Patent ID: 6568064
Filing Date: 2003-05-27
Classification: H02K,Y10S,Y10T

Abstract:
A method of manufacturing a cup shaped motor yoke having circumferential walls at given angular regions for accommodating magnets and circumferential walls at remaining angular regions for forming main magnetic paths, by drawing a flat sheet of a metal plate, comprising steps of:putting the metal plate between a die having a cavity and a holding plate having a through-hole which is axially aligned with the cavity so that the metal plate is in contact with and held down therebetween at positions around outer circumferences of the cavity and the through-hole at first and second angular regions spaced circumferentially and is loosely placed therebetween at positions around the outer circumferences of the cavity and the through-hole at third and fourth angular regions circumferentially sandwiched between the first and second angular regions, respectively, so that a clearance having a predetermined distance is provided between the metal plate and at least one of the die and the holding plate at the third and fourth angular regions, and pressing down a punch against the metal plate through the through-hole into the cavity so that material flow of the metal plate extending axially into the cavity is restricted at the first and second angular regions, while the material flow of the metal plate within the cavity moves circumferentially from each side of the first and second angular regions to sides of the third and fourth angular regions oppositely adjacent thereto to form a first cup having a circumferential wall, whereby each thickness of the circumferential wall of the first cup formed by passing through the first and second angular regions, which corresponds to the circumferential wall of the yoke at the given angular regions is thinner than that formed by passing through the third and fourth angular regions, which corresponds to the circumferential wall of the yoke at the remaining angular regions.