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There are two main techniques used to manufacture investment castings depending on the type of mould used. These are either block moulds or shell moulds:(1) Block moulds -this was the main technique used until the mid-1950s, and involves pouring a refractory ceramic around a wax pattern assembly contained in a flask. One of the main disadvantages of this technique is that the cast metal is surrounded by a very thick ceramic shell. This is an insulator and causes slow cooling and, therefore, poor metallurgical structures. Another problem is that the solid ceramic block inhibits contraction of the metal as it cools and this can lead to failure of the casting.(2) Shell moulds -these are produced by "investing" a wax assembly with several ceramic layers. The first layer is normally a fine coating so that a good surface finish on the casting will be obtained. Subsequent layers are made up of a ceramic slurry and refractory granules. The shell will normally be made up of between five and eight layers depending on the cooling rate required and the subsequent metallurgical properties.Once the ceramic has dried, the wax is removed by placing the block or shell in a steam autoclave at 150-200°C and 6-7 bar.The wax can be reclaimed and used for moulding the runner systems. Although the coefficient of thermal expansion for wax is much greater than the ceramic, the shells do not usually crack. This is because initially the heat melts the outer layer of wax and this acts as a "buffer zone" which allows expansion of the main body of wax. After dewaxing, the moulds are fired in a furnace to give full strength and to bring them nearer to the melt temperature of the metal. Using rapid prototype models for investment castingInvestment casting [1,2] and rapid prototyping[3] have the potential for an ideal marriage in that they are both techniques suited to complex parts. Two of the main commercial rapid prototyping systems, selective laser sintering (SLS) and fused deposition modelling (FDM), are capable of producing wax models which can be used almost directly in investment casting [4,5]. However, these 4