Development of weldability diagrams for ultrasonic welding of thermoplastics in far field

Ultrasonic welding has been shown to be an efficient way of joining thermoplastic parts. It is accomplished by applying high frequency, small amplitude vibrations to the pieces to be joined together. To make satisfactory products, the material, the horn, and the process parameters determine the weldability of a specific system. The concept of welding areas on the critical plane can be extended from injection moulding to the ultrasonic welding system of thermoplastics. This work was devoted to the development of a proper weldability diagram for ultrasonic welding in far field. The first aim of the study was to identify the relative importance of the process parameters. The results showed that weld time and amplitude of vibration are the two factors that most significantly affect the ultrasonic welding process. The second part of the study defined weldability based on these critical parameters. The application of the weldability concept is demonstrated by the selection of the optimum part and energy director geometry. In addition, temperature variations at the joint interface were recorded to understand the welding process better. These weldability studies are intended to give initial guidelines for system optimisation.