Understanding the Basics of Injection Molding

“There are injection molding parts everywhere,” says Kyra Stawson. The technical sales engineer at Xometry, the world’s largest digital manufacturing marketplace, goes on to explains that injection molding parts can be found in “anything that you can see around your house, from consumables, and medical, to aerospace and defense.” (See more injection molded products here.)

Injection molding is a manufacturing process in which molten plastic is injected into a mold tool and then ejected as a solidified part. Although it might seem like the latest buzz phrase in manufacturing, it’s actually been around for more than a century. Brothers Isaiah and John Hyatt invented the first molding machines in 1872 to create hair combs, buttons, and other small products.

“It’s the most commonly used plastics processing method for high volume of parts,” Stawson says.

Today, you can upload a 3D CAD file to Xometry’s website to get a quote in just a few seconds. The global company, headquartered in Gaithersburg, Maryland, provides 24-hour responses on quotes with design-for-manufacturing (DFM) feedback. Lead times for Xometry’s injection molding parts start at 10 business days.

The available injection molding machines include single, multi-cavity, and family molds. Aluminum and steel mold types are available. The mold cavity tolerances are +/- 0.005” when the mold is being machined. When calculating for the shrink rate, there’s a further +/- 0.002.” That said, for critical features, Xometry can machine to a steel-safe condition if an even tighter tolerance is needed.

Production grades are usually Class 102-104, with Class 101 used for an extremely high production mold and Class 105 for a simple prototype. For more information on Xometry’s injection molding mold classes, see the handy chart on their website here. There, you can also find a list of their plastic injection molding materials, which includes rigid and flexible resins, elastomers and synthetic rubbers for molding, and custom sourced materials. You can also find a guide to Xometry’s wide variety of injection mold finishes.

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