Friction Stir Welding Technology for Marine Applications

Abstract

Friction Stir Welding (FSW) is a very attractive alternative to MIG welding for joining aluminium alloys and is an established joining technique in the marine industry. One of the limitations of FSW is that the process requires relatively high levels of force to be applied, primarily to maintain the correct tool position, during welding. This requirement typically results in large, heavy, expensive FSW machines with limited scope for making very large panels. A new FSW technique called “floating-bobbin” which allows welds to be made with almost zero vertical force on the weld, offers the potential for smaller, less expensive, and critically mobile equipment to be developed. Floating Bobbin Friction Stir Welding (FBFSW) is accomplished with a “fixed” bobbin tool where the two shoulders and pin features are constrained rigidly to each other however the whole tool can float in a holder in the vertical axis. This arrangement has advantages in that the tool automatically compensates its position relative to the component eliminating the need for accurate set up procedures and sophisticated position or force control systems. This approach is designed to provide uniform heat input, minimising distortion and eliminate the potential for root defects. This paper describes the development and assessment of joining aluminium alloys using the FBFSW technique and its suitability for use on a mobile FSW system designed for use in a shipyard. The principles of this technique are explained including the assessment of welding forces, tool life, weld properties and panel distortion when compared to conventional welding techniques. The development and exploitation of FBFSW offers the potential for a low cost, reliable solid-phase joining technique and the possibility of mobile FSW equipment to be developed.