Do you want to learn more about injection molding? Before we look at important injection molding terms you need to remember, you must understand how the process works. Otherwise, knowing a few disparate terms won’t help much!

Injection molding starts with solid plastic, usually in pellets or granules. These pellets go into the injection molding machine (IMM) and are heated until they become liquid. The machine’s nozzle then injects the liquid plastic into a mold, which is like a cast of your product. When the plastic inside the mold cavity cools down, it hardens to become a solid, final product.

A-Side and B-Side

The molds that IMMs fill with plastic typically come in halves. The molds come together with a great deal of force to ensure that no plastic leaks out of them. These halves are referred to as the “a-side” and the “b-side.” The a-side contains gates, which are areas that the IMM can inject plastic through.

The b-side, however, has a different function. Since plastic shrinks slightly during the cooling process, it sticks to whichever side has the more convex surface area. While the a-side has gates, the b-side has ejector pins.

Ejector Pins

Ejector pins push the plastic off the mold to unstick it. That means you need to design your mold to ensure that the plastic will stick to the b-side—otherwise, your product will stick to the a-side and won’t have a way to become unstuck from the mold!

Knit Lines

Dealing with two halves means that there is a small seam where the different sides meet. These seams are known as “knit lines.” Depending on the material you use, the knit lines could be invisible or obvious—work with an injection molding company to figure out how to reduce the mold lines on your product.

If you need injection molding expertise, we’re here to help. With plastic finishing plugs and end caps, we can help you keep your products protected while giving them a clean, finished look.

Now that you know these important injection molding terms that you should remember, reach out to Polymer Molding, Inc. for all your plug and end cap needs!