFRP: Tool geometry, hole quality and process monitoring analysis

Abstract

Due to their lightweight and high strength properties, components made of CFRP play a fundamental role in the aerospace industry. Hole-making of these parts is usually required for the following assembly process, with the drilling process of composite parts being one of the most important and critical manufacturing process steps. However, due to the non-homogeneous anisotropic nature of the material and highly abrasive and hard reinforced fibers, CFRP is usually regarded as difficult-to-machine material. Several drilling-induced defects can arise such as delamination, fiber pull-out and uncut fibers, burrs or micro cracking, leading to the rejection of costly aerospace parts. A correct choice of cutting tools and conditions is essential in addition to process monitoring techniques for ensuring desired hole quality. In this context, the present work presents an experimental work where the benchmarking of two cutting tool geometries and cutting conditions are carried out to analyze their effect on the drilled holed quality. Additionally, a novel cutting force-based process monitoring analysis is presented for online hole damage identification, focusing on cutting tool entry and exit regimes. Based on the results of this study, optimum cutting geometries are identified, and the importance of the tool point geometry and tool wear are highlighted as the main aspects affecting the generation of push-out delamination defects. Within this context, the suitability of twist drills with higher point angles is observed, achieving high quality holes. Hence, the present work introduces a drilling process optimization methodology applicable to aerospace assembly industrial processes.