Injection moulding is a mass production process capable of creating multiple quantities of solid plastic parts repeatedly at fast cycle times. Consequently, it is very suited for high volume manufacturing.

The injection moulding process

Step 1 – The mould tool is securely mounted into a moulding machine of relevant size, with the two halves of the tool held into place by clamps. A machine setter prepares for production by entering the specific tool settings into the machine.

Step 2 – Plastic pellets are fed into the moulding machine using a hopper and passed into a heated barrel to melt the granules. Within the barrel a reciprocating screw plasticises and compresses the material, driving the molten plastic towards the mould tool.

Step 3 – A nozzle forms a seal between the barrel and the mould tool. Under high pressure the molten plastic is passed from the barrel, through the nozzle, and into the cavity of the mould tool. Tools can contain multiple cavities to produce more than one part each time.

Step 4 – Temperature controlled water or oil circulates the body of the mould tool for a specific length of time to cool the plastic within. As the plastic cools it solidifies to the shape of the mould cavity or cavities.

Step 5 – The moulding machine uses its moving platen to open the mould tool and ejector pins extend into the mould cavity to push the part out. Often a robot collects the finished moulding from the mould and places it on a conveyor belt or final working area. They then retract to their original position allowing the mould to be closed and the cycle repeated.

Injection Moulding Cycle Times

The cycle time of the injection moulding process is defined by the time it takes to make a complete part from closing the tool, injecting the plastic, cooling the polymer under pressure, opening the tool and ejecting a full part. A short cycle time will improve manufacturing efficiency, allowing more parts to be made for the customer in a shorter time. A short cycle time is also paramount to achieve a competitively priced component.