A Guide to Plastic Injection Molding

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The use of plastic injection molding in manufacturing industries is getting popular with every passing day. It is a manufacturing technique for producing complex parts. This is a guide about plastic injection molding.

How Plastic Injection Molding Works

Plastic injection molding involves the forcing of thermoplastic polymer pellets into a preheated mold. As the forced polymer cools down, it takes the shape of the mold it’s forced in.

The machine that carries thermoplastic pellets and transforms them into a liquid state is called an extruder. An extruder uses a rotating screw to push thermoplastic pellets inside a heated barrel at high speed. The heat then transforms solid thermoplastic pellets into a liquefied state.

The help of a chute then forces liquified thermoplastic pallets into an injection unit.  The injection unit then transfers the liquid plastic through its nozles into a molds cavity using the same rotating screw method. Once the mold is filled with liquid plastic, it’s left to cool down. After cooling down to a sufficient temperature,  the liquid plastic inside the mold transforms to its solid-state again while taking the shape of the mold.

It’s crucial to understand both the processes that happen simultaneously during plastic injection molding: melting the thermoplastic polymers and injection molding. To make the process simpler, we have broken down the entire process into four comprehendible steps.

Plastic granulation

This is the process where thermoplastic polymer pellets are heated to be transformed into a liquid state. The melted pellets form a stream of molten plastic.


Once melted, the thermoplastic polymer is cooled down enough to retain its shape in a molten state. The cooling of the melted thermoplastic polymers is done by making them pass through a series of inline heaters. These heaters maintain the temperature that hardens the plastic to the desired state.

Managing the Temperature

After cooling down the molten plastic, an associated heating plant is used to regulate the temperature of the molten plastic according to the need.


Only after the completion of all these stages, the injection process should begin. During the injection molding process, the pressure, speed, and flow of each material that is to be injected into the mold cavity is closely monitored and controlled.

3D printed models next to a 3D printer and laptop

For those looking for an engineering design services company, check out Connekt, LLC. They have years of experience providing 3D printing, injection molding, rapid prototyping services, and much more. Their team has skilled designers, technicians, and engineers on board to help your business grow. Reach out to them for a quote.

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