3D Printing: A Multitude of Machines & Materials- SLA/DLP Printing
3D printing comes in more forms than you may realize. In a previous article we focused on FDM (Fused Deposition Modeling) 3D printing, the most common and popular form of 3D printing. I’d like to introduce you to a more complex and precise method of 3D printing which is also consumer available. Let’s talk about Stereolithography and Digital Light Processing 3D printing.
The basics of both processes is that a photosensitive resin is selectively hardened and adhered to a gradually moving platform. Let’s break that down a bit, shall we? Like FDM printing, SLA and DLP printing work on the premise of building up layer after layer of material in order to create an object. Unlike FDM printing, which takes solid plastic, melts it into a liquid, then cools it back into a solid, SLA and DLP printing turn a liquid resin into a solid using light. Both SLA and DLP printing use some form of light to harden their photo sensitive resin. SLA uses a laser to draw out each layer, in a sort of winding path. DLP exposes an entire layer of a model to the light at one time using a specialized projector. If you are interested in looking at more the intricacies of the two processes, I suggest looking at this article from Formlabs.
Let’s talk materials. Whereas FDM printing can print in a variety of plastics and hybrid filaments, SLA and DLP printers are far more limited. The resins used in SLA and DLP can be had in many generic colors, and in a few different transparencies, but “exotic” resins akin to metal/wood hybrid FDM filaments have yet to become available.
How about print area? Most consumer available SLA/DLP printers print areas are noticeably smaller than their FDM counter parts. In general, hobbyist FDM printers (sub $1000 range) have print areas from 4”x4”x4” to 8”x8”x8”. Most consumer available resin printers have print areas in the ballpark of 4”x4”x4” to 6”x6”x6”. Note, these measurements are by no means exact. Resin printers often have the interesting quality of having rectangular print areas (opposed to more common square print areas). If you want to print anything massive, stick to FDM, your sanity and wallet will thank you later. You don’t need the amount of detail that resin printing offers on something larger than a softball. Which is why resin printing is used mostly for very intricate operations.
Another component to resin printing is the higher cost compared to FDM. Though FDM and resin printing is already like comparing apples to oranges, let’s do our best to not throw and bananas into the mix. For this comparison lets focus on the costs associated with using generic resins and generic PLA filament.
A 1kg spool of generic PLA plastic for FDM printing can be had for ~$20. SLA/DLP resins commonly come in 500g bottles, the prices vary a bit, but you can expect to spend ~$50 per 500g bottle. In both cases, buying in bulk can save money, whereas fancy colors/effects bump up the price (these numbers are derived from a quick search of Amazon for both products, a greater study about the costs of different printing types can be found at this link by All3DP). But how far does this material get you? This question is hard to answer, as changing the smallest print setting can drastically affect the amount of material used for a print. Infill percentage, infill type, types of external support structure, wall thickness, these are just a few settings which can affect the amount of materials used. The point being, resin printing is generally slower, prints smaller things, and is more expensive compared to FDM printing.
So why would you ever use a printer which is slower, less versatile, more expensive to own and use? The most significant pro for resin printing is the resolution at which it can print. If you recall from my previous article, it was mentioned that in general, FDM printers are capable of .1mm or 100-micron printing. Meaning that they can produce layers which are 100 microns thick, the thinner the layers the more layers are required, which means more time, but also means more detail. Where an average FDM printer can print 100-micron layers, and an expensive FDM printer can print ~50-micron layers, whereas resin printers can print ~25-micron layers. This means that you can get more detail into your print where it counts. Why might you need this extra level of detail you ask?
There are several applications/use cases where you might want/need this high level of detail. One of these applications is for tabletop game figurines/pieces. If you find yourself engaging in a game of DnD for example. Players can design their characters and have accurate physical representations of them for playing the game. Though you can print these models with an FDM printer, their details may not be accurately recreated due to inaccuracies and limitations of FDM printing, and due to the scale of the figures desired.
Another high detail application is the creation of jewelry. When a high level of dimensional accuracy is key, especially on a small scale, resin printing is appropriate. Whether you are printing a piece which will be used in the casting of jewelry (in which case metal will replace the plastic and the form will be an exact copy), or as an example of the final product, you want that piece to be an accurate representation of the final product. This same mentality can be applied to the prototyping of small mechanical devices where the dimensions of parts must be exact.
A third example for high detail resin printing is for medical applications. The most common application for this type of 3D printing in the medical field is to make dental aligners, those plastic retainer devices. Each patients mouth is different, meaning that their teeth are in different positions and in need of different levels of correction. A scan or mold (which can then be scanned) can be made of the patients mouth which can then be made into an alignment device, which is custom printed for the client. This article by CNN details how a college student did just this, saving himself tons of money.
So, resin printing is not only more expensive, and has a more limited niche of uses, but it has another significant factor to consider. Where FDM printing requires that you remove the scaffolding (support material which allows overhangs to be printed), resin printing requires this step and more to finalize a print. Most resins require that you clean the print gently with isopropyl alcohol. Once you’ve done this, you still have another step. Most resins also require that you cure them with UV light before they are ready to use/display. Hobbyists have done this by setting their prints outside or by a window on a sunny day. Others have used UV lamp devices (commonly used to set manicure products) to accomplish the same thing. High end products do exist which are effectively a large version of one of those UV nail polish curing stations, but they allow for the speedy curing of larger prints.
So, is resin printing for you? That I can’t really say, but hopefully this information has helped you decide if ponying up the extra cash for a resin printer and its accompanying tools is worth it for you. If high levels of detail are your goal, and you don’t mind the smelly resins and cleaning solutions and the accompanying price tag, maybe pick one up and give it a try.