Method for manufacturing metal parts with split ends joined

A method for manufacturing metal parts with split ends joined, the method comprising:

• determining a desired length of cutting plane in the thickness direction of a metal plate having any of a rectangular, polygonal, or elliptical shape, or in the diameter direction of a solid metal rod having a cross-section of any of a circular, elliptical, rectangular, or polygonal shape;
• applying a slitting punch or a cleaving punch on the cross-section of the split-desired end of the metal plate, or the metal rod, on a boundary created by the cutting plane;
• securing the metal plate by pinching both sides of a split-desired portion thereof with a clamping device, or securing the metal rod by pinching at least two opposite-facing portions on the periphery of a split-desired portion thereof with a clamping device;
• advancing splitting by pressing a slitting punch or a cleaving punch against a cleft of a split for repeatedly two or more times until a split length reaches a specified extent;
• inserting another metal plate between the split ends of the metal plate or the metal rod split;
• and
• joining both the metals mutually and permanently by a method including any of pressing perpendicular to a splitting direction of the metal plate or the solid metal rod, welding, fusing, bolting, riveting, or gluing,
• wherein, in advance of each time of each subsequent splitting operation of the two or more times,
• a position of at least one side of the clamping device that pinches both sides of the metal plate in a prior operation of securing or that pinches at least two opposite-facing portions on a periphery of the solid metal rod in the prior operation of securing, is moved along the metal plate or the solid metal rod in advance by a stroke corresponding to a distance from a position of the cleft of the split toward a distal end of a split desired position, followed by securing of the metal plate by pinching both sides thereof with the clamping device, or by securing of the solid metal rod by pinching at least two opposite-facing portions on the periphery thereof with the clamping device;
• and
• thereby the metal plate, or the metal rod, is partially split in a longitudinal direction along the cutting plane,
• wherein, in each interval between splitting operations of the two or more times, pressing of the splitting punch or the cleaving punch is suspended,
• wherein, on both sides in the case of the splitting punch or on one side in the case of the cleaving punch, a cutting edge is given a tapering shape having at least two taper portions of different angles or curvatures so that the taper portion of the side closer to a tip end of the cutting edge has a smaller inclination angle when measured counterclockwise from a horizontal axis extending perpendicular relative to a longitudinal axis passing through the cutting edge of the splitting punch or the cleaving punch, or a smaller curvature than that of the taper on the side apart from the tip end of the cutting edge.