Optimizing Design

Examination of a weldment for potential casting conversion also provides an opportunity to optimize the component’s design. As part of the casting conversion process, a finite element analysis should be performed and confirmed with actual testing. During this activity, the design can be optimized for load-carrying capability.

Time may not have been available during the prototype stage to perform this type of in-depth analysis. Instead, reliance was placed on experience and a liberal safety factor. Hence, examining it for a casting conversion provides a unique opportunity to reinvestigate the part. A redesign may improve its function or merely improve cosmetic appearance.

Casting the weldment also will result in fewer internal stresses, depending on how it is cooled, which results in less distortion during subsequent machining operations. This will aid in more accurate dimensional conformance.

Weldments inherently contain residual tensile stresses that can approach the material’s yield strength. Removing material during machining operations has the tendency to relieve these residual stresses and generates distortion. Only if the weldment is stress-relieved before machining can the distortions be eliminated. These benefits lend justification to converting the weldment into a casting.

—Robert M. Hathaway, Material Process Engineer, Oshkosh Truck Corp., Oshkosh, Wisconsin