Fig 4. The maximum principal stress distribution of the shell at the end of flash firing and for aged and unaged foam patterns shows maximum stress in the shell occurs when the boundary temperature reaches the foam softening temperature.


treatment depends on multiple groups of parameters: Foam Properties—elastic modulus,


3


thermal expansion, softening tempera- ture and aging. Shell Properties—failure stress,


Results and Conclusions During the study, the


researchers discovered crack formation during rigid foam pattern removal by heat


Table 1. Comparison of Simulation Results and Experimental Results


Case # Shell Thickness (in.) Aging Shell Fail (Simulation) Shell Fail (Experiment) 1 2 3 4


0.25 0.15 0.25 0.15


Not aged Not aged Aged 212F Aged 212F


elastic modulus and shell wall thickness. Firing Regime—continuous heat-


No


Yes No No


No


Yes No No


ing vs. flash firing in a high tempera- ture, preheated furnace. The authors concluded that aging


42 | MODERN CASTING August 2012


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