20240119-Protolabs Insight: SLS vs. MJF

30 Jun, 2021

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20240119-Protolabs Insight: SLS vs. MJF

At first glance the parts that SLS and MJF produce may seem similar, but a closer look reveals there are some key differences that may sway you to using one over the other.

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Insight: SLS vs MJF


Hello and welcome to this week’s Insight.

Today I’m going to compare two industrial 3D printing technologies that at first glance seem to produce similar parts from the same material, but if you take a closer look there are some differences that might sway your decision one way or the other.

We’re going to make a head-to-head comparison between Selective Laser Sintering, or SLS for short, and Multi Jet Fusion or MJF.

Both processes build parts by thermally fusing, or sintering, polymer powder particles one layer at a time and both use thermoplastic polymers which are usually nylon. The difference is that SLS uses a laser to scan and sinter each cross section, while with MJF ink is dispensed onto the powder as a fusing agent to promote the absorption of infra-red light which fuses these inked layers.

It’s fair to say that both produce durable parts for functional testing and end use.

MJF is quicker, so manufacturing costs tend to be lower, but that does not mean you should simply go for it over SLS.

As with any selection process, you need to ask yourself what are your requirements for the part? This could include feature resolution, surface finish, materials, colours and mechanical properties.

So, let’s go through these points one by one.

First of all, feature resolution.  Using Multi Jet Fusion parts you can produce smaller features down to 0.5 millimetres whereas SLS comes in at between 0.75 to 1 millimetre depending on which material you use. There is another consideration here though. While you can have smaller features using MJF, SLS has a better small feature accuracy. 

If it’s a smooth surface finish that you want, then MJF edges it, but realistically both technologies produce parts with a grainy texture so you will need to consider some post processing for both.

Next on our list is materials. The main material for both processes is nylon, but SLS does offer you more options such as carbon filled PA and glass filled PA which give additional mechanical properties.

Ultimately any material selection really depends on what you need your part or prototype for.

It’s also worth pointing out that things change and more materials become available for different processes over time.

A good example is 3D printed parts made from thermoplastic polyurethane.  Until recently SLS could produce these and MJF could not, but now you can get parts from this great material using MJF as well.

Okay so the next thing on my list is colour.  If this is important, then suppliers should be able to dye SLS parts to almost any colour that you want.

Sadly, things are a bit more limited with MJF because the fusing agent used is black since dark materials tend to absorb infrared radiation better.  It means MJF parts have a light grey appearance, which your supplier can dye to black for cosmetic reasons if needed.

Right so that brings me to mechanical properties.  The main thing to be said about this is that due to the way that Multi Jet Fusion builds parts you tend to get more consistent mechanical properties along all directions of its geometry.  It means that if you have key features on multiple surfaces then MJF may be the better option. 

Don’t forget my previous point though that SLS offers you more materials, which will have different mechanical properties to the standard PA nylon.

It just proves that it’s never a simple choice, so guess what, as always, I’d say get your supplier involved early on, they know what works for different applications.

Okay a couple of final points that may sway your final decision between these two processes.

Number one, check with your supplier if there are any size limitations for the two processes. At Protolabs for example we can produce far bigger parts using SLS than MJF.

And number 2, think about the number of parts that you need.  As I mentioned earlier MJF is a faster process so it can produce more parts in a shorter time period so you would expect delivery to be faster.

Ultimately both SLS and MJF are great for producing functional parts with good dimensional accuracy in pretty much any geometry that you want.

Both are excellent technologies and which one you choose will come down to exactly what you want from your part.

That’s it for this week. I look forward to seeing you again next Friday.

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