TWI Industrial Member Report Summary 668/1999
W M Thomas, I Munns and P T Smith
Friction stir welding (FSW) is a new technique for the butt and lap welding of metals and plastics and was invented at TWI and patented.  It has a number of advantages over competing well-established welding techniques, which include: good mechanical properties, low distortion, no requirements for consumables, suitability for automation, limited degradation of the weldments, and absence of welding fume. The detailed form of the welding tool is critical in achieving sound welds and this report gives details to the effect of the shape of the welding tool when butt welding aluminium plate.
Since 1992, FSW has been applied to a number of materials, which include Pb, Zn, Mg alloys, Ti and low carbon steel. In general, the process is most readily applied to those metals and alloys with melting points below about 1000°C because of the excessive temperatures (and hence wear) which would otherwise be generated at the welding tool.
To date, most work on the process has been conducted on a confidential Group Sponsored Project by TWI*. Studies have been made of the welding of various Al alloy sheets and plate of 1.5-12mm thickness where welding speeds of up to 6.6 mm/sec (396 mm/min) have been employed.  This work has generated detailed welding schedules and procedures and the construction of prototype welding equipment.
This report covers work conducted to understand some of the mechanisms occurring at the tool, during the welding of aluminium alloy plate. Various generic tool shapes have been employed in the expectation that knowledge of their effect on the welding process will allow the design of tools which give optimum weld properties and maximum productivity.
To determine the effect of certain tool geometries on weld consolidation when butt welding 6.4mm aluminium alloy plate and to demonstrate the capability of FSW for welding 50 and 75mm thick plate.