Interview: Laser Beam Remote Welding of Aluminum

Dr. Jan-Philipp Weberpals during the interview with Laser Technik Journal editor Oliver Dreissigacker (Source: Wiley)

Dr. Jan-Philipp Weberpals during the interview with Laser Technik Journal editor Oliver Dreissigacker (Source: Wiley)

The core of future automotive lightweight design is a flexible and at the same time stable joining technology of lightweight materials. A new approach in particular is laser beam remote welding of aluminum. The continuous challenge during this innovation was to combine the known options of laser beam remote welding of steel components with the material-specific properties of aluminum materials within a process.

Laser Technik Journal: Dr. Weberpals – congratulations for the nomination and the second prize! In your case: What has there been first, the hen or the egg, in other words, the technology which had to be applied to a process or a specific problem that had to be solved?
Jan-Philipp Weberpals: The nice thing about it was: There was no need. We were some sort of end user, looked at things, had an idea, saw something that didn’t work in the first place and then worked out how to do it in a better way.

LTJ: Up to now, laser beam welding of monolithic aluminum joints, in particular using a fillet weld connection in a lap joint, has been realized only with tactile-guided processing optics. Other car manufacturers do it like that, too?
Weberpals: Absolutely – that is the typical approach to join aluminum alloys. The wire is necessary to handle the alloys, especially those that have a hot crack susceptibility. The protective gases are used for their cosmetic effects.

LTJ: How does the new process work?
Weberpals: Let me first explain some details of the tactile process: The main feature is, that with the relatively large spot size of around 600 micrometer and the typical metal sheet thicknesses that are used for door components and other assembly seams, we always have a full penetration welding. The flange, the part that remains, moves under the thermal influence and this motion eventually results in a crack, that needs to be healed through succeeding melt.
So the solution would be to avoid full penetration welding and apply only partial penetration welding, make sure, there is a remaining amount of the sheet left and – in this way – prevent the motion of the flange and hence the occurrence of cracks.
The key problem is to adjust the parameters in such a way that the result is stable, process-safe and repeatable partial penetration welding. And that is much more complicated in aluminum than in steel. The latter has much more stable processes. In aluminum, it is much more chaotic, and to make it more orderly, we had to go the way of modulation.
First, we there have a spatial modulation that directs the beam onto specific parts of the process zone. Second, we adjust the laser power at the same time point for point, in order to deploy just enough energy to produce the joint but also to prevent full penetration welding. And by repeating this with every new oscillation, we start – simply put – this process anew frequently, earning the initial stability and don’t leave it to itself, like in an unmodulated process. That way, we realize a constant welding depth along the complete seam.

LTJ: Compared to the tactile welding – are you using a different optics set?
Weberpals: We are using a laser head which includes the welding optics and the sensor optics.

LTJ: How do you verify the pointing and the position of the head?
Weberpals: We are using laser triangulation that helps us to exactly measure the edge, the interaction zone, right before the point of incidence of the laser beam. So we have immediate information on the gap that might differ from the intended value and can adjust the process, to have the gap filled with the melt to the right amount. This is done for every point of the seam, that gives us an effective control loop.

LTJ: How much are the savings achieved with this process?
Weberpals: Let’s begin with the process technology: We save, compared to the tactile process, were we need to heat the wire and the sheet, around fifty percent of energy. On the other hand we need a source with a higher beam quality. So we do have conversion losses but in the end, there is an energy saving at the wall plug – and with that a CO2 reduction – of 25 %.
Then, at the tactile process, we have extensive movements of the head towards and away from the assembly, around the clamping elements. In the case of the car door, we took the time we need for the tactile and the remote process, and the latter is around a third faster, if you include the advancing and driving off, we’re at about 50% time saving in total.
From the financial side, the beam source with its higher brilliance is more expensive to buy and also the optical system – that includes the integrated sensor technology and quality monitoring – is more elaborate. But if we add these features to the cost of the tactile hardware, where quality control is necessary subsequently, we end up with savings in the investment of 25 %.
Even more important are the running costs. We don’t need the wire anymore, including its guidance system, no more protection gas, and because of the larger distance from the process, the protection glasses for the optics have less wear and the machine has less down time.
If you add all this, we save up to 95 % of running costs, so this technology unfolds a lot of potential.

LTJ: Although you save a lot of time in welding the car door, the conveyor belt won’t run faster. So how do you draw a benefit out of the time saving.
Weberpals: That’s right, but in the assembly line, you usually have more than one system for working on specific parts. So you may be able to do the job with one machine less. Or combine specific tasks in such a way that you are able to make use of the time savings.

LTJ: How long did the development take and how big was your team?
Weberpals: From the point when we said, we’ll go for it until the series-production readiness was two and a half years. The greatest challenge was to understand the process so well to know, where the hot crack susceptibility comes from and how to avoid that. But we were making progress on that quite rapidly and could develop our ideas into the now established method. We were essentially a team of three: Daniel Böhm was working with me on the development and then our Department Head Steffen Müller, who encouraged us to do this and covered our backs so we had the capacities to focus on the essentials of the work. So he deserves credits for making it possible.

LTJ: Did other manufacturers attempt to develop an according process?
Weberpals: Other car makers also use aluminum in their premium model lines and many have come up with solutions for a remote process. But they are in need of special alloys. The unique feature of our method is that we can handle to 6000-class of alloys that you can buy off the shelf and that has the hot crack susceptibility. To be able to join this by a remote process is our USP.

LTJ: Are there contenders who were watching your progress?
Weberpals: I know the colleagues in the other companies that have models using aluminum in their bodies. They are aware of our work and have commented very positively on it.

The Interview was conducted by Oliver Dreissigacker. (Source: Laser Technik Journal, Wiley-VCH)

Links: International Laser Technology Congress AKL’16, www.lasercongress.org • Innovation Award Laser Technology • Audi AG, Neckarsulm, Germany

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