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24. Hegde, S. and Prabhu, K.N., “Modification of Eutectic Silicon in Al–Si Alloys,” Journal of Materials Science, vol. 43(9) pp. 3009–3027 (2008).
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technical Review & discussion
Rapid Casting of Light Metals: an experimental investigation Using taguchi Methods S. Singamneni, O. Diegel, D. Singh and N. McKenna, School of Engineering, AUT University, Auckland, New Zealand
Reviewer: The choice of material is not a true variable for metalcasting and is likely predetermined by the application.
Authors: Most of reviewer’s comments on the choice of differ- ent casting alloy grades in the current experimental investiga- tions are valid and represent true concerns. It is agreed that considering the cast alloy as a variable is not a valid experi- mental factor, provided the overall aim of the experiment is to find optimum combinations of all experimental factors, for the best values of specific responses. However, the main objective of the current experimental plan is to establish the validity of a relatively new casting technique for light metals processing under varying conditions. While mould materials, coatings and pouring temperature are the true variable factors, different al- loys are included to simultaneously experience the process per- formance over a range of light metals. This approach, together with the use of Taguchi L9 design allowed rather economically, some preliminary experiences with using rapid prototyped moulds for different light metals casting. The experiment is not to find the optimum factor combinations for the best strength or other properties, but to establish, if essential characteristics with any of the alloys tested are lost due to any inherent weak- nesses of the process, as yet unknown.
Reviewer: The statistical analyses presented for UTS and elongation are a serious concern. It is not really appropri- ate to conduct an analysis of this type with different alloys.
36
Science, vol. 34, pp. 3555–3564 (1999).
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It also appears that metallurgical factors important for cast- ing quality were over looked. The authors concluded that; “Overall, the combination of unmodified eutectic silicon, porosity and Fe inclusion led to the brittle fracture and poor strength of the aluminum specimens, indicating a poor melt quality rather than the ability of the RP process.” What then, was the purpose of the preceding statistical analysis?
Authors: The overall objective is to experimentally inves- tigate the effectiveness of RP moulds for casting selected light metals. A separate set of experiments could have been conducted for each alloy system, considering variation of selected process parameters. As the total number of experi- ments in that case is high, and considering that these are initial trials to get an overall impression of the performance of the moulds, cast metals are included in the parameter set of a Taguchi L9 experimental design, from time and cost considerations. The statistical analysis on mechanical prop- erties is conducted mainly to find if castings of any alloys considered produced inferior properties compared to their traditionally cast counter parts. While both alloy grades of magnesium showed no loss of properties, the aluminium alloy castings exhibited relatively poor mechanical proper- ties. The metallurgical factors are considered as much as possible, and the aluminium melt was lance degassed, be- fore introducing into the moulds, however, there were some practical difficulties due to insufficient facilities. This was reflected in the results of the post-mortem analysis on the aluminium castings, which revealed issues such as iron con- tamination and hydrogen porosity and hence the conclusion that it was due to these practical problems, aluminium cast- ings did not fare well, but not due to any inherent inabilities of RP moulds. Further experiments with aluminium casting using ZP 131 moulds under controlled conditions revealed much better casting characteristics.
International Journal of Metalcasting/Summer 2011
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