Types of Plastic Molding

Chances are, you’ve seen various videos on YouTube about how different everyday products are made. For a surprisingly large amount of different products, there’s some kind of molding involved in the manufacturing process. Even loaves of bread are baked in bread pans to give them a shape. And most candies – whether chocolate bars or jelly babies – are poured into molds of some sort.

Molding is a quick and convenient way to reproduce the same shape over and over while getting the same result every time. Because if this, it’s the most popular way of producing plastic parts. In the modern world, plastic is all around us. From children’s toys and kitchenware, to vehicles and medical equipment.

With the wide variety of uses plastic has, there are many things to consider during the process of designing parts. Not only will you have to choose the right polymer to ensure optimum part performance, you’ll need to know about different injection molding techniques that will ultimately shape your polymer into a usable plastic part.

How to Design a Plastic Product

Assuming you’re starting from scratch, with nothing but an idea for a plastic product you’d like to create in mind, there are a couple of things you should know about the creation of plastic products:

  • It’s good to have a design on hand for any product you want to make, but ultimately, you’ll have to get engineers and professional designers involved somewhere during the process.
  • 3D printing is a great way to help you create a cost effective prototype of any product you wish to create. Because 3D printing doesn’t require a specially designed mold, it’s easy to use this method without blowing the bank. However, 3D printing fails to be a viable long-term option for part production, as it’s not very versatile and takes much longer.
  • If you need to have a plastic mold specially designed and made in order to produce your product parts, you’re looking at a hefty sum of upfront investment. Plastic molds are very specialized pieces of precision-engineered equipment. That said, a good mold can complete 500,000-2,000,000 cycles in its lifetime, depending on what kind of mold you’re looking at.

With so many plastic products on the market, many people might not realize the sheer amount of work and dedication that goes into designing and creating these products.

With that said, let’s have a look at some of the molding processes used to create plastic parts.

Injection Molding

To explain injection molding simply, it’s the process where molten plastic is injected into a mold, then left to cool. Once the plastic has cooled, the plastic part is ejected and the process is repeated.

Plastic injection molds usually consist of two halves. Think about these halves as two halves of a hollow egg shell – when pressed tightly together, this shell with form a cavity into which the molten plastic can be poured. Obviously the mold won’t have an egg-shaped cavity unless you aren’t trying to mold egg shapes, though. The cavity will be shaped like whatever part is being produced.

Plastic injection molding is incredibly versatile, and is used to produce a large variety of differently shaped parts.

Rotational Molding

Rotational molding is mostly used to create parts that are hollow on the inside.

The process of rotational molding uses centrifugal force to form parts. During the process, liquid or powder-form resin is placed into a mold. The heated mold is then rotated, causing the resin to evenly coat the inside of the mold.

Blow Molding

Things like plastic bottles (like the ones in which soft drinks are often sold) are usually made using the blow molding process.

Like with most other forms of plastic molding, there’s a mold shape that serves as the “shell” of the shape you want to produce. But unlike with injection molding, the plastic isn’t simply injected into the mold. Instead, the plastic blown into the mold shape by filling it with air, much like when you blow up a balloon. As air is blown into the plastic, it takes the shape of the mold it’s blown into.

Compression Molding

With compression molding, the plastic is poured into a mold. Different parts of the mold then compress the plastic so that it’s literally squeezed into shape. This produces strong parts, and so the process is often used in the automotive industry.

Extrusion Molding

The basic concept behind extrusion molding is that the plastic is squeezed into a long cavity to shape it. It’s basically like if you were to squeeze cookie dough into a round, plastic pipe. You’d be left with cookie dough in a long, round cylindrical shape. If the pipe where square, you’d have cookie dough in a long, rectangular kind of shape.

This is the basic concept behind extrusion molding. And so this manufacturing process is used mostly to make long, cylinder-type shapes like pipes, for instance.

Those are just basic explanations of the main processes used to mass produce plastic parts. In some cases, a single plastic product will consist of different parts, and these different parts might be produced using different molding processes.

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