Choosing Your 3D Printing Material: It’s About More Than Strength!

The pace with which 3D Printing materials are being developed appears to be gaining momentum. With the introduction of some many different how can you stay informed about what materials are most suited for your project, or even other applications?

CAPUniverity is here to help, and they’ve just released an infographic that’ll make your job of understanding 3D printing materials much easier.

It seems like 3D printers can use any material nowadays. There are some that use lasers to print in metal, additively fusing layer after layer of powder into intricate shapes. There are some that can print in chocolate. Most 3D commercial printers create parts in some sort of plastic. However, even among plastic printers, there is a wide range of what material can be used: ABS, Nylon, PLA, PC, PEI. So how do you choose which 3D printing material is right for you? Which one makes your parts the best?

When choosing a material to print in, a lot of people only look at the reported strength of the raw stock. In fact, when I made that list of typical printer plastics (ABS, Nylon, PLA, PC, PEI), I actually ordered them from lowest ultimate tensile strength to highest:

Tensile Strength

But Tensile Strength Doesn’t Always Determine If A Part Will Be ‘Stronger’

If you were forced to make a hammer from either hardened glass (ultimate tensile strength 175 MPa) or 3003 Aluminum (tensile strength 110 MPa) and you chose the glass, you’d have a hammer that was technically ‘stronger’, but would shatter after just a few blows. That’s because there’s another material property that also affects how long our parts last called ‘toughness’.

A pane of glass will shatter if you hit it with a real hammer. A sheet of steel might either bend or shatter under a hammer blow, depending on the type and temperature of the steel. Lead is not as ‘strong’ as either glass or steel, but it is tougher than both, since hammer blows that would break glass and steel usually deform, but not break, a similarly sized sheet of lead. This is one reason they make bullets out of lead (you wouldn’t want a bullet to shatter when the hammer of a gunpowder explosion hits it).

*There is a third component to material definition, called ‘hardness’, but since most 3D printed parts aren’t knives or cutting surfaces, we’ll leave that out for now. In general, things that are ‘Strong’ are ‘Hard’, but things that are ‘Hard’ aren’t ‘Tough’. For more information about how the Strength-Toughness-Hardness triad affects engineering decisions and a fun look at how Materials Science has guided human history, read Mark Eberhart’s excellent book “Why Things Break”)

And if you look at the rated toughness of the different plastic materials, you start to notice something:

Screen Shot 2015-01-21 at 4.31.53 PM

Things that are ‘Strong’ aren’t necessarily ‘Tough’, and things that are ‘Tough’ may not be ‘Strong’. This is why we don’t have glass hammers or high carbon steel bullets.

Another dimension to consider with your printed parts is temperature. Fused Deposition Modeling (FDM) printers melt their plastic stock so that the nozzle can lay it down in the path you want before it hardens.

FDM Nozzel

This means FDM materials must be ones that melt at a temperature low enough to be generated and contained in a machine. (Which is why we won’t soon have FDM printing with nickel (melting point 2,600 °F) or ceramic (melting points ~ 1,800-3,000 °F)).

And so a 3D printing material that you think is strong or tough enough for your desired application may not be, as the temperature rises. The scale we’ll use is not melting point (your part fails long before it becomes a sloshing puddle of liquid) but Heat Deflection Temperature (HDT). That’s the temperature at which a sample becomes soft enough to deform a specific amount under a specific stress. (Deforming 0.010 inches under 66 psi, for you stat geeks out there.)

Adding that dimension to our list we get:

Heat Deflection

So if you were printing parts that often needed to go into boiling water (212 °F), some of those materials wouldn’t hold their shape well and some would. But what finished parts would ever need to go into a place that hot? Well, any medical device that needed to be sterilized by steam autoclaving, for example.

Some of the last material properties to consider in 3D printing are the niche, application-specific ones. For example, parts you don’t want showing up in medical MRI scans need to be made from PC, and parts you don’t want building up static electricity to destroy circuit boards need to be made with a specific type of ABS (ABS-ESD7).

How Do You Decide Which 3D Printing Material Is Right For You?

With so much to consider it can be hard to sort through the details and decide which material is best for your project. To help we’ve made CAPINC’s 3D Printing Material Guide, which ranks current 3D printing materials by strength, toughness, resolution, heat deflection temperature and even application properties, such as medical, electronic, military and consumer applications. Download your copy here!

Source: CAPUniversity

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