JP2007050411A - Method and device for forming mounting cup and mounting cup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method and a forming device of a mounting cup for reducing working force when punching a through hole in the top plate part of the mounting cup as much as possible and the mounting cup. <P>SOLUTION: A hollow 61 provided with a slope part 63, which is gradually inclined toward the bottom part 62 at a diameter larger than the outside diameter of a punching punch 130 and is situated in the top plate part 60 of the cup part 1A formed on an intermediate formed body 10A of the mounting cup, is formed beforehand. A stem hole 7 is formed by punching the halfway part of the slope part 63 with the punching punch 130 and also a bent piece 64 consisting of the residual portion of the slope parts 63 is formed on the hole edge of the stem hole 7. An erected part 65 is formed by erecting this bent piece 64 and a curled part 8 is formed by curling the erected part 65. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for forming a mounting cup used for an aerosol can or the like, and more particularly, to a molding method, a molding apparatus, and a mounting cup for forming a through hole in a top plate portion.

A conventional method for forming this type of mounting cup is described in, for example, Patent Document 1.
That is, as shown in FIG. 4, a punching punch 503 is preliminarily provided at the center of the top plate portion 502 of the cup portion 501 with respect to the intermediate molded body 510 of the mounting cup formed with the cup portion 501 for supporting the injection mechanism. A forming process for forming a recess 504 having a smaller diameter (see FIGS. 4A and 4E), and a punching process for punching a through hole 505 by punching a central portion including the recess 504 with a punching punch 503 (see FIG. 4 (B), (F)), a rising step of raising the hole edge of the through-hole 505 to form the rising portion 506 (see FIGS. 4C and 4G), and the rising portion 506 A curling process (see FIGS. 4D and 4H) for forming the curled portion 507 by curling.

However, in the method described in Patent Document 1, the horizontal hole edge portion of the through hole 505 is bent into a cylindrical shape by the punch 510 in the rising process of rising the hole edge of the through hole 505. The frictional force acting between the contact surfaces with the portion 506 is large, and the machining force is very large. In particular, in the case of a material having a coating film or a resin film on the metal surface, there is a problem that the coating or coating film on the surface of the start-up portion 506 is rubbed and frequently peels off.
JP-A-11-193083

  The present invention has been made in order to solve the above-described problems of the prior art, and the object of the present invention is to allow a processing force when starting up the edge of the through hole drilled in the top plate portion of the cup portion. It is an object of the present invention to provide a molding cup molding method and molding apparatus, and a mounting cup that can be reduced as much as possible.

In order to achieve the above object, the invention according to claim 1 is directed to an intermediate molded body of a mounting cup in which a cup portion for supporting an injection mechanism is molded.
A step of forming a recess having an inclined surface portion gradually inclined toward the center bottom portion with a diameter larger than the outer diameter of the punch punch in the top plate portion of the cup portion;
Forming a through hole by punching a midway portion of the inclined surface portion of the recess with a perforation punch, and forming a bent piece constituted by a remaining portion of the inclined surface portion at a hole edge of the through hole;
A step of raising the bent piece in a direction parallel to the hole axis to form a raised portion;
And a step of forming the curled portion by rounding the rising portion outward in an arc shape.
The invention described in claim 2 is characterized in that after punching the through hole, an edge treatment is performed to eliminate the acute corner formed on the cut end surface of the bent piece.
The invention according to claim 3 is characterized in that the surface of the metal material forming the mounting cup is coated with a coating film or a resin film, and the through hole is punched in the coated state.

The invention according to claim 4 has a diameter larger than the outer diameter of the punching punch in the top plate portion of the cup portion relative to the intermediate molded body of the mounting cup formed with the cup portion for supporting the injection mechanism. A hollow forming device for forming a hollow having an inclined surface portion gradually inclined toward the bottom of the center, and a through hole is formed by punching the middle portion of the inclined surface portion of the hollow with a perforation punch, and at the hole edge of the through hole A punching device for forming a bent piece constituted by the remaining portion of the inclined surface portion, a rising portion forming device for raising the bent piece in a direction parallel to the hole axis to form a rising portion, and the rising portion And a curling device for forming a curled portion by rounding the outer side into an arc shape.
According to a fifth aspect of the present invention, there is provided a punching device comprising: a die having a punched hole on an upper surface; a pressing die for pressing a top plate supported by the upper surface of the die against the upper surface of the die; A perforated punch for punching the placed top plate portion to form a through hole, and at the periphery of the punched hole on the top surface of the die, an annular stepped portion is provided that is one step lower from the top surface of the die corresponding to the inclined surface portion. The inclined surface part extends from the inner diameter end of the die through the inner diameter end of the annular step portion into the punched hole, and the through hole is formed by punching the inclined surface portion by the inner diameter end corner portion of the annular step portion and the outer peripheral corner portion of the tip of the punching punch. It is the structure which carries out.
The invention according to claim 6 is provided with an edge processing device that crushes acute corners formed on the cut end face of the bent piece after punching the through hole.

The invention which concerns on Claim 7 has a cup part for supporting an injection mechanism, the through-hole by which a part of injection mechanism is penetrated by the top plate part of a cup part is provided, and the hole edge of this through-hole is provided. In a mounting cup provided with a hole edge curl portion that is rounded in an arc shape on the outside, the end surface of the hole edge curl portion is an inclined surface that is inclined obliquely so that the inner corner portion becomes an obtuse angle. It is characterized by.
The invention according to claim 8 is characterized in that an edge treatment is performed on an outer corner portion of the tip end portion of the hole edge curl portion to eliminate an acute corner.

According to the first and fourth aspects of the present invention, before punching the through hole, a recess having a diameter larger than the outer diameter of the punching punch is formed on the top plate portion, and the middle portion of the inclined surface portion of the recess is punched. Since the bent piece formed by the punch and the remaining portion of the inclined surface portion is raised, it is possible to reduce the processing force when forming the raised portion.
In addition, according to the invention described in claim 2, after punching the through hole, the edge treatment for eliminating the acute corner formed on the cut end surface of the bent piece is performed, so that the scratch can be prevented. it can.
When the surface of the metal material for forming the mounting cup is coated with a coating film or a resin film and the through hole is punched in the coated state, the bent piece is And the frictional force between the contact surfaces of the punch is reduced, and peeling of the coated film or resin film can be prevented.

According to the fifth aspect of the present invention, the inclined surface portion can be reliably punched by providing the annular step portion that is one step lower from the upper surface of the die corresponding to the inclined surface portion at the periphery of the punched hole on the upper surface of the die.
According to the sixth aspect of the present invention, since the acute corners formed on the cut end surface of the bent piece are crushed, the edge processing can be easily performed by molding.
According to the mounting cup of the invention described in claim 7, since the hole edge curled portion is curled outward, when the inner corner portion of the end surface of the tip portion is a right angle, the inner corner portion projects upward, When transporting, transporting, or packing a cup, there is a risk that adjacent mounting cups may hit the inner corners from above, but the tip end face is inclined so that the inner corners are obtuse as in the present invention. In the case of a surface, when the warpage is small, the inner corner is retracted downward, so that it can be prevented from hitting the inclined end surface without hitting the inner corner and damaging the bumped counterpart surface. As for the outer corner portion, since the acute corner portion faces the outside, even if it hits, it is the side surface on the end face side of the tip portion, and the impact is small. Further, even when the shape is such that the warp is large and the inner corner portion protrudes upward, the inner corner portion has an obtuse angle configuration, so that the impact is dispersed and damage to the mating surface can be prevented.
According to the mounting cup of the invention described in claim 8, since the outer corner portion of the tip end portion of the hole edge curled portion is subjected to the edge processing to eliminate the acute corner, it hits the outer corner portion from the side. Even so, it is possible to prevent the other party from being damaged.

  Hereinafter, the present invention will be described based on illustrated embodiments.

FIG. 3A shows a mounting cup formed by the mounting cup forming method according to Embodiment 1 of the present invention.
The mounting cup 10 is attached to a container opening such as an aerosol can, and has a cup section 1 having a hat-shaped cross section, and an annular bottom plate 2 projecting radially outward from the opening end of the cup section 1. The outer cylinder part 3 extending so as to surround the cup part 1 from the outer periphery of the bottom plate part 2 and the outer peripheral curl part 4 projecting outward from the end of the outer cylinder part 3 are provided.
The cup portion 1 includes a circular top plate portion 6 and a cylindrical portion 5 extending from the outer peripheral edge of the top plate portion 6. A housing 90 constituting an injection mechanism is inserted into the cylindrical portion 5, and the base portion of the cylindrical portion 6 is crimped to fix the housing 90.

A stem hole 7 as a through hole through which a stem 91 extending from the housing 90 is inserted is drilled in the center of the top plate part 6. The hole edge of the stem hole 7 is provided with a hole edge curled portion 8 having an arcuate cross section bent back to the outer surface side in a ring shape over the entire circumference. As shown in FIG. 3B, the hole edge curled portion 8 is configured to protrude from the top plate portion 6 by a predetermined height, and rises upward from the base position with the top plate portion 6. The end edge 81 of the hole edge curled portion 8 is an inclined surface that is inclined so that the inner corner C1 with the inner surface 82 is an obtuse angle, and the outer corner C2 with the outer surface 83 is an acute angle. It has become a shape.
When the mounting cup 10 is transported, transported, or packed, the mounting cup 10 adjacent to the tip of the hole edge curled portion 8 may collide from above, but the inner corner C2 is retracted downward. It is a part end surface 81, and it can prevent that the other surface which collided is damaged. As for the outer corner C2, the acute corner faces the outside, so even if it hits from above, it is a side face on the tip end face 81 side and the impact is small. Further, even if the amount of warpage of the hole edge curled portion 8 increases and the inner corner portion C2 of the tip end surface 81 protrudes upward, the inner corner portion C2 has an obtuse angle, so that the impact surface is dispersed and collided Can be prevented from being damaged.
The outer peripheral curl portion 4 of the mounting cup 10 is fixed to the container by clinching the bead portion provided at the container opening end portion 92. The container opening end 90 includes not only the opening end of the container itself but also the opening end of the eyeglass lid fixed to the opening end of the container body.
The inner and outer surfaces of the mounting cup 10 may be appropriately coated with a coating material such as a coating film or a resin coating. In this example, the case where the stem hole 91 is formed in the top plate portion 6 will be described. However, the present invention is not limited to the case where the stem 91 is inserted, and a configuration in which a valve or the like constituting the injection mechanism is inserted in addition to the stem 91. In short, the present invention is applied to a through-hole through which a part of a constituent part constituting an injection mechanism supported by a cup part is inserted.

FIG. 1 shows the method of forming the mounting cup in the order of steps.
As shown in FIG. 1, the mounting cup is formed on the intermediate molded body 10 </ b> A of the mounting cup formed with the cup 1 </ b> A. Although not specifically described, the mounting cup intermediate molded body 10A is a shaped material that is formed by being pressed stepwise from a metal blank, and is the same as the finished product of the mounting cup except for the top plate portion 60 of the cup portion 1A. . That is, the cup portion 1A having a hat-shaped cross section, the annular bottom plate portion 2 projecting radially outward from the opening end of the cup portion 1A, and the outer cylinder portion extending so as to surround the cup portion 1A from the outer periphery of the bottom plate portion 2 3 and an outer peripheral curl portion 4 projecting outward from an end portion of the outer cylinder portion 3. The cup portion 1 </ b> A includes a circular top plate portion 60 and a cylindrical portion 5 extending from the outer peripheral edge of the top plate portion 60. At this time, the stem hole is not formed in the top plate portion 60.
When the surface of the metal material forming the mounting cup is coated with a coating film or a resin film, the intermediate molded body 10A is molded in the coated state, and the stem hole 7 is punched.

  A mounting cup is molded from the intermediate molded body 10A of the mounting cup through the following steps. That is, the forming step includes a forming step of forming a recess 61 having a diameter larger than that of the punching punch 130 at the center of the top plate portion 60 of the cup portion 1A provided in the intermediate formed body 10A (see FIGS. 1A and 1E). ), The middle portion of the inclined surface portion 63 of the recess 61 of the top plate portion 60 is punched to form the stem hole 70, and the bent piece 64 constituted by the remaining portion of the inclined surface portion 63 is formed at the hole edge of the stem hole 70. A drilling process (see FIGS. 1 (B) and 1 (F)), and a rising process in which a bent piece 64 at the edge of the stem hole 70 is raised to form the rising portion 65 (FIGS. 1 (C), ( G)), and a curling step (see FIGS. 1D and 1H) for curling the rising portion 65.

Hereinafter, each step will be described in detail.
In the forming process, as shown in FIGS. 1 (A) and 1 (E), before punching out the stem hole 7 by the recess forming device 310, the top plate portion 60 is previously subjected to the outer diameter of the punch punch 130 in the next process. Also, the depression 61 having an inclined surface portion 63 which has a large diameter and is gradually inclined toward the center is formed.
The indentation forming apparatus 310 includes a cylindrical die 110 provided with a forming hole 111 in the center that supports the outer half of the outer surface of the top plate 60 and an inner surface of the top plate 60 facing outward. And a preforming punch 120 for pressing. The preforming punch 120 has a columnar shape substantially equal to the inner diameter of the cylindrical portion 5 of the intermediate molded body 10 </ b> A, and a convex portion 121 projects from the center of the end surface of the preforming punch 120. The diameter of the forming hole 111 of the die 110 is set to be larger than the diameter of the punching punch 130 in the next drilling step. On the other hand, the diameter of the convex portion 121 of the preforming punch 120 is set to be smaller than the diameter of the forming hole 111, and can be projected and retracted in the forming hole 111. Further, the outer diameter edge of the convex portion 121 is rounded in an arc shape.

The hollow 61 is formed by pressing the preforming punch 120 against the inner surface of the top plate 60 while the outer surface of the top plate 60 is supported by the die 110. Then, the outer diameter side half portion of the top plate portion 60 is sandwiched between the end surfaces of the die 110 and the preforming punch 120 to maintain a flat plate state, and the central portion facing the forming hole 111 is the convex portion 121 of the preforming punch. The depression 61 is formed by being pushed by the.
The depression 61 is bent from the hole edge 111a of the molding hole 111 of the die 110, and has a conical inclined surface portion 63 extending toward the outer diameter end of the end surface of the convex portion 121, and a flat bottom portion 62 that contacts the end surface of the convex portion. It is formed into a truncated cone shape. The outer diameter of the recess 61 is determined by the hole diameter of the forming hole 111 of the die 110, and the depth of the recess 61 is determined by the protruding dimension of the convex portion 121 of the preforming punch 120.

In the drilling step, as shown in FIGS. 1B and 1F, a hole is formed in the middle of the inclined surface portion 63 of the recess by the punching punch 130 by the punching device 320 to form the stem hole 7 and the stem hole. 7 is formed with a bent piece 64 constituted by the remaining portion of the inclined surface portion 63.
The punching device 320 is mounted on the die 140 having a punched hole 141 opened on the upper surface, a pressing die 150 for pressing the top plate portion 60 supported on the upper surface of the die 140 against the upper surface of the die 140, and the upper surface of the die 140. And a punching punch 130 for punching the top plate portion 60 and forming the stem hole 7.

  On the periphery of the stem hole 7 on the upper surface of the die 140, an annular step portion 142 is provided that is one step lower from the upper surface of the die 140 corresponding to the inclined surface portion 63. The die upper surface inner diameter end 140 a located at the boundary with the annular step portion 140 on the upper surface of the die 140 is set as the outer diameter end position of the recess 61 of the top plate portion 60, and the inclined surface portion 63 of the recess 61 extends from the upper surface inner diameter end 140 a of the die 140. It is configured to extend into the punched hole 141 through the inner diameter end 142 a of the annular stepped portion 142. In addition, the stem surface 7 is formed by punching the inclined surface portion 63 by the shearing action of the inner diameter end portion 142 a of the annular step portion 142 and the outer peripheral corner portion of the tip end portion of the punching punch 130. After the punching, the bent piece 64 is formed by the remaining portion of the inclined surface portion 63.

In the start-up process, as shown in FIGS. 1C and 1G, the start-up portion 65 is formed in a direction parallel to the hole axis N by the start-up portion forming apparatus 330 to form the start-up portion 65.
The riser molding device 330 is inserted into a die 160 having a molding hole 161 that supports the top plate portion 60, a pressing die 150 that holds the top plate portion 60 against the die 160, and a molding hole 151 of the die 160. Thus, it is configured to include a rising punch 170 that lifts the bent piece 64 by squeezing. The tip end portion 171 of the rising punch is inclined in a conical shape so that the diameter decreases toward the tip end.
The rising punch 170 is inserted into the molding hole 161 of the die 160 in a state where the outer diameter side half of the top plate portion 60 is pressed by the die 160 and the pressing die 150 and the bent piece 64 protrudes into the molding hole 161. The raised portion 65 is formed by inserting and extending the bent piece 64 into a cylindrical shape. The bending position of the rising portion 65 coincides with the outer peripheral edge of the preformed recess 61.
As described above, since the inclined bent piece 64 is raised vertically, the processing force when forming the raised portion 65 can be reduced. Further, the frictional force between the contact surfaces of the bent piece 64 and the rising punch 170 is reduced, and peeling of the coated film or resin film can be prevented.

In the curling step, as shown in FIGS. 1D and 1H, a curling device 340 rounds the rising portion 65 outward to form the hole edge curled portion 8.
The curling device 340 includes a holding die 150 that holds the top plate portion 60 and a curling die 180 that includes an arc-shaped forming curved surface 181 that is inserted into the holding die 150 from below. The molding curved surface 181 of the curling die 180 is a curved surface that gradually increases in diameter in an arc shape downward, and is gradually expanded to a large diameter from the leading end side of the rising portion 65 to follow the molding curved surface 191 to be a curled portion. 8 is formed.

FIG. 2 shows a method for forming a mounting cup according to Embodiment 2 of the present invention.
In this embodiment, only the parts different from those of the first embodiment will be mainly described, and the same steps are denoted by the same reference numerals and the description thereof is omitted.
In the second embodiment, the lower edge of the cut end surface of the bent piece 7 punched out in the drilling process has a sharp and sharp shape, so that the sharp end 64a is formed between the drilling process and the starting process. A crushing edge processing step is provided.
That is, the forming procedure includes a forming step for preliminarily forming a recess in the portion of the stem hole (see FIGS. 2A and 2F), and a drilling step for drilling the stem hole (FIG. 2B). (See (G)), an edge processing step of crushing the acute-angled end (see FIGS. 2 (C) and (H)), a startup step of raising the edge of the stem hole (FIG. 2 (D), (See (I)), and a curling step (see FIGS. 2E and 2J) for curling the rising portion.

In the edge processing step, as shown in FIGS. 2C and 2H, the edge processing device 350 punches out the inclined surface portion of the recess 60 and then forms an acute corner portion formed on the cut end surface of the bent piece 64. The edge processing which crushes and eliminates is performed.
As shown in an enlarged view in FIG. 2H, the edge processing device 350 includes a receiving die 220 and a pressing die 210. The receiving die 220 is provided with a slope 221 on which the acute-angled end portion 64a is pressed. On the other hand, the pressing die 210 is provided with a pressing surface 211 that presses the punched bent piece 64, and the pressing surface 211 presses against the inclined surface 221 of the receiving die 220 to crush the acute-angled end portion to be flat. The tip processing part is formed.
FIG. 3C shows a tip end surface 81 of the hole curl portion 8 of the mounting cup molded by the molding method of the second embodiment.
That is, the tip end surface 81 of the hole edge curled portion 8 is an inclined surface that is inclined so that the inner corner C1 with the inner surface 82 becomes an obtuse angle, and the outer corner C3 with the outer surface 83 is edge-treated. It has a chamfered shape. By doing so, there is no acute angle portion on the end surface 81 of the end edge curl portion 8 of the stem hole 7, and the adjacent mounting cup is laterally moved to the outer corner portion C3 when the mounting cup is transported, transported and packed. Even if it hits, the other side can be prevented from being damaged.

FIGS. 1A to 1D are process diagrams showing a molding procedure of a method for molding a mounting cup according to Embodiment 1 of the present invention, and FIGS. 1E to 1H are (A) to (D), respectively. FIG. 2 (A) to 2 (E) are process diagrams showing the molding procedure of the mounting cup molding method according to Embodiment 2 of the present invention, and FIGS. 2 (F) to (J) are (A) to (E), respectively. FIG. 3A and 3B show a mounting cup molded by the molding method of the present invention. FIG. 3A is a longitudinal sectional view, and FIG. 3B is a hole of a stem hole molded by the molding method of the first embodiment. FIG. 4C is an enlarged cross-sectional view showing the shape of the curl portion, and FIG. 4C is an enlarged cross-sectional view showing the shape of the edge curl portion of the stem hole formed by the forming method of the second embodiment. FIGS. 4A to 4D are process diagrams showing a molding procedure of a conventional mounting cup molding method, and FIGS. 4E to H are partial enlarged views of (A) to (D), respectively. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Mounting cup 1 Cup part, 2 Bottom plate part, 3 Outer cylinder part, 4 Outer periphery curl part 5 Cylindrical part, 6 Top plate part, 7 Stem hole (through hole), 8 Hole edge curl part 10A Intermediate molded object (mounting cup)
1A Cup part, 60 Top plate part 61 Dimple, 62 Bottom part, 63 Inclined surface part, 64 Bending piece, 64a Sharp edged end 65 Rising part 110 Die, 111 Molding hole 120 Pre-formed punch, 121 Convex part 130 Perforated punch 140 Die , 141 punching hole, 142 step recess 150 top plate presser 160 die 170 rising punch 180 curling die, 181 forming curved surface 210 pressing die, 211 pressing surface 220 receiving die, 221 slope 310 recess forming device 320 punching device 330 starting portion Molding device 340 Curling device 350 Edge processing device

Claims (8)

For the intermediate molded body of the mounting cup in which the cup part for supporting the injection mechanism is molded,
A step of forming a recess having an inclined surface portion gradually inclined toward the center bottom portion with a diameter larger than the outer diameter of the punch punch in the top plate portion of the cup portion;
Forming a through hole by punching a midway portion of the inclined surface portion of the recess with a perforation punch, and forming a bent piece constituted by a remaining portion of the inclined surface portion at a hole edge of the through hole;
A step of raising the bent piece in a direction parallel to the hole axis to form a raised portion;
And a step of forming the curled portion by rounding the rising portion outward in a circular arc shape.   2. The method of forming a mounting cup according to claim 1, wherein after punching the through-hole, an edge treatment for eliminating an acute corner formed on the cut end surface of the bent piece is performed. 3.   The method of forming a mounting cup according to claim 1 or 2, wherein the surface of the metal material for forming the mounting cup is coated with a coating film or a resin film, and the through hole is punched in the coated state. For the intermediate molded body of the mounting cup in which the cup part for supporting the injection mechanism is molded,
A recess forming device for forming a recess having an inclined surface portion that is larger in diameter than the outer diameter of the perforated punch and gradually inclined toward the center bottom portion in the top plate portion of the cup portion;
A punching device that forms a through hole by punching a midway portion of the inclined surface portion of the recess with a perforation punch, and forms a bent piece composed of the remaining portion of the inclined surface portion at the hole edge of the through hole;
A rising part forming device for forming the rising part by raising the bent piece in a direction parallel to the hole axis;
A mounting apparatus for forming a mounting cup, comprising: a curling device that forms a curled portion by rounding the rising portion in an arc shape to the outside.   The punching device includes: a die having a punched hole on an upper surface; a pressing die that presses a top plate portion supported by the upper surface of the die against the upper surface of the die; and a top plate portion placed on the upper surface of the die. A perforation punch for punching to form a through-hole, and an annular step portion is provided on the periphery of the punch hole on the upper surface of the die so as to be lowered by one step from the upper surface of the die corresponding to the inclined surface portion. From the inner diameter end of the annular step portion into the punched hole, and the through hole is formed by punching the inclined surface portion by the inner diameter end corner portion of the annular step portion and the outer peripheral corner portion of the tip end portion of the punching punch. Item 5. An apparatus for forming a mounting cup according to Item 4.   6. The mounting cup molding apparatus according to claim 4 or 5, further comprising an edge processing device that crushes an acute corner formed on the cut end surface of the bent piece after punching the through hole. A hole having a cup portion for supporting the injection mechanism, a through hole into which a part of the injection mechanism is inserted is provided in the top plate portion of the cup portion, and a hole rounded in an arc shape on the outer edge of the through hole In the mounting cup provided with the edge curl part,
The mounting cup is characterized in that the end surface of the tip end of the hole edge curl portion is an inclined surface that is inclined obliquely so that the inner corner becomes an obtuse angle.   The mounting cup according to claim 7, wherein an outer corner portion of the tip end portion of the hole edge curl portion is subjected to an edge treatment that eliminates an acute corner.

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