TWI

By: Stephan Kallee^[1] (TWI)

Stephan Kallee
TWI Ltd
Granta Park
Great Abington
Cambridge CB1 6AA
United Kingdom
Tel No : +44 1223 891162
Fax No : +44 1223 894367
E-mail : stephan.kallee@twi.co.uk
Website: www.twi.co.uk

TWI's expertise

TWI provides services to industry and individuals worldwide. It encompasses a professional engineering institution, an international training and certification activity and a large consultancy R&D establishment dedicated to transferring technology to industry. It is one of Europe's largest independent contract research and technology organisations, for which a new building will be constructed (Fig.1). Over 400 staff, with a unique blend of technical backgrounds, international experience and language skills, work regularly with some 2500 companies in over 50 countries to apply joining technology effectively.

Fig.1. Artist Impression of TWI's new building © 2001, Bovis LLP

Industrial exploitation of friction stir welding

The industrial interest in friction stir welding is clearly demonstrated by the number of organisations wishing to participate in the EuroStir^® project and it is firmly believed that even these will increase in number as the project proceeds.

The potential for exploitation and implementation is therefore significant, given that the need for capital investment by users is addressed. The engagement of small and medium sized job shops is planned to serve this purpose by enabling the proof of application economics prior to investment decision.

Undoubtedly the FSW process will in time be fully recognised and more widely applied in Europe, especially since the EuroStir^® project makes the know-how more accessible. TWI is expecting a large number of visitors to see the new EuroStir^® demonstration facility, which will be will be conveniently situated at the main access road to TWI's new site development.

Fig.2. Artist Impression of the EuroStir demonstration facility at the main access road to TWI's new site development © 2001, Bovis LLP

Friction stir welding - a TWI invention

TWI invented and patented the friction stir welding process in 1991. Friction stir welding (FSW) is arguably the most significant joining process to be developed since the laser. The fact that simple machine tool technology can join materials in the solid phase without, in most cases, the need for any consumables, gives rise to numerous benefits. The absence of fusion in the joining process avoids weld defects, reduces distortion, and results in superior mechanical properties. Furthermore, the lack of consumables and need for weld preparation or after-weld correction results in major cost savings. Equally important are the health and safety benefits of a process that involves no fume, radiation, or significant noise.

Following the invention of FSW various confidential single and group sponsored projects were conducted to fully evaluate the FSW of aluminium alloys up to 12mm thickness. It is testament to the success of these projects that numerous organisations in Japan and the USA were able to use the experimental results directly in production and since then have been further optimising and refining the process, such that they are today in advance of European technology and exploitation.

European research has continued to have some involvement with the development of FSW and has usefully indicated the potential for tool and procedure development. In addition very limited tests have shown that very thick sections (~50mm) may be welded in one pass and even titanium, nickel alloys, stainless and ferritic steels are weldable.

All previous work has shown that the success of the process is controlled by tool design (material and shape) and the welding forces and their control, thus these are the areas to be researched for the various materials and applications to be investigated. The uncertainty of a successful outcome has to be very low in view of the Japanese and US leadership in the technology and the observed adaptability of the process.

Results that have been revealed indicate that FSW is not simply a new welding process for soft, low melting point materials in relatively thin sections. On the contrary, the process is instrumental in enabling new design where castings may be joined to a variety of wrought materials in a wide range of section thicknesses. This broad capability plus the attendant substantial cost savings makes the process of unique value to the fabricator who is able to offer improved quality and lower prices than the competitors.

Search the TWI website for information on friction stir welding.

TWI's contributions to EuroStir^®

Project Management of EuroStir^®
To develop innovative FSW tool designs and new welding procedures to increase industrialisation of FSW
To train and coach potential FSW operators and technical staff.
To disseminate at conferences and exhibitions how environmentally friendly and economic the FSW process is

References

1. Project Manager of EuroStir^® is Stephan Kallee (TWI), stephan.kallee@twi.co.uk

EuroStir^® homepage

TWI

By: Stephan Kallee[1] (TWI)