Automatic tracking of blind sealant paths in friction stir lap joining

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.