Theory question regarding SLA printers

[soofle616]

Prior to purchasing my creator pro I spent a great deal of time looking at the Formlabs Form 1 (now Form 1+) as I liked the enhanced resolution of the SLA process over FDM. I eventually nixed the idea after reading about a LOT of problems with producing larger prints since the majority of what I plan to use my printer for will end up using most or all of my build volume. It seems the main issue the Form 1 faces is during it's peel cycle where large prints take too much force to peel from the resin vat surface causing it to be damaged or knocked out of position. The other problem many seem to have is with adhesion to the build surface. Both problems, from what I see, are the direct result of the top-down build flow rather than bottom-up. I'm curious as to why the form 1 and so many other SLA printers use this method. It would seem that placing the laser above the build surface and lowering the platform after each layer like the fdm machines do would eliminate these problems entirely. The ONLY downside i see to this approach is that a much larger volume of resin would need to be in the machine at all times since the full volume of the build area would have to be completely filled with the material. Given the cost of resin I can see why it would be desirable to have only a minimal amount of resin in the machine but at the cost of failed prints and damage to other components it would seem to be somewhat false economy. Is there another reason for the top-down build method that I'm just not seeing?

[richardphat]

Bottom to up vs top to bottom. That will make a big difference when you have to pour 3000+$ of resin vs 40-60$ to get the reservoir filled. No one wants to go even there, it's the reason why our university sold the SLA machine.
In industrial grade machine, you might waste in the 5k$ of resin to get the print ready, that means you have to waste that much ammount of resin to print a small object.

Not to mention bottom to top is a freaking mess because the resin height will always drop and you have to keep an eye for it , constantly. Which is less problematic for the current formlab, because you're printing under and it only needs to refill when it's about to dry.

Not to speak about the sealing issue and a bigger design that will end up taking too much volume in your house.

[Feign]

Bottom to up vs top to bottom. That will make a big difference when you have to pour 3000+$ of resin vs 40-60$ to get the reservoir filled.

Kind of trick of the trade, in almost any top-down SLA process you can float a layer of resin on top of saline or sugar water rather than filling the whole build volume with resin. Doesn't solve other problems with top-down, but it does help enormously on the material costs.

[soofle616]

Kind of trick of the trade, in almost any top-down SLA process you can float a layer of resin on top of saline or sugar water rather than filling the whole build volume with resin. Doesn't solve other problems with top-down, but it does help enormously on the material costs.

I did not know that was possible but that's pretty cool. So what are the other problems with top down?

Bottom to up vs top to bottom. That will make a big difference when you have to pour 3000+$ of resin vs 40-60$ to get the reservoir filled. No one wants to go even there, it's the reason why our university sold the SLA machine.
In industrial grade machine, you might waste in the 5k$ of resin to get the print ready, that means you have to waste that much ammount of resin to print a small object.

Not to mention bottom to top is a freaking mess because the resin height will always drop and you have to keep an eye for it , constantly. Which is less problematic for the current formlab, because you're printing under and it only needs to refill when it's about to dry.

Not to speak about the sealing issue and a bigger design that will end up taking too much volume in your house.

You seem to be assuming that any unused resin is simply wasted material. Unless I'm completely wrong, my understanding is that any leftover resin can be used for a later print. So yes, you have a significant investment in resin to keep the machine full but it's not wasted, just sitting unused. You also assume that the build area would have to be constantly topped off which is definitely not true. A large chamber can be used to hold the resin. The build platform sits inside that chamber with x/y dimensions slightly smaller than the internal dimensions of the chamber. As the platform drops into the chamber after each layer is printed, it displaces the resin underneath it which flows to the top, covering the previous layer and leveling the surface for the next layer to be printed.

The only real issue you've mentioned is size of the machine but again you make a false assumption here. The resin chamber determines your build volume, the laser assembly sits on top of that build volume, and whatever support equipment is needed sits where ever you want. This is no different than a top down machine which has all the equipment underneath, and the z axis above. The only difference in machine volume is that the build volume of the top down machine is empty air space while in the bottom up machine it's filled with resin.

[Feign]

I did not know that was possible but that's pretty cool. So what are the other problems with top down?

Going by the Peachy Printer (since that one definitely has the most in-depth coverage of the development process that one can find on a SLA printer), surface tension and stability are both concerns, either raising the fluid level or lowering a plate, you have to make sure that the layer thickness is enough to break the surface tension on the resin or else you run the risk of developing small intermittent holes or bubbles in the print. Also, you have to make sure the layer doesn't change fast enough to cause a ripple in the resin, which can cause an unwanted bumpy texture in the layer (never was a huge problem for the Peachy, since it fills so slowly).

A bottom-up process manages to avoid both of these, but it requires a peel-action between each layer, which runs the risk of breaking delicate features of the part if not designed properly.

[richardphat]

We used the SLA2500 (90's ish) that was back in the days from 3D systems.

Our tech guy had to fill to max just to use it. That means if you have to print few things for a project and that's it, well then, you won't be able to re-use it unless you do it fast. The resin you used was a complete ripped off. I was lying about 3000$+, in fact that it did cost more.

Here's the idea for the price of the machine in the 90'
http://www.solidimaging.com/2500.htm

Why our universities brought it? They tried to make a campaign introducing 3D printing through SLS, SLA and FDM machine. The campaign was ..... lol, I'll just keep it for myself. You guys don't want to know how it ends up being "efficient" product.

[JSenior]

We used the SLA2500 (90's ish) that was back in the days from 3D systems.
Our tech guy had to fill to max just to use it. That means if you have to print few things for a project and that's it, well then, you won't be able to re-use it unless you do it fast. The resin you used was a complete ripped off. I was lying about 3000$+, in fact that it did cost more.

The resin doesn't cost any more. If you want lower quality resin, you can use the same stuff that the bottom down machines use. If you want Somos/3D Systems etc. resin then you have to pay more for it, but then you get a much higher level of service and a consistent resin that you can trust. If you use a lot then the price comes down dramatically.

Of course you need a full tank if you want to do a full size build (you can use a smaller tank if you don't want the full z height.) But you'll get a full tanks worth of prints from that resin eventually. You can just add the initial resin as part of the machine. If you keep your resin under a constant temperature and don't expose it to uv lights then it takes a long time to go off. If it does go off then you can 're-initiate' it. The professional companies which I have talked to will swap your bath out as well for free if it does go off and can't be saved.

[Marm]

Why our universities brought it? They tried to make a campaign introducing 3D printing through SLS, SLA and FDM machine. The campaign was ..... lol, I'll just keep it for myself. You guys don't want to know how it ends up being "efficient" product.

Uni's are great for that, back in the early 2000's, a friend of mine who went to RIT told me they bought 5-6 segways. After an intensive study, they found the most efficient use for a segway was the changing of large quantities of light bulbs in hallways.