Multi-focus optics for gas-tight welding of aluminium alloys in e-mobility

Electric mobility (e-mobility) is undergoing very rapid maturation. While conventional vehicle design disciplines such as car body design are established, e-mobility-specific disciplines are still in the phase of technological orientation and ramp-up.

In particular, the demand for components like batteries, e-motors and power electronics is growing continuously. 

Some of the major materials chosen for these parts are aluminium alloys. Next to the material-specific challenges, there is a requirement for the gas-tight welding of such alloys for parts like casted power electronics housings and heat exchangers made of sheet metal or extrusion profiles.

This is to both shield the electronic components from the influence of the surrounding environment, and prevent leakage of the water-cooling circuit.

Demand for gas-tight joints in e-mobility applications

Typically, the welding of electronics housings and cooling plates involves the joining of an aluminium wrought alloy cover sheet with stamped cooling channels onto another flat sheet metal part made of an aluminium wrought alloy. Representative material choices for this are aluminium alloys from EN AW-1xxx, AW-3xxx, AW-5xxx and AW-6xxx series. If the EN AW-6xxx series alloys are used, it is important to choose material combinations that avoid material mixtures susceptible to hot cracking. In this application field the weld joint is often executed as an I-seam and the weld depth is adjusted so that it corresponds to the cover thickness. 

Trumpf’s new MultiFocus optics rely on the firm’s existing TruDisk laser portfolio and are usable with fixed optics and scanner optics 

The special challenges in welding aluminium lie in the viscosity of the weld pool, the small interaction zone in terms of laser welding, and the chemical composition of the specific aluminium alloy. These aspects lead, among others, to the phenomena of bulging, pore formation and even hot cracking.

Innovative optics enable reliable gas-tight welding of aluminium parts

For these applications, Trumpf’s new MultiFocus optics have been developed to make the laser the manufacturing technology of choice. This solution enables the gas-tight welding of aluminium components at high welding speeds and consistently high component quality.

The MultiFocus optics contribute a key effect in aluminium gas-tight welding. When the beam exits the fibre, 

it is split and focused into four different spots. Each of the four individual beams continues to use its power efficiently thanks to the ring-core division of the BrightLine weld fibre. Positioned in a square, the effective radii of the spots overlap. This creates a single large vapour capillary. The laser power is now distributed more homogeneously over the effective process area, and the keyhole remains constantly open.

Stable welding process of aluminium ensured by spatial power distribution of the MultiFocus optics

Measurement results from comprehensive tests at the DESY research centre in Hamburg – performed using synchrotron imaging – confirmed that the keyhole area was increased and its fluctuating standard deviation was reduced from more than 50 to less than 7 per cent. The capillary collapse in aluminium laser welding is now no longer a problem, nor are annoying pores produced from this collapsing. Four spots proved to be the most energetically favorable arrangement for the purpose of gas-tight welding. At the same time, the optics work omnidirectionally and avoid even more spatter than conventional laser processes alone.

The MultiFocus optics facilitate laser welding of electronics housing made from casted aluminium 

This technology is a real breakthrough in the processing of aluminium parts: tests showed well over 99 per cent reliability as far as the gas-tightness of the weld seams is concerned. And this is achieved at high welding speeds of currently up to 15 metres per minute, which competing welding technologies rarely reach. Laboratory tests at Trumpf are already running at 30 metres per minute.

Economical and process-reliable laser welding 

Now that the laser’s fields of application are expanded to aluminium materials, this makes it appealing for other additional processes. For example, millions of components such as electric motors and power electronics are housed in die-cast aluminium housings, many of which have to be gas-tight.

Gas-tight welding of cooling plates for e-mobility battery packs using the new MultiFocus optics 

There are also application opportunities for white goods, photovoltaic applications and industry electrification. However, in order to first advance the initial application in the automotive industry, Trumpf is already working on technical solutions for the series production process for the aforementioned laser welding of power electronics housings, also with a view to an accompanying inline weld seam analysis and quality assurance. The flexibility of laser production technologies enables short-term adaptation of manufacturing strategies as well as barrier-free use in inter-linked production facilities. 

The innovative Trumpf MultiFocus optics ensure the economical and reliable gas-tight welding of casted and wrought sheet metal aluminium components.

Dr Mauritz Möller is automotive industry manager at Trumpf Laser- und Systemtechnik 

Philipp Scheible is head of customer laser welding applications at Trumpf Laser- und Systemtechnik 

This article was co-authored by Sabrina Vogt and Patrick Haug, of Trumpf Laser- und Systemtechnik

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