Guide to Post-Processing and Finishing SLA 3D Prints
Stereolithography (SLA) 3D printing has become vastly popular for its ability to produce high-accuracy, isotropic, and watertight prototypes and parts in a range of advanced materials with fine features and smooth surface finish.
However, parts do not come out of the printer 100% finished: they often require post-processing. While parts directly off the build platform are ready to use and smooth, a few extra finishing touches will make parts suitable for a wide range of applications.
In this guide, we cover everything you need to know about post-processing SLA parts, from washing parts in IPA, post-curing them with light and heat, painting, sanding, and more.
SLA Post-Processing Basics
Many users want to know how to paint SLA 3D printed parts, or how to smooth and polish them to create beautiful, customer ready models. In order to do this, parts must be washed to remove sticky, excess resin from the surface. Failing to properly wash parts will leave the parts sticky and unseemly, so post-processing is vital to successful 3D printing.
Washing SLA Parts Tips:
- Formlabs recommends washing SLA parts with isopropyl alcohol (IPA) or tripropylene glycol monomethyl ether (TPM). Most users find IPA is more effective for washing parts. Note that IPA solutions can often only be bought in large quantities, so you should be prepared to store excess IPA for future use. Check for local availability before deciding the best course of action.
- Parts should be moved around in the solvent as well as soaked for optimal cleaning.
- Parts should be washed before removing supports.
- When creating designs with narrow channels, such as microfluidics, a syringe may be necessary to clean our internal resin and stop resin from curing and blocking channels.
- Some parts may require two washes in IPA or TPM to be fully clean. Before finishing, we recommend washing in water. For each part, you should use your own judgement whether the part is fully cleaned.
Form Wash automates the wash process. Parts can be transferred directly from the printer to Form Wash, still on the build platform, or removed and placed in the basket. Once you set the time and press start, you can simply walk away, for as long as you want.
When an SLA part finishes printing, the polymerization reaction may not yet be completed. This means parts have not achieved their final material properties and may not perform as expected, especially tough parts under stress. Exposing the print to light and heat, called post-curing, will help solidify its materials properties.
Curing SLA Parts Tips:
- Post-curing is optional for standard resins. Other resin types require post-curing to achieve their optical mechanical properties.
- Each material should be exposed to the curing process for a specific amount of time. View curing times for each resin here.
To make the curing process seamless and effective, Formlabs designed the Form Cure. Take your parts right out of the wash, let them dry, and place them into the Form Cure; the machine combines temperature and light for optimal post-curing. Select your resin, and the Form Cure will begin the curing process at exactly the right amount of time to maximize the physical properties of your print.
Form Cure is designed for curing parts printed on SLA printers, such as the Form 2 and Form 3, and Form 3B.
Many other methods for post-curing exist, such as natural sunlight, UV nail salons, DIY cure boxes, etc. We strongly recommend using a set up that utilizes both light and heat. While the Form Cure was built to guarantee the perfect cure, with a built in timer for each resin type, users can create or buy custom devices for curing as long as parts are adequately exposed to both heat and light.
Sanding SLA 3D printed parts is often the best method or smoothing edges, removing blemishes, and getting rid of any left over support marks. Hand sanding is most effective on simple shapes, but it can be hard or impossible to sand complex objects with deep crevices and internal supports.
The best way to sand SLA parts is to start with a low grit sandpaper, and slowly move to finer grit levels over time. For example, SLA 3D printed parts can be sanded to be smooth and glossy with 3,000 grit sandpaper. Slowly increase the grit, polishing and smoothing the part until it reaches its desired texture. At around 12,000 grit, the parts should become reflective. If you’re having trouble, sanding your part under running water or on a wet piece of sandpaper can sometimes help create a smooth surface on tough parts.
SLA parts come off the build platform with notably less layer lines than parts printed with other 3D printing processes, like FDM. Oftentimes, the layer lines on SLA printers are not noticeable. This means FDM prints often require significantly more sanding to smooth parts. That said, if you need a glass-smooth finish, SLA does require sanding to fully remove any trace of layers, especially on spherical parts. Slowly increasing sandpaper grit will allow you to eliminate or reduce layer lines to a miniscule level on any SLA part.
The most common reason for sanding 3D printing parts is to remove support markings. As you become more comfortable with 3D printing, it may be worth spending additional time during the print preparation process to angle 3D prints in ways that remove or reduce supports from important parts of a print. For example, if you are printing a bust or model, it is often possible to angle the part so that the model face does not require supports. This will make the sanding process much easier.
Once you are happy with the sanding process, a basic microfiber cloth can be used to remove any minor imperfections and sandpaper powder left on the surface of the print.
If you are performing a significant amount of sanding on a single part, we have found that rubbing the part in mineral oil after a wash can create a super smooth surface finish. Like most techniques, mineral oil may or may not produce significant benefits for your print based on part geometry; you may have to try sanding multiple parts before finding the perfect finishing technique.
Printing With Dyed Resin: This process requires taking 1L of Clear Resin and dyeing it, normally with Alcohol Ink, to create a custom color. The modified Clear Resin can then be put into a Formlabs 3D printer for use, and the part will print in the new customer color that you have created. Alcohol inks completely dissolve into Clear Resin, making it the ideal coloring agent to give you consistent colors throughout your print. If you are going to be coloring 3D printed parts with dyed resin, note that you will want to use a separate wash solution for these parts, as the colored resin will dissolve in the wash. Label your wash solution based to keep track of which types of dyes have been used to make sure you don’t accidentally wash a White Resin part in water containing a dark dye.
Tip: Formlabs Color Kit is a standard integrated color mixing package offered by Formlabs. Color Kit enables 3D printing in a range of colors without the manual work of finishing and painting. To see how the coloring kit works, view the video below.
To see Color Kit in action, check out how birdkids developed a new product using 3D printing with a wide range of materials, including Color Kit, to prototype the color palette for the new product.
Dyeing SLA Parts After Printing: If you don’t want to mix an entire batch of dyed material, but still want to dye your parts, you can apply the dye after printing. You can easily dip regions of interest into different dye solutions to obtain multi-colored parts.
Certain resin are going to be easier to dye than others, such as Clear Resin and Elastic Resin. Once again, we recommended creating an alcohol ink solution and soaking your 3D printer parts, with the supports, in the solution.
One benefit of coloring 3D printed parts with dyed resin is that you do not need to change the color of an entire liter of resin. Instead, you can print multiple parts in Clear Resin and dye them in different colors. Dyed 3D printed parts are also much easier to clean with IPA, as they do not require a dedicated IPA wash.
Painting With Acrylic: For complex models with intricate details, it might only be possible to add some color with the use of paint. Although this process can be time-consuming and the result is determined by your painting abilities, it offers more artistic license to the user. Dyeing SLA parts after printing, or using the Formlabs color kits, will require a separate washing unit so as to not contaminate other parts. Painting with Acrylic eliminates this issue, since parts can be washed and cured like normal, and then painted after they have dried.
Spray Painting: Spray paint creates smooth surfaces and deep color gradients, and is especially efficient for large or flat prints. In the hands of a skilled user, SLA 3D printed parts can quickly be spray painted. The best technique for spray painting is to use multiple, thin coats, ideally done in a single session. A spray-on primer is the best way to paint your printed parts because it quickly covers a surface with an even coating. We recommend you read the Formlabs “How to Prime and Paint 3D Printed Parts” guide for a step-by-step tutorial on best practices on spray painting SLA 3D printed parts.
Final Touch: Coating
For parts that are created to truly impress, there is one alternative step users can take in the polishing process. To fully polish SLA 3D printed parts, you may want to coat them instead of using one of the painting methods mentioned above. Generally a clear spray coating is best to bring parts to a glistening finish. Spray coatings should be applied only after the part has been meticulously sanded.
When coating 3D printing parts, it is recommended to skip the curing process for Clear Resin, as it can sometimes cause yellowing in parts. If the part you are coating is going to be used for pure aesthetics, then curing to bring out its mechanical properties may not be necessary. Instead of curing, a part should be left to air dry after an IPA and water wash. Once it’s completely dry, apply two to three spray coats in a dust-free environment.
Coating can also open up new avenues for using 3D printed parts. One of those is to electroplate the parts in order to change and enhance their useability. Electroplating is an electro-chemical process in which metal ions are deposited in a thin layer on the surface of a part. Electroplating surfaces significantly strengthen their underlying parts and improve material resistance to wear, UV exposure, and corrosion. This is excellent for end-use parts, and is a cheaper alternative to metal 3D printing.
Want to see electroplating in action? Volkswagen printed hubcaps on a Formlabs desktop SLA 3D printer using Clear Resin, then electroplated them with a 0.004-inch-thick layer of nickel. The resulting parts look and feel like metal, but they could be produced quickly as designs evolved, with minimal geometric constraints.
Learn More About 3D Printing
Post-processing SLA parts is not a daunting task. After a few prints, most users are washing, post-curing, painting, sanding, and more with ease. Bringing your creation to life has never been easier with affordable, desktop 3D printing and the knowledge of how to post-process your parts.
Want to hold a high-quality SLA part in your hands? Order a free sample part below.