Automated Underwater Welding with Reactive Nanoheater Foils

Abstract

Underwater manufacturing and maintenance processes such as welding are accompanied by high occupational risks for welder-divers. This thesis research attempts to offer a new underwater technique that can be easily automated in the future. These hazards are eliminated by introducing an underwater welding robotic system to ignite nanoheater foils for metal joining, thus extending the use of these nanoheaters from soldering, brazing and joining of components in microchip industry, to underwater welding. Ni-Al reactive multilayers are utilized to perform aluminum sheet component joining. These commercially available nanoheaters release large amounts of heat when an exothermic reaction is initiated by an electrical ignition stimulus. Integrity of the welds performed by nanoheater underwater welding is insured through introducing openings on the nanoheater foil, allowing for weld areas in a lap joint. The generated temperature field is simulated during such welding, establishing optimal values for the Al sheet and nanoheater thickness, as well as the opening geometry conditions, for reaching the melting temperature at the weld interface to generate successful and sound joints in the experiments. These simulation results are compared with the thermal results obtained by an infrared pyrometry camera and J-type thermocouple. Parts that serve a dual purpose have been designed and fabricated to punch holes and compress nanofoils while ignition. Uniaxial tensile tests were performed to quantitatively measure the strength of welds performed. Results showed that increasing the hole size to 4 mm had almost no effect on the average strength and toughness of the welds. However, the average strength and toughness almost doubled when increasing the thickness of aluminum to 0.2 mm. Electrical ignition successfully occurred for all three conditions; air, water and saline water. Analysis of ignited nanofoils using SEM and EDX was carried out to confirm integrity of the welded joint section structure and composition.

Date of Award	Jun 2017
Original language	American English
Supervisor	Doumanidis Harris (Supervisor)