when you see all those plastic-based 3d printer advertisements on the news, with perfect parts and flawless print processes, you might know better that it actually looks like however, a new type of printer is becoming more affordable right now, the resin-based printers. which sports even shinier ads. however, in practice, it looks like so let's understand these 3d printers better?
fused deposition modeling 3d printing, ok, i got it - you are well acquainted with fdm 3d printing. you know all about 3d printing with plastics, right? but you have been reading about this sla technology lately and want to know more about the practice - not just the theory. i made this video for you. this is meant to be a very quick video to acquaint you with the practice of using sla 3d printing, specially when compared to fdm.
it does not dwelve deeply on theory but this channel will sport a more comprehensive video about it eventually. stay tuned. with the sla technology you have clearer, smoother, more high-resolution parts than with fdm, although with a build volume usually 3-4 times smaller than a typical fdm printer. this is a typical fdm printer called sethi3d aip. this is a typical sla printer called ctc euroway, it's a form1 clone. this is the vat, also called resin tank. this fuse here raises and lowers the stage, which is this part here - which can be removed. the stage is the build platform, to which the print sticks to upside-down. after the print is finished you have to remove it from the stage. this particular printer has an usb cable which will be connected to the computer when the slicer is running but can be disconnected when the printing starts. this acrylic lid filters ambient ultraviolet light which could harden the resin (albeit slowly). that would ruin the vat because the hardened resin would stick to it. this printer uses an ultraviolet beam from below to harden the resin, which is directed by these mirrors on the bottom. there is also a motor here than inclines this support where the vat is, it makes that movement.
this is a typical resin, yellow and opaque. there are also transparent or clear resins, like the one on this part. while for fdm the layer height typically goes from 0.1mm to 0.3mm, for a sla printer they usually range from 0.025 mm (25 micra) to 0.1mm. this year shows signs of a high raise in sales of this kind of printers. just like the fdm patent expired in 2009 which led to the 3d printing explosion, the stereolithography patent expired in 2014, paving the way for the appearance of low cost sla 3d printers. even before the patent expired, two sla printers, one in 2012 (b9 creator) and the other in 2013 (formlabs form1) were successfully crowdfunded through kickstarter, both of which became successful to the point of becoming de-facto market standards on which most other brands now rely. while the form1 is a "pure" sla printer, that is, uses a computer controlled uv light beam which "plots" its trajectory in each layer of the fabrication proccess, the b9 creator is a "sla/dlp" printer - usually also referred as simply "dlp" - because instead of a focused light beam, it uses a "digital light processing" device, also known as a projector, for projecting each layer at once in a defined resolution (usually 1080p). from this description you can guess some artifacts of each method upfront: while the form1-like slas might have inaccuracy from distortion of the light beam in the corners, the b9-creator-like sla/dlps have to deal with the (barely visible) staircase effect of using digital resolution. these two 3d printers also differ very much on their market strategy. the b9 creator relies on a much more open approach to the point of open-sourcing several parts of the printer, specially the slicer ("b9creator software") which is multiplatform.
formlabs, the form1 company, chose to control every little part of their 3d printing ecosystem, which led to a proprietary slicer (preform) for mac and windows only which uses a secret, proprietary protocol to communicate with the printer. even with that, it seems that the form1 design is more often copied than the b9 creator's. the similarities between the two printers are also worth the mention. as they are meant to be low cost, both chose the cheapest of layering strategies. an sla printer can be top-down or bottom-up, and this refers to the direction of the light, not of the movement of the resin vat. the more rare top-down slas beam from the top into the vat below, which might be increasingly filled with resin or have a platform which is lowered into the vat. however, the much more popular bottom-up method sports a vat with a transparent bottom which is hit by the beam, and a rising platform to which the first layer of hardened resin sticks, pulling the part. the bottom-up approach requires a lot less resin to print and has less waste, but suffers from degradation of the vat due to loss of transparency. it also prints the part upside-down.
so, we got right to the problems of sla. the vat is a consumable and formlabs recommends replacing it after only 2 liters of resin have been used on it. the transparent and non-sticking slab, tho, is what matters, so some people came up a way to change it - it's made of pdms, a silicone-based compound. a few brands use transparent ptfe instead of pdms. it's cheaper to replace only the pdms layer, but not much cheaper. a standard form1+ vat costs us$ 60, a half-liter of sylgard 184, the most used brand of pdms, goes for about us$ 45. what about raw material? you can buy a spool of abs for us$ 22, but a liter of sla resin goes from us$ 60 to about us$200. usually you can consider your cost to be three to five times bigger than with fdm. more specialized, industrial resins might cost even more. usually the resins for form1-like slas are marginally us$ 10-20 more expensive than the ones for b9 creator-like slas. yes, they are not completely compatible due to already mentioned factors and you have to pay attention to the specifications when buy one. if you want to assure compatibility with your sla, you must pay attention at least to the curing wavelength - e.g. 405nm (uv is from from 100 to 400nm, visible light from 400 to 700nm) - and power of the beam (e.g. 120mw) or dlp brightness (e.g. 2700 lumens).
it is usually more difficult to make a b9-compatible resin work in a form1-like sla than the opposite due both to the method peculiarities and the lack of flexibility of the sla slicers. as i have stated in the introduction, advertisements do not prepare you for the failure rate of fdm. same thing can be said about sla, although as it has less mechanical parts and no heating element, it is theoretically less prone to danger and failures. but failures exist, and you should be aware of that. first of all, it's very messy; you have to deal with a mildly toxic slime which is very viscous and sticks to everything, being also a pain to clean. you'll have to use vinyl gloves and other forms of protection and also have liters, maybe gallons of isopropanol to help you deal with it. you will also need microfiber cloths and paper towels. aside from the resins, you are dealing with intense light here, so keep in mind that there is a risk of blinding if you accidentally expose yourself to the beam. and also, sla printers require a big deal of maintenance. a few domestic solutions might help, like cleaning the lens with a dslr lens cleaning kit for the lens mirrors. there are lots of stuff to learn - from cleaning the vat to reusing the resin to properly taking care that the stage gets very close and aligned to the bottom,
lest the first cured layer will not stick to it and remain in the bottom, morphing into a barely recognizable horizontal blob of your print. adhesion, by the way, is a big issue in sla too, just as it was with fdm. you will also need a spatula to get prints off the stage, which you might want to remove from the printer. a thin, metal spatula is best, some plastic ones can also work. as you are dealing with a viscuous resin, if your layer has a big continuous flat section, when it is being lifted by the stage if will form a big negative pressure that could just release the part and ruin your print. to prevent this you can alter the geometry with holes or hollow sections to decrease the areas of negative pressure, and the easiest kind of prints for sla are the voronoi sculptures. most of these changes are usually made outside the slicer, in a specialized 3d model fixing software like autodesk meshmixer. in sla slicers you can add supports and rotate/incline the part. this usually thins the cross-sectional areas of the part and also makes otherwise uniform sections to be more gradual, distributing the pressure. note that, different from fdm slicers, it is not common for sla slicers to have infill percentage, it is usually just solid or hollow. the difference on supports from fdm is that the sla print is upside-down, so the supports resists pulling rather than pushing from gravity.
also, you don't have the weak layer adhesion problem from fdm - in sla, the layers are so continuous you can have properly transparent solid parts - so you are able to print very thin cylinders instead of big pillars, which saves on materials. there is another big issue about layers in sla: the cutting mechanism. after each hardened layer, you cannot just raise the stage. the just-cured layer has a big potential to stick to the bottom, so first you have to perform a small motion to unstick this layer and also to dislodge the resin so it fills the voids. the form1 does this with a leaning motion from the vat, the b9 creator does this with a lateral motion and the open-source autodesk ember printer does this with an arc motion. you might have heard of the speedy carbon3d m1 sla printer with an innovative technology which uses oxygen to prevent the layers from sticking to the bottom, saving the need for the time-expensive cutting motion and enabling the printing to be completely continuous. some people even adapted their b9 creator (leveraging its open-source nature, of course) to use something like that. and just as with fdm, there is post-processing or finishing the parts. although horizontal layer lines are often invisible, sometimes they happen.
sometimes you might suffer from alignment and calibration problems which distort the part. you might have rough or swollen surfaces where the light beam was too strong, hardening more resin than it should. you might have weak spots due to weak beams. as with fdm, in large parts you might experience warping effects depending on the resin. most times you will also have sticky parts right out of the stage, because curing is a slow proccess. typically, you will want first to bath the part in isopropanol for a while, to clean the sticky residues, and then, only then, cut the supports. only then you will want to sand rough surfaces, if needed. even then, the part might still be somewhat soft or weak, and might take weeks to complete the curing process or get to its maximum strength. in flexible resin, for example, that can mean as much as three times stronger than when fresh printed.
you want to avoid oxygen when post-curing, because it slows the process. instead of putting the part in direct sunlight, for example, you will prefer submerging it in clean water and let it rest in the sun. an uv curing chamber might be useful, some printers like the titan 1 dlp have the device as an optional. some people use nail curing lamps or diy chambers with uv leds to perform this task. post-curing in excess can also cause warping, along with cracks, decrease of surface quality and pigmentation problems. some upsides are also shared with fdm printers: a great variety of materials are appearing. flexible, castable, extra hard and high resolution resins are already available. with mass adoption, this market is prone to great diversification. there are even businesses that make customized resins for you. by the way, how can a resin be "high resolution"? well, different materials have different energy absorptions, different wavelength curing and so on. some formulations are better to focus the hardening energy in a small spot than others (which spread the energy).
so, they are adequate for smaller "voxels", like "pixels" in 3d, fine details. on the other hand, they will naturally make the print process go slower (because of the high definition) and will be more prone to fail at lower resolutions. so, as with fdm, it is a matter of balance. which one is better, abs or pla? the answer is: depends on the application.
so, these are the main points of dealing with a sla printer. since more people are buying it to use at home, there are some specialized products appearing, like more durable vats, cleaning solutions, special cloths and so on. as an example, there is yellow magic, a cleaning solution sold on amazon which performs better than isopropanol. i hope you find the information here useful and feels motivated to join us in exploring this wonderful technology. happy printing!
