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Anyone tried MIM Metal Injection moulding or sintering?

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bambuko:

--- Quote from: Lew_Merrick_PE on February 06, 2011, 06:23:30 AM ---... Remember that your dieset has to withstand molten metal...
--- End quote ---

My experience of MIM/sintering involved injection moulding of metal powder mixed with plastic binders, using bog standard injection moulding machine and die.
This moulded part (called at this stage "green part") would be cured, binders would be removed and eventually sintered, resulting in finished part without the need for secondary processes.
No molten metal involved...? ?
Typical example of application of MIM would be making parts in tungsten - because of the extremely high melting point of tungsten it is not possible to produce finished parts by the usual methods (casting, extrusion, stamping etc.).
The project (as is often the case...) came to nothing, but experience was most interesting.
Most difficult thing, was getting shrinkages right.
See also:
http://www.epma.com/New_non_members/MIM.htm

bry1975:
Sounds very interesting Bam I can imagine shrinkage being a right problem!

Bry

Lew_Merrick_PE:

--- Quote from: bambuko on February 06, 2011, 11:52:50 AM ---
--- Quote from: Lew_Merrick_PE on February 06, 2011, 06:23:30 AM ---... Remember that your dieset has to withstand molten metal...
--- End quote ---

My experience of MIM/sintering involved injection moulding of metal powder mixed with plastic binders, using bog standard injection moulding machine and die.
This moulded part (called at this stage "green part") would be cured, binders would be removed and eventually sintered, resulting in finished part without the need for secondary processes.
--- End quote ---

MIM (Metal Injection Molding) is to PM/sinter (Powder Metallurgy) as HIP (Hot Isostatic Processing) is to casting.  That's the explanation I was given back in the 1970's.  A better analogy might be to state that PM is like unto soldering whereas MIM is like unto welding.  Both use metal powder material at the base of the operation.  A PM-part is held together by the binders (solder analogy) whereas MIM is metallurgically bonded to itself (welding analogy).  That is the difference within the (American) military standard and aerospace process definitions.

I can tell you that the little "blade bolt" for the knife was 4130 powder injected into a die that was then heated into the 2200°F range, held for a few minutes at that temperature, and then compressed to 55 ksi before it was cooled.  The resulting part is virtually indistinguishable (metallurgically speaking) from a part machined from solid bar.  Our supplier spent no small amount of time qualifying the process.

Back in the late-1980's and early 1990's I was the "chief mechanical engineer" on the program that developed the modern airbag restraint systems for automobiles.  (This sounds impressive until you realize that (A) airbags are chemical, not mechanical; and (B) I spent nearly three years developing a product that was designed to blow up in my face.)  The "problem" was (is) that the propellants are highly sensitive to changes in humidity and must be hermetically sealed in their containers.  PM parts do not qualify for hermetic seals, MIM parts do qualify.  Helium gas (the test of hermeticity) will pass right through a PM part, but not through a MIM part.

People are using these terms as if they are interchangeable today.  That may be fairly common, but it is incorrect from a technical standpoint.

bry1975:
Thanks Lew,

Good to know what the differences are.

Certainly sounds a great responsibility developing parts for life savers/air bags!

Bry

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