Investment Castings - an Overview

Posted in Reflections on 8th August 2011

Investment casting, the lost wax process, Cire perdue, are all terms used to describe a form of producing castings to very nearly a finished condition. This production method is thousands of years old.

Broadly speaking, the method of production starts with the formation of numerous wax patterns made from a synthetic wax. A "tree" shape is made of the patterns its size being determined by the number of patterns on the tree is determined by the size and weight of patterns.

The "tree" of patterns then has numerous dips in a slurry mixture that produces a hard ceramic shell around the wax. The coated "trees" are then dried in controlled conditions. Once the coatings have dried and set the moulds are de-waxed by being placed in an oven, the wax melts and is "lost" (hence the name "Lost wax") and the ceramic shell is left behind. And it is into this that the metal of choice is poured in via a gated feeding system after the shell has been pre-heated.

After the molten metal has been poured into the mould it is left to cool and solidify. The cooling process can take some time depending on the composition, complexity and weight of the casting being made.

Once the castings have cooled the shells are broken and the castings removed from the gating system and sent for finishing and sometimes additional process like, for instance, heat treatment.

Castings produced using this method can be made from virtually any metal or alloy, Aluminium, Bronzes, tool steels, stainless steels and alloy compositions. Lost wax casting methods produce a huge variety of complex and high integrity castings like turbine blades, pump impellors, valve parts and intricate pieces for computers and medical applications.

Other sectors that make use of this type of casting method are the jewellery and model making trades producing smaller specialist castings.

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