WO2024154371A1

WO2024154371A1 - Can lid shell and manufacturing method for same, and forming device

Info

Publication number: WO2024154371A1
Application number: PCT/JP2023/026734
Authority: WO
Inventors: 拓郎新宮領
Original assignee: 拓郎新宮領
Priority date: 2023-01-18
Filing date: 2023-07-21
Publication date: 2024-07-25
Also published as: JP7526436B1

Abstract

A can lid shell 10 is provided with a panel section 11 having a circular rim, a countersink section 12 formed and indented along the rim of the panel section 11, a chuck wall section 13 rising from an edge of the countersink section 12, and a flange section 14 overhanging from an upper end of the chuck wall section 13. The countersink section 12 is provided with a first curved section 123C that is convex with respect to an internal space SP1. The chuck wall section 13 is provided with a second curved section 131 that is connected to the first curved section 123C and is concave with respect to the internal space SP1. Furthermore, the second curved section 131 and the first curved section 123C are formed progressively thicker as they extend from an edge p8 on the flange section 14 side to an edge p6 on the panel section 11 side.

Description

Can lid shell, its manufacturing method and molding device

The present invention relates to a can lid shell for a beverage can, a manufacturing method thereof, and a molding apparatus. This application claims priority to Patent Application No. 2023-006121, filed on January 18, 2023, the contents of which are incorporated herein by reference.

The can lid shell 700 for a beverage can is manufactured by pressing a circular blank punched from an aluminum alloy plate, and as shown in FIG. 35, comprises a panel portion 710, a countersink portion 720 provided around the panel portion 710, and an attachment portion 730 that extends from the outer wall portion of the countersink portion 720, has a hook-shaped cross section, and tightens the flange of the can body. A conversion press is used to provide tear lines for opening and tabs for opening the can shell 700, and the can lid is manufactured.

Also, a can lid shell 800 shown in FIG. 36 is known that has a reduced thickness and weight (Patent Document 1).

Comparing the can lid shell 700 and the can lid shell 800, the area where the flange of the can body is rolled up to form the chuck wall is linear in the conventional can lid shell 700, as surrounded by the dashed line in Figure 35, whereas in the can lid shell 800, it is made up of multiple curved surfaces connected together, as surrounded by the dashed line in Figure 36.

After filling the bottomed cylindrical can body with the contents and gas ( _CO2 or _N2 ), the can lid shell 800 is seamed onto the flange portion of the can body 900 as shown by the solid line in Fig. 37 to complete a can product with the can lid shell 800 attached. However, in Fig. 37, tab rivets, tear lines, debossing, etc. that will be added to the panel portion 810 in the next conversion process are omitted.

Furthermore, in a can product to which the can lid shell 800 is attached, the pitch diameter PD2 of the countersink is smaller than the pitch diameter PD1 of the countersink of the can lid shell 700 (PD2 < PD1), and the area of the panel portion 810 is designed to be smaller.

The panel portion 810 of the can lid shell 800 is small, so even if the internal pressure of the can is the same, a smaller internal pressure acts on the panel portion 810 than the internal pressure that acts on the panel portion 710 of the can lid shell 700.

JP 2022-119588 A

In the filling and distribution process, in which the contents and gas are filled into the can body and then closed with a lid, if the can product is exposed to excessively high temperatures, the internal pressure of the can rises and exceeds the limit of the pressure resistance strength of the can lid, causing a phenomenon known as buckling, in which part of the can product's lid protrudes outward, as shown by the dashed line in Figure 37. When part of the can lid protrudes outward in this way, cracks can form in the protruding part or in the tear line, causing leakage of the contents or gas, or making the can impossible to open.

The present invention aims to provide a can lid shell that prevents buckling, a manufacturing method for this can lid shell, and a molding device.

The can lid shell of the present invention comprises a panel portion having a circular periphery, a recessed countersink portion formed along the periphery of the panel portion, a chuck wall portion rising from the edge of the countersink portion, and a flange portion projecting from the upper end of the chuck wall portion. The can lid shell has an internal space defined inside the panel portion, the countersink portion, and the chuck wall portion, the countersink portion including a first curved surface portion that is convex toward the internal space, and the chuck wall portion including a second curved surface portion that is connected to the first curved surface portion and is concave from the internal space. Furthermore, the thickness of the first curved surface portion and the second curved surface portion increases from the edge on the flange portion side toward the edge on the panel portion side.

In the can lid shell of the present invention, the first curved surface portion and the second curved surface portion, which have different curved surface directions (convex and concave), are thickened, which increases the mechanical strength of the inflection portion formed by the first curved surface portion and the second curved surface portion, thereby increasing the pressure resistance. This makes it possible to further reduce the thickness and weight of the can lid.

The can lid shell of the present invention preferably includes a third curved surface portion in which the countersink portion is connected to the first curved surface portion by disposing the first curved surface portion between the countersink portion and the second curved surface portion, and which is formed so that its thickness increases from the edge on the panel portion side to the edge connected to the first curved surface portion. By thickening the third curved surface portion, the mechanical strength is increased, and the pressure resistance can be improved.

The can lid shell of the present invention preferably has a plurality of thin-walled sections formed on the front or back surface of the can lid shell, recessed from the second curved surface portion to the third curved surface portion and spaced apart in the circumferential direction of the can lid shell, and thick-walled sections are formed between the thin-walled sections and are thicker than the thin-walled sections, and the dimension along the radius of the can lid shell of the plurality of thin-walled sections and the plurality of thick-walled sections is set to be longer than the dimension along the direction perpendicular to the direction of the radius when viewed from above or below the can lid shell.

In the can lid shell of the present invention, the first curved surface portion, which is convex toward the internal space, has a plurality of thin and thick portions extending from the second curved surface portion to the third curved surface portion in the circumferential direction. The area extending from the second curved surface portion to the third curved surface portion constitutes an increased thickness portion, and by providing this increased thickness portion with a first curved surface portion consisting of a thin and thick portion, deformation such as bending toward the internal space is prevented. This further increases the mechanical strength of the increased thickness portion, including the inflection portion consisting of the first curved surface portion and the second curved surface portion, improving pressure resistance.

The present invention is a molding device that includes a lower die and an upper die, and that clamps a circular blank between the lower die and the upper die to form a can lid shell. The lower die includes a die core ring and a panel punch arranged inside the die core ring, and the upper die includes a cylindrical upper piston, a cylindrical inner sleeve arranged inside the upper piston, and a die center arranged inside the inner sleeve.

In this molding device, the outer portion of the tip of the die core ring and the tip of the upper piston are arranged opposite each other, the inner portion of the tip of the die core ring and the tip of the inner sleeve are arranged opposite each other, and the panel punch and the die center are arranged opposite each other. The inner portion of the tip of the die core ring has a first lower curved surface portion that is concave toward the inner sleeve, and a second lower curved surface portion that is connected to the first lower curved surface portion and is further shifted toward the central axis and is convex toward the inner sleeve.

The tip of the inner sleeve is provided with a first upper mold curved surface portion that is convex toward the first lower mold curved surface portion, a second upper mold curved surface portion that is connected to the first upper mold curved surface portion and is positioned further toward the central axis, and is an arc whose radius of curvature differs from the radius of curvature of the first upper mold curved surface portion and is convex toward the first lower mold curved surface portion, and a third upper mold curved surface portion that is connected to the second upper mold curved surface portion and is positioned further toward the central axis, and is concave toward the second lower mold curved surface portion.

The die clearance formed between the first lower curved surface portion and the second lower curved surface portion of the die core ring and the second upper curved surface portion and the third upper curved surface portion of the inner sleeve is equal to or greater than the plate thickness of the circular blank, and widens as it approaches the central axis.

In the molding device of the present invention, a die clearance is formed between the first lower curved surface portion and the second lower curved surface portion of the die core ring and the second upper curved surface portion and the third upper curved surface portion of the inner sleeve, and this die clearance widens as it approaches the central axis. Since this die clearance has a distance equal to or greater than the plate thickness of the circular blank to be machined, it is possible to increase the thickness of a portion of the circular blank by machining.

In this molding device, the die core ring comprises a cylindrical fixed portion fixed to the lower mold, a movable portion provided inside the fixed portion, and a biasing member configured to be freely expandable and contractible along a central axis, supporting the movable portion from below and biasing the movable portion; the tip of the fixed portion of the die core ring and the tip of the upper piston are arranged opposite each other, the tip of the movable portion of the die core ring and the tip of the inner sleeve are arranged opposite each other, and the panel punch and the die center are arranged opposite each other.

The tip of the movable part has a lower curved surface portion that is convex toward the inner sleeve, and the tip of the inner sleeve has an upper curved surface portion that is concave toward the lower curved surface portion, the die clearance formed between the lower curved surface portion of the movable part and the upper curved surface portion of the inner sleeve is a distance equal to or greater than the plate thickness of the circular blank and widens as it approaches the central axis, and further, the movable part is pushed by the intermediate forming body when the circular blank is deep drawn and retreats toward the biasing member.

Here, the intermediate formed body refers to the shape in the process of deformation of the circular blank until it becomes the first formed body through the deep drawing process.

The molding device of the present invention preferably further comprises a cylindrical lower piston surrounding a portion of the outer peripheral surface of the die core ring, the fixed part comprises a through hole leading from the inside of the fixed part to the outside of the fixed part and a block arranged in the through hole, the block has an outer inclined surface that protrudes to the outside of the fixed part and an inner inclined surface that protrudes to the inside of the fixed part, the lower piston has an inner inclined surface that abuts on the outer inclined surface of the block, the movable part has an outer inclined surface that abuts on the inner inclined surface of the block, and when the lower piston is pressed down by the upper mold, the inner inclined surface of the lower piston abuts on the outer inclined surface of the block, and the outer inclined surface of the retracted movable part abuts on the inner inclined surface of the block, and the lower piston further descends in this state, whereby the movable part moves towards the inner sleeve.

The molding device of the present invention is provided with the biasing member that supports the movable part, and the movable part is moved back by the intermediate molded body, thereby making it possible to suppress a decrease in the plate thickness of the intermediate molded body due to friction with the movable part during deep drawing. The biasing member can be, for example, a spring or a pneumatic piston.

The present invention is a manufacturing method for can lid shells in which a circular blank is sandwiched between a lower die and an upper die to form a can lid shell, and includes a deep drawing process in which the circular blank is shaped into a tray-shaped first formed body, and a reverse process in which the flat portion of the bottom of the first formed body sandwiched between a panel punch and a die center is moved in the opposite direction to form a countersink portion recessed around the flat portion. In the deep drawing process, a part of the circular blank is deformed by the tip of the die core ring and the tip of the inner sleeve, and a first inflection portion consisting of a concave surface and a convex surface is formed between the flat portion and the flange portion of the first formed body.

In the reversing process, with the space between the tip of the die core ring and the tip of the inner sleeve configured as a die clearance that widens as it approaches the central axis, a portion of the first molded body that protrudes from between the panel punch and the die center is pushed into the gap in the die clearance that is not filled by the first inflection portion, and the first inflection portion is molded into a thicker second inflection portion.

In the manufacturing method of the can lid shell of the present invention, a part of the first molded body to be processed is deformed and pushed into the die clearance, and the first molded body and the adjacent area are compressed from the flat portion side toward the flange portion side, increasing the plate thickness. The work hardening caused by compression and the increased plate thickness improve the pressure resistance of the can lid.

The die clearance can be configured during deep drawing, at the start of the reverse process, or during the reverse process.

In the can lid shell manufacturing method of the present invention, preferably, the die core ring includes a movable part that constitutes the part of the tip of the die core ring that faces the tip of the inner sleeve, and a biasing member that holds the movable part in a position that constitutes the mold clearance, and in the deep drawing process, the intermediate molded body presses the movable part, causing the movable part to retreat toward the biasing member.

In the present invention, before the reverse process is performed, the movable part is retracted by the intermediate formed body, thereby making it possible to suppress the reduction in thickness of the circular blank caused by friction with the movable part during deep drawing. Furthermore, by forming the first formed body in such a state where the reduction in thickness is suppressed, and then forming the first curved surface portion and the second curved surface portion on this first formed body, it is possible to suppress deformation and distortion of the curved portion at the start of the reverse process.

According to the present invention, the inflection section, which has a concave curved surface and a convex curved surface, is configured to have high pressure resistance, making it possible to prevent buckling.

Fig. 1A is a plan view showing a can lid shell according to a first embodiment of the present invention, and Fig. 1B is a cross-sectional view of the can lid shell taken along line S1-S1 in Fig. 1A. FIG. 2 is an enlarged view of a cut end surface of a portion surrounded by a dashed line circle in FIG. 1B. FIG. 3 is an enlarged cross-sectional view of an inflection portion of a can lid shell according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view of a molding device for molding a can lid shell according to the first embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view of a part of the lower mold and the upper mold of the molding apparatus of FIG. FIG. 6 is an enlarged view of the area surrounded by the dashed-dotted circle in FIG. FIG. 7 is a diagram showing a method for manufacturing a can lid shell according to the first embodiment of the present invention. 8A and 8B are views for explaining a blanking step in the manufacturing method for a can lid shell according to the first embodiment of the present invention. 9A and 9B are views for explaining a deep drawing step in the manufacturing method for a can lid shell according to the first embodiment of the present invention. 10A and 10B are views for explaining a reversing step in the manufacturing method for a can lid shell according to the first embodiment of the present invention. FIG. 11 is a view showing a cross section of the first molded body. FIG. 12 is a diagram for explaining the manufacturing method of a can lid shell according to the first embodiment of the present invention. FIG. 13 is a diagram for explaining the method for manufacturing a can lid shell according to the first embodiment of the present invention. FIG. 14A is a plan view showing a can lid shell according to a second embodiment of the present invention, and FIG. 14B is a view showing a cross section of the can lid shell taken along line S2-S2 in FIG. 14A. FIG. 15 is an enlarged view of the area surrounded by the dashed-dotted circle in FIG. 14A. FIG. 16 is a cross-sectional view of the shell taken along line S3-S3 in FIG. FIG. 17 is an enlarged view of the area surrounded by the dashed line in FIG. 14B. FIG. 18 is an enlarged view showing a modified example of the recessed portion and the protruding portion of the can lid shell according to the second embodiment of the present invention. FIG. 19 is an enlarged view showing a modified example of the recessed portion and the protruding portion of the can lid shell according to the second embodiment of the present invention. FIG. 20 is an enlarged view showing a modified example of the recessed portion and the protruding portion of the can lid shell according to the second embodiment of the present invention. FIG. 21 is a diagram for explaining the reforming process of the second embodiment of the present invention. FIG. 22 is an enlarged view of the area surrounded by the dashed line in FIG. FIG. 23 is a cross-sectional view of a molding device according to a first modified example of the present invention. FIG. 24 is a diagram showing a cross section of the die core ring. FIG. 25 is an enlarged view of a part of a cross section of the movable portion and the opposing portion of the upper piston. FIG. 26 is an enlarged view of a portion of a cross section of a molding device according to a first modified example of the present invention. 27A to 27D are views for explaining a method for manufacturing a shell by a molding apparatus according to a first modified example of the present invention. FIG. 28 is a diagram for explaining a method for manufacturing a shell by a molding apparatus according to a first modified example of the present invention. FIG. 29 is a cross-sectional view of a molding device according to a second modified example of the present invention. FIG. 30 is a diagram showing a cross section of the die core ring, lower piston, movable part, block and spring. FIG. 31 is an enlarged cross-sectional view of the block. FIG. 32 is an enlarged cross-sectional view of the extension portion of the lower piston. FIG. 33 is an enlarged cross-sectional view of the movable portion. FIG. 34 is a diagram for explaining a method for manufacturing a shell by a molding apparatus according to a second modified example of the present invention. FIG. 35 is a cross-sectional view of a conventional can lid shell. FIG. 36 is a cross-sectional view of a lightweight can lid. FIG. 37 is a diagram showing a cross section of a can lid during buckling.

The can lid shell 10 according to the first embodiment of the present invention will be described with reference to the drawings.

As shown in Figures 1A and 1B, the can lid shell 10 comprises a panel portion 11 having a circular outline in plan view, a recessed countersink portion 12 formed along the periphery of the panel portion 11, a chuck wall portion 13 rising from the edge of the countersink portion 12 and defining an internal space SP1 together with the panel portion 11 and the countersink portion 12, and a flange portion 14 extending from the upper end (the end portion on the radially outward direction Do side) of the chuck wall portion 13. The internal space SP1 is the space inside the chuck wall portion 13 and above the panel portion 11, as shown in Figure 1B.

In the following explanation, among the directions along the radius from the central axis C that passes through the center of the panel portion 11 and is perpendicular to the panel portion 11, the direction from the central axis C toward the outside is referred to as the radially outward direction Do, and the direction from the outside toward the central axis C is referred to as the radially inward direction Di. In addition, the direction along the central axis C from the countersink portion 12 side toward the chuck wall portion 13 is referred to as the first direction D1, and the direction opposite to the first direction D1, that is, from the chuck wall portion 13 toward the countersink portion 12 side along the central axis C is referred to as the second direction D2 (see Figure 2).

The front and back surfaces of the can lid shell 10, including the area defining the internal space SP1 and one surface of the flange portion 14 adjacent thereto, are referred to as the surface SF1 of the can lid shell 10, and the surface opposite to this surface SF1 is referred to as the back surface SF2.

1B and 2 show the cross-sectional shape of the can lid shell 10 when cut along an imaginary plane that passes through the central axis C and extends in the radially outward direction Do. The cross-sectional shape of the can lid shell 10 is described below.

(Panel section 11)
The panel portion 11 is formed as a flat circular plate, and its thickness is set to be approximately uniform.

(Countersink portion 12)
The countersink portion 12 comprises a groove bottom 121 which constitutes a deep portion, a first groove wall portion 122 which extends from the edge of the groove bottom 121 on the radially inward direction Di to the peripheral edge of the panel portion 11, and a second groove wall portion 123 which extends from the edge of the groove bottom 121 on the radially outward direction Do to the edge of the chuck wall portion 13 on the radially inward direction Di.

The groove bottom 121 has a cross section formed as an arc of radius r12 from a center C12 located in the internal space SP1, and presents a curved surface that is concave from the internal space SP1 side. The groove bottom 121 has a deepest part, and the connection point (first connection point p1) where the groove bottom 121 and the first groove wall 122 are connected is shifted radially inward Di from the deepest part, and is also shifted in the first direction D1 from the deepest part.

Furthermore, the connection point (second connection point p2) where the groove bottom 121 and the second groove wall 123 are connected is positioned offset in the radial outward direction Do from the deepest part, and is also positioned offset in the first direction D1 from the deepest part. Note that in FIG. 2, the position of each connection point is indicated by a circle.

(First groove wall portion 122)
The first groove wall portion 122 has one edge connected to the edge of the groove bottom portion 121 on the radially inward direction Di to form a first connection point p1, and further has a first inclined groove cross section formed with a constant inclination with respect to the central axis C. and a first convex groove cross-section portion 122B that is formed from the other edge of the first inclined groove cross-section portion 122A to the peripheral edge of the panel portion 11 and is a circular arc that is convex toward the internal space SP1. There are.

The connection point (third connection point p3) where the first inclined groove cross-sectional portion 122A and the first convex groove cross-sectional portion 122B are connected is shifted in the radial inward direction Di from the first connection point p1 and is also shifted in the first direction D1 from the first connection point p1.

The connection point (fourth connection point p4) where the first convex groove cross-section portion 122B and the panel portion 11 are connected is positioned offset in the radial inward direction Di from the third connection point p3, and is also positioned offset in the first direction D1 from the third connection point p3. The first convex groove cross-section portion 122B presents a curved surface whose radius from the central axis C gradually becomes smaller (reduced diameter) from the third connection point p3 to the fourth connection point p4.

(Second groove wall part 123)
The second groove wall portion 123 has one edge connected to the edge of the groove bottom portion 121 on the radially outward direction Do side to form a second connection point p2, and further has a second inclined groove cross section formed with a constant inclination with respect to the central axis C. a second convex groove cross section 123B (a third curved surface of the present invention) having one edge connected to the other edge of the second inclined groove cross section 123A and having a circular arc shape that is convex toward the internal space SP1; The second convex groove cross section 123B has one edge connected to the other edge of the second convex groove cross section 123B, and the second convex groove cross section 123B has a radius of curvature different from the radius of curvature of the second convex groove cross section 123B and is convex toward the internal space SP1. and a third convex groove cross-sectional portion 123C (corresponding to the first curved surface portion of the present invention) having a circular arc shape.

The connection point (fifth connection point p5) where the second inclined groove cross-section portion 123A and the second convex groove cross-section portion 123B are connected is positioned offset in the radially outward direction Do from the second connection point p2 and is also positioned offset in the first direction D1 from the second connection point p2. The connection point (sixth connection point p6) where the second convex groove cross-section portion 123B and the third convex groove cross-section portion 123C are connected is positioned offset in the radially outward direction Do from the fifth connection point p5 and is also offset in the first direction D1 from the fifth connection point p5.

The connection point (seventh connection point p7) where the third convex groove cross-sectional portion 123C and the chuck wall portion 13 are connected is positioned at a position shifted radially outwardly in the direction Do from the sixth connection point p6, and is also positioned at a position shifted in the first direction D1 from the sixth connection point p6.

The second convex groove cross-section 123B presents a curved surface whose radius from the central axis C gradually increases (widens) from the fifth connection point p5 to the sixth connection point p6.

The third convex groove cross-section 123C presents a curved surface whose radius from the central axis C gradually increases (widens) from the sixth connection point p6 to the seventh connection point p7.

As shown in FIG. 3, on the surface SF1 of the can lid shell 10, the center C56 of the arc formed by the second convex groove cross-section portion 123B is located in the outer space SP2, and the center C67 of the arc formed by the third convex groove cross-section portion 123C is located in the outer space SP2, and the center C56 of the arc of the second convex groove cross-section portion 123B is slightly shifted toward the radially inward direction Di from the center C67 of the arc of the third convex groove cross-section portion 123C, and is also slightly shifted toward the first direction D1. In addition, the radius r56 of the arc of the second convex groove cross-section portion 123B is set smaller than the radius r67 of the arc of the third convex groove cross-section portion 123C.

Furthermore, the back surface SF2 of the can lid shell 10 is formed as an arc of a constant radius r57 from the center C57, from the fifth connection point p5 through the sixth connection point p6 to the seventh connection point p7.

In the third convex groove cross-sectional portion 123C, the center C67 of the arc on the front surface SF1 is shifted toward the radially inward direction Di from the center C57 of the arc on the back surface SF2, and is also shifted toward the first direction D1. In addition, the radius r57 of the arc on the back surface SF2 is set to be smaller than the radius r56 of the arc on the second convex groove cross-sectional portion 123B and the radius r67 of the arc on the third convex groove cross-sectional portion 123C.

(Chuck wall portion 13)
The chuck wall portion 13 has one edge (radially inward Di side) connected to the edge on the radially outward direction Do side of the second convex groove cross-sectional portion 123B of the countersink portion 12, forming a sixth connection point p6, and has a first concave surrounding cross-sectional portion 131 (corresponding to the second curved surface portion of the present invention) of a circular arc that is concave toward the internal space SP1 side, and one edge (radially inward Di side) connected to the other edge (radially outward direction Do side) of the first concave surrounding cross-sectional portion 131, and has a curvature radius different from that of the first concave surrounding cross-sectional portion 131. The second concave surrounding cross-sectional portion 132 is an arc that is concave toward the internal space SP1 at a radius, an inclined surrounding cross-sectional portion 133 whose one edge (radially inward Di side) is connected to the other edge (radially outward Do side) of the second concave surrounding cross-sectional portion 132 and whose inclination with respect to the central axis C is constant, and a convex surrounding cross-sectional portion 134 whose one edge (radially inward Di side) is connected to the other edge (radially outward Do side) of the inclined surrounding cross-sectional portion 133 and whose convex shape is toward the internal space SP1.

(First concave surrounding cross section 131)
The eighth connection point p8 where the first surrounding cross-section 131 and the second surrounding cross-section 132 are connected is disposed at a position shifted in the radial outward direction Do from the seventh connection point p7. The seventh connection point p7 is disposed in the first direction D1 away from the eighth connection point p8. The first concave surrounding cross-section portion 131 has a radius from the central axis C that gradually increases from the seventh connection point p7 to the eighth connection point p8. It presents a curved surface (expanded diameter).

Note that the first concave surrounding cross-section 131 of the chuck wall portion 13 and the third convex groove cross-section 123C of the countersink portion 12 have curved surfaces in opposite directions, so the seventh connection point p7 constitutes an inflection point.

(Second concave surrounding cross section 132)
A connection point (ninth connection point p9) where the second concave surrounding cross-section portion 132 and the inclined surrounding cross-section portion 133 are connected is disposed so as to be shifted in the radial outward direction Do from the eighth connection point p8. The second concave surrounding cross-section portion 132 has a radius from the central axis C that gradually increases (expands) from the eighth connecting point p8 to the ninth connecting point p9. It has a curved surface with a diameter of 1 mm.

As shown in FIG. 3, the center C89 of the arc formed by the surface SF1 in the second concave surrounding cross-sectional portion 132 is disposed within the internal space SP1, and the center C78 of the arc formed by the surface SF1 in the first concave surrounding cross-sectional portion 131 is disposed within the internal space SP1. The center C89 of the arc formed by the surface SF1 in the second concave surrounding cross-sectional portion 132 is shifted toward the radially inward direction Di from the center C78 of the arc of the first concave surrounding cross-sectional portion 131, and is also shifted toward the first direction D1.

In addition, the radius r89 of the arc formed by surface SF1 in second concave surrounding cross-section 132 is set to be larger than the radius r78 of the arc formed by surface SF1 in first concave surrounding cross-section 131.

The back surface SF2 of the can lid shell 10 is formed as an arc of a constant radius r79 from the center C89, from the seventh connection point p7 through the eighth connection point p8 to the ninth connection point p9.

(Slanted surrounding cross section 133)
The connection point (tenth connection point p10) where the inclined surrounding cross-section portion 133 and the convex surrounding cross-section portion 134 are connected is disposed in the radially outward direction Do from the ninth connection point p9. The inclined surrounding cross-section portion 133 is inclined such that the radius from the central axis C gradually increases (expands) from the ninth connection point p9 to the tenth connection point p10. presents a constant inclination surface.

(Convex surrounding cross section 134)
The connection point (eleventh connection point p11) where the convex surrounding cross section 134 and the flange portion 14 are connected is disposed at a position shifted in the radially outward direction Do from the tenth connection point p10 and at a position shifted in the first direction D1 from the tenth connection point p10. The convex surrounding cross section 134 presents a curved surface whose radius from the central axis C gradually increases (expands) from the tenth connection point p10 to the eleventh connection point p11. The eleventh connection point p11 is the point on the can lid shell 10 that is furthest away from the deepest part along the first direction D1, i.e., it constitutes the highest point (apex).

(Flange portion 14)
The flange portion 14 has one edge (radially inward Di side) connected to the other edge (radially outward Do side) of the convex surrounding cross section portion 134 to form an eleventh connection point p11 (vertex), and protrudes in the radially outward direction Do. The tip of the flange portion 14 is shifted in the radially outward direction Do from the eleventh connection point p11 and is shifted in the second direction D2 from the eleventh connection point p11.

The tip of the flange portion 14 is curled in the next curling process, as shown in Figure 2.

In the can lid shell 10 configured in this manner, the cross section formed by the chuck wall portion 13 and the flange portion 14 is hook-shaped, and further, the section from the convex surrounding cross section portion 134 of the chuck wall portion 13 to the tip of the flange portion 14 is flange-shaped.

The reinforcing structure of the can lid shell 10 is explained below.

As shown in FIG. 3, in the can lid shell 10, the back surface SF2 from the fifth connection point p5 through the sixth connection point p6 to the seventh connection point p7 (inflection point) is formed as an arc of a constant radius r57 from the center C57. In the can lid shell 10, the front surface SF1 from the fifth connection point p5 to the sixth connection point p6 is formed as an arc of a radius r56 longer than the radius r57 from the center C56 that is positioned offset from the center C57. The second convex groove cross-sectional portion 123B is formed so that its thickness gradually increases from the fifth connection point p5 to the sixth connection point p6.

In the cross-sectional view of Figure 3, each connection point is represented by a ● mark indicating a position on the front surface SF1, a ● mark indicating a position on the back surface SF2, and a solid line connecting these.

In addition, in the can lid shell 10, the surface SF1 from the sixth connection point p6 to the seventh connection point p7 is formed by an arc of radius r67 longer than radius r57 from a center C67 that is positioned offset from the center C57 of the arc on the back surface SF2. The third convex groove cross-sectional portion 123C is formed so that its thickness gradually decreases from the sixth connection point p6 to the seventh connection point p7.

The can lid shell 10 has a back surface SF2 extending from the seventh connection point p7 through the eighth connection point p8 to the ninth connection point p9, which is formed by an arc of a constant radius r79 from the center C89, and a front surface SF1 extending from the eighth connection point p8 to the ninth connection point p9, which is formed by an arc of a radius r89 that is concentric with the center C89 of the arc of the back surface SF2 and is shorter than the radius r79, and the second concave surrounding cross-sectional portion 132 is formed to have a constant thickness from the eighth connection point p8 to the ninth connection point p9.

The seventh connection point p7 is the inflection point between the third convex groove cross-sectional portion 123C and the first concave surrounding cross-sectional portion 131, and is located on the imaginary line LX1 (shown by a dashed line) connecting the centers C89 and C57 of the figure.

The surface SF1 of the can lid shell 10 from the seventh connection point p7 to the eighth connection point p8 is formed with a radius r78 that is shorter than the radius r89 from a center C78 that is offset from the center C89 of the arc on the back surface. The first concave surrounding cross-sectional portion 131 is formed so that its thickness gradually decreases from the seventh connection point p7 to the eighth connection point p8.

Specifically, the thickness of the inflection portion of the can lid shell 10 satisfies the relationship t8<t7<t6, where t6 is the thickness at the sixth connection point p6, t7 is the thickness at the seventh connection point p7, and t8 is the thickness at the eighth connection point p8. Thickness t6 is the dimension along a virtual line (not shown) extending from center C57, thickness t7 is the dimension along a virtual line LX1 extending from center C57 and center C89, and thickness t8 is the dimension along a virtual line (not shown) extending from center C89.

In this way, the can lid shell 10 has an inflection point (seventh connection point p7) located in the middle, forming an inflection section 17 consisting of the third convex groove cross-section 123C of the countersink section 12 and the first concave surrounding cross-section 131 of the chuck wall section 13, which is bent in the opposite direction. The thickness of the inflection section 17 increases from the eighth connection point p8 to the sixth connection point p6, and is at its maximum near the sixth connection point p6.

The thickness of the inflection portion 17 is equal to or greater than the thickness of the base plate 400 (circular blank 410) used to form the can lid shell 10, and is, for example, 106% or more of the thickness of the base plate 400 (circular blank 410).

Furthermore, the thickness of the can lid shell 10 increases from the fifth connection point p5 to the sixth connection point p6. If the thickness at the fifth connection point p5 is t5 and the thickness at the sixth connection point p6 is t6, then the relationship t5<t6 holds. Thicknesses t5 and t6 are dimensions along an imaginary line (not shown) extending from the center C57. The thickness from the fifth connection point p5 to the sixth connection point p6 is also greater than or equal to the thickness of the base plate 400 (circular blank 410) used to form the can lid shell 10.

In this way, the area from the fifth connection point p5 to the eighth connection point p8 is thicker than the adjacent second inclined groove cross-sectional portion 123A and second concave surrounding cross-sectional portion 132. It is also thicker than the base plate 400 (circular blank 410). Hereinafter, the area from the fifth connection point p5 to the eighth connection point p8, which is formed by increasing the thickness including the inflection point (seventh connection point p7), will be referred to as the thickened portion 18.

The can lid shell 10 has the above cross-sectional structure configured throughout around the central axis C, and the thickened bend portion 17 is arranged in a ring shape in a plan view.

The can lid shell 10 is formed by pressing a circular blank 410 made of an aluminum alloy (e.g., 5000 series). The thickness of each part of the can lid shell 10 is, for example, 0.20 mm or more and 0.26 mm or less.

The can lid includes the above-mentioned can lid shell 10, a tear line for forming an opening formed on the can lid shell 10, and a tab for opening the can.

The can lid manufacturing method includes a can lid shell forming process in which the can lid shell 10 is formed, and a conversion molding process in which tear lines, tabs, etc. are provided on the can lid shell 10 using a conversion press.

The following describes the molding device 2 that performs the can lid shell molding process (the manufacturing method of the can lid shell 10) in the can lid manufacturing method.

(Molding device 2)
As shown in FIG. 4, the molding device 2 includes a lower die 200 and an upper die 300 in a press machine (not shown).

The central axes of the lower die 200 and the upper die 300 are set coaxially with the central axis C of the can lid shell 10 to be molded, and these axes are hereinafter collectively referred to as the central axis C. In addition, in the following explanation, among the directions along the radius from the central axis C, the direction toward the outside from the central axis C is referred to as the radially outward direction Do, and the direction from the outside toward the central axis C is referred to as the radially inward direction Di.

Furthermore, among the directions along the central axis C, the direction from the lower die 200 to the upper die 300 corresponds to the first direction D1 of the can lid shell 10 in the molding device 2, so the direction from the lower die 200 to the upper die 300 is also referred to as the first direction D1, and the direction from the upper die 300 to the lower die 200 is sometimes referred to as the second direction D2. Furthermore, in the molding device 2, the first direction D1 will be described as upward, and the second direction D2 as downward.

(Lower mold 200)
The lower mold 200 includes a lower retainer 210, a cut edge portion 220 held at the tip of the lower retainer 210 on the upper mold 300 side (first direction D1 side), a die core ring 230 held inside the lower retainer 210, a panel punch piston 240 provided inside the die core ring 230, a panel punch 250 fixed to the tip of the panel punch piston 240, and a lower piston 260 surrounding a portion of the die core ring 230.

The lower retainer 210 comprises a base portion 211 having a hole 211A penetrating the center, and a tube portion 212 fixed to the upper portion of the base portion 211 and having an inner peripheral surface with an inner diameter larger than that of the hole 211A. The tube portion 212 has a step portion 212A on the inside of the tip end opposite the base end fixed to the base portion 211.

The cut edge portion 220 is formed in a ring shape and is disposed in the step portion 212A of the lower retainer 210, with the inner peripheral surface 221 protruding further toward the central axis C than the inner peripheral surface of the tubular portion 212 of the lower retainer 210. The lower surface 222 of the cut edge portion 220 is fixed to the step portion 212A, and a corner portion 224 is formed by the top surface 223 opposite the lower surface 222 and the inner peripheral surface 221.

The die core ring 230 comprises a base 231 fixed to the upper surface of the base portion 211 of the lower retainer 210, and an extension portion 232 that has a thickness in the radial direction from the central axis C that is thinner than that of the base 231 and extends from the base portion 231 to the opposite side of the base portion 211, has a hole penetrating along the central axis C, and is disposed inside the tubular portion 212 of the lower retainer 210.

The panel punch piston 240 is integrally equipped with a piston body 241 that rubs against the inner circumferential surface of the die core ring 230 and an extension 242 that extends from the piston body 241, and can move along the central axis C. The piston body 241, the die core ring 230, and the lower retainer 210 form a space SP21. Air is supplied to this space SP21 via a flow path not shown, to control the panel punch piston 240.

As shown in FIG. 5, the panel punch 250 has a punch flat portion 251 that cooperates with the flat portion 341 of the die center 340 to clamp the circular blank, and a punch step portion 252 having a receiving surface 252A that is provided along the periphery of the punch flat portion 251 and is offset toward the panel punch piston 240 side from the punch flat portion 251. The receiving surface 252A has a cross section formed into a circular arc that is concave toward the upper die 300.

The lower piston 260 is formed in a cylindrical shape as a whole, and includes a piston body portion 261 that rubs against the inner peripheral surface of the lower retainer 210 and the outer peripheral surface of the die core ring 230, and an extension portion 262 that extends from the piston body portion 261 and has a thinner thickness in the radial direction from the central axis C than the piston body portion 261. The lower piston 260 can move along the central axis C.

The piston body 261 of the lower piston 260, the lower retainer 210, and the die core ring 230 form a space SP22. Air is supplied to this space SP22 via a flow path not shown, to control the lower piston 260.

(Upper mold 300)
The upper mold 300 includes an upper retainer 310, a blank draw die 320 held by the upper retainer 310, a die center piston 330 provided inside the upper retainer 310, a die center 340 fixed to the tip of the die center piston 330, an inner sleeve 350 surrounding the die center 340, and an upper piston 360 surrounding the inner sleeve 350.

The upper retainer 310 integrally comprises a first tubular portion 311, a second tubular portion 312 formed with an inner diameter smaller than that of the first tubular portion 311, and a third tubular portion 313 formed with an inner diameter larger than that of the second tubular portion 312. The inside of the third tubular portion 313 is formed as a step portion 313A, which forms an open end. The space between the inner circumferential surface of the first tubular portion 311 and the inner circumferential surface of the second tubular portion 312 forms a step portion 314.

The blank draw die 320 includes a base 321 formed in a ring shape, and a tubular portion 322 extending from the base 321 and having a thickness along the radius from the central axis C that is thinner than that of the base 321. The base 321 is disposed in the step portion 313A of the upper retainer 310, and the inner peripheral surface side protrudes further toward the central axis C than the third tubular portion 313 of the upper retainer 310.

The die center piston 330 has a rod-shaped portion 331 and a flange-shaped protruding end portion 332 provided at the end of the rod-shaped portion 331, and the rod-shaped portion 331 is arranged to extend from the lower open end of the upper retainer 310 toward the lower die 200.

The die center piston 330 can move along the central axis C, and is configured so that the protruding end 332 abuts against the step portion 314 of the upper retainer 310. The protruding end 332 and the inside of the first cylindrical portion 311 form a space SP31, and air is supplied through a flow path not shown to control the die center piston 330.

The inner sleeve 350 is integrally formed into a cylindrical shape as a whole, and includes a piston body portion 351 that rubs against the inner circumferential surface of the upper retainer 310 and the die center piston 330, and an extension portion 352 that extends from the piston body portion 351 and has a thinner thickness in the radial direction from the central axis C than the piston body portion 351. The inner sleeve 350 can move along the central axis C.

The upper piston 360 is formed in a cylindrical shape as a whole, and includes a piston body 361 that rubs against the inner circumferential surface of the upper retainer 310 and the extension 352 of the inner sleeve 350, and an extension 362 that extends from the piston body 361 and has a thinner thickness in the radial direction from the central axis C than the piston body 361. The upper piston 360 can move along the central axis C.

The piston body 351 of the inner sleeve 350, the die center piston 330, and the upper retainer 310 form a space SP32. The piston body 351 of the inner sleeve 350, the upper retainer 310, and the piston body 361 of the upper piston 360 form a space SP33. Air is supplied to these spaces SP32 and SP33 via a flow path not shown in the figure, to control the inner sleeve 350 and the upper piston 360.

As shown in FIG. 5, in the molding device 2, the lower piston 260 and the blank draw die 320 are configured to align the flat surface 262B of the tip 262A of the extension portion 262 with the flat surface 322B of the tip 322A of the tubular portion 322. The tip 322A of the tubular portion 322 of the blank draw die 320 has a rounded portion 322D with a cross section formed in an arc between the flat surface 322B and the inner circumferential surface 322C.

As shown in Figures 5 and 6, the extension portion 232 of the die core ring 230 has a tip portion 232A that faces the tip portion 362A of the extension portion 362 of the upper piston 360 and the tip portion 352A of the extension portion 352 of the inner sleeve 350.

The tip 232A of the die core ring 230 is formed at the highest point, faces the tip 362A of the extension 362 of the upper piston 360, and has a cross section formed in an arc that is convex toward the tip 362A side. A first inclined surface portion 232C is formed connected to the edge of the first convex surface portion 232B in the radial inward direction Di, is formed at a constant inclination with respect to the central axis C, and descends as it goes in the radial inward direction Di. A first inclined surface portion 232C is formed connected to the lower end of the first inclined surface portion 232C, and is formed so that the cross section of the first inclined surface portion 232B is inclined toward the central axis C. It is provided with a concave surface portion 232D (corresponding to the first lower mold curved surface portion of the present invention) whose cross section is formed in an arc concave toward the C side, a second convex surface portion 232E (corresponding to the second lower mold curved surface portion of the present invention) which is connected to the edge of the concave surface portion 232D on the radially inward direction Di side and whose cross section is formed in an arc convex toward the central axis C side, and a second inclined surface portion 232F which is connected to the edge of the second convex surface portion 232E on the radially inward direction Di side and is formed at a constant inclination with respect to the central axis C and descends as it goes in the radially inward direction Di.

Compared to the connection point (first lower die connection point P21) where the first inclined surface portion 232C and the concave surface portion 232D are connected, the connection point (second lower die connection point P22) where the concave surface portion 232D and the second convex surface portion 232E are connected is shifted in the radial inward direction Di and is also shifted in the second direction D2. The concave surface portion 232D presents a curved surface whose radius from the central axis C gradually decreases (reduced diameter) from the first lower die connection point P21 to the second lower die connection point P22. In the cross-sectional view of Figure 6, each connection point is highlighted with a ● mark, but in reality it is a smooth surface.

The connection point (third lower die connection point P23) where the second convex surface portion 232E and the second inclined surface portion 232F are connected is shifted in the radial inward direction Di with respect to the second lower die connection point P22, and is also shifted in the second direction D2. The second convex surface portion 232E presents a curved surface whose radius from the central axis C gradually decreases (reduced diameter) from the second lower die connection point P22 to the third lower die connection point P23. The second convex surface portion 232E and the adjacent concave surface portion 232D have inverted curved surfaces, differing in convex and concave directions, and therefore the second lower die connection point P22 constitutes an inflection point.

As shown in FIG. 5, the tip 362A of the upper piston 360 has a concave surface 362B that faces the first convex surface 232B of the die core ring 230. The concave surface 362B of the tip 362A of the upper piston 360 and the first convex surface 232B of the die core ring 230 sandwich a circular blank (described below) between them to form the flange portion 14.

As shown in FIG. 6, the tip 352A of the inner sleeve 350 is formed with one edge connected to the lowest point (lowest point P30) and extending from the lowest point P30 in the radially outward direction Do, and has a cross section formed in an arc that is convex toward the tip 232A of the die core ring 230. The sleeve concave portion 352C (corresponding to the third upper mold curved surface portion of the present invention) is formed by connecting to the edge of the sleeve concave portion 352C on the radially outward direction Do side and has a cross section formed in an arc that is concave toward the tip 232A of the die core ring 230. The sleeve concave portion 352C is formed by connecting to the edge of the sleeve concave portion 352C on the radially outward direction Do side and has a cross section formed in an arc that is concave toward the tip 232A of the die core ring 230. The second sleeve convex surface portion 352D (corresponding to the second upper mold curved surface portion of the present invention) has a cross section formed in an arc that is convex toward the 232A side, a third sleeve convex surface portion 352E (corresponding to the first upper mold curved surface portion of the present invention) that is connected to the edge of the second sleeve convex surface portion 352D on the radially outward direction Do side and has a cross section formed in an arc that is convex toward the tip portion 232A side of the die core ring 230 with a radius of curvature different from the radius of curvature of the arc of the second sleeve convex surface portion 352D, and a sleeve inclined surface portion 352F that is connected to the edge of the third convex surface portion 352E on the radially outward direction Do side and is formed at a constant inclination with respect to the central axis C, and expands in diameter as it moves in the radially outward direction Do.

The connection point (first upper die connection point P31) where the first sleeve convex surface portion 352B and the sleeve concave surface portion 352C are connected is positioned offset in the radially outward direction Do from the lowest point P30, and is also positioned offset in the first direction D1. The first sleeve convex surface portion 352B presents a curved surface whose radius from the central axis C gradually increases (widens) from the lowest point P30 toward the first upper die connection point P31.

The connection point (second upper die connection point P32) where the second sleeve convex surface portion 352D and the sleeve concave surface portion 352C are connected is positioned offset in the radially outward direction Do from the first upper die connection point P31, and is also positioned offset in the first direction D1. The sleeve concave surface portion 352C presents a curved surface whose radius from the central axis C gradually increases (expands in diameter) from the first upper die connection point P31 to the second upper die connection point P32. Since the orientation of the curved surface of the sleeve concave surface portion 352C and the adjacent first sleeve convex surface portion 352B differs between concave and convex, the first upper die connection point P31 constitutes an inflection point.

The connection point (third upper die connection point P33) where the third sleeve convex surface portion 352E and the second sleeve convex surface portion 352D are connected is positioned offset in the radially outward direction Do from the second upper die connection point P32, and is also positioned offset in the first direction D1. The second sleeve convex surface portion 352D presents a curved surface whose radius from the central axis C gradually increases (widens in diameter) from the second upper die connection point P32 to the third upper die connection point P33. Since the second sleeve convex surface portion 352D and the adjacent sleeve concave surface portion 352C have different curved directions, convex and concave, the second upper die connection point P32 constitutes an inflection point.

The connection point (fourth upper die connection point P34) where the sleeve inclined surface portion 352F and the third sleeve convex surface portion 352E are connected is positioned offset in the radially outward direction Do from the third upper die connection point P33, and is also positioned offset in the first direction D1. The third sleeve convex surface portion 352E presents a curved surface whose radius from the central axis C gradually increases (widens) from the third upper die connection point P33 to the fourth upper die connection point P34.

In the molding device 2, the circular blank 410 is pressed by being sandwiched between the tip 232A of the die core ring 230 and the tip 352A of the inner sleeve 350 at a predetermined pressure. A spacer 370 of a predetermined thickness is attached to the flange portion underside 351A (on the second direction D2 side) of the piston body 351 of the inner sleeve 350.

When the inner sleeve 350 descends (in the second direction D2) towards the die core ring 230 during the deep drawing process, the spacer 370 comes into contact with the upper piston, thereby maintaining the position of the tip 352A of the inner sleeve 350 relative to the tip 232A of the die core ring 230, and a mold clearance CL1 for forming the inflection portion 17 can be formed between the tip 232A of the die core ring 230 and the inner sleeve 350.

As shown in Figures 5, 6, 12 and 13, in the molding device 2, the tip 352A of the inner sleeve 350 is closest to the tip 232A of the die core ring 230, and a mold clearance CL1 is set between the tip 232A of the die core ring 230 and the tip 352A of the inner sleeve 350. The mold clearance CL1 is set to be larger than the thickness of the blank 400 from the third upper die connection point P33 to the first upper die connection point P31 of the inner sleeve 350.

If the spacer 370 is not present, the circular blank 410 is deep drawn while being sandwiched between the inner sleeve 350 and the die core ring 230 at a constant pressure, and the plate thickness of the inflection portion including the eighth connection point p8 to the sixth connection point p6 is reduced. In addition, the reduction in plate thickness reduces the die clearance at this inflection portion.

The mold clearance CL1 is explained below.

Figure 6 shows the surface of the tip 232A of the die core ring 230. The concave surface 232D is formed from a circular arc of a constant radius r212 from the center C212. The second convex surface 232E is formed from a circular arc of a constant radius r223 from the center C223.

When the inner sleeve 350 is closest to the die core ring 230, the concave surface 232D of the tip 232A of the die core ring 230 faces the second sleeve convex surface 352D and the third sleeve convex surface 352E of the tip 352A of the inner sleeve 350.

Here, the third sleeve convex portion 352E is an arc centered at the same point as the center C212 of the concave portion 232D of the die core ring 230, and the radius r334 of this arc is shorter than the radius r212 of the concave portion 232D of the die core ring 230. As a result, the distance between the third sleeve convex portion 352E of the inner sleeve 350 and the concave portion 232D of the die core ring 230 when they are closest to each other is constant.

The center C323 of the arc of the second sleeve convex surface portion 352D is shifted radially outwardly Do from the center C212 of the arc of the concave surface portion 232D of the die core ring 230, and is also shifted in the second direction D2. In addition, the radius r323 of the arc of the second sleeve convex surface portion 352D is set shorter than the radius r212 of the arc of the concave surface portion 232D of the die core ring 230 and the radius r334 of the arc of the third sleeve convex surface portion 352E.

Assuming a first tangent T1 that touches each point located between the second upper die connection point P32 and the third upper die connection point P33 of the second sleeve convex surface portion 352D in the cross section, and a second tangent T2 that touches each point located between the third upper die connection point P33 and the fourth upper die connection point P34 of the third sleeve convex surface portion 352D, the angle θ1 between the first tangent T1 and the horizontal line HL is set to be smaller than the angle θ2 between the second tangent T2 and the horizontal line HL (θ1 < θ2) (excluding the tangent that touches the third upper die connection point P33).

As a result, when the distance between the second sleeve convex portion 352D of the inner sleeve 350 and the concave portion 232D of the die core ring 230 is measured along an imaginary line extending from the center C212, it is formed so that it becomes wider from the third upper die connection point P33 of the inner sleeve 350 to the second upper die connection point P32.

The center C312 of the arc of the sleeve concave portion 352C is shifted in the radially inward direction Di from the center C223 of the arc of the second convex portion 232E of the die core ring 230, and is also shifted in the first direction D1. In addition, the radius r312 of the arc of the sleeve concave portion 352C is set to be longer than the radius r223 of the arc of the second convex portion 232E of the die core ring 230.

Here, the second lower die connection point P22 and the second upper die connection point P32, both of which are inflection points, are located on the imaginary line LX2 connecting the centers C212 and C223 shown by the dashed dotted line in the figure.

When the distance between the sleeve concave portion 352C and the second convex portion 232E of the die core ring 230 is measured along an imaginary line extending from the center C223, it is formed so that it becomes wider from the second upper die connection point P32 of the inner sleeve 350 to the first upper die connection point P31.

In this way, the mold clearance CL1 is formed to become wider from the third upper mold connection point P33 to the first upper mold connection point P31 of the inner sleeve 350. If the clearance dimension at the third upper mold connection point P33 is CL33, the clearance dimension at the second upper mold connection point P32 is CL32, and the clearance dimension at the first upper mold connection point P31 is CL31, then the relationship CL33 < CL32 < CL31 holds.

CL33 is the dimension along an imaginary line extending from the center C212 through the third upper die connection point P33 into the die core ring 230. CL32 is the dimension along an imaginary line extending from the center C212 or center 223 and passing through the second upper die connection point P32 and the second lower die connection point P22. CL31 is the dimension along an imaginary line extending from the center 223 through the first upper die connection point P31 into the inner sleeve 350.

The die clearance CL1 from the third upper die connection point P33 to the first upper die connection point P31 of the inner sleeve 350 is set to be larger than the thickness of the blank 400.

(Method of manufacturing the can lid shell 10)
As shown in FIG. 7 , the manufacturing method of the can lid shell 10 by the forming device 2 includes a blanking process ( FIG. 8 ) in which a circular blank is punched out from an aluminum alloy raw plate, a deep drawing process ( FIG. 9 ) in which the circular blank is deep drawn to form a shallow-bottomed first formed body, and a reverse process ( FIG. 10 ) in which the bottom side of the first formed body is moved in the opposite direction to form a countersink portion 12.

The steps will be explained using Figures 8 to 10 (Figures 8A, 8B, 9A, 9B, and 10A, 10B). Note that Figures 8 to 10 show the left side of the central axis C of the molding device 2 shown in Figure 4.

(Blanking process)
First, as shown in Fig. 8A, with the upper die 300 disposed above the lower die 200, the blank 400 is placed on the lower die 200. In the lower die 200, the cut edge portion 220 and the tip portion 262A of the lower piston 260 are disposed at the same height, and the blank 400 is supported by their upper ends.

Then, as shown in FIG. 8B, the upper die 300 descends and the blank draw die 320 presses a portion of the blank 400 toward the inside of the cut edge portion 220 to punch out the circular blank 410. The punched circular blank 410 is held by having its peripheral edge sandwiched between the tip 262A of the lower piston 260 of the lower die 200 and the tip 322A of the blank draw die 320 of the upper die 300.

(Deep drawing process)
In the deep drawing process, first, as shown in FIG. 9A, the upper die 300 descends and the circular blank 410 is sandwiched between the tip 232A of the die core ring 230 and the tip 362A of the upper piston 360.

Next, as shown in FIG. 9B, the upper die 300 is further lowered to place the tip 322A of the blank draw die 320 between the cut edge portion 220 and the die core ring 230, and the tip 352A of the inner sleeve 350 is brought closer to the tip 232A of the die core ring 230 until a die clearance CL1 is formed between them, and the flat portion 341 of the die center 340 is placed inside the die core ring 230.

In other words, deep drawing is performed by sandwiching the central portion of the circular blank between the flat portion 341 of the die center 340 and the punch flat portion 251 of the panel punch 250 and moving them in the second direction. Figure 9B shows the first formed body 420 formed by the deep drawing process with the upper die 300 at the bottom dead center.

As shown in FIG. 11, the first molded body 420 has a bottom portion (flat portion) 421 sandwiched between the panel punch 250 of the lower mold 200 and the die center 340 of the upper mold 300, a clamping portion (flange portion) 422 that is shifted from the bottom portion 421 in the first direction D1 and also shifted in the radially outward direction Do and is sandwiched between the die core ring 230 and the upper piston 360, and a first inflection portion 423 that is positioned in the mold clearance CL1 between the tip portion 352A of the inner sleeve 350 and the tip portion 232A of the die core ring 230.

The first bend portion 423 is configured by connecting a convex portion 423A, the cross section of which is formed into a curved surface whose direction of curvature is convex toward the internal space SP4 of the first molded body 420, and a concave portion 423B, which is positioned toward the clamping portion 422 from the convex portion 423A and has a cross section formed into a curved surface that is concave toward the internal space SP4. In the following explanation, the intermediate form in which the circular blank 410 is deformed to become the first molded body 420 is referred to as the intermediate molded body.

(Reverse process)
10A, the panel punch 250 of the lower die 200 and the upper die 300 are raised. During the process in which the panel punch 250 of the lower die 200 and the upper die 300 are raised, the die clearance CL1 between the tip portion 352A of the inner sleeve 350 and the tip portion 232A of the die core ring 230 is maintained.

As the panel punch 250 of the lower die 200 and the upper die 300 rise, the portion of the first molded body 420 sandwiched between the panel punch 250 and the die center 340 that protrudes beyond the bottom portion 421 is folded back to form a curved portion 424 with a U-shaped cross section that is convex downward, as shown in FIG. 12.

As shown in FIG. 12, the curved portion 424 is disposed in the mold clearance CL1 between the tip 352A of the inner sleeve 350 and the tip 232A of the die core ring 230, with the first bend portion 423 of the first molded body 420 sandwiched between them.

In this die clearance CL1, a minute gap (space) CL0 that is not filled by the first inflection portion 423 of the first molded body 420 remains, for example, between the first inflection portion 423 and the sleeve concave portion 352C or the second sleeve convex portion 352D of the inner sleeve 350. The minute gap (space) CL0 is formed at the stage where the deep drawing process is completed.

The depth dimension h of the curved portion 424 gradually increases as the panel punch 250 rises, and when it reaches a predetermined depth, it comes into contact with the receiving surface 252A of the punch step portion 252 provided around the punch flat portion 251 of the panel punch 250, as shown in Figures 10B and 13. After coming into contact with the receiving surface 252A, the curved portion 424 is pushed by the receiving surface 252A and moves (rises) in the first direction D1.

In the reverse process, the curved portion 424 is pushed up by the receiving surface 252A of the panel punch 250, and as shown in FIG. 13, a part of the first molded body 420 being processed is deformed to fill the minute gap (space) CL0. This causes the first inflection portion 423 to thicken and become the second inflection portion 425 (inflection portion 17).

In this way, the panel punch 250 is moved (raised) in the first direction D1 to a predetermined position (height) until a portion of the first molded body 420 fills the minute gap (space) CL0, and the reverse process ends. The curved portion 424 at this end stage forms the countersink portion 12, and the formed second inflection portion 425 forms the inflection portion 17.

After the reverse process is completed, the upper die 300 rises and the flat portion 341 of the die center 340 moves away from the bottom portion 421 of the first molded body 420 in the first direction D1.

Then, the upper die 300 is further moved to a position above the lower die 200, and the completed can lid shell 10 is removed.

In the next lining process, rubber is applied to the back surface SF2 of the formed can lid shell 10 to maintain the coating seal. Then, in the next conversion process, tear lines for opening the can are formed and tabs for opening the can are attached, completing the can lid.

Furthermore, after filling the bottomed cylindrical can body with the contents and gas ( _CO2 or _N2 ), the flange portion of the can lid shell 10 of the can lid (the flange portion 14 and the convex surrounding cross-sectional portion 134 of the chuck wall portion 13) is wrapped around the flange portion of the can body to attach the can lid, completing the can product.

In a can product using a can lid equipped with the can lid shell 10 of this embodiment, even if the internal pressure of the can product rises and causes internal pressure to expand part of the countersink portion 12 of the can lid outside the can, the inflection portion 17 around the countersink portion 12 is reinforced and deformation of the countersink portion 12 can be suppressed.

For example, even if an internal pressure is applied that changes the angle θ23 of the concave opening on the back surface of the second groove wall portion 123 shown in FIG. 1B, deformation can be suppressed because the thickness gradually increases from the first concave surrounding cross-sectional portion 131 of the chuck wall portion 13 to the third convex groove cross-sectional portion 123C and the second convex groove cross-sectional portion 123B of the countersink portion 12. This makes it possible to prevent buckling.

Second Embodiment
As shown in Figures 14A and 14B, compared to the can lid shell 10 of the first embodiment, the can lid shell 10A of the second embodiment has a plurality of thin-walled portions (recesses) 15 formed along the radial direction, including the inflection points, on the surface SF1 of the can lid shell 10A.

The thin-walled portions 15 are configured as recessed portions as shown in Figures 15, 16, and 17. In a plan view of the can lid shell 10A, the thin-walled portions 15 are arranged at equal angular intervals around the center of the panel portion 11. Furthermore, each thin-walled portion 15 is formed in the same shape (rounded rectangle). In a plan view, each thin-walled portion 15 is formed such that the dimension Da along the radially outward direction Do is longer than the width dimension Db perpendicular to this. In Figure 15, the line along the radially outward direction Do is represented by a two-dot chain line.

The areas between these thin-walled portions 15 constitute thick-walled portions (convex portions) 16 that are formed thicker than the thin-walled portions 15. Each thick-walled portion 16 is also formed so that the dimension along the radially outward direction Do in plan view is longer than the width dimension perpendicular to this. In other words, the distance between each thin-walled portion 15 along the circumferential direction relative to the central axis C is smaller than the dimension Da.

In Figure 15, dashed line B11 indicates the boundary line formed by the fifth connection point p5, dashed line B12 indicates the boundary line formed by the sixth connection point p6, dashed line B13 indicates the boundary line formed by the seventh connection point p7 (inflection point), and dashed line B14 indicates the boundary line formed by the eighth connection point p8.

As shown in Figures 15 and 17, one end 15A of each thin-walled portion 15 located toward the center is located closer to the fifth connection point p5 than the sixth connection point p6, and the other end 15B located toward the flange portion 14 is located closer to the eighth connection point p8 than the seventh connection point p7 (inflection point), for example, one end 15A is located between the fifth connection point p5 and the sixth connection point p6, and the other end 15B is located between the seventh connection point p7 and the eighth connection point p8.

In this way, the thin-walled portion 15 is formed in the thickened portion 18, and is configured to include at least the area from the seventh connection point p7, which is the inflection point, to the position that constitutes the maximum thickness (the sixth connection point p6).

The thick-walled portion 16 arranged between the thin-walled portions 15 also has one end 16A arranged toward the center, which is closer to the fifth connection point p5 than the sixth connection point p6, and the other end 16B arranged toward the flange portion 14, which is closer to the eighth connection point p8 than the seventh connection point p7 (inflection point). For example, one end 16A is arranged between the fifth connection point p5 and the sixth connection point p6, and the other end 16B is arranged between the seventh connection point p7 and the eighth connection point p8. In other words, the thick-walled portion 16 is also formed in the thickened portion 18, and is configured to include at least the area from the seventh connection point p7, which is the inflection point, to the position that constitutes the maximum thickness (the sixth connection point p6).

As a result, the thickness of the thick portion 16 from the front surface SF1 to the back surface SF2 increases from the end portion 16B to the sixth connection point p6, and also increases from the end portion 16A to the sixth connection point p6. In other words, the thickness of the thick portion 16 is the thickest at the sixth connection point p6.

The surface SF1, on which these thin-walled portions 15 and thick-walled portions 16 are alternately arranged in the circumferential direction of the can lid shell 10A, is formed in an uneven shape as shown in FIG. 16.

The shapes of the thin and

thick portions

15 and 16 are not limited to the illustrated examples, and may be formed in an elliptical shape in plan view as shown in FIG. 18. As shown in FIG. 19, the extending direction of the thin and

thick portions

15 and 16 in plan view may intersect with the radially outward direction Do at a predetermined angle θ15. Furthermore, as shown in FIG. 20, they may extend in an arc shape in plan view. An example of the extending direction of the thin and

thick portions

15 and 16 and the radially outward direction Do is shown by a two-dot chain line in each figure.

(Remodeling process)
The can lid shell 10A of the second embodiment can be manufactured by additionally performing a reforming process on the can lid shell 10 of the first embodiment.

The reforming device 40 for carrying out the reforming process includes a reforming die 41, a reforming punch 42, and a conveying section 43 that conveys the can lid shell 10 between the reforming die 41 and the reforming punch 42, as shown in FIG. 21. The reforming die 41 and the reforming punch 42 are provided in a press machine (not shown).

In the reforming process, as shown in the left half of Figure 21, the can lid shell 10 is transported to a position above the reforming die 41 with the flange portion (flange portion 14, etc.) hung over the edge of hole 43B of belt 43A of conveying section 43 and supported by belt 43A. After the can lid shell 10 has been transported, as shown in the right half of Figure 21, the reforming punch 42 is lowered and the thickened portion 18 of the can lid shell 10A is sandwiched between the reforming punch 42 and the reforming die 41 to process the thickened portion 18.

As shown in FIG. 22, a plurality of protruding projections 42B are formed on the contact surface 42A of the reform punch 42 that contacts the thickened portion 18 of the can lid shell 10A. The projections 42B are pressed into the thickened portion 18 from the surface SF1 to form the thin-walled portion 15. The area between the thin-walled portions 15 is formed as the thick-walled portion 16.

When the multiple protrusions 42B of the reform punch 42 are pressed into the third convex groove cross-sectional portion 123C (thickened portion 18), the back surface of the thickened portion 18 is supported by the reform die 41, and the spring 44 supporting the reform die 41 from below absorbs part of the load from the reform punch 42.

(Action)
In the thickened portion 18, each thick portion 16 is formed to extend from the fifth connection point p5 side to the eighth connection point p8 side, including at least the portion from the sixth connection point p6 to the seventh connection point p7, to prevent the thickened portion 18 from being deformed, such as being bent toward the internal space SP1. In this way, the mechanical strength of the thickened portion 18 (inflection portion 17) is further increased, and the pressure resistance of the can lid shell 10A is improved.

Note that the protrusions for forming the thin-walled portion 15 and the thick-walled portion 16 into the thickened portion 18 are not limited to being provided on the reform punch 42. A recess forming the thin-walled portion 15 may be formed on the back surface SF2 facing the external space SP2 using multiple protrusions provided on the contact surface of the reform die 41 that contacts the thickened portion 18 of the can lid shell 10A. In this case as well, a similar effect of improving mechanical strength can be obtained.

(First modified molding device 2A)
A molding apparatus 2A of a first modified example shown in Fig. 23 is different from the molding apparatus 2 of the first embodiment in that a lower die core ring 500 is different from the die core ring 230 of the first embodiment. At the tip of the die core ring 500 of the first modified example, an inner part facing the tip of the inner sleeve 350 is configured to be movable relative to an outer part facing the upper piston 360. The same components as those of the molding apparatus 2 of the first embodiment are denoted by the same reference numerals, and their description will be omitted.

As shown in FIG. 24, the lower die core ring 500 includes a cylindrical first fixed portion (fixed portion) 510 and a second fixed portion (fixed portion) 520, a spring (biasing member) 530 held by the second fixed portion 520, and a cylindrical movable portion 540 provided inside the second fixed portion 520 and supported at its lower end by the spring 530 so as to be movable along the central axis C.

The first fixing part 510 comprises a base end 511 fixed to the lower retainer 210, and a spring support part 512 extending from the base end 511 and having a radial thickness thinner than the radial thickness of the base end 511. The base end 511 of the first fixing part 510 protrudes in the radially outward direction Do beyond the outer circumferential surface of the spring support part 512, and has a mounting surface 511A along the radially outward direction Do. The spring support part 512 has a recess 512A on the tip side that accommodates a part of the spring 530. This recess 512A opens in the opposite direction (first direction D1) from the base end side.

As shown in Figures 24 and 25, the second fixed part 520 includes a base end 521 that is placed on the support surface 511A of the base end 511 of the first fixed part 510 and fixed to the first fixed part 510, and an upper piston opposing part 522 that is formed so that its radial thickness is thinner than the radial thickness of the base end 521, extends from the base end 521, and has a tip end 522A that faces the upper piston 360.

The upper piston opposing portion 522 is formed in a cylindrical shape, with the movable portion 540 rubbing against its inner circumferential surface and the lower piston 260 rubbing against its outer circumferential surface. The tip portion 522A of the upper piston opposing portion 522 has a portion having the same shape as the first convex surface portion 232B of the die core ring 230 in the molding device 2 of the first embodiment.

(Spring 530)
The spring 530 is provided coaxially with the first fixed portion 510, and expands and contracts along the axis (central axis C).

When the movable part 540 is placed on the spring 530, the lower part fits into the recess 512A of the spring support part 512, and the remaining tip part is positioned outside the recess 512A.

(Movable part 540)
The movable part 540 is formed in a ring shape and includes a base end 541 supported by the tip portion of the spring 530, and an inner sleeve facing part 542 that is thinner in the radial direction than the base end 541, extends in a cylindrical shape from the base end 541, and faces the inner sleeve 350.

The tip 542A of the inner sleeve facing portion 542 has a portion with the same shape as the second convex surface portion 232E (corresponding to the lower mold curved surface portion of the present invention) of the die core ring 230 in the molding device 2 of the first embodiment.

The movable part 540 moves along the central axis C with its outer circumferential surface abutting against the inner circumferential surface of the upper piston facing part 522 of the second fixed part 520, and further with the inner circumferential surface of the inner sleeve facing part 542 abutting against the outer circumferential surface of the panel punch 250.

As shown in FIG. 25, the movable part 540 is pushed by the spring 530, and the movable side step 543 formed on the outside abuts against the fixed side step 523 formed on the inner circumferential surface of the upper piston opposing part 522 of the second fixed part 520, and is held in a position close to the tip 522A of the upper piston opposing part 522.

The outside of the movable part 540 has a first outer peripheral surface 540A located at a low position adjacent to the lower end, and a second outer peripheral surface 540B located at a higher position. The radius of the first outer peripheral surface 540A is larger than that of the second outer peripheral surface 540B. The first outer peripheral surface 540A and the second outer peripheral surface 542A are connected via the movable side step surface 540C to form the movable side step part 543.

The fixed side step portion 523 of the upper piston facing portion 522 of the second fixed portion 520 is configured by connecting a first inner peripheral surface 522B that abuts against a first outer peripheral surface 540A of the movable portion 540 and a second inner peripheral surface 522C that abuts against a second outer peripheral surface 540B of the movable portion 540 via a fixed side step surface 522D.

When the movable part 540 is pushed by the spring 530, the movable side step 543 abuts against the fixed side step 523, and the movable part 540 is positioned at the highest position within its range of movement, as shown in FIG. 26, the second convex surface 232E of the tip 542A of the inner sleeve opposing part 542 is shifted in the radially inward direction Di from the first convex surface 232B of the tip 522A of the upper piston opposing part 522, and is also shifted in the second direction D2.

In addition, when the movable part 540 is positioned at the highest position, the tip 542A of the inner sleeve facing part 542 is positioned near the tip 352A of the inner sleeve 350, and the mold clearance CL2 is set to mold the inflection part 17.

Compared to the mold clearance CL1 of the molding device 2 of the first embodiment, the mold clearance CL2 of the molding device 2A of this first modified example is set to mold the third convex groove cross-sectional portion 123C of the inflection portion 17, and is configured in a small range from the first upper mold connection point p31 to the second upper mold connection point p32 of the inner sleeve 350. In this range, the distance along the imaginary straight line extending from the center C223 of the arc of the second convex surface portion 232E of the movable part 540 becomes wider from the second upper mold connection point p32 to the first upper mold connection point p31.

The arc formed by the second convex surface portion 232E of the tip portion 542A of the movable portion 540 has its upper end set at position P220 above the center C223 (on a vertical line), and is formed from the third lower die connection point P23 through the second lower die connection point P22 to the upper end position P220.

In addition, the tip 542A of the movable part 540, which extends from the position P220 of the upper end of the arc formed by the second convex surface part 232E in the radially outward direction Do, is arranged as a surface that does not contact the intermediate molded body. The tip 522A of the upper piston opposing part 522 extends in the second direction D2 from the lower end P24 on the central axis C side of the first convex surface part 232B, and has a non-contact inner circumferential surface 522E that does not contact the intermediate molded body.

(Method of manufacturing the can lid shell 10)
As in the above embodiment, the manufacturing method for the can lid shell 10 includes a blanking process in which a circular blank 410 is punched out from an aluminum alloy base plate, a deep drawing process in which the circular blank 410 is deep drawn to form a shallow-bottomed first formed body 420, and a reverse process in which the bottom of the first formed body 420 is moved upward (in the first direction D1) to form a countersink portion.

The deep drawing process and reverse process are explained below.

(Deep drawing process)
27A , in the deep drawing process, the tip 352A of the inner sleeve 350 is first lowered to a position close to the tip 542A of the movable part 540 of the die core ring 500, and a part of the circular blank 410 is pressed into the inside of the upper piston facing part 522 of the die core ring 500. Thereafter, the panel punch 250 and the die center 340 sandwich the circular blank 410 and move in the second direction D2, and deep drawing is performed.

As the deep drawing process progresses, the spacer 370 attached to the inner sleeve 350 comes into contact with the upper piston 360, preventing the inner sleeve 350 from descending independently of the upper piston 360.

When the central portion of the circular blank 410 sandwiched between the panel punch 250 and the die center 340 becomes lower than the lower end of the upper piston 360, a part of the intermediate formed body 410A that protrudes from between the panel punch 250 and the die center 340 pushes the movable part 540, causing the movable part 540 to retreat (descend) toward the spring 530.

After the intermediate molded body 410A hits the movable part 540, the distance between the tip 542A of the movable part 540 and the tip 352A of the inner sleeve 350 gradually increases until the upper die 300 reaches the bottom dead center by the press machine.

Figure 27B shows the state after deep drawing is completed, the upper die 300 is at bottom dead center, and the first molded body 420 has been molded. At this time, the distance (see Figure 25) between the movable side step surface 540C of the movable part 540 and the fixed side step surface 522D of the second fixed part 520 is at its maximum, for example 0.25 mm.

(Reverse process)
In the reverse process, the bottom portion 421 of the first compact 420 sandwiched between the panel punch 250 and the die center 340 is moved in the direction (first direction D1) opposite to the deep drawing direction (second direction D2) by the panel punch 250 and the panel punch piston 240 of the lower die 200. As the bottom portion 421 moves, a part of the first compact 420 protruding from between the panel punch 250 and the die center 340 is folded back to form a curved portion 424 having a U-shaped cross section that is convex downward (see FIGS. 12 and 13).

As the panel punch 250 rises, the internal depth dimension h along the central axis C of the curved portion 424 gradually increases. In addition, the load with which the first molded body 420 presses the movable portion 540 decreases, causing the movable portion 540 to move toward the tip 352A of the inner sleeve 350, gradually narrowing the distance between the tip 542A of the movable portion 540 and the tip 352A of the inner sleeve 350.

Figure 27C shows the state in the middle of the reverse process where the movable side step surface 540C abuts against the fixed side step surface 522D, bringing the tip 542A of the movable part 540 and the tip 352A of the inner sleeve 350 closest to each other. In this state, as shown in the enlarged view of Figure 28, a mold clearance CL2 for molding the inflection portion 17 is formed between the tip 542A of the movable part 540 and the tip 352A of the inner sleeve 350.

When the die clearance CL2 is formed, a minute gap CL0 is disposed between the sleeve concave portion 352C (corresponding to the upper die curved surface portion of the present invention) of the tip portion 352A of the inner sleeve 350 and the first inflection portion 423 of the first molded body 420. In addition, the spacer 370 attached to the inner sleeve 350 is in contact with the upper piston 360 (see FIG. 23).

When the reverse process continues with the die clearance CL2 formed, the curved portion 424 is pushed up by the receiving surface 252A of the panel punch 250, and a part of the first formed body 420 being processed is pushed into the die clearance CL2. A part of the first formed body 420 is deformed, and the minute gap (space) CL0 is filled. As a result, the first inflection portion 423 is thickened and formed into the second inflection portion 425, and the reverse process ends (Figure 27D).

In the deep drawing process of the manufacturing method of the first variation, the movable part 540 is pressed down by the intermediate formed body 410A, and the gap between the inner sleeve facing part 542 of the movable part 540 and the inner sleeve 350 increases, reducing deformation of the intermediate formed body 410A due to contact with the inner sleeve facing part 542 and suppressing the reduction in plate thickness during deep drawing.

In a can product using a can lid equipped with a can lid shell 10 molded in this manner, even if the internal pressure of the can product rises and causes internal pressure to bulge part of the countersink part 12 of the can lid outward, the inflection part 17 around the countersink part 12 is formed with an increased thickness, so buckling, in which part of the countersink part 12 deforms in an outward bulging shape, can be suppressed.

(Second modified molding device 2B)
29, in comparison with the molding apparatus 2A of the first modification, the molding apparatus 2B of the second modification includes a die core ring 1500, a spring (biasing member) 1530, and a lower piston 1260 instead of the die core ring 500, the spring 530, and the lower piston 260, and is configured to push up the movable part 1540, which has been pushed by the intermediate formed body 410A and retreated toward the first fixed part 510 during the deep drawing process, toward the inner sleeve 350 against the pressure exerted by the intermediate formed body 410A. The same components as those of the

molding apparatuses

2 and 2A described above are designated by the same reference numerals, and their description will be omitted.

As shown in FIG. 30, the die core ring 1500 includes the first fixed part 510, a block 550, a second fixed part 1520 that supports the block, a spring 1530 that has a smaller spring constant than the spring 530, and a movable part 1540.

The second fixed part 1520 has a base end 521 and an upper piston facing part 1522. This upper piston facing part 1522 differs from the upper piston facing part 522 of the second fixed part 520 in that it has a through hole 525 through which the block 550 passes.

The through-hole 525 is formed through the upper piston facing portion 1522 so as to communicate from the inside to the outside at a position lower than the fixed side step surface 522D (see FIG. 25). A plurality of through-holes 525 are formed around the central axis C of the second fixed portion 1520, for example at equal angular intervals.

(Block 550)
As shown in Figure 31, the block 550 is positioned in the through hole 525 of the upper piston opposing portion 1522 of the second fixed portion 1520, and has an outer end portion 551 protruding toward the lower piston 1260, and an inner end portion 552 protruding toward the movable portion 1540.

The outer end 551 has an outer vertical surface 551A and an outer inclined surface 551B extending from the upper edge of the outer vertical surface 551A. The outer inclined surface 551B has a radius (distance) from the central axis C that decreases as it moves from the upper edge of the outer vertical surface 551A in the first direction D1, and the inclination θ51 with respect to the central axis C is set constant.

The inner end 552 has an inner vertical surface 552A and an inner inclined surface 552B extending from the upper edge of the inner vertical surface 552A. The inner inclined surface 552B has a radius (distance) from the central axis C that increases as it moves from the upper edge of the inner vertical surface 552A in the first direction D1, and the inclination θ52 with respect to the central axis C is set constant. Comparing the angles θ51, θ52 of the outer end 551 and the inner end 552 with the horizontal plane, the angle θ51 that the outer end 551 makes with the horizontal plane is set larger than the angle θ52 that the inner end 552 makes with the horizontal plane.

(Lower piston 1260)
The lower piston 1260 includes a piston body 261 and an extension 1262. The extension 1262 is different from the extension 262 of the lower piston 260 described above in the shape of its inner circumferential surface.

As shown in FIG. 32, the extension portion 1262 has a first inner circumferential surface 262C formed on the piston body 261 side, a second inner circumferential surface 262D provided on the tip portion 262A side and formed with a smaller diameter than the first inner circumferential surface 262C, and an inner inclined surface 262E disposed between the first inner circumferential surface 262C and the second inner circumferential surface 262D.

The radius (distance) of the inner inclined surface 262E from the central axis C decreases as one moves from the upper edge of the first inner circumferential surface 262C to the lower edge of the second inner circumferential surface 262D, and the inclination with respect to the central axis C is set to be constant. The inclination angle θ62 of the inner inclined surface 262E with respect to the central axis C is set to be equal to the angle θ51 of the outer inclined surface 551B of the block 550. Furthermore, when the lower piston 1260 descends, the outer inclined surface 551B of the block 550 is positioned on the movement trajectory of the inner inclined surface 262E.

The lower piston 1260 configured in this manner descends a predetermined distance along the central axis C, causing the inner inclined surface 262E to come into contact with the outer inclined surface 551B of the block 550, and as it descends further, it pushes the outer inclined surface 551B of the block 550, moving the block 550 in the radial inward direction Di.

(Movable part 1540)
As shown in Figure 33, the outer peripheral surface of the movable part 1540 is formed by a first outer peripheral surface 1540A rising from the periphery of the lower surface, the second outer peripheral surface 540B formed at a position shifted in the first direction D1 from the first outer peripheral surface 1540A, a third outer peripheral surface 540D arranged between the first outer peripheral surface 1540A and the second outer peripheral surface 540B, a movable side step surface 540C arranged between the second outer peripheral surface 540B and the third outer peripheral surface 540D and together constituting the movable side step part 543, and an outer inclined surface 540E arranged between the first outer peripheral surface 1540A and the third outer peripheral surface 540D.

The radius of the first outer peripheral surface 1540A is set to be smaller than the radius of the second outer peripheral surface 540B, and the radius of the third outer peripheral surface 540D is set to be larger than the radius of the second outer peripheral surface 540B.

The outer inclined surface 540E has a radius (distance) from the central axis C that increases from the upper edge of the first outer peripheral surface 1540A to the lower edge of the third outer peripheral surface 540D, and is set at a constant inclination with respect to the central axis C. The inclination angle θ540 of the third outer peripheral surface 540D with respect to the horizontal plane is set to be equal to the angle θ52 of the inner inclined surface 552B of the block 550.

The dimension h31 along the central axis C from the movable side step surface 540C of the movable part 1540 to the upper edge of the outer inclined surface 540E is set to be larger than the dimension h32 (Figure 30) along the axis from the fixed side step surface 522D of the upper piston opposing part 1522 to the edge of the through hole 525.

As shown in FIG. 30, when the movable part 1540 is not retracted toward the spring 1530 and the block 550 is not retracted into the through hole 525 (the movable side step surface 540C is in contact with the fixed side step surface 522D and the outer inclined surface 551B protrudes toward the lower piston 1260 without contacting the inner inclined surface 262E of the lower piston 1260), the outer inclined surface 540E of the movable part 1540 and the inner inclined surface 552B of the block 550 are separated, and the inner inclined surface 552B of the block 550 is positioned below the outer inclined surface 540E with the lower part of the surface protruding from the through hole 525 into the interior of the upper piston opposing part 1522.

Note that above the lower portion (inner circumference side) of the inner inclined surface 552B of the block 550, the higher portion (outer circumference side) of the outer inclined surface 540E of the movable part 1540 is located.

In the deep drawing process, the movable part 1540 is pushed by the intermediate molded body 410A and retreats towards the spring 1530, but the outer inclined surface 540E of the movable part 1540 comes into contact with the inner inclined surface 552B of the block 550, preventing the movable part 1540 from retreating. Furthermore, while the movable part 1540 is in contact with the block 550, the block 550 can push the outer inclined surface 540E of the movable part 1540 in the radially inward direction Di with the inner inclined surface 552B, thereby moving the movable part 1540 towards the inner sleeve 350.

(Method of manufacturing the can lid shell 10)
As in the above embodiment, the manufacturing method for the can lid shell 10 includes a blanking process for punching out a circular blank 410A from an aluminum alloy raw plate, a deep drawing process for deep drawing the circular blank 410 to form a shallow-bottomed, tray-shaped first formed body 420, and a reverse process for moving a flat portion at the bottom of the first formed body 420 toward the mouth side located above it to form a recessed countersink portion around the flat portion.

The deep drawing process and reverse process are explained below.

(Deep drawing process)
34A, in the deep drawing process, first, the tip 352A of the inner sleeve 350 is lowered to a position close to the tip 542A of the movable part 1540, and a part of the circular blank 410 is pressed into the inside of the upper piston facing part 1522 of the die core ring 1500. Thereafter, the panel punch 250 and the die center 340 sandwich the circular blank 410 and move in the axial direction to perform deep drawing.

When the center portion of the circular blank 410 sandwiched between the panel punch 250 and the die center 340 becomes lower than the lower end of the upper piston 360, a part of the intermediate formed body 410A that protrudes from between the panel punch 250 and the die center 340 pushes against the movable part 1540, causing the movable part 1540 to retreat (descend) toward the spring 1530.

After the intermediate molded body 410A hits the movable part 1540, the distance between the tip 542A of the movable part 1540 and the tip 352A of the inner sleeve 350 gradually increases until the movable part 1540 hits the block 550.

Furthermore, as the panel punch 250 and the die center 340 move, the blank draw die 320 also enters the inside of the lower die 200, and the lower piston 1260 is also pushed down by the blank draw die 320. When the lower piston 1260 moves down a predetermined distance, the inner inclined surface 262E comes into contact with the outer inclined surface 551B of the block 550.

As shown in FIG. 34B, the timing at which the inner inclined surface 262E of the lower piston 1260 hits the outer inclined surface 551B of the block 550 and the timing at which the outer inclined surface 540E of the movable part 1540 hits the inner inclined surface 552B of the block 550 are designed to be simultaneous. With the movable part 1540 hitting the block 550 in this manner, the distance along the central axis C between the movable side step surface 540C and the fixed side step surface 522D is, for example, 0.5 mm.

In molding device 2B, after the lower piston 1260 and the movable part 1540 hit the block 550, the lower piston 1260 further descends, causing the block 550 to retreat into the through hole 525 and causing the inner end 552 to protrude further into the interior of the upper piston opposing part 1522. As a result, the block 550 pushes the movable part 1540, causing the movable part 1540 to move in a direction approaching the inner sleeve 350.

In this way, the movement of the movable part 1540 toward the inner sleeve 350 begins midway through the deep drawing, and the distance between the tip 542A of the movable part 1540 and the tip 352A of the inner sleeve 350 gradually narrows until the panel punch 250 and the die center 340 complete the deep drawing process.

As shown in FIG. 34C, when the upper die 300 reaches the bottom dead center, the tip 542A of the movable part 1540 is positioned closest to the tip 352A of the inner sleeve 350. In this close position, a die clearance CL2 is formed for molding the deformation part 17. The movable side step surface 540C of the movable part 1540 abuts on the fixed side step surface 522D of the upper piston opposing part 1522. The spacer 370 comes into contact with the upper piston 360, and a die clearance CL2 is formed between the tip 542A of the inner sleeve opposing part 542 (between the inner sleeve 350 and the movable part 1540).

(Reverse process)
In the reverse process, the bottom portion 421 of the first compact 420 sandwiched between the panel punch 250 and the die center 340 is moved in the direction opposite to the deep drawing direction by the panel punch 250 and the panel punch piston 240 of the lower die 200. As the bottom portion 421 of the first compact 420 moves, a part of the first compact 420 protruding from between the panel punch 250 and the die center 340 is folded back to form a curved portion 424 having a U-shaped cross section that is convex downward, as shown in Fig. 34D.

When the curved portion 424 is positioned above the receiving surface 252A of the punch step portion 252, as shown in FIG. 28, a minute gap CL0 is disposed between the sleeve concave portion 352C of the tip portion 352A of the inner sleeve 350 and the first inflection portion 423 of the first molded body 420.

When the lower piston 1260 rises together with the panel punch 250 and its inner inclined surface 262E separates from the outer inclined surface 551B of the block 550, as shown in FIG. 34D, the block 550 is released from the force from the lower piston 1260 that pushes it backward in the radially inward direction Di and returns to its original position. Note that the die core ring 1500 is provided with a block spring (not shown), and this block spring allows the block 550 to return from the retracted position to the extended position.

As the reverse process progresses further, the curved portion 424 is pushed up by the receiving surface 252A of the panel punch 250, forcing a part of the first formed body 420 being processed into the die clearance CL2. Part of the first formed body 420 deforms and fills the tiny gap (space) CL0. This causes the first inflection portion 423 to thicken and become the second inflection portion, completing the reverse process (Figure 34E).

In the deep drawing process of the manufacturing method of the second modified example, the force of the spring 1530 that holds the movable part 1540 in the position where it is closest to the inner sleeve 350 and forms the mold clearance CL2 is weaker than the force of the spring 530 of the molding device 2A of the first modified example, so that during deep drawing, the intermediate molded body 410A easily retreats as it is pushed back by the deforming intermediate molded body 410A. This makes it possible to further suppress the reduction in plate pressure caused by contact of the intermediate molded body 410A with the movable part 1540 (the inner sleeve facing part 542) during the deep drawing process.

Furthermore, as the deep drawing process progresses, the block 550 is retracted and the movable part 1540 is moved toward the inner sleeve 350 as the lower piston 1260 descends, so that a portion of the intermediate molded body 410A, which has had its thickness reduced, is sandwiched between the movable part 1540 (the inner sleeve facing part 542) and the inner sleeve 350 to form the first inflection part 423.

In this way, by suppressing the reduction in sheet pressure that accompanies deep drawing before the reverse process, it is possible to prevent deformation or distortion of the curved portion 424 that is formed by folding back at the start of the reverse process.

The present invention can be practiced without being limited to the above explanation and illustrated examples. The manufacturing method of the first embodiment has been explained based on a molding device (Figure 4), but the gist of the present invention is that the mold clearance CL1 is formed between the upper and lower molds facing the first curved surface portion and the second curved surface portion. As long as this mold clearance can be formed, it is not limited to the molding device shown in Figure 4, and other molding devices may be used. The ratio of the dimensions along the central axis C of the countersink portion, chuck wall portion, and flange portion, the ratio of the dimensions along the direction perpendicular to the central axis C of the panel portion, countersink portion, chuck wall portion, and flange portion, the angle of expansion around the center of each arc, etc. may also be changed.

In addition, with regard to the cross-sectional structure of the can lid shell, the above explanation and drawings show cases in which the surfaces constituting the front surface SF1 and back surface SF2 of the third convex groove cross-sectional portion 123C (corresponding to the first curved surface portion of the present invention), the first concave surrounding cross-sectional portion 131 (corresponding to the second curved surface portion of the present invention), and the second convex groove cross-sectional portion 123B (corresponding to the third curved surface portion of the present invention) are each formed as an arc (a perfect circle arc). However, in the third convex groove cross-sectional portion 123C (corresponding to the first curved surface portion of the present invention), the first concave surrounding cross-sectional portion 131 (corresponding to the second curved surface portion of the present invention), and the second convex groove cross-sectional portion 123B (corresponding to the third curved surface portion of the present invention), the surfaces constituting the front surface SF1 and back surface SF2 may be formed as surfaces whose cross sections are not perfect circular arcs but are curved like a bow.

In this way, the inflection portion 17 and the thickened portion 18 can be formed by the third convex groove cross-section portion 123C (corresponding to the first curved surface portion of the present invention), the first concave surrounding cross-section portion 131 (corresponding to the second curved surface portion of the present invention) and the second convex groove cross-section portion 123B (corresponding to the third curved surface portion of the present invention). In this way, the inflection portion 17 and the thickened portion 18 are formed by a curved surface consisting of an arc (a perfect circular arc) or a curved surface that is curved like an arch, thereby improving the pressure resistance of the can lid shell.

A can shell for a 200-diameter beverage can was manufactured from an aluminum plate (thickness 0.208 mm) made of aluminum alloy (5182) coated on both sides with modified epoxy paint (total thickness of both sides 0.012 mm), and pressure resistance was confirmed.

The can lid shell has a panel section, a countersink section, a chuck wall section, and a flange section, and the inflection point is located between the chuck wall section, which is a concave arc section facing the internal space, and the countersink section, which is a convex arc section facing the internal space, with the inflection point between them. The example shows an inflection point that is thickened, while the comparative example shows one that is not thickened.

The can lid shell of the example was manufactured using the molding device of the first embodiment. In this molding device, the mold clearance CL1 is set to 0.220 mm at the third upper mold connection point P33 of the tip portion 352A of the inner sleeve 350, 0.234 mm at the second upper mold connection point P32, and 0.250 mm at the first upper mold connection point P31, as shown in FIG. 6, and the distance between the inner sleeve 350 and the die core ring 230 increases from the third upper mold connection point P33 to the first upper mold connection point P31.

The panel punch 250 of the lower die 200 of the molding device has a stepped punch step 252 around the punch flat portion 251 with which the blank plate comes into contact, and during the reverse process to form the countersink portion, the receiving surface 252A of the punch step 252 pushes up the curved portion 424 formed during the reverse process, deforming a part of the first molded body being processed and pushing it into the die clearance CL1, thereby forming the thickened inflection portion 425.

The comparative example can lid shell was manufactured using a conventional molding device.

Fifty samples of each of the inventive examples and comparative examples were manufactured, their respective compressive strengths [psi] were measured, and the average value (average compressive strength) was calculated. In addition, the thicknesses of the inflection points of the samples, between the arc at the chuck wall that is concave toward the internal space and the arc at the countersink that is convex toward the internal space, were measured, and the percentage increase in thickness compared to the thickness of the circular blank before processing (sheet thickness after processing / sheet thickness of circular blank before processing x 100) [%] was calculated. Note that 1 [psi] = 6894.76 [Pa].

Table 1 shows the compressive strength, thickness, and thickness ratio.

In the can lid shell of the invention example, the inflection part is formed to be about 9% thicker than the base plate, and the average pressure resistance is also high at 106.7 [psi].

In the comparative example, no increase in thickness at the bent portion was observed compared to the thickness of the base plate. The average pressure strength of 98.2 [psi] was equivalent to the strength of a conventional can lid.

We can provide a can lid shell that prevents buckling, a manufacturing method for this can lid shell, and a molding device.

2,

2A Molding device

10, 10A Can lid shell 11 Panel portion 12 Countersink portion 123B Second convex groove cross-sectional portion (third curved surface portion)
123C Third convex groove cross section (first curved surface part)
13 Chuck wall portion 131 First concave surrounding cross section portion (second curved surface portion)
132 Second concave surrounding cross section 133 Sloped surrounding cross section 134 Convex surrounding cross section 14 Flange portion 15 Thin portion (concave portion)
16: thick portion (convex portion) 17: inflection portion 18: thickened portion 40: reforming device 200: lower mold 210: lower retainer 220: cut edge portion 230: die core ring 232A: tip portion 232D: concave portion (first lower mold curved surface portion)
232E Second convex surface part (second lower mold curved surface part) (lower mold curved surface part)
240 Panel punch piston 250 Panel punch 260 Lower piston 300 Upper die 310 Upper retainer 320 Blank draw die 330 Die center piston 340 Die center 350 Inner sleeve 351 Piston body portion 352A Tip portion 352B First sleeve convex portion 352C Sleeve concave portion (third upper die curved portion) (upper die curved portion)
352D Second sleeve convex surface portion (second upper mold curved surface portion)
352E Third sleeve convex surface portion (first upper mold curved surface portion)
352F Sleeve inclined surface portion 360 Upper piston 362A Tip portion 370 Spacer 400 Raw plate 410 Circular blank 410A Intermediate formed body 420 First formed body 421 Bottom portion (flat portion)
422 Clamping part (flange part)
423 First inflection portion 425 Second inflection portion 500 Die core ring 510 First fixing portion (fixing portion)
520 Second fixed part (fixed part)
522, 1522 Upper piston opposing portion 522A Tip portion 523 Fixed side step portion 530 Spring (biasing member)
540 Movable portion 542 Inner sleeve opposing portion 542A Tip portion 550 Block 551B Outer inclined surface 552B Inner inclined surface 2B Molding device 1260 Lower piston 262E Inner inclined surface 1500 Die core ring 1520 Second fixed portion (fixed portion)
525 through hole 1530 spring (biasing member)
1540 Movable part 540E Outer inclined surface C Central axis CL1, CL2 Mold clearance SF1 Surface SF2 Back surface SP1 Internal space

Claims

A can lid shell,
A panel portion having a circular periphery;
a recessed countersink portion formed along the periphery of the panel portion;
a chuck wall portion rising from an edge of the countersink portion; and a flange portion extending from an upper end of the chuck wall portion,
an internal space defined inside the panel portion, the countersink portion, and the chuck wall portion;
The countersink portion includes a first curved surface portion that is convex toward the internal space,
The chuck wall portion includes a second curved surface portion that is connected to the first curved surface portion and is concave from the internal space,
A can lid shell, wherein a thickness of the second curved surface portion and a thickness of the first curved surface portion increase from an edge on the flange portion side to an edge on the panel portion side.
The can lid shell according to claim 1, characterized in that the countersink portion includes a third curved portion that is connected to the first curved portion by disposing the first curved portion between the second curved portion and the third curved portion, and that is formed so that its thickness increases from the edge on the panel portion side to the edge connected to the first curved portion.
a can lid shell having a plurality of thin-walled portions formed by recessing from the front or back surface of the can lid shell to the second curved surface portion to the third curved surface portion, the thin-walled portions being spaced apart in a circumferential direction of the can lid shell; and a thick-walled portion that is thicker than the thin-walled portions and is provided between the thin-walled portions of the can lid shell,
The can lid shell according to claim 2, characterized in that the multiple thin-walled portions and the multiple thick-walled portions have a dimension along a radius of the can lid shell that is longer than a dimension along a direction perpendicular to the radial direction when viewed in a plan view or a bottom view of the can lid shell.
A forming apparatus including a lower die and an upper die, the apparatus sandwiching a circular blank between the lower die and the upper die to form a can lid shell,
The lower mold includes a die core ring and a panel punch disposed inside the die core ring,
the upper die includes a cylindrical upper piston, a cylindrical inner sleeve disposed inside the upper piston, and a die center disposed inside the inner sleeve;
An outer portion of the tip of the die core ring and a tip of the upper piston are disposed opposite to each other,
An inner portion of the tip end of the die core ring and a tip end of the inner sleeve are disposed opposite to each other,
The die punch and the die center are disposed opposite to each other,
an inner portion of the tip of the die core ring includes a first lower curved surface portion that is concave toward the inner sleeve, and a second lower curved surface portion that is connected to the first lower curved surface portion and is further shifted toward the central axis and is convex toward the inner sleeve,
the tip portion of the inner sleeve comprises: a first upper mold curved surface portion that is convex toward the first lower mold curved surface portion; a second upper mold curved surface portion that is connected to the first upper mold curved surface portion and is disposed further shifted toward the central axis and is a circular arc having a radius of curvature different from that of the first upper mold curved surface portion that is convex toward the first lower mold curved surface portion; and a third upper mold curved surface portion that is connected to the second upper mold curved surface portion and is disposed further shifted toward the central axis and is concave toward the second lower mold curved surface portion,
A molding apparatus characterized in that a mold clearance formed between the first lower mold curved portion and the second lower mold curved portion of the die core ring and the second upper mold curved portion and the third upper mold curved portion of the inner sleeve is a distance greater than or equal to the plate thickness of the circular blank, and further widens toward the central axis.
A forming apparatus including a lower die and an upper die, the apparatus sandwiching a circular blank between the lower die and the upper die to form a can lid shell,
The lower mold includes a die core ring and a panel punch disposed inside the die core ring,
the upper die includes a cylindrical upper piston, a cylindrical inner sleeve disposed inside the upper piston, and a die center disposed inside the inner sleeve;
the die core ring comprises a cylindrical fixed portion fixed to the lower die, a movable portion provided inside the fixed portion, and a biasing member configured to be extendable and contractible along a central axis, supporting the movable portion from below and biasing the movable portion;
a tip end portion of the fixed portion of the die core ring and a tip end portion of the upper piston are disposed opposite to each other,
the tip end of the movable portion of the die core ring and the tip end of the inner sleeve are disposed opposite to each other,
The panel punch and the die center are disposed opposite to each other,
a tip end of the movable portion includes a lower curved surface portion that is convex toward the inner sleeve,
The tip portion of the inner sleeve includes an upper curved surface portion that is concave toward the lower curved surface portion,
a die clearance formed between the lower die curved surface portion of the movable part and the upper die curved surface portion of the inner sleeve is equal to or greater than a plate thickness of the circular blank and is wider as it approaches the central axis,
A forming apparatus, characterized in that the movable part is pushed by an intermediate forming body and retreats toward the urging member when the circular blank is deep drawn.
The lower die further includes a cylindrical lower piston that surrounds a portion of an outer circumferential surface of the die core ring,
the fixing portion includes a through hole communicating from the inside of the fixing portion to the outside of the fixing portion, and a block disposed in the through hole;
the block has an outer inclined surface that protrudes to the outside of the fixing portion and an inner inclined surface that protrudes to the inside of the fixing portion,
the lower piston has an inner inclined surface that abuts against the outer inclined surface of the block,
the movable portion has an outer inclined surface that abuts against the inner inclined surface of the block,
6. The molding apparatus according to claim 5, wherein when the lower piston is pushed downward by the upper mold, the inner inclined surface of the lower piston abuts on the outer inclined surface of the block, and the outer inclined surface of the retracted movable part abuts on the inner inclined surface of the block, and the lower piston further descends in this state, causing the movable part to move toward the inner sleeve.
A method for manufacturing a can lid shell, comprising the steps of: sandwiching a circular blank between a lower die and an upper die to form a can lid shell,
a deep drawing step of forming the circular blank into a tray-shaped first formed body;
a reverse process of moving upward a flat portion at the bottom of the first molded body sandwiched between a panel punch and a die center to form a countersink portion recessed around the flat portion,
In the deep drawing step, a part of the circular blank is deformed by a tip end of a die core ring and a tip end of an inner sleeve to form a first inflection portion having a concave surface and a convex surface between the flat portion and a flange portion of the first formed body,
a die center that is formed by pressing a portion of the first molded body protruding from between the panel punch and the die center into a gap in the die clearance that is not filled by the first inflection portion, the gap being configured as a die clearance that widens as the gap approaches a central axis, and the first inflection portion is molded into a second inflection portion having an increased thickness.
the die core ring includes a movable part that constitutes a portion of the tip of the die core ring that faces the tip of the inner sleeve, and a biasing member that is configured to be freely stretched and contracted along the central axis and supports the movable part from below to hold the movable part at a position that constitutes the die clearance,
The method for manufacturing a can lid shell according to claim 7, wherein in the deep drawing step, an intermediate forming body presses the movable part, so that the movable part retreats toward the biasing member.