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Metal
injection moulding (MIM) has over the past decade established
itself as a competitive manufacturing process
- for
small precision components which would be costly to produce
by alternative methods.
- It
is capable of producing in both large and small volumes
- complex
shapes
- from
almost all types of materials including metals, ceramics,
intermetallic compounds, and composites.
Components made by MIM technology are finding new applications
in industry sectors such as automotive, chemical, aerospace, business
equipment, computer hardware, bio-medical and armaments.
MIM
and Powder Metallurgy.Metal injection moulding (MIM) is
a development of the traditional powder metallurgy (PM) process and
is rightly regarded as a branch of that technology.
- The
standard PM process is to compact a lubricated powder mix in a rigid
die by uniaxial pressure, eject the compact from the die, and sinter
it.
- Quite
complicated shapes can be and are regularly being produced by the
million, but there is one significant limitation as regards shape.
- After
compaction in the die the part must be ejected, i.e. pushed out
of the die cavity. It will be obvious, therefore, that parts with
undercuts or projections at right angles to the pressing direction
cannot be made directly.
-
That limitation is substantially removed by the metal injection
moulding process developed during the last decade and now expanding
rapidly.
PLASTIC
MATERIAL The use of injection moulding for the production
of quite intricate parts in a number of plastic materials has
been known for many years, and most of us come into contact with them
in some form or other every day.
- One
important feature of such parts is that they are relatively cheap.
- However,
for engineering applications these thermo-plastic materials
have quite inadequate mechanical properties.
METAL
AND CERAMIC MATERIAL Some improvement is made possible
by the use of solid fillers - ceramic or metal powders - but
the real breakthrough occurred when it was found possible to incorporate
a very high volume fraction of metal powder in a mix so that, instead
of a filled plastic part, a plastic-bonded metal or ceramic part
is produced.
- Careful
removal of the plastic binder leaves a skeleton of metal or ceramic
which, although fragile, can be handled safely and sintered in much
the same way as traditional die compacted parts.
- After
sintering densities of 95% or more are reached and the mechanical
properties are, for that reason, generally superior to those of
traditional PM parts.
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