Plastics Decorating - January/February 2008 - (Page 16) ASSEMBLY UPDATE continued from page 14 lower frequencies. So all other things being equal, a lower frequency tool will be simpler and potentially more durable than a higher frequency tool doing the same application. The Machines High frequency welders typically run small tools - making small, delicate parts with great precision. They typically have small, light slides driven by small air cylinders. Low frequency welders typically run large tools at high amplitudes, making larger parts made of softer materials. They typically have large, heavy slides driven by larger air cylinders. The Rest of the Story Going back to the beginning of the article, the answer to the story about the medical device manufacturer who didn’t have the right tool for the job was to switch frequencies to 40 KHz. UEI Group com www.ueigroup. The assembly itself was quite small - a cylinder split lengthwise that was smaller in diameter than a pencil and somewhere around 30 millimeters in length. The weld was delicate because the nominal wall was quite thin and there were internal components that were easy to damage. The 20 KHz welder was the same make and model the manufacturer used throughout its plant. It was capable of about 2000 Newtons of clamp force, and the minimum trigger force setting was supposed to be about 170 Newtons. At less than 70 milliseconds of weld time, the tool had not yet run up to full amplitude. Given this fact and the reduction booster, it is clear that the assembly did not need much amplitude to weld. With a 40 KHz machine, available amplitude at the converter/transducer dropped about in half, and a 1.5 booster was used. Weld time came up to over 650 milliseconds - a much more controllable situation. The welder was capable of about 400 Newtons of clamp force, so it was still very controllable at about 130 Newtons, and a force trigger setting of about 80 Newtons worked very well. Since changing welders, the company has made millions of acceptable parts with very few quality issues. It’s amazing how much better the results are when you use the right tool for the job. n Tom Kirkland has over twenty years of experience as both a user and supplier of plastics assembly equipment and tooling. He has been active in several professional societies, is a past president of the Ultrasonic Industry Association, and is well versed in a wide variety of plastic welding/joining processes. Tom has conducted over a thousand plastics assembly training sessions, conference presentations, and talks in many countries. He is currently a consultant in plastic welding, and is the proprietor of www.tributek.biz, a supplier of parts and supplies for plastic welding. http://www.ueigroup.com http://www.ueigroup.com http://www.tributek.biz
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