A method of roll forming hollow parts comprises introducing a workpiece into the space between a plurality of rolls rotatably arranged in spaced and parallel relationship, in parallel with the axes of the rolls, imparting rotation to the workpiece from drives through either the rolls or flanges disposed at both ends of the workpiece, at the same time forcing mandrels, slidably fitted at ends in the central openings of the flanges, through the openings into the workpiece, longitudinally from the both ends thereof, toward each other, and removing the excess metal left in the midportion of the workpiece between the mandrels by slightly moving the rolls toward each other for added compression, thereby producing spaces between the mandrels and the workpiece, and by moving the mandrels axially together with the excess metal to separate the latter from the rest of the workpiece.
Grooves are formed on a rotor by rotor holders for holding a rotor at both ends of a rotary shaft thereof, a groove rolling die for forming grooves in the outer surfaces of the field cores of the rotor, and a holder die having a groove pattern in conformity with a pattern of the grooves that are formed in the outer surfaces of the field cores by the groove rolling die. When the grooves are formed, the grooves are uniform in depth over the entire length of the magnetic poles from the root to the top, thereby preventing the eddy-current loss reduction effect from being deteriorated.
A process of making wheels in which a pair of rams press an initial mass of material for shaping a central disc part. A portion of the material is extruded out from between the interface of the rams. A roller unit having several rollers simultaneously forms rim parts by pressing the extruded material into desired shapes as it passes beyond the periphery of the rams.
