Investment Casting Technique Explained

The investment casting process is made up of the following techniques:-

. Tooling

. Wax pattern injection

. Structure assembly

. Mold making

. De-Waxing

. Mould firing

. Pouring

. Finishing

. Heat treatment method

. Inspection

. After casting finish processes

1. Tooling

A pattern die is designed and made using CAD/CAM processes. Professional toolroom personnel make dies using precision CNC machining/EDM methods. Investment tools are developed fundamentally of Aluminium with cores/ retractable slides manufactured in Brass or Steel.

As no draft is necessary in the technique of wax pattern manufacture parrallel sided Chassis/Boxes may be created with ease. Reverse form elements/undercuts and complicated internal 3 Dimensional structures can also be developed by "Collapsing" the cored feature or by using "Soluble" wax inserts.

2. Wax Design Injection

Liquid pattern wax is injected under temperature/pressure controlled conditions so that dimensional consistency from the 1st to the one hundred and 1st injection cycle. After solidification the wax pattern is removed freely from the die.

Manual or automatic tooling can be created dependant on the manufacturing demands. Tool life is incredibly high due to lower temperatures/pressures and lower abrasive nature of the waxes employed.

3. Structure Assembly

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

With over 30 basic variations of "Runners" (Trees/Assemblies/Frames), castings of all dimensions and sections [from postage stamp to pedal bin size] may be designed to a excellent degree of accuracy.

4. Mold Production

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

A totally automatic "Shellmaking" robot system is used to invest the assemblies. Several layers are used until the "Investment Shell" is thick enough to withstand the heat stresses of pouring.

5. De-Waxing

The complete mould is then placed into a steam pressure container and the wax steamed out to leave the negative hollow cavities of the components inside the "Investment Shell".

6. Mold Firing

Ceramic Shell moulds are heated at one thousandC to remove residual traces of wax, enhance the mechanical strength of the shell and to preheat in preparation for the casting technique.

7. Pouring

The required alloy is melted in either an induction furnace or electric resistance furnace and gravity poured into the pre-fired investment mould. Cast mould weights of up to 35KGs are cast [steel/copper/nickel] and 10KGs [aluminium alloys].

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 obtain a high level of accuracy.

8. Finishing

When the metal has solidified the ceramic mould is taken off and cleaned away with pneumatic vibratory machine. The castings are then cut away from the runner, fettled and shot blasted in preparation for heat treatment or quality assurance.

9. Heat Treatment

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

10. Quality assurance

Finished castings are visually/dimensionally examined and if required NDT is undertaken to test soundness.

Namas approved laboratories are utilised for MPI / DPI / RADIOGRAPHY. On site facilities exist for Spectrographic analysis of alloys.

11. Post Cast Finishing Techniques

The majority customers prefer to buy machined / painted / polished / plated parts. Investment casting companies can offer many post cast finishes such as:-

Machining

Zinc plating

Cadmium Plating

Alocroming /Anodising

Barrel Rumbling

Electropolishing

Hand polishing

Part Assemblies

Powder Coating

Silk Screening

The detailed 11 actions complete the investment casting technique which is also known as lost wax casting.