Manufacturing Technology Today

Abstract

The mechanical properties of a metal casting are governed by grain size and microstructure in the metal, and isotropic microstructure leads to better mechanical properties. However, in practice, it is difficult to ensure cooling rates such that uniform microstructure in the cast occurs. In this paper, we propose a model for controlled cooling of the casting in order to achieve uniform microstructure and desired grain size throughout the cast product.

The main concept is that the microstructure of the casting depends on the rate of heat extraction. A faster rate of heat extraction leads to smaller grain size while a slower rate of heat extraction results in larger grain size. Generally, the geometry of the mould and the cast is such that the distance of cast from the external surface of the mould is continuously varying. This leads to variations in the rate of heat extraction which results in non-uniform grain development during the cooling process.

Since cooling rates are the primary concern, and this depends on the external temperature (T_e ) of the mould, this temperature needs to be controlled. Our proposed model controls this temperature by using multiple variable speed fans to control T_e. The relevant heat transfer equations comprising of conduction and convection will be used to model the temperature throughout the mould. A feedback system will be incorporated which will consist of temperature sensors and a cooling system that will be integrated with a data processing unit. The temperature (T_e ) so measured will be used to control the fan speeds such that heat extraction rates are controlled to achieve uniform grain size and arrangement in the cast product.

Although the present model has been developed for relatively simple geometries, the same can be extended for more complicated casting geometries. This will form the next phase of our work.

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