Water modeling of mould filling during suction casting process of automotive exhaust valves of γ-TiAl based alloys

Abstract

Investment and suction casting represents a more cost effective route to produce automotive exhaust valves of γ-TiAl based alloys, but the castings have severe gas porosities in the preliminary suction casting. It has been conferred that the generation of the porosity defects in the castings is a result directly associated with the entrapped air during filling flow. In order to investigate the filling patterns and the entrapped air during the suction casting process of automotive exhaust valves of γ-TiAl based alloys, water modeling experiments have been done. The effect of three types of filling pressure control methods and two types of moulds on the filling patterns are systematically investigated in this paper. Results show that serious entrapped air occur during the filling flow with an rough pressure control method by means of the vents at the top of the moulds (called a general suction casting); Tranquil filling patterns are obtained under an accurate pressure control method ("gas charging" or "air leakage"), and if the gas charging flow is smaller than 1.7 m 3/h or the air leakage flow is smaller than 1.5 m 3/h, the entrapped air phenomenon disappear. Meanwhile, the general and the "air leakage" suction casting of TiAl automotive exhaust valves are implemented using the conclusions of the corresponding water modeling experiments, and the real casting results claim good qualitative agreement with that of the water modeling experiments. Finally, The reasonable explanation for the aforementioned results of the water modeling experiments is given using the filling kinetic principle of suction casting. © Copyright.