Dynamic beam shaping: The next step in laser materials processing
Matthew Dale learns how Bosch Research plans to use one of the most recent developments in laser technology
In developing its extensive range of products, spanning from home appliances to automotive parts, Bosch researches and wields the latest production technologies.
In the field of laser materials processing, for example, which has become one of the many tools in Bosch’s production arsenal over the years, the firm works with the absolute cutting-edge. Last year, for example, it announced its partnership with the European photonics consortium LAMpAS to develop a laser system capable of structuring metal surfaces to give them antibacterial, water-repellent and grease-repellent properties. The work could lead to home appliances that remain clean for longer periods of time.
‘We have a lot of applications that rely on laser material processing, and look to adopt the latest technologies as they emerge,’ confirmed Dr Reiner Ramsayer, Bosch Researcher’s chief expert in joining technology and the manager of its laser materials processing group. ‘Over the years we’ve seen laser sources continually increase in terms of both beam quality and power. We’ve also seen innovative optics developed and new wavelengths emerge – for example in the visible (blue and green) part of the spectrum for copper processing. We continually develop new processes with these evolving technologies.’
And so with the firm at the forefront of technology development, who better to ask the simple question: ‘What’s next in laser materials processing?’
Beam shaping for new opportunities
The answer, according to Ramsayer, is being able to change the profile and parameters of laser beams during processing, without requiring a change in optics.
‘From my point of view, beam shaping is a parameter field ripe for exploring in order to further optimise processes, as today 99 per cent of all laser processes work with a single round beam with either a Gaussian or top hat profile,’ he said. ‘While in the last 3-4 years we have witnessed the emergence of so-called “ring-in-ring” technology for lasers with adjustable beam quality, its beam shaping functionality is actually quite limited. Such systems do not enable you to achieve whatever beam shapes you want, and the shapes they do offer can be quite static. While you can change the sub-power in the ring and in the core, it's unfortunately not very flexible or dynamic.’
Copper-aluminium welds achieved using different beam profiles from Civan's Dynamic Beam Laser.
Which is why the firm has recently begun working with Civan Laser’s dynamic beam lasers (DBLs) wielding coherent-beam-combining technology. Here, numerous beams of differing phase are overlapped to produce a wide range of beam shapes at up to megahertz frequencies, and at high power. This enables full control of the keyhole during welding, thus opening new possibilities in increasing process quality, speed, and creating new applications entirely.
The concept of coherent beam combining is not new, however it is only in recent years that it has been adapted for high-power (kilowatt-level) material processing lasers. ‘Over the past decade a lot of experts in laser technology identified it as a good approach, but many didn’t think it would work with lasers tens of kilowatts in power, or that it would be too expensive,’ said Ramsayer. ‘Civan has since overcome these issues. They introduced the concept to us 4-5 years ago and we recognised it to have great potential as the next step forward in laser materials processing. It offered a completely new field of adjustable parameters.’
Getting to grips with new technology
Civan has since adapted the technology to materials processing and released systems that it and Bosch Research can experiment with together at research institutes. ‘And so now we are at the stage of conducting lots of research to increase our understanding of the process fundamentals – determining the relationship between different beam shapes and other parameters such as laser power, weld depth, material type, etc’ said Ramsayer. ‘This will enable us to identify which shapes can be used to, for example, influence welding speeds in certain materials without inducing additional defects such as pores or cracking.
‘This is exactly what our corporate research team does at Bosch: take emerging technologies and identify where they can be used in the future.’
During this work the firm will explore completely new ideas on what can be done with the new DBL technology. ‘While you can do a lot of processes with the state-of-the-art adjustable beam quality lasers now available, this new option to change the beam shape during the process will create a lot of freedom for future process design,’ said Ramsayer.
Another advantage of Civan’s coherent-beam-combining technology is that it enables small spot sizes to be achieved over large working distances. ‘Currently the optics have to be very close to your part if you want to have a small spot size on the workpiece, however with this technology you can increase the distance, enabling you to cover a larger working field with a scanner,’ said Ramsayer. ‘This will be very important for increasing remote welding speeds, or improving remote welding quality at the same speeds, which will enable more reliable and efficient production of a lot of products in the future.’
This is why, in his opinion, high-frequency dynamic beam shaping is one of the next steps for laser material processing. ‘While it certainly won’t be applicable to all of our processes, I believe we will find numerous instances where it is beneficial,’ Ramsayer continued. ‘This is why Bosch is very interested in the technology.’
Putting it to work
However, in order to bring the DBL into production, Bosch still has to conduct more fundamental research on how it can be used to influence processes. ‘Once we achieve this we can find applications for it,’ affirmed Ramsayer. ‘We certainly have applications in mind, for example in the production of fuel cells, electric drives and power electronics for future vehicles, so we’ll likely start with these and then find other processes where it's also beneficial.’
While the beam shapes achievable with Civan’s DBLs are possible with other lasers, expensive, specialised optics are currently required to do this, and even then these don’t enable the beam shape to be adjusted during processing. ‘So the innovation of DBL technology is that you now have one system that can produce numerous beam shapes at high frequency without first having to change in optics,’ Ramsayer remarked. ‘This will be very useful if you have to perform different welds on a single part, or across multiple parts in quick succession.’
Bosch Research envisions the technology being particularly applicable to the field of e-mobility, where it will put it to work in the welding of hairpins, busbars and bipolar stacks for battery, electric drives, and fuel cells respectively. ‘These require lots of high quality, long welds to be made, and all have a very high cost pressure associated with them due to the expense of e-mobility,’ said Ramsayer. ‘This technology should enable us to ramp up the production of such parts while also making them smaller and better.’
The laser is regarded as an important technology in e-mobility production, but the quality and reproducibility of the welds must improve over what they are currently, Ramsayer continued. ‘While today, we adjust all the parameters we have currently available to achieve this – welding speed, laser power, focus diameter, etc – we can not currently change the beam profile during the process with ease,’ he concluded. ‘We believe high-frequency dynamic beam shaping could be used to improve the quality and speed of our processes, ultimately allowing us to provide better products at lower prices for our customers.’