The investment casting procedure is made up of the following actions:-
. Tooling
. Wax pattern injection
. Structure assembly
. Mold making
. De waxing
. Mould firing
. Pouring
. Finishing
. Heat treatment
. Quality Assurance
. Post cast finishing processes
1. Tooling
A pattern die is designed and produced using CAD/CAM procedures. Professional toolroom workers produce dies using precision CNC machining/EDM systems. Investment tools are created primarily of Aluminium with cores/ retractable slides produced in Brass or Steel.
As no draft is required in the procedure 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 built by "Collapsing" the cored feature or by using "Soluble" wax inserts.
2. Wax Pattern Injection
Liquid pattern wax is injected under temperature/pressure controlled conditions so that dimensional consistency from the 1st to the 1 hundred and 1st injection cycle. After solidification the wax structure is ejected freely from the die.
Automatic or Manual tooling may be developed dependant on the creation standards. Tool life is incredibly high due to the low temperatures/pressures and reduced abrasive nature of the waxes used.
3. Structure Assembly
Wax patterns are then put together onto a wax runner device which gives entry for the molten metal.
With over thirty basic variations of "Runners" (Trees/Assemblies/Frames), castings of all sizes and sections [from postage stamp to pedal bin size] may be developed to a high amount of soundness.
4. Mould Production
Following the finished wax assemblies are developed and cleaned, a ceramic shell is made by repeatedly dipping the wax assembly initially in a liquid ceramic slurry followed by coating with ceramic stucco.
A totally automatic "Shellmaking" robotic program is used to invest the assemblies. Several coats are applied until finally the "Investment Shell" is solid enough to withstand the heat stresses of pouring.
5. De-Waxing
The entire mold 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. Mould Firing
Ceramic Shell molds are heated at 1000C 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 required 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 [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 gain a high level of soundness.
8. Finishing
When the metal has solidified the ceramic mould is taken off 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 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 by using atmosphere controlled furnaces.
10. Examination
Finished castings are visually/dimensionally assessed and if required NDT is undertaken to verify soundness.
Namas approved laboratories are utilised for MPI / DPI / RADIOGRAPHY. On site facilities exist for Spectrographic analysis of alloys.
11. Post Cast Finishing Methods
The majority customers choose 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 11 actions complete the investment casting process which can be also known as lost wax casting.
Investacast is a leading investment casting company that offers the full range of investment castings and associated services including in house tooling and post cast finishing.
