Positive pressure and side pressure two-way driving piano-shaped part forming die and forming method

The forming die comprises an upper die assembly and a lower die assembly, the upper die assembly comprises an upper die plate, an eraser, a side pressing block, a male die and a step-shaped screw, the upper die plate is provided with a square inner cavity, the eraser is arranged in the square inner cavity, and the step-shaped screw is arranged in the lower die plate. A square through hole and an inner inclined sliding surface are formed in the center of the side pressing block; the male die is arranged in the square through hole of the side pressing block; the lower die assembly comprises a lower die plate, a fixing plate, an elastic ejector, a containing frame and a female die mechanism, the lower die plate is a die base, the fixing plate is provided with a central rectangular hole, the elastic ejector is installed in the rectangular hole, the containing frame is provided with a central square hole, and the movable female die mechanism is installed in the central square hole. The upper die assembly moves dow