Key Components of an Injection Molding Press

Key Components of an Injection Molding Press

Injection molding is much, much more than just pouring liquid into a mold and letting it cool. It's a complex set of processes and temperatures that must be engineered with precision from start to finish. We like for our customers to know what we're up to, so we've put together a high-level overview of how the process works. 

Get to the hopper!

Every cycle starts with resin, or raw plastic. Raw plastic comes to us in granular form, so we stock pellets of all different materials, colors, and types. The pellets we've chosen for a particular job are fed by computer to an injection molding press, where they come to rest in a dedicated hopper. Acting as a reservoir for that machine, the hopper holds the pellets en masse and feeds them to the machine as required.

Leaving the hopper, the plastic resin next travels to the injection unit itself, where it encounters a barrel and a large internal screw. The screw rotates, or augurs, the material into the barrel while being heated from the outside. Our computers ensure that the material reaches the injection unit at a specified temperature and consistency. Each type of end product and material comes with its own required set of properties to be properly molded.

Injection junction

Once the plastic is loaded and melted in the injection unit, it gets injected. The screw pushes forward in the barrel, forcing the molten plastic inside through a nozzle at the end. This nozzle mates with a sprue hole in the mold that will create the final product.

The mold is what finally forms the molten plastic into a part. Molds typically consist of 2 mating sides; once these sides are pushed together, they create the necessary cavity that creates the three-dimensional part. Injected plastic travels through the sprue hole and other channels into the cavity. Once the mold is full of molten plastic, the part begins to cool, eventually solidifying and splitting the mold apart. When it completely opens, internal pins in the mold with push the completed plastic part out. As the completed part is fully ejected, the mold clamps back together and the cycle begins again.