A complete guide to plastic Injection Moulding

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Description

• Injection moulding turns molten plastic into the
  shape of the desired product using custom made
  tools with a selection of machines. Injection
  moulding is used to make products like chairs,
  musical instruments, automotive parts, toys,
  parts for electrical appliances, preform for
  bottles, tables and other similar products. Using
  injection moulding the products are usually
  created in bulk, as it is well known for
  successful mass production.

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How was injection moulding invented?

• During the mid 1800s the use of ivory was
  replaced by plastics and plastic injection
  moulding was introduced. The plastic was heated
  in a large heating barrel, and then a plunger was
  injected into the melted plastic into the mould.
  Plunger systems/ mechanism of injecting plastics
  were replaced by reciprocating screws in the
  1950s which helped in even distribution of heat,
  mixing of material. Auxiliary heaters were used
  and the screw supplied mechanical energy which
  together help these plastic (or other materials)
  granual form to melt and homogenise.
• Presently there are a plethora of injection
  moulding machines that can be customised for the
  mass production of objects. New injection
  moulding machines can not only mould plastics but
  also biodegradable products, which promotes
  environmental conservation.

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Functional units of injection moulding machine

• 1. The injection unit
• The injection unit is the primary part of the
  entry point for the material that needs to be
  melted and moulded. The barrel is located in the
  middle with the hopper on one end and a mould
  cavity on the other.
• The Hopper Dried plastic or the material to be
  moulded is placed into the hopper, which also
  contains a drier to ensure that moisture stays
  away from the material inside it. A hopper is
  located at the end of the barrel. The material
  inside the hopper is mixed with the required
  compounds like strengthening and coloring
  substances.
• The Screw Barrel The material now passes to
  the barrel from the hopper where it is completely
  melted by a heater that is provided on the
  barrel. A rotating screw allows a path for the
  material while heating and act as a hydraulic ram
  (pump powdered by hydropower) pushes the heated
  material into mold.

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• 2. The Mould Cavity The material then passes
  through a runner system and enters the mould
  cavity which is located on the other end of the
  barrel. In the mould cavity, the melted material
  will fill the cavity completely, cool down,
  solidify and hence adapt the shape of the mould.
  The solid material is then ejected from the mould
  cavity, is placed on a conveyer belt and then
  moves to a storage container. After this process
  the final product is ready to be used, no other
  modification is required in most cases.
• The time taken for the above process depends on
  the size, shape of the mould cavity, nature of
  the machine and the plastic raw material that
  requires it to be moulded. The process is
  repeated automatically. The more advanced the
  machine is, the faster and efficient it will be.

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Manufacturing of the mould cavity

• Because the shape of the final product will be
  identical to the mould cavity, it requires a
  change of shape and size in accordance with the
  product. The mould cavity also needs to maintain
  structural integrity despite the amount of heat
  it is subjected to, hence the mould cavity is
  made from aluminium or steel through CNC
  machining.

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Custom Injection Moulding

• If the product that needs to be moulded through
  injection moulding is different from the usual
  products, then the machine manufacturers require
  custom injection moulding. It is usually required
  to create military and medical products. Custom
  Injection moulding is very different from general
  injection moulding and requires specialised
  designers and engineers.
• Injection moulding produces high volumes of high
  quality, good looking and cost-effective
  products. It is highly used to produce automotive
  parts (materials like polypropylene and PVC)
  toys, bottle caps (using Polypropylene(PP)),
  models of aeroplanes (using Polystyrene (PS)),
  consumer electronic products (using Polystyrene
  (PS)) and bio-friendly medical equipment.

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