[TheJollyRoger]

Hi all, first post on here. I am currently building 3D printers for a company and have been tasked with trying to solve the problem we are having with our prints rounding/bulging at the tops.

The printers are SLA resin printers, which use 2D images and UV light from projectors to cure a photopolymer resin. The projectors sit above a pool of resin, which the build plate is submersed in. We display an image for a certain amount of time which hardens part of the resin, then dip the build plate to recoat said hardened resin, before raising it up approximately 50 micron below the original position and repeating the process.

The problem we are facing is that when we raise the build plate again, we are seeing a bulging effect on the top of the resin, which makes large flat surfaces become slightly rounded after printing. I suspect this is partly due to the viscous resin simply taking time to flow across the part, however mostly due to the surface tension of the resin.

I am trying to come up with a solution for this, however I am at a bit of a loss as I am not very experienced in chemistry. I know from fluid mechanics that I can introduce a surfactant to reduce the effect of surface tension with some liquids, but I am not sure how to go about finding the correct one for our resins. I would need to find one that is much less dense than our resin, and doesn't block UV light.

Would anyone be able to offer some advice on what they would do to go about narrowing down a surfactant to use in the scenario? I have access to a mass spectrometer to find the resin makeup, however am still to make use of it.

Any help would be really appreciated.

[Enthalpy]

I haven't tried to model how slow the monomer flows when 50µm thin, but intuitively, natural flow won't make flat surfaces with a liquid that shallow.

Usually, 3D printing have a wiper to achieve a flat surface of thin liquid or powder. Why shouldn't you have one? It's the universal solution, and I just feel it's needed.