Analysis of the interactions between the morphology and the properties of weld seams during laser transmission welding of plastics by a three-dimensional, spatially re-solved determination of the crystallinity of the weld seam by means of Raman microscopy

• Applicants: Professor Dr.-Ing. Michael Schmidt; Professor Dr.-Ing. Stefan Will
• Subject Area: Production Automation and Assembly Technology ; Analytical Chemistry
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 399619237

In this project, the cause-and-effect relationships between the temperature field present in the weld seam, the weld seam morphology and the mechanical properties of laser-welded plastic components are to be determined. For this purpose, a new spatially resolved measuring method based on Raman spectroscopy for the determination of the local degree of crystallization in semicrystalline materials is to be scientifically developed and qualified, and the influence of the degree of crystallization in the weld seam on the short-term and long-term properties of laser-welded components is investigated. The measurement method to be developed is suitable, on the one hand, for the predictive material analysis in order to determine material properties for the subsequent joining process. Local different degrees of crystallization can be identified in the component and compensated by a suitable process parameter adjustment during laser beam welding. On the other hand, process-structure-property relationships in laser transmission welding are to be analyzed, understood and optimized.Based on preliminary work, the Raman microscopy is to be further developed and validated for the determination of locally spatially resolved crystallization degrees. Various semi-crystalline materials (PA6, PP and PE-HD) are to be used for this purpose. Here, the development of an approach for the depth-resolved determination of polymer properties is an important step. Subsequently, the degree of crystallization in the weld seam of laser welded test specimens is to be analyzed as a function of different process parameters. Furthermore, relationships between the degree of crystallization and the short-term and long-term properties of the weld connection are investigated. A thermal FEM model of the laser transmission welding process is intended to represent the temperature field during the welding process and thus to determine the cause-and-effect relationships between the parameters of the temperature field (maximum temperature, heating and cooling rate) and degree of crystallization. The degree of crystallization in the weld seam is to be adjusted by adapted irradiation strategies (controlled cooling by multiple crossings, generation of quasi-stationary temperature fields by oscillating movement of the laser beam).

• DFG Programme: Research Grants