#EBSstories Studying laser beam welding in situ to improve engineering processes

04-10-2021

A very complex experiment, where scientists from the Technische Universität Ilmenau (Germany), Coherent Inc. and the ESRF recreate the conditions in laser beam welding, is taking place this week on ID19. The results will help the US company Coherent, leader in laser solutions and photonics technologies, to support their customers with optimized process results.

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Many alloys today are welded using the so-called laser beam welding technique. However, laser beam welding with solid-state lasers leads to the formation of defects due to the wavelength characteristics.

Spatter formation is a major issue, especially for alloy steels. This phenomenon takes place due to the interaction of melt and metal vapour inside the keyhole. Due to the higher inclination of the keyhole front at increasing welding speeds, absorption changes and this causes an increased metal vapour flow interacting with the keyhole rear wall. This causes rear-sided melt pool fluctuations and, by exceeding a critical threshold, spatter formation occurs.

“We wanted to know what the mechanism behind the formation of spatters is and what is the secret to avoid them, so we came here to get answers”, explains Peter Kallage, lab manager at Coherent Inc.

“Spatter formation depends significantly on keyhole stability, which is determined by the pressure balance inside the keyhole”, explains Leander Schmidt, scientist at the Production Technology Group of the Technische Universität Ilmenau. “So in the experiment we manipulate keyhole stability by using a local gas flow and an adapted intensity distribution”, he adds.

The team arrived at the ESRF in big vans carrying a team of 12 engineers and a huge, complex set-up consisting of two lasers and an in-house developed gas nozzle. “This is among the most demanding experiments done so far: we had to install dedicated power lines to feed the big laser needed for welding. Experiments with sample environments are core expertise of ESRF and thanks to our experience with complex set-ups such as furnaces, gas guns or high-pressure cells; we are perfectly adapted for this study. The white undulator light with EBS is bright enough to shine light through 3 mm of steel while welding and we take high-speed X-ray movies with microseconds exposure time. The data looks impressive: one can see pores dancing in a sea of molten steel!”, explains Alexander Rack, scientist in charge of beamline ID19.

The outcome of this experiment will help Coherent Inc. to better cater for its customers: “The goal is to improve the process for our customers. So the results will be applied to our industrial activity straight away”, concludes Kallage.

This video has received funding from the European Union’s Horizon 2020 research and innovation programme under the grant agreement No 870313

Text by Montserrat Capellas Espuny. Video by Montserrat Capellas Espuny and Mark McGee.

Top image: Leander Schmidt places the sample on the sample holder. Credits: S. Candé.