Friction stir welding is a remarkable welding process - materials in sheet or plate form can be joined in a butt or lap weld. As with all friction processes, there is no fusion of the pieces being joined.
The process operates by passing a rotating tool between two closely butted plates, which generates heat, and passes the material from the front of the tool to the rear, where it is consolidated to form a high quality solid stateweld. Since its invention by TWI in the early 1990s, the process has been well developed for joining aluminium alloys, and is now in commercial use. To date it has been very successful in joining 2xxx, 7xxx and Al-Li alloys,traditionally difficult to join by fusion processes.
Based on machine tool technology, friction stir welding can be fully automated, requires no special power source or welding skill, and uses no filler or shielding gas. There is now a strong demand to develop the process for othermaterials such as titanium and its alloys, particularly ones which are difficult to fusion weld.
In order to meet this need, TWI is launching a group sponsored project to study this topic in depth, involving several different titanium alloys. Various tool materials and designs will be tested - the major initial challenge withtitanium alloys is to find a suitable tool material, as the high operating temperatures will make tools normally used for aluminium ineffective.
The project starts this autumn and will be run by TWI and EWI in partnership, with TWI having overall management responsibility. Further details can be obtained from Philip Threadgill and Dave Nicholas at TWI (e-mail: philip.threadgill@twi.co.uk , dave.nicholas@twi.co.uk ) or Mary Juhas at EWI (e-mail: Mary_Juhas@ewi.org)
