Investment Casting Process Outlined

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

. Tooling

. Wax pattern injection

. Structure assembly

. Mold making

. De-Waxing

. Mould firing

. Pouring

. Finishing

. Heat treatment method

. Quality Assurance

. After casting finishing processes

1. Tooling

A pattern die is designed and created using CAD/CAM procedures. Specialist toolroom workers produce dies using precision CNC machining/EDM procedures. Investment tools are built fundamentally of aluminium with cores/ retractable slides manufactured in brass or steel.

As no draft is needed in the process of wax pattern manufacture parrallel sided Chassis/Boxes can be produced with ease. Reverse form elements/undercuts and complex internal 3 Dimensional forms can also be developed by “Collapsing” the cored element or by working with “Soluble” wax inserts.

2. Wax Pattern Injection

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

Automatic or Manual tooling may be developed dependant on the creation demands. Tool life is extremely high due to the low temperatures/pressures and lower rough dynamics of the waxes employed.

3. Structure Assembly

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

With over 30 standard designs of “Runners” (Trees/Assemblies/Frames), castings of all sizes and sections [from postage stamp to pedal bin size] can be designed to a high amount of accuracy.

4. Mold Making

After the completed wax assemblies are produced and cleaned, a ceramic shell is built by repeatedly dipping the wax assembly initially in a liquid ceramic slurry followed by coating with ceramic stucco.

A fully automatic “Shellmaking” robot system is used to invest the assemblies. Several layers are used until the “Investment Shell” is thick enough to withstand the thermal stresses of pouring.

5. De-Waxing

The whole mould is then placed into a steam pressure vessel 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 1000°C to remove residual traces of wax, improve the mechanical strength of the shell and to preheat in readiness 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 mould weights of up to 35KGs are cast [nickel/steel/copper] 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 reach a high level of integrity.

8. Finishing

When the metal has solidified the ceramic mould is removed and cleaned off with pneumatic vibratory equipment. 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 strengthen mechanical attributes, improve machinability or to homogenise as cast structures. Heat treatment is carried out on site working with atmosphere controlled furnaces.

10. Examination

Finished castings are visually/dimensionally assessed and if required NDT is carried out to confirm integrity.

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

11. Post Cast Finishing Processes

Most 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 eleven actions complete the investment casting technique which can be also known as lost wax casting.

Leave a Reply

Your email address will not be published.