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Most home metal-casters use traditional green-sand molding techniques to cast parts. Typically, a two-part molding flask is packed with specially-treated sand around a pattern, then the flask is carefully opened, the pattern removed, and the flask reassembled, being careful not to disturb the sand impressions, leaving a negative space in the exact shape of the original. In lost-foam casting, however, the pattern does not have to be removed before pouring in the molten metal; rather, the hot melt simply vaporizes the foam as it flows in, and replaces it. This process has a number of advantages to recommend it over the traditional technique. It does not require a two-part flask, and can be performed in a simple metal bucket. Nor does it require special sand, or special techniques for handling it. Dave Kush has a great overview on his site. Among other things, Dave uses the lost-foam process to cast homemade linear bearings for his CNC equipment.

Sean Michael Ragan

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and My work has also appeared in ReadyMade, c’t – Magazin für Computertechnik, and The Wall Street Journal.

10 Responses to How-To: Lost foam metal casting

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  1. gyziger on said:

    Where is a good place to get aluminum for casting?

    • Wilson! on said:

      Aluminum pistons or other engine parts, aluminum car rims, etc., are all good sources of aluminum for casting. Just read a few of the web pages dedicated to getting set up in this, and they go into what aluminum works well, and what doesn’t (i.e., a crucible full of pop cans).

  2. SimEnzo on said:

    I’ve done this a few times… the one step mold making process is satisfying quick & easy. But the process gives off toxic fumes. Be sure to do it in a very well ventilated area and wear a organic vapor filter respirator.

  3. This is the level of casting that we did in Junior High Metal Shop. I’m pretty sure you could only do it once per semester. It was the only project that everyone wanted to do.

  4. Anonymous on said:

    One further advantage of the lost foam casting method worth mentioning is the ability to cast complex, undercut shapes as the pattern need not be removed prior to the pour.

  5. Anonymous on said:

    What kind of foam is he using ?

  6. Looks like sheets of polystyrene insulation: Styrofoam qua such. A bit of logo is visible in the first photo.

    Anything based on polystyrene will work similarly, though I bet the uniformity of insulation boards gives a nicer surface finish.

    On toxicity: I would consider baking the foam out in an oven, in such a way that the fumes are burned, but I guess the thin plaster shell might not survive the pressure of the sand through much handling.

    • Sean Michael Ragan on said:

      Good comments, Joel, thank you.

      I do not think toxicity is a significant concern in this case. Presumably if you’re pouring molten aluminum, you’re doing it outdoors and/or with good ventilation already. If not I think you probably should be.

      Even the denser polystyrene foams are mostly air, I think. Anyone who’s ever dissolved styrofoam in acetone or gasoline or something knows how little “stuff” there really is in it.

      I’m not saying the phenyl rings on the polymer might not get up to some nasty business when boiled away, but between the two points–use decent ventilation and realize you’re really not burning that much polymer by mass–I don’t see the risk as justifying the extra step of using a burnout oven.

  7. I use the lost foam casting method and it works very well for me. The basic tool you need is a hot wire foam cutter to make nice straight cuts, some rubber glue and you can make any shape you want. To have the best surface finish I use XPS foam (extruded poystrene) and plaster of Paris to dip the foam in. The plaster takes a whole day to dry but it is worth the ‘investment’. It is called investment casting :) Be sure that the casting sand surrounds all surfaces of the foam object, otherwise the hot metal will break through the plaster. Don’t forget the safety aspect when pouring aluminium. The process needs any absolutely moisture free environment. If you cannot guarantee this (and you can’t) you must wear full body protection. Leather is a good choice, I use Nomex in combination with leather.

  8. Jerimiah on said:

    White (expanded) stryofoam burns out much more easily than pink or blue (crosslinked) styrofoam. 1/4 inch cross sections were the thinnest I was able to get without the header. Pieces may look dry even when they aren’t! Any water at all turns to steam and creates an explosion in your part, deforming it.

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