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  • Casting powder metal

    How this for an idea: Wax patterns coated in slurry and dried and wax melted out ala Investment Casting, but instead of molten metal poured into the ceramic mold, powdered metal is poured into the mold and manually compacted, mold placed in kiln or furnace cranked up past the metal's melting point. Would it work? By theory it should greatly reduce the common difficulty of hot-casting thin wall sections, and greatly reduce the risk of injury. Any fairly inexpensive (up to $1000 or so) kilns/furnaces that get hotter than say 2800 F/1400 C?
    I thought of this idea myself, as far as I know no one has tried this, I sure can't find any reference to this method anywhere.
    What do you guys think? Would a MAPP torch suffice for small parts experimenting with this theory?

    'Slinger out.

  • #2
    Hi, Slinger.

    I think you would have some problems compacting the powdered metal properly in thin sections of the mold. Also, powdered metal has a much greater surface area to oxidize before the melt. Could be a problem with some metals. But, as I always say, you won't find out until you try!

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    • #3
      Slinger.
      It is a half-good idea that has already been acted on many years ago. Products made from powder metallurgy require require high strength molds because of the extreme tonnage used to compress the metal. When a slug is removed from a die it looks (somewhat) and feels like a solid hunk of metal. The high temperature fusing of the particles of metal have proven to produce better cutting edges than the equivelant cast piece.

      The pressure required would destroy your mold cavity. In addition, the powdered metal presents an added expense to the material (someone has to finely divide it). Thus, the expense alone for powdered metal makes it impractical.

      The other half-good idea you had was the investment casting part of it. Investment casting can produce near finished parts of high quality. So you have two different processes that each have their own merits.

      On the other hand, I should not say it cannot be done. Arthur Bishop (father of variable ratio rack and pinion steering) was told by experts, Ph's., and machinists that his splayed tooth rack was impractical and impossible to produce for mass production. So he went ahead and built the rack and the tools to build it.

      SO in that light, do not stiffle your creative urge - do it. If it cannot be done, maybe you are the one to accomplish this.

      Follow your dreams...

      Vendetta!!


      [This message has been edited by Thrud (edited 11-02-2002).]

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      • #4
        Slinger,

        I've been thinking about your idea over the weekend and here are some of my thought.

        - first of all, I think the casting will work using metal powder however...

        - As the powder melts it will trap lots of tiny air bubles which will make the cast porous.

        - In all types foundry work when the metal melts, it forms sludge that floats to the top or sinks to the bottom. Usually this stuff is skimmed off before being poured into the mold. In the case of the powder metal because of it's large surface area, you'll get a lot more of this oxidized material which will get trapped in the cast.

        I'm what you might call, an armchair foundry guy, so I might be kicking lies and telling tires heres. How about doing this in a low pressure (low vacuum) induction furnace?

        BTW, was there ever a plan for a small induction furnace that HSM can use?

        Albert


        [This message has been edited by Rotate (edited 11-03-2002).]

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        • #5
          Thanks for the replies, guys. Anyone know a small furnace around $1000 that goes to 3000 F? I really wanna try this out, see what kind of density/strength I get with different materials, most powder metals are highly atomized particles, about the diameter of a human hair.

          'Slinger out.

          [This message has been edited by 'Slinger (edited 11-03-2002).]

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          • #6
            Rotate is pretty much on the money. The powder in the mold will be at something less than the solid material density so when it melts you will come up short on material in the mold. Sintered metal parts are green compacted at very high pressures before sintering and even then the part density is less than solid material because of residual porosity.

            ------------------
            Neil Peters
            Neil Peters

            When on the hunt, a broken part is better than no part at all.

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            • #7
              Slinger:
              There is a lab at either University of Kentucky or University of Tennessee that developed a rapid prototyping process that uses powdered metal but instead of raising to full temperature for sentering they place the powdered metal part in a box with a sloped bottom. They then place copper slugs above the powdered metal part and place the whole thing in an oven with a reducing atmosphere. They only have to heat to the melting temperature of the copper. The copper wicks into the powdered metal part and upon cooling they have a solid metal part. They offer this as a service to industry for rapid prototyping. I think the powdered metal has a plastic coating to hold it together as a molded part before the copper sentering process.

              ------------------
              Dick
              Dick

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