What You Should Know About Plastic Molding

Plastic molding is a manufacturing and fabrication technique that produces parts by injecting liquid material into a mold. It is most commonly performed with thermoplastic polymers, but it can also be performed with metals and glass. 

The process involves melting small pellets of material and forcing the molten liquid through a nozzle into a mold whose internal cavity is the negative of whatever part is being created. Ejector pins remove the molten parts from the mold after they have cooled.

How does plastic molding work?

Plastic injection molding is a four-stroke process. The mold cavity is first filled with molten material, which is then rapidly cooled, causing it to harden (turn solid). The mold cavity then opens, exposing the part to air and providing a place for it to fall when it is finally ejected by pins.

After an engineer has designed a part, a toolmaker will create a metal mold, normally out of either steel or aluminum. A single cavity or multiple cavities precision-machined to produce a particular part can be used in the mold.

Plastic injection molding can also be done with a variety of polymers, including thermoplastics, thermosets, and elastomers. The selected material’s pellets or granules are heated in the barrel of an injection molding machine until the mixture is pliable enough to be injected into the mold. While the mold’s two halves are tightly clamped together, a ram- or screw-type plunger forces the correct volume or “shot” of material to fill the cavities under pressure.

The material cools and hardens into the form of the part before being removed from the opened mold to restart the process.

How to know if plastic molding fits your needs?

Calculate the number of parts produced at which injection molding becomes the most cost-effective manufacturing method.

Following that, you’ll need to determine the number of parts produced at which you expect to recoup your investment (consider the costs of design, testing, production, assembly, marketing, and distribution as well as the expected price point for sales). Make a conservative profit margin.

Don’t forget about entry fees. Preparing a product for injection molding requires a significant initial investment. Make sure you understand this critical point right away.

What are the vital points of the molding process?

The cycle time is critical in this case. Reduce the cycle time as much as possible. Using machines with hot runner technology, as well as well-thought-out tooling, will help. Simple changes can cause a big difference, and shaving a few seconds off your cycle time can add up to significant savings when producing millions of parts.

The assembly process is linked to production. You should design your part to require as little assembly as possible. The expense of assembling simple parts during an injection molding run is a major reason injection molding is done in Southeast Asia. You will save significant money on labor costs if you can design assembly out of the process.

Why should you invest in plastic injection molding?

In most production runs, the molding process yields finished parts with the manufacturing process completed, unless the part requires extra finishing steps, such as painting and sealing. Plastic injection molding is a significant cost-cutting measure because multi-step manufacturing processes can be prohibitively expensive. 

The production cycle is comparatively brief, which means that the parts can be moved on to the next steps quickly. Plastic injection molding is one of the most cost-effective and convenient manufacturing options for producing large part volumes because the molding process can be repeated thousands of times.

Key Takeaway

Since injection molding can be fully automated, it allows for very high production rates (you can mass-produce parts very efficiently through this).

Injection molding can produce incredibly detailed and intricately tailored parts. To create credible designs, you will need an engineering design firm or an in-house department; however, once the part is ready for injection molding, there is very minor finishing work that needs to be done. Parts appear to be very well finished.

Plastic injection molding is well known for its ability to consistently produce thousands, if not millions, of plastic components or products, aftermarket suppliers, packaging companies, and consumer goods. Plastic injection molding can create a wide range of products with varying sizes, complexity, and composition.