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What is Injection Molding:

Injection Molding 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.

Why Use 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. Other advantages include the following:

Injection Molding produces low scrap rates relative to traditional manufacturing processes like CNC rubber machining which cut away substantial percentages of an original plastic block or sheet. This however can be a negative relative to additive manufacturing processes like 3D printing that have even lower scrap rates.

Note: waste plastic from injection molding manufacturing typically comes consistently from four areas:

The sprue

The runners

The gate locations

Any overflow material that leaks out of the part cavity itself (a condition called “flash”).

A sprue is simply the channel that guides molten plastic from the nozzle of the injection molding machine to the entry point for the entire rubber injection machine tool. It is a separate part from the mold tool itself.

A runner is a system of channels that meet up with the sprue, typically within or as part of the mold tool, that guides the molten plastic into the part cavities within the mold tool. There are two principal categories of runners (hot and cold) which you can read about here.

Lastly, the gate is the part of the channel after the runner that leads directly into the part cavity. After an injection mold cycle (typically only seconds long) the entirety of the molten plastic will cool leaving solid plastic in the sprue, runners, gates, part cavities themselves, as well as a little bit of overflow potentially on the edges of the parts (if the seal isn’t 100% right).

Thermoset material, such as an epoxy resin that cures once exposed to air, is a material that cures and would burn after curing if one attempt is made to melt it. Thermoplastic material by contrast, is a plastic material that can be melted, cool and solidify, and then be melted again without burning.