Design of replacement structural components for fabrication using metal big area additive manufacturing

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Greer, Clayton M.
Kurfess, Thomas R.
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Since the 1980s, additive manufacturing processes, commonly called 3D printing, have been used for prototyping applications due to low part strength. A new wire-feed metal additive manufacturing process called Metal Big Area Additive Manufacturing (MBAAM) addresses the component strength and deposition rates for large structural components. MBAAM uses gas metal arc welding to deposit steel welding wire in 3D structures. The design protocols for designing structural components using MBAAM are presented in this thesis using a case study in designing and printing a replacement excavator arm. In additive manufacturing, deposition rate and feature resolution are inversely related, which affects the design strategy of additive manufacturing processes that use high deposition rates. For instance, MBAAM deposits steel beads that are 6mm. The excavator arm is designed to use plates with thicknesses intermediate between the thickness of one and two beads deposited with MBAAM, so topology optimization is used to reduce the weight of the arm design using thicker walls. Structures printed with MBAAM must be designed to adhere to an overhang constraint of 15° and minimize the use of support structures because the support structures are full strength steel. Removal of the solid supports requires CNC machining, which is expensive and time consuming. The overhang constraint requires the modification of features in the excavator arm, requiring geometry changes and post-processing machining to implement the needed features. The structural integrity of this modified arm is analyzed using finite element analysis to ensure that the arm will not fail in normal operation. The printed arm is subsequently installed on an excavator and used in a real world demonstration.
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