Experimental investigations on the polypropylene behavior during ultrasonic welding

Abstract

The polypropylene material meets the needs and requirements in automotive industry due to its features such as wide range of physical properties, ease of processing, and low cost. This research has focused on the investigation of the behavior of polypropylene during ultrasonic welding process. The lap welded samples were examined by modern methods such as Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR). Also, the morphology of the non-welded and welded regions of the polypropylene samples was analyzed by Scanning Electronic Microscopy (SEM) method. TGA and DSC results showed a negligible difference between the mass loss of the molded and the welded propylene materials. Furthermore, the SEM images revealed the formation of voids in close correlation with vibration amplitude. The weld strength and bond integrity appears to be higher for higher vibrations, emphasizing that the lap joint interface strength is higher when the tendency of voids formation is decreasing. The stress-strain curve of the material, plotted for three ultrasonic welding variants, illustrated that increasing the main process parameters (pressure, time, and vibration amplitude) makes the weld strength higher, but a decrease in plasticity was noticed in the welded polypropylene samples.