How Injection Molding Works

Process: Start to Finish

A green wintec Injection molding machine

A plastic filling granulate mixture (plastic pellets, colorant, or recycled material) is fed into the hopper. The hopper is a tank that supplies the injection molding machine with the pellets, while also ensuring plastic material is moisture-free.

Next, the pellets flow from the hopper to the barrel, where the heating elements and the reciprocating screw are found. The pellets are caught within the flights of the screw and are pushed forward as the screw rotates. The screw also pushes the pellets along the sides of the barrel, which creates the friction needed to melt the plastic. Additional heat is supplied by the heater bands.

The molten mixture is then pushed to the front of the screw through flutes, which are indentations on the screw tip. The front of the screw also acts as a plunger. When there is enough plastic in front of the screw, the screw pushes forward forcing the molten material into the molds. The molten plastic cannot flow backward through the flutes, as a check ring acts as a one-way valve.

The molten material then fills the mold, forcing air out. The air escapes through tiny vents that are too small for the plastic to escape.

The plastic material cools (with help of coolant or water) and the mold is opened. Ejector pins then push the plastic unit out of the mold.

Any excessive plastic is then ground down to complete a fully closed-loop solution to minimize waste. This computer-controlled system automatically repeats to produce large unit quantities at high speeds and accuracy.

Pros vs. Cons


  1. Injection molding has relatively low unit costs. Due to the speed and efficiency of injection molding, labour costs, material costs, and logistic costs can be reduced.
  2. Injection molding can produce detailed parts. The high-pressure system can force the molten plastic into every crevice. Small details, logos, print, or designs can all be produced with ease.
  3. Injection molding is consistent and high quality. Because of the high level of detail, molded parts will look identical giving a more professional feel to consumer products. 
  4. Injection molding is expandable. Since this system has been used for decades, there is no shortage of global injection molders. Therefore, you can save on freight costs or expand your geographical customer base if you produce units near the end-users.


  • Molds can be costly to produce. These molds are usually made overseas, can take weeks to build, and cost hundreds of thousands of dollars. 
  • Once a mold is made, it is hard to modify. Molds are made out of either steel or aluminum. If the product size needs to be increased, the mold may be able to be modified by removing some material. However, if there is a fundamental design change or the product is reduced in size, an entirely new mold is usually needed to be built.
  • Designing a product can be labour and time intensive. Because designing the mold correctly is so important, perfecting the product design is crucial. It would not be cost-effective to take multiple prototypes to market in order to do consumer research. All consumer research, designs, material, and engineering considerations should be done beforehand.

Plascon Plastics has the expertise to help you minimize these downsides.


Plascon Plastics are pioneers in the sustainability aspect of injection molding. We invest in research to increase the efficiency of recycling plants while building technologies to improve current injection molding techniques. We also work with PCR such as ocean plastic and recycled consumer waste.

Plascon Plastics holds multiple patents to injection mold with waste stream materials, such as car tires. Car tire recycling is often done with compression molding; an expensive and labour investive process. However, using our technology, car tires can be injection molded into countless different products.