Injection Moulding
In a similar manner to extrusion, a plastic mix is prepared
and heated in the barrel of the moulding machine until
it is at the correct temperature at which the mix has
a sufficiently low viscosity to allow flow if pressure
is applied.
A plunger is pressed against the heated mixture forcing
it through an orifice and on into the tool cavity. The
moulded part is removed from the die and the organic binder
slowly burnt out in a controlled atmosphere by means of
a carefully controlled heating schedule, prior to sintering.
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| Injection Moulded Silicon Carbide
Components |
Low Pressure Injection Moulding
Technology has jumped forward in great leaps and bounds over
the last ten years to arrive at a position were high volume
ceramic components can be made using injection moulding techniques.
Injection moulding of ceramic components has several major
benefits over more traditional manufacturing techniques such
as die pressing and green machining.
Excluding the obvious; that it is a good technique for very
high volume parts, injection moulding has also proved to be
an excellent technique for making components such as turbo charger
rotors and thrust bearings which would be too expensive if the
parts were machined.
Low pressure injection moulding (LPIM) provides an excellent
option for producing ceramic components using low cost tools
in comparison to high pressure moulding techniques.
The LPIM process enables fabrication of very complex shapes
as well as simpler components. The essence of the process is
that parts can be produced with a higher level of integrated
function to meet the customers needs then other process are
able to achieve.
The main process features are:
- Small diameter holes, LPIM is able to produce parts
with hole diameters as small as 0.1 mm (0.004")
through walls as thick as 6.5 mm (1/4"). The hole
geometry is not restricted to simple shapes but can
be complex polygonal shapes.
- Internal and External threads, LPIM is flexible enough
to allow any configuration of thread to be moulded without
any further machining.
- Tolerances, through Statistical Process Control of
raw materials it is possible to achieve "as fired"
tolerance as small ±0.5%. Tighter tolerances
can be achieved by machining the injection moulded blanks.
- Process capabilities, minimum wall thickness 0.5
mm (0.020") to a length of 12.5 mm (0.5").
Maximum wall thickness 6.5 mm (1/4") and the maximum
over all dimension must not exceed 150 mm (6").
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