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A Brief Introduction to Plastic Injection Molding

[fa icon="calendar"] Feb 3, 2016 2:11:00 PM / by Jon Gelston

"Plastic Injection Molding: A Brief Introduction" thumbtack, clear

You’ve been asked to source small plastic parts for your company’s product (we define “small” as the size of your fingernail to the size of your hand), but are unfamiliar with the plastic injection molding process. Here’s a quick overview to give you a baseline understanding. And, of course, we’re always happy to answer your questions on the phone or via email.

What is Plastic Injection Molding? 

Plastic injection molding is the process of heating raw material (plastic resin in pellet form, in our case) to its melting point, forcing the viscous material into a mold, and allowing it to cool into a hardened shape. Injection molded parts are used in virtually every product you encounter, from electronics to housewares to automotive to food packaging. At the highest level, it’s a very simple process, but there’s a very complex science that goes into doing it well—from creating the molds to understanding the chemical and physical properties of the materials. 

Plastic injection molding owes its existence to pressure die casting processes used for metals in the late 1800s. Plastics were introduced in the 1920s, although the process was still very crude at that time, with simple two-piece molds being manually clamped together. The art and science of plastic injection molding has come a long way since then.


Eight Steps to Perfect Parts

The plastic injection molding process can be summarized into eight steps:

  1. The part is designed, and prototypes are created and tested.
  2. A durable steel or aluminum mold (or tool) is designed and built. This process takes several weeks and includes a lot of complicated systems to control the process.
  3. In production, raw material is loaded into a “feed hopper.”
  4. The material is fed into a heated “barrel” where it becomes viscous—a state somewhere between solid and liquid.
  5. The viscous material is forced by a plunger into a mold, which is held shut by hydraulics to withstand the pressure of the incoming material.
  6. The material cools quickly in the mold and is ejected as a finished part after a predetermined time.
  7. Quality assurance checks are performed on the part.
  8. Meanwhile, the mold is closed again in preparation for the next processing cycle. 

Everything from colors and textures, to lettering, logos, and designs, to hinges and other functionality can be incorporated into the creation of a plastic part.


The Many Benefits of Plastic Injection Molding 

There are a host of benefits that come from producing parts through plastic injection molding. They include:

  • Infinite variety. Virtually any shape you can think of can be manufactured as a plastic part.
  • Intricate details. The force with which plastic is injected into a mold ensures that even the tiniest spaces are properly filled.
  • Low per-piece cost. While there are upfront costs for creating the mold, highly automated production processes result in a very low cost per part.
  • High output. Parts can be produced very quickly.
  • More cost-effective than machining. While the upfront cost of machining may, in some cases, be lower, in the long run, plastic injection molding is much more cost-effective.
  • Resource-conscious process. The injection process uses only as much material as needed for each part, and any material left at the end of a process can be ground up and recycled.


Questions? We’ve Got Answers.

To sum it up… Plastic injection molding is a fast, efficient, cost-effective way to create any type of part you can imagine. If you have questions about a project you are considering, don’t hesitate to contact us. We’re happy to share our expertise from more than two decades in this industry.

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Topics: Plastic Injection Molding

Jon Gelston

Written by Jon Gelston