Injection Molding

Injection molding is the process of choice for companies looking to produce repeatable parts with strict mechanical requirements. It is a manufacturing process for producing parts in large volume. It is most typically used in mass-production processes where the same part is being created thousands or even millions of times in succession. Injection molding is a popular manufacturing option for high-production runs, not only because of the consistent quality of the manufactured plastic parts, but also because the price-per-part decreases with higher quantity manufacturing runs. Additionally, Expedited offers injection molding production runs as small as 100 parts.

An injection mold consists of two halves that are forced together to form a cavity in the shape of the part to be produced. Hot, liquid plastic is then injected at high pressure into this cavity.The high pressure is needed to ensure that the plastic resin fills in every crook and cranny of the mold cavity. Once the plastic has had time to cool, the two halves of the mold are pulled apart, and the part is ejected. Although designing for injection molding can be quite complicated, and the cost of the molds themselves are incredibly expensive, there is one huge reason why injection molding is still used today. No technology can beat injection molding when it comes to producing millions of identical copies of a part at an incredibly low price.

Materials used in injection molding

Selection of the material used for your project depends on the application. The materials used when creating parts and products with injection molding vary in mechanical, thermal, chemical, electrical, and optical properties.

Most Common Materials Acrylonitrile Butadiene Styrene (ABS)
Polyethylene (PE)
Polypropylene (PP)
Polycarbonate (PC)
Other Supported Materials Nylon (PA 6)
Polycarbonate /Acrylonitrile Butadiene Styrene (PC/ABS)
Polyurethane (PU)
Polymethyl Methacrylate (PMMA/Acrylic)
High Density Polyethylene (HDPE)
Low Density Polyethylene (LDPE)
Polystyrene (PS)
Polyvinyl chloride (PVC)

Why Injection Molding:

The principal advantage of injection molding is the ability to scale production en masse. Once the initial costs have been paid the price per unit during injection molded manufacturing is extremely low. The price also tends to drop drastically as more parts are produced. Before you endeavor to produce a part via injection molding consider a few of the following things:

Financial Considerations

Entry Cost

Preparing a product for injection molded manufacturing requires a large initial investment. Make sure you understand this crucial point up front

Production Quantity

Determine the number of parts produced at which injection molding becomes the most cost effective method of manufacturing, and you expect to break even on your investment (consider the costs of design, testing, production, assembly, marketing, and distribution as well as the expected price point for sales). Build in a conservative margin.

Design Considerations

Part Design

You want to design the part from day one with injection molding in mind. Simplifying geometry and minimizing the number of parts early on will pay dividends down the road.

Tool Design

Make sure to design the mold tool to prevent defects during production. Consider gate locations and run simulations using mold flow software like Solid works Plastics.

Production Considerations

Cycle Time

Minimize cycle time in as much as it is possible. Using machines with hot runner technology will help as will well-thought-out tooling. Small changes can make a big difference and cutting a few seconds from your cycle time can translate into big savings when you’re producing millions of parts.


Design your part to minimize assembly.To the extent that you can design assembly out of the process you will save significant money on the cost of labor.