BMW tests optical coherence tomography for better welding

19 Dec 2017

Imaging technology could be used to improve on-the-fly assessment of remote laser welding applications in auto production.

OCT: on-the-fly quality assurance for laser welding

Germany’s Federal Ministry of Education and Research (BMBF) has backed a project to explore the potential of optical coherence tomography (OCT) to improve remote laser welding in car production.

Funded under the country’s “Photonics Research Germany” program, the effort includes representatives from auto giant BMW, who will work alongside laser welding and OCT experts at Precitec, Blackbird Robotersysteme, Emil Bucher, and the Technical University of Munich.

The project utilizes a Blackbird scanner comprising an “intelliWELD” PR scan head provided by Scanlab, a control unit, and an integrated OCT scanner.

The team adds that imaging relies on ultra-fast workpiece scanning with a dedicated OCT scanner coaxially coupled in the weld scanner. “This welding solution thus provides integrated edge tracking and seam topology measurement,” they say.

Ophthalmic to auto?
While more normally associated with ophthalmology applications, where it can offer early diagnosis of sight-threatening conditions like retinitis pigmentosa or glaucoma, OCT is also able to scan components before welding, and spot potential defects or imprecisions during the weld process.

That detailed information allows assessment of weld-seam quality, as well as recording of defects such as inadequate width or penetration, open pores and faulty positioning. “This data can be used for quality assurance procedures that eliminate the need for downstream quality assurance steps,” points out the team.

Blackbird Robotersysteme CTO Ulrich Munzert said: “It's conceivable the future will offer numerous additional application possibilities – even reaching beyond the auto industry.”

He believes that the demanding requirements of the automotive sector will see the research project accumulate plenty of practical experience promising to simplify manufacturing approaches and processes.

That should prove valuable as part of the German government’s wider effort to advance the development of electric vehicles, where slow sales have been explained in part by the high cost of the new technology – itself a manifestation of the large, inflexible production lines that are geared to making vehicles in much larger volumes.

“Future-proof production systems and bonding techniques need to work flexibly, adaptively and with connectivity,” reports Scanlab in its release announcing the project.

“To maximize efficiency and autonomy, machines will require much more information about their surroundings and the objects to be processed.

“This is precisely where contactless methods such as OCT, combined with photonic sensors, offer tremendous potential for detecting orientation and status, assessing process results, and sharing and documenting this information within the manufacturing process.”

Accurate laser positioning
According to a 2016 study by Munich-based Lessmüller Lasertechnik, which sells OCT seam tracking equipment, the technique is able to profile weld joints with high resolution in both the axial and lateral directions.

“Thus the exact welding position can be detected in real-time regardless of the viewing angle, a change of the focusing distance or the welding direction,” the firm concluded, suggesting that the maintenance-free option could be easily adapted to any conventional laser processing head, without any need for sophisticated alignment.

At the moment camera-based and laser triangulation methods are used, but the heat generated by the welding process – along with metal spattering, fixtures and clamping – can all obscure the view of the weld joint.

“The benefit of OCT over other inspection techniques is that it enables not only multidimensional visualization of the welding process but also direct real-time height measurements with high degree of accuracy,” reported Lessmüller, adding:

“An advantage of seam tracking with OCT is that by more accurate positioning of the laser remotely it enables precise laser edge welding…moreover, OCT may be easily assembled to the existing remote laser optics through the existing camera port.”