What You need to Know about the Injection Molding Process ?

Manufacturers have been producing plastic parts for many years. Over time, they have gained expertise, allowing them to improve the speed and quality of the plastic parts manufacturing process. Most plastic parts are produced using a process called injection molding. This involves injecting molten plastic into an open space of a mold.

Basic Injection Molding Process

There are four steps that make up the injection molding process:

  1. Melting the pellets through a combination of heat and pressure.
  2. Injecting the melted plastic into the mold, this is where the part takes shape.
  3. Letting the molded part cool.
  4. Ejecting the finished part out of the mold.

 Features of a Mold

Molds are made out of metal plates and pieces. They consist of a few important components:

  • Core: The interior, non-cosmetic side of the part.
  • Cavity: The empty space inside of the mold that houses the molten plastic.
  • Runner System: This comprises a series of channels within the mold.
  • Gate: An opening at the top of the mold. The molten plastic is poured into the mold from the gate.

The runner system is an important part of the mold, as it maintains a smooth flow of material while ensuring the cavity gets filled correctly. It regulates the speed as well as pressure of the molten plastic. The gate connects the runners to the cavity. This allows the plastic to flow to all parts of the mold cavity.

There are a few characteristics to consider when looking at a well-designed injection-molded plastic part, these four details occur by design not coincidence. Most, if not all, of the main walls have consistent thickness. The faces of the part are angled around the main shape. Many of the part’s corners are rounded. The part has a thin line around it.

Common Features of Injection Molded Plastic Parts

Although every plastic component will have different features, there are two common aspects in every part:

  • Ribs: Ribs are the internal walls of a part. They help make the molding process easier, as well as support the part in its operation. When designing the ribs, it is important to consider the thickness and draft angle. A rib thickness of 40-60 percent thickness is recommended, as it help the ribs to cool faster after the injection molding process has been completed. The draft angle needs to be checked so that it doesn’t cause the rib to taper to a sharp edge.
  • Boss: Another common internal feature is a boss. A boss is a raised portion of the component. Bosses perform several functions such as supporting other parts, or providing a place for screws. Ribs can be added to bosses for support.


Choosing the texture for a part depends on the application. A coarse texture can hide imperfections, but a polished finish may be desirable. Also, different textures can be combined on a single part.

Text can be added to parts during the injection molding process. The text size needs to be large enough for the resin to fill the mold and it needs to be legible.

There are also finishing touches that can be added to injection-molded parts. Color is a common finishing touch that can be added with paint after the part has been removed from the mold, or by adding a colorant to the resin before it’s injected into the mold.

Knowledge of the components and the injection molding process can help customers make wiser decisions before ordering the manufacture of custom injection molded parts.