Plastic Injection Molding

Plastic injection molding is the process of creating different parts from thermoplastic or thermo-set plastic materials, for a particular product by using a custom designed mold. These machines are designed with custom plastic molding to serve various industries.

Plastic injection molding materials:

The commonly used materials are acetal, acrylic, cellulose acetate, polyamide, polyester thermoplastic, polycarbonate, polyether sulphone, polyethermide, high and low density polythene, polyphenylene oxide, polyphenylene sulphide, polypropylene, high impact polystyrene, rigid and plasticised polyvinyl chloride and thermoplastic rubber.

Plastic Injection Molding Machine Overview:

The plastic injection molding machinery consists of three parts- the injection unit, the mold assembly and the mold assembly.

  • Injection unit: It contains a hopper, into which the plastic granules are poured. This hopper is connected to a barrel, which contains the reciprocating screw. This screw is powered by a hydraulic motor. The length of the screw of a plastic injection molding is divided into feeding, transition and metering zone, depending on its depth, which decreases as it reaches the nozzle. This unit’s work is to heat and inject the raw material into the mold.
  • Mold assembly: The nozzle will inject the heated plastic granules into the mold cavity attached to the stationary platen. It will continuously fill the mold until the material is tightly packed, after which it retracts to carry out the process again.
  • Clamping unit: This unit contains a movable platen, which slides along the tie bars. This movable platen is attached with the mold core. The plastic injection molding unit works by clamping the movable platen against the stationary platen, until the nozzle finishes injection of raw material, with the use if hydraulic motor.
  • Ejection Bars: These are connected to the mold core through the ejection plate. These bars will slide out the molded part after solidification.


Plastic Injection Molding process:

1) The first step of the injection molding process is to securely clamp the front and rear half of the mold.

2) Then, the plastic granules are poured into the hopper, which leads them into the barrel.

3) As the plastic granules are pushed towards the mold assembly, they are heated and inserted into the mold for plastic injection molding.

4) Once the mold is filled with the melted plastic, the walls will help bring down the temperature of the hot plastic.

5) After it is cooled, the ejection system will remove the solidified mold.

6) To remove the mold effectively, a mold release spray product can be used on the walls of the mold assembly.

7) If the molded material includes any extra material, which is attached to it, this has to be scraped off to give a smooth appearance to the final product.

Plastic injection molding pros and cons:

  • Pros: This custom plastic injection molding process will increase the production output while decreasing the cost of labor. Its results produce a smooth finish product with minimal or no requirement for manual finish work. It other benefit is that the scrap can be recycled.
  • Cons:It has a long lead time and the equipment is expensive.