Introduction


Friction stir welding (FSW) [1] is an emerging technology invented in 1991 at The Welding Institute, Cambridge. Since then, it has developed from an experimental joining procedure to a technology used commercially. The potential of this technology has not been used fully as there is not enough practical information about it in open literature.

Aeronautical engineering can make use of FSW at many fronts. It can be used to weld items that are not possible to be welded by conventional fusion welding such as aluminium alloys of 2XXX and 7XXX series [2] and serve as a riveting replacement [3]. It can also replace conventional TIG and MIG welds to provide significantly better corrosion resistance [4, 5] and fatigue properties [6, 7].

In the Czech Republic research on FSW is conducted in Aeronautical Research and Test Institute in Prague as a part of progressive joining technologies research [8].

In this thesis, we focused on friction stir welds of aluminium alloys of 2XXX and 7XXX series and provided guidelines to the practical application of FSW on aircraft structures.

1.1      Benefits of FSW

FSW brings many benefits when comparing to traditional fusion welding and other joining methods commonly used on aircraft structures. Mishra [9] names many benefits of FSW. The most crucial of them for application in aircraft industry are:

-          Low distortion of work piece

-          Good dimensional stability and repeatability

-          Absence of cracking

From production technology point of view Mishra [9] states these benefits:

-          No shielding gas required

-          No surface cleaning required

-          Eliminate grinding waste

-          Eliminate solvents required for degreasing

-          Improved material use

-          Low energy needed for weld creation (compared to fusion welding)

It also generally offers better mechanical properties when compared to fusion welds, however, the resulting properties strongly depend on welding process parameters such as welding tool shape [10-15], tool revolutions [12, 16-18] and welding speed [16, 19, 20].



1.2      FSW as riveting substitution

FSW is a very promising technology in the field of riveting substitution on the aircraft structures. Using riveting technology in current aircraft design limits the productivity levels manufacturers can reach for the aluminium aircraft structures. Use of the rivets also introduces unwanted stress concentrators and can induce crevice and fretting corrosion.

1.3      Current use of FSW

Today, the FSW technology is used mainly in aerospace industry where its benefits can be utilized fully. The technology brings significant weight savings into aluminium fuselage construction where riveting is usually the main mean of joining. Generally, FSW is well suited mainly for long straight welds, like the ones on stringer-reinforced panels, which are a vital part of today’s most common aluminium fuselage, wing and other constructions in aerospace industry.

Automotive industry can also take advantage of FSW. Wider use of aluminium alloys and together with FSW joining techniques helps to create lighter and more economical car construction [21].



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