Effect of molding parameters on chemically bonded sand mold properties

Chemically bonded sand molds and cores have better mechanical properties and produce more dimensionally accurate castings, compared to green sand molds, and hence are being increasingly preferred for near net shape metal parts. While it is well known that the properties and quality of a mold depend on its material composition and molding process, this has not been investigated well for chemically bonded molds. In this work, the effect of sand grain size, binder percentage and curing time (each varied in three levels) on the mechanical properties (compression strength, shear strength and core hardness) as well as dimensional changes (shrinkage) of no-bake chemically-bonded molds and cores was studied through lab experiments. Their mechanical properties were found to increase with an increase in binder content and curing time; and decrease with increasing grain fineness number. The shrinkage was found to increase with an increase in all three process parameters. The results are explained in terms of bonding and curing phenomena of binders, and evaporation of solvent. These are also supported by SEM analysis of crosslinked resin bridges between sand grains. The findings were incorporated into a multi-objective optimization model to obtain the desired combination of mold properties, which is solved as a linear programming problem. The model and its results were successfully verified through experiments. This work paves the way for automatic optimization of molding parameters of chemically-bonded sand molds and cores, to achieve the desired quality. (C) 2016 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.