Things to know about Injection Moulding of Plastics
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A Guide to Injection Moulding of Plastics

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Injection moulding Process involves:


  • Understanding cavity pressure profile and pvT diagram and Wander - Wall’s equation.
  • Understanding of melt flow characteristics.
  • Softening / melting of plastics granules, (Screw plasticising)
  • Screw design is responsible for consistent quality of melt production.
  • Consistency of raw material is also important.
  • Dosing of the plastic melt,
  • Precise dosing controls can be achieved by well designed m/c controls.
  • 3 steps of RPM controls and 3 steps of back pressure control are useful for ensuring precision.
  • Understanding of screw plasticising is essential.
  • Injection of melt in a closed and clamped MOULD.
  • Clamp force should be 20% more than the cavity pressure to prevent opening of mould during injection.
  • Melt must flow in balanced manner and fill mould uniformly to avoid moulded-in stresses, which causes in failure of parts in use.
  • Understanding of flow pattern is very important while finalising part design.
  • Mutisteps Injection speed ∓ pressure control on machine are helpful.
  • Understanding of cavity pressure profile and pvT diagram is most essential.
  • Understanding of injection speed and pressure during filling phase ∓ pressure phase is very important.
  • Cooling time allows melt to freeze and retain the shape of space between core and cavity.

Well designed cooling system in mould ensures.

  • Uniform mould surface temperature which is very essential for avoiding warpage and dimensional accuracy. This can be achieved by balancing of heat in ∓ out of the mould.
  • Turbulent water flow through cooling channel is desired for efficient heat exchange in the mould.
  • Understanding heat exchange in mould is essential.
  • Ejection of solidified part after the mould is opened sufficiently
  • Understanding of various ejection mechanisms in mould is required.

To know all about injection moulding of plastics, you must refer "A Guide to Injection Moulding of Plastics" by Prabodh C. Bolur.

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