How is a first-class finish achieved for SLA parts?
As the first commercial 3D printing technology, Stereolithography (SLA) offers a cost-effective way to produce parts with high accuracy and a smooth surface using different materials.
However, to achieve a truly high-quality finish on your SLA parts, you should consider a range of post-processing options. This is especially true for SLA prints, as they require support structures that can leave marks or ridges on the surface of your part when removed. In today's tutorial, we'll explore a number of post-processing options for SLA printed parts, as well as things to consider during the post-processing phase.
Post-processing steps for SLA
Clean your SLA print
After your SLA part has been printed and removed from the build plate, it will still contain some liquid resin on the surface that needs to be removed. To clean your part, you will need isopropyl alcohol (IPA) and a container large enough to submerge your print. Place your SLA print in the IPA and leave it there for around 10-20 minutes before removing it and allowing it to dry.
Remove supports
Supports are an essential part of the SLA printing process and help to prevent warping and distortion. As the supports are made of the same material as the final part, the support for SLA must be removed manually. The use of chemical baths (FDM) or other hands-free processes is not possible in this case. Fortunately, the manual removal of supports is relatively simple. For example, they can be easily removed with pliers or by snapping them off by hand. However, for small and delicate parts, it is recommended to remove them with a razor blade or an X-Acto knife.
Post-curing
While this is an optional step, post-curing your SLA part can significantly improve the mechanical properties, strength and performance of your part by completing the polymerization process. The post-curing process works by exposing your part to UV light and heat. This involves placing the part in a UV oven for approximately 10-20 minutes and rotating it once or twice to ensure that all areas of the part have been exposed. Post-curing can also be achieved with natural sunlight.
Finishing options for your SLA print
With a variety of finishing options for SLA prints, you can achieve a smooth, premium finish for your parts.
Sanding
Once the support structures have been removed from your part, sanding will remove any smoothed spots or stains on the surface of the print. It is usually better to sand the part by hand, lightly finishing the surface with a lower grit sandpaper and increasing the sandpaper grade at least four times to finish with the finest sandpaper.
The areas of the print that do not have touch points from the support structures are much less labor intensive, but still need to be sanded to remove any layer lines and ensure uniformity. Use a light touch to avoid damaging small details or compromising the dimensional accuracy of your part. Mineral oil can also be used after the sanding process to achieve an even finish to your part.
You can also apply wet sanding to your SLA prints to achieve an even smoother finish, with the supported side of the part requiring several sandpaper gradations.
Primer
If you are looking to paint your SLA print, it is often a good idea to prime your part first to achieve an even more uniform appearance to the print. Aerosol priming is an option for priming that will quickly and evenly cover the surface and hide any layer lines. For best results, apply three to five thin coats of primer every 10-15 minutes. To remove any imperfections that may occur during priming, you can use 800-grit sandpaper a few hours after the final coat.
Spray Painting
If you want to go a step further to change the look of your part, spray painting can often do the trick. Spray painting can also help hide any visible plane lines. Before applying paint, however, it's important to clean any dust or dirt from the print with a duster. Once this is done, your print can easily be painted with the desired color. It is advisable to spray the piece over its surface and rotate it to ensure even coverage. Make sure the paint has dried before applying the next coat of paint. Two to three coats of paint are usually required. A glossy varnish followed by painting gives a great finished look.
Things to look out for
Isopropyl alcohol is a volatile solvent. Therefore, remember to wear safety goggles and protective clothing such as latex gloves and ensure adequate ventilation in the workplace. When washing a print in IPA, be careful to find a balance, as washing your SLA part too often or for too long can cause the wet part to absorb IPA. It is advisable to remove support structures only after washing your part in IPA, as freshly built parts tend to warp. When sanding, make sure you wear gloves to protect your hands from resin dust.