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

在该项目中，将确定焊缝中存在的温度场、焊缝形态和激光焊接塑料部件的机械性能之间的因果关系。为此，需要科学地开发和验证一种新的基于拉曼光谱的空间分辨测量方法，用于确定半结晶材料中的局部结晶度，并研究焊缝中的结晶度对激光焊接部件的短期和长期性能的影响。一方面，所开发的测量方法适用于预测性材料分析，以便确定后续连接过程的材料特性。在激光束焊接过程中，可以识别部件中的局部不同结晶程度，并通过适当的工艺参数调整进行补偿。另一方面，激光透射焊接过程中的工艺-结构-性能关系有待分析、理解和优化，在前期工作的基础上，拉曼显微镜技术有待进一步发展和验证，以确定局部空间分辨的结晶度。各种半结晶材料（PA 6、PP和PE-HD）可用于此目的。在这里，开发一种用于聚合物性质的深度分辨测定的方法是重要的一步。随后，激光焊接试样焊缝中的结晶度将作为不同工艺参数的函数进行分析。此外，结晶度和焊接连接的短期和长期性能之间的关系进行了研究。激光透射焊接过程的热有限元模型旨在表示焊接过程中的温度场，从而确定温度场参数（最高温度、加热和冷却速率）与结晶度之间的因果关系。焊缝中的结晶度将通过适当的辐照策略（通过多个交叉点控制冷却、通过激光束的振荡运动产生准稳态温度场）进行调整。

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).