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Ultrasonic Bonding of Plastic Parts (Sonic Welding)

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Ultrasonic bonding, also known as sonic welding, is a process in which high-frequency (ultrasonic) sound waves are applied to two or more workpieces that are being held together under pressure to fuse them into a single piece. Commonly used to join plastic parts—especially those made of different types of plastic—ultrasonic welding permanently bonds the individual workpieces without the need for adhesives or mechanical fasteners.

How Does Sonic Welding Work?

Every ultrasonic bonding operation is different, and will vary based on the plastic materials being joined, the shape of the workpieces, and other factors. However, the overall process is generally the same. The parts being sonically welded are fitted together and sandwiched between a metal “nest”, which holds them in place, and a metal sonotrode, or horn.

The horn is connected to a transducer, which creates extremely high speed vibrations; the horn transfers this vibratory motion to the workpieces it is pressed against. The vibrations cause the plastic to melt slightly, and pressure applied by the nest fuses them together, creating a joint. Typically, the interface area where the two parts come together is specially designed to facilitate the melting and bonding processes.

After the parts are joined properly, the vibrations stop and the plastic cools very rapidly, creating an incredibly strong bond.

Ultrasonic Bonding Processes

There are two general methods of ultrasonic bonding: single-strike, or “plunge”, welding, and continuous rotary drum welding. Single-strike ultrasonic bonding is most often used for spot welding, attaching ties, straps, or similar components, and to create smaller, more localized joints. Continuous sonic welding is typically used for longer welds and/or for those that require unique geometries.

Sonic welding is most often used to join smaller plastic parts, such as those in portable electronics or medical devices, but can also be used to bond larger parts for automobiles, aerospace equipment, and other advanced applications. The ultrasonic bonding process can be modified to provide the best results for the application at hand.

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Sonic Welding from Stack Plastics

Stack Plastics offers a number of secondary services, including ultrasonic bonding. Our ultrasonic bonding process uses highly advanced equipment to ensure superior quality bonds and fast, efficient processing.

Design Considerations for Ultrasonic Bonding

Stack Plastics' ultrasonic bonding services are made possible not only by our state-of-the-art equipment, but also by the design of the injection molded parts. Not every plastic part can be sonically welded successfully: parts must be designed in such a way that the energy delivered by the ultrasonic bonding machine translates correctly to the areas where the melting and bonding processes need to take place. As needed, our team will work with you to suggest design alterations that will better facilitate the sonic welding process.

Contact Stack Plastics for Ultrasonic Bonding & More

Ultrasonic bonding adds quality and value to your plastic injection molded parts. Request a quote on sonic welding for your plastic parts, or contact Stack Plastics to learn more about our ultrasonic bonding capabilities.