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Technical Review and Discussion


Quality Aspects of A356 Castings with Multiple Gates


R. Lett, S. Felicelli and J. Berry; Dept. of Mechanical Engineering and Center for Advance Vehicular Systems (CAVS), Mississippi State University, Mississippi State, MS USA R. Cuesta, A. Rivas, M. Estibaliz Alcalde; Foundation for the Research and Development in Transport and Energy, Boecillo Technology Park, Valladolid, Spain


Reviewer: The cause and effect of confluence welds (or more commonly referred to as “cold shuts”) is well known. How does this work add to the existing knowledge base?


Authors: The term “cold shut” commonly designates poor fusing of molten metal streams because of their low temper- ature, most frequently yielding a visible defect. This paper examines the problem from a wider perspective, as the type of welds studied is not necessarily associated with low tem- peratures or visible defects. Moreover, for the first time, this works analyzes the effect of gating design over the statistical distribution of mechanical strength in parts liable to contain confluence welds.


Reviewer: Bend testing is normally performed on brittle materials, not ductile metals, which is why no ASTM stan- dard for bend testing of ductile metals exists. Bend testing is not recommended for ductile metals since the equations used to calculate outer fiber stress does not account for plastic deformation.


Authors: Literature shows a good number of examples in which bend testing is used as a useful tool to characterize the relationships between mould geometry, flow conditions, microstructure, and mechanical integrity. Note the follow- ing references. • Green N.R., Campbell J. Transactions of the American Foundrymen’s Society, V. 10, pp. 341- 347(1994).


• Cox M., Wickings M., Kuang J.P., Harding R.A., Campbell J. “Effect of Top and Bottom Filling on Reliability of Investment Castings in Al, Fe, and Ni Based Alloys” Materials Science and Technology, V. 16 pp. 1445-1450 (November-December 2000).


• Cox M., Harding R.A., Campbell J. “Optimized Running System Design for Bottom Filled Alumi- num Alloy 2L99 Investment Castings” Materials Science and Technology, V. 19, pp. 613-625 (May 2003).





Sirrell B., Campbell J. “Mechanism of Filtration in Re- duction of Casting Defects Due to Surface Turbulence during Mold Filling” Transactions of the American Foundrymen’s Society, V. 104, pp. 645-650 1997).


Reviewer: What is the measurement error of the density measurement? An oil, such as kerosene, is typically used for density measurements since it wets the metal surface and reduces measurement error by eliminating attached air bub- bles. Why was water used and how was the density of the water determined?


Authors: Water with some drops of tensioactive agent was used in line with previous works. The density was measured with a picnometer. The estimated error of this instrument is assumed to be very low, (below 0.01 % or less).


Reviewer: Why was Weibull analysis used? Weibull analy- sis is only valid for a normal distribution. Software packages, such as Minitab, are typically used to determine the equation that best fits the data, thus making statistical comparisons valid. Figure 23 clearly shows that Weibull is a poor fit for the data from A2 and B.


Authors: Green et al. (Green N. R., Campbell J. “Statistical Distributions of Fracture Strengths of Cast Al-7Si-Mg Alloy” Materials Science and Engineering A173, pp. 261-266, 1993) showed that the Weibull statistical distribution reproduces the scatter of mechanical property values of cast specimens better than the normal distribution. Ever since, the Weibull analysis has been successfully used to characterize the quality of cast specimens (see the following references) and relate it to filling conditions. In many of these references, the fit is actually quite worse than the one obtained for A2 and B plates. • Green N.R., Campbell J. Transactions of the American Foundrymen’s Society, V. 102, pp. 341- 347(1994).


• Cox M., Wickings M., Kuang J.P., Harding R.A., Campbell J. “Effect of Top and Bottom Filling on Reliability of Investment Castings in Al, Fe, and Ni Based Alloys” Materials Science and Technology, V. 16, pp. 1445-1452 (November 2000)


• Cox M., Harding R.A., Campbell J. “Optimized Run- ning System Design for Bottom Filled Aluminium Alloy 2L99 Investment Castings” Materials Science and Technology, V. 19, pp. 613-625 (May 2003).





Sirrell B., Campbell J. “Mechanism of Filtration in Reduction of Casting Defects Due to Surface Tur- bulence during Mold Filling” Transactions of the American Foundrymen’s Society, V. 104, pp. 645- 654(1997).


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International Journal of Metalcasting/Spring 2012


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