Ultrasonic welding is a widely recognized and accepted process for joining thermoplastic materials. It offers many advantages, including process reliability and repeatability, lower energy usage than other joining techniques, material savings (because there is no need for consumables, such as glue or mechanical fasteners), and labor savings.
But as with any process, there are situations where apparent problems with this technique may interrupt the production process. The key to resolving and avoiding these problems is to understand their likely origins.
Issues usually occur in one of four areas:
1. Equipment: The ultrasonic welding equipment or various welding components are not suited to the application.
2. Process parameters: The parameters used are not suited to the parts being joined.
3. Materials: Changes are made in the type, composition, or physical/mechanical characteristics of the materials used in the parts.
4. Part design: Certain details of the part’s geometry are not suited to repeatable or successful welding.
It should also be noted that sometimes a problem identified in one area may expose a weakness or deficiency in another area.
Let’s start with equipment. It is easy and usually logical to think the equipment and approaches that produce successful welds in one application will do so in another. But that is not universally true. Worldwide, 20-kHz ultrasonic welders are by far the most widely used; due to their versatility, these welders can deliver high-power (up to 6000 W) and high-amplitude outputs, and they can accommodate a wide range of available tooling sizes. For a contract manufacturer that produces ultrasonically welded parts, 20-kHz equipment can be a great investment since it offers the promise of future use in many applications.
However, there are some instances—especially with small and delicate parts—where the high-power, high-amplitude capabilities of 20-kHz equipment may prove too “aggressive” for certain assemblies, potentially resulting in damage. One possible solution is to reduce the input amplitude, but this won’t work if the amplitude applied is below the recommended level for the polymer being welded.
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