Lost Wax Casting

Lost wax casting is a type of casting which has survived the test of time and is regularly employed nowadays to produce complex and inticate items.

The lost wax casting technique includes the following processes:-
 
. Tooling
 
. Wax pattern injection
 
. Structure assembly
 
. Mould production
 
. De waxing
 
. Mould firing
 
. Pouring
 
. Finishing
 
. Heat treatment method
 
. Inspection
 
. After casting finish processes
 

Tooling

 
A pattern die is developed and made using CAD/CAM procedures. Skilled toolroom workers manufacture dies employing precision CNC machining/EDM techniques. Lost wax casting tools are developed fundamentally of Aluminium with cores/ retractable slides produced in Brass or Steel.
 
As no draft is required for the technique of wax pattern creation parrallel sided Chassis/Boxes can be created with ease. Reverse form features/undercuts and complex internal 3D varieties can be developed by "Collapsing" the cored feature or by using "Soluble" wax inserts.
 

Wax Design Injection

 
Liquid pattern wax is inserted under temperature/pressure controlled conditions to ensure that dimensional consistency from the initial to the one hundred and first injection cycle. After solidification the wax pattern is ejected freely from the die.
 
Automatic or Manual tooling may be developed dependant on the manufacturing demands. Tool life is very high due to the lower temperatures/pressures and lower abrasive characteristics of the waxes employed.
 

Pattern Assembly

 
Wax patterns are then assembled onto a wax runner device which gives accessibility for the molten metal.
 
With over 30 basic designs of "Runners" (Frames/assemblies/trees), castings of all dimensions and sections [from postage stamp to pedal bin size] can be created to a good level of accuracy.
 

Mold Making

 
After the completed wax assemblies are produced and cleaned, a ceramic shell is created by repeatedly dipping the wax assembly initially in a liquid ceramic slurry followed by coating with ceramic stucco.
 
A fully automatic "Shellmaking" robot procedure is used to invest the assemblies. A number of layers are used until finally the "Investment Shell" is solid enough to withstand the heat stresses of pouring.
 

De-Waxing

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

Mould Firing

 
Ceramic Shell molds are heated at one thousand°C to eliminate residual traces of wax, improve the mechanical strength of the shell and to preheat in preparation for the casting procedure.
 

Pouring

 
The required alloy is melted in either an induction furnace or electric resistance furnace and gravity poured into the pre-fired lost wax cast mold. 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 reach a high level of integrity.
 

Finishing

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

Heat Treatment

 
Lost wax castings are heat-treated either to enhance mechanical qualities, increase machinability or to homogenise as cast structures. Heat treatment is carried out on site utilizing atmosphere controlled furnaces.
 

Quality assurance

 
Completed lost wax castings are visually/dimensionally inspected and if required NDT is undertaken to verify integrity.
 
Namas approved laboratories are utilised for MPI / DPI / RADIOGRAPHY. On site facilities exist for Spectrographic analysis of alloys.
 

Post Cast Finishing Techniques

 
Most customers prefer to buy machined / painted / polished / plated parts. Lost wax casting companies can offer many post cast finishes such as:-
 

Barrel Rumbling
 
Hand polishing
 
Part Assemblies
 
Powder Coating
 
Silk Screening
 
Machining
 
Zinc plating
 
Alocroming /Anodising
 
Electropolishing
 
Cadmium Plating
 
The above eleven steps complete the lost wax casting technique which is also known as investment casting.

Investacast is a leading lost wax casting company that offers the full range of lost wax castings and services including in house tooling and post cast finishing.
 
See their website at http://www.investacast.com