Ultrasonic welding of hygroscopic materials-influence of moisture on the welding process

摘要

The welding of hygroscopic materials such as polyamide can lead to unstable conditions during the welding process. Due to changing material properties the ultrasonic welding process is influenced largely by the moisture level of the welding parts. To achieve stable welding processes and high weldline qualities it is necessary to learn more about the influence of moisture on the material properties and the ultrasonic welding process. To perform a scientific examination of the influence of moisture on the ultrasonic welding process, the interactions between the material properties and the welding process are determined in relation to the moisture content. With the aid of welding tests, it can be shown that with constant welding parameters the attainable weld strength decreases with increasing moisture content. With a process-integrated control of the actual moisture content and a strategy to adapt welding parameters to the actual moisture content, poor-quality welds can be avoided. By making use of the process-integrated moisture control and the adaption of welding parameters to the actual moisture content, it is possible to eliminate a complete predrying, which has until now been seen as the only way to ensure reliable welding of hygroscopic materials.