Post-processing techniques in 3D Printing

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Post-processing techniques in 3D Printing

In this article we are going to discuss in detail some of the most commonly used post-processing techniques on 3D Printed parts.

Finishing:

The finishing operation usually consists of polishing the parts. We use Vibratory Polishing as a finishing process to improve surface finish of the parts by removing minor surface irregularities. The setup consists of a tumbler and polishing media. The size of the polishing media and type is chosen based on the material of the part geometry that needs to be polished, and level of polishing desired. The parts are then put into a tumbler — housing the polishing media — which vibrates at a certain frequency for a stipulated time duration.

Vibratory polishing process

Vibratory polishing is extensively done on parts fabricated through Selective laser Sintering(SLS) technology, to improve the grainy surface inherently achieved through this technology.

Vibratory polished part which was later dyed Red.

The maximum part size that can be vibratory polished is 100 x 100 x 100 mm. Vibratory polishing usually adds an extra day to project’s lead-time.

Painting:

Since majority of the 3D Printed materials have an inherent whitish color, most of the times the parts are painted to give them a desired color and finish. A typical painting process consists of coating the parts with a layer of putty followed by a coat of primer, after which, the parts are painted in the desired color. This gives the 3D Printed parts a smooth surface finish. The parts can either be painted matte or glossy. Primer and Putty usually adds an extra layer of material on the part and the part dimensions increase by approx. (+/-)200–300µm. As a result, we do not advise painting(putty+primer) on functional parts unless a suitable allowance is given in the design.

When functional parts need painting, we ‘smoke coat’ the parts with a layer of paint without applying any layer of putty or primer. What this smoke coat does is, it retains the part’s original material texture without hampering the tolerances. But since smoke coat is a single layer of paint applied directly to part’s surface, the paint is susceptible to wear.

3D Printed part with black smoke coat

Painting is a manual and skilled job, and the entire process adds 2 extra days to project’s timeline.

Painting can be done on almost all of the 3D Printing materials. Painting is a bit difficult on powder based materials like Nylon when multiple colors are to be painted on the same part. These materials are slightly porous in nature and thus the color has a tendency to bleed near the boundaries where two or more colors meet. When painting Nylon parts, the non-paint areas have to be masked, which makes painting a fairly tricky job.

Dyeing:

Just like painting, dyeing too is a coloring process. The parts are immersed in a container with a solution of water and dye(color). Dyeing is facilitated by capillary action, and thus it is well suited for materials that are slightly porous in nature. Hence, dyeing is done on powder based materials like Nylon and Glass-Filled Nylon.

Dyeing is a surface phenomena, so when the parts are dyed, the dye sits comfortably within the pours of the part. As a result, dyeing doesn’t add any extra layer of color on the parts. Hence, dyeing is well-suited for functional parts subjected to assembly. The maximum part size that can be dyed is 100 x 100 x 100 mm. Dyeing process adds 2 extra days to project’s timeline.

Dyed 3D Printed part

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