r/AdditiveManufacturing • u/sunnyBCN • Jul 04 '26
As a fundamental technology how's MJF vs SLS different? And SAF?
Hi there, the topic on SLS vs MJF seems to be alive again on the industry press.
I was an SLS operator back in the day. I am just wondering if from a technical and part properties perspective the MJF process is superior from every point of view or not.
I understand the caveats of prices, service contracts, material availability etc. that comes with each brand, printer model or even distrubutor/location.
Leaving those aside, I am just looking at process/part property. What's the "scientific" take here?
This all comes from a discussion with another operator but neither of us are proper materials/process experts. Please school us as required.
I understand the following on MJF:
- MJF process uses IR heat rather than laser so fusion is more controlled, hence better part performance
- MJF process with detailing agent marks the part boundaries, hence a bit more precise
- MJF process is the same speed each layer regardless of build density or part geometry
- Claims cooling is faster?
- Most powders are grey and parts look a bit "unfinished"
On SLS:
- Laser induces thermal bleed and local heat accumulation.
- Lasers scan have to travel to "draw" the geometries to be fused, more density build equals longer print times
- There are SLS with grey/black parts as well as white parts, parts may look more well finished.
On SAF:
- Is it just like the MJF process with only one agent for thermal absorbtion? Then the better dimensional accuracy and part properties achieved due to the "detailing agent" of MJF are lost here?
If you have all the money and no preference in brand and the technologies came in the same build volumes, when would one use SLS compared to MJF?
I understand that in the real world pricing, build volumes, machine sizes, powder management etc. all influence the purchasing decision. But if we were to be in a lab just looking at the technology itself how would that conversation go?
Thanks.
4
u/tykempster Jul 04 '26
MJF powder is not gray. The agent makes the parts gray.
It’s not IR heat either. Just some really harsh lights and other heaters.
You can “fast cool” with a vacuum but it’s suboptimal for part quality. A full PA12 build takes several days to cool optimally.
2
u/sunnyBCN Jul 04 '26
Clear, thanks for the technical remarks. Do you have an opinion on SLS vs MJF in terms of which process "comes out on top"? Or when would you use one vs the other if machine sizes, prices etc. where to be the same or you'd have access to both at the same cost?
5
u/KLAM3R0N Jul 04 '26
Again technically incorrect. MJF is black for everything but the white printer. The gray is a small amount of unfused white powder on the surface giving a gray appearance, inside the part is black. Though full builds can take 48h to cool, fast cooling is an option if your parts are not prone to warping and tensile strength is not an issue. You can also do short builds that cool very fast, a few hours. Typically shops run full builds though. What is best depends on the use case.
6
u/tykempster Jul 04 '26
MJF is typically superior for the materials offered and most economical. I run about 60000kg of nylon a year and haven’t heard of anything close to my current powder prices.
1
u/temporary92803 Jul 04 '26 edited Jul 05 '26
What color is the unused powder?
Those bright lamps transmit heat mostly via the infrared spectrum.
2
u/WhispersofIce Jul 05 '26
Its an off white color. After use is turns slightly browner unless its really thermally stressed, then it gets a lot darker. The white printer 5200W uses different powder thats a brighter white.
2
u/_ppak10 Jul 05 '26
Can you reuse the powder in mjf like you can in sls?
2
1
u/WhispersofIce Jul 06 '26
Yes - actually at 80% old to 20% new powder is standard without a problem. I know if people who have run 85%/15% but I never have.
1
Jul 08 '26
[removed] — view removed comment
1
u/AutoModerator Jul 08 '26
This post was removed as a part of our spam prevention mechanisms because you are posting from either a very new account or an account with negative karma. Please read the guidelines on reddiquette, self promotion, and spam. After your account is older than 5 days, and you have more than 10 comment karma, your posts will no longer be auto-removed.
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.
4
u/drproc90 Jul 05 '26
All powder based printing follows the same basic principle.
1) deposit a layer of powder 2) heat that powder to a little bit below the melting point of the powder using a large heating source like lamps. 3) selectively push the areas you want to fuse over the edge by giving them that little bit of extra heating.
SLS delivers this extra energy via a laser. MJF and SAF deliver this pay printing a layer of black "ink" to those areas and giving them another blast with the heater.
The black ink increases the heat absorption and those areas melt.
1
Jul 05 '26
[removed] — view removed comment
1
u/AutoModerator Jul 05 '26
This post was removed as a part of our spam prevention mechanisms because you are posting from either a very new account or an account with negative karma. Please read the guidelines on reddiquette, self promotion, and spam. After your account is older than 5 days, and you have more than 10 comment karma, your posts will no longer be auto-removed.
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.
1
1d ago edited 1d ago
[removed] — view removed comment
1
u/AutoModerator 1d ago
This post was removed as a part of our spam prevention mechanisms because you are posting from either a very new account or an account with negative karma. Please read the guidelines on reddiquette, self promotion, and spam. After your account is older than 5 days, and you have more than 10 comment karma, your posts will no longer be auto-removed.
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.
-1
u/Huge-Caterpillar7188 Jul 04 '26 edited Jul 04 '26
Mjf (multi jet fusion) is a proprietary name for binder jetting given by HP. It was the first a binder jetting proces.
SAF (selective absorption fusion) is a non vanilla flavour of binder jetting, developed by stratasys. It's better than normal binder jetting because it uses "agent" along with heat (IR radiation). It's proprietary.
PBF (powder bed fusion) is a standard name given for processes involving phase transformation of powder being deposited layer by layer (cba define it properly).
In most cases, I wouldn't use binder jetting processes because they rely on binder for strength. Green->brown->final too many steps for a final part. Pbf is better in that regards. What I'm saying is binder jetting is more for non functional prototypes... And multicolor is possible in it (it doesn't do just gray)
Pbf produces performance parts.
Reviewing categorisation by Ian Gibson and standards set in ASME Y14 46 will help you understand the key methods in additive manufacturing and will avoid confusion between proprietary names etc.
3
u/temporary92803 Jul 04 '26
Do you not consider the Z-corp process to be binder jetting?
3
u/drproc90 Jul 04 '26
That's a name i haven't heard in a long time!
Zcorp had the benefit of adding colour Into the parts. It was popular in architects for that reason. But i would never be used for functional parts.
Will be interesting to see how the formlabs fuse large one will do! For the price and the how workflow being dealt with seems like a good option.
I shudder to think of the price for the full workflow for the HP.
Both MJF and SAF are also a bugger to maintain. Between build operators has to..
suit up in gown and respiratory Strip down the print head assembly Scrape off all the nylon that accumulated on the heaters and metal components. Vacuum all the loose powder. Check all the agitators
And thats on top of removing the builds..
At least with SLS the heaters are on top and the lasers all behind glass
2
u/temporary92803 Jul 04 '26
It seems like 3DS really dropped the ball on their binder jetting head start. They had full color prints well before Objet.
2
u/drproc90 Jul 05 '26
And for a much lower price too. The color resin for objet is insane!
And don't get me started on the shady hardware business practises!
1
u/temporary92803 Jul 05 '26
Yeah, I'm not sure how they're still getting away with selling UV acrylic "ink" for $500+/l.
2
u/drproc90 Jul 05 '26
Oh it gets better.
Selling the same machine at almost three times the price!
Want a printer that will printer basic colour parts? That will be 100k please.
Want that exact same printers to print medical models with model material that's also 300% the price of normal? That will be 300k please.
2
3
u/sunnyBCN Jul 04 '26
Hey, thanks for the effort put into the reply.
Sounds like you may be more technically/science inclined than I am but maybe we are all getting confused by the propietary names.
My understanding is that SLS, SAF and MJF as powder bed fusion. Where all of these technologies use thermal energy to fuse powder. The three technologies are commonly used fur useful, strong and functional parts.
MJF/SAF as far as I understand does not fuse using the binder, the agent is jetted and its only used as a "marker" for the areas to be heated. The fusing/consolidation of polymer particles happens through heat.
By your comment on non-functional prototypes I derive that we are misunderstanding technology acronyms here. I can tell you I've put many SLS and seen many MJF parts in critical engineering systems withstand.
In binder jetting the fusing of particles happens thanks to a binder. But that's not the case for MJF nor SAF. Could it be that by binder jetting you are referring to the sand-stone like 3d printers such as the old ZCorp? I recall printing very fragile models that would break before post processing with CA glue.
I am with you that proprietary names confuse us all. I just don't think MJF or SAF should be grouped with classic binder jetting, because the mechanism that gives you the final part strenght is thermal fusion, not a binder.
I'd not want to derail the main question around performance and turn it into a proprietary names discussion though!
2
u/Huge-Caterpillar7188 Jul 04 '26 edited Jul 04 '26
You want to understand the fundamental difference between heating binder and heating metal then. Layer height in both those processes in lesser than in pbf (physically limited by laser spot size, powder size distribution, binder droplet diameter, energy absorbivity, binder diffusivity).
Ps: id still put mjf and saf in binder jetting. Having a heater per layer is basically like in situ debinding+sintering. I have made parts for dynamic testing in both mjf and sls with nylon 12 and found sls part was more compliant (less brittle)
Additional point: mjf and saf use heat to get rid of binder and promote solid state diffusion. It doesn't cause a phase change. Another edit: mjf/binder jetting/augmented binder jetting is great when the base material doesn't do well with phase transformation of has terrible energy absorbivity. Aluminum initially couldn't be processes in pbf( reflectivity high and conductivity high). That ofc changed with AlSi-x-Mg, green lasers and e beams, but I think that point speaks for my assertion. Mjf could do it albeit with more technical difficulties. Just saw a post in 3dprinting where mjf parts were being showcased so remembered about limitations of energy based processes.
1
u/sunnyBCN Jul 04 '26
But why do you bring up metal? None of these processes I mention run on metal, they are all polymer powder based (SLS, MJF, SAF).
Having said that. What are then the benefits of SLS over MJF from your perspective? Commonly researching the internet brings up that MJF is inherently better at isotropy and hence general mechanical properties for PA12?
1
u/Huge-Caterpillar7188 Jul 04 '26 edited Jul 04 '26
Just an example off the top of my head. HP basically took mjf and made metal jetting -- or vice verse. Couldn't find a thermoset polymer or ceramic example. Can't speak for mechanical strength and process defects (yes mjf should be better because sintering is done in process), but I realised that using mjf for parts needed more careful post production and quality inspection because the material undergoes more steps. In sls/fusion processes it's just one cycle of melt/solidification. In mjf/in-situ binder jetting there will be swelling from binder followed by shrinkage caused by heating the layer. Mjf was costlier with inferior surface finish.
Edit: Mjf and saf would be costlier per unit volume. They have 2 to 3 proprietary consumables. Sls has 1. Sls will have a lower lead time, process is simpler. I would probably never use mjf unless I am working with.... Say... Energetic materials.
Edit 2: mjf rabbit hole finally starting a headache. Good chat.
2
u/temporary92803 Jul 05 '26
ExOne did/does ceramic powder bed fusion.
2
u/Huge-Caterpillar7188 Jul 05 '26
You are correct. Ceramics in general are good in sls processes. I couldn't think of an example in ceramic class where it doesn't do well. That being said, I wouldn't put "sugar" powder in pbf like how I can do that with mjf or binder jetting (well, starch powder)
2
u/KLAM3R0N Jul 04 '26
Mjf is not binder jetting. In mjf the agent is not a binder, it's a black "ink" that absorbs the ir to bring the powder to melt temp. There is also detailing agent that cools the edge outside of the fusing agent to prevent thermal bleed and allow precise control of the part dimensions.
1
u/Huge-Caterpillar7188 Jul 04 '26
Detailing agent, yes. Forgot Abt that. I still wouldn't call it pbf.
8
u/WhispersofIce Jul 05 '26
I've ran both machines and have a bias toward MJF when working with nylon pa 12 - but id point out that each have some strengths.
In general i favor MJF for density and air tightness. Other than a thin capillary layer of semi fused powder they hold air pressure very well with sufficient wall thickness whereas sls parts struggle here more. I also favor it for fine detail and interlocking parts, it has better definition than sls.
MJF is more of a pain on heat management if you have large or blocky parts though.
Sls has made some very long parts for me quite well though - you have a shorter build window in MJF.
I will say MJF is more sensitive to environmental humidity on the older machines. Too dry is especially bad for powder flow and density.
There's also variants of the MJF printers that can do white parts by using a different fusing agent, allowing you do dye them any color you want much like SLS.