Executing Organisation: German Research Foundation
Through the use of welding as a cohesive joining process for producing media-tight connections, positive and non-positive joining methods can be avoided, such as the addition of further elements. Semi-crystalline thermoplastics are frequently used as joining partners in laser transmission welding of plastics, since they have high fatigue strength and good chemical resistance compared to amorphous plastics. The aim of this research project is to compensate the locally different degrees of crystallization by defined adjustment of the temperature field in the welding process as well as a suitable process parameter adjustment.
For weld characterization, the components are subjected to a strength analysis and microscopic investigations on thin sections (see left picture). Raman microscopy shows gradients of crystallinity as well as gas inclusions and defects within the weld. By linking these results, a thermal simulation of the welding process (see right picture) is carried out in order to derive suitable temperature fields for the purposeful adjustment of the degree of crystallization.
Test specimens made of PA6, PE and PP were joined in two different joint configurations (overlap and T-joint) by means of laser transmission welding and characterized in terms of their morphology. The contour-welded PA6 samples showed more air pockets. The reason for this are decomposition processes which occur as a consequence of the smaller melting temperature range of the PA6 and the associated smaller process window. Nevertheless, in the short-term tensile test PA6 contour-welded specimens achieved the highest strength. Currently, the evaluation of Raman microscopy with respect to the heat distribution in the weld takes place.