Can lid shell, its manufacturing method and molding device

Abstract

A can lid shell 10 comprises a panel portion 11 having a circular periphery, 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 a flange portion 14 projecting from the upper end of the chuck wall portion 13, wherein the countersink portion 12 comprises a first curved surface portion 123C that is convex toward the internal space SP1, and the chuck wall portion 13 comprises a second curved surface portion 131 that is connected to the first curved surface portion 123C and is concave toward the internal space SP1, and further wherein the second curved surface portion 131 and the first curved surface portion 123C are formed so as to increase in thickness from an edge p8 on the flange portion 14 side to an edge p6 on the panel portion 11 side.

Description

[Technical field]

[0001] 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 Publication No. 2023-006121, filed on January 18, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] A 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, includes a panel portion 710, a countersink portion 720 provided around the panel portion 710, and an attachment portion 730 extending from the outer wall portion of the countersink portion 720, having a hook-shaped cross section, for tightening the flange of the can body. A tear line for opening and a tab for opening operation are provided on this can lid shell 700 by a conversion press, and a can lid is manufactured.

[0003] Further, a can lid shell 800 shown in FIG. 36 is known which has a reduced thickness and weight (Patent Document 1).

[0004] 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 composed of multiple curved surfaces connected together, as surrounded by the dashed line in Figure 36.

[0005] After filling the bottomed cylindrical can body with the contents and gas (CO2 or N2), the can lid shell 800 is wrapped around the flange 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, and the like that will be added to the panel portion 810 in the next conversion process are omitted.

[0006] In addition, in a canned product with a can lid shell 800 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.

[0007] In the can lid shell 800, since the panel portion 810 is formed small, 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 received by the panel portion 710 of the can lid shell 700.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] In the filling process of filling the can body with contents and gas and closing it with a can lid, and during the distribution process, if the canned product is exposed to an excessive high temperature, the internal pressure of the can rises and exceeds the limit of the pressure resistance of the can lid, as shown by the broken line in Fig. 37, a phenomenon occurs where a part of the can lid of the canned product protrudes outward, so-called buckling. If a part of the can lid protrudes outward in this way, cracks will occur in the protruding part and the tear line, and the contents and gas will leak, or problems such as inability to open the can will occur.

[0010] Therefore, an object of the present invention is to provide a can lid shell that prevents buckling, a manufacturing method of this can lid shell, and a molding device.

Means for Solving the Problems

[0011] 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 an 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 thicknesses of the first curved surface portion and the second curved surface portion increase from the edge on the flange portion side to the edge on the panel portion side.

[0012] 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, so that the mechanical strength of the inflection portion formed by the first curved surface portion and the second curved surface portion is increased, thereby improving the pressure resistance, thereby enabling the can lid to be further thin-walled and lightweight.

[0013] In the can lid shell of the present invention, the countersink portion preferably includes a third curved surface portion, the first curved surface portion being disposed between the countersink portion and the second curved surface portion, the third curved surface portion being connected to the first curved surface portion and being convex toward the internal space, and the thickness of the third curved surface portion increasing 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.

[0014] The can lid shell of the present invention preferably has a front or back surface of the can lid shell having a plurality of thin-walled portions formed 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 a thick-walled portion is formed between the thin-walled portions and is thicker than the thin-walled portions, and the plurality of thin-walled portions and the plurality of thick-walled portions are set so that the dimension along the radius of the can lid shell is longer than the dimension along a direction perpendicular to the direction of the radius when viewed from above or below the can lid shell.

[0015] In the can lid shell of the present invention, the first curved surface portion that is convex toward the internal space includes a plurality of thin and thick portions in the circumferential direction that extend from the second curved surface portion to the third curved surface portion. A portion extending from the second curved surface portion to the third curved surface portion constitutes an increased thickness portion, and the increased thickness portion is provided with the first curved surface portion that is composed of a thin and thick portion, thereby preventing deformation such as bending toward the internal space. This further increases the mechanical strength of the increased thickness portion including the inflection portion composed of the first curved surface portion and the second curved surface portion, thereby improving pressure resistance.

[0016] The present invention relates to a molding device that has 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, wherein the lower die has a die core ring and a panel punch arranged inside the die core ring, and the upper die has a cylindrical upper piston, a cylindrical inner sleeve arranged inside the upper piston, and a die center arranged inside the inner sleeve.

[0017] In this molding apparatus, an outer portion of the tip of the die core ring and a tip of the upper piston are arranged opposite to each other, an inner portion of the tip of the die core ring and a tip of the inner sleeve are arranged opposite to each other, and the panel punch and the die center are arranged opposite to 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 arranged further shifted toward the central axis and is convex toward the inner sleeve.

[0018] 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 positioned further shifted toward the central axis and is an arc whose radius of curvature is different 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 shifted toward the central axis and is concave toward the second lower mold curved surface portion.

[0019] The die clearance formed between the first lower die curved surface portion and the second lower die curved surface portion of the die core ring and the second upper die curved surface portion and the third upper die curved surface portion of the inner sleeve is a distance greater than or equal to the plate thickness of the circular blank, and widens as it approaches the central axis.

[0020] In the molding apparatus 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 processed, it is possible to increase the thickness of a portion of the circular blank by processing.

[0021] The present invention relates to a molding device that has 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, wherein the lower die has a die core ring and a panel punch arranged inside the die core ring, and the upper die has a cylindrical upper piston, a cylindrical inner sleeve arranged inside the upper piston, and a die center arranged inside the inner sleeve.

[0022] In this molding apparatus, 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, wherein 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.

[0023] The tip of the movable part has a lower mold curved surface portion that is convex toward the inner sleeve, and the tip of the inner sleeve has an upper mold curved surface portion that is concave toward the lower mold curved surface portion, and a mold clearance formed between the lower mold curved surface portion of the movable part and the upper mold 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 an intermediate forming body and retreats toward the biasing member when the circular blank is deep drawn.

[0024] Here, the intermediate formed body refers to a shape in the process of being deformed until the circular blank becomes the first formed body through the deep drawing process.

[0025] The molding apparatus of the present invention preferably further includes a cylindrical lower piston surrounding a portion of the outer peripheral surface of the die core ring, the fixed portion including a through hole leading from the inside of the fixed portion to the outside of the fixed portion and a block arranged in the through hole, the block having an outer inclined surface extending to the outside of the fixed portion and an inner inclined surface extending to the inside of the fixed portion, the lower piston having an inner inclined surface that abuts on the outer inclined surface of the block, and the movable portion having an outer inclined surface that abuts on the inner inclined surface of the block, and when the lower piston is pressed 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 portion abuts on the inner inclined surface of the block, and the lower piston further descends in this state, whereby the movable portion moves toward the inner sleeve.

[0026] In the molding apparatus of the present invention, the biasing member that supports the movable part is provided, and the movable part is moved back by the intermediate molded body, so that a reduction in the thickness of the intermediate molded body due to friction with the movable part during deep drawing can be suppressed. The biasing member can be, for example, a spring or a pneumatic piston.

[0027] The present invention is a method for manufacturing a can lid shell by sandwiching a circular blank between a lower die and an upper die, the method comprising: a deep drawing process for forming the circular blank into a tray-shaped first formed body; and a reverse process for moving a flat portion of a bottom of the first formed body sandwiched between a panel punch and a die center 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 a tip end of a die core ring and a tip end of an inner sleeve, and a first inflection portion consisting of a concave surface and a convex surface is formed between the flat portion and a flange portion of the first formed body.

[0028] In the reverse process, with the space between the tip of the die core ring and the tip of the inner sleeve configured as a mold 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 a gap in the mold clearance that is not filled by the first inflection portion, and the first inflection portion is molded into a thicker second inflection portion.

[0029] In the method for manufacturing a can lid shell of the present invention, a part of a first molded body to be processed is deformed and pressed into a die clearance, and the first molded body and its adjacent areas 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.

[0030] The die clearance can be established during deep drawing, at the start of the reversing process, or during the reversing process.

[0031] In the can lid shell manufacturing method of the present invention, preferably, the die core ring is provided with a movable part that constitutes the portion 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.

[0032] In the present invention, before the reverse step is performed, the movable part is retracted by the intermediate formed body, thereby making it possible to suppress a reduction in the thickness of the circular blank due to friction with the movable part during deep drawing. Furthermore, by forming the first formed body in a state in which the reduction in thickness is suppressed in this way, 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 step. Effect of the Invention

[0033] According to the present invention, since the inflection portion having the concave curved surface and the convex curved surface is configured to have high pressure resistance, buckling can be prevented. [Brief description of the drawings]

[0034] [Figure 1] Fig. 1A is a plan view showing a can lid shell according to a first embodiment of the present invention, Fig. 1B is a cross-sectional view of the can lid shell taken along line S1-S1 in Fig. 1A. [Diagram 2] FIG. 2 is an enlarged cut end surface view of the area surrounded by the dashed-dotted circle in FIG. 1B. [Diagram 3] 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. [Figure 4] 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. [Diagram 5] 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. [Figure 6] FIG. 6 is an enlarged view of the area surrounded by the dashed-dotted circle in FIG. [Figure 7] FIG. 7 is a diagram showing a method for manufacturing a can lid shell according to the first embodiment of the present invention. [Figure 8] 8A and 8B are views for explaining a blanking step in the manufacturing method of a can lid shell according to the first embodiment of the present invention. [Figure 9] 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. [Figure 10] 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. [Figure 11] FIG. 11 is a view showing a cross section of the first molded body. [Figure 12] FIG. 12 is a view for explaining the method for manufacturing a can lid shell according to the first embodiment of the present invention. [Figure 13] FIG. 13 is a view for explaining the method for manufacturing a can lid shell according to the first embodiment of the present invention. [Figure 14] 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. [Figure 15] FIG. 15 is an enlarged view of the area surrounded by the dashed-dotted circle in FIG. 14A. [Figure 16] FIG. 16 is a cross-sectional view of the shell taken along line S3-S3 in FIG. [Figure 17] FIG. 17 is an enlarged view of the area surrounded by the dashed line in FIG. 14B. [Figure 18] 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. [Figure 19] 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. [Figure 20] 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. [Figure 21] FIG. 21 is a diagram for explaining the reforming process according to the second embodiment of the present invention. [Figure 22] FIG. 22 is an enlarged view of the area surrounded by the dashed line in FIG. [Figure 23] FIG. 23 is a cross-sectional view of a molding device according to a first modified example of the present invention. [Figure 24] FIG. 24 is a diagram showing a cross section of the die core ring. [Diagram 25] 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. [Figure 26] FIG. 26 is an enlarged view of a part of a cross section of a molding device according to a first modified example of the present invention. [Figure 27] 27A to 27D are views for explaining a method of manufacturing a shell by a molding apparatus according to a first modified example of the present invention. [Figure 28] FIG. 28 is a view for explaining a method for manufacturing a shell by a molding apparatus according to a first modified example of the present invention. [Figure 29] FIG. 29 is a cross-sectional view of a molding device according to a second modified example of the present invention. [Diagram 30] FIG. 30 is a diagram showing a cross section of the die core ring, lower piston, movable part, block and spring. [Diagram 31] FIG. 31 is an enlarged cross-sectional view of the block. [Diagram 32] FIG. 32 is an enlarged cross-sectional view of the extension portion of the lower piston. [Diagram 33] FIG. 33 is an enlarged cross-sectional view of the movable portion. [Diagram 34] FIG. 34 is a view for explaining a method for manufacturing a shell by a molding apparatus according to a second modified example of the present invention. [Diagram 35] FIG. 35 is a cross-sectional view of a conventional can lid shell. [Diagram 36] FIG. 36 is a cross-sectional view of a lightweight can lid. [Figure 37] FIG. 37 is a diagram showing a cross section of a can lid during buckling. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] A can lid shell 10 according to a first embodiment of the present invention will be described with reference to the drawings.

[0036] 1A and 1B, the can lid shell 10 includes a panel portion 11 having a circular outline in a 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 an upper end (an end portion on the radially outward direction Do side) of the chuck wall portion 13. The internal space SP1 is a space inside the chuck wall portion 13 and above the panel portion 11, as shown in FIG. 1B.

[0037] In the following description, 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 FIG. 2).

[0038] The front and back surfaces of the can lid shell 10, including the portion defining the internal space SP1 and one surface of the flange portion 14 adjacent thereto, are designated as the front surface SF1 of the can lid shell 10, and the surface opposite to this front surface SF1 is designated as the back surface SF2.

[0039] 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 will be described below.

[0040] (Panel section 11) The panel portion 11 is formed as a flat disk having a substantially uniform thickness.

[0041] (Countersink part 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 side 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 side Do to the edge of the chuck wall portion 13 on the radially inward side Di.

[0042] The groove bottom 121 has a cross section formed as an arc of radius r12 from a center C12 disposed 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 a connection point (first connection point p1) where the groove bottom 121 and the first groove wall 122 are connected is shifted toward the radial inward direction Di from the deepest part and is also shifted toward the first direction D1 from the deepest part.

[0043] Furthermore, the connection point (second connection point p2) where the groove bottom 121 and the second groove wall 123 are connected is shifted toward the radially outward direction Do from the deepest part, and is also shifted toward the first direction D1 from the deepest part. In FIG. 2, the positions of each connection point are indicated by circles.

[0044] (First groove wall part 122) The first groove wall portion 122 comprises a first inclined groove cross-sectional portion 122A having one edge connected to the edge on the radially inward direction Di of the groove bottom portion 121 to form a first connection point p1 and further formed with a constant inclination relative to the central axis C, and a first convex groove cross-sectional portion 122B which is formed from the other edge of this first inclined groove cross-sectional portion 122A to the peripheral edge of the panel portion 11 and is an arc convex toward the internal space SP1.

[0045] The connection point (third connection point p3) where the first inclined groove cross-section portion 122A and the first convex groove cross-section 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.

[0046] A connection point (fourth connection point p4) where the first convex groove cross-section portion 122B and the panel portion 11 are connected is disposed shifted toward the radial inward direction Di from the third connection point p3 and is disposed shifted toward 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.

[0047] (Second groove wall part 123) The second groove wall portion 123 comprises a second inclined groove cross-sectional portion 123A having one edge connected to the edge on the radially outward direction Do of the groove bottom portion 121 to form a second connection point p2 and further formed with a constant inclination relative to the central axis C, a second convex groove cross-sectional portion 123B (corresponding to the third curved surface portion of the present invention) having one edge connected to the other edge of this second inclined groove cross-sectional portion 123A and being an arc 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 one edge connected to the other edge of this second convex groove cross-sectional portion 123B and being convex toward the internal space SP1 with a radius of curvature different from the radius of curvature of the second convex groove cross-sectional portion 123B.

[0048] A 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 disposed offset in the radially outward direction Do from the second connection point p2 and is disposed offset in the first direction D1 from the second connection point p2. A 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 disposed offset in the radially outward direction Do from the fifth connection point p5 and is disposed offset in the first direction D1 from the fifth connection point p5.

[0049] 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 shifted in the radially outward direction Do from the sixth connection point p6, and is also shifted in the first direction D1 from the sixth connection point p6.

[0050] The second convex groove cross-section portion 123B presents a curved surface whose radius from the central axis C gradually increases (expands) from the fifth connection point p5 to the sixth connection point p6.

[0051] The third convex groove cross-section portion 123C presents a curved surface whose radius from the central axis C gradually increases (expands) from the sixth connection point p6 to the seventh connection point p7.

[0052] 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, 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 radial inward direction Di and also slightly shifted toward the first direction D1 from the center C67 of the arc of the third convex groove cross-section portion 123C. 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.

[0053] In addition, the rear surface SF2 of the can lid shell 10 is formed as a circular arc having 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.

[0054] In the third convex groove cross-section portion 123C, the center C67 of the arc of the front surface SF1 is shifted toward the radial inward direction Di from the center C57 of the arc of the back surface SF2, and is also shifted toward the first direction D1. The radius r57 of the arc of the back surface SF2 is set smaller than the radius r56 of the arc of the second convex groove cross-section portion 123B and the radius r67 of the arc of the third convex groove cross-section portion 123C.

[0055] (Chuck Wall Part 13) The chuck wall portion 13 has one edge (radially inward Di side) connected to the edge of the radially outward 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 edge of the other edge (radially outward Do side) of the first concave surrounding cross-sectional portion 131, forming 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 which is further formed at a constant inclination relative to the central axis C, 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 which is convex toward the internal space SP1.

[0056] (First concave surrounding cross section 131) The connection point (eighth connection point p8) where the first concave surrounding cross-sectional portion 131 and the second concave surrounding cross-sectional portion 132 are connected is disposed at a position shifted radially outwardly from the seventh connection point p7 and at a position shifted in the first direction D1 from the seventh connection point p7. The first concave surrounding cross-sectional portion 131 presents a curved surface whose radius from the central axis C gradually increases (expands) from the seventh connection point p7 to the eighth connection point p8.

[0057] In addition, since the first concave surrounding cross-section portion 131 of the chuck wall portion 13 and the third convex groove cross-section portion 123C of the countersink portion 12 have curved surfaces in opposite directions, the seventh connection point p7 constitutes an inflection point.

[0058] (Second concave surrounding cross section 132) A connection point (ninth connection point p9) where the second concave surrounding cross-sectional portion 132 and the inclined surrounding cross-sectional portion 133 are connected is disposed at a position shifted radially outwardly Do from the eighth connection point p8 and at a position shifted in the first direction D1 from the eighth connection point p8. The second concave surrounding cross-sectional portion 132 presents a curved surface whose radius from the central axis C gradually increases (expands) from the eighth connection point p8 to the ninth connection point p9.

[0059] 3, a center C89 of the arc formed by the surface SF1 of the second concave surrounding cross section 132 is disposed within the internal space SP1, and a center C78 of the arc formed by the surface SF1 of the first concave surrounding cross section 131 is disposed within the internal space SP1. The center C89 of the arc formed by the surface SF1 of the second concave surrounding cross section 132 is shifted toward the radially inward direction Di from the center C78 of the arc of the first concave surrounding cross section 131, and is also shifted toward the first direction D1.

[0060] Furthermore, the radius r89 of the circular arc formed by the surface SF1 of the second concave surrounding cross section 132 is set to be larger than the radius r78 of the circular arc formed by the surface SF1 of the first concave surrounding cross section 131.

[0061] On the rear surface SF2 of the can lid shell 10, the section from the seventh connection point p7 through the eighth connection point p8 to the ninth connection point p9 is formed as a circular arc of a constant radius r79 from the center C89.

[0062] (Slanted surrounding section 133) A connection point (tenth connection point p10) where the inclined surrounding cross-sectional portion 133 and the convex surrounding cross-sectional portion 134 are connected is disposed offset in the radially outward direction Do from the ninth connection point p9 and is disposed offset in the first direction D1 from the ninth connection point p9. The inclined surrounding cross-sectional portion 133 has a gradually larger radius from the central axis C (widening diameter) from the ninth connection point p9 to the tenth connection point p10, presenting an inclined surface with a constant inclination.

[0063] (Convex surrounding cross section 134) The connection point (eleventh connection point p11) where the convex surrounding cross-section portion 134 and the flange portion 14 are connected is disposed offset in the radially outward direction Do from the tenth connection point p10 and offset in the first direction D1 from the tenth connection point p10. The convex surrounding cross-section portion 134 presents a curved surface whose radius from the central axis C gradually increases (expands in diameter) from the tenth connection point p10 to the eleventh connection point p11. The eleventh connection point p11 is the point in the can lid shell 10 that is farthest from the deepest part along the first direction D1, i.e., it constitutes the highest point (apex).

[0064] (Flange part 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.

[0065] As shown in FIG. 2, the tip side of the flange portion 14 is formed into a curled shape in the next curling process.

[0066] 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 portion 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.

[0067] The reinforcing structure of the can lid shell 10 will be described below.

[0068] 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 disposed offset from the center C57. The second convex groove cross-section portion 123B is formed so that its thickness gradually increases from the fifth connection point p5 to the sixth connection point p6.

[0069] In the cross-sectional view of FIG. 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 marks.

[0070] In the can lid shell 10, the front surface SF1 from the sixth connecting point p6 to the seventh connecting point p7 is formed by a circular arc of radius r67 longer than the radius r57 from a center C67 that is positioned offset from the center C57 of the circular arc of the back surface SF2. The third convex groove cross-section portion 123C is formed so that its thickness gradually decreases from the sixth connecting point p6 to the seventh connecting point p7.

[0071] The can lid shell 10 has a back surface SF2 from the seventh connection point p7 via the eighth connection point p8 to the ninth connection point p9 formed by an arc of a constant radius r79 from a center C89, and a front surface SF1 from the eighth connection point p8 to the ninth connection point p9 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-section portion 132 is formed to have a constant thickness from the eighth connection point p8 to the ninth connection point p9.

[0072] The seventh connection point p7 is an inflection point between the third convex groove cross-section portion 123C and the first concave surrounding cross-section portion 131, and is located on the imaginary line LX1 (shown by a dashed line) connecting the center C89 and the center C57 of the figure.

[0073] For the lid shell 10, the surface SF1 from the seventh connection point p7 to the eighth connection point p8 is formed with a radius r78 shorter than the radius r89 from the center C78, which is displaced from the center C89 of the arc on the back surface thereof. The first concave surrounding section 131 is formed such that its thickness gradually decreases from the seventh connection point p7 towards the eighth connection point p8.

[0074] Specifically, regarding the thickness of the bent portion of the lid shell 10, if the thickness at the sixth connection point p6 is t6, the thickness at the seventh connection point p7 is t7, and the thickness at the eighth connection point p8 is t8, the relationship t8 < t7 < t6 holds. The thickness t6 is the dimension along a virtual line (not shown) extending from the center C57, the thickness t7 is the dimension along the virtual line LX1 extending from the centers C57 and C89, and the thickness t8 is the dimension along a virtual line (not shown) extending from the center C89.

[0075] Thus, in the lid shell 10, the bending point (seventh connection point p7) is arranged in the middle to form a bent portion 17 composed of the third convex groove section 123C of the countersink portion 12 and the first concave surrounding section 131 of the chuck wall portion 13 formed in the direction opposite to the bending direction thereof. The thickness of the bent portion 17 increases from the eighth connection point p8 towards the sixth connection point p6, and is set to be maximum in the vicinity of the sixth connection point p6.

[0076] The thickness of the bent portion 17 is equal to or greater than the thickness of the base plate 400 (circular blank 410) for forming the lid shell 10. For example, it is 106% or more of the plate thickness of the base plate 400 (circular blank 410).

[0077] Furthermore, the thickness of the lid shell 10 increases from the fifth connection point p5 towards 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, the relationship t5 < t6 holds. The thicknesses t5 and t6 are the dimensions along a virtual line (not shown) extending from the center C57. The thickness from the fifth connection point p5 to the sixth connection point p6 is also equal to or greater than the thickness of the base plate 400 (circular blank 410) for forming the lid shell 10.

[0078] 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. Also, the area is 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.

[0079] In the can lid shell 10, the above-described cross-sectional structure is configured over the entirety around the central axis C, and the thickened inflection portion 17 is arranged in an annular shape in a plan view.

[0080] The can lid shell 10 is formed by pressing a circular blank 410 made of an aluminum alloy (for example, 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.

[0081] 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 operation.

[0082] The method for manufacturing can lids includes a can lid shell forming process for forming the can lid shell 10, and a conversion forming process for providing tear lines, tabs, etc. on the can lid shell 10 by a conversion press.

[0083] The forming device 2 for performing the can lid shell forming step (the method for manufacturing the can lid shell 10) in the can lid manufacturing method will be described below.

[0084] (Forming 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).

[0085] 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 hereinafter these axes are collectively referred to as the central axis C. In the following description, 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.

[0086] 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 forming device 2, so the direction from the lower die 200 to the upper die 300 may also be referred to as the first direction D1, and the direction from the upper die 300 to the lower die 200 may be referred to as the second direction D2. In addition, in the forming device 2, the first direction D1 will be described as the upward direction, and the second direction D2 will be described as the downward direction.

[0087] (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.

[0088] Lower retainer 210 includes base portion 211 having hole portion 211A passing through the center, and tube portion 212 fixed to the upper portion of base portion 211 and having an inner circumferential surface with an inner diameter larger than that of hole portion 211A. Tubular portion 212 includes step portion 212A on the inside of the tip end opposite the base end fixed to base portion 211.

[0089] Cut edge portion 220 is formed in a ring shape and is disposed in step portion 212A of lower retainer 210, with inner peripheral surface 221 protruding further toward central axis C than the inner peripheral surface of tube portion 212 of lower retainer 210. Lower surface 222 of cut edge portion 220 is fixed to step portion 212A, and corner portion 224 is formed by inner peripheral surface 221 and top surface 223 opposite lower surface 222.

[0090] 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 which 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 passing through along the central axis C, and is positioned inside the tubular portion 212 of the lower retainer 210.

[0091] The panel punch piston 240 integrally comprises a piston main body 241 that rubs against the inner circumferential surface of the die core ring 230, and an extension 242 that extends from the piston main body 241, and can move along the central axis C. A space SP21 is defined by the piston main body 241, the die core ring 230, and the lower retainer 210. Air is supplied to this space SP21 via a flow path not shown, to control the panel punch piston 240.

[0092] 5, the panel punch 250 includes a punch flat portion 251 which cooperates with the flat portion 341 of the die center 340 to sandwich a circular blank, and a punch step portion 252 having a receiving surface 252A which is provided along the periphery of the punch flat portion 251 and is shifted toward the panel punch piston 240 side relative to the punch flat portion 251. The receiving surface 252A has a cross section formed into an arc which is concave toward the upper die 300.

[0093] The lower piston 260 is formed in a cylindrical shape as a whole, and includes a piston main body 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 262 that extends from the piston main body 261 and has a thickness in the radial direction from the central axis C that is thinner than that of the piston main body 261. The lower piston 260 can move along the central axis C.

[0094] A space SP22 is defined by the piston body 261 of the lower piston 260, the lower retainer 210, and the die core ring 230. Air is supplied to this space SP22 through a flow path not shown, to control the lower piston 260.

[0095] (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.

[0096] The upper retainer 310 integrally comprises a first cylindrical portion 311, a second cylindrical portion 312 formed with an inner diameter smaller than that of the first cylindrical portion 311, and a third cylindrical portion 313 formed with an inner diameter larger than that of the second cylindrical portion 312. The inside of the third cylindrical portion 313 is formed as a step portion 313A and forms an open end. A step portion 314 is formed between the inner peripheral surface of the first cylindrical portion 311 and the inner peripheral surface of the second cylindrical portion 312.

[0097] 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 a radius from a central axis C that is thinner than the base 321. The base 321 is disposed in a stepped 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.

[0098] The die center piston 330 comprises a rod-shaped portion 331 formed in a rod shape 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 opening end below the upper retainer 310 toward the lower die 200.

[0099] The die center piston 330 is configured to be movable along the central axis C, and the protruding end 332 is configured to abut 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 in the figures to control the die center piston 330.

[0100] The inner sleeve 350 is integrally provided with a piston body 351 that rubs against the inner circumferential surface of the upper retainer 310 and the die center piston 330, and an extension 352 that extends from the piston body 351 and has a thickness in the radial direction from the central axis C that is thinner than that of the piston body 351. The inner sleeve 350 is capable of moving along the central axis C.

[0101] The upper piston 360 includes a piston main body 361 that rubs against the inner circumferential surface of the upper retainer 310 and the extension portion 352 of the inner sleeve 350, and an extension portion 362 that extends from the piston main body 361 and has a thickness in the radial direction from the central axis C that is thinner than that of the piston main body 361. The upper piston 360 is capable of moving along the central axis C.

[0102] A space SP32 is defined by the piston body 351 of the inner sleeve 350, the die center piston 330, and the upper retainer 310. A space SP33 is defined by the piston body 351 of the inner sleeve 350, the upper retainer 310, and the piston body 361 of the upper piston 360. Air is supplied to these spaces SP32 and SP33 via a flow path not shown, to control the inner sleeve 350 and the upper piston 360.

[0103] 5, in the molding apparatus 2, the lower piston 260 and the blank draw die 320 are configured so that the flat surface 262B of the tip end 262A of the extension portion 262 and the flat surface 322B of the tip end 322A of the tubular portion 322 are aligned with each other. The tip end 322A of the tubular portion 322 of the blank draw die 320 has a rounded portion 322D whose cross section is formed into an arc between the flat surface 322B and the inner circumferential surface 322C.

[0104] As shown in FIGS. 5 and 6, the extension 232 of the die core ring 230 has a tip 232A facing a tip 362A of the extension 362 of the upper piston 360 and a tip 352A of the extension 352 of the inner sleeve 350.

[0105] The tip portion 232A of the die core ring 230 is formed at the highest point, faces the tip portion 362A of the extension portion 362 of the upper piston 360, and has a cross section formed in an arc that is convex toward the tip portion 362A side. A first inclined surface portion 232C is formed connected to the edge of the first convex surface portion 232B on the radially inward direction Di side, is formed at a constant inclination with respect to the central axis C, and descends as it goes in the radially inward direction Di. A second inclined surface portion 232C is formed connected to the lower end of the first inclined surface portion 232C, and has a cross section formed in a circular arc that is convex toward the tip portion 362A side. The molded product has a concave surface portion 232D (corresponding to the first lower mold curved surface portion of the present invention) whose cross section is formed into an arc that is concave toward the central axis C side, a second convex surface portion 232E (corresponding to the second lower mold curved surface portion of the present invention) formed connected to the edge of the concave surface portion 232D on the radially inward direction Di and whose cross section is formed into an arc that is convex toward the central axis C side, and a second inclined surface portion 232F formed connected to the edge of the second convex surface portion 232E on the radially inward direction Di and formed at a constant inclination with respect to the central axis C and descending as it goes in the radially inward direction Di.

[0106] With respect 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 FIG. 6, each connection point is highlighted with a ● mark, but in reality it is a smooth surface.

[0107] The connection point (third bottom mold 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 bottom mold 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 bottom mold connection point P22 to the third bottom mold connection point P23. The second convex surface portion 232E and the adjacent concave surface portion 232D have inverted curved surfaces, differing in convexity and concavity, and therefore the second bottom mold connection point P22 constitutes an inflection point.

[0108] 5, the tip end 362A of the upper piston 360 has a concave surface portion 362B facing the first convex surface portion 232B of the die core ring 230. The concave surface portion 362B of the tip end 362A of the upper piston 360 and the first convex surface portion 232B of the die core ring 230 sandwich a circular blank described below to form the flange portion 14.

[0109] As shown in FIG. 6 , the tip portion 352A of the inner sleeve 350 is formed of a first sleeve convex surface portion 352B having one edge connected to the lowest point (lowest point P30) and extending from the lowest point P30 in the radially outward direction Do, the first sleeve convex surface portion 352B having a cross section formed in an arc that is convex toward the tip portion 232A of the die core ring 230, a sleeve concave surface portion 352C (corresponding to the third upper mold curved surface portion of the present invention) formed to be connected to the edge of the sleeve concave surface portion 352C in the radially outward direction Do and the sleeve concave surface portion 352C having a cross section formed in an arc that is concave toward the tip portion 232A of the die core ring 230, and the sleeve concave surface portion 352C (corresponding to the third upper mold curved surface portion of the present invention) formed to be connected to the edge of the sleeve concave surface portion 352C in the radially outward direction Do, the sleeve concave surface portion 352B having a cross section formed in an arc that is concave toward the tip portion 232A of the die core ring 230. a second sleeve convex surface portion 352D (corresponding to the second upper mold curved surface portion of the present invention) having a cross section formed into an arc convex toward the tip 232A side of the die core ring 230, a third sleeve convex surface portion 352E (corresponding to the first upper mold curved surface portion of the present invention) formed connected to the edge of the radially outward Do side of the second sleeve convex surface portion 352D and having a cross section formed into an arc convex toward the tip 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 formed connected to the edge of the radially outward Do side of the third convex surface portion 352E, formed at a constant inclination with respect to the central axis C, and increasing in diameter as it approaches the radially outward Do direction.

[0110] 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 shifted in the radially outward direction Do from the lowest point P30 and is shifted 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 (expands) from the lowest point P30 to the first upper die connection point P31.

[0111] The connection point (second upper mold connection point P32) where the second sleeve convex surface portion 352D and the sleeve concave surface portion 352C are connected is disposed offset in the radially outward direction Do from the first upper mold connection point P31, and is disposed 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 mold connection point P31 to the second upper mold connection point P32. Since the sleeve concave surface portion 352C and the adjacent first sleeve convex surface portion 352B have different concave and convex curved surfaces, the first upper mold connection point P31 constitutes an inflection point.

[0112] The connection point (third upper mold connection point P33) where the third sleeve convex surface portion 352E and the second sleeve convex surface portion 352D are connected is disposed offset in the radially outward direction Do from the second upper mold connection point P32 and is disposed 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 (expands in diameter) from the second upper mold connection point P32 to the third upper mold connection point P33. The second sleeve convex surface portion 352D and the adjacent sleeve concave surface portion 352C have different curved surfaces, convex and concave, so the second upper mold connection point P32 constitutes an inflection point.

[0113] A 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 disposed offset in the radially outward direction Do from the third upper die connection point P33 and also 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.

[0114] 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 lower surface 351A (on the second direction D2 side) of the piston main body 351 of the inner sleeve 350.

[0115] When the inner sleeve 350 descends toward the die core ring 230 (in the second direction D2) during the deep drawing process, the spacer 370 contacts the upper piston, thereby maintaining the position of the tip portion 352A of the inner sleeve 350 relative to the tip portion 232A of the die core ring 230, and a mold clearance CL1 for forming the inflection portion 17 can be formed between the tip portion 232A of the die core ring 230 and the inner sleeve 350.

[0116] 5, 6, 12, and 13, in the molding apparatus 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.

[0117] In the absence of the spacer 370, the circular blank 410 is deep-drawn while being sandwiched at a constant pressure between the inner sleeve 350 and the die core ring 230, so that 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.

[0118] The die clearance CL1 will be described below.

[0119] 6 shows the surface of the tip portion 232A of the die core ring 230. The concave surface portion 232D is formed as an arc of a constant radius r212 from the center C212. The second convex surface portion 232E is formed as an arc of a constant radius r223 from the center C223.

[0120] When the inner sleeve 350 is closest to the die core ring 230, the concave surface 232D of the tip end 232A of the die core ring 230 faces the tip end 352A of the inner sleeve 350, the second sleeve convex surface 352D, and the third sleeve convex surface 352E.

[0121] Here, the third sleeve convex surface portion 352E is a circular arc centered at the same point as the center C212 of the concave surface portion 232D of the die core ring 230, and the radius r334 of this circular arc is shorter than the radius r212 of the concave surface portion 232D of the die core ring 230. As a result, the distance between the third sleeve convex surface portion 352E of the inner sleeve 350 and the concave surface portion 232D of the die core ring 230 when they are closest to each other is constant.

[0122] The center C323 of the arc of the second sleeve convex surface portion 352D is shifted in the radially outward direction 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.

[0123] In the cross section, assuming a first tangent T1 that contacts each point located between the second upper mold connection point P32 and the third upper mold connection point P33 of the second sleeve convex surface portion 352D, and assuming a second tangent T2 that contacts each point located between the third upper mold connection point P33 and the fourth upper mold connection point P34 of the third sleeve convex surface portion 352D, the angle θ1 formed by the first tangent T1 and the horizontal line HL is set to be smaller than the angle θ2 formed by the second tangent T2 and the horizontal line HL (θ1<θ2) (excluding the tangent to the third upper mold connection point P33).

[0124] 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 viewed as a dimension along an imaginary line extending from the center C212, it is formed so that it becomes wider as it goes from the third upper mold connection point P33 of the inner sleeve 350 to the second upper mold connection point P32.

[0125] The center C312 of the arc of the sleeve concave surface portion 352C is displaced in the radially inner direction Di from the center C223 of the arc of the second convex surface portion 232E of the die core ring 230 and is also displaced in the first direction D1. Further, the radius r312 of the arc of the sleeve concave surface portion 352C is set longer than the radius r223 of the arc of the second convex surface portion 232E of the die core ring 230.

[0126] Here, the second lower mold connection point P22 and the second upper mold connection point P32, both of which are inflection points, are arranged on a virtual line LX2 connecting the center C212 and the center C223 shown by a one-dot chain line in the figure.

[0127] When capturing the distance between the sleeve concave surface portion 352C and the second convex surface portion 232E of the die core ring 230 as a dimension along a virtual line extending from the center C223, it is formed so as to widen as going from the second upper mold connection point P32 to the first upper mold connection point P31 of the inner sleeve 350.

[0128] In this way, the mold clearance CL1 is formed wider as going from the third upper mold connection point P33 to the first upper mold connection point P31 of the inner sleeve 350. Let the dimension of the clearance at the third upper mold connection point P33 be CL33, the dimension of the clearance at the second upper mold connection point P32 be CL32, and the dimension of the clearance at the first upper mold connection point P31 be CL31. Then, the relationship of CL33 < CL32 < CL31 holds.

[0129] CL33 is the dimension along a virtual line extending from the center C212 through the third upper mold connection point P33 to the inside of the die core ring 230. CL32 is the dimension along a virtual line extending from the center C212 or the center 223 and passing through the second upper mold connection point P32 and the second lower mold connection point P22. CL31 is the dimension along a virtual line extending from the center 223 through the first upper mold connection point P31 to the inside of the inner sleeve 350.

[0130] Note that the mold clearance CL1 from the third upper mold connection point P33 to the first upper mold connection point P31 of the inner sleeve 350 is set larger than the thickness of the blank sheet 400.

[0131] (Method of manufacturing can lid shell 10) As shown in FIG. 7, the manufacturing method of the can lid shell 10 using the forming apparatus 2 includes a blanking process (FIG. 8) in which a circular blank is punched out from an aluminum alloy base 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.

[0132] Each step will be described with reference to Figures 8 to 10 (Figures 8A, 8B, 9A, 9B, and 10A, 10B). Figures 8 to 10 show the left side of the central axis C of the molding apparatus 2 shown in Figure 4.

[0133] (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.

[0134] 8B, the upper die 300 descends, and a part of the blank 400 is pressed toward the inside of the cut edge portion 220 by the blank draw die 320 to punch out a 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.

[0135] (Deep drawing process) In the deep drawing process, first, the upper die 300 descends as shown in FIG. 9A, 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.

[0136] Next, as shown in FIG. 9B, the upper mold 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 until a mold clearance CL1 is formed between the tip 232A of the die core ring 230 and the tip 352A, and the flat portion 341 of the die center 340 is placed inside the die core ring 230.

[0137] That is, deep drawing is performed by sandwiching the central portion of the circular blank between flat portion 341 of die center 340 and punch flat portion 251 of panel punch 250 and moving them in the second direction. Fig. 9B shows a first formed body 420 formed by the deep drawing process with upper die 300 at the bottom dead center.

[0138] As shown in Figure 11, the first molded body 420 comprises 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 in the first direction D1 from the bottom portion 421 and also shifted in the radial 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.

[0139] The first inflection portion 423 is configured by connecting a convex portion 423A having a cross section formed into a curved surface whose curved surface is convex toward the internal space SP4 of the first formed 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 description, the intermediate form of the circular blank 410 until it is deformed into the first formed body 420 is referred to as an intermediate formed body.

[0140] (Reverse process) 10A, the panel punch 250 and the upper die 300 of the lower die 200 are raised. During the process in which the panel punch 250 and the upper die 300 of the lower die 200 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.

[0141] As the panel punch 250 and upper die 300 of the lower die 200 rise, as shown in Figure 12, the portion of the first molded body 420 sandwiched between the panel punch 250 and the die center 340 that protrudes outward from the bottom portion 421 is folded back to form a curved portion 424 with a U-shaped cross section that is convex downward.

[0142] As shown in Figure 12, the curved portion 424 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, with the first inflection portion 423 of the first molded body 420 being sandwiched between them.

[0143] In this die clearance CL1, a minute gap (space) CL0 that is not filled by the first inflection portion 423 of the first compact 420 remains, for example, between the first inflection portion 423 and the sleeve concave surface portion 352C or the second sleeve convex surface portion 352D of the inner sleeve 350. The minute gap (space) CL0 is formed at the stage at which the deep drawing process is completed.

[0144] 10B and 13, when the curved portion 424 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. 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.

[0145] In the reverse process, the curved portion 424 is pushed up by the receiving surface 252A of the panel punch 250, and a part of the first molded body 420 being processed is deformed to fill the minute gap (space) CL0, as shown in Fig. 13. This causes the first inflection portion 423 to increase in thickness and become the second inflection portion 425 (inflection portion 17).

[0146] In this manner, the reverse step is completed when the panel punch 250 is moved (raised) in the first direction D1 to a predetermined position (height) until the minute gap (space) CL0 is filled with a part of the first formed body 420. The curved portion 424 at this final stage constitutes the countersink portion 12, and the formed second inflection portion 425 constitutes the inflection portion 17.

[0147] After the reverse step 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.

[0148] Next, the upper mold 300 is further moved to a position above the lower mold 200, and the completed can lid shell 10 is removed.

[0149] In the next lining process, rubber is applied to the back surface SF2 of the formed can lid shell 10 to maintain the coating sealability. Then, in the next conversion process, a tear line for opening the can lid and a tab for opening the can lid are formed, and the can lid is completed.

[0150] Furthermore, after filling the contents and gas (CO2 or N2) into the bottomed cylindrical can body, 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.

[0151] 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 increases and internal pressure acts to cause a part of the countersink portion 12 of the can lid to bulge outward from the can, the inflection portion 17 around the countersink portion 12 is formed to be reinforced, thereby suppressing deformation of the countersink portion 12.

[0152] For example, even if an internal pressure is applied that changes the concave opening angle θ23 of the back surface of the second groove wall portion 123 shown in Fig. 1B, deformation can be suppressed because the thickness is gradually increased from the first concave surrounding cross section 131 of the chuck wall portion 13 to the third convex groove cross section 123C and the second convex groove cross section 123B of the countersink portion 12. This makes it possible to prevent buckling.

[0153] 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.

[0154] The thin-walled portion 15 is configured as a recessed portion 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 to have the same shape (rounded rectangle). Furthermore, each thin-walled portion 15 is formed such that a dimension Da along the radially outward direction Do in a plan view is longer than a width dimension Db perpendicular to the radially outward direction Do. In Figure 15, the line along the radially outward direction Do is represented by a two-dot chain line.

[0155] The portions between these thin portions 15 constitute thick portions (protruding portions) 16 that are formed thicker than the thin portions 15. Each thick portion 16 is also formed such that the dimension along the radially outward direction Do in plan view is longer than the width dimension perpendicular thereto. In other words, the distance between each of the thin portions 15 along the circumferential direction relative to the central axis C is smaller than the dimension Da.

[0156] In Figure 15, the dotted line B11 indicates the boundary line formed by the fifth connection point p5, the dotted line B12 indicates the boundary line formed by the sixth connection point p6, the dotted line B13 indicates the boundary line formed by the seventh connection point p7 (inflection point), and the dotted line B14 indicates the boundary line formed by the eighth connection point p8.

[0157] As shown in Figures 15 and 17, each thin-walled portion 15 has one end 15A located toward the center, which is located closer to the fifth connection point p5 than the sixth connection point p6, and the other end 15B located closer to the flange portion 14, which 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.

[0158] In this way, the thin 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 (sixth connection point p6) that constitutes the maximum thickness.

[0159] The thick-walled portion 16 arranged between the thin-walled portions 15 has one end 16A arranged on the center side arranged closer to the fifth connection point p5 than the sixth connection point p6, and the other end 16B arranged on the flange portion 14 side arranged 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 (sixth connection point p6) that constitutes the maximum thickness.

[0160] As a result, in the thick portion 16, the thickness from the front surface SF1 to the back surface SF2 increases from the end portion 16B to the sixth connection point p6, and further increases from the end portion 16A to the sixth connection point p6. In other words, the thickness of the thick portion 16 is the largest at the sixth connection point p6.

[0161] The surface SF1, on which the thin-walled portions 15 and the 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.

[0162] The shapes of the thin portion 15 and the thick portion 16 are not limited to the illustrated examples, and may be formed into an elliptical shape in plan view as shown in Fig. 18. Furthermore, as shown in Fig. 19, the extending direction of the thin portion 15 and the thick portion 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. Note that an example of the extending direction of the thin portion 15 and the thick portion 16 and the radially outward direction Do is shown by a two-dot chain line in each figure.

[0163] (Renovation process) The can lid shell 10A of the second embodiment can be manufactured by additionally carrying out a reforming process on the can lid shell 10 of the first embodiment.

[0164] 21, a reforming device 40 for performing the reforming process includes a reforming die 41, a reforming punch 42, and a conveying section 43 that conveys the can end shell 10 between the reforming die 41 and the reforming punch 42. The reforming die 41 and the reforming punch 42 are provided in a press machine (not shown).

[0165] In the reforming process, as shown in the left half of Fig. 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 on the edge of the hole 43B of the belt 43A of the transport section 43 and supported by the belt 43A. After the can lid shell 10 is transported, as shown in the right half of Fig. 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.

[0166] 22, a plurality of protruding projections 42B are formed on a contact surface 42A of the reforming 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 portions between the thin-walled portions 15 are formed as the thick-walled portions 16.

[0167] 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 this reform die 41 from below absorbs part of the load from the reform punch 42.

[0168] (action) In the thickened portion 18, each thick-walled 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, and prevents the thickened portion 18 from being deformed, such as bending 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.

[0169] The protrusions for forming the thin-walled portion 15 and the thick-walled portion 16 in the thickened portion 18 are not limited to those 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 by using a plurality of 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, the same effect of improving the mechanical strength can be obtained.

[0170] (First modified molding device 2A) 23, the molding apparatus 2A of the 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 end of the die core ring 500 of the first modified example, an inner portion facing the tip end of the inner sleeve 350 is configured to be movable relative to an outer portion 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.

[0171] As shown in Figure 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 further supported at its lower end by the spring 530 so as to be freely movable along the central axis C.

[0172] The first fixing portion 510 includes a base end 511 fixed to the lower retainer 210, and a spring support portion 512 extending from the base end 511 and having a radial thickness smaller than the radial thickness of the base end 511. The base end 511 of the first fixing portion 510 protrudes in the radially outward direction Do beyond the outer circumferential surface of the spring support portion 512, and has a mounting surface 511A along the radially outward direction Do. The spring support portion 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.

[0173] As shown in Figures 24 and 25, the second fixed portion 520 comprises a base end 521 placed on the mounting surface 511A of the base end 511 of the first fixed portion 510 and fixed to the first fixed portion 510, and an upper piston opposing portion 522 having a radial thickness formed thinner than the radial thickness of the base end 521, extending from the base end 521, and having a tip end 522A that opposes the upper piston 360.

[0174] The upper piston opposing portion 522 is formed in a cylindrical shape, with its inner circumferential surface being rubbed by the movable portion 540 and its outer circumferential surface being rubbed by the lower piston 260. A 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 apparatus 2 of the first embodiment.

[0175] (Spring 530) Spring 530 is provided coaxially with first fixed portion 510, and expands and contracts along the axis (central axis C).

[0176] With movable portion 540 placed thereon, spring 530 has a lower portion housed in recess 512A of spring support portion 512, and the remaining tip portion is disposed outside recess 512A.

[0177] (Movable part 540) The movable part 540 is formed in a ring shape. The movable part 540 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 cylindrically from the base end 541, and faces the inner sleeve 350.

[0178] A tip portion 542A of the inner sleeve facing portion 542 has a portion having 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 apparatus 2 of the first embodiment.

[0179] The movable portion 540 moves along the central axis C with its outer circumferential surface abutting against the inner circumferential surface of the upper piston opposing portion 522 of the second fixed portion 520, and further with the inner circumferential surface of the inner sleeve opposing portion 542 abutting against the outer circumferential surface of the panel punch 250.

[0180] As shown in Figure 25, the movable part 540 is pushed by the spring 530, and the movable side step portion 543 formed on the outside is abutted against the fixed side step portion 523 formed on the inner surface of the upper piston opposing portion 522 of the second fixed part 520, and is held in a position close to the tip portion 522A of the upper piston opposing portion 522.

[0181] The outside of the movable part 540 has a first outer peripheral surface 540A disposed at a lower position adjacent to the lower end, and a second outer peripheral surface 540B disposed 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.

[0182] The fixed side step portion 523 of the upper piston opposing portion 522 of the second fixed portion 520 is configured by connecting a first inner circumferential surface 522B that abuts against the first outer circumferential surface 540A of the movable portion 540 and a second inner circumferential surface 522C that abuts against the second outer circumferential surface 540B of the movable portion 540 via a fixed side step surface 522D.

[0183] When the movable part 540 is pushed by the spring 530, the movable side step portion 543 abuts against the fixed side step portion 523, and the movable part 540 is positioned at the highest position within its moving range, as shown in Figure 26, the second convex surface portion 232E of the tip portion 542A of the inner sleeve opposing portion 542 is shifted in the radially inward direction Di and also in the second direction D2 from the first convex surface portion 232B of the tip portion 522A of the upper piston opposing portion 522.

[0184] Furthermore, when the movable part 540 is positioned at the highest position, the tip 542A of the inner sleeve opposing part 542 is positioned close to the tip 352A of the inner sleeve 350, and a mold clearance CL2 for molding the inflection part 17 is set.

[0185] Compared with the mold clearance CL1 of the molding apparatus 2 of the first embodiment, the mold clearance CL2 of the molding apparatus 2A of this first modified example is set so as 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.

[0186] The arc formed by the second convex portion 232E of the tip 542A of the movable part 540 has its upper end set at position P220 above the center C223 (on a vertical line), and is formed from the third lower mold connection point P23, through the second lower mold connection point P22, to the upper end position P220.

[0187] Furthermore, in the tip end 542A of the movable part 540, a portion extending in the radially outward direction Do from the upper end position P220 of the arc formed by the second convex surface portion 232E is disposed as a surface that does not contact the intermediate formed body. The tip end 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 portion 232B, and is provided with a non-contact inner circumferential surface 522E that does not contact the intermediate formed body.

[0188] (Method of manufacturing 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.

[0189] The deep drawing process and the reverse process will be described below.

[0190] (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.

[0191] During the process of deep drawing, the spacer 370 attached to the inner sleeve 350 comes into contact with the upper piston 360 , thereby preventing the inner sleeve 350 from descending independently of the upper piston 360 .

[0192] 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 protruding 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.

[0193] 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 is gradually increased by the press until the upper die 300 reaches the bottom dead center.

[0194] 27B shows a state in which the deep drawing is completed, upper die 300 is at the bottom dead center, and first compact 420 is formed. At this time, the distance (see FIG. 25) between movable-side step surface 540C of movable part 540 and fixed-side step surface 522D of second fixed part 520 is maximum, for example, 0.25 mm.

[0195] (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. With this movement of the bottom portion 421, 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).

[0196] As the panel punch 250 rises, the internal depth dimension h along the central axis C of the curved portion 424 gradually increases. Also, the load with which the first molded body 420 presses the movable portion 540 is reduced, and the movable portion 540 moves toward the tip portion 352A of the inner sleeve 350, so that the distance between the tip portion 542A of the movable portion 540 and the tip portion 352A of the inner sleeve 350 gradually narrows.

[0197] 27C shows a state in which, during the reverse process, movable-side step surface 540C abuts against fixed-side step surface 522D, and tip end 542A of movable part 540 and tip end 352A of inner sleeve 350 are closest to each other. In this state, as shown in the enlarged view of FIG. 28, a mold clearance CL2 for molding inflection portion 17 is defined between tip end 542A of movable part 540 and tip end 352A of inner sleeve 350.

[0198] When the die clearance CL2 is formed, a minute gap CL0 is disposed between a 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 compact 420. In addition, the spacer 370 attached to the inner sleeve 350 is in contact with the upper piston 360 (see FIG. 23).

[0199] When the reverse step 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 molded body 420 being processed is pushed into the die clearance CL2. A part of the first molded body 420 is deformed to fill the minute gap (space) CL0. As a result, the first inflection portion 423 is thickened and formed into the second inflection portion 425, and the reverse step ends (FIG. 27D).

[0200] In the deep drawing process of the manufacturing method of the first modified example, the movable part 540 is pressed down by the intermediate formed body 410A, and the gap between the inner sleeve opposing part 542 of the movable part 540 and the inner sleeve 350 widens, thereby reducing deformation of the intermediate formed body 410A due to contact with the inner sleeve opposing part 542 and suppressing reduction in plate thickness during deep drawing.

[0201] In a can product using a can lid having a can lid shell 10 molded in this manner, even if the internal pressure of the can product increases and internal pressure acts to cause a part of the countersink portion 12 of the can lid to bulge outward, the inflection portion 17 around the countersink portion 12 is formed with an increased thickness, so that buckling, in which a part of the countersink portion 12 deforms in an outward bulging shape, can be suppressed.

[0202] (Second modified molding device 2B) 29, in comparison with the molding apparatus 2A of the first modified example, the molding apparatus 2B of the second modified example is equipped with 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 molded 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 molded 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.

[0203] As shown in FIG. 30, the die core ring 1500 includes the first fixed portion 510, a block 550, a second fixed portion 1520 that supports the block, a spring 1530 having a smaller spring constant than the spring 530, and a movable portion 1540.

[0204] The second fixed part 1520 has a base end part 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 described above in that it has a through hole 525 through which the block 550 passes.

[0205] The through hole 525 is formed penetrating 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 the through holes 525 are formed around the central axis C of the second fixed portion 1520 at equal angular intervals, for example.

[0206] (Block 550) As shown in Figure 31, when the block 550 is positioned in the through hole 525 of the upper piston opposing portion 1522 of the second fixed portion 1520, the block 550 has an outer end portion 551 protruding toward the lower piston 1260 and an inner end portion 552 protruding toward the movable portion 1540.

[0207] The outer end portion 551 includes an outer vertical surface 551A and an outer inclined surface 551B extending from an 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 has a constant inclination θ51 with respect to the central axis C.

[0208] The inner end 552 includes an inner vertical surface 552A and an inner inclined surface 552B extending from an upper edge of the inner vertical surface 552A. The inner inclined surface 552B has a radius (distance) from the central axis C that increases from the upper edge of the inner vertical surface 552A in the first direction D1, and has a constant inclination θ52 with respect to the central axis C. 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 to be larger than the angle θ52 that the inner end 552 makes with the horizontal plane.

[0209] (Lower piston 1260) The lower piston 1260 includes a piston body 261 and an extending portion 1262. The extending portion 1262 is different from the extending portion 262 of the lower piston 260 described above in the shape of its inner circumferential surface.

[0210] As shown in FIG. 32, the extension portion 1262 includes 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 arranged between the first inner circumferential surface 262C and the second inner circumferential surface 262D.

[0211] The radius (distance) of inner inclined surface 262E from central axis C decreases from the upper edge of first inner circumferential surface 262C to the lower edge of second inner circumferential surface 262D, and the inclination with respect to central axis C is set to be constant. Angle θ62 of inclination of inner inclined surface 262E with respect to central axis C is set to be equal to angle θ51 of outer inclined surface 551B of block 550. In addition, when lower piston 1260 descends, outer inclined surface 551B of block 550 is disposed on the movement trajectory of inner inclined surface 262E.

[0212] When the lower piston 1260 configured in this manner descends a predetermined distance along the central axis C, the inner inclined surface 262E comes into contact with the outer inclined surface 551B of the block 550, and as the lower piston 1260 descends further, it pushes the outer inclined surface 551B of the block 550, thereby moving the block 550 in the radially inward direction Di.

[0213] (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 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 portion 543, and an outer inclined surface 540E arranged between the first outer peripheral surface 1540A and the third outer peripheral surface 540D.

[0214] The radius of first outer circumferential surface 1540A is set smaller than the radius of second outer circumferential surface 540B, and the radius of third outer circumferential surface 540D is set larger than the radius of second outer circumferential surface 540B.

[0215] Outer inclined surface 540E has a radius (distance) from central axis C that increases from the upper edge of first outer peripheral surface 1540A to the lower edge of third outer peripheral surface 540D, and is set at a constant inclination with respect to central axis C. Angle θ540 of inclination of third outer peripheral surface 540D with respect to the horizontal plane is set to be equal to angle θ52 of inner inclined surface 552B of block 550.

[0216] 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.

[0217] 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 (when the movable side step surface 540C is in contact with the fixed side step surface 522D and the outer inclined surface 551B is protruding 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 its surface protruding from the through hole 525 into the inside of the upper piston opposing part 1522.

[0218] It should be noted 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 portion 1540 is disposed.

[0219] In the deep drawing process, movable part 1540 is pushed by intermediate formed body 410A and retreats toward spring 1530, but outer inclined surface 540E of movable part 1540 abuts against inner inclined surface 552B of block 550, thereby preventing the retreat of movable part 1540. Furthermore, while movable part 1540 abuts against block 550, block 550 presses outer inclined surface 540E of movable part 1540 in radial inward direction Di with inner inclined surface 552B, thereby moving movable part 1540 toward inner sleeve 350.

[0220] (Method of manufacturing 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 410A is punched out from an aluminum alloy raw plate, a deep drawing process in which the circular blank 410 is deep drawn to form a shallow-bottomed, tray-shaped first formed body 420, and a reverse process in which a flat portion at the bottom of the first formed body 420 is moved toward the mouth side located above it to form a recessed countersink portion around the flat portion.

[0221] The deep drawing process and the reverse process will be described below.

[0222] (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.

[0223] 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 protruding 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.

[0224] After the intermediate molded body 410 A abuts against the movable portion 1540 , the distance between the tip portion 542 A of the movable portion 1540 and the tip portion 352 A of the inner sleeve 350 gradually widens until the movable portion 1540 abuts against the block 550 .

[0225] Furthermore, together with the movement of the panel punch 250, the die center 340, etc., 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 descends a predetermined distance, the inner inclined surface 262E comes into contact with the outer inclined surface 551B of the block 550.

[0226] 34B, the timing at which inner inclined surface 262E of lower piston 1260 abuts against outer inclined surface 551B of block 550 and the timing at which outer inclined surface 540E of movable part 1540 abuts against inner inclined surface 552B of block 550 are designed to be simultaneous. With movable part 1540 abutting against block 550 in this manner, the distance along central axis C between movable-side step surface 540C and fixed-side step surface 522D is, for example, 0.5 mm.

[0227] In the molding apparatus 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 part 552 to protrude further into the inside of the upper piston opposing part 1522. As a result, the block 550 pushes the movable part 1540, and the movable part 1540 moves in a direction approaching the inner sleeve 350.

[0228] In this way, the movement of the movable part 1540 toward the inner sleeve 350 begins halfway 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.

[0229] As shown in Fig. 34C, when the upper die 300 reaches the bottom dead center, the tip 542A of the movable part 1540 is located at the position closest to the tip 352A of the inner sleeve 350. In this close state, a die clearance CL2 for molding the deformation part 17 is formed. Also, the movable side step surface 540C of the movable part 1540 abuts on the fixed side step surface 522D of the upper piston facing part 1522. The spacer 370 contacts the upper piston 360, and a die clearance CL2 is formed between the tip 542A of the inner sleeve facing part 542 (between the inner sleeve 350 and the movable part 1540).

[0230] (Reverse process) In the reverse process, bottom portion 421 of first compact 420 sandwiched between panel punch 250 and die center 340 is moved in the direction opposite to the deep drawing direction by panel punch 250 and panel punch piston 240 of lower die 200. As bottom portion 421 of first compact 420 moves, a part of first compact 420 protruding from between panel punch 250 and die center 340 is folded back to form curved portion 424 having a U-shaped cross section that is convex downward, as shown in Fig. 34D.

[0231] In addition, when the curved portion 424 is positioned above the receiving surface 252A of the punch step portion 252, as shown in Figure 28, a small 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 formed body 420.

[0232] 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, the block 550 is released from the force of the lower piston 1260 urging it backward in the radial inward direction Di and returns to its original position, as shown in Fig. 34D. Note that the die core ring 1500 is provided with a blocking spring (not shown), which allows the block 550 to return from the backward position to the protruding position.

[0233] As the reverse step progresses further, the curved portion 424 is pushed up by the receiving surface 252A of the panel punch 250, and a part of the first molded body 420 being processed is pushed into the die clearance CL2. A part of the first molded body 420 is deformed to fill the minute gap (space) CL0. As a result, the first inflection portion 423 is thickened and formed into a second inflection portion, and the reverse step is completed (FIG. 34E).

[0234] In the deep drawing step of the manufacturing method of the second modified example, the force of the spring 1530 that holds the movable part 1540 at the position where it comes closest to the inner sleeve 350 and forms the die clearance CL2 is weaker than the force of the spring 530 of the forming apparatus 2A of the first modified example, so that the intermediate formed body 410A easily retreats during deep drawing by pushing it back as it deforms. This makes it possible to further suppress a decrease in plate pressure due to contact between the intermediate formed body 410A and the movable part 1540 (the inner sleeve facing part 542) during the deep drawing process.

[0235] Furthermore, as the deep drawing process progresses, as the lower piston 1260 descends, the block 550 is retracted and the movable part 1540 is moved toward the inner sleeve 350, whereby a portion of the intermediate molded body 410A, the thickness of which has been reduced, is sandwiched between the movable part 1540 (the inner sleeve opposing part 542) and the inner sleeve 350 to form the first inflection part 423.

[0236] In this manner, by suppressing the reduction in plate pressure that accompanies deep drawing before the reverse process, it is possible to prevent the occurrence of deformation or distortion of curved portion 424 that is formed by folding back at the start of the reverse process.

[0237] The present invention can be implemented without being limited to the above description and illustrated examples. The manufacturing method of the first embodiment has been described based on the molding device (FIG. 4), but the gist of the present invention is to configure the mold clearance CL1 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 configured, it is not limited to the molding device shown in FIG. 4 and other molding devices may be used. The ratio of dimensions along the central axis C of the countersink portion, chuck wall portion, and flange portion, the ratio of 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, and the like may be changed.

[0238] Furthermore, with regard to the cross-sectional structure of the can lid shell, the above explanation and drawings have shown cases in which the surfaces constituting the front surface SF1 and the back surface SF2 of the third convex grooved 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), the second convex grooved cross-sectional portion 123B (corresponding to the third curved surface portion of the present invention), etc. are formed as arcs (arcs of a perfect circle). However, in the third convex grooved 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), the second convex grooved cross-sectional portion 123B (corresponding to the third curved surface portion of the present invention), etc., the surfaces constituting the front surface SF1 and the back surface SF2 may also be formed as surfaces whose cross sections are not arcs of a perfect circle but are curved like a bow.

[0239] In this way, the inflection portion 17 and the thickened portion 18 can be formed by 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) having a curved surface curved like an arch. By forming the inflection portion 17 and the thickened portion 18 by a curved surface consisting of an arc (an arc of a perfect circle) or a surface curved like an arch, the pressure resistance of the can lid shell can be improved. EXAMPLES

[0240] 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 a modified epoxy-based paint (total thickness on both sides 0.012 mm), and the pressure resistance was confirmed.

[0241] The can lid shell had a panel portion, a countersink portion, a chuck wall portion, and a flange portion, and the inflection point was located between the inflection point and the inflection portion consisting of an arc portion in the chuck wall portion that is concave toward the internal space and an arc portion in the countersink portion that is convex toward the internal space.The example had an increased thickness at the inflection portion, and the comparative example had no increase in thickness.

[0242] The can end 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.

[0243] In addition, the panel punch 250 of the lower die 200 of the molding device has a stepped punch step portion 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 curved portion 424 formed during the reverse process is pushed up by the receiving surface 252A of the punch step portion 252, deforming a part of the first molded body being processed and pushing it into the die clearance CL1, thereby forming a thickened inflection portion 425.

[0244] Comparative example can end shells were produced using conventional molding equipment.

[0245] Fifty samples of each of the inventive examples and comparative examples were manufactured, and the compressive strength [psi] of each was measured, and the average value (average compressive strength) was calculated. In addition, the thickness of the inflection points of the samples between the arc part of the chuck wall part that is concave toward the internal space side and the arc part of the countersink part that is convex toward the internal space side was measured, and the percentage increase (sheet thickness after processing / sheet thickness of circular blank before processing x 100) [%] was calculated compared to the thickness of the circular blank before processing. Note that 1 [psi] = 6894.76 [Pa].

[0246] Table 1 shows the compressive strength, thickness, and thickness ratio.

[0247] [Table 1]

[0248] In the can lid shell of the embodiment of the invention, the inflection portion is formed to be about 9% thicker than the base plate, and the average pressure resistance is also high at 106.7 [psi].

[0249] In the comparative example, no increase in thickness at the bent portion was observed compared to the thickness of the blank. The average compressive strength of 98.2 [psi] was equivalent to the strength of a conventional can lid. [Industrial Applicability]

[0250] A can lid shell that prevents buckling, a manufacturing method for the can lid shell, and a molding device can be provided. [Explanation of symbols]

[0251] 2,2A molding equipment 10,10A Can lid shell 11 Panel section 12 Countersink section 123B Second convex groove cross section (third curved surface part) 123C Third convex groove cross section (first curved surface part) 13 Chuck wall section 131 First concave surrounding cross section (second curved surface part) 132 Second concave surrounding cross section 133 Slanted enclosure section 134 Convex Encircled Section 14 Flange section 15 Thin-walled section (recess) 16 Thick section (convex section) 17 Inflection section 18 Thickened section 40 Renovation Equipment 200 Lower mold 210 Lower Retainer 220 Cut edge part 230 Dicor Ring 232A Tip 232D Concave part (first lower mold curved part) 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 mold 310 Upper Retainer 320 Blank Draw Die 330 Die Center Piston 340 Die Center 350 Inner Sleeve 351 Piston body 352A Tip 352B First sleeve convex part 352C Sleeve concave part (third upper mold curved part) (upper mold curved part) 352D Second sleeve convex surface (Second upper mold curved surface) 352E Third sleeve convex surface (first upper mold curved surface) 352F Sleeve slope section 360 Upper piston 362A Tip 370 Spacer 400 Plain board 410 Circular Blank 410A Intermediate molding 420 First molded body 421 Bottom part (flat part) 422 Clamping part (flange part) 423 First Inflection 425 Second inflection section 500 Dicor Ring 510 First fixed part (fixed part) 520 Second fixed part (fixed part) 522,1522 Upper piston facing part 522A Tip 523 Fixed side step part 530 Spring (biasing member) 540 Moving parts 542 Inner sleeve opposing part 542A Tip 550 Block 551B Outside slope 552B Inner inclined surface 2B Molding equipment 1260 Lower piston 262E Internal slope 1500 Dicor Ring 1520 Second fixed part (fixed part) 525 through hole 1530 Spring (biasing member) 1540 Moving parts 540E External slope C center axis CL1,CL2 mold clearance SF1 surface SF2 Back SP1 interior space

Claims

1. 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.

2. 2. The can lid shell according to claim 1, wherein the countersink portion includes a third curved surface portion that is connected to the first curved surface portion, the first curved surface portion being disposed between the third curved surface portion and the second curved surface portion, the third curved surface portion being convex toward the internal space, and the thickness of the third curved surface portion being increased from the edge on the panel portion side to the edge connected to the first curved surface portion.

3. 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 from each other 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.

4. 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 panel 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, the second upper mold curved surface portion being an arc having a radius of curvature different from that of the first upper mold curved surface portion and being 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, the third upper mold curved surface portion being 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 surface portion and the second lower mold curved surface portion of the die core ring and the second upper mold curved surface portion and the third upper mold curved surface 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.

5. 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 freely stretched and contracted 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.

6. 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.

7. A method for manufacturing a can lid shell, comprising the steps of: clamping 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 the flange portion of the first formed body, a die core ring having a tip end and a tip end of the inner sleeve, the die core ring being provided with a die clearance that widens as the die core ring approaches a central axis; a part of the first molded body protruding from between the panel punch and the die center being pushed into a gap in the die clearance that is not filled by the first inflection portion, and the first inflection portion is molded into a second inflection portion having an increased thickness.

8. 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.

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