Assembly - January 2009 - (Page 80) ASSEMBLY Ultrasonics Plastic Welding by Numbers Today’s ultrasonic plastic welders offer unprecedented control over the joining process. But what exactly do all those settings mean? T hese days, every cell phone has a tiny digital camera. Welding the camera’s clear plastic lens to the case is tricky. There’s not much room for tooling, the seal must be watertight, and the process window is very small. What’s more, a cosmetic appearance is absolutely critical. No marks or particulates can be tolerated. With feedback from load cells, encoders and other sensors, today’s microprocessor-controlled ultrasonic plastic welders offer extraordinary command over every aspect of the joining process. Depending on the machine, engineers can monitor and control ram force, ram speed, amplitude, power, energy, weld distance, weld time and hold time. These parameters can be measured individually or in combination to produce a good weld every cycle, regardless of the size, shape or composition of the parts. The ability to fine-tune such variables as force and amplitude enables engineers to use ultrasonic welders to assemble delicate parts and challenging materials. To learn more, we asked three ultrasonic welding experts to share thoughts on the major parameters of the process. Frequency The first variable engineers need to think about is actually one they can’t change much—the operating frequency. The frequency is determined by the ultrasonic stack, and it can’t be changed significantly without changing the stack. The most common frequency is 20 kilohertz, though 15-, 30-, 35-, 40- and even 50-kilohertz models are also available. High-frequency welders are best for small, delicate parts. Lowfrequency machines are best for large parts. “There’s an inverse relationship between frequency and amplitude,” explains Vasko Naumovski, product manager for plastics at Herrmann Because of the interplay between variables, more control also gives engineers greater flexibility in developing just the right parameters for their application. Photo courtesy Herrmann Ultrasonics Inc. By John Sprovieri Editor “Without a high level of control, such as amplitude profiling or welding by distance, that application would be very difficult,” says Jeff Frantz, director of applications and ultrasonic tooling at Branson Ultrasonics Corp. (Danbury, CT). 80 ASSEMBLY / January 2009 www.assemblymag.com http://www.assemblymag.com
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