Quasi-Simultaneous Laser Transmission Welding

A key aspect in the production of individual plastic components is the joining together of the different parts. Plastic welding processes enable media-tight joints combined with low production costs and short cycle times.

One of these processes is laser trans­mission welding. Here, a laser-transparent part and a laser-absorbing part are in contact with one another while a laser beam passes through the trans­parent part with a low energy loss. In the absorbing part, the energy of the laser is converted into heat. Through the contact in the joining zone, the transparent part is heated by heat conduction and the weld seam is formed.

Process schematic of quasi-simultaneous laser transmission welding (Source: KTP UPB)

With the quasi-simultaneous laser trans­mission welding process, quasi-simulta­neous radiation of the complete joining zone takes place through the fast movement of the laser.

Previous scientific studies on the laser transmission welding process are aimed primarily at small weld seams. For this, the correlation between the individual process parameters of the weld temperature and the mechanical properties of the weld can already be effectively characterized. Here, the process parameters can be described with the aid of the line energy. This is calculated with the help of the used laser power, radiation time and rate of advance of the laser. By adjusting these individual parameters, identical weld results can be obtained.

The scientific studies can, however, only be applied to contour welding. With quasi-simulta­neous and simulta­neous welding, other parameters come into effect. Because of the simulta­neous melting process, a squeeze flow occurs in the complete welding zone, thus producing an energy loss.

The latter is not taken into account in the line energy. The line energy thus loses its significance. In addition, other influences such as the length and width of the laser path also play an important role and exert a considerable influence on the weld result.

Laser and workpiece fixture in the experimental set-up at Kunststofftechnik Paderborn (Source: T. Arndt, UPB)

These influences have not yet been adequately studied and thus prevent a transfer of the results from small weld seams to complex components. The aim is to make such transfers possible through the develop­ment of scale-up rules for the quasi-simultaneous welding of thermo­plastics. This will provide an opportunity to transfer optimum process parameters through simple laboratory tests to real parts.

At present, for every new product, a complicated procedure of deter­mining the process parameters has to be carried out, and to prevent transfer problems, this must be done on the actual production plants while halting production, thus generating high costs. A direct transfer of the optimum process parameters from labora­tory tests would thus have numerous advantages (cost and time savings) and, at the same time, enable the use of the quasi-simulta­neous laser trans­mission welding process in a wider range of application.

The project concerned is IGF project 20335 N from the Forschungs­vereinigung Schweißen und verwandte Verfahren of the German Welding Society (DVS). Via the AiF, the project is funded by the German Ministry for Economic Affairs and Energy. The project has already started and is being supported by eighteen industry representatives. Other interested companies can contact T. Arndt, MSc. Theresa Arndt, KTP UPB

Links: Entwicklung von Scale Up-Regeln für das quasi­simultane Laser­durchstrahl­schweißen von Thermo­plasten, Vorhaben-Nr. 20335 N, DVS-FV, AiF „Otto von Guericke“ eV, Cologne, GermanyKunststoff­technik Paderborn (KTP), University of Paderborn, Germany

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