PERFORMANCE STUDIES OF EVAPORATIVE PATTERN CASTING PROCESS

Abstract

Evaporative pattern casting process, popularly called the full mold process or lost foam molding process was developed in 1958. It utilizes physical bonding only in dry and free flowing sand without any conventional binders. It has gained considerable importance due to its capability to produce dimensionally accurate and smooth casting of complicated shapes. The objective of the present work was to study the various process parameters which effect the quality of casting produced by evaporative pattern casting process. In the present investigation sand grain size and its distribution, vibrating frequency, vibrating time, degree of vacuum imposed and metal pouring temperature process variable have been selected. The other variables like amplitude of vibration, sand type, composition of alloy, pouring time of molten metal was kept fixed during the entire experimentation. The aluminum silicon alloy generally have a excellent casting properties and very good resistance to corrosion. In the present work Al-7%Si alloy has been chosen. The standard alloy designation is A356 (Al 7Si Mg). This alloy normally has excellent castability property and relatively long freezing range alloy (600 C) In order to evaluate the effect of selected process parameters the response surface methodology has been used to correlate the independent process variable with desired quality characteristics by a mathematical model. The central composite rotatable design was used to plan out the experiment. This design provides the necessary information with minimum experimental trials. The sand mold characteristics, such as bulk density, packing factor and void ratio have been measured in a specially designed sand testing rig that simulates the actual condition of process. It has been observed that the grain fineness number, frequency of vibration and its time significantly affect the bulk density. The casting quality characteristics studied are dimensional accuracy, soundness, surface finish and mechanical properties (tensile strength and percentage elongation hardness ). It is found that sand grain fineness number, metal pouring temperature and degree of vacuum contribute more to the variation of surface finish. It is found that the effect of vacuum imposed is insignificant, to the soundness. It is found that the sand grain fineness number and pouring temperature significantly affect the mechanical properties where as the effect of frequency are insignificant. iv