Injection Moulding Process Explained
Injection moulding is a manufacturing process for producing parts by the high-pressure injection of molten plastic material into a mould, where it is then cooled prior to mould opening then ejection or removal by a robot or machine operator.
The mould or ‘tool’ has two halves, one containing a ‘male’ core and the other a cavity. When closed, the gap between core and cavity is where the moulding is formed. Limitations relate to the need to be able to remove the finished item once cooled, so for example, a hollow ball couldn’t be produced without making it in two halves and then welding or bonding these together.
Initial tooling costs can be relatively high, but tools can have a long service life. Injection moulding machines can also run continuously for prolonged periods of time, making this process best suited to high volume production of identical components.
There are a wide variety of polymer grades that can be selected, this depending on the application. Colour and additives can also be introduced, for example, the addition of glass fibre can produce plastic components that are sufficiently strong to allow for the replacement of metal parts.
The speed at which components can be produced (cycle time) depends on the wall thickness of the plastic in combination with the amount of cooling capacity within the production tool. Thin walled food containers can be produced with sub five second cycle times, often using multi-impression tools.
Moulding machines are highly accurate and range widely in their physical size. This means that components weighing a few grams or bulky items such as car bumpers can be made by injection moulding.
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