WARPAGE REDUCTION IN MMII-FABRICATED INVESTMI CASTING PATTERNS: AN FEM INVESTIGATION

摘要

Despite the better dimensional precision that can be achieved with the Model Maker II (MMII) RP system over other RP systems. MMII fabricated parts warp easily during the part removal stage whereby the part is heated to dislodge it from the foam plate. As the dimension and surface quality of the MMII part used for investment casting directly affects the quality of the metal castings the warpage of MMII built investment casting patterns need to be adressed. From experimental observation, it can be noted that the main cause of warpage is the rapid change in the temperature encountered by the part during the heating and cooling cycle. In this paper, a simple analytical model was developed and used to investigate the effects of heating on the amount of warpage encountered by the MMII part. The analytical result obtained confirms the fact that warpage is caused by the formation of internal stress due to the high temperature' gradient encountered by the part during the removal process. Further analysis shows that controlled heating can be used to effectively reduce the amount of warpage encountered during part removal.