Users often think of the direct usage of the 3D printer’s output part as the final product that the machine can deliver. More often than not, a simple step is overlooked, including the support removal, for example. Post processing a 3D printed model enhances the design, function and sometimes even quality of the part.

In this example, a medical sample of a foot was printed with the Objet Connex series, with a mixed material part consisting of VeroWhitePlus bone structure surrounded by VeroClear outline as the flesh. This part is made possible only with the proprietary technology of Polyjet Matrix, where separate photopolymers of different properties are simultaneously jetted onto the build tray and cured by Ultra-Violet light every 30 micron layer height. The result: a see-through rigid medical sample of a foot that displays an embedded bone structure.

However, as seen in the image below, certain parts are blurry and not entirely transparent. This is due to the geometry of the sample part causing over-hangs which requires generation of support material in the building process. The effect, termed “puff-ups”, is where support material is in contact with the built material, restricting the gloss finishing. Without this support material in the building process however, will cause the over-hanging geometry to fall over, resulting in a failure to build. Therefore, the generation of support material is an essential cause.

VeroClear Foot Raw — 3D Printed Foot with visible support puff ups

The solution in this case is rather simple: Manual Sanding and apply a consistent coat of clear lacquer.

After all the support material has been removed, clean the printed part in water and wipe dry. Be sure to inspect the part for any residual support material, as they may affect the overall sanding if you are going for perfection.

Due to malleable nature of polyjet materials, it is not advisable to use rough sanding. In this case, 800 grit sand paper was used in a wet sanding method. First run the sand paper through water and start polishing areas with “puff ups”. Try to grind against the grains of the printing layer orientation for better effect in smoothing the surface area. For a more consistent job, sand the glossy surfaces too.

As the part begins to accumulate misty or cloudy residue, rinse the printed part with clean water and sand again. Repeat until a generally consistent and smooth surface is achieved before moving up the grit value. For our case, we progressed from 800 to 1000 grit, and eventually 1200 grit. It took an amateur approximately 20 minutes to achieve an acceptably smooth part.

Once completed, rinse the printed part to clear away any sand, dust, dirt or polymer residue. Clean and wipe the part dry, ensuring no foreign article left on the part. A solution to this is to use pressurized gun to blast cool air at the part to dry it completely. You may also leave the part in a cool area overnight to dry it out. Only when the part is dry should the lacquering process begin.

Place part on flat surface where it is stable, or prop it on a jig or fixture for the spraying process. Choose an open area to avoid inhaling the spray fumes, and do remember to shake the can well before spraying. You should also test a few jets of spray to ensure there is no splatter or residual substances from the spray.

At a distance of 10 to 15cm, spray a consistent layer at the printed part and wait for it to dry. Do apply 2 to 3 swift coats of lacquers for better results. Too thin and the effects would not be visible; too thick and the lacquer would start forming liquid trails. When the lacquer coat is dry after approximately 20 to 25 minutes in well-ventilated conditions, flip it over to expose the underside and apply a similar layer of lacquer coating. Again, allow it to fully dry before polishing with dry cloth.

The end result is a more consistent and smooth part, and with overall clarity that would allow visibility on the internal structures.

For more information, please contact us.

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