Sunday, December 2, 2012

Pourable OOGOO

Recently I have developed an interest in using resin casting to produce small numbers (several dozen at most) of high-quality plastic parts.  The motivation for this is to be able to produce stiffer epoxy parts for my CNC quickly and at relatively low cost.  I've mostly been investigating a material called OOGOO, a Sugru 'substitute' made from silicone and cornstarch which is cheap, easy to get the raw ingredients for, and seems very well suited to casting resin parts, based on my experiments.  Below you can see the first ever resin casting I've made; I freely admit that it's a piece of junk, but turned out surprisingly well given the amount of knowledge I had about casting and is impressively strong compared the the 3D printed original.

However a drawback of OOGOO is that it basically forms a putty, so quite a bit of care is needed to make sure that you get good contact with the pattern in order to not leave voids in the mold.  People have tried making a pourable OOGOO using Xylene as a thinner (see comments in the OOGOO Instructable link above), but I can't seem to get Xylene in quantities less than about 4L, which is way too big a container to store in my apartment.

I've read in random forums that White Gas can be substituted for Xylene to thin OOGOO. 'White Gas' appear to be a catchall term and may or may not be lighter fluid depending on the brand and region where you live. So I decided to give it a go with lighter fluid to see i) if it thinned OOGOO to the point where it could be poured and ii) if the thinned OOGOO would ever set up properly.  The results, at least at the early stages, are 'yes' and 'maybe' respectively.  I'm hoping that a bit of time will change this to 'yes' and 'yes'.

After mixing a lot of lighter-fluid into the OOGOO, I definitely obtained something pourable.  I have no idea how much, I was simply winging it, but I would guess two parts lighter-fluid to one part each of silicone and corn-starch.  I poured it over a scrap PLA printed part, not knowing if the lighter-fluid would dissolve it:

At this (estimated) ratio, it was still quite thick, probably comparable to a cold molasses and so some coaxing was required to get it onto the part.  However it slowly settled on the part and settled around it.  I used PAM cooking spray as a release agent, again hearing on a random forum that it worked well.

Next time I would skip the release agent since I don't think the OOGOO sticks particularly well to the PLA printed part, and wherever it contacted the part but other OOGOO flowed over it the two bits of fluid would not adhere well.

Detail transfer from the part was excellent, but the OOGOO remained very, very soft after about an hour.  I'm hoping that this is simply because the majority of the solvent (lighter fluid) hasn't evaporated yet, and that once it does the mold will be more rigid.  At the moment the material is not stiff and tear-resistant enough to be usefully used as a mold, it will simply get destroyed when demolding the first few parts.

The bits left inside the jar that I mixed the thinned OOGOO appear to be much stiffer, so I'm hoping that a few days left to blow off the volatiles from the lighter-fluid will result in a stiffer material, but even several hours in the mold is still quite spongy.  I'll check it again after a few days and see if the mold is somewhat usable.  If so then I will probably start thinning my OOGOO.  I've also disccovered a tin of Xylene on the shelf in the parking garage, so I may steal a hundred mL or so, and if it works better, replace the tin with one I can dip into guilt-free from time to time.


treg said...

Can you tell me if this ended up working for you? Also, after curing was your mold still flexible? I'm thinking of making a silicone "pan" for the bottom of a small china cabinet that I am turning into a reptile cage. It would need to remain flexible be able to remove it from the door opening which is smaller than the bottom of the cage. Thanks for your time.

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coal4k said...

Why not just use the liquid silicone and omit the corn starch? Maybe a bit of mineral oil to keep it from drying too stiff?