No cracks were found in the final castings.


program using the original design predicted stress in the locations the crack had been appearing per- fectly, confirming the origin of the crack was built into the customer’s design and not the result of poor casting practice. “The big thing was the signifi-


cance of the change that had to be made,” Burita said. “We wanted to make sure we were confident the design was going to work because we had metal tooling. Before we cut it, we wanted to make sure we were right.”


The engineers discovered the


stress in the casting was occurring in the original design because the base was so large and voluminous it took much longer to solidify than the rest of the casting. The bottom was pulling down on the ribs that connected to the top rim, while the top was resisting be- cause it was already frozen solid. This caused a pull where the rib attached to the sidewall, leading to the stress cracking. “There is nothing you could do


in the process to prevent, change or alter that,” Burita said. “The


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Sept/Oct 2015 | METAL CASTING DESIGN & PURCHASING | 27


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