Plastic injection molding is a manufacturing technique in which molten plastic is injected into a mold to give it a predetermined, fixed form. It is one of the most common and efficient ways to make many different kinds of plastic products, from Lego bricks to water bottles. The plastic is melted and injected into a plastic injection mold using high pressure, where it can cool and solidify to become the final product. It is an ideal method to make complex products with a predetermined shape, making it perfect for mass production of plastics.
The process of plastic injection molding begins with the product design, which can be created by a skilled designer or engineer. This design is then used to create a mould, which can be made from a variety of materials including tool steels and aluminium. The tooling of a mould is a very important part of the injection molding process as it ensures that the molded plastic will have the right characteristics.
Once the tooling has been designed and created, the plastic resin pellets are loaded into a plastic injection molding machine where they are heated to their melting point and then injected into the mold. The injection process can take as little as a minute or less, which makes it extremely quick and efficient. It also produces far less waste material than other methods of plastic fabrication such as CNC machining, with only 20g of original plastic being lost on average per injection cycle.
During the injection process, temperature control units (TCU) circulate a steady flow of coolant through passages in injection molds to help maintain correct and consistent internal temperatures. The TCU also helps remove heat from the plastic shot after injection, allowing it to cool and solidify quickly. When the injection process is complete, the mould is opened and the cooled plastic ejected from the tooling.
Achieving the required appearance, strength and quality of many injection-molded parts requires a consistent blend of raw materials — virgin polymer pellets, pelletized post-consumer material, recycled material, colorants and performance or property additives. Achieving this consistency and removing moisture is essential when processing hygroscopic resins such as PET, polycarbonate and ABS. Internal moisture in these resins can cause voids, discoloration and other defects that reduce the appearance, performance and durability of a molded plastic product.
Once the molded plastic has been cooled and solidified, it is removed from the mould using a set of plates or pins. The finished product is then inserted into a conveyor belt or a compartment where it will be packaged and shipped unless other finishing processes are needed.