Injection Molding Materials

There are two types of materials (resins) which can be used in the injection molding industry; Thermoplastic and Thermoset.

A thermoplastic, or thermosoftening plastic, is a plastic material, a polymer, that becomes pliable or moldable above a specific temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight.[1]

thermoset also called a thermosetting plastic, is a plastic that is irreversibly cured of a soft solid or viscous liquid, prepolymer or resin.[1]


Figure source:

Resin selection is a very critical step for the injection molding. There are many material suppliers offering quality materials for the injection molding.

They can formulate a plastic to meet the consumer needs properly. For example, the applications of the product play a key role in the choosing material properties. For High voltage connector, the resin has to provide chemical resistance, excellent tracking defense and heat& humidity resilience. For a Fluid Engineering Components, the resin has to have a good hydrolytic stability, excellent resistance to water and FDA approved. The formulated resin has the processability and consistent properties after molding process and in the final use.



Reference :


Molding Machine & Process

Parts of a Typical Molding Machine:



Hydraulic injection cylinder
Screwdriver motor
Control panel
Clamp mechanism

Molding Process :

  1. The plastic raw material is stored in the hopper.
  2.  The plastic falls on the rotating screw.
  3. It is conveyed forward by the flights of the screw and is gradually melted as it moves forward.
  4. When enough melted plastic has accumulated ahead of the screw, the screw stops rotating.
  5. The screw, acting as a plunger, pushes the melted plastic out of the injection barrel.
  6. The plastic goes through the nozzle, sprue, runner, gates, and on into the mold cavities.
  7. Packing occurred- a little more plastic is forced in after the cavities are full.
  8. packing continued until the gate freeze.
  9. when the plastic in the gate freezes, the pressure on the screw is released. The screw rotates back to melt and convey the next shot of plastic ahead of the screw.
  10. when the parts are cool enough to hold their shape, the mold opens, the parts are ejected, and the cycle is repeated.