A Simple Guide on Plastic Injection Molding

Globally, the demand for plastic injection molded parts is estimated to be $325 billion, with a consistent annual growth projection of 5.7% as we reach 2025. This growth is primarily attributed to the fast-growing Asian economies leveraging on process efficiencies and new resin chemistry.

However, plastic manufacturing is also flourishing in the U.S. This industry alone provides close to one million jobs. In fact, plastic plays a vital role in manufacturing many household objects that are used on a daily basis. For such industries to be able to produce goods at a rate to meet demand, components must be manufactured efficiently.

Plastic injection molding is a manufacturing process used to fabricate plastic parts in large volumes. By using hot runner systems, plastic manufacturers can produce millions of components that are identical in shape and size in only a short time.

How Does the Plastic Injection Molding Process Work?

The injection molding process requires the use of hot runner systems, raw plastic material, and a mold. First, an industrial designer or engineer designs the product to be produced. The design is then passed on to a mold maker to create a mold that is usually made of steel or aluminum.

To ensure the manufactured component can perform its function well, the mold maker accounts for the following essential conditions.

  1. The features of the product
  2. How the material will be used
  3. Properties of the hot runner systems available for use

Once the design and mold have been optimized, the manufacturing process begins. The raw plastic is melted in the molding machine and then injected into the mold under high pressure using a hot runner nozzle.

In the mold, the molten plastic cools and solidifies, after which it is released by opening the two halves of the mold. With plastic injection molding, manufacturers can produce products with a predetermined and fixed form. As such, with the perfect mold, they are assured of consistent quality products.

Here are some of the benefits of plastic injection molding:

Low Scrap Rates

When using traditional plastic manufacturing techniques, a significant portion of the plastic block or sheet is wasted. However, with injection molding, there is minimal wastage of raw plastic. The little waste that does occur typically comes from the hot sprue bushings, runners, and valve gate systems.


Injection molding offers high degrees of accuracy when fabricating plastic components. Though there may be some design restrictions, the mold allows the accuracy of finished components to be within 0.005 inches of each other.

As a result, components are practically identical. This ensures that components can help with brand consistency and guarantee quality consistency, even with high volume production.


Once the design and mold have been prepared, producing components using injection molding is relatively fast. This is why this technique is arguably the most reliable when it comes to long manufacturing runs.

Production speeds depend on the specific component and the complexity of its design. However, it usually only takes 15-30 seconds to pass between cycle times.

Cheap cost

After the initial costs of designing and producing the mold, injection molding costs are meager. Since the technique is suitable for mass production, the costs can be reduced even further with long manufacturing runs.

Also, injection molding machines use a self-gating automatic tool. This streamlines operations and ensures production can continue with minimal supervision. As such, manufacturers can save on labor costs.

Better for the Environment

In addition to the efficiency and cost benefits, plastic injection molding is also better for the environment. This is because there is little waste because only as much plastic as is needed is used during manufacturing. Also, excess plastic can be ground up and recycled after use.


When it comes to the manufacturing sector, the speed and cost of production significantly affect a company’s profitability. By shifting to plastic injection molding to produce components, manufacturers will serve a larger market at a lower cost, thus sparking business growth.