Replacing Metal with Plastics

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Protolabs’ Insight video series

Our Insight video series will help you master digital manufacturing.

Every Friday we’ll post a new video – each one giving you a deeper Insight into how to design better parts. We’ll cover specific topics such as choosing the right 3D printing material, optimising your design for CNC machining, surface finishes for moulded parts, and much more besides.

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Insight: Replacing Metal with Plastics


Hi and welcome to another one of our insight videos looking at the various tech, processes and other things related to manufacturing.

Now, this week we’re going to be taking a look at why – and how – people in plenty of industries are replacing metal parts with injection-moulded plastic ones.

If you haven’t encountered it before, this idea may seem a little weird. Metal parts have been the gold standard in many applications since humans worked out how to heat up these weird rocks and turn them into pointy things.

However, advances in tech and materials mean that this isn’t always the case right now. Yes, there are probably going to be some parts that are always going to need a bit of metal in them, but in high-tech sectors like the automotive and aerospace industry, there’s been a shift towards advanced, highly-engineered plastics.

So, why is this?

Well, one of the big reasons is often weight. Unless you’re dealing with some very weird situations, metal parts are going to be heavier than plastic ones. And when those parts are going in a high-performance car, or even an aeroplane, every gram that you can squeeze out of your design can result in a real boost in performance.

But you don’t need to be running a billion-dollar project for weight to come into play. Think about how much you spend on shipping costs, for example. Yes, it may not seem wildly significant, but if you can cut the weight of your products by, say, ten percent… well, that’s going to have a real impact.

And while we’re talking about things that may seem small, but can have an oversized impact on the bottom line, there’s finishes to look at. Metals all tend to look, well, metallic, but injection moulded plastics can be pretty much any colour or texture you want. You want the company logo on there? No need to paint it on with plastic, just work it into the design.

This even feeds into plenty of other secondary operations. Plastic parts don’t need the intensive de-burring of metal, and assembling the finished product can be much easier when you don’t need welding.

Next up… well, this one might be a little surprising, but sometimes improved strength can also be a factor. Yes, metals are probably the first thing comes to mind when you want a strong, sturdy material, but engineering-grade plastics can often come out on top of metals when it comes to staying power, especially in terms of tensile strength. When you weigh this in alongside the weight, the performance of the plastic parts can be really impressive.

On top of this, the strength of plastic parts can last even longer than their metal counterparts. Now, this isn’t going to apply to every metal out there, but when you’re using plastics, some offer additive agents that help slow down the process of oxidisation and degradation, which in turn, increases product shelf-life when compared to some metals. Many plastics even have a greater chemical resistance than metals, and don’t get corroded so easily. This can mean you don’t need to treat things quite so extensively before they go into use, or that you can simply sell products that last longer or don’t need as much maintenance.

Of course, everything does eventually reach the end of its product lifespan, but even here plastics can offer an advantage. Recycling metal is a great way to reduce the environmental impact – and cost – of your product, but melting down and re-smelting takes a lot more time and energy than recycling thermoplastics.

Finally, one of the really big advantages is cost. Now, some of this comes as a consequence of things we’ve mentioned earlier – less weight to ship, fewer logos to paint, that kind of thing – but simply making the parts is usually much cheaper. Injection moulding plastics comes with a much faster cycle time than metals, making them easier and cheaper to produce.

Right. After hearing all that you’re probably about to call up your fellow engineers and get them to toss all the metal into the scraps bin. But hold your horses.

Plastics are great, but they aren’t always going to be able to replace metals in every situation. This is why it’s always a good idea to have a chat with the experts if you are looking to maybe switch out some metal parts with plastics.

Without getting too product-placement-ey, this is a great example of how tools like our design cube can come in handy – it should be able to flag up any issues with your design, so you can at least get in touch with our engineers to talk them though.

Anyway, that’s enough for today. I’ll see you next week for another video and in the meantime have a great weekend.



With special thanks to Natalie Constable.