A chain has pairs of outer link plates provided with connecting pin-insertion connecting holes; connecting pins disposed in the connecting pin-insertion connecting holes and crimped at pin ends thereof; and inner link plates disposed inside and rotatably connected to the pairs of outer link plates. Each of the connecting pin-insertion connecting holes is provided with tapered surfaces at outer hole edges thereof formed by chamfering a corner edge formed by a straight hole. The tapered surfaces are located at two places opposing in a direction perpendicular to a longitudinal direction of the outer link plates. The pin ends of the connecting pins protruding outwardly from the connecting pin-insertion connecting holes are crimpled by pressing the pin ends against two places opposing in a direction perpendicular to the intermittently conveying direction to crimp the connecting pins at the segments where the tapered surfaces are provided.

A punch and die assembly for a forming assembly for forming flared openings in commercial forming steel sheeting, includes a punch. The punch has a punching element having a base portion and a working portion that extends from a face of the base portion, the working portion defining a working edge with more than two substantially evenly spaced peaks and troughs for forming an opening in the steel sheeting during a working stroke. A flaring element is mountable on the base portion of the punching element, a side of the flaring element defining an arcuate flaring surface that tapers inwardly in the direction of the working stroke. A die supports the steel sheeting, the die having a die opening with a flared die face for facing the flaring surface of the flaring element such that the opening in the steel sheeting is flared by the flaring surface of the flaring element and the die face in the working stroke.

A punch and die assembly for a forming assembly for forming flared openings in commercial forming steel sheeting, includes a punch. The punch has a punching element having a base portion and a working portion that extends from a face of the base portion, the working portion defining a working edge with more than two substantially evenly spaced peaks and troughs for forming an opening in the steel sheeting during a working stroke. A flaring element is mountable on the base portion of the punching element, a side of the flaring element defining an arcuate flaring surface that tapers inwardly in the direction of the working stroke. A die supports the steel sheeting, the die having a die opening with a flared die face for facing the flaring surface of the flaring element such that the opening in the steel sheeting is flared by the flaring surface of the flaring element and the die face in the working stroke.

There is provided a cutting method for cutting a workpiece using a cutting tool comprising a die and a punch, including: arranging the workpiece between the die and the punch, and in a state in which a wedge-shaped first cutting part of the die and a wedge-shaped second cutting part of the punch are opposed, pushing the punch relatively to the die side to cut the workpiece; wherein: a front end angle θ.sub.1 of the first cutting part and a front end angle θ.sub.2 of the second cutting part are each 100 or more and 1200 or less, and a front end radius R.sub.1 of the first cutting part and a front end radius R.sub.2 of the second cutting part are each 0.5% or more and 35.0% or less of a sheet thickness.

There is provided a cutting method for cutting a workpiece using a cutting tool comprising a die and a punch, including: arranging the workpiece between the die and the punch, and in a state in which a wedge-shaped first cutting part of the die and a wedge-shaped second cutting part of the punch are opposed, pushing the punch relatively to the die side to cut the workpiece; wherein: a front end angle θ.sub.1 of the first cutting part and a front end angle θ.sub.2 of the second cutting part are each 100 or more and 1200 or less, and a front end radius R.sub.1 of the first cutting part and a front end radius R.sub.2 of the second cutting part are each 0.5% or more and 35.0% or less of a sheet thickness.

The present invention has as its technical problem to provide a punching method able to stably secure a stretch-flangeability equal to or greater than the case of using a punch having a flat blade at its bottom surface. The punching method of the present invention is a method of punching a metal sheet using a punching and shearing device provided with a punch having an upper blade having a horizontal part with respect to the cutting line in part and having parts other than the horizontal part comprised of inclined parts and a die having a lower blade wherein the upper blade used for the punching process has a shape where the inclined parts first contact the metal sheet at the time of a punching process.

The present invention has as its technical problem to provide a punching method able to stably secure a stretch-flangeability equal to or greater than the case of using a punch having a flat blade at its bottom surface. The punching method of the present invention is a method of punching a metal sheet using a punching and shearing device provided with a punch having an upper blade having a horizontal part with respect to the cutting line in part and having parts other than the horizontal part comprised of inclined parts and a die having a lower blade wherein the upper blade used for the punching process has a shape where the inclined parts first contact the metal sheet at the time of a punching process.

A method of stamping for separating a workpiece part of sheet metal to obtain a workpiece, the method including a work-hardening step of generating work-hardening at vicinity of outline of the workpiece part of the sheet metal by moving a work-hardening punch having an end side facing the sheet metal toward the sheet metal and locally pressing the vicinity of the outline along the outline with a work-hardening projection provided on the end side of the work-hardening punch, and a separation step of punching the workpiece part of the sheet metal which has finished the work-hardening step with a separation punch and thereby separating the workpiece part from the sheet metal, wherein the work-hardening projection is formed to have V-shaped cross-section with both inner wall and outer wall of the work-hardening projection being inclined to pressing direction of the work-hardening punch.

In a brake-disc intermediate product, a corrugated portion is molded using an upper mold and a lower mold. The brake-disc intermediate product is set in a mold, the mold has a slope corresponding to the corrugated portion, and an angular portion formed along the outer circumferential edge of the corrugated portion is in contact with the slope in a state where the brake-disc intermediate product is set in the mold. The angular portion in contact with the slope is deformed by pressing the brake-disc intermediate product in a direction of the mold, to mold a chamfer portion. The slope is formed so that a chamfering angle formed with respect to an inner bottom surface of the mold is larger at a portion in contact with the concave portion than a chamfering angle at a portion in contact with the convex portion.

In a brake-disc intermediate product, a corrugated portion is molded using an upper mold and a lower mold. The brake-disc intermediate product is set in a mold, the mold has a slope corresponding to the corrugated portion, and an angular portion formed along the outer circumferential edge of the corrugated portion is in contact with the slope in a state where the brake-disc intermediate product is set in the mold. The angular portion in contact with the slope is deformed by pressing the brake-disc intermediate product in a direction of the mold, to mold a chamfer portion. The slope is formed so that a chamfering angle formed with respect to an inner bottom surface of the mold is larger at a portion in contact with the concave portion than a chamfering angle at a portion in contact with the convex portion.