REDUCTION OF SHRINKAGE DEFECTS IN INVESTMENT CASTING PROCESS

Abstract

Investment casting is widely used for producing ferrous and non-ferrous metal parts. Investment casting is a versatile and precise process, which allows the fabrication of components requiring intricate shapes, the filling of thin sections and the reproduction of fine details. Investment casting is also known for its ability to produce components of intricate geometry combined with high accuracy, greater dimensional accuracy and excellent surface finish. Better composition of wax, selection of coating material for shell mould and material selection for casting defines the fate of the final casting. Aluminium-silicon (Al-Si) alloys are widely used in the automotive, aerospace and general engineering industries due to their excellent combination of properties such as good castability, low coefficient of thermal expansion, high strength-to-weight ratio and good corrosion resistance. Hence, in the present study, an attempt has been made to improve the properties and reduction of shrinkage defects in casting. A443 aluminum alloy has maximum shrinkage and porosity among all the Al-Si alloys, so the experiments are conducted taking the A443 allloy. First of all, a standard wax composition is selected. The shell mould is prepared by taking a plaster of paris as a coating material because plaster of paris is considered a best moulding material with excellent surface finish. After that experiments were conducted with the addition of trace elements in the A443 aluminum alloy to improve the properties with varying their process parameters such as pouring temperature, preheat temperature and preheat time in both the cases. In each experiment, properties of casting like percentage shrinkage, surface finish, tensile strength and hardness were determined. The optimization of the input parameters with respect the response parameter has been carried out by Taguchi's design using L9 orthogonal array. An attempt was made to compare the input parameters of A443 alloy and A443 alloy added trace element with their response parameters and their effects has been plotted. Keywords: Investment casting, A443 aluminium alloy, Trace elements, Plaster of paris, Process variables.