Extending Tool Life:
High Frequency Induction + Friction Stir Welding
Friction Stir Welding (FSW) was introduced in 1991 by The Welding Institute as a modified method of friction welding. The novelty was in not needing to rotate the parts. It presented a revolutionary method of joining dissimilar and previously un-weldable materials through solid-state bonding. The advantage of this process is that no melting is involved during welding, which eliminates the problems associated with solidification.
In conventional fusion welding, the work pieces are joined together by the application of heat, melting the materials together at the junction of the joint often with the addition of a filler material. The disadvantage of conventional fusion welding is that the melting of the parent material often brings about microstructure problems associated with re-solidification. Many materials lose strength due to the undesirable microstructure produced by melting and re-solidification. One way FSW differs from conventional fusion welding is that there is no melting, and thus, no microstructure re-solidification issues.
The way FSW works is a tool consisting of a pin and a shoulder is pressed into the junction between the parts to be joined. The tool spins as it moves along the seam of the weld. The tool is sunk into the parent material the depth of the pin; the pin stirs the material together while the shoulder stirs and helps to form and shape the surface of the weld.
Presently, the most common use of FSW is for welding aluminum. Aluminum alloys are vulnerable to re-solidification issues, so friction stir welding is an ideal process to use. Some alloys of aluminum used in aircraft were joinable only by rivets (which produce stress points) until the FSW process came about. The Eclipse 500 aircraft is one such application in which FSW replaces rivets. FSW is widely used in a growing number of aluminum applications from car parts to ship decks.