Drilling of CFRP/Al multi-material stacks using WC-Co CVD diamond coated tools

Abstract

In recent years, promising solutions have emerged to address the need to reduce structural weight in the modern transportation (aeronautical and automotive) industry, namely multi-material assemblies combining fibre-reinforced polymers and aluminium alloys. Given the distinct mechanical and thermal characteristics of each component, the drilling process, fundamental for creating holes in riveted or bolted assemblies, presents significant challenges in achieving damage-free holes with precise tolerances. This is due to defects formation, such as metal burrs, incomplete fibre cutting, delamination, and tool wear. Consequently, meticulous selection of cutting conditions and tools becomes imperative to mitigate these issues effectively. In this work, the drilling process of two types of multi-material laminates (with alternate CFRP and Al2024 layers) using two distinct geometries of CVD diamond coated WC-Co single-shot drilling tools, was studied to find the ideal operating conditions. Different levels of feeds and cutting speeds were considered and an additional wear inspection experimental campaign was carried out. Results revealed considerably higher thrust force and torque in the aluminium layers, when compared to the CFRP, which suffered some delamination, contrarily to the burrs present in the aluminium. The feed was the parameter which most contributed to the appearance of defects. After an approximate drilling distance of 1550 mm in both types of plates, a slight abrasive wear was detected for multi-material type I and some aluminium adhesion on the cutting edge for type II, indicating a potential wear tendency (associated with built up edge) for this specific configuration. Nevertheless, no major wear was verified overall.