Burring processing method, method for manufacturing burring processed product, burring processing mold, burring processing device, and burring processed product

A method for manufacturing a burring processed product comprising a burring processed portion forming process of increasing a diameter of a prepared hole provided in a metal component and bending a part of the metal component to form a burring processed portion including an upright portion and a curved portion,

• wherein, in a cross-section that passes through an axis of the burring processed portion and is parallel to the axis of the burring processed portion, a cross-sectional shape of the curved portion on an inner surface of the curved portion consists of a curve, and a length of the curved portion in a direction perpendicular to the axis of the burring processed portion is at least 1.2 times a height of the curved portion in a direction parallel to the axis of the burring processed portion,
• wherein, when a plate thickness around the prepared hole of the metal component is defined as t, and a height of the curved portion in the direction parallel to the axis of the burring processed portion is defined as h, the following Expression 1 is satisfied,
• h/t<0.6 Expression 1,
• when the plate thickness around the prepared hole of the metal component is defined as t, and a plate thickness of an opening side end portion of the upright portion is defined as tb, the following Expression 2 is satisfied,
• tb/t<0.9 Expression 2,
• wherein a value obtained by differentiating an expression y=f(x) twice with respect to x is larger than 0, and
• wherein in a cross section passing through the axis of the burring processed portion and parallel to the axis of the burring processed portion, the direction parallel to the axis of the burring processed portion is defined as an x-axis, and the direction perpendicular to the axis of the burring processed portion in the cross-section is defined as a y axis, in an x-y coordinate system defined with the x axis and the y axis, a contact point between an outer circumferential surface of a rising portion and an inner surface of the curved portion is defined as an origin O, a side on which the curved portion is located is defined as a positive region, and the expression y=f(x) represents the cross-sectional shape of the curved portion on the inner surface in the x-y coordinate system.

A burring processing mold comprising a die having a die hole, a holder holding a workpiece together with the die, and a punch movable relative to the die and the holder,

• wherein, in a cross-section that passes through an axis of the die hole and is parallel to the axis of the die hole, a cross-sectional shape of a die shoulder consists of a curve, and a length of the die shoulder in a direction perpendicular to the axis of the die hole is at least 1.2 times a height of the die shoulder in a direction parallel to the axis of the die hole,
• wherein the punch includes a cylindrical portion having a diameter smaller than a diameter of the die hole, and the punch is configured to be inserted into the die hole along the axis of the die hole, and
• when a clearance between the die hole and the cylindrical portion is defined as cl and a height of the die shoulder in a direction parallel to the axis of the die hole in the cross-sectional shape is defined as hd, the following Expression 3 is satisfied,
• cl<1.5hd Expression 3,
• wherein a value obtained by differentiating an expression y=f(x) twice with respect to x is larger than 0, and
• wherein in a cross section passing through the axis of the die hole and parallel to the axis of the die hole, the direction parallel to the axis of the die hole is defined as an x-axis, and the direction perpendicular to the axis of the die hole in the cross-section is defined as a y axis, in an x-y coordinate system defined with the x axis and the y axis, a contact point between a cylindrical inner circumferential surface and a surface of the die shoulder is defined as an origin O, a side on which the die shoulder is located is defined as a positive region, and the expression y=f(x) represents the cross-sectional shape of the die shoulder in the x-y coordinate system.

A burring processed product comprising a burring processed portion including an upright portion and a curved portion,

• wherein, in a cross-section that passes through an axis of the burring processed portion and is parallel to the axis of the burring processed portion, a cross-sectional shape of the curved portion on an inner surface of the curved portion consists of a curve, and a length of the curved portion in a direction perpendicular to the axis of the burring processed portion is at least 1.2 times a height of the curved portion in a direction parallel to the axis of the burring processed portion,
• wherein, when a plate thickness around the curved portion is defined as ts, and a height of the curved portion in the direction parallel to the axis of the burring processed portion is defined as h, the following Expression 4 is satisfied,
• h/ts<0.6 Expression 4,
• wherein, when the plate thickness around the curved portion is defined as ts, and a plate thickness of an opening side end portion of the upright portion is defined as tb, the following Expression 5 is satisfied,
• tb/ts<0.9 Expression 5,
• wherein a value obtained by differentiating an expression y=f(x) twice with respect to x is larger than 0, and
• wherein in a cross section passing through the axis of the burring processed portion and parallel to the axis of the burring processed portion, the direction parallel to the axis of the burring processed portion is defined as an x-axis, and the direction perpendicular to the axis of the burring processed portion in the cross-section is defined as a y axis, in an x-y coordinate system defined with the x axis and the y axis, a contact point between an outer circumferential surface of a rising portion and an inner surface of the curved portion is defined as an origin O, a side on which the curved portion is located is defined as a positive region, and the expression y=f(x) represents the cross-sectional shape of the curved portion on the inner surface in the x-y coordinate system.