Abstract

Historically, automotive body panels have been made of steel and joined by a process called resistance spot welding (RSW). However, in efforts to reduce vehicle weight to improve the energy efficiency of the vehicle, automotive manufactures have begun substituting aluminum in place of steel. While aluminum can be joined with RSW, a myriad of challenges arise from doing so. These challenges result in less consistent weld quality and accelerated electrode wear. Refill friction stir spot welding (RFSSW) is an emerging joining technology that could replace RSW as it is believed to be capable of creating superior joints in thin sheet aluminum. This research's goal is to compare RFSSW and RSW for joining aluminum automotive body panels. To accomplish this goal two studies were conducted and reported on in this thesis. The first focused on evaluating the manufacturing performance of RFSSW and RSW while the second focused on comparing the microstructure and mechanical performance of RFSSW and RSW joints. To improve the relevance of the study, a Toyota automated welding cell was used as a case study. The cell utilizes AA6061-T4 in 8 unique stack-ups to create door frames. This cell served as the base for the manufacturing performance comparison while also providing the three stack-ups used to compare microstructure and mechanical performance. The study compares manufacturing performance utilized a digital twin to compare how each technology would interact within the manufacturing cell. Parameters such as joining time and maintenance time were considered while overall output of the manufacturing cell was recorded. The results showed that RFSSW and RSW could produce the same number of parts in the given manufacturing cell. However, as modifications were made to the cell to increase output RFSSW proved to be capable of greater output due to its longer tool life. Concluding that RFSSW is a viable option from a manufacturing performance view. The second study conducted a comparison of the microstructure and mechanical properties of RFSSW and RSW. This study found that each technology created unique surface topographies and grain structures. Mechanical performance testing found that depending on the stack-up RFSSW joints were between 16% and 73% stronger than RSW joints in tensile loading conditions. RFSSW also showed improved fatigue life, in one test surviving 2600% more cycles. Concluding that RFSSW joints have superior mechanical performance over RSW joints.

Degree

College and Department

Ira A. Fulton College of Engineering; Manufacturing Engineering

Rights

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