Patent ID: 7823432
Filing Date: 2010-11-02
Classification: B21J,B21K

Abstract:
1. A method of forming spring washer blind-holes in a piston for an automobile transmission, comprising: flattening an annular region of a metallic sheet blank to form a secondary workpiece, the annular region to be located along a peripheral edge portion of an end plate of a piston body, said flattening including: forming a plurality of spring washer blind-holes along the peripheral edge portion at the rear of the end plate of the secondary workpiece, said forming of the plurality of spring washer blind-holes including performing an extrusion process comprising projecting a plurality of pins into the peripheral edge portion at the rear of the end plate to form the spring washer blind-holes, a quantity and location of the pins corresponding to a desired quantity and location of the spring washer blind-holes; and performing said extrusion process so that all of the material extruded by the extrusion process due to the projecting of the pins flows so as to project out of a front surface of the end plate to form front surface projections.