Plastic Welding Machine

Metal is not the only substance that can be welded – plastics can be welded also, using an ultrasonic welding machine, and in fact, many of the articles which we take for granted in the modern world are created partly or wholly using this process. Welding plastics by using an ultrasonic welding machine received a huge boost, ironically, with a failed experiment with an all-plastic car in the late 1960’s in the United States. The plastic car was built successfully using ultrasonic welding, but was a complete failure on the marketplace. However, the ultrasonic welding process was perfected during this minor footnote to the auto industry’s development, and it is in very wide use today.

Ultrasonic welding machines weld plastics and thermoplastics by putting an ultrasonic pulse through them vertically (unlike the ultrasonic welding techniques used on metals, which employs horizontal oscillations). As is usual in most types of welding, heat is involved in the process, and this heat is generated at the bonding point by several different factors. The vibrational energy of the ultrasound itself contributes to heating, as does the reflection of the sound vibrations, with the friction of the two plastic surfaces as they vibrate against each other providing additional heat. Heating these facing points on the two plastic surfaces causes them to melt, the molten plastic merges, and the bond is made – generally very cleanly and strongly.

Plastic welding of this kind is most successful when both pieces of plastic have identical melting points. Some preparation of the surfaces is often carried out as well, although this is not as necessary as with ultrasonic welding of metals.

How the Plastic welding machine works

Most ultrasound welding machines operate on the same basic principle, and bear a closer (if somewhat vague) resemblance to a drill press or sewing machine than to arc welders and other welding machines that most people are familiar with. The two pieces of plastic that are to be joined must be pressed against each other and under pressure as well, so there is a “nest” or “anvil” where the parts are placed, and a press there to bind them together for welding.

The sonotrode is the part of the welding machine that provides the ultrasonic pulse that actually causes the two pieces of plastic to bond together. The sonotrode must be designed specifically for plastics, because of the necessity for vertical oscillations – an ultrasonic welder built for metals will do absolutely nothing to plastic, since its oscillations are horizontal, just as a plastic welding machine cannot weld metals despite the fact that both use ultrasound.

Plastic welding is carried out with high-frequency vibrations in the 20 to 70 kilohertz range, which are needed to create enough vibration and friction to melt the plastics. Some hand-held models of plastic welding machines are available on the market as well, with a sonotrode which fits in the hand and must be held precisely at right angles to the two clamped pieces of plastic that the user is attempting to fuse.

Uses of plastic welding machines

Plastic items are everywhere in the modern world, and many of the objects that are used in everyday life feature plastic welding because of the security, uniformity, and clean characteristics of the join. Glue, for example, can get into electronics parts very easily, so plastic pieces close to electronics are often welded with ultrasound for a completely clean join. Ultrasonic plastic welding is often used for the tiny circuits and other parts found inside computers, as well as medical machinery (which often needs to be free of all potential contaminants such as glues), packaging for combustible or explosive items, water, milk, and juice containers, cell phones, and even panels and ducts in cars. Ultrasonic welding machines are an excellent example of the clever application of a few basic physical principles to create a clean, durable weld in plastic without the need for glues or high temperates – and these principles can be useful in the home as well thanks to the hand-held units now available.