APPLICATION FOCUS: WELDING


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 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


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


in the weld metal. This, in turn, can make the weld more brittle and more susceptible to hydrogen embrittlement. Certain gases also work better


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


laser welding


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


higher absorption in any plasma that does form, which as explained earlier, can block and/ or distort the beam.


Lasers used for welding Laser sources often 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 of the spectrum 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, which due to their lower wavelength not only see better absorption in certain metals, but can also have their beam delivered via flexible optical fibre to the workpiece, increasing their versatility in welding applications. However, CO2


lasers are still


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


laser compared to other


lasers due to its relatively large wavelength, which is 10 times that of widely used fibre lasers. The larger wavelength exhibits


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


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Civan Lasers OPA 6 Weld – next generation laser for welding applications


The unique Dynamic Beam capabilities enable new applications, as well as improving speed and quality in existing applications. The laser features open a new set of parameters for laser welding, including:


1. Beam shaping – design and use new beam shapes in less than five minutes


2. Shape frequency – control the melt pool dynamics by steering the beam at up to 50MHz


3. Shape sequence – change between beam shapes in 1 microsecond


4. Focus steering – steer the focus up at to 50MHz


OPA 6 Weld can replace old joining methods, such as vacuum brazing. The advantage is not only in the system cost, which is a third of the price, but most importantly in that it allows the user to reduce power consumption by a significant factor of 72, from 4MW to 55kW, reduce floor footprint by a factor of 20, and enable the welding of recyclable Al alloys such as Al 5xxx and Al 6xxx.


More information: www.civanlasers.com


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


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 (see page 8) have all released such lasers, which are being shown to improve welding


by reducing porosity, spatter, enable higher travel speeds and smoother bead surfaces. Trumpf’s BrightLine Weld technology, for example, alters the distribution of the laser power between an inner and outer core within the beam profile. Similar to the wobble welding technique previously mentioned, 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


SUMMER 2022 LASER SYSTEMS EUROPE 33


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