model for cast iron casting

[Andrea]

Hello guys,

I would like to create a 3d model to be used as "model" for foundry process.

I try to explain that better.... I need to create a "negative part" of the part to be produced in the sand of foundry. Instead of model made with wood I'd like to try to use a 3d printed model.

Someone of you have tried to use 3d printed model for this process?

[awerby]

Usually, with the sand-casting process, you make a positive form to use as a pattern, not a negative mold. The sand itself becomes the mold once you press it around the form, at which point the pattern is removed. Basically, you split your model in half across the parting line, and attach a piece to both sides of a board, keeping them registered top-to-bottom.

If you're building a model to use directly as a sandcasting pattern, make it strong enough to withstand the pressure of the jolt-squeeze machine, give it enough draft to remove cleanly (2%+) and make sure the surfaces are smooth, especially any that aren't facing straight up.

Andrew Werby
Juxtamorph.com

[Sebastian Finke]

Something like this may interest you: ExOne S-Print

[Frazveragan]

Hi Andrea,

I'm actually a bronze sculptor and the process is pretty identical to cast iron. You have a few options. Essentially you have to get your object into a positive medium the foundry can use to create the investment mold (sand). Traditionally this is wax.
I have heard of foundries using ABS and PLA as that positive, but you'll want to check with the foundry first. Since most casting patterns are wax, you might run into a lot of foundries that won't want to use ABS and PLA because during burn out (melting wax out of the investment sand). The reason is that it has to be burned out separately from any wax because the wax is reused.

Traditionally, your fist "model" is used to create a mold, which is then used to cast the wax the foundry uses. It is possible to 3D print your molds to cast the waxes as an alternative to sending the foundry the actual 3D Print. You can also use the 3D print to make the traditional silicone or urethane rubber mold to cast waxes.

If any of that doesn't make sense, I'd be happy to describe the process in more detail.

[curious aardvark]

you can also buy wax filament suitable for foundry moulding that works in most standard fdm printers

[awerby]

I've done both sand and investment casting, and they're quite different processes. It sounds like the original poster was talking about sand-casting, since iron is rarely cast any other way. For that, you use a pattern board, not a wax pattern. The advantage is that a single pattern board can be reused to make a large number of sand molds, while one must make a separate positive wax form for each lost-wax investment casting.

I've heard of people using PLA prints in place of wax; apparently it burns out pretty well. ABS is less suitable for that, but it would work as a master for silicone molding, as you mention.

[Frazveragan]

I've done both sand and investment casting, and they're quite different processes. It sounds like the original poster was talking about sand-casting, since iron is rarely cast any other way. For that, you use a pattern board, not a wax pattern. The advantage is that a single pattern board can be reused to make a large number of sand molds, while one must make a separate positive wax form for each lost-wax investment casting.

I've heard of people using PLA prints in place of wax; apparently it burns out pretty well. ABS is less suitable for that, but it would work as a master for silicone molding, as you mention.

This is true, a pattern board vs. lost-wax really changes the op's options. My bad in not distinguishing: I know of some foundries that use lost wax for cast-iron, which is what I was trying to say.

I've also heard the PLA burns out well, whereas ABS often taints the investment molds with a residue. As I understand it, the issue more foundries appear to take, if they're going to take one, is that they can't burn the PLA out in the some kiln as investments with wax, but again that's foundry to foundry so it's worth asking. As far as the quality of the cast, if the original PLA has a lot of visible layers, those will all show up in the metal. In my case, I've stayed away from PLA because the filament printers I'm working with don't hit the level of detail I need in my casts/require too much clean up and re-texturing. Naturally, it all just depends on what you're going for as the end result.

[Andrea]

Usually, with the sand-casting process, you make a positive form to use as a pattern, not a negative mold. The sand itself becomes the mold once you press it around the form, at which point the pattern is removed. Basically, you split your model in half across the parting line, and attach a piece to both sides of a board, keeping them registered top-to-bottom.

If you're building a model to use directly as a sandcasting pattern, make it strong enough to withstand the pressure of the jolt-squeeze machine, give it enough draft to remove cleanly (2%+) and make sure the surfaces are smooth, especially any that aren't facing straight up.

Andrew Werby
Juxtamorph.com

You have understand what I need to do! I will use the 3d printed pattern in order to create a sand mold.

The pla resist to compression forces in order to create the sand mold? Or do I need some others materials?

I think that the pla is very easy to print.
so if it's possible to use that material it's better