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December 21, 2022
6 min read time

Plastic Injection Molding 101: From Design to Production

A woman working using plastic injection molding manufacturing.



Mass Production for High-Performance, Complex Parts

Injection molding is a common plastics manufacturing process with various applications across the medical, consumer goods, electronics, automotive, energy, and food and beverage industries. It's so common that the global market size came in well over $280 billion in 2021, with significant growth predicted through 2030.

Despite the ubiquity of injection-molded thermoplastics, most people are unaware of how much we depend on these products, nor do they consider the manufacturing method. That's where we come in. Let's take a closer look at plastic injection molding.


What is injection molding?

Injection molding is almost precisely what it sounds like: the manufacturing process of injecting molten material — in our case, thermoplastics — into a mold, then cooling and solidifying it to produce a part.

Although it seems simple, it's an exacting, complex process well suited to manufacturing unusual shapes and large volumes of components. It's efficient, repeatable, and cost-effective without sacrificing quality
Chances are you've encountered an injection molded component today, whether you know it or not. Injection molding technology produces:

  • Lifesaving medical devices
  • Automotive components
  • Oil and gas complex products
  • Electronic component productive covers and housings
  • Consumer products
  • Countless other items

Parts produced with injection molding are light, durable, and resistant to extreme temperatures, depending on the type of resin used


What is the plastic injection molding process?

1. Designing and Prototyping

Before molten plastic becomes a component, there must be a design. The DFM (design for manufacturability) process starts with blueprints, specs, and CAD files that are revised, tested, and refined until they are ready for production. The appropriate type of thermoplastic is chosen at this stage to ensure that the final component has the right properties.

2. Tooling

Once the prototype is approved, the final mold is created for mass production. Each mold tool consists of a cavity (the fixed part that the plastic is injected into) and a core (a moving part that fits into the cavity to help form the component's final shape). Manufacturers like HPP custom build each mold in-house for maximum efficiency, quality, and cost savings.

3. Feeding and Melting

Raw pellets of the chosen engineering-grade thermoplastic are fed into the hopper of an injection molding machine. A long, cylindrical heated barrel with an injection screw sits next to the hopper. A gate sits at the end of the barrel, and the mold tool is connected to the gate. Turning the screw and the heat from the barrel, gradually warm and melt the thermoplastic until it is molten and ready to inject.

4. Injection

When the molten plastic reaches the end of the barrel, the gate closes, and the injection screw moves back, drawing through a set amount of plastic. As the pressure in the screw builds up, the two parts of the mold tool close together. The clamp pressure from the mold and the injection pressure must be balanced to ensure that the part forms correctly. When the proper pressure is reached, the gate opens, the screw moves forward, and the molten plastic is injected into the mold.

5. Holding and Cooling

After injection, the plastic is held under pressure in the mold for a set period. The holding period allows the plastic to pack out the mold fully, ensuring the part is formed correctly. After holding, the injection screw draws back, the pressure is released, and the part is allowed to cool in the mold. Cooling can take anywhere from seconds to a few minutes. 

6. Finishing

After cooling, the plastic injection molding machine will eject the part. Any finishing needed, such as polishing, dying, or removing excess plastic, is completed.


Custom Plastic Injection Molding

Because plastic injection molding is so versatile, it lends itself to customization. Every part of the process can be tailored to fit your unique needs, from material selection to component color and custom mold design. There's no reason to rely on off-the-shelf solutions regarding injection molding. 

  We specialize in customized plastic injection molding solutions for more than 15 industries. Our rapid prototyping process, in-house fabrication and tool maintenance capabilities, and dedication to finding the best solution for your injection molding need to ensure that you'll come out on top.   
  Show us where your finish line is, as we'll build a custom injection molding solution to get you there on time and within budget. Request a quote today!  


Start molding your vision today