Frequently Asked Questions

Should I use SLS or SLA for a functional prototype?

The immediate reaction to a question of this sort is to say Selective Laser Sintering (SLS) - after all, a large part of the growth in laser sintering applications is due to the functionality offered by nylon. However, if we look at the material properties of Duraform (standard nylon for laser sintering) in comparison to Stereolithography (SLA) resins (in this case Xtreme), we can see how far SLA resins have developed. 

All might not be what it appears to be!

That said, all might not be what it appears to be! For example, as engineers we are really interested in the material yield data and these figures are frequently not quoted. The reason is that for most, SLA materials yield and ultimate values are virtually identical. In some cases SLS may offer a difference, but getting consistent repeatable data is another thing altogether.

Elongagtion to break

Taking elongation to break, the figures look better for SLA. That said, and particularly with SLA materials, what is not quoted is the effect of age. Data is difficult to come by, but whatever the specification says, these numbers will fall substantially with time. Further, if this is an issue, then Duraform is not the best SLS material. Alternatives such as EX will do a much better job (i.e. 30 – 45%).

Impact

Looking at impact, the figures quoted for Xtreme are surprisingly good. DMX is also pretty good (65 – 80 J/m), but choosing Duraform as the benchmark is not doing SLS any favours either (again EX is much better).

Temperature, humidity and moisture

Finally we have temperature/humidity/moisture to contend with. The heat deflection temperatures for SLA materials are all well down on the equivalent for SLS materials and thus load at temperature is a real issue. In this case Xtreme is one of the better SLA materials, but this should be watched even in our climate!

Both temperature and moisture can destroy the properties of an SLA part as well as leading to enough growth as to render the part unusable. Fortunately with wise material selection this can be controlled or at least reduced within the realistic operating life. Nylon also absorbs water. The standard materials are nylon 12’s with circa 0.2% absorption, this can be more of an issue with nylon 11, i.e. the EX based material.

A thermal postcure of SLA materials can significantly improve heat deflection (HDT) data. For example on ProtoGen 18420, a thermal postcure can raise the HDT from 53 to 93 degrees C, tensile and flexural strengths also improve, but elongation is adversely affected. Nanotool has one of the highest HDT’s of all SLA resins at 225 degrees C and even this can be raised to 260 degrees C.

It's all about the trade offs...

So, don’t loose sight of SLA. It has not been superseded by SLS. It still has a better surface finish, typically better accuracy. It just offers different advantages – but check which resin you are getting! Bottom line, it’s all trade offs.

 

 

ASTM

Duraform

Xtreme

Tensile strength, yield

D638

N/A

 

 

 

Tensile strength, ultimate

D638

43

Mpa

38-45

Mpa

Tensile modulus

D638

1586

Mpa

1790-1980

Mpa

Elongation at yield

D638

N/A

 

 

 

Elongation at break

D638

14%

 

14-22%

 

Flexural strength yield

D790

N/A

 

 

 

Flexural strength ultimate

D790

48

Mpa

52-72

Mpa

Flexural Modulus

D790

1387

Mpa

1520-2070

Mpa

Impact strength,Notched Izod

D256

32

J/m

35-52

J/m

Heat deflection temperature

D648

 

 

 

 

 

@0.45MPa

180

deg C

62

deg C

 

@1.82MPa

95

deg C

54

deg C

 

 

Related Processes

Stereolithography (SLA)

Produces accurate 3D models with a range of material choices. High Res SLA and Micro SLA for smaller parts.

more info

Selective Laser Sintering (SLS)

Selective Laser Sintering (SLS) is the second most commonly used process after Stereolithography (SLA). SLS parts can be produced with high functionality in very short lead times.

more info

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