INVESTIGATION OF EFFECT OF PROCESS PARAMETERS AFFECTING THE QUALITY OF CASTINGS PRODUCED BY LOST WAX PROCESS

Abstract

There are number of advantages that have been claimed for Investment Casting Process in comparison to ordinary sand casting process. It is an ideal process for achieving desired dimensional accuracy as no rapping allowance has to be given, thus eliminating machining which is very difficult, if not impossible especially for esoteric metals. Although the process was put to industrial applications in early fifties, their use was limited to artistic value only. As investment castings grow in size and complexity, control of their dimensions becomes increasingly important. The traditional method is to pour castings, measure them, and adjust the tooling by trial-and-error procedures until casting dimensions are produced within acceptable dimensional tolerances. This is a costly, time-consuming task. It is much preferable to predict casting dimensions from first stage, and build accurate tooling to produce them. The accuracy of the wax patterns used in the investment casting process has a direct bearing on the accuracy achievable in the final cast part. It is usual for the investment caster to use precision machined full-metal dies for producing wax pat-terns when large numbers of highly accurate components are required. A die of this kind can be costly, and there is usually a considerable lead time associated with its production. Dimensional changes between the pattern tooling and its corresponding cast part occur as a result of thermal expansion, shrinkage, creep of the pattern material (wax), mould material (shell), and solidifying alloy during the processing. The criteria for comparing the effect of parameters were dimensional accuracy, surface finish, tensile strength properties and hardness. Aluminium-7% silicon alloy has been used for making all the castings. Colloidal Silica has been found to be the best binder for giving best dimensional accuracy, surface finish, tensile strength and hardness. The aim of this work is. to acquire a better understanding at the die making, pattern making, and casting stages in investment casting process. Although each step seems to be easily understandable, in reality, they are very complex