Friday, 22 July 2016

Investment Casting Process

Investment Casting is a manufacturing method that is used to produce a great variety of components for a wide range of industries. The process is sometimes referred to as the “Lost Wax Process” due to the role that wax has to play in the casting process.

1. STAGE 1:

The first stage of the Investment Casting process is to produce an exact replica (or “pattern”) of the required casting. This is made by injecting wax into a die. Aluminium dies are used, which are economical to make and easily modified if design changes are required. Loose pieces may be used to form any undercuts and internal detail.

2. STEP 2:

The wax pattern is assembled onto a wax feeder system. Each assembly or “tree” may have just one large pattern or many small patterns.

3. STEP 3:

The wax assembly is dipped by a large robot into a high-grade ceramic slurry. This stage is known as the investment stage – the part of the process from which the production method gets its name.

4. STEP 4:

Whilst the assembly is still wet, larger particles of ceramic are dropped onto its surface. This is done to build up a thicker coating. After drying, this coating process (or “investment” process) is repeated several times, building a shell mould thickness of approximately 10mm.

5. STEP 5:

After the final shell mould is dried, the wax is melted out in a steam autoclave (hence why the process is sometimes referred to as the “lost wax process”. The moulds are fired at over 1000°C to remove any remaining wax and to strengthen the mould.

5. STEP 6:

Molten metal is poured into the moulds, whilst they are still hot, enabling the metal to run into thin wall sections.

6. STEP 7:

After cooling, the ceramic shell mould is broken away and the casting is cut away from the feeder system.

6. STEP 8:

The castings are carefully fettled, blasted and heat treated. Setting operations may also be required. Material testing, x-ray, dye penetrant testing or machining can then be carried out, if this is required.

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