Re: Minimum Thickness for a Reliable Leak Proof Part

From: Sean Wise <sean_at_repliforminc.com>
Date: Thu, 31 Oct 2013 14:25:41 +0000

Since we need to seal FDM parts before we electroplate them we have become quite familiar with how to make things tight and have been surprised at the variables. I'll just list a few observations about the sealing methods first.

1. We have been successful on ABS with both the halocarbon solvent mixtures like those contained in Weldon 3 or 4 or polyurethane clear coats (2 part reactive systems). We have not been able to make things like acetone or MEK work.

2. Polycarbonate needs an impregnation and epoxy sealers seem to work well or high end epoxy paints. PC is very sensitive to aromatic hydrocarbons and it's very easy to degrade your part if you choose the wrong system like a polyester or vinyl ester clear coat.

3. The Ultem can be sealed with a vinyl ester sealer

4. With both the PC and the Ultem you have to design a sealing strategy that does not let the resin leak back out after you've applied them. We often pre-heat parts before coatings are applied so they penetrate and begin to harden while the part is still hot. We always apply two coats but the wait times between coats for the epoxies on the PC and vinyl esters on the Ultem are very different.

We have also found the type of machine matters - a lot. If you have access to high end machines like the Fortus where you can control the overlap of the roads, the smaller gaps between resin beads are easier to seal. If you have a low end system, the machines set the spacing between roads at the factory and they are quite permeable. Some of these are so coarse that solvent sealing with Weldon becomes risky because the solvent penetrates so deeply into the part and wrecks the part. We have also worked with parts from a couple of the low end systems like Makerbot and Afinia. Their parts can be sealed using solvent dipping but I was quite surprised at how easy it was to seal the Afinia parts which have only 0.040" walls that have a cross-hatched fill inside. Apparently, they set their machine parameters to make the walls as tight as possible. They still need to go through a sealing process but they seal up more reliably and I am more confident running a hollow part built on an Afinia machine than any others.

Sean Wise
RePliForm Inc.



From: rp-ml-owner_at_rp-ml.org [mailto:rp-ml-owner_at_rp-ml.org] On Behalf Of ChathamRes_at_aol.com
Sent: Wednesday, October 30, 2013 7:24 PM
To: rp-ml_at_rp-ml.org
Subject: [rp-ml] Minimum Thickness for a Reliable Leak Proof Part

We are trying to determine the reliable minimum thickness for an FDM type process for making a vessel to hold water.

Does anybody have experimental experience with this type of process.

Doug
Received on Thu Oct 31 2013 - 16:25:54 EET