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ANALYSIS: BLUE LASERS


Figure 3: This joint, connecting 70 separate 8µm-thick foils with a 254µm- thick copper busbar, was produced in a single step with a blue laser weld. This is not possible with either ultrasonic or infrared laser welding


years later, we have introduced a second system that outputs 500W at 450nm through a 400µm core optical fibre. With a beam-parameter-product of better than 30mm.mrad, the system offers exceptional brightness. The firm also introduced a high-efficiency non-contact welding head this year, as well as a dual-lens assembly that efficiently combines the outputs of two 500W systems for a power-to-the-target of 1kW.


Nuburu’s blue laser design is based on


making defect-free joints. In addition to making defect-free joints, the blue laser has another advantage: it can produce very compact joints of almost arbitrary geometries. Whereas alternative welding methods require a weld head of some finite dimension to be in contact with the material — and often require a unique head for each geometry — the blue laser just needs a few simple process adjustments to accommodate any geometry. Two years ago, Nuburu introduced the


first, 150W version of its blue diode laser, which was adopted almost immediately by battery fabricators due to its ability to create compact, defect-free foil joints at a speed unmatched by any alternative approach. Two


combining 2D arrays of GaN (gallium nitride) blue diodes. The high power is achieved by individually collimating the beamlets and combining them with a combination of spatial interleaving and polarisation optics. Although the design is efficient, improvements are possible in all three aspects, meaning the next generation of refinements are already under way. In addition, GaN diode technology is


relatively immature. Current chips convert about 38 per cent of their input electrical energy into output laser energy. When the


“The blue laser is poised to bring increased flexibility and efficiency to a wide range of industrial applications”


technology is mature, it’s expected to near the 70 per cent efficiency of the GaAs (gallium arsenide) diodes used in fibre lasers. The ongoing system design


improvements and the improvement in output power from the chip-based packages are both leading to higher brightness systems. This is important because higher brightness leads directly to faster weld speeds and/or increased penetration depth, as shown in Figure 2. It also opens up the application space further: for example, our initial system is ideal for joining foils in rechargeable batteries, but the currently available higher brightness system can not only weld the heavier gauge leads that connect the foils in a battery, but also the busbars that connect those assemblies, as in Figure 3. In fact, the current high-brightness blue laser system can also weld windings in solenoids or drive motors and lighting assemblies – essentially every copper joint in a motor vehicle is now a candidate for high-quality, high-efficiency blue laser welding.


Copper is not the only target material standing to benefit from the blue laser’s advantages – aluminium, gold, stainless steel, and even the tough problem of joining dissimilar materials will benefit as well. High brightness also opens up other materials processing applications, such as etching and cutting, so it appears as if the blue laser is poised to bring increased flexibility and efficiency to a wide range of industrial applications. l


NOTE FROM THE EDITOR: HYBRID WELDING WITH BLUE AND INFRARED WAVELENGTHS


In addition to speaking with Jean-Michel at Laser World of Photonics to learn about Nuburu’s latest 500W blue diode laser installment – and arrange the writing of the above article – I also stopped by Laserline’s booth to discover other developments taking place in blue laser processing. In addition to exhibiting it’s


latest 1kW CW blue diode laser, the firm was also introducing a new concept that combines beams in both the blue and infrared wavelengths to increase welding capability when processing highly reflective metals, such as copper, aluminium and gold. The firm told Laser Systems


Europe how bringing together the two wavelengths will enable


the high-quality, spatter-free aspects of the heat-conduction welds achievable with blue diode lasers to be combined with the large penetration depths enabled through using multi-kW infrared lasers. In practice, the new technique


will use a large, blue spot to form and stabilise the melt pool, and then use a centred infrared beam to create and maintain the keyhole – at depths larger than those achievable solely with Laserline’s blue diode laser. The firm has seen success


in testing the concept using varying levels of power between the two sources – blue diode lasers ranging from 1 to 1.5kW and infrared lasers between 1.5 and 4kW. For example, using a 1.2kW blue laser (the


WWW.LASERSYSTEMSEUROPE.COM | @LASERSYSTEMSMAG


firm has sources up to at least 1.5kW that it hasn’t yet released commercially) and a 1.5kW infrared laser, the firm could achieve 1.4mm weld depth in copper at a velocity of 6.5m per minute.


In addition to increasing


weld depth when processing highly reflective metals, the new hybrid concept will bring further benefits to additive manufacturing, cladding and heat treatment applications.


AUTUMN 2019 LASER SYSTEMS EUROPE 17


Nuburu


Laserline


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