A Mathematical Model for Air-gap Formation at the Metal—Mould Interface in the Computer Simulation of the Solidification of Al—12%Si in a Sand Mould

Abstract

The outcome of a long-term programme on the computer-aided design of castings, carried out at Sharif University of Technology, has been the development of computer simulation software known as SUTCAST. This is currently employed in 16 local foundries. The program is based on a numerical method involving a classical approach to an explicit three-dimensional heat-transfer finite difference method. The software has been designed for the solidification simulation of pure metals, and eutectic and long-freezing-range alloys. It has been written for IBM personal computers and compatibles in the Turbo C version 2.01 programming language.

This paper discusses the computer solidification simulation of an Al—12%Si casting poured in a sand mould and the heat- transfer coefficient at the metal—mould interface. A mathematical model for the estimation of the gap width at the metal—mould interface during solidification based on the plane strain thermoelasticity equations is suggested.

The solidification process for Al—12%Si contained with a sand mould was monitored by measuring temperature at different locations within the casting and the sand mould. An experimental procedure was employed to measure the displacement of the metal and mould walls during solidification. The width of the gap was measured as the difference between the location of the casting and the inner surfaces of the mould, which varies with time.

The computer results are compared with the experimental data and are shown to be in good agreement as regards to cooling curves, solidification time and gap size.