I’ve got an invention in prototype. 3-D Printing is great for this step, but to do the production run it is apparent that pouring molds is the way to go.
I’ve got a ton of questions about this process. The sheer mess of it doesn’t worry me at all and I know I need to have more than one mold made.
Past that, I’m all ears for avoiding awful newbie traps and listening to good tricks for successful pours. I’ll be using a 2-part epoxy resin likely with carbon fibers OR fiberglass particulate mixed in for additional strength in the walls.
Been looking into a vacuum chamber of sufficient size to do 2-3 molds per pour. Cuts down on the repetitions, and hopefully won’t reduce the quality and strength at all.
How best to proceed?
The part is roughly .5" wall, 4-sided shape about 8" tall by 4" wide by 3" deep. It’ll have holes and such that I’ll drill in after.
( As an aside, my OtherHalfBrain™ friend urges me to consider a production run in Injected Molding plastic. Seems prohibitively expensive for a run of 40-50 units at a time. )
The biggest pitfall I’ve encountered working with epoxies is timing. Depending on the mixture, catalyst, etc., when it starts to set, you’re done, ready or not.
A source of terror. There are quite a range of set times in the epoxies I am looking at using. That said, I figure I need enough time to SLOWLY pour each of 1-3 molds. Even though I’ll use a vacuum chamber to beat bubbles.
There are 60 minute set times listed. I’m in no rush.
Use a slow hardener to start, and keep heat far away from whatever you’re working on. Epoxy hardening is an exothermic process, and extra heat just accelerates your timing.
What are the3d parts to be replicated like? How many parts are we talking about here? I did this for a living for ten+years so ask away. Any chance all the parts can be 3D printed??
Why are you set on a rigid mold? it just makes getting the parts out more difficult. A silicone mold can be flexed aarounf to releae the part: much easier,
I 've just bothered to reread your OP and the hitch is going to be getting the portion of the parrt that’s inside of this rectangular cylinder.
Have you considered pouring the part in two halves to be glued together after demolding? It would make for much easier demolding.
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There are two different general methods for eliminating bubbles/voids in resin pouring:
Vacuum degassing:
often this is performed on the resin while it is still in the pot (before pouring into the mould) - the vacuum causes any small bubbles to become big bubbles, which forces them to float up and burst - when the vacuum is released, the resin will also flow in to penetrate the materials of any porous filler such as wood flours or fibres
Vacuum degassing can also be done after pouring, while the resin is setting, but this may cause the resin to bubble up and spill out of the mould - also, if the mould is intricate, there is no guarantee that the bubbles will make it out and the space they left will be filled with resin.
Pressure-Potting:
The resin is mixed and poured into the mould and the whole thing is put into a sealed chamber which is pressurised to many times atmospheric pressure - the resin is left under pressure until fully hardened. Any bubbles that were present are not removed, but (in theory, and usually in practice), they shrink right down to the point where they are invisible and no longer a structural problem
I do always wonder if they remain pressurised forever, or if the pressurised air inside gradually leaks away through the material of the resin
I know someone who was rotomolding a very large part in polyethylene and had to refinish the mould every three parts or so. This probably doesn’t apply to your job, but you will need time to maintain the mold.
Can you vacuum bag to a one sided mold, or do you need a 3-D part?
Honestly, you probably should ask your materials supplier for tips. I’ve done just a (very) little bit of fiberglass work, but fiberglasssupply.com has answered my questions. What you’re doing is more complex than anything that I’ve even thought of doing.
