Friction welding. 

Rotary Friction Welding: Out of the two materials, one is rotated over the surface of the other where the weld is required. The process uses compressive axial force and the high rotation speeds.This combination causes the plasticizing of the two materials, eventually leading to a bond between the two.

Linear friction welding: In this type of friction welding, one of the materials oscillates in relation with the other at high speeds with high compressive forces in a reciprocating motion. The resulting heat generated at the surfaces causes the metal to plasticize, and the oxides or surface-level contaminants are burned off or expelled at the sides.

Friction Stir Welding: Friction  stir welding uses a special tool with a cylindrical shoulder and a profiled pin to create welds. The pin drives along the seam of the two workpieces until the shoulder rests on the seam.The tool then rotates where the friction between the shoulder and the seam softens the metal. The profiled pin is moved linearly through the line of the seam stirring the soft metal and creating a bond in the process.

Linear Friction weldingLinear friction welding (LFW) is similar to spin welding, except that the moving chuck oscillates laterally instead of spinning. The speeds are much lower in general, which requires the pieces to be kept under pressure at all times. This also requires the parts to have a high shear strength. Linear friction welding requires more complex machinery than spin welding, but has the advantage that parts of any shape can be joined, as opposed to parts with a circular meeting point. Another advantage is that in many instances quality of joint is better than that obtained using rotating technique.