strength models revealed that no significant differences exist between the two tested ZCorp materials, and ZP131 seems to be more rigid and much better in terms of the definition of the mould faces and edges. Also, the plaster gives a better surface finish, which was clearly evident from the initial casting trials. Based on all of these con- siderations, it was understood that both materials equally qualify as mould materials, and the following experimen- tal evaluation of the system includes these two as possi- ble experimental factors. The optimum mould processing conditions being already established, the next stage is to produce cast specimens using rapid prototyped moulds of optimum properties and subsequently conduct mechani- cal testing and micro structural examination to establish the overall suitability of these moulds to process light al- loys and produce adequate castings.


experimental design and Methodology


The experimental design considers three significant factors, mould material, pouring temperature and mould coating, while three alloys are considered for casting. The approach is to establish the variation of responses such as tensile strength, surface roughness and microstructural appearance, as these factors are simultaneously varied at different lev- els, within the selected ranges. However, three of the four factors being qualitative in nature, traditional factorial ex- perimental designs were avoided. The Taguchi L9 orthogo- nal array was finally chosen and each factor was varied at three different levels. This design allowed consideration of three different levels for each of the factors. While the two Zcast materials discussed in the previous section are com- bined with a traditional foundry sand to constitute the mould


Table 1. Taguchi L9 Experimental Design


Table 2. Compositions of Alloys Considered


28


International Journal of Metalcasting/Summer 2011


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