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.
Introduction to 3D Printing With Desktop Stereolithography (SLA)
Looking for a 3D printer to realize your 3D models in high resolution? Download our white paper to learn how SLA printing works and why it's the most popular 3D printing process for creating models with incredible details.
SLA Post-Processing Basics
Washing
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.
Formlabs recommend Form Wash alongside Formlabs desktop printers, and Form Wash L for large-format SLA printers to automate washing and rinsing your printed parts.
Curing
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.
- For biocompatible materials, post-curing is necessary to achieve the safety standards determined by regulatory agencies.
- Each material should be exposed to the curing process for a specific amount of time. View curing times for each resin here.
Form Cure and Form Cure L, the two post-curing solutions from Formlabs for desktop and large-format SLA 3D printers, are designed to post-cure parts printed in Formlabs Resins with speed and consistency. With Form Cure and Form Cure L, SLA 3D printed parts can be post-cured at precisely the correct wavelength, at different temperatures, and for varying lengths of time.
A Guide to Post-Curing Stereolithography (SLA) 3D Prints
In this white paper, learn the basics of post-curing and how to adjust your process to save time and achieve the best performance.
Sanding
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.
For anyone focused on high-quality, precise SLA parts, Formlabs Finishing Tools is a set of curated products designed to streamline the SLA post-processing workflow and help users achieve superior surface finish, perfectly smooth planes and edges, and an elevated appearance, all while driving down your labor time and cost per part.
Painting
An example of a SLA 3D printed part painted with acrylic.
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.
Clear resin mixed with alcohol ink.
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 printed 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. As painting is done after the part is already washed and cured, this workflow also does not require a dedicated IPA wash.
A skilled painter using acrylic can bring parts to life.
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.
Coating
For an installation in Times Square, Window to the Heart, the Formlabs and Aranda/Lasch teams worked with an auto body shop to spray coat each tile in Lesonal Universal Clear.
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.
Electroplating
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 SLA 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.
Download our white paper to learn more about SLA 3D printing. Want to hold a high-quality SLA part in your hands? Order a free sample part below.
