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A Monolithic Internal Strain-Gage Balance Design based on Design for Manufacturability

A MONOLITHIC INTERNAL STRAIN-GAGE BALANCE DESIGN BASED ON DESIGN FOR MANUFACTURABILITY Thomas Ladson Webb III Old Dominion University, 2018 Director: Dr. Drew Landman This paper proposes an alternative approach to internal strain-gage balance design driven by Design for Manufacturability (DFM) principles. The objective of this research was a reduction in fabrication time and, subsequently, cost of a balance by simplifying its design while maintaining basic stiffness and sensitivity. Traditionally, the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) balance designs have relied on Electro-Discharge Machining (EDM), which is a precise but slow and, therefore, expensive process. EDM is chosen due to several factors, including material hardness, surface finish, and complex geometry, including blind cuts. The new balance design objectives require no blind cuts, and offered a significant reduction in fabrication time, sufficient stiffness, and an acceptable level of sensitivity at the gages for the current design loads. The FF09X is designed to be a direct replacement for the NASA Langley FF09, retaining the same external dimensions, 2-inch x 2-inch x 6-inch, as well as the same load requirements and mounting configuration. Starting with the existing FF09A design, multiple design concepts were considered, including several two-piece designs, before a single-piece design was chosen. The final design is a monolithic balance with the center bored at both the metric and non-metric end and all fillets and rounds not less than 0.0625-inch in radius. Using Design of Experiments (DOE), a Central Composite Design (CC) was used to optimize the cage beam cross-sectional areas and moments of inertia. The FF09X was shown to measure applied forces and moments as effectively as the FF09, while only realizing a small increase in total deflection and decrease in resonant frequency. The overall manufacturing time required to fabricate the FF09X was estimated at 160 hours, which represents a 73% reduction in time when compared to the FF09.