Choosing the Right Materials for SLA 3D Printing

In 3D printing choosing the right materials can be a complicated and sometimes confusing process. There are so many different properties to consider and complex terminology to deal with. There is no magic material that performs well in all areas, strength in one area will generally lead to weakness in another areas, so it's important to be aware of the relative pros and cons of each characteristic. This article will act as a guide to the process of selecting the right material and give an in-depth look into the specific materials that ProtoFab offers.

First, let's discuss some of the main properties that you need to consider in SLA 3D printing.

Strength and robustness

The concept of strength and robustness are quite broad and cover a range of different properties. One of the best measures of how robust a material will be is tensile strength. This is a measure of how much force is necessary to stretch a material until it breaks. Related to this is tensile modulus (Young's modulus), which is a measure of how much force is required to deform a material (in other words its stiffness).

In the automotive and aeronautical industries, generally it is critical that materials do not deform at all and will not break or snap under pressure, so people usually want these values to be high. Another aspect of strength is impact strength, which is a measure of how a material stands up to being struck or dropped. Often stiff materials with a high tensile modulus perform poorly in this regard as they do not absorb force very well, so what exactly makes a part "robust" is complex and multifaceted.

Flexibility and brittleness

Flexibility and brittleness are closely related to strength and are one of the most central properties of any material. tensile strength isn't the only way of assessing whether a material is robust or not. Flexural modulus, flexural strength and elongation at break or all good indicators of how flexible or brittle are part will be. Flexural strength and flexural modulus are the same as tensile strength and tensile modulus except they are a measure of the force needed to bend a part rather than pull it apart. Elongation at break is the percentage that a part can be extended before it comes apart. Very flexible materials can be extended by more than 25% without break, while particularly brittle parts may snap after being extended only by 5%.

Parts which are extremely rigid will have a tendency to snap suddenly, while parts with some degree of flexibility may be able to withstand much higher forces before finally breaking. However, in many contexts rigidity is crucial, so there is always going to be some degree of trade-off between these related properties. For snap-fit assemblies brittleness is the characteristic that most needs to be avoided so flexibility is a must, even if that means sacrificing ultimate strength by some other measures.

Resistance to heat

Heat resistance is a property which can be critical in some applications but is also sometimes irrelevant, so materials should be chosen accordingly. Heat resistance tends to come at the cost of brittleness so if thermal performance isn’t required it’s often best to avoid materials specializing in this. With the right kind of post-curing we have materials that will hold their shape even at well over 200 degrees Celsius, while our flexible materials will start to deform at around 30 degrees, so the disparity in performance in this regard is significant.

Color and transparency

SLA resins generally only come in pure white, off-white or clear. At ProtoFab we refer to this off-white color as ivory. Parts can be painted in post-processing so often the color of the material is not important at all, but sometimes clients will want to minimize post-processing or have specific reasons to avoid paint (for example in dental applications). In such cases pure white is sometimes preferred to ivory. Transparent resins are more difficult to produce and some mechanical properties will have to sacrificed to achieve this effect. However, our Clear series holds up pretty well against our other opaque materials in terms of strength and are suitable for most applications, with the exception of snap fit assemblies.

Summary of ProtoFab materials ProtoFab

ProtoFab currently offers 10 different materials in 5 different families. Let's take at look at each in turn and quickly summarize their main strengths and weaknesses.

ABS-like

ABS is a mainstay of injection molding and prototyping in general, and it can be closely recreated as a printable resin for SLA. Our ABS-like Formula W and Formula L1 are good all-round performers that are suitable for a very wide range of applications. Compared to our other materials they don't excel in any particular property but neither do they have any major drawbacks. Both Formula W and Formula L1 are excellent choices for general purpose models and for automotive parts.

• Formula W:White in color and gives solid all-round performance in all areas.
• Formula L1:Ivory colored rather than pure white. Very similar to Formula W but slightly stronger and with better moisture resistance.

Heat-resistant

Sometimes parts need to be able to withstand a variety of thermal conditions, and that's what our heat resistant series is formulated to do. As mentioned earlier, heat-resistance can lead to brittleness, so we offer 3 different materials to try to meet the widest range of scenarios possible. All three of these materials are great for wind-tunnel testing.

• Magna W120:Offers by far the best thermal performance of all our materials when given 2 hours of 160-degree thermal post-curing. This step maximizes the mechanical properties of the part and gives a part that can stand up to extreme temperatures. Even without this extra post-curing it still copes well in high heat. The main drawback of Magna W120 is that it is quite inflexible and brittle, more so than Magna L100 and Magna L90. Magna W120 is an attractive white color, while the other two materials in this series are ivory colored.
• Magna L100:Without thermal post-curing Magna L100 actually has better heat resistance than Magna W120 (with thermal post-curing process W120 is considerably better). It is also much less brittle than Magna W120 with better all-round performance.
• Magna L90:Very similar to Magna L100 but with slightly less heat-resistance and slightly better impact strength.

Tough and Durable

For some specialist applications our regular ABS-like resins may not be strong enough, and for such cases we offer the Tough and Durable series. Tensile strength is similar to our ABS-like series, but the Tough and Durable series has much better performance in elongation at break and impact strength.

• Robusta G:This is the strongest of all our materials and is able to withstand extremely strong blows or drops from a high height. Its main drawbacks are relatively poor thermal performance and a slightly lower degree of printing accuracy.
• Robusta LR:Not quite as strong as Robust G in terms of impact strength and elongation at break, but possesses higher tensile strength and flexural modulus. Thermal performance is also better than Robusta G and there are no accuracy issues when printing.

Clear

The primary property of our Clear series is that the material is transparent, but these resins also hold up well in their other mechanical properties. There are two materials in the Clear series, each offering different specializations and applications.

• Clara E:Similar to ABS-like in terms of strength and overall performance. Clara E is excellent for investment casting. Although it is transparent it isn't quite as clear as Clara S.
• Clara S:Similar to Clara E but even more clear. Its mechanical properties generally resemble Clara E, although Clara S is designed more with general purpose models in mind and is suitable for automotive parts.

Polypropylene-like

Finally, we have our polypropylene-like series, which is formulated to give flexibility.

• Flexa W:This is much more flexible than all our other materials and is an outlier in many of its mechanical properties compared to the rest of our range. For example, it performs significantly better in flexural strength, elongation at break and impact strength, and has much lower values for tensile strength, tensile modulus and flexural modulus. In other words, it is extremely hard to break but very easy to bend and flex. This makes it perfect for snap-fit assemblies and many other specialized applications where brittleness and breakages need to be avoided, or where a softer and more giving material is needed. Its main downsides are poor resistance to heat and moisture relative to our other materials. It also can’t be printed quite as accurately as other less flexible materials.

Flewa W

Below you can download our material selection guide to review the summary of the properties for each of the materials we offer.