3D Printing post processes – Part 2: Smoothing
Just like any end product, a smooth to touch surface is preferred over an uneven feel. Time to polish those diamonds in the rough!
Sanding for Polyjet
Even though 3D printed polymers from the Polyjet technology are attributed with smooth surfaces and fine features, the meticulous craftsman would further polish his creation for added effect. Additionally, it has been tested that sanded parts achieves a smoother coat of paint, lacquer or gloss.
Using a sanding medium of no less than 800 grit, gradually progress up the sanding resolution to achieve smoothed surfaces. Wet sanding is recommended and always ensure that part is fully dry before applying paint or lacquer coating. Enthusiastic craftsman would even go to the extent of applying Autosol or Metasol for finishing off their sanding process.
Bead Blasting for Thermoplastics
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. Simply subject your prototype to soft cutting mediums such as Plastic blast media (PMB) which ranges in size and abrasiveness. An ideal PMB is Polyplus®, which has a Mohs hardness of 3.5. Use a bead blaster with no more than the recommended 100 psi in a sweeping manner with roughly 60 degrees towards the area in question.
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.
Mass smoothing station for Thermoplastics
Similar to bead blasting, a PMB is usually used to smooth out the printed plastic part. However, this station performs the technique through supersonic/ vibratory agitation for the cutting mediums to smooth the parts out in all directions. Other options for the mediums include ceramics, synthetics, corn cob and plastics.
This process takes slightly longer, but achieves an overall consistency with even the internal structures being considered smoothed out (dependant on geometry and allowance). It is also automated so time taken to smooth a part can be used to print another. This is usually used for large printed parts.
Acetone treatment for ABS
While most thermoplastics are affected by acetone, the impact is most visible on ABS. Industrial grade acetone can dissolve ABS quite strongly and therefore it is advisable to take precautions when handling acetone.
First method involves hanging the printed ABS part over a beaker of heated acetone to generate vapour from its boiling point. Ideally a covered container to trap the vapour would yield better results (as opposed to a upwards smoothing effect only). Take precautions as acetone is highly flammable.
Second method is to apply acetone directly on your ABS surface using a paint brush. Be careful not to over apply the amount of acetone as it would erode the plastic. While the acetone is still wet on your FDM piece, subject hot air using a blaster or dryer to the part to hasten the chemical effects. Sand against the grain while the plastic is still malleable. Apply acetone thinly again for a glossed finish.
Benefits of using acetone treatment on ABS are in its ability to produce a smoothed part with glossy finishing. However, as acetone is an irritant, practice care when handling the chemical. Expect minimal results if you are using nail polish instead of industrial grade acetone.
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