Plastics, which are produced from petroleum, began to be developed in the second half of the twentieth century. Today plastic items are so overwhelmingly present in our lives it is nearly impossible to imagine what life would be like without them. This could not be if it weren't possible to weld separate items of plastic into one.
We may be inclined to think of welding as a process that is limited to use on metals, but many things made of plastic are also welded. This can occur because plastic has the requisite quality to be a candidate for welding. When it is heated it melts and becomes malleable rather than burn. If the heat applied does not reach the point the plastic is consumed the object can be welded together with another simultaneously heated piece. The two joined pieces are cooled together and are permanently made one.
In addition to the initial heating phase and the final cooling (also called the holding phase) period there is a third part used in plastic welding, the application of pressure. Pressure, usually applied from the beginning and throughout the process ensures that the molecules from the two separate materials being welded combine completely and evenly.
Most if not all plastic welding is done by machines.
The use of machines to do the welding is a key reason why plastic is so prevalent in our lives. It would simply not be possible to mass produce it all if each individual piece had to be made using hand tools. The truth of the matter is that a number of plastic welding processes could only be done at all with machines. The use of machines:
- Allows for greater speed. John Henry may have beat the steam drill, but he died doing it and may have been the last man to beat a machine.
- Greater precision is possible because settings and measurements can be exact.
- More methods are possible with the use of machines.
- Set up times are reduced because more than one item can be welded at one time.
- Pressure and heat can be applied uniformly.
There are several different methods of welding plastic. These differ from one another primarily in the source of heat and in some cases how it is applied to achieve the melting required for the two pieces to be joined.
In implant welding a foreign object, typically a gasket or wire, is placed in the piece to be welded. That object is heated and it, in consequence, heats the surrounding area to permit the weld.
Radio frequency welding works by causing friction in the target materials. This is a good method but only works if the materials are subject to the influence of the radio waves.
Laser and Infrared are also used as a method of plastic welding and can be very precise.
Hot plate welding is basically what it sounds like. The plate is heated while the materials are in contact then they are removed and pressure is applied and cooling allowed.
Spin welding and vibration welding are two different types of plastic welding. They are similar, however, in using movement and friction to produce the heat needed for the weld.
Ultrasonic welding uses alternating current (AC) to produce friction which generates heat. This may be the fastest of all methods as welds can be produced in as little as one tenth of a second to two seconds.
It is not easy to imagine how any of these methods, except perhaps hot plate and implant welding, would even be possible without a machine. The outdated method of hot gas welding could be but is very inefficient.
The different methods of plastic welding and the machines that make them possible have produced items for a broad spectrum of application. These include consumer products, medical supplies, the auto industry, fabrics, and the military. Plastic is everywhere and plastic welding machines are a big reason they are.