Original Date: 11/03/1996
Revision Date: 01/18/2007
Information : Casting and Machining of Complex-Shaped Parts
The Oak Ridge Y-12 Plant was compelled to address producibility issues in the early stages of one of its fusion energy experiments. The complex geometry of a cast stainless steel twisted tee section posed problems in both near net shape casting and final machining. In total, 24 machined tee sections were required to complete the final doughnut-like double helix assembly.
Initially, because of the unknown process variances in the casting process (thermal growth/shrinkage from uneven heating and cooling) for this type of geometry, an additional .75-inch of extra stock was added to the final machined features, adding 1,500 pounds of unwanted material to the first prototype casting. Three months later, under constant machining operations, the first prototype twisted tee section was still months from completion, and performance cost-to-contract was exceeding the original budget constraints.
The Y-12 Plant therefore utilized a conventional coordinate measurement machine (CMM) to model a second prototype casting. Through the mathematical use of an optimization theory for this non-linear shape, a least-squares computer analysis provided the best-fit placement of the complex final machined part within the given casting envelope. This modified data was then relayed back to the casting vendor and used to provide a near net shaped part with only .125-inch extra stock. When the new castings arrived, a temporary hard mounted conventional tooling ball was mounted to each twisted tee section to provide a durable and accurate data referencing point. The CMM and the optimization program were again used on each of the 24 cast segments to accurately describe each of the as-cast geometries. This data was then applied to develop customized NC programs that provided the best-fit for the final machined configuration. This innovative use of the CMM as a process development tool for casting and machining of complex geometries saved the Department of Energy (DOE) millions of dollars on this project.
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