Sealing FDM Parts Overview
For any FDM application, bead blasting with plastic media is an ideal solution. Inexpensive and quick, your model, part, pattern or tool can have a great surface finish without sandpaper, fillers or solvents. While sanding a rapid prototype can take hours, bead blasting an FDM part takes only a few minutes. This simple process also preserves a part’s quality since it will not distort it or change its dimensional accuracy. Plastic blast media (PMB) is a recycled material made of finely reground thermoplastics. This media lasts longer than glass bead, and it is available with abrasiveness that ranges from mild to harsh. PMB costs U.S. $110.00 per 50 pound (22.7 kg) bag.
1. Prepare Model: After removing support structures, apply masking tape to areas of the model where a bead blasted surface is undesirable. Masked areas may include parting surfaces of tools or sharp, outside corners that could be rounded by bead blasting.
2. Setup Bead Blaster: Plastic blast media (PMB) ranges in size and abrasiveness. An ideal PMB is Polyplus®, which has a Mohs hardness of 3.5 and a 20/30 U.S. standard sieve size (0.84/0.58 mm). Loaded with PMB, set your bead blaster to a pressure that does not exceed 100 psi (689 kPa). Start with a low pressure and gradually increase it until you get the desired result. Excessive pressure will make divots on the part surface and break down the media.
3. Bead Blast Part: Holding the spray gun at a 60 degree angle from the part, lightly bead blast all surfaces (fi gure 2). Do not dwell in one area. Instead, use a continuous sweeping motion similar to that for spray painting. To avoid damaging the part, use several light passes of the bead blaster rather than one aggressive pass. After bead blasting the part, inspect it and repeat as necessary.
When complete, rinse the part. The FDM part is now ready for use as a functional prototype, pattern or tool,