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Hollow-core fibre enables flexibility for USP laser processing in CFRP component production

Hollow-core fibres have successfully been used to guide pulses from an ultrashort pulsed laser (USP) laser to a scanner on a robotic arm, in a project intended to enhance the production of carbon fibre reinforced polymer (CFRP) components.

Delivering ultrashort laser pulses of high energy and high average power has previously proven challenging, due to their exotic nature preventing them from being coupled into conventional glass fibres. As a result, the majority of today’s ultrafast laser systems generally use an array of mirrors and lenses to direct the pulses to the workpiece, a method that is both extremely complex and costly.

Unlike conventional glass fibres, however, light travelling through hollow-core fibres instead travels through either a vacuum, air or another gas. The vacuum and materials involved enable the fibres to control the exotic, non-linearity effects of ultrashort pulses, meaning integrators can now use them to deliver ultrashort pulses to a workpiece in a flexible manner.

The partners of the ‘CarboLase’ project have used hollow-core fibres in a new robotic system that combines USP laser processing, CNC cutting and automated handling to produce CFRP components in an efficient and flexible manner. Using the hollow-core fibre enables ultrashort laser pulses to be guided to a scanner on the end of a robotic arm, which can move more freely than the static mechanical machining centres previously used to process CFRP parts. According to Fraunhofer ILT, one of the project partners, this would be impractical using the conventional system of mirrors typically used for USP laser processing.

A carbon fiber preform drilled using a USP laser beam with a star-shaped cut-out and a perfectly proportioned metal insert. (Credit: Fraunhofer ILT)

The new system will offer designers considerably more creative freedom when designing customised lightweight CFRP parts – which will be of particular interest to the aerospace and automotive sectors.

Such components are usually assembled by drilling holes in a fabricated CFRP module and then glueing in metal fasteners, such as threaded inserts. The CarboLase partners are instead integrating the fasteners in textile preforms, and then producing the final CFRP with an additional curing process that includes the fasteners. This new method only works, however, if the cut-outs for the fasteners in the textile preform are drilled with the extreme precision offered by USP lasers. In a series of both pullout and torsion tests, the joints produced using the CarboLase method performed better than those in CFRP components produced by conventional means. Thanks to the interlocking connection between the inserts and the matrix material, the CFRP components produced can withstand a maximum pullout force up to 50 per cent higher than conventionally manufactured components with glued-in inserts.

Other CarboLase partners include system integrator Lunovu, and USP laser manufacturer Amphos, a subsidiary of Trumpf. Trumpf recently expressed its own interest in hollow-core fibre technology when it acquired a minority stake in French startup GLOphotonics, a developer and manufacturer of hollow-core fibres. The investment is intended to support the ongoing development of GLO’s technology, and help make it industry-ready.