MICROFUSION
The process of investment casting is distinguished by the use
of an expendable pattern and the basic steps in the process
are shown in figure below:
A metal die is used to produce the pattern, now almost universally
of wax.
Patterns are mounted onto a runner system to give an assembly
ready for subsequent coating with refractory (fig. 2).
The covering of the wax assembly with a refractory is known
as investing – hence the modern name of the process (fig.
3-4).
At the end of the investing process, the wax pattern material
is removed by thermal or chemical means, steam autoclaving being
usual (fig. 5). The mould is then heated to a high
temperature to eliminate any residual wax and to induce chemical
and physical changes in the refractories that will ensure maximum
strength and stability combined with minimal reaction between
the mould surface and the liquid metal to be poured into it
(fig. 6).
When the mould has cooled sufficiently, the mould material is
removed by impact, vibration, grit-blasting, high pressure water-blasting
or chemical dissolution, to leave the castings which are then
removed from the runner system. Various post-casting operations
(eg heat treatment, surface treatment or coating, hipping) may
be carried out, to meet customer requirements (fig. 7-8).
BASIC STEPS OF THE PROCESS
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Wax injection
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Assembly
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Investing
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Stuccoing
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Dewaxing
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Casting
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Know-out
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Finishing
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INVESTMENT
CASTING AND M.I.M. COMPARISON |
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