While ultrasonic welding is one of the most popular plastic welding processes, it is also the most sensitive. There are many interdependent factors that make this welding process a nightmare in many manufacturing environments including complex joint designs, material considerations, tooling, and environmental factors.
Ultrasonic welding can be very successful if its limitations and process requirements are understood. Once appropriate parameters have been identified and controlled, the process itself should remain consistent and repeatable. The fast cycle times and versatility also gives ultrasonic welding an edge over competing technologies. The same equipment can be used to weld a variety of parts with quick tooling modifications. Modern ultrasonic equipment provides unique feedback control with the ability to flag suspect parts.
If your welding process is no longer producing acceptable welds, don’t panic! Although it is tempting to start making “small” adjustments to weld pressure and amplitude, these uncontrolled changes can quickly make everything worse and impossible to retrace. Even small adjustments to weld parameters can significantly impact your weld characteristics.
Your process suddenly doesn’t work because something has changed. I normally check process parameters, compare recent feedback to past feedback, evaluate tooling and part fit-up, verify horn tuning, and measure the horn amplitude. After those assessments, the most common culprits are material or part tolerances changes. If you need to identify new welding parameters, it is best to follow an experimental design with appropriate responses rather than trying random conditions.
So, don’t get frustrated with your ultrasonic welding equipment when you get unacceptable welds! Before making any sudden process changes take a step back and consider your process variables: materials, tooling, and part tolerances. If changes have occurred, the process will need to be redeveloped – systematically!