Insight

Stereolithography Material Selection

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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: Stereolithography - Material Selection

Transcript

Hi.  It’s time for another insight video.

This week I’m going to take a closer look at material selection for stereolithography 3D printing.

This form of 3D printing uses photopolymer, thermoset resins – in other words the raw material is cured with Ultraviolet light.  The technology is competitively priced, produces an excellent surface finish and is great for complex geometries.  It is often a top choice for producing prototypes and models.

It also offers a broad range of different materials with a large range of tensile strengths, flexibility and elongation to break point.

Before I start talking about some of the materials commonly used, it’s worth noting that a part’s properties will be a combination of both the material itself and the production process.  This means that the same thermoplastic can have different properties after it is 3D printed, injection moulded or CNC machined.

So, for example 3D printing processes often give anisotropic properties, or put more simply its characteristics can vary according to its direction in the x, y or z axis. 

The materials used for all types of 3D printing are improving all the time, but it’s worth designing a part specifically for the 3D printing process.  By adjusting the build orientation, you can overcome anisotropism.

At the beginning I mentioned that you can use a lot of different plastics or resins with stereolithography and this can sometimes make the choice confusing. sigh.  Generally, one or two properties will distinguish any additive manufacturing material from another.

So, before you look at what’s on offer, it is best to define what mechanical or thermal properties are critical for your part.  After that, review the material options you have and consider other properties that are desirable to determine which is the most suitable for your project.

Which material you choose and what characteristics you require may then determine which 3D printing process you use whether its direct metal laser sintering for metals and alloys or selective laser sintering or stereolithography for plastics and resins.

But this week I’m focusing on stereolithography.  Now you might remember that I mentioned that the raw material, in the form of a powder, is cured layer by layer using ultraviolet light.  The photopolymers used are also hygroscopic which means they absorb moisture.  This means that exposure to UV light and moisture will alter the appearance, size, and mechanical properties, so I wouldn’t use it for a part used outdoors.

Modern stereolithography machines offer a range of thermoplastic like materials. Different variants mimic polypropylene, ABS and glass filled polycarbonate.  There are some great materials with excellent properties, so let’s take a closer look at some of the more popular options.

First up is ABS-Like white.  In terms of flexibility and strength it falls somewhere between polypropylene and ABS.  If you are producing a prototype from this material, then it has a slightly higher tensile strength than injection moulded ABS but a slightly lower elongation to break.

It’s very durable and has a high impact strength.  This makes it a good choice for snap fits, master patterns and demanding applications.  On the downside, it has the lowest heat distortion temperature of any of the stereolithography materials at just 47 degrees centigrade.

ABS-Like black is like ABS Like White, but you’ve guessed it, it’s black.  Similarly, ABS-Like Grey is grey.  Sometimes you simply want a different colour for prototypes.

The next one on the list is ABS-Like Translucent. A great advantage of this is that it has a near colourless translucency.  Unusually for stereolithography materials it also has a low moisture absorption.  It’s good for general purpose applications and pattern making, but where it really comes into its own is for flow visualisation models, lights pipes and lenses.

It’s also worth noting that tensile strength and elongation to break are among the highest of any 3D printed thermoplastic like material, so it’s a tough and durable choice.

Okay let’s move onto a material called PC-Like Translucent, which if you are using it for prototyping would closely match 10 percent glass filled polycarbonate.  It provides a strong stiff part with a high temperature resistance.  In fact, if you choose a thermal post cure option this can increase the heat distortion temperature up to a whopping 250 degrees centrigrade, but this process does make it less durable.

Next on my list is a material called Advanc Ceramic-Like High Temperature.  This is perfect if you want to create strong stiff parts with excellent heat resistance.  And again, an additional thermal post cure can increase the already high heat distortion temperature of 132 degrees centigrade to a record breaking 268 degrees centigrade.  This material is often used for producing tooling and in wind tunnel applications.

 There are many more materials available but I’m going to finish off with something a little bit special called Microfine Green and Grey.  In terms of mechanical properties this material falls pretty much in the middle of other SL materials for strength and is on the low end for impact strength and elongation to break.  It’s similar in stiffness and tensile strength to injection moulded ABS.

Why is this material special?  because it can deliver the highest level of detail with features all the way down to 0.07mm possible and it gives the tightest tolerance of any SL material.  This makes it great for making small to micro parts.

They are just a few of many materials and if you explore what’s available from the other 3D printing technologies then we’d be here all afternoon.

Deciding what material to use for prototyping or producing parts using 3D printing depends very much on what properties you want your part to have.  As I said at the beginning of this video, the production process and the material will both have a bearing on this, so it is best to involve your supplier and use their expertise to help you get it right.

Okay I’ll leave it there for this week. Have a great weekend and I hope to see you again next Friday.

 

 

 

With special thanks to Natalie Constable.


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