Nice welding, laser!

Steinbeis and Stadtmüller develop innovative laser welding process

In many fields of manufacturing, the number of models and variants is expanding continuously. It is only partly right to surmise that this is due to poor coordination and shortfalls in companies’ R&D management processes. “If you study the issue in detail,” explains Professor Dr.-Ing. Herbert Emmerich, director of the Pforzheim-based Steinbeis Transfer Center for Production and Organization, “changes in geometry and design are necessary simply due to physical properties and efficiency requirements, especially for market leaders. Companies may want to push the technical systems used in specific applications to the limit in terms of technical or economic feasibility, but this is often not achievable with ‘standard components’”, he continues. Emmerich’s transfer center is working for and with the Osterburken-based company Stadtmüller on a process which makes it possible to produce protective grids and engine suspensions, even in small batches, that are not only economically viable but, more than anything else, in real demand. The two project partners have been working together successfully for some time. In 2010, they won the Steinbeis Foundation Löhn Award for a new laser welding technique for rotationally symmetric components.

Ventilation and air-conditioning systems create high operating costs, so a key requirement placed on systems is to optimize performance and reduce noise emissions. But at the same time, the types of subsystems required lead to a sharp rise in the number of models and variants. This is because, typically, assemblies are unique to specific applications. Take adjoining protective grids, where design and geometry are central to the energy efficiency and performance of the overall systems. With previous production and assembly technology, it was not possible to produce small batches of grids in economically viable quantities because of the huge effort involved just to construct assemblies for each model.

As part of a scheme introduced by the Federal Ministry of Education and Research (BMBF) called “KMU-Innovativ: Production Research,” the Steinbeis experts joined forces with Stadtmüller and took on the challenge of reducing the number of steps previously needed to produce a protection grid (five separate stages) into just one procedure. They were able to drastically cut the modeling-related cost of fittings and tooling, as well as improve the overall throughput for each individual production batch. According to the team’s analysis, it would be possible to integrate all connections into a single assembly, just by using a new kind of laser welding process. A fundamental concept was born for a special type of laser welding. In the meantime, this process has been patented.

When rotationally symmetric components need connecting to one another, there is only one point of contact. Until now, it has not been possible to laser-weld this point of contact, as the contact area on the mating parts needed to be flat and free of gaps. The newly developed process involves partially fusing an abutting protective ring above the assembly with a fine laser beam. This creates a tiny melt area inside the adjoining protective ring, which is cylindrical in shape and is centered exactly around the contact point of the two mating parts. By intensifying the power of the laser beam, the material on the lower component is also fused into the weld; and by squeezing the two mating parts together through exterior force, the size of the joint cross-section increases, improving the hold and resilience of the new join. Simultaneously, the mating parts move relative to each other along a central axis.

The project team used a laser scanner which was moved into place by an industrial robot positioned over the protective grid being welded. The laser beam can be redirected and focused precisely on the point being welded thanks to small motors which reposition mirrors inside the scanner unit. This cuts the welding time per connection point to approximately 200 ms – a significant saving given that protective grids have up to 500 points of contact between the touching protection rings and individual diagonals. To reduce tooling and programming times, it was necessary to program a CAD-CAM link to generate sequence programs for the production cells operating with the robots. As there was no offthe- shelf solution for such a complex application, the project team developed a user-friendly offline programming and simulation environment. This covered the industrial robot, the laser scanner, the laser itself, a series of basic mechanical fixtures and the safety system. An interactive process draws on protective grid CAD data to generate an executable sequence program for the production cell. In the virtual world, sequence programs tend to be based on hypothetical or ideal CAD data, so compared to the positions of settings in the real world, which are based on actual assemblies, their positions will deviate. Because of this, a camera was mounted on the scanner monitoring system to compare virtual position data with real data and make automatic adjustments. Finally, by working with component suppliers, specialist machine makers and control engineers, a production cell was constructed for use in serial production and this has now entered into operation.

Apart from drastically reducing throughput times, not only is it now possible to make smaller batches, economically, and for a broader variety of models and variants, the new protective grid production procedure offers quality advantages. Compared to conventional solutions, less heat is now needed during welding so part dimensions are now extremely accurate, meaning it is no longer necessary to make additional adjustments. The Stadtmüller engineers can now respond to their ventilation and airconditioning clients’ needs with customized solutions that are economically viable. They have at their disposal the ideal answer to customer demands for highly efficient, application-specific ventilation systems.

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