Guide to Post-Processing and Finishing SLA Resin 3D Prints

The foundational step in any SLA post-processing workflow is to remove any excess resin on the surface of the parts through an alcohol or ether wash. This washing step can be done manually by soaking the parts in the solution, or by using an automated machine that agitates the liquid for a pre-set amount of time. The easiest and most effective washing workflow is detailed below. This step prepares parts for secondary processes such as painting, dyeing, smoothing, or polishing. 

Tips for Washing Resin 3D Printed Parts:

• Formlabs recommends washing SLA parts with Formlabs Resin Washing Solution, isopropyl alcohol (IPA), or tripropylene glycol monomethyl ether (TPM). IPA is the most commonly known and used solution for washing resin parts, while Formlabs Resin Washing Solution is a non-flammable alternative that is safe enough for any workspace and can dissolve twice as much resin before becoming saturated to reduce cost per washed part.
• The Form Wash and Form Wash L automatically agitate the liquid to effectively clean parts, even those with channels, negative features, or surface texture. If using a manual solution, move the liquid around yourself to achieve the same result. When creating designs with narrow channels, such as microfluidics, a syringe may be necessary to clean out internal resin and stop resin from curing and blocking channels.
• Some parts may require two washes in IPA or TPM to be fully clean. Many higher volume printing locations have a ‘clean’ wash and a ‘dirty’ wash, to make this step even more efficient. All parts get rinsed in the ‘dirty’ wash first (which can be a manual soaking solution), before moving to a more extreme clean in fresher IPA (often this ‘clean’ wash is the Form Wash or Form Wash L). 
• Formlabs recommends Form Wash alongside Formlabs desktop printers, and Form Wash L for large-format SLA printers to automate washing and rinsing your printed parts.
• Certain materials can be washed together, while others should be separately washed to avoid any particles dissolved in the isopropyl alcohol from affecting the color, finish, or performance of others. The chart below details which resins should be grouped together for best results and for adherence to biocompatible guidelines.

^{*Silicone 40A Resin must be washed in a mixture of 80% IPA and 20% n-Butyl Acetate. If using the Form Wash, add a 2 L bottle of n-Butyl Acetate to the wash bucket and then fill to the maximum fill line with IPA. ** Alumina 4N Resin requires a separate wash. Do not allow Alumina 4N Resin parts to come into contact with water or IPA, as this will cause cracking. Only wash Alumina 4N Resin in the Ceramic Wash Solution.}

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 material properties.

Tips for Curing Resin 3D Printed Parts:

• Post-curing is optional for standard resins. Other resin types, such as Rigid 10K Resin, require post-curing to achieve their optimal 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.

Sanding 3D printed parts is often the best method for smoothing edges, removing blemishes, and getting rid of any leftover support marks. Hand sanding is most effective on simple shapes, but it can be hard or nearly impossible to sand complex objects with deep crevices and internal supports. Media blasting or polishing might be more effective solutions in these cases. 

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 fewer layer lines than parts printed with other 3D printing processes, like fused deposition modeling (FDM). Oftentimes, the layer lines on resin 3D 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 minuscule 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.

Smoothing, coating, and coloring processes can add mechanical benefits as well as aesthetic improvements to SLA 3D printed parts. Each of these processes has its own benefits and drawbacks, and each can impact different material properties to different degrees. When considering these workflows, including whether to bring the equipment and skills in-house or to outsource it, consider the capital cost and skill required.

The summary below shows the barrier to entry and potential outcomes of different advanced post-processing techniques on SLA 3D printed parts.

These steps can be done in sequence to achieve multiple attributes. In this article, we will discuss each option separately. If you are interested in stacking post-processing techniques to achieve a specific outcome, contact our team to speak with a specialist who can consult on your use case.

For certain resins, media blasting can be helpful for smoothing the surface and even improving mechanical properties. In testing conducted on Rigid 10K Resin parts before and after media blasting, the material’s elongation at break improved by 70%, ultimate tensile strength improved by 35%, and impact strength improved by 180%.

Manual media blasting solutions have been available for years and are suitable for low-volume applications or situations where blasting is required once or twice a week for large parts. Manual media blasters are affordable and do not require complex infrastructure. 

For higher volumes, Formlabs’ Fuse Blast is the first affordable, automated media blasting solution on the market. It is designed to complete the Fuse Series selective laser sintering (SLS) 3D printing ecosystem, but can be used as a media blaster for SLA parts as well.