Investment casting vs. sand casting of aluminum

I’d like to get a vessel cast in aluminum, but would like some advice;

I’ve never done an investment cast - I though it was like lost wax casting - can anyone explain the steps?

i have a CAD file to make an SLA part; can you use an actual SLA part for investment casting? Does the melted resin mess up the mold?

how good are the surfaces once the part is complete?

I thought about sand casting, but I fear the surfaces will require a lot of benching to get the smooth - chromelike surface I desire for this part - Will investment casting get me any closer to a chromelike polished surface than sand casting?

Any ideas or advice? Thank you

I’m no metal casting expert, but I know you can do an investment cast straight from a rapid prototype…not a SLA though. The finish from the investment casting wont be perfect and will need a bit of post work. You also need to watch your tolerances to make sure your mating parts will still fit. Castings shrink as well…so your best bet for more info would be to go speak to a metal casting shop or a RP place with metal casting contacts and I’m sure they will be able to give you far more info.

also…take a look here on the investment cast process,

…as I think you have missed the fact that your ‘pattern’ and ‘ceramic mould’ gets lost every time you make a casting. So if you need more castings you make more ‘patterns’ from separate mould

sounds like you’re looking to do a one off piece right?

You can do investment casting with a piece from an SLA, FDM, 3DP or similar rapid prototype machines, but different machine at different places are going to use different base materials based on their needs. They also make some base materials specifically for casting.

The surface quality with this will however be somewhat limited by the fidelity of the machine, but rather than cast and work the Aluminum to achieve a better surface, why not sand / finish the rapid prototype part? This may be complicated by your base material, but this is pretty common. If you go this route, you may want to scale the form up just a little bit prior to rapid prototyping to adjust for the little bit of material you will be taking away.

If you want a mirrorlike finish, you’ll need to polish it no matter what you do. Unless you have a very good sand caster, you’re probably going to get some small surface voids here and there which might be a problem if you really need a mirror smooth finish. If this is a one off or short run, investment casting from an RP part is probably going to be the best bet. As IDiot said, there are a number of ways to get there- whatever casting shop you choose will probably have a process they prefer. Some of the materials melt/burn out more cleanly than others.

Thank you very much for sharing this knowledge - In regards to the rapid prototype part, can I use an ABS prototype in such a cast? Will the melted ABS interfere with the molten aluminum in any way?

really not sure if ABS would be a suitable material for an investment, it is definitely not one of the the base materials I was referring to that was made specifically for investment casting = ]

you may have to break down and do a test, you could use something you already have made of ABS with a similar wall thickness (and ideally) size to your design, this way you can see if it works before you INVEST (sorry) any time in prototyping.

Stratasys FDM machines use ABS material, and those can be used for investment casting. But again, you’re going to want to find a casting shop that has done this before. Stratasys (or whatever machine you’re using) can probably give you some referrals. Also, FDM surface quality is pretty far from mirrorlike- you’ll want to smooth it out as much as possible before casting. It’s a lot easier to sand ABS than aluminum.

CRDM are a UK company who can arrange castings from RP files. Take a look over here

They mention Castform or thermojet Wax Patterns

If you’re in the US you might want to contact these guys:

They are a prototype vendror based in Seattle and offer a service called Quickcast.

The above link should get you to their Quickcast information page. Also check out the gallery for some pics. Looks like they may have used Quickcast to produce the Salt Lake Olympic Torch.

Just an FYI, my experience with Moeller has been crap.

I’ve seen people get some great finishes with sand, espeically if the part isn’t too intricate, so I wouldn’t rule it out. And mabye the time and money you save with prototyping makes up for the work at the end.

visited moeller a couple weeks ago on a tour. I’ve never worked with them however, but heard some scary things. heres the steez on their quickcast…
its a lighter RP part that has a honeycomblike interior… allows the burnout to properly occur and is cheaper than regular SLA part. This process is typically used for HIGH tolerance parts to be cast in Titanium for like aircraft stuff. probably not the right process for a vessel… unless it sounds like it is to you.

i have done some sand casting of aluminum and it’s probably a good way to go, like everybody else has said, depending on the time you’re willing to put into the part after the casting is complete.

you can, however use an RP part as a pattern for sand casting…

Great information!

I may still contact Moeller - I’d like to ultimately try a small run of vessels and the less work I have to to postcast, the better.

With the vessel, the tolerances are not really crucial, so I guess I have some flexibility with which direction to go.

Thank you all!

Hi, any chance you will let us know how it worked out?

I am looking to investment cast a part myself and am wondering what the restrictions are for the wax master pattern.

  • Can it be designed like any injection molded polymer or are there specific requirements (wall thickness, draft, sliders, split mold etc.)
  • Can threads be achieved with good tolerances, are there any tricks do achieve that? Because the standard tolerance mentioned for a cap nearing 2" diameter is +/- 0.35mm and that is far too much.

The rule of thumb in the my old machine tool tech textbook is that casting patterns should add an extra 0.125" on precision mating surfaces. Then machined to tolerances with a secondary operation like thread cutting and facing. Metal casting like injection molding uses a sprue and gate system for mold flow but can accommodate a much greater variation in wall thickness. Ceramic shell investment process requires no draft angles as the part is broken out of the ceramic as a one-off waste mold.

Thanks! That must be 0.0125" extra instead of 0.125" I assume. If threads always have to be machined after casting this is going to be a bit above budget. I hear some factories can work with close tolerances up to about +/-0.010 in/in.