Effects of Specialized Drill Bits on Hole Defects of CFRP Laminates

摘要

Drilling is a conventional machining process widely applied to carbon fiber reinforced plastics (CFRP) for the riveting and fastening purposes in the aerospace and automotive industries. However, the machining mechanism of CFRP composites differ significantly from that of homogeneous metal alloys owing to their prominent anisotropy and heterogeneity. Serious hole defects such as fiber pullout, matrix debonding and delamination are generally produced during the hole-making process, resulting in the poor machined surface quality, low fatigue durability or even the part rejections. In order to minimize the defects especially the delamination damage in composites drilling, specialized drill bits are often a primary choice being widely adopted in a real production. This paper aims to study the effects of two drills differing in geometrical characteristics during the drilling of CFRP laminates. A number of drilling experiments were carried out with the aim to evaluate the drilling performance of different drill bits. A scanning electron microscope (SEM) was used to observe the drilled surfaces to study the surface roughness. A high frequency scanning acoustic microscope (SAM) was applied to characterize the drilled hole morphologies with a particular focus on the delamination damage occurring in the CFRP laminates. The obtained results indicate that the fiber orientation relative to the cutting direction is a key factor affecting hole morphology and hole wall defects can be reduced by utilizing specialized drill geometries. Moreover, the dagger drill was confirmed outperforming the brad spur drill from the aspect of reducing drilling-induced delamination.