EFFECT OF PROCESS VARIABLES ON THE QUALITY OF INVESTMENT CASTINGS PRODUCED BY USING EXPANDABLE POLYSTYRENE PATTERN

Abstract

Ceramic shell investment casting is known for its good quality castings with fine intricate details and improved mechanical properties. The terms "Lost wax process" and "Investment castings" are being used for synonyms of each other. Investment casting is not only limited to the wax patterns but also patterns of different materials can be used to form the moulds of desired shapes. Ice patterns are one of the non-conventional practice of doing investment castings. A lot of research and findings have been made upon the wax patterns and their effects on the final castings surface roughness and dimensional are studied. A713 alloys find applications in the automotive industries and for the manufacturing of aircraft parts because of its light weight and high strength characteristics. The present study is concerned with the investigation of mechanical properties of A713 alloy castings produced by investment casting process using expandable polystyrene as the pattern material and the plaster of Paris as the mould material. Experiments were conducted as per Taguchi's L9 orthogonal array. Castings were made under the constraint of different process parameters like mould firing temperature, pouring temperature, firing time and mixing of silica sand of different grain fineness numbers to investigate their effects on the surface hardness, impact strength, tensile strength, surface roughness and the porosity of the final castings. The variations in the trend of the aforesaid mechanical properties were observed and it was deduced out that high mould firing temperature, higher pouring temperature, maximum firing time and high grain fineness number significantly reduce the mechanical properties of A713 alloy castings produced by the above process and the aforesaid parameters significantly affect the surface roughness and porosity of the final castings.