Development of a high-speed laser welding process for joining plastics (High Speed Weld)

• Applicant: Professor Dr.-Ing. Christian Hopmann
• Subject Area: Plastics Engineering
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 460251723

Laser transmission welding (LTW) of plastics is a joining technology that has been established in series production since the 1990s. The advantages lie in the precise energy input, the flexibility with regard to the seam geometries or very short heating times in the range of seconds. The temperatures in the welding process and the time that the plastic remains in the molten state and during which the interdiffusion of the polymer chains between the two joining partners takes place are decisive for the weld strengths that can be achieved. In order to predict the strengths of welded joints, a methodology was developed within the framework of the DFG predecessor project at the Institute of Plastics Processing (IKV) in Aachen, with which the strengths can be calculated on the basis of a simulation model for the temperature distributions in the welding process. The thermal material input data was identified as a source of error, which can only be determined with conventional measurement methods in an order of magnitude significantly below that of real plastic processing processes.The aim of this research project is the development of a high-speed laser welding process (H-LTW) and corresponding equipment technology and optical systems, which, using laser power in the kW range, enable irradiation times in the order of µs and thus a significant reduction in welding time. To implement this technology, the first step is to expand the simulation model developed in the previous DFG project for strength prediction of laser-welded joints in order to generate fundamental findings on the heating, cooling and welding behaviour in the high-speed process. In particular, a testing and evaluation methodology is being developed to determine the material input data under high heating and cooling rates, as they occur in real thermal plastics processing. The simulation model is first adapted to the plant technology available at the ILT and then to the H-LDS. With the competences in process-specific optical systems available at the Fraunhofer ILT, a system technology will be realised, which will be completed by the application partners with corresponding laser sources and system technology to form flexible production facilities. Industrial demonstrators will be used to implement the H-LDS on an industrial scale in the near future, and the industrial partners will place them on the market in corresponding industrial applications.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: Laserline GmbH; Leister Technologies AG
• Cooperation Partner: Professor Dr.-Ing. Arnold Gillner