Injection Molding Machines

Plastic injection molding machines are designed to create plastic pieces by injecting molten plastic into a mold. As the plastic cools in the mold in the plastic injection molding machine, the plastic takes on the shape of the mold. The mold is split open once the plastic has sufficiently cooled to remove the formed plastic product.

Injection molding machines will use the shear of a screw against plastic pellets inside a heated barrel to melt the plastic. The molten plastic is then injected into the mold to fill in the cavity of the mold in the injection molding machine. Depending on the size and shape of the mold, molten plastic will be injected by one or more ports into the mold. Because of the latent heat of the plastic, the molds, which are usually made of metal, tend to maintain the heat. To accelerate the plastic cooling process, molds for injection molding machines are often designed with pipes for cooling water within the mold. By piping cold water through an injection molding plastic mold, the mold temperature can be reduced and the amount of time necessary for the plastic to cool and solidify is also reduced.

Because the molten plastic is pushed into the plastic injection mold under pressure, there is the possibility of injection too much plastic or not enough plastic. Injecting too much plastic into the injection mold will result in plastic squeezing into the seam of the mold. This type of defect is known as flash. Not injecting enough plastic into an injection mold results in the mold not being completely filled and a product that is missing some of its shape. This type of product is called a “short shot”.

Injection molding machines can come in all shapes and sizes and can be used for an incredibly varied number of applications. Injection molding machines can be used to make plastic caps on containers to running boards on heavy duty pick-up trucks, and anything in between.