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11 May 2018 15:31
Achieving a First-Class Finish for Your SLA Parts
As the first ever 3D printing technology, Stereolithography (SLA) offers a cost-effective way to produce parts with a high degree of accuracy and smooth surface finish using a range of materials.
However, to achieve a truly high-quality finish for your SLA parts, a range of post processing options should be considered. This is especially the case for SLA prints as they require support structures which, when removed, can leave marks or ridges on the surface of your part. In today’s tutorial we’ll explore a range of post-processing options for SLA printed parts as well as the things to watch out for during the post-processing stage.
Post-Processing steps for SLA
- Clean your SLA print
Once your SLA part has been printed and removed from the build plate, it will still have some liquid resin on its surface that will need to be removed. To clean your part, you will require Isopropyl Alcohol (IPA) as well as a container large enough to dip your print into. Put your SLA print into the IPA and leave it there for about 10-20 minutes before taking it out and letting it dry.
- Remove support constructs
Support constructs are an essential part of the SLA printing process, helping to prevent deformation and warping. As the supports are made from the same material as the final part, support removal for SLA must be done manually – the use of chemical baths (FDM) or other hands-free methods are, in this instance, not possible. Luckily, manually removing supports is relatively simple; for example, they can be easily removed using a pair of pliers or by snapping them off by hand. However, with small and delicate parts, a better option would be to remove them with a razor blade or an X-Acto knife.
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 polymerisation process. The post-curing process works by exposing your part to UV light and heat. To do this, the part must be placed into a UV oven for roughly 10-20 minutes, and rotated once or twice to ensure that all areas of the part have been exposed. Post-curing can also be achieved using natural sunlight.
Finishing options for your SLA print
With a variety of finishing options for SLA prints, it is possible to achieve a smooth first-class surface for your parts.
Once the support structures have been removed from your part, sanding is done to smooth out any marks or blemishes that have been left on the surface of the print. It is typically better to hand sand your part, lightly working the surface with a lower grit sandpaper and gradually increasing the sandpaper grades at least four times to finish with the finest grit sandpaper.
The areas of the print that have no touch points from the support structures are considerably less labour-intensive, but still require sanding to remove any layer lines and to ensure uniformity. Be sure to use a light touch to avoid damaging small details or affecting the dimensional accuracy of your part. Mineral oil can also be used following the sanding process to create an even finish for your part.
Wet sanding can also be applied to your SLA prints to achieve an even smoother surface finish, with the supported side of the part requiring several graduations of sandpaper.
If you want to paint your SLA print, it is often a good idea to prime your part first, to achieve an even more uniform look for the print. Aerosol primer is a one priming option that covers the surface quickly and evenly, concealing any layer lines. For the best results apply three to five thin coats of primer every 10-15 minutes. To eliminate any imperfections that may appear during the primer coating, you can an 800 grit sandpaper a few hours after the last coat.
If you want to go one step further to transforming the look of your part, then spray painting it can often do the trick. Spray painting can also help to hide any visible layer lines. Before applying any paint, however, it’s important to clean the print of any dust or dirt using a tack cloth. Once this is done, your print can easily be painted with the desired colour. It is advisable to spray paint your part across its surface, rotating it to ensure an even cover. Ensure that the paint has dried before applying the next layer of paint – typically two to three layers of paint will be required. A glossy varnish followed by painting will create a great finished look.
Things to watch out for
- Isopropyl Alcohol is a volatile solvent, so consider wearing goggles and protective clothing such as latex gloves and make sure your workspace has proper ventilation.
- When washing a print in IPA, be careful to strike a balance between neither underwashing nor overwashing your SLA part. This is because you may either not have cleaned your part of all the liquid resin, or the print might absorb IPA, affecting its integrity.
- It is advisable to remove supports after washing your part in IPA, since freshly built parts are prone to warping.
- When sanding, ensure that you wear gloves to protect your hands from resin dust.