US-12623270-B2 - Burring processing method, burring processing mold, burring processing device, and burring processed product

US12623270B2US 12623270 B2US12623270 B2US 12623270B2US-12623270-B2

Abstract

Provided is a burring processing method, which is a method for forming a buffing processed portion including a raised portion and a curved portion in a metal component having a pilot hole formed therein, the method being characterized by including: a preforming step of enlarging a diameter of the pilot hole, moving an edge portion of the pilot hole relative to the metal component in a first direction of a thickness direction of the metal component in a first range around the pilot hole of the metal component, and forming the whole first range into a preformed portion raised from the metal component in the first direction; and a main forming step of deforming the preformed portion in a second direction opposite to the first direction, forming a second range on an outer diameter side of the preformed portion to have the same height as the first range in the first direction, and forming part of a third range on an inner diameter side of the preformed portion from the second range to be part of the curved portion and the raised portion.

Inventors

Kenichiro Otsuka
Masafumi Azuma
Koichi Hamada
Ryo Tabata
Ryo URUSHIBATA
Yuuki KITAHARA

Assignees

NIPPON STEEL CORPORATION

Dates

Publication Date: 20260512
Application Date: 20220112
Priority Date: 20210224

Claims (4)

1 . A burring processing method, which is a method for forming a burring processed portion including a raised portion and a curved portion in a metal component having a pilot hole formed therein, the metal component being a steel member having a thickness of 1.8 to 4.2 mm at a location the burring processing method is performed, using a burring processing mold including: a first die that includes a first die hole and a first support surface perpendicular to an axis of the first die hole, and a second die that includes a second die hole and a second support surface perpendicular to an axis of the second die hole; a holder that includes a third support surface facing the first support surface and the second support surface and holds the metal component between the first die and the second die; and a punch that includes a shaft portion and is movably provided along the axis of the first die hole and the axis of the second die hole, in which the first support surface, the second support surface, and the third support surface are disposed parallel to each other, a diameter of the second die hole is smaller than a diameter of the first die hole, and an outer diameter of the second support surface is smaller than the diameter of the first die hole, the method comprising: a preforming step of enlarging a diameter of the pilot hole, moving an edge portion of the pilot hole relative to the metal component in a first direction of a thickness direction of the metal component in a first range around the pilot hole of the metal component, and forming a whole first range into a preformed portion raised from the metal component in the first direction; and a main forming step of deforming the preformed portion in a second direction opposite to the first direction, forming a second range on an outer diameter side of the preformed portion to have a same height as the first range in the first direction, and forming part of a third range on an inner diameter side of the preformed portion from the second range to be part of the curved portion and the raised portion, wherein an outer diameter of the curved portion is smaller than an outer diameter of the preformed portion, a maximum radius of curvature of the curved portion is smaller than the minimum radius of curvature of the preformed portion in a cross-sectional view parallel to the first direction and passing through a center of the pilot hole, the preformed portion is formed between the punch and the first die by holding the metal component between the first support surface of the first die and the third support surface of the holder and moving the punch relative to the first die in the first direction to insert the punch through the first die hole, the burring processed portion is formed between the second die, the punch, and the holder by moving the second die relative to the holder in the second direction to insert part of the second die between the punch and the first die in a state in which the metal component is held between the first support surface and the third support surface, when a difference between a radius of the first die hole and a radius of the second die hole is defined as U, a diameter of the shaft portion of the punch is defined as P, and the diameter of the pilot hole of the metal component is defined as A, Expression 1 below is satisfied, and when a height of the edge portion of the pilot hole of the metal component is defined as t, and a height of an outer surface of the curved portion in the first direction is defined as h, Expression 2 below is satisfied, 0.5×( P−A )/2< U< 20×( P−A )/2 Expression 1 0.2< h/t< 0.6 Expression 2.
2 . The burring processing method according to claim 1 , wherein a tensile strength of the metal component is 780 MPa or more.
3 . The burring processing method according to claim 1 , wherein, when the height of the edge portion of the pilot hole of the metal component is defined as t, and a thickness of an opening side end portion of the raised portion is defined as tb, Expression 4 below is satisfied, tb/t< 0.9 Expression 4.
4 . The burring processing method according to claim 1 , further comprising a pilot hole forming step of forming the pilot hole in the metal component before the preforming step.

Description

TECHNICAL FIELD The present invention relates to a burring processing method, a buffing processing mold, a burring processing device, and a burring processed product. Priority is claimed on Japanese Patent Application No. 2021-027954, filed Feb. 24, 2021, the content of which is incorporated herein by reference. BACKGROUND ART There is a technique for forming a burring processed portion having a substantially cylindrical shape by burring a pilot hole provided in a metal component or a metal sheet serving as a workpiece. In this burring process, a circumferential edge portion of the pilot hole is extruded and part thereof is formed into a cylindrical shape to form the burring processed portion. In this burring processed portion, a cylindrical flange (raised portion) is connected to part of the metal component or the metal sheet at a circumferential edge portion thereof via a curved portion. This buffing processed portion is required to have fatigue characteristics and dimensional accuracy. For example, Patent Document 1 discloses a technique for relaxing tensile residual stress by applying compressive stress due to coining to an end portion of a buffing processed portion and inhibiting wrinkles and cracks generated on an inner surface of a bend of a bent portion that constitutes a base of the burring processed portion by locally concentrating compressive stress on the inner surface. In addition, as a technique for burring, a method for performing stepwise forming as described in Patent Document 2 has also been proposed. CITATION LIST Patent Document [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2018-051609 [Patent Document 2] Japanese Patent No. 5636846 SUMMARY OF THE INVENTION Problems to be Solved by the Invention Incidentally, buffing processed portions are also used for vehicle underbody components. In particular, vehicle underbody components such as lower arms and trailing arms are required to have fatigue characteristics, but depending on a burring processing method, tensile residual stress tends to be generated on an inner side of a curved portion of a burring processed portion. If a fatigue load is applied to a component in which tensile residual stress is generated on an inner side of a curved portion of a burring processed portion, the burring processed portion may be deformed. In addition, it is generally known that, depending on a burring processing method, minute cracks (bending inward cracks) of about several tens of μm are generated on the inner side of the curved portion, and a shape change such as enlarging a radius of curvature of the curved portion may be required. The present invention has been made in view of the above problems, and an object of the present invention is to provide a burring processing method, a burring processing mold, a burring processing device, and a burring processed product in which generation of cracks in a curved portion of a buffing processed portion can be inhibited. Means for Solving the Problem (1) A burring processing method according to an aspect of the present invention is a method for forming a burring processed portion including a raised portion and a curved portion in a metal component having a pilot hole formed therein, using a burring processing mold including: a first die that includes a first die hole and a first support surface perpendicular to an axis of the first die hole, and a second die that includes a second die hole and a second support surface perpendicular to an axis of the second die hole;a holder that includes a third support surface facing the first support surface and the second support surface and holds the metal component between the first die and the second die; anda punch that includes a shaft portion and is movably provided along the axis of the first die hole and the axis of the second die hole,in which the first support surface, the second support surface, and the third support surface are disposed parallel to each other,a diameter of the second die hole is smaller than a diameter of the first die hole, and an outer diameter of the second support surface is smaller than the diameter of the first die hole,the method including:a preforming step of enlarging a diameter of the pilot hole, moving an edge portion of the pilot hole relative to the metal component in a first direction of a thickness direction of the metal component in a first range around the pilot hole of the metal component and forming the whole first range into a preformed portion raised from the metal component in the first direction; anda main forming step of deforming the preformed portion in a second direction opposite to the first direction, forming a second range on an outer diameter side of the preformed portion to have the same height as the first range in the first direction, and forming part of a third range on an inner diameter side of the preformed portion from the second range to be part of the curved portion and the r