Introduction to Injection Moulding Machines
These machines vary in the physical size and locking force (tonnage) they can apply, this to accommodate varied sizes of product and associated moulding tools. Machines consist of two distinct halves-
The Injection Unit
This half of the machine is used to convert granular plastic material (pellets) into their molten state through the introduction of both frictional and direct heat. It then injects this material into an opening on the rear of the mould tool using extremely high pressure.
The Clamping unit
This consists of two large metal plates called platens.
One platen is fixed to the machine bed (the fixed platen). One half of the mould tool (the fixed half) is bolted or clamped onto this platen. This fixed platen has a large diameter hole in it’s centre, this allowing the nozzle at the front of the injection unit to come into direct contact with the material injection point (the sprue bush) on the rear face of the tool.
The second platen, called the moving platen, allows the tool to open and close. It is supported by high strength bearings and guides. On the rear of this platen is housed the ejection unit. This is used to couple to and move devices within the mould tool that force the moulding off the tool once cooled and the mould is open. Components then either drop into a suitable container positioned below the tool or are taken off the tool by a machine operator or robot.
The moving platen is also used to apply locking force to the tool when closed. This is to prevent the tool from being forced open as high-pressure materials enter its internal structures.