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Laser Cutting of Carbon Fibre-Reinforced Polymer Composite Materials

Negarestani, Reza

[Thesis]. Manchester, UK: The University of Manchester; 2010.

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Abstract

Carbon fibre-reinforced polymer (CFRP) composite materials are in increasingly highdemand, particularly in aerospace and automotive industries for reduced fuelconsumption. This is due to their superior structural characteristics (both in fatigue andstatic conditions) and light weight. Anisotropic and heterogeneous features of thesematerials, however, have posed serious challenges in machining of CFRPs. Hence newmachining technologies need to be investigated. Laser is a non-contact (eliminating toolwear) thermal process. Therefore, the thermal properties of the material are of crucialimportance. Especially for composite materials which consist of different constituentmaterials. In CFRPs, carbon fibres are excellent conductors of heat (thermalconductivity of 50 W/(m.K)) while the polymer matrix is poor conductor (thermalconductivity of 0.1-0.3 W/(m.K)). This significant difference that can be similarlytraced for other thermal properties such as heat of vaporisation and specific heatcapacity are the source of defects in laser cutting of CFRP composites. Major qualitychallenges in laser cutting of these materials are delamination and matrix recession.Various laser systems and cutting techniques are investigated in this work to minimisethese defects.Multiple-pass cutting using a high beam quality continuous wave (CW) mode fibre laseris found to be effective to minimise delamination at low power level and high scanningspeeds. Multiple-pass cutting using nanosecond pulsed DPSS Nd:YAG laser is shownto reduce matrix recession. A novel technique using mixing of reactive and inert gasesis introduced and demonstrated to minimise the matrix recession.In order to improve the quality and dimensional accuracy of CFRP laser machining, it isimportant to understand the mechanism of transient thermal behaviour and its effect onmaterial removal. A three-dimensional model to simulate the transient temperature fieldand subsequent material removal is developed, for the first time, on a heterogeneousfibre-matrix mesh. In addition to the transient temperature field, the model also predictsthe dimensions of the matrix recession during the laser machining process.