Stereolithography, or SLA, is an amazing technology that has come a long way in a short period of time. From the prohibitively expensive professional 3D printers to prosumer and hobbyist alternatives, resins are here to stay.
How to know if this technology is suitable for a project, or whether or not we should get an SLA printer? This is without a doubt one of the best alternatives available for representing products, but it is no silver bullet. Let’s talk about it from a product design perspective.
What It Is
SLA 3D printing is a process where photosensitive resin is cured, or solidified, with light. While traditional FDM printing deposits molten plastic on a predetermined path, SLA printers cast a light beam that follows a path across the resin tank to create the part, one layer at a time.
At 0.025 mm layer resolution, the accuracy and detail you can get with SLA printing is very high, and details that often get missed in FDM printing -such as fine logo engravings- are easily visible and represented much more accurately, which helps a great deal when planning products, enclosures, etc. Resin for a Formlabs printer is not too expensive — when compared to a Stratasys printer, at least — and there are a few good, cheaper generic alternatives.
We were able to work with 0.004” allowances with SLA printing
SLA 3D printing is not impossibly slow if you are printing thin-walled enclosures at medium resolution, but if you plan on printing thick walls (thicker than 4 mm or so), then get ready for some +15 hours printing jobs.
The Not so Good
Uncured resin (in a liquid state) is messier than you would anticipate. It has the consistency of thick condensed milk, and it will stick to anything. Removing it is no easy task. Post-processing takes time too. Printed parts straight out of the printer are not ready to use by any means. They are just getting started, actually. After printing, you have to wash away all the uncured resin that is still covering the part. For this you will need gallons and gallons of +90% pure isopropyl alcohol, which, if you planned on having the printer at home, is not something you really want lots of around. Oh, and good luck disposing of all that used, gunky alcohol. After washing the printed parts, it is time to post-cure the resin -provided that you have the appropriate tools around-, then clip off all the support structures, then sand away all the excess, and finally paint or apply some finishing to the parts.
Prototyping Enclosures for Electronics
Electronics is a precision game, so the more accurate an enclosure is, the better. That is the case with resins. Tiny features in an assembly can be represented and evaluated out of a SLA print. And unless we are talking about a component that gets really warm, resin enclosures can take reasonably well the temperature most chips generate. Screw inserts can be accurately placed and it will allow enclosure assembly/disassembly a number of times.
While it is perfectly possible to print walls that represent the actual thickness of an injected plastic part, most resins will not have the same strength, mechanical or impact resistance properties. If you are prototyping for visual evaluation, light ergonomics, and the mechanical testing is aligned to both the resin and target plastic’s properties, this should not be a problem.
Another thing to keep in mind is warping. Once the part is out of the printer, the solid resin keeps curing further, slowly and almost unnoticeably. This process can lead to a slight warping that can prevent a clean assembly. This can be mitigated with post curing.
Despite a few significant shortcomings, SLA printing is probably the best technology available when it comes to representing and assessing new concepts.