Navy as well as commercial divers currently use a friction stud welding process to install threaded steel studs below sea on a variety of vessels for a variety of applications ranging from cathode installation and repair to installing mounts in the preparation for hull repair using Cofferdams. The friction welding method has proven to be one of the best wet stud welding technologies for steel because it is a solid-state joining process that produces coalescence in materials using the heat developed between surfaces through a combination of mechanically induced rubbing motion and applied load. Since there is no melting of the materials, no solidification defects occur, e.g. gas porosity, segregation or slag inclusions. Friction welding produces forged quality joints, with a 100% butt joint weld through the contact area with a narrow Heat-Affected weld Zone (HAZ) resulting in a weld strength that is equal to or better than the parent material. Filler metal, flux and shielding gas are not required with this process. The Littoral Combat Ships (LCS) utilize 5000 series aluminum hulls that may require underwater ship husbandry, emergency repair or damage control. The Navy requires a stud friction welding device that can produce top quality, repeatable wet friction welds (minimum ½ OD to 3/8 thick plate) in a system that is ergonomically and operationally safe and easy for the diver to maneuver and handle with little training to be operated by a 150ft minimum umbilical length attached to a hydraulic power unit (HPU) on ship. The Navy states in their SBIR request that underwater friction stud welding in aluminum has not been achieved commercially or within the government. This proposal explores, defines, and tests the process parameters required to perform both dry and wet welds using 5000 series aluminum with the goal of providing a sound, hydraulically based concept underwater stud welding handheld system that is diver safe and friendly.
