Despite the strong market for investment castings, there is little doubt that end-users are concerned about the quality and reliability of safety critical components. While the choice of gating systems for investment castings is influenced by a number of factors-including ease of processing and cost of cleaning machining-the effect of the gating system design on casting quality and reliability is usually ignored. This may be because information on the effect of different designs is lacking. In this article, the effect of controlled and uncontrolled bottom-filled gating systems on casting reliability for aluminum alloy A356 and low alloy chrome-molybdenum steel are compared with a typical top-filled system used as a benchmark for poor practice. Controlled systems are those in which metal flow is constrained for most of the filling time by the gating system, which remains completely full for a very high proportion of the filling time. In addition, these systems promote minimal formation of free surfaces.
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