Mr. Rethmeier, what is your area of expertise?
In general, I carry out research on welding technology – mainly laser-beam, arc and resistance-spot welding. At the German Federal Institute for Materials Research and Testing, I head up the Welding Technology division.
At the start of this year, we conducted an “Environmental Audit of Welded Joints Using Resistance-Spot and Laser-Beam Methods.”
What is an environmental audit?
In an environmental audit, we evaluate the environmental impact of different welding methods. For our project, my colleague Professor Matthias Finkbeiner and I carried out research at the Technische Universität Berlin with 25 other scientists in the specialist research field of sustainable manufacturing. The focus here is on the entire manufacturing process chain. The scientists involved in the project come from a wide range of fields and include engineers, mathematicians, sociologists, and more.
My research area was welding. I asked myself the questions: What does the welding process look like? What materials does it consume? And how can I evaluate it?
Prof. Michael Rethmeier
was born on October 1, 1972 in the German city of Detmold. He is married with two children.
1999: Graduated from TU Braunschweig with a degree in mechanical engineering
2003: Earned his Engineering PhD; dissertation on “MIG Welding of Magnesium Alloys”
Since 2009: Head of Joining and Coating Technology division at Fraunhofer Institute for Production Systems and Design Technology IPK, Berlin
Since 2011: Head of Welding Technology division, German Federal Institute for Materials Research and Testing (BAM), Berlin
Since 2015: Chair of Joining Technology at the Institute for Machine Tools and Factory Management (IWF), TU Berlin
How did you measure it?
As with any scientific enterprise, you start out an environmental audit by clearly defining it: What is the scope of the project? In my case, the task was to weld steel sheets in a U profile. The strength was then determined by means of tensile shear tests. In these load tests, the steel sheets are supposed to perform equally well. Only then is the welded joint good enough and also comparable. Strength is decisive for achieving a good result. Once this is accomplished, the more efficient method is evaluated.
Which welding methods did you compare?
For a long time, resistance-spot welding was the ideal solution for vehicle construction on account of its technical and design possibilities.
But times and needs change, and sustainable manufacturing is increasing in importance. That’s why we decided to compare laser welding with resistance-spot welding. And now we know: things look very positive for lasers!Sheet consumption is the most important factor.
Which method was more efficient?
Laser welding, by a big margin. Sheet consumption is overwhelmingly the most important factor in the environmental auditing of both methods. This is usually the case in environmental audits: material is particularly expensive, and the more material you can save, the better.
As we looked at the entire process chain, our audit also takes into account steel production and the associated mining activities. Laser welding substantially reduces sheet consumption, because it fulfills the same design requirements with much narrower flanges.
Laser welding robots are significantly smaller and therefore consume less energy
In this way, we were able to demonstrate in a direct comparison that laser welding is more efficient than resistance-spot welding.
Were you surprised by your findings?
Yes, I was! In the overall analysis, the energy input is namely almost 50 percent less than that of resistance-spot welding. I didn’t expect there to be such big differences, even if we completely disregard the material aspect. In addition, laser welding saves a lot of time. In short, our findings indicate that laser welding saves steel, energy and time.
How is it that less energy is consumed?
When the laser is used with the right PFO scanning optics, we can work much faster. In turn, this gives us shorter laser times. Moreover, the robot is not only significantly smaller, but also belongs to a completely different weight and power class – a big part of why it consumes less energy.
But there are always ifs and buts, aren’t there?
Yes, and they’re here too. At high standby times, we naturally could not replicate this result. In the study, we calculated the laser within a network, just like you would in industry. This excellent result with little negative impact on the environment can be achieved only if the design possibilities offered by laser welding are actually utilized. However, in a manufacturing operation that is running as it should, this will be the case anyway. Downtime will be reduced. There’s no doubt about that.
Will there be follow-up studies?
Yes, the sustainability of manufacturing processes will continue to be highly relevant. I think that, in the future, manufacturers and customers will be interested in a vehicle’s environmental footprint – including the manufacturing, operation and recycling of the vehicle.
Manufacturers and customers are increasingly interested in a vehicle’s environmental footprint – including its manufacture.
In that case, various kinds of information should be clearly available: How much material was consumed? How much energy went into the manufacture of the vehicle? We have identified an important link in the process chain toward improving this footprint. With laser welding, we can provide a sustainable manufacturing step.