Before You Start: Plastic Injection Molding Terms to Know

If you’re looking to partner with an injection mold maker or an injection molding parts prototype designer, having common ground in terminology can go a long way toward both your understanding of the process and your ability to communicate it to your manufacturer. Below, we list out common plastic injection molding terms to know, categorized by their step in the injection molding design and manufacturing process.

Injection Molding Materials Terms

At the core of the plastic injection molding process is the material that is refined into the final parts: plastic. However, it can go by many names. Resin, polymer, and plastic are the most common terms in the industry. As we explain in our blog, Resin, Polymer, and Plastic: What Difference Do These Terms Have?, all can be used interchangeably, but may also refer to a specific step in the process, with resins referring to raw, naturally occurring plastics, while polymers may refer to artificially produced stock.

Types of Plastics: Thermoset vs. Thermoplastics

The types of plastics used in injection molding fall into two broad categories: thermosets and thermoplastics. Thermoset plastics can only be heated once. After they cool, they cannot melt again. Thermoplastic resins can be melted again. Not only are they recyclable, but they are often cheaper to use, as discarded material from the process can be fed back into the stock. Learn more in our blog, Injection Molding Plastic: Thermoplastic vs. Thermoset.

Picking the right plastic for your product is important, so make sure to read up on the various kinds.

Injection Molding Design Terms

Mold design is important, and understanding it can help you and your manufacturer not only produce a better mold but also better parts through prototyping.

• Mold or Tool: These terms are interchangeable for the mechanism through which the plastic is injected to produce parts. The mold is designed to both produce specific parts and cool them effectively for an efficient manufacturing process.
• Cavity & Core: A mold has two parts. The “A” side is the cavity, and the “B” side is the core. Of the two, the core is the primary working part, including the mechanisms for ejecting parts.
• Runners & Gates: Plastic is injected into the mold, where it runs down runners (which may be heated) into gates. Gates feed plastic into the mold cavity.

Injection Molding Process Terms

The entire process includes three elements: the machine that holds the mold and heats the resin, the mold through which the plastic flows, and the molten plastic itself.

• Injection Molding Process: In short cycles, plastic pellets are melted, injected into the closed mold, cooled, and then ejected, before starting over. Deep dive here.
• Melt & Flow: Melt is the process by which the plastic becomes molten, while flow is the flow of that heated plastic through the mold.
• Clamping Force: The force applied to the mold by the clamping mechanism to keep it closed, opposing the pressure exerted by the melt as it’s injected into the mold.

Interested in learning more injection molding terminology? Check out our blog here: 15 Plastic Injection Molding Top Key Terms.

Understanding plastic injection molding terms will promote better communication between the manufacturer and the client. At Midstate Molding & Engineering, our team of experienced industry professionals has combined over 180 years of experience in mold making, part prototyping, and injection molding parts manufacturing. Contact us today to discuss your next project or dive right in to get a quote.