A PRELIMINARY INVESTIGATION OF GYPSUM BONDED MOULDS BY THREE DIMENSIONAL PRINTING

Abstract

Gypsum is used as binder in traditional moulding sand system for non-ferrous casting. New Zealand silica sand is the best sand as near white, high purity (silica 99.32%) can be used for foundry application. An attempt has been made to use this material system in 3DP systems to study the behaviour and suitability to print moulds for non-ferrous casting with and without coating application at various baking conditions. The result shows that the importance of the calcination and the relation between the density and porosity, when density increases the mould strength increases but the porosity decreases and it is understood that the baking temperature and the type of coating influence the surface roughness. The dimensional error result shows the percentage swelling and shrinkage errors which is non-linear, but the result shows 0.5 % shrinkage in lateral axis, 1% in horizontal axis, and 5% in vertical axis. Based on the volume the average error is been drastically reduced from 64.5% to 6.5%. These result shows that the mould shrinkage can be reduced by further optimizing the baking condition and or adding suitable additives. There were no casting defects like mould wash, mould burn or distortion, and etc. It shows that the gypsum bonded mould have enough mould strength for casting at various conditions. In general surface roughness is the main concern in sand casting, it can be improved by adding suitable additives and coatings. Compare with two bench marked values the tensile strength value is higher and it's proved that the locally available material system used to print moulds by 3DP is not an inferior with commercially available material system.