Investment Casting Method Outlined

The investment casting procedure consists of the following techniques:-

. Tooling

. Wax pattern injection

. Structure assembly

. Mould production

. De-Waxing

. Mould firing

. Pouring

. Finishing

. Heat treatment

. Quality Assurance

. After casting finishing processes

1. Tooling

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

As no draft is needed for the procedure of wax pattern production parrallel sided Chassis/Boxes may be created with ease. Reverse form elements/undercuts and complex internal 3 Dimensional forms can be produced by "Collapsing" the cored feature or by using "Soluble" wax inserts.

2. Wax Structure Injection

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

Automatic or Manual tooling can be developed dependant on the manufacturing requirements. Tool life is incredibly long due to the lower temperatures/pressures and low abrasive nature of the waxes employed.

3. Pattern Assembly

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

With over 30 basic styles of "Runners" (Frames/assemblies/trees), castings of all dimensions and sections [from postage stamp to pedal bin size] can be produced to a good level of exactness.

4. Mold Creation

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

A totally automatic "Shellmaking" robot program is employed to invest the assemblies. A number of coats are used until the "Investment Shell" is thick enough to withstand the thermal stresses of pouring.

5. De-Waxing

The complete mold is then put into a steam pressure container and the wax steamed out to keep the negative hollow cavities of the components within the "Investment Shell".

6. Mold Firing

Ceramic Shell moulds are heated at 1000°C to eradicate residual traces of wax, enhance 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 [copper/steel/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 achieve a high level of soundness.

8. Finishing

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

9. Heat Treatment

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

10. Inspection

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

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 above eleven processes complete the investment casting procedure which is also known as lost wax casting.

Investacast is a leading investment casting company that offers the full range of investment casting services including in house tooling and post cast finishing.

See their website at http://www.investacast.com

Address:Investacast Ltd

Mullacott Industrial Estate

Ilfracombe

Devon

EX34 8PL

Tel: 01271 866200

Email: info@investacast.com