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.
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″).