applications Materials processing
Cut it out T
stephen Mounsey looks at some of the latest developments in laser technology’s staple application areas: cutting, welding, and drilling
he majority of lasers with power outputs of a kW or more are produced for materials processing applications, although the term means different
things to different people. While steel cutting remains the bread and butter of industrial laser use, more diverse applications with other materials are finding their way out of the laboratory and into everyday use. Whether because of its relatively large budget, demanding specifications, or safety-critical nature, the aerospace industry has traditionally been a driver and early adopter of novel materials. In the case of carbon fibre composites, which were first developed in the 1960s for use in jet engines, cost-effective methods of processing the materials are only just being developed. The need for lighter, more fuel-efficient aircraft, driven by rising fuel prices and environmental considerations, has led to the use of composite materials in new aircraft such as the Airbus A380, the airframe of which is composed of 20 per cent composite materials. Innovative, laser-based processing methods are being developed to meet the industry’s demand for these new materials. Currently, composite materials are cut using saws, which can leave damage along the cut surface that can weaken the component unpredictably. Mo Naeem, an applications expert at GSI, explains that laser cutting of composite materials presents a better alternative: ‘Composites have been around for a long time, and many industrial players have historically already tried to use lasers to cut and drill holes
14 electro optics l MAY 2011
lasers are now more versatile in cutting, welding and drilling. Image courtesy of IPG
in them, but they’ve been unsuccessful so far,’ says Naeem. ‘We’ve been working with a team at Liverpool John Moores University to find ways of using fibre lasers to cut, drill, and perform surface modifications on these composite materials.’ Naeem explains that, when cutting composites, the beam quality produced by fibre lasers has proved important. ‘The processing techniques we’re developing use our fibre lasers, whereas many of the other companies trying to work with composites have been using CO2
or
Nd:YAG lasers. Although these technologies can achieve results, they do tend to result in thermal degradation of the fibres at the interface [between individual fibres and the resin matrix material].’ The small spot size and relatively low power
of the fibre lasers used by GSI mean that the substrate is not significantly heated during the process, avoiding thermal damage. ‘In the past we used lasers with a higher power, and the only variable when making a cut was the cutting speed. Sometimes that cutting speed wasn’t fast enough for the power level used, and so it caused thermal damage. Now we’re using only 50 to
100W of power, and rather than doing very slow cuts we’re doing multiple very fast passes for each cut, to reduce the thermal damage. This approach gives us more control over cut quality,’ he says. ‘With a fast scanning head, we can do maybe 10 to 20 passes depending on the thickness of the workpiece. The most important thing is not the speed, but the quality of the cut, and with more passes there is very little damage done to the fibres or the resin, or the interface between them.’ In the safety-critical aerospace market in
particular, the quality of the finished product is of greater importance than the speed of the process. ‘Speed does come into it, but the quality is the number one consideration,’ says Naeem. Elsewhere, GSI has applied its lamp-pumped solid state lasers to drilling holes in turbine blades designed to operate in the hottest parts of gas turbines, both in the aircraft engines and in the power-generating turbines on the ground. These components have a ceramic thermal barrier coating (TBC) applied in order to allow them to operate at temperatures above the melting point of the nickel superalloys used, and networks
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