Stack drilling of CFRPT/TI using coated and uncoated tools.

The aerospace industry is increasingly utilising composite-metal stacks due to their superior mechanical properties and variable physical functions. Energy saving and increased strength/weight ratio are the two main factors why manufacturers are replacing separate composites and metal alloys with the hybrid stacks. These stacks are drilled and joined together with mechanical fasteners such as rivets. Single-shot drilling is a relatively new method and allows for time and cost reduction. But, because of the disparate nature of materials, drilling them at the same time poses great manufacturing challenges. Tool wear, increased temperature and poor machining quality are some of the issues encountered. This study investigated the performance of tools coated with diamond-like carbon (DLC) and boron-aluminium-magnesium (BAM) coatings which were deposited using physical vapour deposition (PVD) method. Drilling experiments were carried out on CFRP/Ti stacks and tool wear and hole quality were assessed. Tool wear results showed that DLC 1 tool had the best performance, showing the least wear. For BAM coatings, higher thickness caused the tools to fail earlier than DLC and BAM 1 tools. Uncoated tool failed after 25 holes. Overall coated tools DLC 1 and BAM 1 showed best performance.