Acoustic Monitoring of an Ultrasonic Welding Process

Ultrasonic welding is a process for joining plastic components with localized heating, very short welding times and a high process efficiency. It is significantly influenced by the process parameters and the tolerances of the parts to be joined. At the same time, welding theories and material models are reaching their limits with ultrasonic welding. This makes it hard to predict weld quality for an individual part. The weld seam quality is typically assessed by subsequent destructive testing of the weld seam. In the present study, we are showing that acoustic monitoring of the ultrasonic welding process allows predictions to be made about the weld seam quality during the process. For that approach, the acoustic monitoring of the mechanical vibration effects occurring in the process is examined using piezo elements, a laser microphone and a laser vibrometer. Besides sound energy density and the non-linear vibration behavior occurring in the process, the weld seam quality is characterized using conventional tensile tests. In the results, both the level of the acoustic energy density and, in particular, the course of the non-linearity during the process show a correlation with the resulting weld seam quality, thus allowing for a non-destructive quality monitoring in real-time.