Numerical simulation of free surface flows in die casting injection processes

Abstract

This paper presents a numerical study of the flow of molten metal in the shot sleeve of horizontal high-pressure die-casting machines during the injection process. The analysis of the wave of molten metal created by plunger motion can be of help in reducing porosity in manufactured parts caused by entrapment in the molten metal of a certain amount of the initial air in the die cavity and in the shot sleeve. The amount of trapped air can be reduced by selecting appropriate operating conditions during the injection process, which are mainly determined by the law of plunger motion, the initial shot sleeve filling fraction, and the geometrical characteristics of the shot sleeve. The proposed model, which considers the problem as two-dimensional, is based on the conservation equations of mass and momentum, and treats the free surface using a capturing method (Scalar Equation Method). Surface tension and solidification effects are neglected. Different approaches are considered to simulate plunger motion, in which either the plunger surface or the end wall of the sleeve moves and contracts a Cartesian grid. In the second case, a horizontal body force per unit mass is introduced and the plunger is assumed to be at rest. When numerical results for the wave profile were compared with those obtained using an analytical model based on the shallow-water approximation, and also with numerical results obtained from a CFD code specifically designed for free-surface flow modeling, a good degree of agreement was found.