Layer resolution vs Layer curing -> strength

Hi there, I just got my form 1+ and started experimenting with it, it’s an amazing printer and I love the prints. I have a few questions to understand more about the capabilities and what to expect

I tried a few prints at different resolutions, 100 microns and 50 microns. For the same print with the same support structures it seems that the 50 micron prints are stronger, is it true that 100 micron prints need more post-curing?
is the laser intensity the same no matter what resolution is set?
if that’s the case I would imagine that when printing at lower resolution you would need a longer post-print cure, is there some measured data that shows that?


You would think that the laser power is different for different resins and layer thicknesses, but it’s not. To the best of my knowledge, the printer doesn’t modulate the laser intensity, it’s either on or off. “Power” is actually “Curing Time”. The laser spot simply goes faster or slower when less or more “power” (respectively) is required.

It makes sense that the thickness of the layer has an equal part in determining cure time, as well as the resin type itself. Thinner layers ought to need less laser exposure time to cure compared to a thicker layer. But whether FormLabs took advantage of that to optimize print times for thinner layers is dubious to me.

You can easily run an experiment. Print an object at 100 microns and then print it again at 50 microns. If the laser cure time is shorter for 50 micron layers than for 100 micron layers, the 50 micron layer print should take markedly less than 2x as long to print as the 100 micron print. If the laser cure time isn’t reduced the 50 micron print should take almost exactly 2x as long to print.

I will post pictures when I get a chance today, I printed the same model in 50 microns and 100 microns, the print time of the 50 microns is almost exactly 2x the 100 microns, so as the layer count. It seems to me that it’s a pure function of layer count, the speed of the laser is the same for both resolutions.
If the curing time of the 100 microns is longer then the laser time should be longer, elongating the print time of 100 microns

It’s not that straight forward.

At 100 microns you’ll have half the layers of the same print @ 50 microns, so the print time will be much faster. You could double the print size to get equivalent layers, but the print volume (and thusly the linear travel of the laser) would be much larger.

Not sure how to make the two prints equivalent to get a valid test.

Is there a way to modulate this in preform?
like slowing the laser down to get more curing time?

You can’t adjust the cure time, the material settings are specifically tested to get the best results, if you cure for too long then the print may stick to the bottom of the tray, and it would have poor detail because the light from the laser will go through the current layer and cure extra material on the underside of the print.
For a print, you want the lowest cure time that will make the layer strong enough not to fall apart. That way you get the best quality. All prints require post curing

Got it, to conclude, post print curing is mandatory not optional to get the quality

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Right, the laser exposure time is low to get higher quality. All materials are soft after printing and require post curing to get their final solid finish. And make sure to cure in water, oxygen prevents curing so the water blocks the oxygen. Otherwise the exterior can still be sticky.

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Thanks for the tip, so after alcohol rinse I should dip the model in a transparent box full of water, and all together inside the UV chamber?


Yep, soak in alcohol for like 10 minutes, rinse in water and then place in container full of water and put the container in the UV chamber. Keep the lights turn down/off while rinsing in water otherwise you’ll get spots on your print where the water is because it will start to cure.

The OP’s point was that 50 microns seems more cured than 100 microns, when printing the same object. He says the 50 micron print time is almost exactly 2x the 100 micron time. This says the laser speed is the same for 50 microns as for 100 microns. which would imply that the 50 micron print layer is getting more cured during each pass of the laser than the 100 micron print.

Beam moves at the same speed but there is less resin to be cured at 50 microns, so the amount of curing the beam performs should be greater. Though when you’re talking layer thicknesses of 50 microns vs. 100 microns there might not be a whole lot of difference in terms of how much laser attenuation occurs as a function of depth of penetration.

but would seem to be a function of resin properties, such as color or lack thereof.

Definitely. The 0.2mm layer height option on my Form1+ is only available for Clear resin even though Black and White resins are the same formulation except of course for pigment. Attenuation as a function of resin pigment is clearly a factor. So attenuation as a function of layer thickness must be as well. I’m just wondering how much more attenuation you get from a 0.1mm thick layer compared to 0.05mm thick. Probably it’s more than my intuition is telling me.

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