how do resin printers work?
In: Technology
I’ll add some to what’s already been said. I was not feeling like writing my reply at the late hour on the phone when I saw this pop up.
Filament printers melt plastic to make a print. Think of it this way: someone already went through the trouble of making the large molecules that make up the polymer (plastic). They’re like spaghetti all tangled together. So you can melt the filament to untangle the spaghetti and make something else with it.
Resin printers work differently. You have the building blocks to make the big polymer molecules rather than the molecules already made. The molecules have chemical groups, usually acrylates, that when exposed to light react together to make the big molecules. Unlike filament where the molecules are basically together but separate, when you expose the resin to light, you also make links between the molecules you make. That means you have something with a lot of chemical links that you can’t melt afterwards, that’s what we call a thermoset polymer.
The resin actually has the building blocks to make the material and something called a photoinitiator. This is basically what uses the light to get the reaction going.
Most resin printers use light at around 405 nm, basically at the edge of visible light and ultra violet. The light hits the photoinitiator which basically says: “it’s go time” and make the resin react to make the solid part.
As to how the printers work, there are basically three types:
1. The original type of SLA printers. You have one or more lasers with mirrors that move to direct the laser on the resin to make the shape you want. You build the part layer by layer. This has some advantages as you have have much higher light power and make things react faster. The laser spot size can also be controlled to an extent to get a nice part definition. The downside is that since you have to have the laser spot “scan” the surface of each layer, it takes time. Original designs had the laser above the resin vat and the build plate lowering in the vat. More recent laser type designs like the Formlab Form 1 to Form 3 series have the laser expose under the vat where the bottom of the vat is transparent.
2. DLP. It works just like home projectors. You have a series of micro mirrors that direct the light to the vat or away from the vat. This lets you expose a complete layer at once. DLP has the advantage of using less power compared to other types of printers and it is faster than laser type printers. It has very sharp definition of pixels too. The projector units have a high lifespan. The main downsides are that Texas Instruments owns the patents on the technology and high resolution projector units are expensive. That is why you only have two consumer DLP printers (Anycubic Photon D2 and Elegoo Mars DLP). You see the tech a lot more in expensive business oriented resin printers.
3. MSLA or masked SLA. This is the tech you will find in most resin printers you can buy for a few hundred dollars. You have a board with an array of 405 nm LEDs with plastic lenses on top of it. Above that is a monochrome LCD display. The LCD does the same thing the DLP projector does, it exposes an entire layer at a time making the prints faster than a laser with mirrors. The main advantage is that it is cheap to produce such printers. They’re great for hobbyists. Disadvantages however are numerous. Firstly, the displays will degrade over time leading to the need to replace them. About 500 hours of light exposure (not print time as the light isn’t on all the time during printing) before you start losing energy and about 2000 hours before you have trouble printing with typical resins you can buy. The LED arrays tend to die at the 5000 to 6000 hours mark (again, time they are on, not print time). Sourcing parts can be difficult as the models get updated often, so you may need to change printer once a display dies. Also, the LCD will let light bleed around pixels like any LCD, this makes for less defined small details, but also prevents the “jaggies” you would see on a DLP print without anti-aliasing. Don’t let that stop you from getting a LCD printer though, in terms of hobbyist use, it will last you a long time. It’s when you get into custom resins and the like that LED printers can really cause you issues.
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