INVESTIGATION OF PARAMETERS AFFECTING MOULD AND CASTING CHARACTERISTICS IN VACUUM MOULDING PROCESS USING AI-4% Cu ALLOY

Abstract

Vacuum moulding is the latest sand moulding process. It utilises physical bonding only in dry and free flowing sand without any conventional binders. The sand mass in moulding box is first vibrated and then enclosed within thin poly—ethylene plastic films followed by compacting the sand grains by applying vacuum which sucks away air existing within the voids of bulk of sand. The future of any process depends upon the quality of the casting and cost of production. The objective of the present investi-gation was to study the effects of parameters on the characteristics like bulk density, permeability and mould hardness of sand mould and dimensional accuracy, surface finish, tensile strength, impact strength and Brinell hard-ness of casting.. The alloy chosen for making casting was aluminium —4X copper. The vacuum test—rig was used to study the behaviour of bulk density and permeability of sand in the vacuum mould box. I A statistical central composite rotatable experimental design was used to plan out the experiment for all studies done in the present investigation. Various measurements were made on mould or casting for a specific characteristic of mould or casting. Based on these observations the regression models were formulated and tested for adequacy. iii The relationships of various parameters for a given characteristics were computed with the help of these models through which the behaviour of the V-Process was analyzed. The following studies were conducted: 1. A four-factors at fine-levels experiment wore conducted to study the behaviour of bulk density and perme-ability of sand. Vibration frequency, vacuum, vibrating times and sand grain fineness directly affect the bulk density. 2. A five-factors at five-levels experiment explored the effect of factors on characteristics of mould hardness, dimensional accuracy and surface finish of casting. Six parameters for this study were found to be effective in the following descending order: (1) Vibration frequency, (2) Sand grain fineness, (3) Vibrating time, (4) Vacuum, (5) Pouring temperature, and (6) Plastic film thickness. 3. Three-factors at five level design of experiment was conducted to test effect of factors on charac-teristics of bulk density, mould hardness, percent mean deviation of casting from pattern dimension, tensile strength, impact strength and Brinell hardness of casting. The-values of these character-istics wera verified by statistical analysis of regression model.