Making light work of cutting composites

Carbon fibre composite materials have become an essential and integral part of many components in multiple sectors such as aerospace, defence, automotive, marine, and consumer products. The strength and durability of these materials, whilst a distinct advantage in the applications where they are used, does however does pose significant challenges when it comes to cutting and machining them.

Conventional machining methods and cutting tools, although highly successful on other specialist steels and alloys used in these industries, often perform poorly on composite materials, leading to premature tool wear. This in turn can exert significant stress on the material which can cause high levels of de-lamination and subsequent de-grading of the structural properties of the part.

Lasers are already recognised as an efficient non-contact method of material processing for many different applications. In the majority of cases, whether it is for laser welding, marking or cutting, selecting the appropriate laser source, often either CO₂ or Fibre with the correct wavelength, will provide a highly efficient and reliable solution. When it comes to carbon fibre reinforced polymers materials however, obtaining the optimum result, with no compromises in edge finish or heat affected zone, is not quite so straight forward. The individual constituent materials which make up carbon fibre reinforced polymers respond differently to particular laser wavelengths.

Andy Toms explains: “For example, whilst a 1.06μm wavelength Yb-doped fiber laser can cut through a CFRP composite, the resultant cut is not optimised as the polymer matrix material is largely transparent to this wavelength. This means that the carbon fibres absorb the 1.06 μm laser energy, converting it to heat. The heat vaporises the carbon fibres cleanly, but residual heat is conducted down the length of the fibres causing decomposition of the polymer matrix material and leaving a large heat affected zone (HAZ). Alternatively, using a CO₂ laser, with a characteristic wavelength of 10.6μm, will cut through a CFRP composite. Both the carbon fibres and the polymer matrix material will readily absorb the 10.6μm laser energy. However, the energy needed to vaporise the carbon fibres is usually much greater than the energy needed to vaporise the polymer. This again leads to excessive decomposition of the polymer matrix material in the vicinity of the cut edge.”

Optimum solution

A unique solution to this conundrum can be found by combining two laser wavelengths into a single, coaxial laser beam. Known as MultiWave Hybrid Technology, a hybrid laser beam is composed of a CO₂ laser beam with a wavelength of 10.6μm, and an Yb-doped fiber laser beam with a wavelength of 1.06μm. When combined into a single beam the 10.6μm laser wavelength cleanly ablates the polymer matrix material, whilst the 1.06μm laser wavelength simultaneously cuts the carbon fibers. This leads to a superior cut quality with minimal heat affected zone (HAZ) and, more importantly, no delamination.

Multiple wavelength laser cutting was tested using the ULS ULTRA X600 System on 1.5mm thick carbon fibre reinforced polymer sheet stock, with the laser cutting process balanced between the 1.06μm and 10.6μm laser energy. Cut quality was observed microscopically using an Opto-digital microscope. In this example, all laser processing was performed using a 40 Watt Yb-doped fibre laser with a wavelength of 1.06μm, and a 75 Watt CO₂ laser with a wavelength of 10.6μm.

The optimum result – right hand circle - was obtained by using the combination of the 10.6μm wavelength of the CO2 laser and the 1.06μm wavelength Yb-doped fiber laser. Using the two laser beams simultaneously results in an efficient process for cutting CFRP. Each of the two laser beam wavelengths was selected to heat and vaporise the individual components of the composite sheet. Using this technology, the CFRP can be cut cleanly using relatively low power lasers. This technology can be extended beyond CFRP, to other types of composite sheets through appropriate selection of the laser wavelengths.

A wide range of Universal Laser System platforms and MultiWave Hybrid Technology TM is available from Bromsgrove based TLM Laser, the UK and Ireland distributors for Universal Laser’s cutting and marking systems. In addition, the company also offers a comprehensive range of Laser processing systems for cutting, welding, marking, engraving, cleaning, 3D additive layer manufacturing, plus laser safety equipment.