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Plastic Molding Manufacturing

Plastic has been a key component of manufacturing since the mid-1800s, when the first man-made plastics, such as celluloid, were developed. One of its early uses was in the production of billiard balls, which had until then been made out of ivory.

Today, the term plastic can be used to refer to a range of synthetic and partly-synthetic materials, such as polyester fabrics or polycarbonate smartphone cases. Other types of plastic are used in construction, such as PVC piping and vinyl siding.

But the technology behind plastic has changed a lot over the years, leading to a more intricate production process that can produce plastic items in all shapes and sizes.

In this article, we’re going to take a close look at the plastic molding process, including six different methods for plastic molding, and how cryogenic processing fits in.

What is plastic molding?

Plastic molding refers to a process in which powdered, sheet, or liquid plastics are put into a mold to produce the desired shape. In fact, the word plastic actually comes from the Greek word plastikos, which translates to “capable of being molded”.

Some manufacturers, especially in the U.K., spell it “moulding,” while U.S. businesses usually prefer “molding.” The mold itself may be referred to as a matrix.

Although the concept is pretty simple, plastic molding is extremely complex, relying on the right combination of heat and pressure to create the finished product. Ultimately, it can be used to produce parts of all sizes and with varying degrees of flexibility.

Let’s take a look at each molding method one-by-one, and see which approaches are used to produce some common plastic products.

Methods for plastic molding

One of the main things to consider when deciding on a molding method is what features you want the finished product to have. Knowing whether it will be large or small, flexible or rigid, can help you determine which method is best for it.

Other things to consider include the quantity and the cost. Some methods can produce a large quantity of items in a year, while others are best for smaller orders. Additionally, the cost can vary widely, depending on the complexity and quality of the process.

These are the six main molding methods used in plastic manufacturing today:

Rotational

Rotational molding is a manufacturing process that relies on centrifugal force to coat the mold and produce a hollow product. The plastic starts out as liquid or powder, and gets heated up in an oven as the mold spins. The mold rotates at high speed so that the plastic coats the sides evenly; then, it’s allowed to cool and harden.

Rotational molding is relatively affordable and efficient, and produces little waste in the process. It can be used to produce anything from recycling bins to kayaks. It isn’t limited to perfectly round or symmetrical objects either: it’s capable of retaining contours and other design features in the finished product, such as logos and inserts.

Rotational molding can be slower than other methods, and isn’t suited for small items, or items with multiple parts. But for large to mid-sized items, it can produce consistent designs, while reusing excess material that would otherwise go to waste.

Injection

Injection molding is one of the most precise manufacturing methods, so it offers a lot of flexibility and can be used to produce a wide range of products. The technology behind this method is exactly what it sounds like: the melted plastic is injected into a mold.

That means it can be used to produce everything from car parts, such as bumpers, to intricate medical devices and bottle caps.

The molds themselves are often made out of metal, so they can be expensive, and the process can take 3 to 4 months to set up. But once the equipment is up and running, it can be a very cost-effective way to produce tens of thousands of items each year.

Extrusion

Extrusion uses a different set of equipment than these other molding methods. Instead of a mold, the most important tool in the process is a die, similar to what’s used in die casting. The melted plastic is forced through the die, rather than injected into a mold, which causes it to take on the shape of the die instead.

This technology is used to produce many common items, such as plastic straws, PVC pipes, and garden hoses. The cross-section determines what the finished product will look like, so items made by this method tend to be fairly uniform in design.

Extrusion molding isn’t only for round or straight objects, though. It can also be used to make U-sections, T-sections, L-sections, and other more complex shapes.

Blow

Blow molding is another form of plastic production that uses the same techniques that are used in glass blowing. In short, air is blown into the heated plastic, which causes it to expand like a balloon and take the shape of the mold surrounding it.

Products produced by blow molding tend to be hollow in shape with thin walls, such as plastic bottles, watering cans, storage drums, and other small to medium objects. Blow molding machines work quickly, taking under two minutes per cycle, making this an efficient process if you need to produce thousands of items per day.

As far as cost goes, blow molding is more expensive than rotational molding, but it’s cheaper than injection molding, depending on the quantity of objects produced.

Compression

While rotational molding uses centrifugal force, and blow molding uses air, compression molding relies on pressure to form the shape of the finished product. In this technique, the plastic often comes in the form of a sheet instead of a liquid, and stronger plastics, such as fiberglass, may be used instead of polyethylenes and vinyls.

Once the plastic is introduced into the mold, the top of the unit comes down to press it into shape. The mold itself is heated to create the right conditions for molding, and to “cure” the plastic before it’s cooled and trimmed.

Compressing molding produces more durable items than other methods, but the initial setup process can be expensive. Once the machines are up and running, they’re more cost-effective, and can turn out high volumes of material at low cost.

This method is used to produce household appliances, car parts (such as hoods and fenders), and plastic versions of items that are ordinarily made out of metal.

Thermoforming

Thermoforming is a manufacturing technique that molds small plastic items from a large thermoplastic sheet. This type of plastic becomes pliable when it’s heated, so the items can be molded and trimmed as they move down the assembly line.

This technique can be used for thick-gauge or thin-gauge materials, and can produce 3D textures with a range of colors and finishes.

Thermoforming is often used to produce thin, disposable plastic items, such as cups, lids, and clamshell containers, but it can also be used to make thicker parts including dashboard panels and truck beds. Molds are usually made from aluminum, and may take up to two months to assemble before they’re reading for production.

Cryogenic treatment for plastic molding manufacturing parts

Regardless which manufacturing method you use, plastic molding is a highly complex process involving a lot of moving parts, including screws, dies, molds, and other metal components. Any mechanical issues can result in production delays, increased costs, excess waste, and other issues eating into your profit margins.

That’s why taking good care of your metal parts is just as important as using the right type of plastic or molding method for your products.

One way to do that is with cryogenic treatment, which strengthens metal components by subjecting them to cryogenic temperatures (−238 °F and below) before heating them up again and letting them cool to room temperature. This finely-tuned process changes the composition of the metal, releasing stress and protecting against wear and tear.

Benefits of cryogenic processing

Whether you’re experiencing seized pins, eroded gates, or worn cavities, there’s a limit to how frequently you can afford to shut down production and replace these parts. With cryogenic treatment, you can extend the life of your metal parts by two to three times their usual lifespan, reducing downtime and saving you money on replacements.

Cryogenic processing results in more stable, wear-resistant parts, such as ejector pins that don’t stick and dies that don’t wear as easily. Sifter screens, extrusion screws and barrels, and other components all last longer when they’ve been cryogenically treated. They’re also less susceptible to abrasive materials like glass.

Cryogenic processing is a one-time treatment that can have a long-term impact on the quality and efficiency of your plastic molding process.

Make better plastic molds today

At CTP Cryogenics, we have over 30 years of experience providing cryogenic treatment across a range of industries, including automotive and industrial manufacturing.Whether you’re producing a single set of molds or dozens, we can help you determine the most effective use of cryogenic processing for your business. Contact us today to request a quote and learn how cryogenic treatment can improve your products!