PURPOSE: To form an annular groove and annular projecting part with high accuracy and to obtain a molded product having a high flatness by forming a specific one-side recessed section in one surface of a plate material by plastic working and at the same time, transferring the volume of the recessed section to the other side of the plate material.
CONSTITUTION: A one-sided recessed section 37 having an inside diameter equal to the outside diameter A of an annular groove 33 is formed in one surface of a plate material 31 and at the same time, the volume of the recessed section 37 is transferred to the other side of the material 31. As a result, an other-side projecting section 39 is formed on the other side of the material 31 by plastic working. Then an other-side recessed section 41 having an inside diameter almost equal to the inside diameter B of the groove 33 is formed in the projecting section 39 by plastic working and the volume of the recessed section 41 is transferred to the one side of the material 31. Then the annular groove 33 and an annular projecting section 35 are formed by plastic working. Thus a molded product can be manufactured with remarkably low pressure.
IGARASHI MASAAKI
YAMAKI TOSHIO
