In almost every industry for almost every application, plastics have revolutionised the way products are designed, manufactured and distributed. This is due in large part to the many cost-effective and versatile characteristics of plastics. One of the most prominent benefits is the ease with which plastics can be moulded to quickly mass produce identical pieces. Most commonly, this process is called plastic injection moulding.
Material Selection
The material used in plastic injection moulding is a polymer called a thermoplastic. This is because the substance becomes soft and liquefies as a high temperature and solidifies upon cooling. Thousands of types of thermoplastics have been created by blending different types of polymers. When beginning the moulding process, the end application determines which polymer is used, based on qualities such as heat tolerance, strength and texture.
Machining and Equipment
The most expensive part of the plastic injection moulding process is the initial equipment and design and manufacturing of the mould. Most commonly, moulds consist of two metal plates that clamp together to create a three-dimensional cavity in the desired shape and size of the finished product. A single mould can create one piece each time it is filled, or multiple small identical pieces. Moulds are usually cooled with water or another coolant to maintain an optimal temperature while they are being filled with the hot plastics.
Injecting the Plastic
The work of a moulding machine starts when solid pieces of plastic are fed into a large hopper. This initial plastic can be chips, blocks or scrap pieces, depending on the application. After collected and fed through the hopper, the pieces are pushed by a rotating screw in a heating chamber. In this chamber, the many plastic pieces become a single liquid mass. The screw continues to push the liquid into the mould. After the polymer cools in the mould, the two plates separate and the hardened piece is ejected.
