Laser transmission welding of plastics has been established as a fixture in mass production since the 1990s. Current research activities focus on whether the welding process can be further accelerated without compromising the quality of the weld seam. In a preceding project, IKV has developed a methodology that uses a simulation model to determine the temperature distributions during welding. In addition to the maximum temperatures reached, the dwell time of the plastic in the molten state is of decisive importance for the permanent strength of the weld seam.
TIn a current joint research project with the Fraunhofer Institute for Laser Technology (ILT), the approach has been enhanced and improved. A key objective was to optimise the energy input so that sufficiently high temperatures and well-defined molten zones are achieved on the one hand, while on the other hand ensuring that the decomposition temperature of the material is not exceeded. To investigate this conflicting objective, the numerical calculation method has been extended to improve the predictive accuracy of the thermal simulation.
© IKVFor this purpose, the latent heat input arising from phase transformations was determined experimentally by Flash-DSC tests at various high heating rates (fig. 1). This latent heat input was integrated into the simulation model, which approximates the three-dimensional temperature distribution. The laser beam heat source used in the model was obtained by statistical ray tracing. In addition, temperature-dependent material parameters such as density, specific heat capacity and thermal conductivity are incorporated into the model, leading to a realistic simulation of the welding process.To describe the thermal-mechanical behaviour of the laser transmission welding process, pressure-volume-temperature effect and thermal elastic-plastic properties were taken into account in the numerical prediction as well. Besides, experimental data and analyses regarding the setting time of laser were integrated it into the numerical prediction of temperature expressly for the high speed welding.
This integration of experimental data and numerical simulation not only enables the prediction of weld seam qualities but also makes a significant contribution to the optimisation and acceleration of laser transmission welding.
Project data and funding
We would like to thank the DFG for funding the project (funding code HO 4776/ 73-1) and the project partners for their cooperation.
Project duration: 03.2022 – 02.2025
Funding:
