Friction Stir Welding is a novel green technology solid joining method. A non-consumable rotating tool with a specially designed pin and shoulder is inserted into the abutting edges of sheets or plates to be joined and subsequently traversed along the joint line. The FSW tool rotates in the counter clockwise direction and travels into the page (or left to right). The advancing side is on the right where the tool rotation direction (sense of tangential velocity) is the same as the tool travel direction and the retreating side is on the left where the tool rotation (sense of tangential velocity) is opposite the tool travel direction.
As compared to the conventional welding methods, FSW consumes considerably less energy, no consumables are use such as a cover gas or ﬂux, and no harmful emissions are created during welding, thereby making the process environmentally friendly. Further, since FSW does not involve the use of ﬁller metal and because there is no melting, any aluminium alloy can be joined without concern for compatibility of composition or solidiﬁcation cracking; issues associated with fusion welding. Also, dissimilar aluminium alloys and composites can be joined with equal ease. In contrast to traditional friction welding, a welding process limited to small axisymmetric parts that can be rotated and pushed against each other to form a joint, friction stir welding can be applied to most geometric structural shapes and to various types of joints such as butt, lap, T-butt, and ﬁllet shapes. The most convenient joint conﬁgurations for FSW are butt and lap joints. A simple square butt joint is two plates or sheets with the same thickness are placed on a backing plate and clamped ﬁrmly to prevent the abutting joint faces from being forced apart. The backing plate is required to resist the normal forces associated with FSW and the workpiece. During the initial tool plunge, the lateral forces are also fairly large and extra care is required to ensure that plates in the butt conﬁguration do not separate. To accomplish the weld, the rotating tool is plunged into the joint line and traversed along this line while the shoulder of the tool is maintained in intimate contact with the plate surface. Tool position and penetration depth are maintained by either position control or control of the applied normal force.
The main advantages of friction stir welding are following: