The invention belongs to a machining process device of an aerospace product, and in particular discloses a positioning support device used for stirring, rubbing and welding a circular seam of a flange disc of a top cover of a storage box. The machining process device comprises a positioning supporting rotary support, wherein a circular base plate is arranged above the positioning supporting rotary support; an outer pressing ring is arranged above the circular base plate; round holes coaxial with a central hole at the lower bottom surface of the positioning supporting rotary support are arranged in the circular base plate and a center of the outer pressing ring; a central shaft is arranged inside the hole; the lower end of the central shaft is fixed on the positioning supporting rotary support; an outer clamping ring is arranged on the circular base plate; the outer clamping ring is connected with the outer pressing ring through a fastening structure; and a lock wire nut is arranged at the top end of the central shaft. The outer clamping ring, the outer pressing ring and the unique fastening structure have a positioning clamping function to a whole welding product; the outer clamping ring and the central shaft are concentric so as to have a function of positioning a rotation center; a design of the fastening structure has a transition function to connection of a whole positioning support device in a mode that bearing outer pressure is converted into a clamping force, and thus the machining process device is applicable to requirements on high precision in welding and assembling.