Narrowing Material Options for CNC

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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: Narrowing Material Options for CNC


Hi, it’s Friday, which means it’s time for another Insight video.

Now, I don’t think anyone’s going to argue when I say that more choice is normally a good thing. Whether you’re looking for a holiday or just going through the menu at the takeaway, the more options you have the better chance you find exactly what you are looking for, right?

However, as the list of options gets longer and longer you can start running into a dilemma – with so many choices, how do you make sure that the one you actually go for is the right one? How do you know the option you go after is a perfect fit?

This is an issue we’ve all probably run into now and again, but it’s surprisingly common when it comes to product design and development. Specifically, when you are choosing materials for machining.

The amount of material options out there is pretty huge, and on top of that your design is usually completely custom. Luckily, there are some ways you can use your knowledge of your part’s function or application to narrow the universe of material options, simplify your search, and get the best possible result.

First up, you need to take a good look at your part’s requirements. Start off by going through the must-haves – the things that are absolutely, 100% vital – and then work your way down to what we call the nice-to-haves.

There are a few common things you usually want to look at first. For example, environmental factors are usually somewhere in must-have territory, with things like heat and cold resistance or flame retardance often being mandatory. If a material doesn’t meet the grade, it’s off the list. Just remember to keep the full scope of the part’s use in mind – if it’s being used in a medical device, for example, it’s going to have to survive the heat of an autoclave and the harsh chemicals used in sterilisation. There’s no use in a material that only does one.

The electrical properties of a material can also be make-or-break, though naturally this is pretty dependant on the application. If it’s in an electrical device, then it’s performance as an insulator or a conductor is probably going to be pretty vital. If it isn’t, that’s not so important.

After that you have mechanical things like strength and flexibility, or the ability to take a beating without breaking, as well as its physical appearance. Colour and texture are usually firmly in the nice-to-have camp, but sometimes the looks can get bumped up the priority list.

Cost is another property that’s hard to decisively place on the list. I don’t think anyone wants to ignore it entirely, but I’m sure we all know that going for the cheapest option can be pretty pricy in the long run.

Anyway, once you have your requirements together, you probably want to run that up against a list of commonly used machining materials.

The reasoning behind this is pretty simple – you don’t want to be reinventing the wheel unless you absolutely have to. There’s a good chance that other people have run into similar requirements in the past, so if you can learn from their experience and cut down on the work you have to do, that’s great.

I’m not going to go into a full list, but in terms of metals we’re talking about things like aluminium, brass, copper and steel – both stainless and otherwise. Plastics are a little more complicated, but I’m sure most of you recognise materials like PVC, Acetal and nylon.

Of course, even when you’ve picked a type of material you’re going to have to think about grades and the like, which is probably the time to pick up the phone and talk to your manufacturer.

The final step in picking a material is to see if you’ll be using machined prototypes.

This is important because while machining is often used for end-use production parts, it can also be used to produce prototypes for parts that will eventually be made with a process like injection moulding. This can save you money, but you’ll want to make sure you choose machinable materials that are close, if not identical, to those that will be used in the ultimate production process.

If you know what material – or materials – you’ll be considering for your moulded parts, your options for the machined prototypes is going to be rather constrained.

For example, some of the most popular moulding resins—ABS and acetal for typical plastic parts, say —are also available in block form for machining. Using the same resin for machined prototypes as you would for the final run will give you prototypes that perform similarly to production parts, which is pretty useful when it comes to testing them.

With a bit of luck these few steps should help you out in narrowing those choices and picking the material that really works for you. Of course, if you’re still weighing things up it never hurts to reach out to an expert.

On that note, this expert is going to call things to a close.

See you next week.


With special thanks to Natalie Constable

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