An outline of the investment casting procedure

The key techniques in the process of investment casting have typically been a mystery, here is a step by step guide to the procedure.The investment casting process is made up of the following processes:

1. Tooling

A pattern die is developed and fabricated by using CAD/CAM systems. Skilled toolroom workers produce dies using precision CNC machining/EDM techniques. Investment tools are constructed basically of Aluminium with cores/ retractable slides produced in Brass or Steel.

As no draft is needed in the technique of wax pattern production parrallel sided Chassis/Boxes can be created with ease. Reverse form elements/undercuts and complicated inner 3 Dimensional varieties can be developed by 'Collapsing' the cored element or by working with 'Soluble' wax inserts.

2. Wax Pattern Injection

Liquid pattern wax is inserted under temperature/pressure controlled conditions to ensure dimensional consistency from the initial to the 1 hundred and first injection cycle. After solidification the wax structure is removed freely from the die.

Manual or automatic tooling may be developed dependant on the production standards. Tool life is incredibly long due to lower temperatures/pressures and reduced rough nature of the waxes employed.

3. Structure Assembly

Wax patterns are then assembled onto a wax runner system which gives accessibility for the molten metal.

With over thirty standard designs of 'Runners' (Assemblies/trees/frames), castings of all sizes and sections [from postage stamp to pedal bin size] may be produced to a excellent degree of soundness.

4. Mould Creation

Following the finished wax assemblies are developed and cleaned, a ceramic shell is produced by repeatedly dipping the wax assembly first in a liquid ceramic slurry followed by coating with ceramic stucco.

A fully automated 'Shellmaking' robot program is used to invest the assemblies. A few layers are used until the 'Investment Shell' is solid enough to withstand the heat stresses of pouring.

5. De-Waxing

The whole mold is then positioned into a steam pressure container and the wax steamed out to keep the negative hollow cavities of the components inside the 'Investment Shell'.

6. Mold Firing

Ceramic Shell molds are fired at 1000°C to clear away residual traces of wax,improve the mechanical strength of the shell and to preheat in preparation for the casting process.

7. Pouring

The specified alloy is melted in either an induction furnace or electric resistance furnace and gravity poured into the pre-fired investment mould.Cast mold weights of up to 35KGs are cast and 10KGs.

Over 50 air melt steel alloys, several Nickel based and most common Copper base alloys are stocked on site at Investacast.Aluminium alloy castings are resistance melted, rotary Nitrogen degassed and gravity poured to acquire a high level of soundness.

8. Finishing

When the metal has solidified the ceramic mould is removed and cleaned off with pneumatic vibratory instruments.The castings are then sliced off the runner, fettled and shot blasted ready for heat treatment or examination.

9. Heat Treatment

Castings are heat-treated either to enrich mechanical attributes,enhance machinability or to homogenise as cast structures.Heat treatment is undertaken on site using atmosphere controlled furnaces.

10. Examination

Completed castings are visually/dimensionally assessed and if required NDT is undertaken to test soundness.


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