Ultrasonic Welding

Ultrasonic welding was invented in the 1960's, when Robert Soloff was a lab manager at Branson Instruments. There, they welded thin plastic films into bags using probes. He accidently moved a probe close to a plastic tape dispenser and the two halves of the dispenser welded together. He discovered that the ultrasound energy could travel around and through rigid plastics to weld the entire part. He didn't have to move the probe to weld. Soloff, working with Seymour Linsley applied for and obtained a patent. They were able to use it in the toy industry first. The first plastic car was produced in 1969. The car did not sell, but the technology did.

Ultrasonic welding is now used for both hard and soft plastics, such as semicrystalline plastics, and metals. This type of welding is unique in that no connective bolts, nails, soldering materials, or adhesives are necessary to bind the two parts together. The parts are sandwiched between a fixed shaped nest (anvil) and a sonotrode (horn) connected to a transducer. The technique uses a very rapid (15-70 KHz), low-amplitude acoustic vibration that is applied to a small welding zone. When welding plastics, the interface of the two parts is specially designed to concentrate the melting process. The energy is converted into heat energy by friction, and the parts are welded together almost instantly. The pieces do not need to remain in a jig for long periods of time waiting for the joint to dry or cure.

The applications of welding with sound waves are found in many industries including electrical and computer, automotive and aerospace, medical, and packaging. The welding lends itself easily to be done with the aid of computers also, making clean and precise joints. It is limited, at this time, to small components such as watches, cassettes, plastic products, toys, medical tools, wires, microcircuit connections, sheet metal, foils, ribbons, and meshes. If the parts are too thick, the weld will not hold, thus limiting its uses. The energy needed to weld something big, like trucks and cars is prohibitive.

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