General Motors Corp
In lost foam casting, a polystyrene pattern is created, aged to obtain dimensional stability, then coated in ceramic slurry. Once the slurry has dried, the patterns are gated and lowered into a flask that is filled with loose sand. The sand is then compacted by vibrating the entire flask. Molten metal is poured directly onto the foam, evaporating it and assuming the shape of the foam in the sand. As lost foam casting becomes a more popular method by which to cast complicated parts, much emphasis has now been placed on eliminating some of the defects associated with the process. One such defect is metal penetration. Metal penetration occurs when molten metal breaks through the coating and penetrates into the sand surrounding the pattern. This defect can adversely affect the integrity of any casting and in severe cases can lead to its rejection as a useful part. The objective of this research was to investigate the effect of the main processing variables on metal penetration. Several variables including static head pressure, pour temperature, double coating application and to a lesser extent, sand pressure were investigated. This investigation was performed by casting several polystyrene patterns designed to create metal penetration. The patterns of original design were assembled, coated, cast, and penetration and performance during processing was evaluated. The results of these experiments showed that head pressure and coating deposition had significant effects on the presence of metal penetration. The pour temperature was less significant in preventing or accentuating the defect.
Worcester Polytechnic Institute
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