Machining method for two concentric through pin holes of rear leg connecting plate of automobile back seat cushion

The invention discloses a machining method for two concentric through pin holes of a rear leg connecting plate of an automobile back seat cushion. The machining method includes the steps: S1 determining the diameters of a first through hole and a second through hole of the rear leg connecting plate of the back seat cushion, the distance between the first through hole and the second through hole and material thicknesses; S2 preparing two phi 10 punches with different lengths, and mounting the punches at positions on one side of two punching processes of a mold for producing the rear leg connecting plate 1 of the back seat cushion; S3 mounting the prepared punches in place and sequentially punching parts in order; S4 punching the first through hole in one side of the rear leg connecting plate 1 of the back seat cushion by the short punch, and then punching the second through hole by the long punch approaching to the other side in the next step. Concentricity of the first through hole andthe second through hole