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An automatic joint-tracking technique that employs an extremum-seeking controller is evaluated as a method for automatically tracking sealant paths that have been applied in dissimilar friction stir lap joints of 2024 and 7075 aluminum alloys. Sealants are commonly used to prevent the ingress of corrosion at the faying surfaces of lap joints, and in this study, an attempt is made to exploit sealant presence to reduce necessary robotic path planning procedures. Controller parameters are tuned, and baseline tracking performance is established with milled channels, which are used to replicate the force signature of sealant, and the tracking technique is then evaluated with Pelseal® 2077 sealant applied in a prescribed fashion in both cured and uncured states. Mechanical testing is conducted to determine the implications for weld strength when welding parameters are selected primarily for successful tracking. Results are promising and demonstrate a new level of interaction between sealants and robotic control techniques.

A pinless friction stir spot welding tool with a scrolled convex shoulder is used to create spot welds on aluminum alloy plates. The effects that the rotation rate, the dwell time, the plunge depth, and the plunge rate have on the spot welding process are investigated. A strong correlation was found to exist between the joint strength versus the tool rotation rate and the joint strength versus the dwell time. Low rotation rates and short dwell times resulted in significantly stronger welds and, conversely, higher rotation rates and longer dwell times resulted in spot welds with hooking defects and lower joint strengths. Using shear tests and macrosection analysis on the spot welds, the dependences of the joint strength, the spindle torque, the temperature and the axial force on the identified process parameters are discussed. A computational fluid dynamics model is created to simulate the effect that the tool rotation rate has on the heat generated and the material flow during spot welding.