Ultrasonic Welding

Ultrasonic welding is the process by which two pieces of plastic are joined together through the use of high-frequency acoustic vibrations. For the process one half of the component is placed on a fixed anvil and the second half is placed on top. An extension, connected to the transducer on the welding machine, called a “horn” is then lowered down on top of the two components. Once the horn is in place a very rapid low-amplitude acoustic vibration is applied to the moulding in a small welding zone. This vibration causes the acoustic energy to be converted into heat energy and the two components are welded together in a short space of time, typically less than one second.

Parts that will be ultrasonically welded together are designed with very small amounts of extra material on the join line on one half, with a slight recess in the second half. This means that when the parts are welded together there is sufficient material for the parts to fuse together with a strong joint. This process also means that no additional adhesives or connective parts are needed to create the joint. This not only saves money but also makes the process quicker to carry out.

The process of ultrasonic welding is also a highly automated process. The welding information, such as time and frequency, is programmed into the welding machine so that each process carried out will be controlled by computer, ensuring they are all the same. This also means that all an operator needs to do is place parts on the anvil and push a button. The rest of the operation is carried out automatically and the operator simply needs to remove the welded part and install the next component.

Due to the high energies that would be involved it is simply too dangerous to weld together large component parts using ultrasonic welding. Even with ultrasonic welding of small components the operator must wear ear defenders due to the acoustic dangers caused by the two parts vibrating together. To weld large parts these vibrations would be substantially larger and the energy involved would be a danger to surrounding operators.

Benefits of Ultrasonic Welding

• Very neat weld seams – due to no additional adhesives or parts needed the welding joins created with ultrasonic welding are extremely neat and visually attractive. This means the process can be used for joins that will be visible once final assembly has been completed.
• High level of quality – as all of the welding part of the operation is automated each part produced will be of high quality. Human error plays a very small part in the operation and so accuracy and repeatability will also be high.
• Low cycle times – the actual time it takes for a part to be welded is typically less than one second. This means that the loading and unloading of the machine will take up the majority of the cycle time, keeping cycle times to a minimum. This low cycle time means that large batches can be produced in a very short space of time.