A burring method includes: a placement process of disposing a sheet-shaped workpiece formed with a through hole such that a punch is positioned on one sheet thickness direction side of the workpiece and a pad is positioned on the opposite side to the one sheet thickness direction side of the workpiece; and an extrusion process of forming a flange by moving the punch toward the opposite side relative to the workpiece and extruding a peripheral rim of the through hole in the workpiece with the punch in a state in which the peripheral rim of the through hole is pressed by the punch and the pad in the sheet thickness direction of the workpiece.

A method for manufacturing a hot pressed product by heating a sheet material and quenching the sheet material while molding the sheet material includes a hole forming step of forming a pilot hole in the sheet material; a heating step of heating the sheet material in which the pilot hole is formed; and a molding step of forming a burred portion at the pilot hole by using a burring punch included in a die set while molding the sheet material in the die set. The pilot hole has an opening shape in which convex portions and concave portions are alternately arranged. A diameter of a circumscribed circle that is in contact with the convex portions is greater than a punch diameter of the burring punch. A diameter of an inscribed circle that is in contact with the concave portions is less than the punch diameter of the burring punch.

A convex portion projecting from a plate member includes a base, a convex body, and a guide. The base is part of the plate member. The convex body erects in a cylindrical shape from the base. The guide is at a top end of the convex body. The base includes a first inner circumferential surface, a second inner circumferential surface, and a third inner circumferential surface. The first inner circumferential surface is continuous with an inner circumferential surface of the convex body and extends in a direction opposite to an erecting direction of the convex body. The second inner circumferential surface is continuous with the first inner circumferential surface and intersects the erecting direction of the convex body. The third inner circumferential surface is continuous with the second inner circumferential surface and is larger in diameter than the first inner circumferential surface.

A bevel stud punch attachment comprising a cylindrical head with an inner lip coupled to a punch to puncture a hole through a preselected material when a force is applied to drive the punch to penetrate the cylindrical head with the inner lip and the hole having a concave rim around an outer edge of the hole created by the inner lip. A method of using the bevel stud punch attachment to puncture a hole with a concave rim, comprising positioning the preselected material between the cylindrical head with the inner lip and the punch and applying a force to drive the punch through the preselected material and into the cylindrical head with the inner lip.

A machining method for a burred flat hole includes first an overhang portion is formed in a flat hole-forming region in a metal plate in a first step, subsequently a flat hole portion is formed in the overhang portion in a second step, and finally burring is formed on the peripheral edge portion of the hole portion in a third step. Accordingly, when burring is to be formed, overhanging machining and perforating machining have been substantially completed, and therefore pressing force of a punch for burring machining can be set to the minimum value necessary for burring formation.

A processing method and a processing apparatus for a metal housing are provided. The method includes: sleeving a metal flat pipe having an end face provided with a curved surface portion on a lower mold; and pressing the curved surface portion by the cooperation between an upper mold and the lower mold, thereby forming a chamfered slanted surface on the curved surface portion. The processing processes and the apparatus involved are simple, the quality of the products is improved, and thus the method may be suitable for mass production.

A method for processing a steel plate capable of removing residual strain at a trim edge thereof without causing overheating in areas of the steel plate other than the trim edge is provided. A method of processing a steel plate includes punching a steel plate and disposing heating electrodes in such a way that a trim edge punched in the punching is positioned between electrode surfaces facing each other and then heating a part of the steel plate including the trim edge.

A manufacturing method of a slinger, includes steps of: molding an annular blank material from a dull-finished steel sheet material through sheet metal press working or the like; and burring the blank material to mold a slinger. The values of the arithmetical mean roughness Ra of faces, of a burring mold, which individually come into contact with first and second slide-contact surfaces of the slinger, are set to 0.03 mRa0.07 m. A ratio of pressure application force for holding the blank material between the faces to the 0.2% proof stress of the dull-finished material, is set to 1.0 or more and 1.53 or less. A clearance for the burring mold is set to T(0.9 to 0.7) where T represents the sheet thickness of the blank material.

A method for processing a steel plate includes punching a steel plate as a workpiece fixed to a punching die by a punch, making a first heating electrode provided on a punch holder for supporting the punch and a second heating electrode provided on the punching die face each other by maintaining the punch in a state in which the punch penetrates the steel plate and heating a part of the steel plate including a trim edge punched in the punching, and pulling out the punch from the punching die.

A burring method includes: a placement process of disposing a sheet-shaped workpiece formed with a through hole such that a punch is positioned on one sheet thickness direction side of the workpiece and a pad is positioned on the opposite side to the one sheet thickness direction side of the workpiece; and an extrusion process of forming a flange by moving the punch toward the opposite side relative to the workpiece and extruding a peripheral rim of the through hole in the workpiece with the punch in a state in which the peripheral rim of the through hole is pressed by the punch and the pad in the sheet thickness direction of the workpiece.