Open to suggestions on what else might be the issue?
I’ve been encountering a significant amount of froth in my prints as well. What I notice is that on the first print of a fresh batch of resin the froth is not a major issue unless its a large print. On the second print (resin is still frothy) using that same resin, I notice a few artifacts like blades of print adhering to random spots and lumps attached to the print. On the third print using this same batch of resin, there are lumps of semi-polymerized resin noticeable in the resin tank and the clear resin has started to turn amber. The print from this is distorted and has a lumpy surface. Some of the artifacts wash away with IPA but the finish is noticeably off. I also notice a lot of random lumps and strings attached to the support structure. The fourth print from this resin is a failure as there are masses of lumps bound everywhere on the print. I hope this helps clarify. So from my perspective, bubbles don’t hurt the first print but in subsequent prints it can be a problem because they may diffract the laser as its passing through the resin and cause unwanted polymerizations, which compromise the resin for future prints.
I agree with moda that if you print while the resin is still frothy, the surface finish will be off.
I’ve had a project last week where I printed 3 small print jobs (< 10ml resin, and <90 mins each job) back to back to finalize tolerance/fitting. After those 3 jobs and getting the fitting perfect, I noticed serious frothing in the resin (since the wiper makes more bubbles each layer). Remembering the constant reassurance by Formlabs on the forum that froth and bubbles are harmless, I started a large print of parts with the finalized dimensions, and I couldn’t use a single one of those finished parts due to large amounts of surface pitting.
I never noticed this with Grey V4 before because my earlier print jobs before this project were at least 1 day apart from one another, and I suppose that gave the bubbles enough time to dissipate.
So I contacted support about this bubbles/froth, and they said
"During the print process, the build platform lowers close enough to the elastic layer of the resin tank to squish any bubbles out, no matter how small. "
That is true, however, the issues arise when the bubbles cling to parts that are still being printed (eg, on a 600 layer job, the bubbles start clinging to your parts at layer 100). The time it takes to finish the print job is enough for the bubbles left on your part to affect the surface finish.
Wouldn’t that mean your cleaning procedure isn’t good enough ? It sounds like the bubbles left on the print are part of the uncured layer of resin that you have to clean off, and should not affect the final surface quality.
Thanks for your input! Right now I’m putting the parts through two IPA 91 cleaning tubs with magnetic stirrers for 15 minutes in teach tub. I hadn’t considered that those weren’t enough and I’m not sure what improvements I can make to my cleaning process.
Do you personally use Grey V4? How do you clean your parts?
We clean with 99% IPA in Formlab’s Wash and were previously using the standard two-buckets kit (without active stirring). I have used Std Grey quite a bit including some 40h, 650ml 172mm tall prints which tended to leave the tank with quite a bit of foam by the end of the print, but I never had surface “pitting” issues.
I would expect your method to be enough, in theory. One thing that comes with the Wash is a hydrometer and that helps in controlling the saturation of the IPA, which is difficult to judge by it’s appearance only given some resin cloud the IPA quickly while leaving it perfectly usable. If you’re using small buckets, the IPA may get saturated sooner than you expect. All of that is only suppositions though, because a lot of people have complained about these bubbles so I can only recognize there might something wrong, but a lot of others like me have foam and no issues so…