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

Ultrasonic welding has been shown to be an efficient way of joining thermop lastic parts. It is accomplished by applying high frequency, small amplitud e vibrations to the pieces to be joined together. To make satisfactory prod ucts, the material, the horn, and the process parameters determine the weld ability of a specific system. The concept of welding areas on the critical plane can be extended from injection moulding to the ultrasonic welding sys tem 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 rime 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 parame ters. The application of the weldability concept is demonstrated by the sel ection of the optimum part and energy director geometry. In addition, tempe rature variations at the joint interface were recorded to understand the we lding process better. These weldability studies are intended to give initia l guidelines for system optimisation. PRCPA/1464 (C) 1998 The Institute of Materials.