The material of the stirring head, the shaft shoulder of the mixing head and the body of the stirring pin are 3 main decisive factors for the quality of the mixing head. The main functions of the mixing head are as follows:
● Heating and softening of materials to be welded (workpiece material);
● Crushing and diffusion of oxide on the surface of joints;
● Drive the material in front of the mixing needle to move backward;
● Drive the upper part of the connector to the lower part;
● To form a solid state joint after transferring the thermoplastic material.
The rheological and thermal shape plastic material mixing head is closely related, and directly affects the quality of the joint, friction stir welding in the early stages of development, the successful development of TWI cylindrical mixing head, the stirring head at the beginning of the study and development of friction stir welding has been widely applied in the. With the development of friction stir welding technology, for the different welding materials and structures, there are a series of mixing head. The WhorlTM and MX TrifluteTM (Figure 7), which was developed by the Welding Research Institute of the United Kingdom, can improve the welding speed and improve the welding quality.