ANALYSIS & OPINION

Fibre lasers now established in industry, say experts at ILAS

Greg Blackman reports from the AILU’s biennial Industrial Laser Applications Symposium, which took place in March in Kenilworth, UK

Fibre lasers are projected to have a 39 per cent share of the macro-processing market in 2015, evidence that the fibre laser is now a leading tool for industrial laser processing. The comment was made by Dr Dirk Petring from Fraunhofer ILT at the Association of Laser Users’ (AILU) Industrial Laser Applications Symposium (ILAS), which took place 17-18 March in Kenilworth, UK.

In 2014, 6,000 lasers at 1kW or higher were sold for macro-processing of which 30 per cent were fibre lasers; this is expected to reach 50 per cent in 2016.

Also speaking at the conference, Professor Eckhard Beyer at Fraunhofer IWS echoed Petring’s statements, saying that ‘solid-state [laser technology] is now more important that CO2 lasers’.

Fibre lasers operating at 1µm are generally considered faster at cutting thin metals than CO2 lasers, but the 10.6µm wavelength produced by CO2 lasers gives a higher quality cut in thicker metals.

Trumpf and Amada have both released variable beam quality functionality in their fibre lasers to improve cutting quality, although Petring commented at the ILAS event that this was only half way to meeting the cut quality from CO2 lasers.

Amada’s Ensis 2kW fibre laser is able to control the shape of the beam depending on the thickness of the material to give a better cut, while Trumpf provides similar technology in its BrightLine fibre technology.

Petring presented results from Fraunhofer ILT’s simulation work to optimise the process parameters when cutting with a fibre laser. This is part of an EU project called FILCO, which aims to build a 1µm laser head capable of cutting 15mm thick stainless steel with a cut quality similar to CO2 systems.

The FILCO beam forming unit has been manufactured and put into operation as a variable zoom beam expander. The results from the simulations show that, for thick sections, ring and bull’s-eye shaped power density distributions are more suitable than Gaussian, and that a lower beam quality can be beneficial depending on the power distribution.

The FILCO project is a good example of developing the science underpinning laser processing, something that Professor Stewart Williams at the UK's Cranfield University feels there should be more of. He commented during the ILAS event that ‘all engineering should be based on sound scientific principles’ and that ‘if we were to apply science to laser processing, we’d get better performance’.

The usual method of developing a laser process is an engineering one - i.e. trial and error to see how a laser source performs - rather than a scientific one, Williams said. He felt that the ‘black art’ of the laser is a barrier to manufacturers using the technology.

Beam delivery

While developments in laser source technology have advanced in recent years, the beam delivery aspects are becoming the speed and process control bottleneck, commented Professor Craig Arnold from Princeton University in the USA. Arnold gave a plenary talk at ILAS on high-speed variable focus elements for advanced beam delivery, including a Tuneable Acoustic Gradient (TAG) index of refraction lens.

The TAG lens is a liquid lens that alters its refractive index in response to sound waves. There are various approaches to control the beam in the x-y directions, but there are fewer options for altering the focus of the beam in the z-direction. This is where the TAG lens excels.

Current z-scanning methods are slow, but the TAG lens can adjust the focus quickly without moving the optics, all through varying the index of refraction. By changing when a pulse of light reaches the TAG lens, any focal length can be selected. Therefore, when processing non-planar surfaces, like stepped surfaces, the laser can scan across the workpiece without having to physically adjust the optics.

Arnold presented results that showed the system based on a TAG lens from TAG Optics was more efficient at removing material in micromachining applications. He said that high-speed scanning elements are the next frontier in advanced laser manufacturing.

The fibre laser might be taking over the macro-processing market, but the technology can also be used for micro keyhole welds and spot welds, according to Tony Hoult, applications manager at IPG Photonics’ Silicon Valley Technology Centre. IPG Photonics is one of the main suppliers of fibre lasers.

Hoult commented during ILAS that single mode low power fibre lasers can be used for micro keyhole welds, while quasi-continuous wave (QCW) fibre lasers can be used in pulsed mode for spot welding. He stated that, with the appropriate optics, QCW fibre lasers are the most appropriate weld mechanism for many applications.

However, Bernhard Kögl at Rofin-Baasel Lasertech commented at ILAS that, although fibre lasers will partially replace pulsed YAG lasers due to new beam delivery and processing methods, YAG lasers will not disappear due to peak power, homogenous beam profile and cost advantage, especially in spot welding applications. He also noted that diode lasers will gain market share in seam welding as the beam quality improves.

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