FEATURE: COPPER PROCESSING IN E-MOBILITY
For welding such copper tabs at depths from 0.2 to 0.5mm, Trumpf has developed its own solution that uses a CW green laser to perform either heat conduction or deep penetration welding. Similar to a blue laser, a green laser’s wavelength of around 515nm is highly absorbed by copper – around 40 per cent of its power is absorbed at room temperature. The laser can also be used for welding the layers of copper foils in battery cells.
‘Our green laser is based on our infrared disk laser technology. However, when the
“Laserline plans to reveal a hybrid laser that will use a combination of blue and infrared wavelengths”
light exits the resonator, it is converted from infrared to a green wavelength,’ explained Buehrle. ‘The good thing about a disk laser is that its robust design prevents any back-reflected radiation from damaging the optics of the laser, which is a potential issue with fibre lasers.’
In addition, Beuhrle continued, Green
Blue diode lasers are absorbed extremely well by copper, enabling them to achieve defect-free welds using a low output power
brightness of its lasers in the future through a reduction in spot size, which Pelaprat says will lead to larger thicknesses of copper being able to be welded, or an increase in speed when welding smaller thicknesses. In addition, he explained that the efficiency of blue diodes made from gallium nitride – which are used in Nuburu’s lasers – is increasing each year, therefore blue diode lasers with higher wall plug efficiency can also be expected in the future. Diode laser manufacturer Laserline announced in February that its LDMblue laser is now able to offer up to 1kW output power, however the laser is currently being targeted at copper welding up to thicknesses of 0.5mm. For applications involving larger thicknesses of copper, Laserline said it has two strategies planned which it will show to Laser World of Photonics attendees in June. In addition to a blue diode laser with even higher output power, the firm plans to reveal a hybrid laser able to use a combination of blue and infrared wavelengths to weld larger
thicknesses of copper. Further details of both could not be released at the time of writing.
Going green In instances where material thicknesses are low and the need for control of heat input is high, rather than using high-power infrared lasers – which according to Buehrle are limited in their suitability to perform controlled welds depths of thin thicknesses of copper – Trumpf subsidiary SPI Lasers has developed a nanosecond welding process using a 100W pulsed fibre laser that can achieve excellent welds in 0.3mm- thick copper tabs. As described by Gabzdyl and Dzurko in our previous issue, this technique enables multiple spots to be made to give appropriate bonding to the focus area using a spiralled spot. An issue with this process, however, is that while control of heat input and penetration is extremely high, the resulting welding time can be quite slow, due to the low average power used.
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lasers are offered in a compact cabinet, similar to a fibre laser but with integrated cooling. They can also offer several outputs from a single laser source, rather than a fibre laser, which needs external components to offer this capability. Trumpf’s CW green laser – the TruDisk 1020 – provides both 1kW of power and a beam parameter product of
2mm.mrad, which according to Buehrle means a 50µm fibre can be connected to the laser, making it suitable for scanning applications. He added that in the lab Trumpf is already working with more kilowatts, so a green laser with more power will be available commercially in the near future. Buehrle believes that while infrared fibre and disk laser technologies are suited to a range of applications in e-mobility involving higher thicknesses of copper, for tab and foil welding, green lasers have the advantage and are the better solution. ‘I think in the future for thicknesses of
copper below 4mm, green lasers will be the preferred solution,’ he said. ‘The future will require green lasers of higher laser power in order to weld thicknesses exceeding 1mm, which is the current limit with a 1kW green laser. Green lasers up to 3kW in power would be suitable for welding copper thicknesses exceeding 1mm at a comfortable rate.’ l
SUMMER 2019 LASER SYSTEMS EUROPE 25
Nuburu
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