LASER WELDING


such size limitations, however, due to it taking place outside a vacuum chamber, a shielding gas is required to prevent the weld reacting with gases in the atmosphere.


Shielding gas required To perform laser welding, shielding gas must also be delivered to the workpiece alongside the beam. This gas serves multiple purposes: it helps maintain a stable process and stable weld pool; keeps the weld material from reacting with the oxygen, nitrogen and hydrogen in the atmosphere (preventing weaker welds filled with defects, such as voids); and minimises the formation of plasma above the weld, which would otherwise partially block and/or distort the laser beam. In general, the type of shielding gas used can influence the speed, microstructure and overall shape of the weld. Shielding gases typically used are helium, carbon dioxide, nitrogen and argon, each with varying degrees of cost, plasma suppression and oxidation prevention. Certain gases work better for certain materials. For example, nitrogen is known to react strongly with titanium (or austenitic stainless steels


“Laser welding provides a number of advantages over conventional arc- based methods, such as MIG, TIG and MAG welding”


alloyed with titanium) to form titanium nitride compounds, which can lead to the resulting weld being brittle. Argon is therefore a suitable alternative for welding titanium-based alloys. Using nitrogen during the welding of ferritic steels also has detrimental effects, leading to an increased quantity of martensite in the weld metal. This, in turn, can make the weld more brittle and more susceptible to hydrogen embrittlement.


Laser welding is also well suited to automation on production lines, as it is easily integrated with robotic technologies Certain gases also work


better for certain laser wavelengths. For example, helium is a suitable shield gas for CO2


optical fibre to the workpiece, increasing their versatility in welding applications. However, CO2


laser welding due to the


excellent plasma suppression it offers. The formation of plasma is more critical when welding with a CO2


such as bubbles and spatter in the final weld. In more recent years,


lasers are still laser due to


its relatively large wavelength, which is 10 times that of widely used fibre lasers. The larger wavelength exhibits higher absorption in any plasma that does form, which can block and/ or distort the beam.


Lasers used for welding Laser sources used for welding include solid-state lasers – such as Nd:YAG lasers, fibre lasers and direct diode lasers – and CO2


lasers. Fibre lasers


operate at around 1μm and offer excellent beam quality, small spot sizes, high reliability and low maintenance. They offer good absorption in non- reflective metals and are a popular choice in modern laser welding applications. While CO2 lasers operating in the 9–11μm region have for many years been used for welding, in recent years they have seen ground increasingly taken from them – in this application at least – by fibre lasers. Due to their lower wavelength, fibre lasers not only see better absorption in certain metals, but can also have their beam delivered via flexible


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sometimes used for creating thicker weld seams designed to resist large amounts of stress – for example, when joining metal sheets in the shipbuilding industry, or when producing differential gears in the automotive industry. Nd:YAG lasers operate at the same wavelength as fibre lasers and offer high peak powers in small laser sizes, enabling welding with large optical spot size. This translates to maximised part fit-up and laser to joint alignment accommodation. Direct diode lasers offer a


larger spot size and higher wall- plug efficiency than fibre lasers, and are available over a broader range of wavelengths, from 780-1,060nm, 1,400-1,500nm, and more recently at the blue wavelength – 450nm. This new wavelength is particularly suited to copper welding due to its relatively high (65 per cent) absorption in copper, compared to standard infrared wavelengths, which only exhibit five per cent absorption in copper due to the material’s high reflectivity. Techniques such as wobble welding are therefore used with infrared lasers to overcome some of the challenges associated with this low absorption, reducing defects


technology has been released that can vary laser beam quality without the use of complex optics (visit www.lasersystemseurope. com/adjustable-beam-quality for more information). Coherent, NLight, Trumpf, SPI Lasers, IPG and Civan Lasers have all released such lasers, which are being shown to improve welding by reducing porosity and spatter, and enable higher travel speeds and smoother bead surfaces. Trumpf’s BrightLine Weld technology alters the distribution of the laser power between an inner and outer core within the beam profile. Similar to the wobble welding technique, this can be used to improve copper welding. The BrightLine Weld laser is able to form a tiny spot, which melts the copper, while a larger spot keeps the weld keyhole open at the surface. Trumpf has shown this to produce copper contacts in e-mobility applications with weld seams free from pores and containing minimal spatter. l


For more on the application of laser systems in welding, visit:


www.lasersystemseurope.com/ applications/welding


THE 2023 GUIDE TO LASER SYSTEMS LASER SYSTEMS EUROPE 59


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