recasting Question

[jwinges]

Hey all you recasters.

Have any of you been watching that creature vs creature show on discovery channel. Each week they make a mold of the skulls of whatever animals will be fighting. The cool thing is is that they are making them out of Aluminum.

What I was wondering is if this process could be reversed so we can make aluminum molds easily so that molds will last longer?

WHat they'be been doing is making the skulls out of styrofoam and putting them in a mold box with sand. THen they pour hot liquid aluminum into the sand via some well placed funnels

So do you think this could work if we used our regular molds instead of styrofoam. I would think that the molten aluminum would melt the mold material. OR do you think we would loose all the detail?

Mods...sorry for posting this since you have reservations on recasting but I thought this might be a good solution for those projects deemed acceptable for this site.

Thanks

[Stamen0083]

Sand casting and resin casting are quite different beasts. From your post, I understand you're saying that they're using sand as the mold material, and aluminum as the skull, right?

Reversing the procedures so that we use aluminum as the mold is not a good idea, since the whole point of resin casting is using the rubber mold's flexibility to capture details and allow undercuts. With metal as a mold, there are many things that must be taken into account.

By the way, Bandai uses metal molds to make plastic models. The process is called injection plastic molding.

As far as using aluminum as the "resin", I don't think the heat will pose much of a problem to the molds. People have been casting white metal for many years now. Of course, white metal has a considerably lower melting point than aluminum.

[kanata67]

why settle. Feel free to make me a completely alluminum 1/55 seeker. Maybe a metal 1/48? It would be the perfect lawn dart

[Mervin]

I havent browsed this site in detail, but it seems they have all you need to make metal molds.

http://shorinternational.com/model.htm

[jwinges]

I'm not talking about making metal recasts...just metal molds so the molds will last longer. I use to work in a plastec injection molding manufacturer (think every 3m or motorola part made). So I know how the injection molding works.

Just trying to find a way to make better molds that last longer for our resin recasts. Or better yet we could make recasts out of plastec.

[Grayson72]

The beauty of the rubber molds is that they're flexible so you can cast complex shapes and bend the mold when you want to pry out the parts. Metal molds you have to break the parts down into separate pieces.

[Valkyrie]

Well, there are a few inherent flaws in that theory. Let's say I were to use that method to make an aluminum mold...

1) I'd have to make a silicone mold with my usual methods, then cast those mold halves in aluminum (more work already)

2) I'd need access to a foundry workshop (which I haven't had since high school)

3) The aluminum mold halves would come out of the sand very rough, and would have to be cleaned up in order to give the resin casts a smooth finish (and not be caught up on the rough mold surface, for that matter)

4) the mating surfaces of the mold hanles would have to be cleaned up also. And since it would be imposible to get them to mate perfectly after all that work, there'd be tons of flash in the resin casts.

5) And most importantly, as Grayson mentioned, by making the molds metal, I'd be losing the most important property of my silicone molds. Their ability to flex. Their flexability is what allows me to make molds of complex shapes, and parts with undercuts. A metal mold can't be used to create parts with even slight undercuts.

I'll stick with my silicone, thank you

[Grayson72]

Ain't nuthin' wrong with sillicone 8

[jwinges]

i see

[MSW]

aluminum is also quite soft and prone to scratching if improperly handled...also the chemical componets in resin may prove damageing to aluminum with repeated exposure...maybe even premature oxidation (yeap, even aluminum "rusts")...

If you are planning on casting many parts, it can be most helpful to develop your molds in such a way as to be easily replaced...typicaly this is done through "skin" molds...basicly each half of the mold is further broken down into two pieces...a larger solid outer shell (fiberglass, plaster, etc..) and a inner easily replaced "skin" of silicone...

gives a brief description:

http://www.resincasting.co.uk/moldmaking.html

[Culverin]

um, what about the injection molds on say a plastic bandai kit?

sure you lose the ability to do undercuts...

but i think a mold that lasts virtually forever kinda offsets more parts... we are modelers we can deal with more parts... i mean like a mastergrade kit for gundam isn't bad at all...

[Grayson72]

Those aren't aluminum though, they're made out of stainless steel and often laser engraved.

[MSW]

And often cost in the region of $150,000 just to machine a set of plastic injection molds...add in half a million or so for the actual injection-molding machine (which can be as large as a city bus), a couple grand for a supply of the materials...and you are all set...course you may also need to contract with an electricion inorder to get electrical power to the machine (some of them run on odd power requirements...208 volt systems...rather then the common 110 and 240 systems ) ...course you may also run into problems with the molds keeping cool, and so may need to contract a plumber to set you up with a water supply system to feed internal cooling passages that will need to be machined into the molds...also a computer material mixing station would prove most helpful if you want to do any "molded in color" parts...

Yeah, all of that would be really nice...but you would have to sell a lot of kits...and I mean a LOT!...just to break even on your costs to produce the molds (let alone pay for any of the other needed equipment)...