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When welding thermoplastics using ultrasonic energy, the welder creates an inseparable bond between two or several parts. Each connection requires a weld joint that is designed in a way that perfectly suits the material, the geometry and the position of the two components to be joined. The process follows a basic rule: the weld joint design needs to guarantee a high level of repeatability at minimum risk when the joint is reproduced in a welding machine.
The high-frequency alternating voltage produced by the generator is converted into mechanical vibration energy of the same frequency by the converter. The molecular and interfacial friction generated by this process will then produce heat that causes the plastic to plasticise. The components are afterwards joined by applying the right amount of pressure. The welding stack required for this process is made up of a converter, a booster (amplitude amplifier) and a sonotrode operating at resonant frequency.
In theory, all components made of thermoplastic materials as well as of amorphous and of semi-crystalline polymers are suitable for welding, although the welding characteristics of these plastics may differ significantly. For instance, amorphous and semi-crystalline polymers cannot be fused together. On the other hand, hard, amorphous plastics such as PC, PS and PMMA possess a coefficient of transmission that is favourable for ultrasonic energy. Finally, semi-crystalline plastics such as PA, PP and POM possess a high acoustic attenuation coefficient.
Plane welding is used wherever materials need to be joined plane to plane or fused tightly with a circumferential weld joint. The planar welding of two components requires a weld joint design created with the help of energy directors.
Compared to other types of joining technologies, ultrasonic welding is not only faster and more efficient, but also safer for the environment. For these reasons and due to the fact that it offers shorter cycle times and lower energy consumption, this technology is well established in the marketplace.