Precision & investment casting


Precision & investment casting

Investment casting involves the use of the lost wax method to produce high quality metal castings. First a wax model, or pattern, is made in the size and shape of the desired end product. The wax is then enclosed in a refractory material. When the whole is heated, the wax melts away and leaves a precise mould into which the molten metal may be poured. When it has cooled down, the outer refractory casing is broken, revealing the cast object.

This process has been used for thousands of years. The basic stages remain the same today but modern techniques incorporate computer aided design tools and 3D printers to make the wax patterns. For smaller products, multiple patterns can be connected into a larger system, known as a tree, using gates and sprues of solid wax. Computer modelling can predict the flow path of the molten metal to ensure that all the pockets of the mould will be completely filled.

When complete, the whole tree is dipped into a series of refractory ceramic slurries, allowing time to dry between each. The first coat is made from very fine particles, like flour, which will leave a smooth finish. Subsequent dippings in coarser grades build up an effective ceramic shell which has good adhesion to the wax and, after firing, can withstand the the heat of molten metal without shrinking or cracking.
The primary advantage of investment casting is the accuracy of the finished product to the pattern even if it includes undercuts, thin walls and complex geometry. A wide range of metals, both ferrous and non-ferrous, can be cast in this way. It does tend to be more expensive than other methods such as sand or die casting, but the greater accuracy and reduced requirement for additional finishing make investment casting the best option for the most complex patterns.

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