Novel side top plate friction stir welding tool with hanging gravity locking cushion block

The novel side top plate friction stir welding tool with the hanging gravity locking cushion block comprises a bottom plate, fixing devices and a friction welding base plate, the friction welding base plate is arranged on the center line of the bottom plate, and at least two sets of fixing devices are arranged on the portions, on the two sides of the friction welding base plate, of the bottom plate with the center line as the symmetry axis. The fixing device is provided with a jacking pressing head which moves in a reciprocating mode, a cushion block on the jacking pressing head is made to be matched with a backer on the side portion of the friction welding base plate, so that the side jacking plate is pressed and fixed to the friction welding base plate, the backer is detachably arranged on the friction welding base plate, and the cushion block is detachably arranged on the jacking pressing head. On the basis of an existing welding tool, the connection relation between the backer and the friction welding bas