TWI Technology Briefing 851a/2007
By M E Nunn
Friction Stir Welding (FSW) was invented by Wayne Thomas at TWI, and the first patent application was filed in the UK in December 1991 (1). Initially the process was regarded as a laboratory curiosity, but it soon became clear that the process had much to offer in the fabrication of aluminium alloys. As it is a solid state process, it was found that 2xxx and 7xxx series alloys, which are difficult to fusion weld because of their solidification characteristics, could be easily welded. Other materials suitable for joining by this process were soon identified and successful welding was quickly demonstrated.
Today, development of the process is underway in many companies, research institutes and universities throughout the world, and the activity level is growing. Applications have been reported in most industry sectors (2). Some examples include marine deck panels and hulls, high-speed trains and lightweight automotive structures. The aerospace sector recognised FSW as a viable joining process and applications include structural and non-structural assemblies. The first civil aircraft with a significant number of structural friction stir welds, the Eclipse 500 executive jet, made its first flight in August 2002. Use of the process to repair fusion welded joints has also been demonstrated. A number of the machines delivered for use in the aerospace and other industries have been described by Kallee et al (3).
Most of these applications are welded using large, heavy and stationary static equipment. The use of lightweight portable equipment for manufacture and repair activities is desirable for many other applications. A number of research organisations have been active in developing portable FSW machines, but at this time no commercially available, versatile systems exist.
The benefits of portable FSW are:
- The possibility of applying FSW in remote applications.
- In-situ repair of components attached to larger structures.
- Increased versatility of process, leading to increased use of the process in industry.
The theoretical physical forces necessary to make welds between thin sheets could prove to be sufficiently low to enable a hand-held, or hand-positioned, portable FSW machine to be developed. Such a machine would provide considerable benefits for both manufacture and repair.
This report is intended as an introduction to the technologies required to make the FSW of aluminium alloys a portable process, as well as providing details of, and solutions to, some of the technical challenges which may restrict the portability of the process.
The objective of this work was to review methods to make the FSW process more flexible and portable using current technology.