Injection Moulding

Injection Moulding is when plastic granules/ granules are heated to a molten state and injected at high pressure into a mould cavity. Typically ABS, Polystyrene & Polyproplene are used but most thermoplastics and thermosetting plastics can be moulded

Plastic granules/powder fed into hopper with coloured dye
Granules/powder moved through heated arcamedies screw and melted to liquid state
Molton plastic is forced at high pressure into the mould cavity
Pressure maintained inside cavity until plastic cool enough to be ejected from the mould block
Ejector pins release the part from the mould block and the process repeats(click herefor an animation of the process)

Injection moulding is the primary method for producing casings for electronic products as they are manufactured in mass quantities. Mass or continuous production is the only viable scale to use Injection moulding on due to very high setup costs. These are incurred by the required moulding which much be precision engineered and carefully designed to allow the process to work effectively

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The more complex a part the higher the cost of the mould block. Typically aluminium or hardened steel is used depending of the required life span of the mould and each mould must have at least two main parts. A sprue hole allows the plastic to enter the mould and runners/gates are used to distribute it to the cavities in the mould. Importantly the mould must be designed to distribute plastic before it cools and hardens limiting the size that can be injected (approx. 500 x 800mm). Key features of injection moulded parts include - ribs for structural strength, posts for joining parts, sprue hole cutoffs and internal indents from the ejector pins

Two Shot injection moulding is when two plastics with different properties are injected into the same mould cavity at different times. This causes them to fuse together in the mould and become bonded a one part. This is used to combine hard ABS with more tactile rubber in a tooth brush and is often used in similar ways for other products

Please see the below videos for further information on Injection Moulding

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The Advantages of Injection Moulding are -

Repeatable - millions of identical parts can be made with one mould block with little finishing required
Speed - Incredible efficient process that allow moulding of many parts per minute and can run continuously
Strength - Design of mould can adjust wall thicknesses & add support to strengthen the part & save weight in other areas
Complex Geometry - parts can have incredibly complex geometry that couldn't be created by any other process
Automation - Requires no human action to form parts, fully automated production process

The Disadvantagesof Injection Moulding are -

Very high setup costs - The cost of the mould for the design and manufacture can exceed £20,000 and take months to finalise
Part Design Restrictions - Each part must be solid, minimum wall thickness of 3mm, two half construction etc.
Material Flashing - Plastic can overflow from the mould cavity between the mould blocks and create flashing which must be removed in the finishing process

Mr BILLINGTON

Manufacturing - Injection Moulding