Laser and Mechanical Hybrid Drilling of Carbon Fibre-Reinforced Polymer (CFRP) Composites

Abstract

Hole drilling on carbon fibre reinforced polymer (CFRP) is a frequently used manufacturing process in critical applications such as aircraft manufacturing. The current and established drilling process is mechanical drilling. However, mechanical drilling of CFRP is often associated with composite layer delamination, fibre pull out and significant tool wear. To mitigate these issues, supporting materials are sometimes added, but this increases preparation time, wastage, and costs. Moreover, the abrasive nature of carbon fibre causes excessive tool wear, resulting in frequent drill bit changes and higher machining costs. Laser beam drilling is considered as an alternative method, as it is contact-free and can reduce delamination. However, it introduces its own set of problems, such as heat-affected zones (HAZ), taper angles, and spatter. This thesis aims to address these challenges by exploring novel hybrid drilling technologies and assessing hole quality, drilling efficiency, and environmental impact by using YLP-500-WC, IPG fibre laser. The research proposes various laser-assisted drilling methods for CFRP, yielding significant improvements. Firstly, a novel stepped process parameter parallel ring method for laser drilling of CFRP sheets leads to a 79% improvement in drilling efficiency and a 78% reduction in carbon emissions compared to the traditional constant laser parameter multiple-ring drilling method. Secondly, simultaneous laser and mechanical hybrid drilling of CFRP sheets eliminates delamination without requiring supporting materials, resulting in an 88% extension in drilling tool life compared to traditional mechanical dry drilling. Life cycle assessment (LCA) of drill bits shows a 36% reduction in carbon emissions in simultaneous laser and mechanical hybrid drilling process. Thirdly, the optimization of the stepped process parameter parallel ring method is conducted and analysed using the Taguchi method and analysis of variance (ANOVA). The results indicate that the top and bottom heat-affected zones are independent of ring number, hatch distance, and pulse frequency. The cross-section heat-affected zone is mainly affected by the number of rings, leading to improved drilling efficiency and increased taper angle with an increase in the number of rings. The life cycle assessment of assist gas reveals that the choice of assist gas plays a crucial role in reducing carbon emissions. Overall, this thesis presents valuable insights into laser-assisted drilling techniques for CFRP, contributing to improved drilling efficiency, reduced environmental impact, and enhanced hole quality. The findings have implications for advancing manufacturing processes in the aerospace, automotive, and other industries that extensively use CFRP components.

Date of Award	25 Mar 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Lin Li (Co Supervisor) & Paul Mativenga (Main Supervisor)