The MIM (Metal Injection Moulding) process was developed in the early '90s in the United
States, mainly for use in the military sector. In the following
years, when the first difficulties were overcome, this method
has been spreading more and more, both because of the interest
shown by a growing number of companies that developed the process,
and because of an increased number of sectors where pieces made
by the MIM process can be used.
At present, companies operating in the aerospace, military,
precision mechanics, medical, optic, photographic, clockwork
and weapon sectors are interested in MIM technology,
and are using it.
Main goals of the MIM process are to realize
average-small pieces with a complex shape, in average-big lots,
in high-resistance materials, using as much automated working
cycles as possible. Moulding is got by ordinary injection moulding
processes, at a high-speed production rate and minimum faultiness.
The so-moulded items undergo de-waxing (de-binding) and sintering
steps, so reaching their final size without further handling.
A final machining, generally limited and roboted, consists of
piece tumbling and polishing. The main steps of the whole process
are described hereafter.
Raw material (nickel alloys, stainless steel, and so on)
is mixed with the so-called binder (made of waxy, jelly-like
plastic materials) in a well-defined ratio to obtain a well-blended
compound needed in the following steps. Such a mixing originates
FEEDSTOCK, which MICROFOND buys as a certified ready compound.
As for plastic, feedstock is used as a moulding material
for the so-called GREEN BODY, i.e. the wished workpiece having
a bigger size and resistance due to the binder only.
Then, the binder is removed making care that no piece failures
or deformation occur. This difficult step is completed after
creating a BROWN BODY, i.e. a workpiece having the necessary
residual binder to keep its own consistency.
Finally, the workpiece is finished by removing the whole
residual binder and vacuum sintering, which enables to obtain
the final mechanical, geometrical characteristics desired.
Tumbling and polishing give pieces brilliance as well as
the lowest roughness. Further thermal treatments can also
be foreseen.
INVESTMENT
CASTING AND M.I.M. COMPARISON
|
|
