Method and apparatus for manufacturing cans

Abstract

To improve formability in the drawing and ironing process, suppress occurrence of wrinkles and cracks, and broaden the range of selectable materials.SOLUTION: A method comprises: a cup forming step in which a metal plate is subjected to a drawing process to form a cup having a bottom plate portion; and a tubular body forming step in which the cup is subjected to redrawing and ironing between a punch sleeve and a redraw die to form a tubular body having a smaller diameter and greater depth than the cup. In the cup forming step, a circular plate portion and a tapered surface portion are formed concentrically in the central portion of the bottom plate portion, where the circular plate portion protrudes from the peripheral portion, and where the tapered surface portion inclines in a direction such that the depth of the cup gradually becomes shallower radially outward from the periphery of the circular plate portion. In the tubular body forming step, the tip of the punch sleeve is brought into contact with the tapered surface portion to perform the redrawing process.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for manufacturing a can applied when forming a bottomed cylindrical can.

Background Art

[0002] As an aluminum can capable of containing contents such as beverages and foods, there are an open-top can in which a can lid is joined by double seaming and a bottle can in which a cap is wound and joined, and a DI forming method is known as a manufacturing method thereof.

[0003] For example, in Patent Document 1, a cup is formed so as to form a tapered surface that bends from a predetermined position at the bottom toward the outer edge at a predetermined angle, and the bending start position of the tapered surface at the bottom is arranged between the holding position of the cup and the punch position. A method of performing redrawing on the cup is disclosed. Since the bending start position is arranged between the holding position of the cup and the punch position, it is described that the rigidity of the non-constrained portion is increased by the bent portion, and the generation of bottom wrinkles is suppressed.

[0004] The cup disclosed in Patent Document 2 has an annular bottom wall extending radially inward from its lower peripheral edge, a cylindrical inner side wall extending upward from the inner peripheral edge of this annular bottom wall, and a substantially circular inner bottom wall connected to the upper end of this inner side wall, which are formed concentrically with respect to the cylindrical outer side wall. In addition, Patent Document 3 discloses that the bottom of the cup is formed in a dome shape in advance.

[0005] On the other hand, in recent years, there has been an increasing demand to reduce energy consumption and greenhouse gas emissions related to the product life cycle, and to reduce the environmental impact. In the above aluminum can, the environmental impact can be reduced by increasing the proportion of recycled raw materials and decreasing the proportion of newly used ingots in the composition of the aluminum alloy sheet material as the material. However, when the proportion of recycled raw materials is increased, compared with the material of a general aluminum can, even if the thickness is the same, it may become a material that is difficult to stretch and form during molding, and wrinkles and cracks are likely to occur at the bottom of the can, especially during ironing.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of such circumstances, and an object thereof is to improve the formability in ironing, suppress the occurrence of wrinkles and cracks, and widen the range of material selection.

Means for Solving the Problems

[0008] The method for manufacturing a can of the present invention includes a cup forming step of performing drawing on a metal plate to form a cup with a bottom plate portion, and a cylinder forming step of redrawing and ironing the cup between a punch sleeve and a lid die to form a cylinder having a smaller diameter and a greater depth than the cup. In the cup forming step, a circular plate portion protruding from the peripheral portion and a tapered surface portion that is inclined in a direction gradually shallowing the depth of the cup are concentrically formed at the center portion of the bottom plate portion. In the cylinder forming step, the tip of the punch sleeve is brought into contact with the tapered surface portion and redrawn.

[0009] In the cylinder forming process, since the tapered surface portion of the cup is arranged between the tip of the punch sleeve and the lid draw die, there is a margin in the material for the bottom plate portion of the cup compared to a flat plate-like one, and cracks are less likely to occur during subsequent processing. Also, in the inner part of the punch sleeve, the bent portion between the circular plate portion and the tapered surface portion of the cup is arranged on the inner side in the radial direction of the punch sleeve. Due to the bending, there is a margin in the material, and even when forming the bottom at the end of ironing, it is not pulled forcibly and cracks are less likely to occur.

[0010] In the method for manufacturing a can of the present invention, it is preferable that the tapered surface portion has an inclination angle of 2° or more and 18° or less with respect to a plane orthogonal to the axial direction of the cup.

[0011] When the tapered surface portion extends to the peripheral edge of the cup, when holding the cup, the peripheral edge portion of the tapered surface portion is formed by the lid draw die. At this time, if the inclination angle of the tapered surface portion becomes too large, it is largely formed by the lid draw die and is likely to cause wrinkles. If the inclination angle is too small, the margin of the material due to the tapered surface portion decreases, and the effect of preventing cracks is reduced. Note that it is not always necessary for the tapered surface portion to reach the lower end of the peripheral wall portion of the cup, and the outer peripheral edge of the tapered surface portion may be arranged on the inner side in the radial direction of the side wall portion.

[0012] In the method for manufacturing a can of the present invention, it is preferable that the circular plate portion has a protruding depth dimension from the inner peripheral edge of the outer peripheral convex bent portion at the lower end of the peripheral wall portion of the cup of 1 mm or more and 10 mm or less.

[0013] As the protruding depth dimension (offset amount) of the circular plate portion increases, the forming by the lid draw die when holding the cup becomes excessive, and wrinkles and the like are likely to occur. If the protruding depth dimension is too small, the margin of the material decreases, so the effect of improving formability is reduced.

[0014] In the method for manufacturing a can of the present invention, it is preferable that the ratio of the diameter of the outer peripheral edge of the circular plate portion to the diameter of the tip of the punch sleeve is 0.61 or more and 0.87 or less. If this ratio is too large (the distance between the inner peripheral edge of the tapered surface portion and the tip of the punch sleeve is too small), the margin of the material inside the punch sleeve will be reduced. If the ratio is too small (the distance is too large), wrinkles are likely to occur in the dome portion.

[0015] The can manufacturing apparatus of the present invention includes a cup forming device for forming a cup with a bottom plate portion, and a cylinder forming device for redrawing and ironing the cup to form a cylinder having a smaller diameter and a greater depth than the cup. The cup forming device has a punch main body portion and a central punch fitted into a hole portion at the tip of the punch main body portion. The central punch has a concentric ring-shaped protrusion protruding from the tip portion, and is provided so that the protruding dimension of the protrusion from the tip surface of the punch main body portion can be adjusted.

[0016] Since the protrusion of the central punch protrudes from the punch main body portion, a circular plate portion and a tapered surface portion around it can be formed on the bottom plate portion of the cup. By adjusting the protruding dimension of the protrusion, the inclination angle of the tapered surface portion can be appropriately adjusted.

Advantages of the Invention

[0017] According to the present invention, a circular plate portion and a tapered surface portion are formed on the bottom plate portion of the cup, and redrawing and ironing are performed while pressing the tapered surface portion with the tip of the punch sleeve. Therefore, a margin of material is generated on both the radially outer side and the radially inner side of the punch sleeve, and wrinkles and cracks are less likely to occur particularly at the bottom of the can during redrawing, ironing, and bottom forming processes. For this reason, even if a material that is disadvantageous for can body forming compared to conventional can materials is used, quality defects caused by forming can be suppressed. Therefore, for example, even a can material with a significantly high proportion of recycled raw materials contained in the material can be used for mass production.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described. The bottle can 1 of one embodiment is formed of a metal plate made of an aluminum alloy. As shown in FIG. 1, it has a bottom portion 2, a cylindrical body portion 3 continuous from the periphery of the bottom portion 2, a tapered diameter-reducing portion 4 that gradually reduces in diameter upward from the upper end of the body portion 3, a cylindrical small-diameter neck portion 5 extending upward from the upper end of the diameter-reducing portion 4, and a mouth portion 6 formed in an upper portion above the neck portion 5 and to which a cap (not shown) is attached. The mouth portion 6 has a bulging portion 7 protruding radially outward at its lower end, a male screw portion 8 above it, and a curl portion 9 formed by rounding the open end above the male screw portion 8.

[0020] The bottom portion 2, the body portion 3, the diameter-reducing portion 4, the neck portion 5, and the mouth portion 6 are arranged coaxially with each other. In this embodiment, their common axis is referred to as the can axis S1 for explanation.

[0021] Also, as shown in FIGS. 1 and 2, the bottom portion 2 has a grounding portion 11 that is smaller in diameter than the body portion 3 and annularly protrudes outward (downward) in the can axis direction, an outer wall portion 12 that connects the body portion 3 and the grounding portion 11, a counter portion 13 connected to the grounding portion 11 and extending upward from the inner peripheral end of the grounding portion 11, and a concave dome portion 15 connected via a concave bending portion 14 from the upper end of the counter portion 13. The grounding portion 11 has an inner bending portion 16 convexly formed radially inward from its apex and an outer bending portion 17 convexly formed radially outward. These inner bending portion 16 and outer bending portion 17 may have different radii of curvature or the same radius of curvature.

[0022] The outer wall portion 12 has a convex curved portion 18 continuous from the lower end of the body portion 3 and a concave curved portion 19 continuous from the lower end of the convex curved portion 18, and the concave curved portion 19 is inclined so as to gradually decrease in diameter downward. And the inner peripheral end of the lower end of the concave curved portion 19 is connected to the outer peripheral end of the outer bending portion 17 of the grounding portion 11. The bottom portion 2 having such a shape is formed symmetrically about the left and right in a longitudinal section passing through the can axis S1 with the center of the dome portion 15 arranged on the can axis S1.

[0023] In this embodiment, although the dimensions are not limited, the cylindrical body 3 is formed with an outer diameter D1 of 65 mm or more and 67 mm or less. The mouth part 6 has an outer diameter of 38 mm nominal.

[0024] Also, for the bottom part 2, for example, the radius of curvature R1 of the dome part 15 is 30 mm or more and 60 mm or less, the radius of curvature R2 of the concave bending part 14 is 2.0 mm or more and 2.5 mm or less, the diameter of the apex of the grounding part 11 (the distance of the straight line passing through the can axis connecting the apexes in the longitudinal section) D2 is 46.8 mm or more and 48.1 mm or less, the radius of curvature R3 of the inner bending part 16 is 1.0 mm or more and 2.5 mm or less, the radius of curvature R4 of the outer bending part 17 is 1.5 mm or more and 2.5 mm or less, the radius of curvature R5 of the concave curved part 19 of the outer wall part 12 is 10 mm or more and 20 mm or less, and the radius of curvature R6 of the convex curved part 18 is 2.5 mm or more and 4.5 mm or less. Note that all the radii of curvature are values on the outer surface of the bottle can 1. The plate thickness t of the can axis S1 of the dome part 15 is approximately the original plate thickness before forming, and is formed to be 0.280 mm or more and 0.400 mm or less, and preferably 0.290 mm or more and 0.320 mm or less.

[0025] Next, a method for manufacturing the bottle can 1 formed as described above will be described. A flat metal plate made of an aluminum alloy is press-worked to form a relatively shallow and large-diameter cup 21 as shown in Fig. 3(A) (cup forming step), and then the cup 21 is further drawn and ironed to form a bottomed cylindrical barrel 22 as shown in Fig. 3(B) (barrel forming step), and the upper end portion of the barrel 22 is processed to form the reduced-diameter portion 4, the neck portion 5, and the mouth portion 6 (upper end portion forming step), whereby the bottle can 1 is formed. The apparatus for manufacturing this bottle can is composed of a cup forming apparatus, a barrel forming apparatus, a printing apparatus, an upper end portion processing apparatus for processing the upper end portion of the barrel, and the like.

[0026] (Cup forming step) The cup 21 has a bottom plate portion 23 and a cylindrical peripheral wall portion 24 around it. The bottom plate portion 23 is formed concentrically with a circular plate portion 25 that protrudes from the peripheral edge and a tapered surface portion 26 that inclines in a direction of gradually shallowing the depth of the cup 21 radially outward from the peripheral edge of the circular plate portion 25. Specifically, as shown in FIG. 4, between the outer peripheral edge of the tapered surface portion 26 and the lower end of the peripheral wall portion 24, it is connected by an outer peripheral convex bending portion 27 that protrudes outward (diagonally downward) of the cup 21, and between the inner peripheral edge of the tapered surface portion 26 and the outer peripheral edge of the circular plate portion 25, it is also connected by a lower convex bending portion 28 that protrudes outward (downward) of the cup 21.

[0027] In this case, although not necessarily limited, the ratio (D4 / D3) of the diameter D4 of the outer peripheral edge of the circular plate portion 25 to the outer diameter D3 of the peripheral wall portion 24 is set to be 0.24 or more and 0.43 or less. For example, the outer diameter D3 of the peripheral wall portion 24 is 95 mm or more and 125 mm or less, preferably 98 mm or more and 105 mm or less, and the diameter D4 of the outer peripheral edge of the circular plate portion 25 is 30 mm or more and 40 mm or less, preferably 33.5 mm or more and 34.5 mm or less. Further, the tapered surface portion 26 is set such that the inclination angle θ1 with respect to the plane orthogonal to the axial direction of the cup 21 is 2° or more and 18° or less, preferably 2° or more and 6° or less. The protruding depth dimension h1 of the circular plate portion 25 is formed to be 1 mm or more and 10 mm or less, preferably 1 mm or more and 3 mm or less, with respect to the depth of the cup 21 to the inner peripheral edge of the outer peripheral convex bending portion 27 at the lower end of the peripheral wall portion 24.

[0028] In the cup forming device for forming this cup 21, a cup forming punch 40, a cup forming die 50, a blank cutter 55, etc. shown in FIG. 5 are used. The cup forming punch 40 has a central punch 42 for forming the circular plate portion 25 detachably provided in the axial direction on the axis S3 of a cylindrical punch main body portion 41 for forming the peripheral wall portion 24 and the outer peripheral convex bending portion 27. A hole portion 43 is formed on the axis S3 of the punch main body portion 41, and the central punch 42 is fitted in the hole portion 43. A convex curved surface 44 for forming the outer peripheral convex bending portion 27 of the cup 21 is formed at the lower end of the outer peripheral portion of the punch main body portion 41.

[0029] The central punch 42 has concentric ring-shaped ridges 45 formed to project downward at the tip around the axis S3, and the tip (lower end) of these ridges 45 is fixed in the hole 43 of the punch main body 41 in a state of protruding along the axis S3 direction from the tip of the punch main body 41. The protruding dimension h2 of the tip of the ridge 45 can be adjusted by appropriately interposing a spacer or the like between the central punch 42 and the punch main body 41. According to the protruding dimension (the distance from the lower edge of the convex curved surface 44 to the tip of the ridge 45) h2 of the ridge 45 of the central punch 42, the protruding depth dimension h1 of the circular plate portion 25 of the cup 21 is determined. The protruding dimension h2 of the ridge 45 and the protruding depth dimension h1 of the circular plate portion 25 of the cup 21 are substantially equal.

[0030] The die 50 for cup formation and the blank cutter 55 are both formed in a ring shape and are arranged on the same axis S3 as the cup-forming punch 40. The die 50 for cup formation is fixed to one end of the inner peripheral portion of the cylindrical blank punch 51. And the cup-forming punch 40 reciprocates along the axis S3 and enters the inside of the die 50 for cup formation.

[0031] Also, the blank cutter 55 is usually arranged on the outer peripheral side of the cup-forming punch 40 and the die 50 for cup formation, and is supported to reciprocate along the axis S3 toward the die 50 for cup formation in the same manner as the cup-forming punch 40, but is movable separately from the cup-forming punch 40. A ring-shaped cutter portion 56 is fixed to the inner peripheral portion of the blank cutter 55, and one end (the lower end in FIG. 5) of the inner peripheral portion of the cutter portion 56 is formed as a cutting edge 56a. The inner diameter of the cutting edge 56a is formed larger than the inner diameter of the die 50 for cup formation.

[0032] On one side, one end of the outer peripheral portion of the blank punch 51 (one end on the side where the cup forming die 50 is fixed: the upper end in FIG. 5) is formed with a sharp cutting edge 51a. Then, the cutting edges 56a and 51a of the blank cutter 55 and the blank punch 51 are arranged to face each other, and the aluminum plate material P1 can be punched into a circular blank P2 between these cutting edges 56a and 51a.

[0033] Then, as shown in FIG. 5, with the cup forming die 50 and the blank cutter 55 separated in the axial direction, the aluminum plate material P1 is placed therebetween. First, by lowering the blank cutter 55 along the axis S3, as shown in FIG. 6, the circular blank P2 is punched by the cutting edges 56a and 51a of the blank cutter 55 and the blank punch 51. Then, as shown in FIGS. 7 and 8 in sequence, the cup forming punch 40 descends to form the cup 21.

[0034] In this case, first, the ridge 45 of the central punch 42 of the cup forming punch 40 abuts against and presses the blank P2, thereby forming a circular plate portion 25 inside the ridge 45 of the central punch 42. Next, when the outer peripheral portion of the cup forming punch 40 abuts against the blank P2, a tapered surface portion 26 is formed between the tip of the ridge 45 and the lower end of the convex curved surface 44 of the punch main body portion 41. Further, when the cup forming punch 40 enters the inside of the cup forming die 50, the blank is drawn and formed between the cup forming punch 40 and the cup forming die 50 to form the peripheral wall portion 24 of the cup 21.

[0035] The cup 21 formed in this way is transferred to the cylindrical body forming process. (Cylindrical body forming process) In the cylindrical body forming process, after the cup 21 is re-drawn and formed into a small-diameter bottomed cylindrical shape, the cylindrical portion is ironed and thinned by ironing to increase the depth, and then bottom forming is performed to form the bottom 2. Thereafter, the opening end portion is cut off to form the cylindrical body 22 (FIG. 3(B)).

[0036] As shown in Fig. 9, the cylinder forming apparatus that performs these ironing, squeezing, and bottom forming processes has a redrawing die 30, a squeezing die 70, and a bottom forming die 80 arranged side by side on the same axis S2, and they are continuously performed using the same punch sleeve 60. Although only one squeezing die 71 is shown in Fig. 9 for the squeezing die 70, a plurality of squeezing dies with sequentially reduced inner diameters are arranged coaxially according to the degree of the intended squeezing process. These redrawing die 30 and squeezing die 70 are usually arranged with their axis S2 oriented in the horizontal direction, and the punch sleeve 60 advances from left to right in Fig. 9 for processing.

[0037] In addition, in front of the advancing direction of the punch sleeve 60, a bottom forming die 80 for forming the bottom 2 including the dome portion 15 of the cylinder 22 is arranged between the tip of the punch sleeve 60 that has passed through the squeezing die 71 at the foremost position. The cylinder forming apparatus for forming the cylinder 22 is composed of the redrawing die 30 having this punch sleeve 60, the squeezing die 70, the bottom forming die 80, etc.

[0038] (Cylinder forming apparatus) As shown in Fig. 10 etc., the redrawing die 30 includes an annular redrawing die 31, a cylindrical cup holder 32 arranged opposite to this redrawing die 31, and a cylindrical punch sleeve 60 arranged inside this cup holder 32. Their axis is indicated by S2. Note that the axial positions of the redrawing die 31 and the squeezing die 71 are fixed, and the cup holder 32 and the punch sleeve 60 are supported so as to be axially movable.

[0039] The lid draw die 31 has a flat contact surface 34 formed on its upper surface to contact the outer surface of the outer peripheral portion (tapered surface portion 26) of the bottom plate portion 23 of the cup 21, and a convex curved surface 36 is formed at the corner of the inner peripheral portion of the contact surface 34 and the forming hole 35 (see FIG. 9). The contact surface 34 is formed in a plane orthogonal to the axis S2. The convex curved surface 36 is formed such that the longitudinal cross-section passing through the axis S2 (see FIG. 9) has an arc angle of 90° or more. As a result, the position where the convex curved surface 36 most protrudes into the forming hole 35 is the portion where the minimum inner diameter D5 of the forming hole 35 is located, and the forming hole 35 gradually expands in the tip direction (the forward direction of the punch sleeve 60), and a relief surface 37 is formed. Note that this convex curved surface 36 is formed by connecting a plurality of arcs with different radii of curvature, but it may also be a convex arc surface consisting of a single radius of curvature.

[0040] The cup holder 32 has a pressing surface 38 facing the contact surface 34 of the lid draw die 31 formed as a flat surface orthogonal to the axis C2, and its outer diameter is formed smaller than the inner diameter of the cup 21. When inserted into the cup 21, a slight gap is formed between the inner peripheral surface of the peripheral wall portion 24 of the cup 21. On the other hand, the inner peripheral surface 32a of the cup holder 32 is formed larger than the maximum outer diameter of the punch sleeve 60 and larger than the inner diameter of the lid draw die 31 (the inner diameter D5 of the minimum inner diameter portion due to the convex curved surface 36).

[0041] The punch sleeve 60 is formed in a cylindrical shape, and a protruding forming die portion 61 protruding in an annular shape is formed at its tip. This punch sleeve 60 is for redrawing the cup 21 between the lid draw die 31, and thus is formed with an outer diameter D6 smaller than the minimum inner diameter D5 of the lid draw die 31. The gap between the punch sleeve 60 and the lid draw die 31 is set to a value slightly larger than the plate thickness of the cup 21.

[0042] As shown in FIG. 10 and the like, the protruding forming portion 61 has a tip arc-shaped surface 62 formed at its tip, and a concave arc-shaped surface 63 and a convex arc-shaped surface 64 are sequentially formed from the outer peripheral edge of the tip arc-shaped surface 62, and the convex arc-shaped surface 64 is connected to the outer peripheral surface of the punch sleeve 60. The range from the tip arc-shaped surface 62 to the concave arc-shaped surface 63 and the convex arc-shaped surface 64 forms the outer portion from the grounding portion 11 of the bottom portion 2 of the cylindrical body 22 in the bottom forming die 80.

[0043] The inner peripheral surface of the punch sleeve 60 is formed in a straight shape in the axial direction from the inner peripheral edge of the tip arc-shaped surface 62. The tip arc-shaped surface 62 is formed in a convex arc shape protruding in the axial tip direction, and the diameter D7 at the tip position thereof is 46 mm or more and 49 mm or less, preferably 47.8 mm or more and 48.2 mm or less, and is set in a dimensional relationship that becomes the diameter at the middle position of the tapered surface portion 26 of the cup 21 in a state where the cup 21 is held between the cup holder 32 and the lid loader 31. In this case, the ratio (D4 / D7) of the diameter D7 at the tip position of the punch sleeve 60 to the diameter D4 of the outer peripheral edge of the cup 21 is 0.61 or more and 0.87 or less, and more preferably 0.69 or more and 0.73 or less.

[0044] The cup holder 32 and the punch sleeve 60 are both attached to the drive portion of the cylindrical body forming device and are reciprocated along the axis S2. However, the cup holder 32 is axially relatively movable with respect to the punch sleeve 60 and is supported in a state of being pressed in the axial tip direction by a biasing means such as a spring.

[0045] The bottom forming die 80 is provided in front of a row of a plurality of ironing dies 71, and includes an annular hold-down ring 81 that forms a concave curved portion 19 from the outer bending portion 17 of the outer wall portion 12 between the tip arc-shaped surface 62 and the concave arc-shaped surface 63 of the punch sleeve 60, and a dome forming die 82 that enters the inside of the punch sleeve 60 and bends the bottom plate portion 23 of the cup 21 with the tip arc-shaped surface 62 of the punch sleeve 60, while forming a counter portion 13, a concave bending portion 14, and a dome portion 15 from the inner bending portion 16. The hold-down ring 81 and the dome forming die 82 are concentrically arranged, and an annular gap is formed therebetween. Further, the hold-down ring 81 is supported so as to be movable in the direction of the axis S2 with respect to the dome forming die 82.

[0046] (Details of the cylindrical body forming process) Next, the details of the processing in the cylindrical body forming process will be described using the cylindrical body forming apparatus configured as described above. Separate the lid draw die 31 and the cup holder 32 in the axial direction, move the cup 21 produced in the cup forming process while moving it in the radial direction, and place it between the lid draw die 31 and the cup holder 32. Advance the cup holder 32 so as to sandwich the tapered surface portion 26 of the bottom plate portion 23 of the cup 21 between the contact surface 34 of the lid draw die 31, and insert it into the cup 21 as shown in FIG. 10. In this state, the tip of the punch sleeve 60 has retreated from the tip of the cup holder 32.

[0047] Next, when the cup holder 32 and the punch sleeve 60 are further advanced, as shown in FIG. 11, the peripheral edge portion of the cup 21 is sandwiched between the pressing surface 38 of the cup holder 32 and the contact surface 34 of the lid draw die 31, so that the outer peripheral portion of the tapered surface portion 26 is deformed so as to be in a direction orthogonal to the axial direction, and the middle position of the tapered surface portion 26 is pressed against the convex curved surface 36 of the lid draw die 31 and is bent and formed along the convex curved surface 36. From the bent portion 39 by the convex curved surface 36 toward the radially inner side, the tapered surface portion 26 and the circular plate portion 25 are maintained substantially in their original shapes. At this time, the punch sleeve 60 has not yet reached the bottom plate portion 23 of the cup 21. Although the shape of the cup 21 changes as the processing progresses, for the sake of convenience, the cup during processing is also referred to as a cup and is described using the reference numerals such as 21 and the reference numerals shown in FIG. 4.

[0048] When the punch sleeve 60 is advanced from the state shown in FIG. 11, as shown in FIG. 12, first, the tip of the tip arc-shaped surface 62 of the punch sleeve 60 contacts the tapered surface portion 26 of the cup 21 at a position radially inward of the radius of the lid draw die 31. When the punch sleeve 60 is further advanced, the tapered surface portion 26 of the cup 21 is pushed by the tip arc-shaped surface 62 of the punch sleeve 60 and is bent by the tip of the tip arc-shaped surface 62 and the convex curved surface 36 of the lid draw die 31, respectively, and is stretched between them (see FIG. 13).

[0049] At this time, since the peripheral edge portion of the cup 21 is clamped between the cup holder 32 and the lid draw die 31, a tension acts between this clamped portion and the tip arc-shaped surface 62 of the punch sleeve 60. As the punch sleeve 60 advances, the tension between the clamped portion and the tip arc-shaped surface 62 of the punch sleeve 60 increases, and the clamped portion of the cup 21 is pulled radially inward while sliding between the cup holder 32 and the lid draw die 31 against the clamping force by the cup holder 32 and the lid draw die 31. The inclination angle of the portion stretched between the tip of the tip arc-shaped surface 62 and the convex curved surface 36 of the lid draw die 31 increases as the punch sleeve 60 advances. On the other hand, in the portion radially inside the tip arc-shaped surface 62 of the punch sleeve 60, the inner peripheral portion of the tapered surface portion 26 and the circular plate portion 25 are maintained substantially in their original shapes.

[0050] When the punch sleeve 60 further advances from the state shown in Fig. 13, the convex arc-shaped surface 64 of the punch sleeve 60 contacts the portion spanned by the tip of the tip arc-shaped surface 62 and the convex curved surface 36 of the lid draw die 31, as shown in Fig. 14, and the spanned portion is bent and formed by the convex arc-shaped surface 64. After Fig. 14, as the punch sleeve 60 further advances and the convex arc-shaped surface 64 enters the forming hole 35 of the lid draw die 31, while drawing the clamped portion of the cup 21 between the cup holder 32 and the lid draw die 31 radially inward, a redrawing process is performed between the convex arc-shaped surface 64 and the convex curved surface 36 of the lid draw die 31.

[0051] After that, in this redrawing die 30, as the punch sleeve 60 advances, the cup 21 is drawn into the forming hole 35 of the lid draw die 31 and redrawn. When the punch sleeve 60 enters the ironing die 71 of the next ironing die 70, an ironing process is performed. This ironing process is carried out in multiple stages by a plurality of ironing dies 71, and a cylindrical body 75 with a large depth is formed while gradually reducing the wall thickness of the body portion.

[0052] Finally, the bottom portion 2 of the cylindrical body 75 is processed by the bottom forming die 80. First, as shown in Fig. 15(A), the outer peripheral portion of the bottom of the cylindrical body 75 is clamped between the outer peripheral side portion from the tip of the punch sleeve 60 and the hold-down ring 81, and the forming of the outer wall portion 12 is started. Next, as shown in Fig. 15(B), in this state, the punch sleeve 60 advances, and the tip arc-shaped surface 62 of the punch sleeve 60 enters between the hold-down ring 81 and the dome forming die 82, thereby forming the grounding portion 11. At the same time, a counter portion 13, a dome portion 15, etc. are formed between the inner side portion from the tip of the tip arc-shaped surface 62 of the punch sleeve 60 and the dome forming die 72. Then, by cutting off about several millimeters in a ring shape from the open end portion toward the bottom side with another device, a cylindrical body 22 having the bottom portion 2 shown in Fig. 3(B) is formed.

[0053] The body portion of the cylindrical body 22 formed in this way is formed into a wall portion 22A that is the thinnest and has a constant thickness from near the bottom 2 to near the middle, as shown in Fig. 3(B), and is formed into a flange portion 22B that is thicker than the wall portion 22A and has a constant thickness from the open end to near the middle. Between the bottom 2 and the wall portion 22A and between the wall portion 22A and the flange portion 22B, it is formed into a transition portion where the thickness changes smoothly. For example, the wall portion 22A is formed with a plate thickness of 0.115 mm or more and 0.135 mm or less, and the flange portion 22B is formed with a plate thickness of 0.200 mm or more and 0.220 mm or less. The shape of the bottom 2 is formed into substantially the final shape of the can 1, such as the plate thickness t on the can axis S1 of the dome portion 15. The height of the cylindrical body 22 is formed, for example, to be 130 mm or more and 136 mm or less, or 162 mm or more and 168 mm or less.

[0054] As described above, the cup 21 is processed with the downward convex bent portion 28 of the tapered surface portion 26 and the circular plate portion 25 arranged at a position radially inward from the tip arc-shaped surface 62 of the punch sleeve 60. Even in ironing, although some springback may occur, since the bent state is substantially maintained, before processing the bottom 2, a margin corresponding to the downward convex bent portion 28 is generated in the material inside the punch sleeve 60. Therefore, it can be processed into a dome shape without causing cracks or the like in the processing of the bottom 2 by the bottom forming die 80.

[0055] After this cylindrical body forming process, printing and the like are performed. In the upper end portion forming process, the upper end portion of the cylindrical body 22 is processed to form the reduced diameter portion 4, the neck portion 5, and the mouth portion 6, thereby manufacturing the bottle can.

[0056] According to this manufacturing method, in the cup forming step, a circular plate portion 25 and a tapered surface portion 26 are formed on the bottom plate portion 23 of the cup 21. In the cylindrical body forming step, the tip of the punch sleeve 60 is abutted against a position in the middle of the tapered surface portion 26 and redrawn and ironed. Therefore, since a margin is created in the material by the tapered surface portion 26 outside the radial direction of the punch sleeve 60, cracks are less likely to occur during the redrawing process. Also, since a margin is created in the material by the downward convex bending portion 28 even in the inner portion in the radial direction of the punch sleeve 60, cracks are less likely to occur even when forming the bottom portion 2 at the end of the ironing process without being excessively pulled. Therefore, the cylindrical body 22 can be manufactured with high precision from the body portion 29 to the bottom portion 2.

[0057] And since this cylindrical body forming step can be performed smoothly, it is possible to select and use a material whose formability is different from that of conventional materials (disadvantageous for forming that is difficult to stretch during the forming of a beverage can). Therefore, it becomes possible to select a material containing a large amount of recycled aluminum raw material compared to conventional materials and reduce the environmental load of the product.

Explanation of Reference Numerals

[0058] 1 Bottle can 2 Bottom portion 22 Cylindrical body 3 Body portion 4 Reduced diameter portion 5 Neck portion 6 Mouth portion 11 Grounding portion 12 Outer wall portion 13 Counter portion 14 Concave bending portion 15 Dome portion 16 Inner bending portion 17 Outer bending portion 18 Convex curved portion 19 Concave curved portion 21 Cup 23 Bottom plate portion 24 Peripheral wall portion 25 Circular plate portion 26 Tapered surface portion 27 Outer peripheral convex bending portion 28 Lower convex bending part 29 Body part 30 Re-drawing die 31 Redraw die 32 Cup holder 34 Contact surface 35 Forming hole 36 Convex curved surface 37 Relief surface 38 Pressing surface 39 Bending part 40 Cup-forming punch 41 Punch body part 42 Central punch 43 Hole part 44 Convex curved surface 45 Rib 50 Cup-forming die 51 Blank punch 55 Blank cutter 60 Punch sleeve 61 Protruding forming die part 62 Tip arc-shaped surface 63 Concave arc-shaped surface 64 Convex arc-shaped surface 70 Ironing die 71 Ironing die 75 Cylindrical body 80 Bottom-forming die 81 Hold-down ring 82 Dome-forming die

Claims

1. A cup forming step of performing drawing on a metal plate to form a cup with a bottom plate portion, and a cylinder forming step of redrawing and ironing the cup between a punch sleeve and a lid die to form a cylinder having a smaller diameter and a greater depth than the cup. In the cup forming step, a circular plate portion protruding from the central portion of the bottom plate portion and a tapered surface portion that is inclined in a direction gradually shallowing the depth of the cup radially outward from the periphery of the circular plate portion are concentrically formed. In the cylinder forming step, a method for manufacturing a can, characterized in that the tip of the punch sleeve is brought into contact with the tapered surface portion for redrawing.

2. The method for manufacturing a can according to claim 1, wherein the inclination angle of the tapered surface portion with respect to a plane orthogonal to the axial direction of the cup is 2° or more and 18° or less.

3. The method for manufacturing a can according to claim 1, wherein the protruding depth dimension of the circular plate portion from the inner peripheral edge of the outer peripheral convex bent portion at the lower end of the peripheral wall portion of the cup is 1 mm or more and 10 mm or less.

4. The method for manufacturing a can according to claim 1, wherein the ratio of the diameter of the outer peripheral edge of the circular plate portion to the diameter of the tip of the punch sleeve is 0.61 or more and 0.87 or less.

5. A can manufacturing apparatus including a cup forming apparatus for forming a cup with a bottom plate portion, and a cylinder forming apparatus for redrawing and ironing the cup to form a cylinder having a smaller diameter and a greater depth than the cup. The cup forming apparatus has a punch main body portion and a central punch fitted into a hole portion at the tip of the punch main body portion. The central punch is provided with a concentric ring-shaped protrusion protruding from the tip portion, and the protruding dimension of the protrusion from the tip surface of the punch main body portion is adjustable. A can manufacturing apparatus.

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