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Investment Casting

The Process
  • Flexibility
  • Economy
  • Precision

Investment casting, or the "Lost Wax" process, has its origins in ancient civilisations, when it was used in casting jewellery and bronzes from wax patterns produced by hand. In present day engineering applications, however, precision made dies are used to produce highly accurate wax patterns of the component to be cast.

Manufacture begins with the dies being mounted in wax injection presses, in which the die halves are clamped under pressure whilst wax is injected into pattern cavity. The die halves are then separated and the wax pattern is extracted.  After inspection, the waxes are assembled onto a suitably designed feed and runner system. These wax assemblies are then coated, or "invested", with a ceramic shell, built up in layers by alternately dipping in a liquid slurry and then in a bed of dry sand.

The first coating is of very fine textures in order to give the casting its excellent surface finish and reproduction of detail. Subsequent coats are of coarser material, repeated according to the strength of shell required to contain the cast weight of the mould. The wax is then melted out, the shell is fired to remove all traces of wax and the mould is ready to receive the molten metal. After casting, when the mould has cooled sufficiently, the shell is removed mechanically and the feed and runner system cut off. And there is the casting.

Advantages
  • Freedom of design.  The process is capable of producing virtually any geometrical shape
  • Near net shape with close dimensional tolerances (+/- 0.13mm per 25mm)
  • Wide choice of alloys, ferrous and non-ferrous
  • Minimum machining required to produce a finished component
  • Excellent surface finish
  • Long life tooling, with relatively easy modification if needed
  • Large or small order quantities can be processed economically

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The Glen Foundry Group Anderson Stewart Castings Precision Tooling The Glen Foundry The Glen Foundry