MULTIPLE DRAWING METHOD Russian patent published in 1995 - IPC

FIELD: metal pressure forming. SUBSTANCE: method comprises steps of making an annular thickened portion on an edge of an outer side of a section at each operation of producing a semifinished product with a thickness of its wall, equal to S_w<0,015 d_s, excluding a final operation. In order to form the annular thickened portion a combination drawing operation is being realized with use of a stepped punch, whose step, having a diameter, equal to an inner diameter of the drawn semifinished product, and a height, equal to a height of that semifinished product without a height of its annular thickened portion, is joined by its cone part with a second step, having less diameter. A formation of an edge portion is being performed with subsequent expansion of the semifinished product along its edge portion. An identical thickened portion is being made by the combination drawing process with limitation of a working stroke in a die, having a cone inlet portion, passing to a profiled one. Dimensions of that profile correspond to dimensions of the annular thickened portion. EFFECT: enhanced efficiency of the process due to using of the combination drawing of the semifinished product, having the annular thickened portion on its edge, providing elimination of riffles formation. 3 cl, 3 dwg