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How to Run a Plastic Injection Molding Machine

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Injection molding is one of the most common manufacturing processes in the world of industry. The process, which is done by injecting a material (typically plastic) into a mold, is used in everything from engineering to the fabrication of jewelry. Injection molding is in theory a simple process, which allows for simple or intricate parts to be manufactured. Although every machine is different, the general method is the same. However, failures can result due to operator error.

Set the mold onto the injection molder. Align the injection nozzle on the machine with the channel on the mold through which the molten plastic flows.

Place the injection material into the injection machine and turn on the heaters to melt the material. The heaters will melt the plastic and will also heat the mold so that the injection material flows completely through it without solidifying.

Shut any safety guards on the machine to protect yourself from splattering material.

Set the clamp pressure on the injection molding machine. The clamp pressure should have been determined during the design process of the mold.

Clamp the mold using the hydraulics on the injection molding machine. This will ensure that material does not leak out of the mold.

Set the injection pressure on the injection molding machine. This should also have been determined during the design process of the part and the mold.

Press the injection button to fire the material into the mold.

Remove the mold from the injection machine and remove the part after the mold is cool enough to handle. Keep the heaters on so you don't have to wait.

Put the mold back into the injection molder and repeat the process.


Try injecting different plastics to obtain different strength products and different surface finishes. Work with a university or a company to save money. Injection molding equipment can be expensive.


Injection molding material can splatter. Always wear work clothes and other safety attire.


James Mulroy started writing in 2010. He writes for PCWorld Geek Tech and the Bugs and Fixes column for the "PCWorld" print magazine. He had two research fellowships and a student research position at the University of Alabama in Huntsville. He will continue a bachelor's degree in aerospace engineering in Fall 2011 and is currently researching composite materials.

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