Plastic injection moulding

Thanks to its convenience and ease of use, plastic injection moulding is the most common and widely used plastic products manufacturing method in the world. Injection moulding means this technique can be used to manufacture, for example, plastic chairs and tables, covers for electronic products, disposable cutlery, and many other products. Injection moulding is commonly used to produce plastic parts, especially in the aerospace and automotive industry, where parts have to withstand high-speed pressure. The basic equipment used in plastic injection moulding consists of two main parts: the injection machine and the mould.

Injection moulding machines, also known as injection presses, consist of a hopper, an injection piston or screw plunger, and a heating unit. The mould is fixed on the work surface of the moulding machine, and the molten plastic is injected into it through a casting hole.

Three main parts can be distinguished in moulds: the sprue, the runner, and the mould cavity. To improve the quality of the final part and the service life of the mould, it is important to design it with the correct demoulding angle in order to separate the moulded parts and allow gases trapped inside to escape.

There are two main methods to produce injection moulds: conventional machining, and electrical discharge machining (EDM).

• Conventional machining. This has traditionally been the method used for injection moulds. CNC machining has become the predominant method in producing complex moulds with more precise details and in less time than traditional methods.
• Electrical discharge machining (EDM). This is widely used for the production of moulds. Apart from forming shapes that are difficult to machine by conventional means, this process also offers the possibility to form pre-hardened materials, removing the need for any subsequent heat treatment.

The first step in the plastic injection moulding process is to melt the plastic in the moulding machine, and then inject it into a mould at high pressure. In this stage, the material is cooled, solidified, and then split into the two mould halves. The result of this technique is a plastic product with a predetermined shape.

Most elastomeric thermoset polymers can be injection moulded, although this may require custom compounding. The type of plastic chosen for injection moulding depends on the type of product being manufactured, its requirements, and the overall budget. Only a few of the hundreds of available plastics are safe for consumer use, and these are the ones we use at Rotolia: polystyrene, polycarbonate , polypropylene , polyethylene , polyamide , polyvinyl chloride , Teflon® , Delrin®, and acrylic, among others.