Post-curing for SLA 3D Printing
Post-curing is a stage of SLA printing that is often overlooked but which can greatly influence the final properties of a printed part. Post-curing isn’t a one-size-fits-all process. There is skill and experience involved in deciding on the right length of post-curing for different materials and part sizes. For some parts post-curing is essential, while for others it is not important at all. Let’s take a closer look at the science behind SLA post-curing and discuss why it important to get it right.
What is post-curing?
During SLA printing, specific areas of resin are exposed to a laser which causes them to cure. Once this process is complete the entire part will be cured, so it may not be completely clear why there is a need to post-cure. To answer this question, we have to understand the properties of hotosensitive resin and how it transforms from a liquid to a solid. While in a liquid state, the resin is made up of lots of unbonded monomers mixed with photoinitiators. Exposing this mix to the strong UV light from the laser causes the photoinitiators to react and for the monomers to bond together and form a polymer. This is the primary curing stage. The cured resin is a crosslinked macromolecule, which means that every part of it is directly connected to every other part of it. However, after printing there will still be many sections which are not crosslinked to the extent they could be, which affects tensile strength and other properties. UV light can be used to complete the molecular bonding and make sure every crosslink that could be made is made.
For the purposes of post-curing, the sun is actually not a bad source UV light. Many hobbyists using consumer SLA printers will simply place printed parts outside in the sun for a while and that gets the job done. However, in more professional settings it is generally standard practice to use a UV oven, which is much more controllable.