Plate material forming method, can lid forming method, and can bottom forming method

Abstract

Provided is a plate material forming method with which it is possible to increase the plate thickness of an annular projecting portion over a wide range, including a required range, using a simple manufacturing process, while preventing unintended deformation of the material through relative pressing.　The plate material forming method according to the present invention includes a step for forming a specific plate portion and a side wall portion, a step for forming an annular curved portion connected to the side wall portion, and a step for deforming at least the annular curved portion to form an annular projecting portion having a selectively increased plate thickness, wherein, in the step for forming the annular projecting portion, the annular projecting portion having a selectively increased plate thickness is formed by applying a pressing force to the specific plate portion in a first direction in which the annular projecting portion to be formed projects, while supporting the annular curved portion using a supporting member that can move relatively in a second direction opposite to the first direction, to thereby cause at least a part of the plate material that constituted the side wall portion to move along a supporting surface of the supporting member while generating compressive stress in the second direction in the side wall portion.

Description

Method for forming plate material, method for forming can lid, and method for forming can bottom

[0001] The present invention relates to a method for forming a plate material to be used for, for example, a can lid, a can bottom, etc., a method for forming a can lid, and a method for forming a can bottom.

[0002] Metal can containers (metal cans) are required to have as small a thickness as possible while still maintaining pressure resistance in order to conserve material resources, reduce weight, etc. For example, in the can lid or can bottom, so-called buckling can occur due to an increase in internal pressure, and therefore there is a strong demand for innovations to maintain pressure resistance.

[0003] For example, in order to reduce the thickness of the plate material that will become the can lid or bottom while maintaining its pressure resistance, it is known to form an annular protrusion consisting of an inner wall portion, a curved convex portion, and a part of the outer wall portion on the outer side of the central plate portion that will become the lid surface or bottom surface, and to increase the plate thickness of the curved convex portion.

[0004] For example, Patent Document 1 describes that in a can lid having a center panel portion (central plate portion), a panel wall portion (inner peripheral wall portion), a chuck wall radius portion (curved convex portion), a chuck wall portion (outer peripheral wall portion), and a curl portion, the plate thickness t2 of the lower end of the panel wall portion is made greater than the plate thickness t1 of the center panel portion (t2 > t1), thereby improving the pressure resistance while reducing the plate thickness of the plate material. Patent Document 1 also describes that the plate thickness t3 of the chuck wall radius portion is made greater than the plate thickness t1 of the center panel portion (t3 > t1), indicating the necessary range for improving the pressure resistance.

[0005] Japanese Patent Application Laid-Open No. 2022-16093

[0006] However, when forming an annular protrusion on a sheet material using a conventional method, such as the method for manufacturing a can lid described in Patent Document 1, if the annular protrusion is formed in a single stroke using upper and lower dies, the sheet thickness of the inner periphery of the annular protrusion increases significantly, making it impossible to increase the sheet thickness of the annular protrusion over a wide range. To increase the sheet thickness of the annular protrusion over a wide range using the conventional method, the central sheet portion must be pressed relative to the central sheet portion in multiple stages, and different shaped dies must be used for each stage, making the manufacturing process complicated.

[0007] Furthermore, the relative pressing (pressing) of the sheet material not only increases its thickness but also attempts to release stress through deformation and material flow, but with conventional methods, the material of the sheet material tends to flow toward the outer wall, making it difficult to maintain the required shape for, for example, a can lid or can bottom. In other words, the range in which relative pressing can be performed while maintaining the shape is narrow, and depending on the required performance, there are cases in which a sufficient increase in sheet thickness cannot be achieved.

[0008] The present invention addresses these circumstances by providing a method for forming a sheet material, a method for forming a can lid, and a method for forming a can bottom that are capable of increasing the sheet thickness of the annular protrusion over a wide range, including the required range, through a simple manufacturing process while preventing unintended deformation of the material due to relative pressing (pressing).

[0009] The method for forming a plate material of the present invention comprises the steps of forming a specific plate portion and a side wall portion, forming an annular curved portion connected to the side wall portion, and deforming at least the annular curved portion to form an annular protrusion having a selectively increased plate thickness, wherein in the step of forming the annular protrusion, the annular curved portion is supported by a support member that is relatively movable in a second direction opposite to a first direction in which the annular protrusion to be formed protrudes, and a pressing force in the first direction is applied to the specific plate portion, thereby generating a compressive stress in the second direction in the side wall portion, and moving at least a portion of the plate material that constituted the side wall portion on the support surface of the support member, thereby forming the annular protrusion having a selectively increased plate thickness.

[0010] The sheet material forming method of the present invention includes the steps of forming a central protrusion consisting of a central sheet portion and a side wall portion on its outer periphery in a plate-like portion of the sheet material, forming an outer peripheral curved portion on the outer periphery of the side wall portion, and deforming at least the outer peripheral curved portion to form an annular protrusion having a selectively increased sheet thickness, wherein the step of forming the annular protrusion includes supporting the outer peripheral curved portion with a support member movable relative to the protruding direction of the central protrusion, applying a pressing force to the central protrusion in a direction opposite to the protruding direction, thereby generating a compressive stress in the side wall portion in the protruding direction, and moving at least a portion that constituted the side wall portion on the support surface of the support member, thereby forming the annular protrusion having a selectively increased sheet thickness. The can end forming method of the present invention is characterized in that it includes the sheet material forming method of the present invention having such characteristics as part of its overall steps. The can bottom forming method of the present invention is characterized in that it includes the sheet material forming method of the present invention having such characteristics as part of its overall steps.

[0011] The present invention relates to a sheet metal forming method including the steps of forming a central sheet metal portion and forming an outer peripheral sheet metal portion via a sidewall portion rising upward on the outer periphery of the central sheet metal portion, forming an annular curved portion on the inner periphery of the sidewall portion, and deforming at least the annular curved portion to form an annular protrusion having a selectively increased sheet thickness, wherein the annular protrusion forming step supports the annular curved portion with a support member relatively movable in a second direction opposite to a first direction in which the annular protrusion to be formed protrudes, applying a pressing force in the first direction to the outer peripheral sheet metal portion to generate a compressive stress in the second direction in the sidewall portion, and moving at least a portion of the sheet metal constituting the sidewall portion on a support surface of the support member to form the annular protrusion having a selectively increased sheet thickness. The present invention also relates to a can end forming method that includes the sheet metal forming method of the present invention having the above-mentioned characteristics as part of its overall steps. The present invention also relates to a can bottom forming method that includes the sheet metal forming method of the present invention having the above-mentioned characteristics as part of its overall steps.

[0012] According to the present invention, the plate thickness of the annular protrusion can be increased over a wide range, including the required range, using a simple manufacturing process, while preventing unintended deformation of the material due to relative pressing (pressing).

[0013] FIG. 1 is a side view of a plate material having an annular protrusion in a first schematic embodiment; FIG. 2 is a flow diagram showing a forming process of a plate material having an annular protrusion in a first schematic embodiment; FIG. 3 is an explanatory diagram of a forming process of a plate material having an annular protrusion in a first schematic embodiment; FIG. 4 is a side view of a can lid in the first embodiment; FIG. 5 is a flow diagram showing a forming process of a can lid in the first embodiment; FIG. 6 is a first explanatory diagram of the forming process of a can lid in the first embodiment; FIG. 7 is a side cross-sectional view showing a schematic configuration of a forming device used in the forming process of a can lid in the first embodiment; FIG. 8 is an explanatory diagram of an annular protrusion forming (plate thickness increasing forming) process and a can lid shape forming process in the forming process of a can lid in the first embodiment; FIG. 9 is a first explanatory diagram of an annular protrusion forming (plate thickness increasing forming) process in the forming process of a can lid in the first embodiment; FIG. 10 is a second explanatory diagram of an annular protrusion forming (plate thickness increasing forming) process in the forming process of a can lid in the first embodiment; 14A is a partial end view partially showing a side end surface of a can lid preform after the annular protrusion forming (plate thickness increasing) process in the first embodiment. FIG. 14B is an explanatory diagram of the annular protrusion forming (plate thickness increasing) process in an example of the first embodiment. FIG. 14C is a diagram showing the lip height [mm] versus the support force [kN] in an example of the first embodiment. FIG. 14D is a partial end view partially showing a side end surface of a can lid preform after the annular protrusion forming (plate thickness increasing) process in an example of the first embodiment. FIG. 14A is a partial enlarged view showing a part of FIG. 14A. FIG. 14C is a diagram showing the plate thickness [mm] at measurement points A to F of the annular protrusion versus the support force [kN] during the annular protrusion forming (plate thickness increasing) process in an example of the first embodiment. FIG. 14D is an explanatory diagram of the can bottom forming process in the second embodiment. FIG. 14C is a side view of a plate material having an annular protrusion in the second schematic form. FIG. 14D is a flow chart showing the forming process of a plate material having an annular protrusion in the second schematic form. FIG. 14D is a first explanatory diagram of the forming process of a plate material having an annular protrusion in the second schematic form. 10 is a second explanatory diagram of a forming process of a plate material having an annular protrusion in a second schematic embodiment; FIG. 11 is a side view of a can lid in a third embodiment; FIG. 12 is a flow chart showing a forming process of a can lid in a third embodiment; FIG. 13 is a first explanatory diagram of a forming process of a can lid in a third embodiment;1 is a second explanatory diagram of the can lid forming process in the third embodiment; 2 is a third explanatory diagram of the can lid forming process in the third embodiment; 3 is a side cross-sectional view showing the schematic configuration of a forming device used in the can lid forming process in the third embodiment; 4 is a partial end view partially showing the intermediate formed body used in Examples 1 to 5 of the third embodiment, showing measurement points a to v for the plate thickness [mm]. (a) shows measurement points a to e and p to v. (b) is an enlarged view of a partial region (region surrounded by a square frame) including the chuck wall radius portion shown in (a), showing measurement points f to o. 5 is a diagram showing the plate thickness [mm] measured for each support force (countersink holding force) [kgf] at measurement points a to v in Examples 1 to 5; and 6 is a table showing the values ​​of the lid diameter, shape, original plate thickness [mm], support force (countersink holding force) [kgf], UD [mm], PH [mm], and pressure resistance value [MPa] for formed cans formed in Examples 6 to 8 of the third embodiment and Comparative Example 1. 10 is a diagram for explaining measurement points of UD [mm] and PH [mm] in formed cans formed in Examples 6 to 8 of the third embodiment and Comparative Example 1. FIG. 11 is a first explanatory diagram of the forming process of a can lid in the fourth embodiment. FIG. 12 is a second explanatory diagram of the forming process of a can lid in the fourth embodiment. FIG. 13 is a third explanatory diagram of the forming process of a can lid in the fourth embodiment. FIG. 14 is a first explanatory diagram of the forming process of a can bottom in the fifth embodiment. FIG. 15 is a second explanatory diagram of the forming process of a can bottom in the fifth embodiment. FIG. 16 is a partial end view partially showing an intermediate formed body of the can bottom used in Example 9 of the fifth embodiment. FIG. 17 is a partial end view partially showing a final formed body of the can bottom used in Example 9 of the fifth embodiment, showing measurement points w1 to w7 of the plate thickness [mm]. FIG. 18 is a table showing measurement results in Example 9 of the fifth embodiment.

[0014] Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. In the following description, the same reference numerals in different drawings indicate parts with the same function, and duplicate explanations in each drawing will be omitted as appropriate. In the following description, "approximately" means "substantially." For example, "approximately circular" means not only a "circular" (perfect circle), but also an elliptical shape or the like that is similar to a circle.

[0015] [Main Mode] A method for forming a sheet material according to a main mode (main mode) of the present invention is for forming a sheet material to become, for example, a can lid, a can bottom, etc. This sheet material forming method includes a step of forming a specific sheet portion to which a pressing force is applied in a first direction (downward) described below by an upper tool for the specific sheet portion, and a side wall portion connected to the specific sheet portion, a step of forming an annular curved portion connected to the side wall portion, and a step of deforming at least the annular curved portion to form an annular protruding portion having a selectively increased sheet thickness.

[0016] In the process of forming the annular protrusion, the annular curved portion is supported by a support member (support tool for the annular curved portion) that is relatively movable in a second direction (upward) opposite to a first direction (downward) in which the annular protrusion to be formed protrudes. In this state, an upper tool for the specific plate portion is lowered to apply a pressing force in the first direction to the specific plate portion.

[0017] This causes compressive stress in the second direction in the side wall portion, and moves at least a portion of the plate material that constitutes the side wall portion on the support surface of the support member (support tool for the annular curved portion).As a result, in the plate material forming method according to the main aspect, an annular protrusion is formed in which the plate thickness is selectively increased based on the moved portion.

[0018] The method of forming sheet material according to this main embodiment does not involve multiple stages in which the pressing is performed using molds of different shapes each time, but rather, with this simple manufacturing process, the thickness of the annular protrusion can be increased over a wide range, including the required range, while preventing unintended deformation of the material due to relative pressing (pressing).

[0019] [First General Form] A sheet material forming method according to a first general embodiment (first general form) of the present invention forms a formed material 1 shown in Fig. 1. The formed material 1 has a center panel portion (center plate portion) 12, which is a substantially circular, substantially flat surface located approximately at the center of a substantially disk-shaped sheet material 11, an annular protrusion portion 13 located on the outer periphery of the center panel portion (center plate portion), and an outer periphery panel portion (outer periphery plate portion) 14 located further on the outer periphery of the annular protrusion portion 13.

[0020] The plate material 11 is made of a material mainly made of metal. The material mainly made of metal is not particularly limited, but may be, for example, a single metal material such as aluminum, an aluminum alloy, or steel, or a clad material of these metals, or a composite metal material in which one or both sides of these metals are subjected to a surface treatment, painting, lamination, or the like.

[0021] A curved portion (curved end) 121 is formed on the outer edge (radially outer end) of the center panel portion (central plate portion) 12, and an inner circumferential wall portion 131 is formed to extend downward in a substantially linear manner from the terminal end (outer end) of the curved portion 121. The curved convex portion 132 is a curved portion formed so that its inner circumferential end (inner end) is connected to the lower end of the inner circumferential wall portion 131 and its outer circumferential end (outer end) is connected to the outer circumferential wall portion 133. The outer circumferential wall portion 133 extends upward in a substantially linear manner from the outer circumferential upper end (outer end) of the curved convex portion 132 and is formed to connect to a curved portion (curved end) 141 of the outer circumferential panel portion (outer circumferential plate portion) 14. The annular protrusion 13 is composed of the inner circumferential wall portion 131, the curved convex portion 132, and the outer circumferential wall portion 133.

[0022] As shown in Fig. 2, the forming process (forming method) of this formed material 1 includes a blank punching step S1, a central protrusion forming step S2, a peripheral curved portion forming step S3, and an annular protrusion forming (plate thickness increasing forming) step S4. In these forming steps (S1 to S4), the shape of the plate material 11 is changed as shown in states a1 to a5 in Fig. 3 to form the formed material 1 in state a6.

[0023] In the blank punching process S1, the shape of the plate material 11 to be processed is formed into an approximately disk shape (state a1 in Figure 3), although the shape varies depending on the target molded product (for example, it may be elliptical, polygonal, etc.). For example, upper and lower punching tools (not shown) are used to punch the plate material 11 into an approximately disk shape (state a1 in Figure 3).

[0024] In the central protrusion forming process S2, for example, using upper and lower central drawing tools (not shown) for drawing the approximately central portion of the approximately disk-shaped plate material 11, the outer peripheral panel portion (outer peripheral plate portion) 25 of the approximately disk-shaped plate material 11 is fixed while drawing the inner peripheral side thereof, thereby forming a central protrusion 22 consisting of a center panel portion (central plate portion) 23 corresponding to the ``specific plate portion'' described in the main form above and a side wall portion 24 on the outer peripheral side thereof, as shown in state a2 in Figure 3.

[0025] In the outer peripheral curved portion forming step S3 and the annular protrusion forming (thickness increase forming) step S4, for example, forming processing is performed on the plate material 11 on which the central protrusion 22 has been formed using an upper tool U1 and a lower tool L1. The upper tool U1 includes an annular upper outer tool U11, an upper central tool (upper tool for a specific plate portion) U12, and an annular side wall portion guide tool U13 located therebetween. The lower tool L1 includes an annular lower outer tool L11, a lower central tool L12, and an annular curved portion support tool (support member) L13 located therebetween.

[0026] In the outer peripheral curved portion forming step S3, as shown in state a3 in Figure 3, the sheet material 11 on which the central protrusion 22 consisting of the center panel portion 23 and side wall portions 24 has been formed is placed on the lower tool L1, and then the upper outer tool U11 is lowered. As a result, the outer peripheral panel portion (outer peripheral plate portion) 25 of the sheet material 11 is sandwiched and fixed between the abutment surfaces U11a of the upper outer tool U11 and L11a of the lower outer tool L11. This fixation of the outer peripheral panel portion (outer peripheral plate portion) 25 continues until the annular protrusion forming (plate thickness increasing) step S4 is completed.

[0027] In this state, in the outer peripheral curved portion forming process S3, the upper central tool U12 and the side wall guide tool U13 are lowered as shown in states a3 and a4 in Figure 3 . As the upper central tool U12 descends, it presses the lower central tool L12 down so that its contact surface U12a sandwiches the center panel portion 23 between itself and the contact surface L12a of the lower central tool L12 (state a4 in Figure 3 ). Furthermore, as the side wall guide tool U13 descends, the side wall portion 24, which slopes outward and downward, is positioned between the inner guide surface U13a of the side wall guide tool U13 and the outer guide surface L12b of the lower central tool L12. Positioning the side wall guide tool U13 and the lower central tool L12 around the side wall portion 24 prevents buckling of the side wall portion 24 due to compressive stress applied to the side wall portion 24 in the subsequent annular protrusion forming (thickness increasing) process S4.

[0028] The upper central tool U12 descends so that the height position of its contact surface U12a approaches the height position of the contact surface (support surface) L13a of the curvature portion support tool (support member) L13. That is, the curvature portion support tool (support member) L13 is relatively movable in the protruding direction of the central protrusion 22 (upward, a second direction opposite to the first direction in which the annular protrusion 13 (state a5 in FIG. 3 ) to be formed later protrudes). The curvature portion support tool L13 applies a support force to the sheet material 11 on its contact surface (support surface) L13a in this protruding direction (second direction). Therefore, as the upper central tool U12 and the side wall guide tool U13 descend, the outer periphery of the side wall portion 24 is supported by the curvature portion support tool L13 that applies this support force, forming an outer periphery curved portion (annular curved portion) 26 having a curved shape that conforms to the shape of the contact surface L13a. In this manner, a preform 11a having an outer peripheral curved portion (annular curved portion) 26 is formed from the plate material 11 (state a4 in FIG. 3).

[0029] In the annular protrusion molding (plate thickness increasing molding) process S4, for example, as shown in states a4 and a5 in Figure 3, while the outer peripheral curved portion (annular curved portion) 26 of the molded preform 11a is supported by the abutment surface (support surface) L13a of the curved portion support tool (support member) L13, a pressing force is applied to the central protrusion 22 in the direction opposite to its protruding direction (second direction) (downward, the first direction in which the annular protrusion 13 (state a5 in Figure 3) to be molded later protrudes).

[0030] At this time, the upper central tool U12 continuously descends, pressing down the lower central tool L12 with its abutment surface U12a. This applies a pressing force to the center panel portion (specific plate portion) 23 sandwiched between the abutment surface U12a and the abutment surface L12a of the lower central tool L12, pushing the center panel portion 23 downward (in the first direction). At the same time, the side wall portion guide tool U13 positions the side wall portion 24 between its inner guide surface U13a and the abutment surface L12b of the lower central tool L12, thereby preventing the side wall portion 24 from buckling due to the compressive stress applied to the side wall portion 24. This allows the upper central tool U12 to apply a pressing force greater than the support force of the curved portion support tool L13 to the outer circumferential curved portion (annular curved portion) 26 via the side wall portion 24.

[0031] The formation of the annular protrusion (thickness increase formation) by such continuous descent of the upper central tool U12 and the side wall guide tool U13 deforms the outer circumferential curved portion (annular curved portion) 26, and generates compressive stress in the protruding direction (second direction) in the side wall portion 24, while moving at least a portion that constitutes the side wall portion 24 on the contact surface L13a of the curved portion support tool L13 outward from the central protrusion 22. As a result, the annular protrusion 13 is formed with a selective increase in thickness based on the moved portion (state a5 in FIG. 3 ).

[0032] After forming the formed workpiece 1 having this annular protrusion 13, the formed workpiece 1 is removed from the upper tool U1 and the lower tool L1 to obtain the formed workpiece 1 in state a6 in Figure 3. In the formed workpiece 1, the annular protrusion 13 has an increased thickness over a wide area, including the curved convex portion 132 between the inner peripheral wall portion 131 and the outer peripheral wall portion 133. Note that the example of state a6 in Figure 3 shows the outer peripheral panel portion (outer peripheral plate portion) 25 and the center panel portion (central plate portion) 23 at approximately the same height, but this is not limited to this example. The height positions of the outer peripheral panel portion 25 and the center panel portion 23 may be different as necessary. For example, the height position of the outer peripheral panel portion 25 may be lower than the height position of the center panel portion 23.

[0033] In this way, in the forming method of the sheet material 11 of the first general form, the center panel portion (specific sheet portion) 23 is continuously (in one stroke) pressed relative to the center panel portion (specific sheet portion) 23 using the same device (upper and lower dies) having the upper tool U1 and the lower tool L1. In other words, the forming method of the first general form does not perform this pressing in multiple stages using dies of different shapes each time, but rather can form the annular protrusion 13 with an increased sheet thickness over a wide range, including the required range, using this simple manufacturing process.

[0034] Instead of the example described here, the forming process of the formed material 1 may use the same apparatus (upper and lower dies) consistently from the blank punching process S1 to the annular protrusion forming (thickness increasing) process S4. Alternatively, the forming process of the formed material 1 may use an apparatus (upper and lower dies) different from the apparatus (apparatus having an upper tool U1 and a lower tool L1) used in the annular protrusion forming (thickness increasing) process S4 from the blank punching process S1 to the outer peripheral curved portion forming process S3. In this case, the preforms 11a are prepared in advance in this different apparatus, and the preforms 11a are sequentially placed between the upper tool U1 and the lower tool L1.

[0035] Furthermore, in the first general embodiment, an example has been described in which the upper central tool U12 is lowered relative to the curvature support tool (support member) L13 so as to approach the curvature support tool (support member) L13, but the present invention is not limited to this. The curvature support tool (support member) L13 is movable relative to the protrusion direction (upward direction, second direction) of the central protrusion 22. Therefore, instead of the example described here, the curvature support tool (support member) L13 may be raised relative to the upper central tool U12 so as to approach the upper central tool U12, thereby applying a pressing force in the protrusion direction (second direction) to the plate material 11 on the abutment surface (support surface) L13a.

[0036] In this case, the center panel portion 23 is sandwiched and fixed between the upper central tool U12 and the lower central tool L12, and in this state, the lower outer tool L11 and the curved portion support tool (support member) L13 rise so as to push up the upper outer tool U11 and the side wall portion guide tool U13. As a result, an outer circumferential curved portion (annular curved portion) 26 having a curved shape that follows the shape of the contact surface L13a of the curved portion support tool L13 is formed on the outer periphery of the side wall portion 24, and then the annular protrusion 13 is formed.

[0037] Next, first and second embodiments of the present invention will be described. In the first and second embodiments, the description of the same configuration as the first general embodiment or the same configuration as each other will be omitted.

[0038] [First Embodiment] In the first embodiment, a sheet material forming method is used to form a can lid 3, as shown in Fig. 4, as a formed material. The can lid 3 has a center panel portion (central plate portion) 31, a panel wall portion (inner peripheral wall portion) 321, a chuck wall radius portion (curved convex portion) 322, a chuck wall portion consisting of a first chuck wall portion (first outer peripheral wall portion) 323 and a second chuck wall portion (second outer peripheral wall portion) 33, and a curl portion 34. Here, the panel wall portion 321, the chuck wall radius portion 322, and the first chuck wall portion 323 form an annular protrusion 32.

[0039] The center panel portion (central plate portion) 31 is located approximately in the center of the can lid 3 and consists of a substantially circular, substantially flat surface. If the can lid 3 is a stay-on-tab type, the center panel portion 31 is provided with a tab, score, or the like for opening.

[0040] A curved portion (curved end portion) 311 is formed on the outer edge (radially outer end portion) of the center panel portion 31, and a panel wall portion (inner peripheral wall portion) 321 is formed so as to extend downward in a substantially straight line from the terminal end (outer end) of the curved portion 311. The chuck wall radius portion (curved convex portion) 322 is a curved portion formed so that its inner peripheral end portion (inner end) is connected to the lower end of the panel wall portion 321 and its outer peripheral end portion (outer end) is connected to a first chuck wall portion (first outer peripheral wall portion) 323.

[0041] The first chuck wall portion (first outer peripheral wall portion) 323 extends upward in a substantially linear manner from the upper end (outer end) on the outer peripheral side of the chuck wall radius portion (curved convex portion) 322. The second chuck wall portion (second outer peripheral wall portion) 33 extends in a substantially linear manner from the upper end (outer end) on the outer peripheral side of the first chuck wall portion 323 so as to be inclined upward and outward, and its upper end is formed so as to connect to the curved portion of the curl portion 34.

[0042] This method for forming can lids 3 includes, as part of all steps, the method for forming the sheet material 11 in the first general embodiment described above. That is, as shown in Fig. 5, this method for forming can lids 3 includes a blank punching step S11, a peripheral drawing step S12, a central protrusion forming step S13, a peripheral curved portion forming step S14, an annular protrusion forming (thickness increasing) step S15, and a can lid shape forming step S16. In these forming steps (S11 to S16), the shape of the sheet material 41 is changed as shown in states a11 to a18 in Figs. 6 and 7 to form the can lid 3 in state a19 in Fig. 7.

[0043] In the blank punching step S11, for example, upper and lower punching tools (not shown) for punching the plate material 41 to be processed into a substantially disk shape are used to form the plate material 41 into a substantially disk shape (state a11 in FIG. 6).

[0044] The plate material 41 is made of a material mainly composed of metal. The metal material is not particularly limited, but may be, for example, a single metal material such as aluminum, an aluminum alloy, or steel, or a clad material of these metals, or a composite metal material in which one or both sides of these metals are subjected to a surface treatment, painting, lamination, or the like.

[0045] In the outer periphery drawing step S12, for example, using an upper and lower outer periphery drawing tool (not shown) for drawing the outer periphery of the substantially disk-shaped plate material 41, the outer periphery is drawn while fixing a plate-like portion on the inner periphery side of the outer periphery of the substantially disk-shaped plate material 41 shown in state a11 in Fig. 6. As a result, an outer periphery (side surface) 43 extending in a direction substantially perpendicular (downward) to the plate-like portion 42 is formed on the outer periphery side of the plate-like portion 42 of the plate material 41, as shown in state a12 in Fig. 6.

[0046] In the central protrusion forming step S13, for example, for the sheet material 41 in state a12 of FIG. 6 , upper and lower center drawing tools (not shown) for drawing the approximately central portion of the plate-shaped portion 42 are used to draw the inner periphery of the outer panel portion 420, which is the outer peripheral portion of the plate-shaped portion 42, while fixing the outer panel portion 420. As a result, as shown in state a13 of FIG. 6 , a central protrusion 44 is formed on the inner periphery of the outer peripheral panel portion (outer peripheral plate portion) 421 of the sheet material 41, the central protrusion 44 being composed of a center panel portion (central plate portion) 45, which corresponds to the "specific plate portion" described in the main embodiment above, and a side wall portion 46 on the outer periphery of the center panel portion (central plate portion) 45. The shape of the center panel portion (central plate portion) 45 is not particularly limited, but may have a curved (dome-like) shape that protrudes gently in the protruding direction of the central protrusion 44 (a second direction opposite to the first direction in which the annular protrusion 32a (state a16 of FIG. 6 ), which will be formed later, protrudes), as exemplified in FIG. 6 .

[0047] In the outer peripheral curved portion forming step S14 and the annular protrusion forming (thickness increase forming) step S15, the plate material 41 (state a13 in FIG. 6 ) on which the central protrusion 44 has been formed is formed using a forming device M1 having an upper tool U2 and a lower tool L2, for example, as shown in FIG. 8 . As shown in FIG. 8 and state a14 in FIG. 6 , the upper tool U2 includes an annular upper outer tool U21, an upper central tool (upper tool for a specific plate portion) U22, and an annular side wall portion guide tool U23 positioned therebetween. The lower tool L2 includes an annular lower outer tool L21, a lower central tool L22, and an annular curved portion support tool (support member) L23 positioned therebetween.

[0048] 8, the molding device M1 has an upper tool U2 equipped with cushion pins Ua1 and Ua2 connected to an air cylinder, and a lower tool L2 equipped with cushion pins La1 and La2 connected to an air cylinder. In the upper tool U2, the upper central tool U22 and the side wall guide tool U23 can be moved up and down by the cushion pin Ua1 connected to the air cylinder, and the upper outer tool U21 can be moved up and down by the cushion pin Ua2 connected to the air cylinder.

[0049] In the lower tool L2, the lower central tool L22 and the curved portion support tool (support member) L23 can be moved up and down by cushion pins La1 connected to an air cylinder, and the lower outer tool L21 can be moved up and down by cushion pins La2 connected to an air cylinder. Note that the forming device M1 may be provided with elastic members such as spring members instead of the cushion pins Ua1, Ua2, La1, and La2 connected to such air cylinders.

[0050] In the outer peripheral curved portion forming step S14, as shown in state a14 in Figure 6, the plate material 41 with the central protrusion 44 formed therein is placed on the lower tool L2, and then the upper outer tool U21 is lowered. As a result, the outer peripheral panel portion (outer peripheral plate portion) 421 of the plate material 41 is sandwiched and fixed between the contact surfaces U21a of the upper outer tool U21 and L21a of the lower outer tool L21. This fixation of the outer peripheral panel portion (outer peripheral plate portion) 421 continues until the annular protrusion forming (plate thickness increasing) step S15 is completed.

[0051] In this state, in the outer periphery curved portion forming step S14, the upper central tool U22 and the side wall portion guide tool U23 are lowered. At this time, as shown in states a14 and a15 in Figure 6, the lowering of the upper central tool U22 presses down the lower central tool L22 so that the abutment surface U22a of the upper central tool U22 sandwiches the center panel portion 45 between the abutment surface L22a and the abutment surface U22a.

[0052] The upper central tool U22 descends so that the height position of its contact surface U22a approaches the height position of the contact surface (support surface) L23a of the curvature support tool (support member) L23. That is, the curvature support tool (support member) L23 is relatively movable in the protruding direction (upward, second direction) of the central protrusion 44. This curvature support tool L23 applies a support force to the plate material 41 on its contact surface (support surface) L23a in this protruding direction (second direction). Therefore, as the upper central tool U22 and the side wall guide tool U23 descend, a peripheral curved portion (annular curved portion) 47 having a curved shape that conforms to the shape of the contact surface L23a is formed on the outer periphery of the side wall portion 46 by being supported by the curvature support tool L23 that applies this support force. In this manner, a preform 41a having a peripheral curved portion (annular curved portion) 47 is formed from the plate material 41 (state a15 in FIG. 6 ).

[0053] In the annular protrusion molding (plate thickness increasing process) step S15 (state a15, state a16 in FIG. 6 ), for example, while the outer peripheral curved portion (annular curved portion) 47 of the molded preform 41a is supported by the abutment surface (support surface) L23a of the curved portion support tool (support member) L23, a pressing force is applied to the central protrusion 44 in the direction opposite to the protruding direction (downward, the first direction in which the annular protrusion 32a to be molded (state a16 in FIG. 6 ) protrudes).

[0054] At this time, the upper central tool U22 continuously descends, pressing the lower central tool L22 downward with its contact surface U22a. This applies a pressing force to the center panel portion (specific plate portion) 45 sandwiched between the contact surface U22a and the contact surface L22a of the lower central tool L22, pushing the center panel portion 45 downward (in the first direction). At the same time, the side wall portion guide tool U23 positions the side wall portion 46 between its inner guide surface U23a and the outer guide surface L22b of the lower central tool L22, thereby preventing the side wall portion 24 from buckling due to the compressive stress applied to the side wall portion 46. As a result, the upper central tool U22 applies a pressing force to the outer peripheral curved portion (annular curved portion) 47 via the side wall portion 46.

[0055] This pressing (thickness increasing forming) caused by the continuous descent of the upper central tool U22 and the side wall guide tool U23 presses the center panel portion 45 downward and deforms the outer circumferential curved portion (annular curved portion) 47. This thickness increasing forming also generates compressive stress in the side wall portion 46 in the protruding direction (second direction) of the central protrusion 44, and moves at least a portion that constitutes the side wall portion 46 outward from the central protrusion 44 on the contact surface L23a of the curved portion support tool L23.

[0056] The annular protrusion forming (thickness increasing forming) step S15 forms a can lid intermediate 30 (state a16 in FIG. 6 ) (before the can lid shape is formed) having an annular protrusion 32a whose thickness is selectively increased based on the moved portion. The annular protrusion 32a has an increased thickness over a wide range, including the chuck wall radius portion (curved convex portion) 322a.

[0057] As described above, in the method for forming the sheet material 41 of the first embodiment, the center panel portion 45 is continuously (in one stroke) pressed relative to one another using the same device (upper and lower dies) having the upper tool U2 and the lower tool L2. In other words, the forming method of the first embodiment does not perform this pressing in multiple stages using dies of different shapes each time, but rather, with this simple manufacturing process, it is possible to form the annular protrusion 32a in which the sheet thickness is increased over a wide range, including the required range.

[0058] After the intermediate can lid formed body 30 (before the can lid shape is formed) having the annular protrusion 32a is formed in this manner, the intermediate can lid formed body 30 is removed from the upper tool U2 and the lower tool L2.

[0059] The can lid shape forming step S16 is a step of reforming the shape of the can lid intermediate formed body 30 to form it into the shape of a can lid. This can lid shape forming step S16 includes a step of forming a chuck wall portion consisting of a first chuck wall portion (first outer peripheral wall portion) 323 and a second chuck wall portion (second outer peripheral wall portion) 33 shown in a later state a19.

[0060] The can lid shape forming process S16 may further include at least one or both of the following steps, in any order or simultaneously with the step of forming the chuck wall portion described above: a known step (not shown) of forming a curl portion 34 on the outer periphery of the annular protrusion 32a (or the annular protrusion 32 after forming) and a step of forming the center panel portion (central plate portion) 45 into a desired shape, for example, into a substantially flat surface.

[0061] In the can lid shaping step S16, as shown in state a17 in FIG. 7 , the shape of the can lid intermediate 30 is reformed using a can lid shaping device M2 having an upper tool U3 and a lower tool L3. The upper tool U3 has an upper outer tool U31, an upper central tool U32, and an annular processing tool U33 located therebetween. The lower tool L3 has an annular lower outer tool L31 and a lower central tool L32. The lower tool L3 also has an annular protrusion support tool L33 located between the lower outer tool L31 and the lower central tool L32.

[0062] In this can lid shaping step S16, as shown in state a17 in Fig. 7 , after placing the can lid intermediate formed body 30 (before the can lid is shaped) on the lower tool L3, the upper outer tool U31, the upper central tool U32, and the processing tool U33 may be lowered, for example, simultaneously to perform the can lid shaping step S16. Alternatively, depending on the shape of the can lid, the timing of the descent of the upper outer tool U31, the upper central tool U32, and the processing tool U33 may be changed as appropriate.

[0063] At this time, as the upper central tool U32 descends, the annular protrusion 32a is supported by the contact surface (support surface) L33a of the annular protrusion support tool L33, and the annular protrusion 32a between the lower central tool L32 and the lower outer tool L31 is formed into the annular protrusion 32 (state a18 in FIG. 7 ) having a shape that conforms to the contact surface (support surface) L33a of the annular protrusion support tool L33. That is, at this time, a first chuck wall portion (first outer peripheral wall portion) 323 (see state a19) of the chuck wall portion is formed.

[0064] At this time, the upper outer tool U31 descends, causing its contact surface U31a to come into contact with the outer peripheral panel portion (outer peripheral plate portion) 421 on the contact surface (support surface) L31b of the lower outer tool L31, thereby fixing the outer peripheral panel portion (outer peripheral plate portion) 421. In this state, the machining tool U33 descends, causing the outer peripheral panel portion (outer peripheral plate portion) 421 to be sandwiched between its contact surface U33a and the contact surface L31a, thereby forming a second chuck wall portion (second outer peripheral wall portion) 33 (see state a19) that conforms to the shapes of the lower outer tool L31 and the machining tool U33. In this way, a chuck wall portion (see state a19) consisting of the first chuck wall portion (first outer peripheral wall portion) 323 and the second chuck wall portion (second outer peripheral wall portion) 33 on its outer periphery is formed.

[0065] At this time, a curled portion 34 can also be formed on the outer periphery of the lid. In this case, the lower tool L3 may be provided with a curling tool (not shown) on the outer periphery of the lower outer tool L31. As described above, when the processing tool U33 is lowered with the outer periphery panel portion (outer periphery plate portion) 421 fixed, the outer periphery panel portion (outer periphery plate portion) 421 sandwiched between the abutment surface U33a and the abutment surface L31a of the processing tool U33 flows toward the outer periphery. When the curling tool (not shown) is lowered in this state, the curled portion 34 is formed in a shape that conforms to the abutment surface U31a of the upper outer tool U31 and the abutment surface (not shown) of the curling tool (not shown) (state a18 in FIG. 7 ).

[0066] At this time, the center panel portion (central plate portion) 45 can also be formed into a desired shape, for example, a substantially flat surface. That is, the upper central tool U32 descends so that its contact surface U32a presses down on the lower central tool L32, thereby forming the center panel portion (central plate portion) 45 sandwiched between the contact surface U32a and the contact surface L32a of the lower central tool L32 into a substantially flat center panel portion (central plate portion) 31 (state a18 in FIG. 7 ).

[0067] The can lid 3 reformed in this way is removed from the can lid shaping device M2 to obtain the can lid 3 shown in state a19 in Fig. 7. The reformed can lid 3 in state a19 has a shape in which the annular protruding portion 32, consisting of the panel wall portion (inner peripheral wall portion) 321, the chuck wall radius portion (curved convex portion) 322, and the first chuck wall portion (first outer peripheral wall portion) 323, protrudes approximately perpendicular to the extension direction of the center panel portion 31, which has been shaped into a substantially flat surface.

[0068] Here, the can lid shape forming process S16 in Figure 7 has been described as simultaneously including a process of forming the chuck wall portion and a process of forming the center panel portion (central plate portion) 45 into a substantially flat surface, but these processes may also be included in any order as separate steps.

[0069] The annular protrusion forming (thickness increasing) step S15 and the can lid shaping step S16 will now be described in further detail. In Fig. 9 , which is drawn without the upper tool, state b1 shows the shape of a portion of the preform 41a formed in the outer periphery curved portion forming step S14. In state b1, the center panel portion 45 is located above the uppermost position H, which is the vertical height of the outer periphery panel portion (outer periphery plate portion) 421.

[0070] In this annular protrusion forming (thickness increasing forming) process S15, as shown in FIG. 10A , the outer peripheral panel portion (outer peripheral plate portion) 421 of the preform 41a is sandwiched between an upper outer tool U21 and a lower outer tool L21 to create a restraint portion K1 and fix the outer peripheral panel portion (outer peripheral plate portion) 421. Then, in this state, an upward support force, as indicated by arrow Y101, is applied to the outer peripheral curved portion (annular curved portion) 47 by the abutment surface (support surface) L23a of the curved portion support tool L23. At this point, the preform 41a having this outer peripheral curved portion (annular curved portion) 47 has the shape shown in FIG. 11A .

[0071] Then, in this state, the upper central tool U22 and the side wall guide tool U23 are lowered. At this time, as shown by arrow Y91 in state b2 in Figure 9, the outer peripheral curved portion (annular curved portion) 47 of the preform 41a is supported by a supporting force from below, and a pressing force is applied to the center panel portion 45 of the preform 41a from above, as shown by arrow Y92. This pressing force from above and below generates compressive stress in the outer peripheral curved portion (annular curved portion) 47.

[0072] Then, in this annular protrusion forming (thickness increasing forming) process S15, the upper central tool U22 and the side wall guide tool U23 are further lowered. Due to this continuous lowering, as shown in states b2 and b3 in Figure 9, the downward (first direction) pressing force (by the upper central tool U22) indicated by arrow Y92 becomes greater than the upward (second direction) supporting force (by the curvature portion support tool L23) indicated by arrow Y91. This causes the curvature portion support tool L23 to be pressed down.

[0073] At this time, the upper central tool U22 applies a further downward pressing force, indicated by an arrow Y102, to the center panel portion 45 of the preform 41a, which presses the center panel portion 45 further downward as shown in Fig. 10B, thereby deforming the outer peripheral curved portion (annular curved portion) 47 shown in Fig. 10A.

[0074] 10B, a compressive stress is applied to the side wall portion 46 (FIG. 10A) in the protruding direction (upward, second direction) of the central protrusion 44 by the downward pressing force indicated by arrow Y103 from the upper central tool U22 and the upward supporting force indicated by arrow Y104 from the curvature portion support tool L23. As a result, as shown in FIG. 10B, at least a portion (FIG. 10A) that constituted the side wall portion 46 on the contact surface L23a of the curvature portion support tool L23 moves outward from the central protrusion 44 as indicated by arrow Y105, while generating a compressed portion K2 due to this compressive stress.

[0075] 11B is formed. This formed body 30a-1 has an annular protruding portion 32a consisting of a panel wall portion (inner peripheral wall portion) 321a, a chuck wall radius portion (curved convex portion) 322a, and a first chuck wall portion (first outer peripheral wall portion) 323a, and the plate thickness is increased over a wide range including the chuck wall radius portion 322a.

[0076] In this way, the intermediate formed can lid 30 (before the can lid is shaped) is formed as shown in state b3 in Fig. 9. As shown in state b3, in the intermediate formed can lid 30, the uppermost position of the center panel portion 45 is located below the uppermost position H of the outer peripheral panel portion (outer peripheral plate portion) 421.

[0077] Then, in the can lid shape forming step S16, as shown in state b4 in Figure 9, downward pressing forces indicated by arrows Y93 and Y94 are applied to the can lid intermediate formed body 30 to reform it. As a result, as shown in state b4, a can lid 3 is obtained that has a formed annular protrusion 32, a chuck wall portion, and a center panel portion (central plate portion) 31 consisting of a substantially flat surface. In the can lid 3, the formed annular protrusion 32 has an increased plate thickness within the required range, including the chuck wall radius portion 322.

[0078] Instead of the example described here, the can lid 3 forming process may use the same apparatus (upper and lower dies) consistently from the blank punching process S11 to the annular protrusion forming (thickness increasing) process S15. Alternatively, the can lid 3 forming process may use an apparatus (upper and lower dies) different from the apparatus (the apparatus having the above-mentioned upper tool U2 and lower tool L2) used in the annular protrusion forming (thickness increasing) process S15 from the blank punching process S11 to the outer periphery curved portion forming process S14. In this case, the preform 41a is prepared in advance in this different apparatus, and the preform 41a is placed between the upper tool U2 and the lower tool L2.

[0079] [Example of First Embodiment] Next, an example of the first embodiment will be described. In this example, as shown in Fig. 12, a can lid intermediate formed body 30A was formed using a previously formed preform (not shown) using a forming device M3. The preform was formed from a plate made of aluminum alloy (A5182P-H19, material plate thickness 0.235 mm) with a coating film formed on both sides.

[0080] The forming apparatus M3 in Figure 12 has the same configuration as the forming apparatus M1 described above. That is, in the forming apparatus M3, the upper tool U2A corresponds to the upper tool U2 described above, and the lower tool L2A corresponds to the lower tool L2 described above. As a result, the upper outer tool U21A, the upper central tool U22A, and the side wall guide tool U23A correspond to the upper outer tool U21, the upper central tool U22, and the side wall guide tool U23 described above. Furthermore, the lower outer tool L21A, the lower central tool L22A, and the curvature portion support tool (support member) L23A correspond to the lower outer tool L21, the lower central tool L22, and the curvature portion support tool (support member) L23 described above.

[0081] Using this forming device M3, a process similar to the above-described annular protrusion forming (plate thickness increasing forming) step S15 was performed. That is, as shown in Fig. 12, a downward pressing force (8.0 kN) indicated by arrow Y202 was applied by the upper outer tool U21A to the lower outer tool L21A, thereby fixing the outer peripheral panel portion (outer peripheral plate portion) 421A sandwiched between the lower outer tool L21A and the upper outer tool U21A.

[0082] In this state, the lower central tool L22A and the curved portion support tool (support member) L23A supported the center panel 45A, which corresponds to the "specific plate portion" described above, and the portion that would become the annular protrusion 32A with the support force in the upward direction (second direction) indicated by arrows Y203 and Y204, while the upper central tool U22A and the side wall guide tool U23A were continuously lowered to continuously apply a pressing force in the downward direction (first direction) indicated by arrow Y201 (thickness increasing forming). This thickness increasing forming process formed the center panel 45A and the annular protrusion 32A.

[0083] In this way, an intermediate can lid formed body 30A (before the can lid shape was formed) was obtained, which had a center panel portion 45A and an annular protrusion portion 32A having a chuck wall radius portion (curved convex portion) 322A on its outer periphery.

[0084] In FIG. 12, LH (Lip Height) is the vertical length [mm] from the uppermost position to the outermost tip of the outer peripheral panel portion (outer peripheral plate portion) 421A.

[0085] In this example, the plate thickness increasing forming was performed by varying the support force [kN] in the upward direction (second direction) indicated by the arrow Y204 by the curved portion support tool (support member) L23A. The measured values ​​of the lip height (LH in FIG. 12) [mm] for each value of the support force [kN] are shown in FIG.

[0086] In Figure 13, the black circles indicate the values ​​of lip height (mm). As shown in Figure 13, there was no significant change in the value of lip height (mm) even when the bearing capacity (kN) was increased. This result indicates that the increased thickness formation did not affect the shape of the outer peripheral panel portion (outer peripheral plate portion) 421A.

[0087] Fig. 14A shows a portion of a can lid formed in this example. Fig. 14B shows an enlarged view of the annular protrusion 32A in Fig. 14A, illustrating the panel wall portion (inner peripheral wall portion) 321A, the chuck wall radius portion (curved convex portion) 322A, and the first chuck wall portion (first outer peripheral wall portion) 323A that constitute the annular protrusion 32A. Also, in Fig. 14B, measurement points for the plate thickness [mm] of the annular protrusion 32A are indicated by A to F.

[0088] In this example, the thickness [mm] of the annular protrusion 32A of the can lid formed as shown in Figure 14 was measured at measurement points A to F (Figure 14B) for each value of the upward support force [kN] indicated by arrow Y204 (Figure 12) by the curved portion support tool (support member) L23A during thickness increasing forming. The measurement results are shown in Figure 15.

[0089] According to this example, as shown in FIG. 15 , by increasing the support force [kN], the plate thickness [mm] was increased from the original plate thickness of 0.235 mm over a wide range of measurement points A to F on the annular protrusion 32A. In this example, when the support force was the highest at 8.9 kN, the plate thickness increased significantly compared to the original plate thickness over a wide range of measurement points A to F. Furthermore, as shown in FIG. 15 , the plate thickness was sufficiently increased at measurement points B to E within the range of the chuck wall radius portion (curved convex portion) 322A. Thus, in this example, the plate thickness increase process in a single step was able to increase the plate thickness not only on the inner periphery of the annular protrusion but also over the required range, including the outer periphery of the annular protrusion.

[0090] [Second embodiment] A method for forming a sheet material in a second embodiment forms a can bottom 6 shown in state a27 of Fig. 16 as a formed material. This method for forming a can bottom 6 includes the method for forming a sheet material 11 in the first general embodiment as part of the overall process.

[0091] This can bottom 6 forming method includes the same steps as those shown in Fig. 5, i.e., the blank punching step S11, the outer peripheral drawing step S12, the central protrusion forming step S13, the outer peripheral curved portion forming step S14, the annular protrusion forming (plate thickness increasing forming) step S15, and the can bottom shape forming step S16, all of which are shown in Fig. 5. In these forming steps (S11 to S16), the shape of the plate material 51 is changed as shown in states a21 to a26 in Fig. 16, and then reformed to form the can bottom 6 in state a27.

[0092] In the blank punching step S11 in the process of forming the can bottom 6, for example, upper and lower punching tools (not shown) are used to punch the plate material 51 to be processed into an approximately disk shape, and the plate material 51 is formed into an approximately disk shape (state a21 in Figure 16).

[0093] In the outer periphery drawing step S12 in the process of forming the can bottom 6, for example, using upper and lower outer periphery drawing tools (not shown) for drawing the outer periphery of a substantially disk-shaped plate material 51, the outer periphery is drawn while fixing the plate-like portion inside the outer periphery of the substantially disk-shaped plate material 51 shown in state a21 in Fig. 16. As a result, an outer periphery (side surface) 53 extending in a direction substantially perpendicular (upward) to the plate-like portion 52 is formed on the outer periphery of the plate-like portion 52 of the plate material 51, as shown in state a22 in Fig. 16.

[0094] In the central protrusion forming step S13 in the can bottom 6 forming process, for example, a sheet material 51 in state a22 of FIG. 16 is formed using a central drawing upper and lower tools (not shown) for drawing the approximately central portion of the sheet-shaped portion 52. The outer panel portion (outer plate portion) 521 of the sheet-shaped portion 52 is formed into an annular curved bottom portion 522 that protrudes gently in the approximately vertical direction (downward), while being fixed, and then the inner peripheral side is drawn. As a result, as shown in state a23 of FIG. 16 , a central protrusion 54 is formed, which is composed of a dome panel portion (central plate portion) 55, which corresponds to the "specific plate portion" described in the main form above, and a side wall portion 56 on its outer periphery. The dome panel portion (central plate portion) 55 has a dome shape that protrudes gently in the protruding direction of the central protrusion 54 (upward, in a second direction opposite to the first direction in which the annular protrusion 62a (state a26 of FIG. 16 ) to be formed later protrudes).

[0095] In the outer peripheral curved portion forming step S14 and the annular protrusion forming (thickness increase forming) step S15, for example, a sheet material 51 (state a23 in FIG. 16 ) on which a central protrusion 54 has been formed is formed using a forming device having an upper tool U4 and a lower tool L4. As shown in state a24 in FIG. 16 , for example, the upper tool U4 includes an annular upper outer tool U41, an upper central tool (upper tool for a specific sheet portion) U42, and an annular side wall portion guide tool U43 located therebetween. The lower tool L4 includes an annular lower outer tool L41 and an annular curved portion support tool (support member) L42 located more inwardly than the annular lower outer tool L41.

[0096] In the outer peripheral curved portion forming step S14, for example, as shown in state a24 in Figure 16, the sheet material 51 with the formed central protrusion 54 is placed on the lower tool L4, and then the upper outer tool U41 is lowered. As a result, the annular curved bottom portion (corresponding to the outer peripheral panel portion) 522 of the sheet material 51 is sandwiched and fixed between the abutment surfaces U41a of the upper outer tool U41 and L41a of the lower outer tool L41. Note that the fixation of this annular curved bottom portion 522 continues thereafter until the annular protrusion forming (plate thickness increasing forming) step S15 is completed.

[0097] At the same time, in the outer periphery curved portion forming process S14, the upper central tool U42 and the side wall portion guide tool U43 are lowered. At this time, as shown in state a24 in Figure 16, the upper central tool U42 is lowered so that its contact surface U42a comes into contact with the dome panel portion 55.

[0098] The upper central tool U42 descends so that the height position of its contact surface U42a approaches the height position of the contact surface (support surface) L42a of the curvature support tool (support member) L42. That is, the curvature support tool (support member) L42 is relatively movable in the protruding direction (upward, second direction) of the central protrusion 54. When the plate material 51 is positioned on its contact surface L42a, the curvature support tool L42 applies a support force to the plate material 51 in the protruding direction (second direction). Therefore, as the upper central tool U42 and the side wall guide tool U43 descend, the outer periphery of the side wall 56 is supported by the curvature support tool L42 that applies this support force, forming a peripheral curved portion (annular curved portion) 57 that conforms to the shape of the contact surface L42a. In this manner, a preform 51a having a peripheral curved portion (annular curved portion) 57 is formed from the plate material 51 (state a25 in FIG. 16 ).

[0099] In the annular protrusion molding (plate thickness increasing molding) process S15 (state a25, state a26 in Figure 16), for example, while the outer peripheral curved portion (annular curved portion) 57 of the molded preform 51a is supported by the abutment surface (support surface) L42a of the curved portion support tool (support member) L42, a pressing force is applied to the central protrusion 54 consisting of the dome panel portion 55 and the side wall portion 56 in the direction opposite to the protruding direction (downward, first direction).

[0100] At this time, the upper central tool U42 continuously descends so as to press down the dome panel portion 55 with its abutment surface U42a, thereby applying a pressing force to the dome panel portion (specific plate portion) 55, and by lowering this dome panel portion 55, applying a pressing force to the outer peripheral curved portion (annular curved portion) 57 located between the tip abutment portion U43a and the abutment surface L42a.

[0101] This pressing (thickness increasing forming) caused by the continuous descent of the upper central tool U42 and the side wall guide tool U43 presses the dome panel portion 55 downward and deforms the outer circumferential curved portion (annular curved portion) 57. This thickness increasing forming also generates compressive stress in the side wall portion 56 in the protruding direction (second direction) of the central protrusion 54, and moves at least a portion that constitutes the side wall portion 56 on the abutment surface L42a of the curved portion support tool L42 outward from the central protrusion 54.

[0102] This annular protrusion forming (thickness increasing forming) step S15 forms a can bottom intermediate formed body 60 (state a26 in FIG. 16 ) (before the can bottom is shaped) having an annular protrusion 62a whose thickness is selectively increased based on the moved portion. This annular protrusion 62a has an increased thickness over a wide range, including a so-called bottom radius portion 622a. Thereafter, the formed can bottom intermediate formed body 60 (before the can bottom is shaped) is removed from the upper tool U4 and the lower tool L4.

[0103] In this way, in the forming method of the plate material 51 of the second embodiment, the dome panel portion (specific plate portion) 55 is continuously (in one stroke) pressed relative to the plate material 51 using the same device (upper and lower dies) having the upper tool U4 and the lower tool L4. In other words, the forming method of the second embodiment also does not perform this pressing in multiple stages using dies of different shapes each time, but rather, with this simple manufacturing process, it is possible to form the annular protrusion 62a with an increased plate thickness within the required range.

[0104] The can bottom shape forming step S16 is a step of reforming the shape of the can bottom intermediate formed body 60 as necessary to form it into the shape of the can bottom, and this step includes a step of forming the shape of the can bottom annular protrusion 62. After reforming in this can bottom shape forming step S16, the can bottom 6 is removed from the reforming device (not shown) to obtain the can bottom 6 (state a27 in Figure 16).

[0105] The can bottom shaping step S16 can be carried out by a conventionally known method, for example, a method using a rotating roll or a method using press molding.

[0106] In the second embodiment, if an inner surface painting step is particularly required, it is desirable to perform this step prior to the can lid shape forming step S16.

[0107] The can bottom 6 in state a27 has a dome panel portion (central plate portion) 61, a dome panel wall portion (inner peripheral wall portion) 621, a bottom radius portion (curved convex portion) 622, a chime lower portion (first outer peripheral wall portion) 623, and a chime portion (second outer peripheral wall portion) 63. Here, the dome panel wall portion 621, the bottom radius portion 622, and the chime lower portion 623 form the can bottom annular protrusion 62. The can bottom annular protrusion 62 has a shape that is slightly inwardly inclined due to reforming, and the plate thickness has been increased within the necessary range, including the bottom radius portion 622.

[0108] Note that the can bottom shape forming step S16 may further include a step of forming the dome panel portion (central plate portion) 55 into a desired shape, such as a shape other than a spherical surface, such as a substantially spheroidal surface, a substantially conical surface, a substantially flat surface, etc. In this case, the can bottom shape forming step S16 may include, simultaneously or in any order, a step of forming the shape of the can bottom annular protrusion 62 and a step of forming the dome panel portion (central plate portion) 55 into, for example, a substantially flat surface, as a step of reforming the shape of the can bottom intermediate formed body 60 in state a26 in Figure 16 .

[0109] [Second General Form] A sheet material forming method according to a second general embodiment (second general form) of the present invention forms a formed piece 1E, as shown in Fig. 17. The formed piece 1E is formed from a substantially disk-shaped sheet material 11E. This formed piece 1E has a center panel portion (center plate portion) 12E which is a substantially circular, substantially flat surface located approximately in the center of the sheet material 11E, an annular protrusion portion 13E located on the outer periphery of the center panel portion 12E, and an outer peripheral panel portion (outer peripheral plate portion) 14E located further on the outer periphery of the center panel portion 12E.

[0110] The plate 11E is made of a material mainly made of metal. The material mainly made of metal is not particularly limited, but may be, for example, a single metal material such as aluminum, an aluminum alloy, or steel, or a clad material of these metals, or a composite metal material in which one or both sides of these metals are subjected to a surface treatment, painting (paint containing a lubricant, etc.), lamination, etc.

[0111] A curved end 121E is molded as the radially outer end (outer edge) of the center panel portion (central plate portion) 12E, and an inner peripheral wall portion 131E is molded to extend downward in a substantially linear fashion from the outer end (terminal end) of the curved end 121E. The curved convex portion 132E is a curved portion molded so that its inner end (inner peripheral end) connects to the lower end of the inner peripheral wall portion 131E and its outer end (outer peripheral end) connects to the lower end of the outer peripheral wall portion 133E. The outer peripheral wall portion 133E extends upward in a substantially linear fashion from the outer end (upper end on the outer peripheral side) of the curved convex portion 132E and connects to a curved end (curved portion) 141E molded as the radially inner end of the outer peripheral panel portion (outer peripheral plate portion) 14E. The annular protrusion 13E is composed of the inner peripheral wall portion 131E, the curved convex portion 132E, and the outer peripheral wall portion 133E.

[0112] The forming process (forming method) of the plate material 11E for forming this formed material 1E includes, for example, a blank punching process S31, a central-peripheral plate portion forming process S32, an annular curved portion forming process S33, and an annular protrusion forming (plate thickness increasing forming) process S34, as shown in Fig. 18. In these forming processes (S31 to S34), the shape of the plate material 11E is changed as shown in states m1 to m6 in Figs. 19 and 20 to form the formed material 1E in state m7 in Fig. 20.

[0113] In the blank punching process S31, the shape varies depending on the target molded product (for example, it may be elliptical, polygonal, etc.), but for example, the plate material 11E to be processed is formed into an approximately disk shape using upper and lower punching tools (not shown) for punching the plate material 11E into an approximately disk shape (state m1 in Figure 19).

[0114] In the central-periphery plate portion forming step S32, for example, upper and lower central drawing tools (not shown) for drawing the approximately central portion of the approximately disk-shaped plate material 11E are used to apply a blank-holding force to the outer peripheral portion of the approximately disk-shaped plate material 11E (the later outer peripheral panel portion (outer peripheral plate portion) 21E), while drawing the inner peripheral side of the outer peripheral portion. As a result, as shown in state m2 in Figure 19, a center panel portion (central plate portion) 22E is formed, and via side wall portions 23E that rise upward on the outer peripheral side of the center panel portion 22E, the outer peripheral panel portion (outer peripheral plate portion) 21E, which corresponds to the "specific plate portion" described in the previous main form, is formed.

[0115] In the annular curved portion forming process S33 and the annular protrusion forming (thickening forming) process S34, the plate material 11E (state m3 in FIG. 19 ) on which the center panel portion (central plate portion) 22E and the outer peripheral panel portion (outer peripheral plate portion) 21E have been formed is formed using an upper tool U5 located above it and a lower tool L5 located below it. The upper tool U5 includes an annular upper outer tool (upper tool for a specific plate portion) U51, an upper central tool U52, and an annular guide tool U53 located therebetween. The lower tool L5 includes an annular lower outer tool L51, a lower central tool L52, and an annular support tool (support member) L53 located therebetween.

[0116] In the annular curved portion forming step S33, the sheet material 11E with the center panel portion 22E and outer peripheral panel portion 21E formed thereon is placed on the lower tool L5 (state m3 in FIG. 19 ). The center panel portion (central plate portion) 22E of the sheet material 11E is then sandwiched and fixed between the abutment surfaces U52a of the upper central tool U52 and L52a of the lower central tool L52 (state m4 in FIG. 19 ). This fixation of the center panel portion 22E continues until the annular protrusion forming (plate thickness increasing) step S34 is completed.

[0117] In this state, in the annular curved portion forming step S33, as shown in state m4 in Fig. 19 and state m5 in Fig. 20, the upper outer tool U51 applies a pressing force in a first direction (downward), which is the direction in which the annular protrusion 13E (state m6 in Fig. 20) to be formed later protrudes. At this time, the upper outer tool U51 presses down the lower outer tool L51 while sandwiching the outer peripheral panel portion (outer peripheral plate portion) 21E between the abutment surface U51a of the upper outer tool U51 and the abutment surface L51a of the lower outer tool L51.

[0118] The guide tool U53 may or may not descend, as shown in state m4 in Fig. 19 and states m5 and m6 in Fig. 20. In either case, the guide tool U53 and the lower outer tool L51 are positioned around the side wall portion 23E. This prevents buckling of the side wall portion 23E due to compressive stress when the side wall portion 23E is subjected to compressive stress in the subsequent annular protrusion forming (thickness increasing) process S34.

[0119] In this annular curved portion forming process S33, the upper outer tool U51 presses down the lower outer tool L51 so that the height position of its contact surface U51a approaches the height position of the contact surface (support surface) L53a of the support tool (support member) L53. That is, the support tool L53 is relatively movable in a second direction (upward), which is the opposite direction to the first direction (downward). The support tool L53 applies a support force in this second direction (upward) to the plate material 11E on its contact surface (support surface) L53a. Therefore, by pressing down the lower outer tool L51 with the upper outer tool U51, the inner periphery of the side wall portion 23E is supported by the support tool L53 that applies this support force, forming an annular curved portion 24E that curves along the shape of the contact surface L53a. The plate material 11E with such an annular curved portion 24E formed therein is referred to as the preform 11Ea (state m5 in FIG. 20 ).

[0120] In the annular protrusion molding (plate thickness increasing molding) process S34, for example, as shown in states m5 and m6 in Figure 20, the annular curved portion 24E of the molded preform 11Ea is supported by the abutment surface (support surface) L53a of the support tool (support member) L53 (by a support force directed in the second direction (upward)), while a pressing force is applied in the first direction (downward) to the outer peripheral panel portion (outer peripheral plate portion, specific plate portion) 21E.

[0121] At this time, the upper outer tool U51 continuously applies a pressing force in a first direction (downward) so as to press down the lower outer tool L51 with its abutment surface U51a. That is, the upper outer tool U51 continuously applies a pressing force to the outer peripheral panel portion (outer peripheral plate portion) 21E sandwiched between the abutment surface U51a and the abutment surface L51a of the lower outer tool L51, thereby pressing the outer peripheral panel portion 21E in the first direction (downward). At the same time, the guide tool U53 positions the side wall portion 23E between its outer guide surface U53a and the abutment surface L51b of the lower outer tool L51, thereby preventing the side wall portion 23E from buckling due to the compressive stress applied to the side wall portion 23E. As a result, the support force of the support tool (support member) L53 can apply a greater pressing force to the annular curved portion 24E via the side wall portion 23E than the upper outer tool U51.

[0122] In this manner, the support tool L53 applies a support force in a second direction (upward) opposite to the first direction (downward) along which the annular protrusion 13E (state m6 in FIG. 20 ) to be formed protrudes, while the upper outer tool U51 presses in. This deforms the annular curved portion 24E and generates compressive stress in the second direction (upward) in the side wall portion 23E, displacing at least a portion of the plate material constituting the side wall portion 23E on the contact surface L53a of the support tool L53 toward the inside of the outer peripheral panel portion (outer peripheral plate portion) 21E. As a result, the annular protrusion 13E is formed with a selective increase in plate thickness based on the displaced portion (state m6 in FIG. 20 ).

[0123] After molding the formed workpiece 1E having this annular protrusion 13E, the formed workpiece 1E is removed from the upper tool U5 and the lower tool L5 to obtain the formed workpiece 1E in state m7 of Figure 20. In the formed workpiece 1E, the annular protrusion 13E has an increased thickness over a wide area, including the area required to improve the pressure resistance of the curved convex portion 132E between the inner peripheral wall portion 131E and the outer peripheral wall portion 133E. Note that the example of state m7 in Figure 20 shows the outer peripheral panel portion (outer peripheral plate portion) 21E and the center panel portion (central plate portion) 22E at approximately the same height, but this is not limited to this example. The height positions of the outer peripheral panel portion 21E and the center panel portion 22E may be different as necessary; for example, the height position of the outer peripheral panel portion 21E may be lower than the height position of the center panel portion 22E.

[0124] In this way, in the forming method of the plate material 11E according to the second general embodiment, the relative pressing (pressing) of the outer peripheral panel portion (outer peripheral plate portion, specific plate portion) 21E is performed continuously (in one stroke) using the same device (upper and lower dies) having the upper tool U5 and the lower tool L5. In other words, the forming method according to the second general embodiment does not perform this pressing in multiple stages using dies of different shapes each time, but rather, with this simple manufacturing process, it is possible to form the annular protrusion 13E in which the plate thickness is increased within the range necessary to improve pressure resistance.

[0125] Instead of the example described here, the forming process of the formed material 1E may use the same apparatus (upper and lower dies) consistently from the blank punching process S31 to the annular protrusion forming (thickness increasing) process S34. Alternatively, the forming process of the formed material 1E may use an apparatus (upper and lower dies) different from the apparatus (apparatus having an upper tool U5 and a lower tool L5) used in the annular protrusion forming (thickness increasing) process S34 from the blank punching process S31 to the annular curved portion forming process S33. In this case, the preform 11Ea is prepared in advance in this different apparatus, and the preform 11Ea is sequentially placed between the upper tool U5 and the lower tool L5.

[0126] In addition, in this second general embodiment, an example has been described in which the upper outer tool U51 applies a pressing force in a first direction (downward) to the plate material 11E on the contact surface (support surface) L53a so that the upper outer tool U51 approaches the support tool (support member) L53, but this is not limiting. The support tool (support member) L53 is relatively movable in a second direction (upward). Therefore, instead of the example described here, the support tool (support member) L53 may apply a pressing force in the second direction (upward) to the plate material 11E on the contact surface (support surface) L53a so that the support tool (support member) L53 approaches the upper outer tool U51.

[0127] In this case, the outer peripheral panel portion 21E is sandwiched and fixed between the upper outer tool U51 and the lower outer tool L51, and in this state, the support tool (support member) L53 pushes up the guide tool U53. As a result, an annular curved portion 24E having a curved shape that follows the shape of the contact surface L53a of the support tool L53 is formed on the inner peripheral side of the side wall portion 23E, and then the annular protrusion 13E is formed.

[0128] Next, third to fifth embodiments, which are specific embodiments of the present invention, will be described. In the third to fifth embodiments, descriptions of the same configurations as those in the second general embodiment or the same configurations as each other will be omitted.

[0129] [Third Embodiment] A sheet metal forming method according to a third embodiment forms a can lid 3E, as shown in Fig. 21 , as a formed sheet. The can lid 3E has a center panel portion (central plate portion) 31E, a panel wall portion (inner peripheral wall portion) 321E, a chuck wall radius portion (curved convex portion) 322E, a chuck wall portion consisting of a first chuck wall portion (first outer peripheral wall portion) 323E and a second chuck wall portion (second outer peripheral wall portion) 33E, and a curl portion 34E. Here, the panel wall portion 321E, the chuck wall radius portion 322E, and the first chuck wall portion 323E form an annular protrusion 32E.

[0130] The center panel portion (central plate portion) 31E is located approximately in the center of the can lid 3E and consists of a substantially circular, substantially flat surface. If the can lid 3E is a stay-on tab type, the center panel portion 31E is provided with a tab or score for opening.

[0131] A curved end (curved portion) 311E is formed as the radially outer end (outer edge) of the center panel portion 31E, and a panel wall portion (inner peripheral wall portion) 321E is formed so as to extend downward in a substantially straight line from the outer end (terminal end) of the curved end 311E. The chuck wall radius portion (curved convex portion) 322E is a curved portion formed so that its inner end (end on the inner peripheral side) is connected to the lower end of the panel wall portion 321E and its outer end (end on the outer peripheral side) is connected to the lower end of a first chuck wall portion (first outer peripheral wall portion) 323E.

[0132] The first chuck wall portion (first outer peripheral wall portion) 323E extends upward in a substantially linear manner from the outer end (upper end on the outer periphery) of the chuck wall radius portion (curved convex portion) 322E. The second chuck wall portion (second outer peripheral wall portion) 33E extends in a substantially linear manner from the upper end (upper end on the outer periphery) of the first chuck wall portion 323E so as to be inclined upward and outward, and its upper end is formed so as to connect to the curved portion of the curl portion 34E.

[0133] This can lid 3E forming method includes, as part of the overall process, the method for forming the sheet material 11E according to the second general embodiment described above. That is, as shown in Fig. 22, this can lid 3E forming method includes a blank punching step S41, a peripheral drawing step S42, a central-peripheral sheet material forming step S43, an annular curved portion forming step S44, an annular protrusion forming (sheet thickness increasing forming) step S45, and a (can lid) shape forming step S46. In these forming steps (S41 to S46), the shape of the sheet material 41E is changed as shown in states m11 to m18 in Figs. 23 to 25, and the can lid 3E in state m19 in Fig. 25 is formed.

[0134] In the blank punching step S41, for example, upper and lower punching tools (not shown) for punching the plate material 41E to be processed into a substantially disk shape are used to form the plate material 41E into a substantially disk shape (state m11 in Figure 23).

[0135] The plate 41E is made of a material mainly composed of metal, and the metal material is not particularly limited, but may be a single metal material such as aluminum, an aluminum alloy, or steel, or a clad material of these metals, or a composite metal material in which one or both sides of the metal are subjected to a surface treatment, painting (paint containing a lubricant, etc.), lamination, or the like.

[0136] In the outer periphery drawing step S42, for example, using an upper and lower outer periphery drawing tool (not shown) for drawing the outer periphery of the substantially disk-shaped plate material 41E, the plate-like portion on the inner periphery side of the outer periphery of the substantially disk-shaped plate material 41E shown in state m11 in Fig. 23 is fixed and the outer periphery is drawn. As a result, as shown in state m12 in Fig. 23, an outer periphery side portion 43E is formed on the outer periphery side of the plate-like portion 42E of the plate material 41E, which hangs down via a curved corner (extending in a direction substantially perpendicular (downward) to the plate-like portion 42E).

[0137] In the central-periphery plate portion forming step S43, for example, for a plate material 41E in state m12 of FIG. 23 , upper and lower center drawing tools (not shown) are used to perform drawing on the approximately central portion of the plate-shaped portion 42E. A blank holding force is applied to the outer panel portion (outer plate portion) 420E, which is the outer peripheral portion of the plate-shaped portion 42E, while drawing is performed on the inner peripheral side. As a result, as shown in state m13 of FIG. 23 , a center panel portion (central plate portion) 45E is formed, and via a side wall portion 46E rising outward from the center panel portion 45E, an outer peripheral panel portion (outer peripheral plate portion) 421E, corresponding to the "specific plate portion" described in the previous main form, is formed. The shape of the center panel portion (central plate portion) 45E may be, for example, a substantially flat surface as illustrated in FIG. 23 , but is not limited to such a substantially flat surface and may be other shapes. The shape of the center panel portion 45E may be, for example, a curved (dome) shape (not shown) that gently protrudes in a first direction (downward) in which the annular protrusion 32Ea (state m16 in Figure 24) to be formed later protrudes, or in the opposite second direction (upward).

[0138] In the annular curved portion forming process S44 and the annular protrusion forming (plate thickness increase forming) process S45, the plate material 41E (state m13 in FIG. 23 ) having the center panel portion (central plate portion) 45E and the outer peripheral panel portion (outer peripheral plate portion) 421E formed therein is formed using a forming device M4 having an upper tool U6 and a lower tool L6, for example, as shown in FIG. 26 . As shown in state m14 in FIGS. 26 and 24 , for example, the upper tool U6 includes an annular upper outer tool (upper tool for a specific plate portion) U61, an upper central tool U62, and an annular guide tool U63 positioned therebetween. The lower tool L6 includes an annular lower outer tool L61, a lower central tool L62, and an annular support tool (support member) L63 positioned therebetween.

[0139] 26, the forming device M4 has an upper tool U6 equipped with cushion pins Ua11 and Ua12 connected to an air cylinder, and a lower tool L6 equipped with cushion pins La11 and La12 connected to an air cylinder. In the upper tool U6, the upper central tool U62 can be moved up and down by the cushion pins Ua11 and Ua12 connected to the air cylinder, and the guide tool U63 can be moved up and down by the cushion pin Ua12 connected to the air cylinder.

[0140] In the lower tool L6, the support tool (support member) L63 can be moved up and down by cushion pins La11 connected to an air cylinder, and the lower outer tool L61 can be moved up and down by cushion pins La12 connected to an air cylinder. Note that the molding device M4 may be provided with elastic members such as spring members, or hydraulic cylinders (e.g., hydraulic cylinders) instead of the cushion pins Ua11, Ua12, La11, and La12 connected to such air cylinders.

[0141] In the annular curved portion forming step S44, as shown in state m14 in Figure 24, the sheet material 41E on which the center panel portion (central plate portion) 45E and the outer peripheral panel portion (outer peripheral plate portion) 421E have been formed is sandwiched between the upper tool U6 and the lower tool L6. At this time, the center panel portion 45E of the sheet material 41E is sandwiched and fixed between the contact surface U62a of the upper central tool U62 and the contact surface L62a of the lower central tool L62. This fixation of the center panel portion 45E continues until the annular protrusion forming (plate thickness increasing) step S45 is completed.

[0142] In this state, in the annular curved portion forming step S44, the upper outer tool U61 applies a pressing force in the first direction (downward) as shown in states m14 and m15 in Fig. 24. At this time, the upper outer tool U61 presses down the lower outer tool L61 while sandwiching the outer peripheral panel portion (outer peripheral plate portion) 421E between the contact surface U61a of the upper outer tool U61 and the contact surface L61a of the lower outer tool L61.

[0143] The guide tool U63 may be either one that does not descend, as shown in states m14 to m16 in Figure 24, or one that descends. In either case, the guide tool U63 and the lower outer tool L61 are positioned around the side wall portion 46E. This prevents buckling of the side wall portion 46E due to compressive stress when compressive stress is applied to the side wall portion 46E in the subsequent annular protrusion forming (thickness increasing) process S45.

[0144] In this annular curved portion forming process S44, the upper outer tool U61 presses down the lower outer tool L61 so that the height position of its contact surface U61a approaches the height position of the contact surface (support surface) L63a of the support tool (support member) L63. That is, the support tool L63 is relatively movable in the second direction (upward). This support tool L63 applies a support force in this second direction (upward) to the plate material 41E on its contact surface (support surface) L63a. Therefore, by pressing down the lower outer tool L61 with the upper outer tool U61, an annular curved portion 47E is formed on the inner periphery of the side wall portion 46E, supported by the support tool L63 that applies this support force, and the annular curved portion 47E is curved along the shape of the contact surface L63a. The plate material 41E with this annular curved portion 47E formed therein is referred to as the preform 41Ea (state m15 in FIG. 24 ).

[0145] In the annular protrusion molding (plate thickness increasing molding) process S45, for example, as shown in states m15 and m16 in Figure 24, the annular curved portion 47E of the molded preform 41Ea is supported by the abutment surface (support surface) L63a of the support tool (support member) L63 (by a support force directed in the second direction (upward)), while a pressing force is applied in the first direction (downward) to the outer peripheral panel portion (outer peripheral plate portion, specific plate portion) 421E.

[0146] At this time, the upper outer tool U61 continuously applies a pressing force in a first direction (downward) so as to press down the lower outer tool L61 with its abutment surface U61a. That is, the upper outer tool U61 continuously applies a pressing force to the outer peripheral panel portion (outer peripheral plate portion) 421E sandwiched between the abutment surface U61a and the abutment surface L61a of the lower outer tool L61, thereby pressing the outer peripheral panel portion 421E in the first direction (downward). At the same time, the guide tool U63 positions the side wall portion 46E between its outer guide surface U63a and the abutment surface L61b of the lower outer tool L61, thereby preventing the side wall portion 46E from buckling due to the compressive stress applied to the side wall portion 46E. As a result, the support force of the support tool (support member) L63 can apply a greater pressing force to the annular curved portion 47E via the side wall portion 46E than the upper outer tool U61.

[0147] In this manner, the upper outer tool U61 is pressed in while the support tool L63 applies a support force in the second direction (upward), thereby deforming the annular curved portion 47E and generating a compressive stress in the second direction (upward) in the side wall portion 46E, and at least a portion of the plate material constituting the side wall portion 46E on the contact surface L63a of the support tool L63 is moved inward of the outer peripheral panel portion (outer peripheral plate portion) 421E.

[0148] The annular protrusion forming (thickness increasing forming) step S45 forms an intermediate formed body 30E (state m16 in FIG. 24 ) of a can lid (before shape forming (reforming)) having an annular protrusion 32Ea whose thickness is selectively increased based on the moved portion. In the intermediate formed body 30E, the annular protrusion 32Ea has an increased thickness over a wide range, including the range required to improve the pressure resistance of the chuck wall radius portion (curved convex portion) 322Ea.

[0149] In this way, in the method for forming the plate material 41E according to the third embodiment, the outer peripheral panel portion (outer peripheral plate portion, specific plate portion) 421E is pressed (pressed) relative to the outer peripheral panel portion (outer peripheral plate portion, specific plate portion) continuously (in one stroke) using the same device (upper and lower dies) having the upper tool U6 and the lower tool L6. In other words, the forming method according to the third embodiment does not perform this pressing in multiple stages using dies of different shapes each time, but rather can form the annular protrusion 32Ea with an increased plate thickness over a wide range using this simple manufacturing process.

[0150] After the intermediate can lid formed body 30E (before shape forming) having the annular protrusion 32Ea is formed in this manner, the intermediate can lid formed body 30E is removed from the upper tool U6 and the lower tool L6.

[0151] The can lid shape forming step S46 is a step of reforming the shape of the can lid intermediate formed body 30E to form the shape of the can lid. This can lid shape forming step S46 includes a step of forming a chuck wall portion consisting of a first chuck wall portion (first outer peripheral wall portion) 323E and a second chuck wall portion (second outer peripheral wall portion) 33E shown in state m19 in Figure 25.

[0152] This can lid shape forming process S46 may further include a known process (not shown) of forming a curled portion 34E (state m18 in Figure 25) on the outer side of the annular protrusion 32Ea (or the annular protrusion 32E after forming), in any order or simultaneously with the process of forming the above-mentioned chuck wall portion.

[0153] The center panel portion 45E of the intermediate formed body 30E may have another shape other than a substantially flat surface as shown in state m16 in Fig. 24 , for example, a curved (dome) shape (not shown) that gently protrudes in the second direction (upward). In this case, the can lid shape forming step S46 may further include at least one or both of the following known steps: forming the center panel portion 45E into a desired shape (for example, a substantially flat surface) and forming the curled portion 34E, in any order or simultaneously with the step of forming the chuck wall portion.

[0154] In the can lid shaping step S46, as shown in state m17 in Figure 25, the shape of the can lid intermediate formed body 30E is reformed using a can lid shaping device M5 having an upper tool U7 and a lower tool L7. The upper tool U7 has an annular upper outer tool U71, an upper central tool U72, and an annular processing tool U73 located therebetween. The lower tool L7 has an annular lower outer tool L71, a lower central tool L72, and an annular protrusion support tool L73 located therebetween.

[0155] In this can lid shaping step S46, as shown in state m17 in Fig. 25 , after placing the intermediate formed body 30E of the can lid (before shaping) on ​​the lower tool L7, the upper outer tool U71, the upper central tool U72, and the processing tool U73 may be lowered, for example, simultaneously to perform the can lid shaping step S46. Alternatively, depending on the shape of the can lid, the timing of the descent of the upper outer tool U71, the upper central tool U72, and the processing tool U73 may be changed as appropriate.

[0156] At this time, as the upper central tool U72 descends, the annular protrusion 32Ea is supported by the contact surface (support surface) L73a of the annular protrusion support tool L73, and the annular protrusion 32Ea between the lower central tool L72 and the lower outer tool L71 is formed into an annular protrusion 32E (state m18 in FIG. 25 ) having a shape that conforms to the contact end U72b of the upper central tool U72 and the contact surface (support surface) L73a of the annular protrusion support tool L73. That is, at this time, a first chuck wall portion (first outer peripheral wall portion) 323E (state m19 in FIG. 25 ) of the chuck wall portion is formed.

[0157] At this time, the upper outer tool U71 descends, causing its abutment surface U71a to abut against the outer peripheral panel portion (outer peripheral plate portion) 421E on the abutment surface (support surface) L71b of the lower outer tool L71, thereby fixing the outer peripheral panel portion 421E. In this state, the machining tool U73 descends, causing the outer peripheral panel portion 421E to be sandwiched between the abutment surface U73a and the abutment surface L71a, thereby forming a second chuck wall portion (second outer peripheral wall portion) 33E (state m19 in FIG. 25 ) that conforms to the shapes of the lower outer tool L71 and the machining tool U73. In this way, a chuck wall portion (state m19 in FIG. 25 ) consisting of the first chuck wall portion (first outer peripheral wall portion) 323E and the second chuck wall portion (second outer peripheral wall portion) 33E on its outer periphery is formed.

[0158] At this time, a curled portion 34E can also be formed on the outer periphery of the lid. In this case, the lower tool L7 may be provided with a curling tool (not shown) on the outer periphery of the lower outer tool L71. As described above, when the processing tool U73 is lowered with the outer peripheral panel portion 421E fixed, the outer peripheral panel portion 421E sandwiched between the abutment surface U73a and the abutment surface L71a of the processing tool U73 flows toward the outer periphery. In this state, when the curling tool (not shown) is lowered, the curled portion 34E is formed in a shape that conforms to the abutment surface U71a of the upper outer tool U71 and the abutment surface (not shown) of the curling tool (state m18 in FIG. 25 ).

[0159] Furthermore, at this time, if the center panel portion (central plate portion) 45E has another shape (for example, a curved (dome) shape that gently protrudes in the second direction (upward) (not shown)), the shape can be formed into a desired shape, for example, a substantially flat surface. In this case, the upper central tool U72 descends so that its abutment surface U72a presses down on the lower central tool L72, thereby forming the center panel portion (central plate portion) 45E having another shape (for example, a curved (dome) shape that gently protrudes in the second direction) sandwiched between the abutment surface U72a and the abutment surface L72a of the lower central tool L72 into a substantially flat center panel portion (central plate portion) 31E (state m18 in FIG. 25 ).

[0160] In this case, in the can lid shape forming process S46 in Figure 22, the process of forming the chuck wall portion and the process of forming the center panel portion (central plate portion) 45E into an approximately flat surface are carried out simultaneously, but these processes may also be carried out in any order as separate steps.

[0161] The can lid 3E reformed in this way is removed from the can lid shape forming device M5 to obtain the can lid 3E shown in state m19 in Fig. 25. The reformed can lid 3E in state m19 has a shape in which an annular protruding portion 32E consisting of a panel wall portion (inner peripheral wall portion) 321E, a chuck wall radius portion (curved convex portion) 322E, and a first chuck wall portion (first outer peripheral wall portion) 323E protrudes downward approximately perpendicularly to the extension direction of the center panel portion 31E.

[0162] Instead of the example described here, the can lid 3E forming process may use the same apparatus (upper and lower dies) consistently from the blank punching process S41 to the annular protrusion forming (thickness increasing) process S45. Alternatively, the can lid 3E forming process may use an apparatus (upper and lower dies) different from the apparatus (the apparatus having the above-mentioned upper tool U6 and lower tool L6) used in the annular protrusion forming (thickness increasing) process S45 from the blank punching process S41 to the annular curved portion forming process S44. In this case, the preform 41Ea is prepared in advance in this different apparatus, and the preform 41Ea is placed between the upper tool U6 and the lower tool L6.

[0163] Examples of the Third Embodiment (Examples 1-5) are described below. In Examples 1-5, an intermediate formed body 40Eb (FIG. 27(a)) was formed from a sheet material by the blank punching process S41 through the annular protrusion forming (thickness increasing) process S45 described above in the third embodiment. The sheet material used was an aluminum alloy (A5182) (metal portion) with an original thickness of 0.218 mm, coated on both sides with a lubricant-containing paint. As shown in FIG. 27(a), the intermediate formed body 40Eb includes a curved (dome-shaped) center panel portion (central plate portion) 45Eb, an outer peripheral panel portion (outer peripheral plate portion, specific plate portion) 421Eb corresponding to the outer peripheral panel portion 421E, and an annular protrusion portion 32Eb.

[0164] In Examples 1 to 5, in the annular protrusion forming (thickness increasing) process S45, the annular curved portion (not shown) was supported by the contact surface (support surface) L63a of the support tool (support member) L63 (by a support force directed upward (the second direction)), while a downward (first direction) pressing force was applied to the outer peripheral panel portion (outer peripheral plate portion) 421Eb. At this time, the support force directed upward (the second direction) by the support tool L63 was applied to the plate portion (of the annular curved portion) located on the contact surface (support surface) L63a of the support tool L63. The magnitude of the support force, i.e., the support force (countersink holding force) [kgf], was varied among Examples 1 to 5, and the plate thickness [mm] of the metal portion of the plate of the intermediate formed body 40Eb was measured for each of the different support forces at measurement points a to v ( FIGS. 27(a) and 27(b) ) ( FIG. 28 ).

[0165] In performing the above-described annular protrusion forming (plate thickness increasing forming) process S45, as shown in Fig. 28, the support force (countersink holding force) [kgf] applied by the support tool L63 was set to 200 kgf in Example 1, 400 kgf in Example 2, 600 kgf in Example 3, 800 kgf in Example 4, and 1000 kgf in Example 5. Graphs G1 to G5 in Fig. 28 are graphs showing the measured values ​​of the plate thickness [mm] of the metal portion at measurement points a to v in the plate material after the process of step S45 in Example 1 (supporting force 200 kgf), Example 2 (supporting force 400 kgf), Example 3 (supporting force 600 kgf), Example 4 (supporting force 800 kgf), and Example 5 (supporting force 1000 kgf), respectively.

[0166] As shown in the measurement results of Fig. 28, in all of Examples 1 to 5 in which the support force (countersink holding force) [kgf] in the upward direction (second direction) was applied by the support tool L63, the thickness of the metal portion of the plate material could be made thicker than the original plate thickness (0.218 mm) over a wide range within the range of measurement points a to v. Furthermore, from the results of Examples 1 to 5 in Fig. 28, it can be seen that the thickness [mm] of the metal portion of the plate material can be made thicker as the support force [kgf] increases.

[0167] Here, it has been confirmed through various experiments, simulations, etc. conducted in advance that the range including measurement points f to i and the range including measurement points l to n on chuck wall radius portion (curved convex portion) 322Eb ( FIG. 27( b) ) of annular protrusion 32Eb are ranges particularly necessary for improving the pressure resistance of a can container (metal can) with a lid attached after shape forming (reforming) that is formed from intermediate formed body 40Eb. In chuck wall radius portion (curved convex portion) 322Eb shown in FIG. 27( b), the range between the dotted lines including measurement points f to i is referred to as the "main pressure-resistant range X1," and the range between the dotted lines including measurement points l to n is referred to as the "main pressure-resistant range X2." As shown in the measurement results in the main pressure-resistance ranges X1 and X2 in Figure 28, by applying a large value as the support force (countersink holding force) [kgf] in the second direction (upward) using the support tool L63, it can be seen that a sufficiently large plate thickness [mm] value can be obtained in both the main pressure-resistance ranges X1 and X2 (for example, Examples 4 and 5).

[0168] Examples of the Third Embodiment (Examples 6 to 8, Comparative Example 1) Next, examples of the third embodiment (Examples 6 to 8, Comparative Example 1) will be described. In Examples 6 to 8 and Comparative Example 1, the can lid 3Ec shown in Fig. 30 was formed from a sheet material by the blank punching step S41 to the can lid shape forming step S46 described above in the third embodiment. The sheet material used was an aluminum alloy (A5182) (Fig. 29) (metal portion) with an original thickness of 0.218 mm, with both sides coated with a paint containing a lubricant.

[0169] In addition, in performing the annular protrusion forming (plate thickness increasing) process S45, the support force (countersink holding force) [kgf] applied by the support tool L63 was set to 700 kgf in Example 6, 800 kgf in Example 7, 900 kgf in Example 8, and 0 kgf in Comparative Example 1 ( FIG. 29 ). As shown in FIG. 29 , the can lids 3Ec formed in Examples 6 to 8 and Comparative Example 1 all had a lid diameter of 206 mm (2 6 / 16 inches), a can lid shape of a CDL (Container Development Ltd.) shape, a unit depth (UD) [mm] of 6.66 mm, and a panel height (PH) [mm] of 2.54 mm.

[0170] As shown by the double-headed arrow in Figure 30, the unit depth (UD) [mm] is the height distance [mm] from the lower end of the outer surface of the can lid 3Ec (i.e., the lower end of the outer surface of the chuck wall radius portion (curved convex portion) 322Ec of the annular protrusion 32Ec) to the upper end of the outer surface of the can lid 3Ec, and the panel height (PH) [mm] is the height distance from the lower end of the outer surface of the can lid 3Ec to the outer surface of the center panel portion (central plate portion) 31Ec.

[0171] In Examples 6 to 8 and Comparative Example 1, a pressure test was conducted in which the formed can lid 3Ec was wrapped around a can container (metal can) and subjected to internal water pressure. As shown in FIG. 29 , Example 6 exhibited a pressure resistance value (pressure strength) of 0.654 MPa, Example 7 exhibited a pressure resistance value of 0.656 MPa, and Example 8 exhibited a pressure resistance value of 0.696 MPa, all of which satisfied the required performance. On the other hand, Comparative Example 1 exhibited a pressure resistance value of 0.630 MPa, which was not a pressure resistance value that satisfied the required performance. These results demonstrate that the pressure resistance of the can lid can be increased by applying a support force (countersink holding force) [kgf] applied by the support tool L63, and that the pressure resistance of the can lid can be further increased as the support force increases.

[0172] [Fourth embodiment] In a sheet material forming method according to a fourth embodiment, a first stage of sheet thickness increasing forming is performed on a sheet material by the process shown in Fig. 31, a second stage of sheet thickness increasing forming is performed by the process shown in Fig. 32, and then a third stage of sheet thickness increasing forming is performed by the process shown in Fig. 33. Note that the height Ht indicated by the dotted line in Figs. 31 to 33 indicates the same height throughout.

[0173] 31 , first, using upper and lower peripheral drawing tools (not shown) for drawing the outer peripheral portion of plate material 51E formed into a substantially disk-like shape by blank punching, a blank-holding force is applied to plate-like portion 52E, which is located on the inner side of the outer peripheral portion of substantially disk-like plate material 51E, to draw the outer peripheral portion. As a result, as shown in state m21 of FIG. 31 , an outer peripheral side portion 53E is formed on the outer peripheral side of plate-like portion 52E, which hangs down via a curved corner (extending in a direction substantially perpendicular (downward) to plate-like portion 52E).

[0174] Next, for the sheet material 51E in state m21, upper and lower center drawing tools (not shown) for drawing the approximately central portion of the plate-shaped portion 52E are used to apply a blank-holding force to the outer periphery of the plate-shaped portion 52E while drawing the inner periphery. As a result, as shown in state m22 in Figure 31 , an outer periphery panel portion (outer periphery plate portion) 521E is formed in the sheet material 51E, and a center panel portion (central plate portion, specific plate portion) 54E is formed via a side wall portion 55E that rises upward on the inner periphery side of the outer periphery panel portion 521E. Here, a central protrusion 56E is formed by the center panel portion (central plate portion) 54E and the side wall portion 55E.

[0175] Next, as shown in state m23 of FIG. 31 , forming is performed using, for example, a forming device having an upper tool U8 and a lower tool L8. The upper tool U8 includes an annular upper outer tool U81, an upper central tool U82, and an annular guide tool U83 positioned therebetween. Note that the guide tool U83 shown in the examples of FIGS. 31 to 33 is integrally formed with the upper central tool U82 on the outer periphery of the upper central tool U82. However, the guide tool U83 is not limited to this configuration and may be provided separately from the upper central tool U82 on the outer periphery of the upper central tool U82. The lower tool L8 includes an annular lower outer tool L81, a lower central tool L82, and an annular support tool (support member) L83 positioned therebetween. As shown in state m23, the plate material 51E on which the center panel portion 54E and side wall portion 55E (i.e., the central protrusion 56E) have been formed is placed between the upper tool U8 and the lower tool L8.

[0176] Then, the upper outer tool U81 and the lower outer tool L81 sandwich and fix the outer peripheral panel portion 521E of the plate material 51E (state m24 in FIG. 31 ). This fixation continues until state m26. With the outer peripheral panel portion 521E fixed in this manner, the upper central tool U82 presses down on the lower central tool L82 while sandwiching the center panel portion 54E between the contact surface U82a of the upper central tool U82 and the contact surface L82a of the lower central tool L82 (states m24 and m25). The side wall portion 55E is positioned between the guide tool U83 and the lower central tool L82.

[0177] The upper central tool U82 presses down on the lower central tool L82 so that the height position of its contact surface U82a approaches the height position of the contact surface (support surface) L83a of the support tool (support member) L83. That is, the support tool L83 is relatively movable in a second direction (upward) opposite to the first direction (downward) in which the annular protrusion 62Ea (state m26 in FIG. 31 ) to be formed later protrudes. The support tool L83 applies a support force in the second direction (upward) to the plate material 51E on its contact surface (support surface) L83a. Therefore, as the upper central tool U82 presses down on the lower central tool L82, the outer periphery of the side wall portion 55E is supported by the support tool L83 that applies this support force, forming an annular curved portion 57E that curves along the shape of the contact surface L83a (state m25 in FIG. 31 ).

[0178] Then, while supporting the annular curved portion 57E with the abutment surface (support surface) L83a of the support tool (support member) L83 (by a support force directed in the second direction (upward)), a pressing force is applied to the center panel portion (specific plate portion) 54E in a first direction (downward) opposite to the second direction.

[0179] At this time, the upper central tool (upper tool for the specific plate portion) U82 continuously applies a pressing force in the first direction (downward) to press down the lower central tool L82 with its contact surface U82a. That is, the upper central tool U82 continuously applies a pressing force to the center panel portion (central plate portion, specific plate portion) 54E sandwiched between the contact surface U82a and the contact surface L82a of the lower central tool L82, pushing the center panel portion 54E in the first direction (downward). At the same time, the guide tool U83 positions the side wall portion 55E between itself and the lower central tool L82, preventing the side wall portion 55E from buckling due to the compressive stress applied to the side wall portion 55E. As a result, the support force of the support tool (support member) L83 can apply a greater pressing force to the annular curved portion 57E via the side wall portion 55E than the upper central tool U82.

[0180] This pressing by the upper central tool U82 deforms the annular curved portion 57E and generates compressive stress in the second direction (upward) in the side wall portion 55E, moving at least a portion of the plate material that constitutes the side wall portion 55E on the abutment surface L83a of the support tool L83 toward the outside of the center panel portion (specific plate portion) 54E.

[0181] As a result, a can lid intermediate 60E having an annular protrusion 62Ea whose thickness is selectively increased based on the moved portion is formed (state m26). In the intermediate 60E, the annular protrusion 62Ea is connected to the outer peripheral panel portion (outer peripheral plate portion) 521E via the side wall portion 61E on its outer periphery. The annular protrusion 62Ea has an increased thickness over a wide range, including the area required to improve the pressure resistance of the chuck wall radius portion (curved convex portion).

[0182] Thereafter, as shown in state m27, the intermediate formed body 60E of the can lid is removed from the upper tool U8 and the lower tool L8. In this way, the intermediate formed body 60E (state m28) that has undergone the first stage of thickness increasing forming is obtained.

[0183] (Second-stage plate thickness increase forming) In the second-stage plate thickness increase forming performed by the process shown in Figure 32, a pressing force in a first direction (downward) is applied to the intermediate formed body 60E (state m29 (i.e., state m28 in Figure 31)) that has undergone the first-stage plate thickness increase forming by the upper outer tool (upper tool for specific plate portion) U81, as in the third embodiment described above. That is, the intermediate formed body 60E is placed between the upper tool U8 and the lower tool L8 (state m30), and then the center panel portion 54E is sandwiched and fixed between the upper central tool U82 and the lower central tool L82 (state m31).

[0184] In this state, a pressing force is applied to the outer peripheral panel portion (specific plate portion) 521E sandwiched between the upper outer tool U81 and the lower outer tool L81, pushing the outer peripheral panel portion 521E in a first direction (downward). This deforms the annular protrusion 62Ea and generates a compressive stress in the side wall portion 61E in a second direction (upward), moving at least a portion of the plate material constituting the side wall portion 61E on the contact surface L83a of the support tool L83 toward the inside of the outer peripheral panel portion 521E. In this way, an intermediate formed body 70E (of a can lid) is formed, which has an annular curved portion 62Eb whose thickness is selectively increased further inward of the outer peripheral panel portion 521E (state m32). The intermediate formed body 70E has a side wall portion 63E that rises upward on the inner circumferential side of the annular curved portion 62Eb, and the side wall portion 63E and a center panel portion (central plate portion) 54E form a central protrusion portion 64E.

[0185] Thereafter, as shown in state m33, the intermediate formed body 70E is removed from the upper tool U8 and the lower tool L8. In this way, the intermediate formed body 70E (state m34) that has undergone the second-stage thickness increasing forming is obtained.

[0186] (Third-stage plate thickness increase forming) In the third-stage plate thickness increase forming performed by the process shown in Figure 33, the intermediate formed body 70E (state m35 (i.e., state m34 in Figure 32)) that has undergone the second-stage plate thickness increase forming is subjected to the same process as the first-stage plate thickness increase forming process described above. That is, the intermediate formed body 70E shown in state m35 in Figure 33 is placed between the upper tool U8 and the lower tool L8 as shown in state m36, and the outer peripheral panel portion 521E is sandwiched and fixed between the upper outer tool U81 and the lower outer tool L81 as shown in state m37.

[0187] In this state, while the center panel portion 54E is sandwiched between the upper central tool U82 and the lower central tool L82, the upper central tool (upper tool for a specific plate portion) U82 presses down on the lower central tool L82, continuously applying a pressing force in the first direction (downward) (state m37, state m38).

[0188] Specifically, while the annular curved portion 62Eb of the intermediate formed body 70E is supported by the contact surface L83a of the support tool L83 (by a supporting force in the second direction (upward)), a pressing force is continuously applied to the center panel portion (specific plate portion) 54E in a first direction (downward) opposite to the second direction (upward). At this time, the supporting force of the support tool (support member) L83 can apply a greater pressing force to the annular curved portion 62Eb via the side wall portion 63E than the upper central tool U82.

[0189] This pressing by the upper central tool U82 deforms the annular curved portion 62Eb and generates compressive stress in the second direction (upward) in the side wall portion 63E, moving at least a portion of the plate material that constitutes the side wall portion 63E on the abutment surface L83a of the support tool L83 toward the outside of the center panel portion 54E.

[0190] As a result, a can lid intermediate 80E having an annular protrusion 82Ea whose thickness is selectively increased further based on the moved portion is formed (state m38). In the intermediate 80E, the annular protrusion 82Ea is connected to the outer peripheral panel portion 521E on its outer periphery via the side wall portion 81E.

[0191] Thereafter, as shown in state m39, the can lid intermediate formed body 80E is removed from the upper tool U8 and the lower tool L8. In this way, the can lid intermediate formed body 80E (state m40) is obtained, which has undergone the third stage of thickness-increasing forming. The intermediate formed body 80E in state m40 has an even greater thickness increase over a wide range, including the range required to improve the pressure resistance of the chuck wall radius portion (curved convex portion) 822Ea of the annular protrusion 82Ea.

[0192] As described above, according to the sheet metal forming method of the fourth embodiment, the sheet metal can be further thickened over a wide range, including the required range for the annular protrusion 82Ea, by performing thickness-increasing forming on the sheet metal in multiple stages, such as the first to third stages shown in Figures 31 to 33. As a result, a can lid with even improved pressure resistance can be formed from the intermediate formed body 80E formed by the sheet metal forming method of the fourth embodiment.

[0193] 31 to 33, the same forming device having an upper tool U8 and a lower tool L8 was used consistently. However, this is not limited to this example. The forming device having the upper tool U8 and the lower tool L8 may have different configurations (particularly in terms of cushion pins (not shown), air cylinders (not shown), etc.) between the forming device used in the first and third stages of thickness increase forming and the forming device used in the second stage of thickness increase forming.

[0194] [Fifth Embodiment] A method for forming a sheet material in a fifth embodiment forms a can bottom 10E as a formed material, as shown in state m48 in Fig. 35. This method for forming a can bottom 10E includes the method for forming a sheet material 11E according to the second general embodiment described above as part of the overall process.

[0195] The method for forming this can bottom 10E includes the same steps as those shown in Fig. 22, i.e., the blank punching step S41, the outer periphery drawing step S42, the central-outer periphery plate portion forming step S43, the annular curved portion forming step S44, the annular protrusion forming (plate thickness increasing forming) step S45, and the (can bottom) shape forming step S46, all of which are shown in Fig. 22. In these forming steps (S41 to S46), the shape of the plate material 91E is changed as shown in states m41 to m47 in Figs. 34 and 35, and then the can bottom is shaped (reformed) to form the can bottom 10E in state m48.

[0196] In the blank punching process S41 in the can bottom 10E forming process, for example, upper and lower punching tools (not shown) are used to punch the plate material 91E to be processed into an approximately disk shape, and the plate material 91E is formed into an approximately disk shape (state m41 in Figure 34).

[0197] In the peripheral drawing step S42 in the can bottom 10E forming process, for example, upper and lower peripheral drawing tools (not shown) for drawing the peripheral portion of a substantially disk-shaped sheet material 91E are used to draw the peripheral portion of the substantially disk-shaped sheet material 91E while applying a blank-holding force to the plate-like portion inside the peripheral portion of the substantially disk-shaped sheet material 91E shown in state m41 in Figure 34. As a result, as shown in state m42 in Figure 34, a peripheral side portion 93E is formed that rises upward (extends approximately perpendicular (upward) to the plate-like portion 92E) via curved corners on the outer periphery side of the plate-like portion 92E of the sheet material 91E. If necessary, known ironing may be added to the peripheral side portion 93E.

[0198] In the central-periphery plate portion forming step S43 in the can bottom 10E forming process, for example, for a plate material 91E in state m42 of FIG. 34 , upper and lower center drawing tools (not shown) are used to draw the approximately central portion of the plate-shaped portion 92E. While applying a blank-holding force to the outer panel portion (outer plate portion) 921E of the plate-shaped portion 92E, the inner periphery of the outer panel portion is drawn. This forms a center panel portion (central plate portion) 94Ea having a substantially flat surface, as shown in state m43 of FIG. 34 . At the same time, a peripheral panel portion (peripheral plate portion) 922E, corresponding to the "specific plate portion" described in the previous main form, is formed via a sidewall portion 95E rising outward from the center panel portion 94Ea. The center panel portion 94Ea is to be formed into the dome panel portion 94E later.

[0199] In the annular curved portion forming step S44 and the annular protrusion forming (thickening forming) step S45 in the can bottom 10E forming process, for example, a sheet material 91E (state m43 in FIG. 34 ) on which a center panel portion 94Ea and an outer peripheral panel portion 922E have been formed is formed using a forming device having an upper tool U9 and a lower tool L9. As shown in state m44 in FIG. 34 , for example, the upper tool U9 includes an annular upper outer tool (upper tool for a specific sheet portion) U91, an upper central tool U92, and an annular guide tool U93 positioned therebetween. The lower tool L9 includes an annular lower outer tool L91, a lower central tool L92, and an annular support tool (support member) L93 positioned therebetween. As shown in state m44 in FIG. 34 , the sheet material 91E on which a center panel portion 94Ea and an outer peripheral panel portion 922E have been formed is placed between the upper tool U9 and the lower tool L9.

[0200] Thereafter, the center panel portion 94Ea is sandwiched and fixed between the contact surfaces U92a of the upper central tool U92 and L92a of the lower central tool L92. By being sandwiched and fixed in this manner, the center panel portion 94Ea is formed into the dome panel portion 94E having a dome shape that gently protrudes in a second direction (upward) opposite to the first direction (downward) in which the annular protrusion 102Ea (state m47 in FIG. 35 ) to be formed later protrudes (state m45 in FIG. 35 ). This fixing of the dome panel portion 94E by the upper central tool U92 and the lower central tool L92 continues until the annular protrusion forming (plate thickness increasing forming) process S45 is completed.

[0201] In this state, in the annular curved portion forming step S44 in the process of forming the can bottom 10E, the upper outer tool U91 applies a pressing force in the first direction (downward) as shown in states m45 and m46 in Fig. 35. At this time, the upper outer tool U91 presses down the lower outer tool L91 while sandwiching the outer peripheral panel portion (outer peripheral plate portion) 922E between the contact surface U91a of the upper outer tool U91 and the contact surface L91a of the lower outer tool L91.

[0202] The guide tool U93 may or may not descend, as shown in states m45 to m47 in Figure 35. In either case, the guide tool U93 and the lower outer tool L91 are positioned around the side wall portion 95E. This prevents buckling of the side wall portion 95E due to compressive stress when compressive stress is applied to the side wall portion 95E in the subsequent annular protrusion forming (thickness increasing) step S45.

[0203] In the annular curved portion forming step S44 in the can bottom 10E forming process, the upper outer tool U91 presses down the lower outer tool L91 so that the height position of its contact surface U91a approaches the height position of the contact surface (support surface) L93a of the support tool (support member) L93. That is, the support tool L93 is relatively movable in the second direction (upward). The support tool L93 applies a support force in the second direction (upward) to the plate material 91E on its contact surface (support surface) L93a.

[0204] Therefore, when the upper outer tool U91 presses down on the lower outer tool L91, an annular curved portion 96E is formed on the inner periphery of the side wall 95E, which is supported by the support tool L93 that applies the supporting force, and has a curved shape that follows the shape of the abutment surface L93a of the side wall 95E. The plate material 91E having such an annular curved portion 96E formed therein is referred to as a preform 91Ea (state m46 in FIG. 35 ).

[0205] In the annular protrusion forming (plate thickness increasing forming) process S45 in the can bottom 10E forming process, for example, as shown in states m46 and m47 in Figure 35, the annular curved portion 96E of the formed preform 91Ea is supported by the abutment surface L93a of the support tool L93 (by a supporting force in the second direction (upward)), while a pressing force is applied in the first direction (downward) to the outer peripheral panel portion 922E.

[0206] At this time, the upper outer tool U91 continuously applies a pressing force in a first direction (downward) so as to press down the lower outer tool L91 with its abutment surface U91a. That is, the upper outer tool U91 continuously applies a pressing force to the outer peripheral panel portion (outer peripheral plate portion, specific plate portion) 922E sandwiched between the abutment surface U91a and the abutment surface L91a of the lower outer tool L91, thereby pressing the outer peripheral panel portion 922E in the first direction (downward). At the same time, the guide tool U93 positions the side wall portion 95E between its outer guide surface U93a and the abutment surface L91b of the lower outer tool L91, thereby preventing the side wall portion 95E from buckling due to the compressive stress applied to the side wall portion 95E. As a result, the support force of the support tool (support member) L93 can apply a greater pressing force to the annular curved portion 96E via the side wall portion 95E than the upper outer tool U91.

[0207] In this manner, the upper outer tool U91 is pressed in while the support tool L93 applies a support force in the second direction (upward), thereby deforming the annular curved portion 96E and generating a compressive stress in the second direction (upward) in the side wall portion 95E, and at least a portion of the plate material constituting the side wall portion 95E on the contact surface L93a of the support tool L93 is moved inward of the outer peripheral panel portion (outer peripheral plate portion, specific plate portion) 922E.

[0208] This annular protrusion forming (thickness increasing forming) step S45 in the can bottom 10E forming process forms a can bottom intermediate formed body 100E (state m47 in Figure 35) (before shape forming (reforming)) having an annular protrusion 102Ea whose thickness is selectively increased based on the moved portion. In the intermediate formed body 100E, the annular protrusion 102Ea has an increased thickness over a wide range, including the range required to improve the pressure resistance of the bottom radius portion (curved convex portion) 112Ea. After the can bottom intermediate formed body 100E (before shape forming) having the annular protrusion 102Ea is formed in this manner, the can bottom intermediate formed body 100E is removed from the upper tool U9 and the lower tool L9.

[0209] In this way, in the molding method for the plate material 91E of the fifth embodiment, the relative pressing (pressing) of the outer peripheral panel portion (outer peripheral plate portion, specific plate portion) 922E is performed continuously (in one stroke) using the same device (upper and lower dies) having the upper tool U9 and the lower tool L9. In other words, the molding method of the fifth embodiment also does not perform this pressing in multiple stages using dies of different shapes each time, but rather can mold the annular protrusion 102Ea with an increased plate thickness within the required range using this simple manufacturing process.

[0210] The can bottom shape forming step S46 is a step of reforming the shape of the can bottom intermediate formed body 100E as necessary (bottom reform) to form it into the shape of the can bottom, and this step includes a step of forming the shape of the can bottom annular protrusion 102E. After reforming in this can bottom shape forming step S46, the can bottom 10E is removed from the reforming device (not shown) to obtain the can bottom 10E (state m48 in Figure 35).

[0211] The can bottom shaping step S46 can be performed by a conventionally known method, for example, a method using a rotating roll or a method using press molding.

[0212] In the fifth embodiment, if an inner surface painting step is particularly required, it is desirable to perform this step before the can bottom shape forming step S46.

[0213] The can bottom 10E in state m48 of Figure 35 includes a dome panel portion (center plate portion) 101E, a dome panel wall portion (inner peripheral wall portion) 151E, a bottom radius portion (curved convex portion) 152E, a chime lower portion (first outer peripheral wall portion) 153E, and a chime portion (second outer peripheral wall portion) 103E. The dome panel wall portion 151E, the bottom radius portion 152E, and the chime lower portion 153E form a can bottom annular protrusion 102E. The can bottom annular protrusion 102E has a shape that is slightly inwardly inclined due to reforming, and the plate thickness is increased over a wide area, including the required range of the bottom radius portion 152E.

[0214] Note that the can bottom shape forming step S46 may further include a step of forming the dome panel portion (central plate portion) 94E into a desired shape, such as a shape other than a spherical surface, such as a substantially spheroidal surface, a substantially conical surface, a substantially flat surface, etc. In this case, the can bottom shape forming step S46 may include, simultaneously or in any order, a step of forming the shape of the can bottom annular protrusion 102E and a step of forming the dome panel portion (central plate portion) 94E into, for example, a substantially flat surface, as a step of reforming the shape of the can bottom intermediate formed body 100E in state m47 of Figure 35 .

[0215] [Example 9 of the Fifth Embodiment] Next, an example (Example 9) of the fifth embodiment will be described. In Example 9, a drawn and ironed can (DI can) with an internal volume of 350 mL (after the can bottom was reshaped (reformed)) was manufactured by the following method. First, an aluminum alloy plate (JIS H 4000 A3104-H19 material, 0.220 mm (original plate thickness)) was prepared as a plate material (base plate) to be processed. Next, a predetermined amount of known cupping oil was applied to both sides of this aluminum alloy plate (plate material) as a lubricant during the drawing process.

[0216] Next, the lubricant-coated aluminum alloy plate was punched into a disk shape (not shown) with a diameter of 160 mm using a drawing machine (upper and lower punching tools) (not shown) (a process corresponding to the blank punching step S41 in the forming process of the can bottom 10E described above). Thereafter, the outer peripheral portion of the disk-shaped plate material was drawn using the upper and lower peripheral drawing tools (not shown) while applying a blank holding force to the plate-shaped portion inside the outer peripheral portion. This resulted in the formation of a drawn cup (not shown) with a diameter of 90 mm.

[0217] This drawn cup (not shown) was transported to a body maker (can body manufacturing machine) and re-drawn to a shape with a diameter of 66 mm, after which a process equivalent to the peripheral drawing step S42 in the process of forming the can bottom 10E described above was carried out using coolant. As a result, a cup body was formed having a bottom shape as shown in state m42 in Figure 34, a diameter of 66 mm, a height of 130 mm, and a minimum body thickness of 0.105 mm.

[0218] Next, this formed cup body was subjected to a process corresponding to the center-peripheral plate portion forming step S43 in the above-described process for forming the can bottom 10E using upper and lower center drawing tools (not shown). This formed a center panel portion (center plate portion) consisting of a flat surface, and also formed a can bottom (corresponding to state m43 in Figure 34 ) formed by forming a peripheral panel portion (peripheral plate portion, specific plate portion) via sidewall portions rising on the outer periphery side of the center panel portion, thereby forming a first precursor of a DI can (not shown).

[0219] Next, the first precursor was placed between the upper tool U9 and the lower tool L9, as shown in state m44 in Figure 34. The center panel was then sandwiched and fixed between the upper central tool U92 and the lower central tool L92, and the center panel was deformed into the shape of the dome panel, as shown in state m45 in Figure 35. In this state, a pressing process was performed in which the upper outer tool U91 applied a pressing force in the first direction (downward), corresponding to the annular curved portion forming step S44 and the subsequent annular protrusion forming (plate thickness increasing forming) step S45 in the can bottom 10E forming process.

[0220] First, in a process corresponding to the annular curved portion forming step S44 in the can bottom 10E forming step described above, the upper outer tool U91 pressed down the lower outer tool L91 while sandwiching the outer peripheral panel portion (outer peripheral plate portion) between the upper outer tool U91 and the lower outer tool L91. This formed a second precursor of a DI can, including a can bottom preform having an annular curved portion as shown in state m46 in Figure 35 .

[0221] Next, in a process corresponding to the annular protrusion forming (thickening) process S45 in the can bottom 10E forming process described above, the annular curved portion of the formed preform was supported by the support tool L93 (by the support force in the second direction (upward) described above), while a pressing force was applied in the first direction (downward) to the outer peripheral panel portion (specific plate portion). This resulted in the formation of a drawn and ironed can (DI can) (before the can bottom shape forming (reforming)) including a can bottom intermediate formed body 510E having a shape corresponding to state m47 in FIG. 35 , i.e., the annular protrusion 512E shown in FIG. 36 . This annular protrusion 512E includes a dome panel wall portion 513E, a bottom radius portion 514E (before the reforming), and a chime lower portion 515E (before the reforming). Furthermore, a chime portion 516E (before the reforming) was formed outside the chime lower portion 515E.

[0222] This intermediate can bottom formed body 510E shown in Figure 36 was subjected to trimming processing to cut the mouth edge to the required can height and bottom reform processing (a process equivalent to the can bottom shape forming process S46 in the can bottom 10E forming process described above) using conventional methods, to obtain the final can bottom formed body 520E (after reforming) shown in Figure 37.

[0223] The thickness [mm] of the metal portion at each location in the final molded body 520E (after reforming) shown in Figure 37 was measured. Figure 37 shows the measurement points w1 to w7. The thickness [mm] was measured as follows. The molded (final molded body) drawn and ironed can (DI can) was embedded in epoxy resin, and then cut along the longitudinal axis (Z-axis) of the DI can, including the epoxy resin. After exposing the central cross section through cutting and careful polishing, the thickness [mm] of the metal portion at each of the measurement points w1 to w7 was measured using a measuring microscope.

[0224] As shown in the table in Figure 38, in Example 9, the height Hp of the dome panel portion 522E (Figure 37) in the drawn and ironed can (DI can) (the final formed product) was 12.3 mm. In the final formed product 520E, the diameter (d1) (Figure 37) between the boundary between the dome panel portion 522E and the (post-reformed) annular bottom protrusion 523E was 47.0 mm, and the diameter (d2) (Figure 37) of the ground contact portion of the annular bottom protrusion 523E was 48.0 mm. The thicknesses (mm) of the metal portions at measurement points w1 to w7 (Figure 37) were as shown in the table in Figure 38.

[0225] [Pressure Resistance Test Evaluation] The drawn and ironed cans (DI cans) obtained (as final formed articles) were subjected to a pressure resistance test evaluation by the following pressure resistance test method. The evaluation results are shown in the table of FIG.

[0226] [Pressure Resistance Test Method] With a cup-shaped container filled with water, the open end is sealed with a plug equipped with a water pipe. Next, pressurized water is sent into the cup-shaped container from a water pump through the water pipe. The internal pressure of the cup-shaped container rises, and at a certain point, the dome panel instantly deforms outward (buckling). Usually, at the same time as this deformation, the internal pressure of the can (DI can) (internal can pressure) drops suddenly. The maximum internal can pressure during this period is taken as the pressure resistance value (pressure resistance) [MPa].

[0227] As shown in the evaluation results in the table of Figure 38, the drawn and ironed can (DI can) (the final product) formed in Example 9 corresponds to a 350 mL can, and its can weight [g] (as the weight of the metal portion after trimming) was 9.9 g. As can be seen from the evaluation results in Figure 38, the plate thickness [mm] of the metal portion increased over a wide range, including the range required to improve the pressure resistance of the annular protrusion (after reforming) on ​​the can bottom. As a result, this DI can achieved a desirable pressure resistance (pressure resistance value [MPa]).

[0228] Furthermore, by adopting the method shown in Example 9, which gave such results, in part of the can-making process, it became possible to manufacture can bodies that were thinner in original thickness to save material resources and reduce weight, while still maintaining pressure strength.

[0229] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and the present invention also includes design changes within the scope of the present invention. Furthermore, the above-mentioned examples can be combined by utilizing each other's technologies as long as there are no particular contradictions or problems in the purpose, configuration, etc.

[0230] 1: forming material, 3: can lid, 6: can bottom, 11, 41, 51: plate material, 11a, 41a, 51a: preform, 12, 23, 31, 45, 45A: center panel portion (central plate portion), 13, 32, 32a, 32A, 62a: annular protrusion, 14, 25, 421, 421A: outer peripheral panel portion (outer peripheral plate portion), 420, 521: outer panel portion (outer peripheral plate portion), 22, 44, 54: central protrusion, 24, 46, 56: side wall portion, 26, 47, 57: outer peripheral curved portion (annular curved portion), 30, 30A: intermediate formed body of can lid (before the shape of the can lid is formed), 30a-1: formed body, 33: second chuck wall portion (second outer peripheral wall portion), 34: curl portion, 42, 52: plate-like portion, 43, 53: outer peripheral portion ( side), 60: can bottom intermediate formed body (before the can bottom is shaped), 121, 141, 311: curved portion, 131: inner peripheral wall portion, 132: curved convex portion, 133: outer peripheral wall portion, 321, 321a, 321A: panel wall portion (inner peripheral wall portion), 322, 322a, 322A: chuck wall radius portion (curved convex portion), 323, 323a, 323A: first chuck wall portion (first outer peripheral wall portion), 522: annular curved bottom portion, 55, 61: dome panel portion (center plate portion), 62: can bottom annular protrusion portion, 63: chime portion (second outer peripheral wall portion), 621: dome panel wall portion (inner peripheral wall portion), 622, 622a: bottom radius portion (curved convex portion), 623: chime lower portion (first outer peripheral wall portion).

[0231] 1E: Molded material, 11E, 41E, 51E: Plate material, 11Ea, 41Ea: Preform, 12E, 22E, 31E, 31Ec, 45E, 45Eb, 54E: Center panel portion (central plate portion), 121E, 141E, 311E: Curved end portion, 13E, 32E, 32Ea, 32Eb, 32Ec, 62Ea, 82Ea: Annular protrusion portion, 131E: Inner peripheral wall portion, 132E: Curved convex portion, 133E: Outer peripheral wall portion, 14E, 21E, 421E, 421Eb, 521E: Outer peripheral panel portion (outer peripheral plate portion), 23E, 46E, 55E, 61E, 63E, 81E: Side wall portion , 24E, 47E, 57E, 62Eb: annular curved portion, 3E, 3Ec: can lid, 30E, 40Eb: can lid intermediate formed body, 321E: panel wall portion (inner peripheral wall portion), 322E, 322Ea, 322Eb, 322Ec, 822Ea: chuck wall radius portion (curved convex portion), 323E: first chuck wall portion (first outer peripheral wall portion), 33E: second chuck wall portion (second outer peripheral wall portion), 34E: curl portion, 42E: plate-shaped portion, 420E: outer panel portion (outer plate portion), 43E: outer peripheral side portion, 52E: plate-shaped portion, 53E: outer peripheral side portion, 56E,64E: central protrusion, 10E: can bottom, 91E: plate material, 91Ea: preform, 92E: plate-like portion, 921E: outer panel portion (outer plate portion), 922E: outer peripheral panel portion (outer peripheral plate portion), 93E: outer peripheral side portion, 94E: dome panel portion (central plate portion), 94Ea: center panel portion (central plate portion), 95E: side wall portion, 96E: annular curved portion, 100E: can bottom intermediate formed body, 101E: dome panel portion (central plate portion), 102E: can bottom annular protrusion, 102Ea: annular protrusion, 112Ea: bottom radius portion (curved convex portion), 103E: chime portion (second outer peripheral wall portion), 151E: dome panel wall portion (inner peripheral wall portion), 152E: bottom radius (curved convex portion), 153E: chime lower portion (first outer peripheral wall portion), 921E: outer panel portion (outer plate portion), 922E: outer peripheral panel portion (outer plate portion), 510E: can bottom intermediate formed body (before reforming), 511E: dome panel portion (of intermediate formed body), 512E: annular protrusion portion (of intermediate formed body), 513E: dome panel wall portion (of intermediate formed body), 514E: bottom radius portion (of intermediate formed body), 515E: chime lower portion (of intermediate formed body), 516E: chime portion (of intermediate formed body), 520E: can bottom final formed body (after reforming), 522E: dome panel portion (of final formed body), 523E: can bottom annular protrusion portion (of final formed body),

Claims

1. A method for forming a sheet material, comprising the steps of: forming a specific sheet portion and a side wall portion; forming an annular curved portion connected to the side wall portion; and deforming at least the annular curved portion to form an annular protrusion having a selectively increased sheet thickness, wherein in the step of forming the annular protrusion, the annular curved portion is supported by a support member that is relatively movable in a second direction opposite to a first direction in which the annular protrusion to be formed protrudes, and a pressing force in the first direction is applied to the specific sheet portion, thereby generating a compressive stress in the second direction in the side wall portion, and moving at least a portion of the sheet material that constituted the side wall portion on the support surface of the support member, thereby forming the annular protrusion having a selectively increased sheet thickness.

2. A method for forming a sheet material, comprising the steps of: forming a central protrusion consisting of a central plate portion and a side wall portion on its outer periphery in a plate-shaped portion of the sheet material; forming an outer periphery curved portion on the outer periphery of the side wall portion; and deforming at least the outer periphery curved portion to form an annular protrusion having a selectively increased plate thickness, wherein in the step of forming the annular protrusion, the outer periphery curved portion is supported by a support member that is movable relatively in the protruding direction of the central protrusion, and a pressing force is applied to the central protrusion in the opposite direction to the protruding direction, thereby generating a compressive stress in the protruding direction in the side wall portion, and at least a portion that constituted the side wall portion is moved on the support surface of the support member, thereby forming the annular protrusion having a selectively increased plate thickness.

3. The molding method according to claim 2, characterized in that in the step of forming the annular protrusion, at least a portion of the side wall portion on the support surface of the support member is moved outwardly of the central protrusion.

4. The forming method according to claim 2 or 3, characterized in that the plate material is made of a material mainly composed of metal.

5. A method for forming can ends, comprising the method according to claim 2 as part of the entire process.

6. The method for forming a can lid according to claim 5, further comprising the step of forming a chuck wall portion as a process for forming the can lid shape after the step of forming the annular protrusion.

7. A method for forming a can bottom, comprising the method according to claim 2 as part of the entire process.

8. The method for forming a can bottom according to claim 7, characterized in that after the step of forming the annular protrusion, the step of forming into the shape of the can bottom includes at least a step of forming the shape of the can bottom annular protrusion.

9. A method for forming a sheet material, comprising the steps of: forming a central sheet portion, and forming an outer peripheral sheet portion via a side wall portion that rises upward on the outer periphery side of the central sheet portion; forming an annular curved portion on the inner periphery side of the side wall portion; and deforming at least the annular curved portion to form an annular protrusion having a selectively increased sheet thickness, wherein in the step of forming the annular protrusion, the annular curved portion is supported by a support member that is relatively movable in a second direction opposite to a first direction in which the annular protrusion to be formed protrudes, and a pressing force in the first direction is applied to the outer peripheral sheet portion, thereby generating a compressive stress in the second direction in the side wall portion, and at least a portion of the sheet material that constituted the side wall portion is moved on the support surface of the support member, thereby forming the annular protrusion having a selectively increased sheet thickness.

10. A molding method as described in claim 9, characterized in that in the process of forming the annular protrusion, at least a portion of the plate material constituting the side wall portion on the support surface of the support member is moved toward the inside of the outer peripheral plate portion.

11. The molding method according to claim 9, wherein the plate material is made of a material mainly composed of metal.

12. A method for forming can ends, comprising the method according to claim 9 as part of the entire process.

13. The method for forming a can lid according to claim 12, further comprising the step of forming a chuck wall portion as a step of forming into a can lid shape after the step of forming the annular protrusion.

14. A method for forming a can bottom, comprising the method according to claim 9 as part of the entire process.

15. The method for forming a can bottom according to claim 14, characterized in that, after the step of forming the annular protrusion, the step of forming into the shape of the can bottom includes at least a step of forming the shape of the can bottom annular protrusion.

Images