Improving the results when using Vapour Polishing MJF 3D printed Parts

Vapour polishing, which can also be referred to as vapour smoothing, is a great way to achieve parts with improved aesthetics, sealing and smoothness.  The effect can be profound, the image below show the difference in the same part.

However, there are design tweaks that can be made to enhance the results.

Wall thickness

In theory any wall thickness can be vapour polished.  However, the process relies on chemical solvents condensing out onto the parts.  Thicker parts will "hold cold" longer and attract more vapour.  This results in a greater smoothing / polishing effort being applied to the parts. Ideally we recommend keeping above a 2mm wall thickness.

Very thin walled parts can be sealed effectively using vapour polishing but it will not smooth to the same degree.

With the above in mind, consider the variation of wall thicknesses in a single part.  If thin and thicker walls are designed in the vapour polishing effort achieved may end up being variable across the parts.  Try to maintain as constant as possible wall thickness for best results.

Bridging

This is the most commonly seen issue with vapour polished parts.  Bridging happens where the solvent pools in corners.  It lifts a "skin" to form a bubble.  This can be post processed away but it is quite labour intensive and difficult to achieve a good finish.

Angles under 90° on parts with a vertical aspect (as hung) are most prone to bridging.

Bridging can be minimised in the process but it will lead to a lighter processed part.

Hanging / mounting of parts for vapour polishing

It is worth consideration in the design phase as to how parts are to be supported during vapour polishing:

Hung parts

Rod mount: The quickest and most efficient for batch / production MJF printed parts

Ideally a hole needs to be available with a 2mm or greater diameter.  This way a stainless steel rod can be quickly threaded through the part.  Take care though that the way the part hangs on the rod does not touch any visible area of the parts or they may be marked.

This can be achieved with a "snap-off" eyelet if no "natural" hole is available in the part.

Clip mount: Good for high quantities but leaves a mark

We use small crocodile clips to attach some parts.  These are great and very quick / secure.  However, the teeth will leave pin prick marks in where they grip.  This is fine on a concealed area of the part  but not on an A-Surface.

Mounted Parts

Heavier parts can be placed on PTFE "pins" to support them.  This is fine but they leave a mark (typically a 2mm diameter circle).  ideally a B-Surface should be available for this approach. 

Material:

Fore knowledge of the material is vital before running a vapour polish run.  Different materials need different "recipes" to achieve the best results.  For example if you run TPU on a Pa12 program the result will be a dripping mess.  If in doubt please consult us as we have run everything from ABS to PEEK.

NOTE:  The above guidelines apply to AMT Postpro machines, for other manufacturers please consult them.

Common issues in Vapour polishing to look out for:

Pitting in Vapour polished parts:

Not so much a concern for AMT systems but can still be an issue if the substrate is quite porous.

Bridging in Vapour polished parts:

As mentioned above bridging will mainly occur in tight corners.

If you have any concerns over your design for Vapour polishing of parts then please do not hesitate to get in touch to talk it over.  You can raise a contact request here via our webform or give us a call.

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