Investment Casting

This method uses a wax pattern to form the required impression in the mould, the wax is then melted out to leave the cavity.

Process In Brief

1. A metal die is made, the impression being the same as required in the final mould.
2. Molten wax is injected into the metal pattern, allowed to solidify and then removed. Some complex wax patterns are fabricated by joining several separate patterns together using an adhesive.
3. The waxes are then assembled on a wax tree, many parts can be put on the tree depending on size, it is common for parts to be about 0.1kg up to 80 kilos.
4. The tree is then immersed in several different slurries to coat the wax, the initial slurry is fine as this will be the surface finish of the final casting.
5. After drying the trees of wax they are put into ovens of about 200 degrees to melt out the wax.
6. When all wax is removed the trees are heated up to about 900 degrees to complete preparation for casting.
7. The metal is then poured into the moulds.

Reasons for using the investment process.

1. Suitable for most casting metals.
2. Castings of irregular shapes and seeing no part line.
3. Very intricate castings produced, which in other processes would be impossible.
4. Dimensional accuracy is very good.
5. Surface finish is very good.
6. High volume can be achieved.
7. It is common to replace fabricated parts with this process, often with good financial savings.
8. Tolerances are generally accepted to be + - 0.5mm.

Impeller wax in preparation	Several waxes before process	Baths holding coating material	Waxes having final coating of gravel applied before going into oven
Example of moulds with wax melted out	Moulds recently cast, cooling down	Impeller awaiting removal from encased ceramic coating	Impeller removed from ceramic coating
Impeller with all coating removed	Impeller with red-oxide paint finish	Thread guage applied for QA process of finished machined casting	Batch of machined impellers awaiting dispatch