Swedish and American conferences joined by friction stir

Citation

(2001), "Swedish and American conferences joined by friction stir", Assembly Automation, Vol. 21 No. 1. https://doi.org/10.1108/aa.2001.03321aab.002

Swedish and American conferences joined by friction stir

Swedish and American conferences joined by friction stir

Keywords: Conferences, Friction, Welding

The successful, and simultaneous, staging of two major events on opposite sides of the world, each featuring friction stir welding (FSW), demonstrated the enormous global importance of this revolutionary, solid state, joining process to manufacturing industry.

The 2nd Friction Stir Welding Symposium in Gothenburg, Sweden, and the Aeromat 2000 Conference in Seattle USA were both held between the 27 and 29 of June 2000. They revealed the speed with which industrial companies are now applying FSW technology, invented and patented by TWI in the UK in 1991, to a great range of products.

In Gothenburg, 155 delegates from 16 countries including Australia, Japan and the USA, listened to 35 papers.

In Seattle, the Aeromat 2000 Conference was organised into eight parallel themes. FSW was one of these themes. It occupied two full days in which 25 papers were presented to audiences of between 50 and 100 at each paper.

Distilling the key issues from both events, it was clear that the aerospace industry sees FSW as a major enabling technology.

A new topic to emerge at both venues was the contribution of FSW to airframe construction. The issue is cost reduction, principally by the replacement of components built up from scores of pieces, each weighing a few grammes, by larger elements (unitisation). Statistics for the F16 aircraft were given. It has 6,965 total parts, 58 per cent of which weigh less than 40 grammes, and uses 117,175 fasteners. FSW is one of the enabling technologies for unitisation.

It also contributes to airframe cost reduction in other ways. One example is the use of a tailored billet for upper and lower wing skins resulting in greatly reduced machining costs. The airframe industry is setting up substantial projects to develop the applications. FSW items are already incorporated into a growing number of aircraft structural components. Some of these components are already built into aircraft for test flights and are performing well. More will take to the skies in the next year.

The concept of the "welded aeroplane", and other demanding applications such as high speed rail vehicles, stimulated a large number of papers reporting on properties. In every instance FSW performs as well as, and frequently better than, an arc weld. Issues attracting attention are ageing whilst the aircraft is on the ground, corrosion, and crack propagation. Results so far suggest FSW is superior to riveted or bolted connections but not enough results are available to satisfy regulators and work continues.

At the latest meeting for friction stir welding of transport structures at the end of September, sponsors were delighted to be told of dramatic results in the development of an advanced FSW tool.

Its use achieved an increase of 150 per cent in travel speed.

Increasing welding speed substantially, while maintaining or improving the existing high weld quality was a prime objective of the project at its inception.

Welding trials have been conducted on the normally difficult-to-weld aerospace Al-Zn alloy 7075-T7351. So far a welding speed of over 400mm/min has been achieved when making butt joints in 6.35mm thick material. This represents an increase of at least 150 per cent on the speed achievable with current commercially available FSW tools. This tool also produces a higher weld nugget hardness leading to higher tensile strength values.

Even higher speeds are expected by changing the tool path about the axis of rotation. Trials will continue.

Extensively covered at both events were: FSW by robot; FSW of copper, titanium, metal matrix composites, and plastics; and applications to repair and reclamation. FSW equipment is now purpose-built with sophisticated control of parameters rather than adapted from other machine tools.

Attempts to understand the process by mathematical modelling and other means, together with non destructive examination technologies, were discussed.

Unquestionably, FSW is a joining technology that has come of age. The transport industry is the pioneer for FSW industrial penetration. The process is in commercial use in ships, automobiles, rail vehicles, and space. It is at an advanced stage of evaluation for commercial and military road vehicles and aircraft.

Most of the work reported at these two events reflected welding based on the early friction stir tool design principles. TWI has been developing a range of high performance tools ready for commercial evaluation and exploitation. A number of Group Sponsored Projects (GSPs), including the welding of steel and titanium, are running at TWI through which companies can exploit these developments on a shared cost and risk basis in return for preferential access to the results.

TWI currently has licensees in all parts of the world who are using the process and there is no sign of the applications slowing down. The Friction Stir Welding Licensees Association will be sponsoring the next big opportunity to measure the march of FSW in Japan in September 2001.