Correlation between weld seam morphology and mechanical properties in laser transmission welding of polypropylene

Abstract

In laser welding of polymers, the morphology of weld seams is decisive for the weld strength. Usually, time consuming parameter screening with subsequent destructive tests are performed in order to find suitable process parameter sets resulting in strong weld seams. For more effective and flexible process development, non-destructive characterization methods which base on, for example, crystal structure detection in the welding zone require a deep understanding of interrelations between weld seam morphology and strength.Therefore, polypropylene samples welded overlapping are analysed regarding crystal structure in the heat-affected zones by microscope before and after tensile testing is used to quantify the weld strength. Experimental results show that there is an almost linear relationship between the increase in force and the cross-sectional area of weld seams in the absorption joining partner. Moreover, it is shown that thermal FE simulations allow the prediction of the size of the heat affected zone, which strongly influences the crystal structures inside the weld.