JP7797899B2 - Metal cup manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a metal cup made of an aluminum alloy or the like.

Existing drinking cups are made of ceramic, glass, metal, paper, plastic, etc. Of these, metal, paper, and plastic cups are lighter than ceramic or glass cups and do not take up much space when stacked, making them easy to carry.

Patent Document 1 discloses a tapered metal cup. This metal cup is made of aluminum and is described as being harder and more durable than plastic cups, as well as being highly recyclable.

The method for manufacturing this metal cup is described as follows: a metal plate is punched and drawn to form a cup, which is then ironed to form a cylindrical vertical-walled preform (DI process); the open end is cut off to set the desired height, and the open end is then rounded to form a curled portion; a stepwise drawing process is then performed to form a vertically drawn cup with vertical wall sections of different heights and with a continuously decreasing diameter from the curled portion to the bottom; a die with a tapered profile is then used to expand each of the vertical wall sections to form a tapered cup with each vertical wall section forming a tapered sidewall; and finally, a dome portion is formed at the bottom of the cup.

Japanese Patent Application Laid-Open No. 2020-508874

When manufacturing a metal cup that is taller than its diameter by drawing a metal plate, as in Patent Document 1, forming the body into a tapered shape can easily result in wrinkles and cracks on the outer surface. In Patent Document 1, the body is formed into a stepped tapered sidewall using multiple sections, but it is desirable to form a body that is smoothly tapered from the bottom to the open end of the cup.

The present invention was made in consideration of these circumstances, and aims to provide a method for manufacturing metal cups that are less likely to develop wrinkles or cracks on the outer surface and have a smoothly tapered body.

The present invention is a method for manufacturing a metal cup by press-forming a metal plate, and includes a drawing and ironing process in which the metal plate is drawn and ironed to form a cylindrical body with a bottom, and a diameter expansion process in which, after the drawing and ironing process, a punch is pressed into the body from the open end side of the body to gradually expand the diameter of the body from the bottom side toward the open end side, forming an intermediate cylinder with a tapered cylindrical portion.

In the manufacturing method described in Patent Document 1, after forming a cylindrical body with a bottom, the body is drawn so that the diameter gradually decreases from the open end toward the bottom. In contrast, in the present invention, the body is formed so that the diameter gradually increases from the bottom toward the open end. In other words, while the process described in Patent Document 1 compresses the metal material radially inward from the outer periphery, in the present invention, the metal material is expanded radially outward from the inner periphery, which makes it possible to form a smoothly tapered body portion with fewer wrinkles.

The drawing and ironing process used to form the cylindrical, bottomed body can be done using the same technology as that used for existing beverage cans. In this case, existing manufacturing equipment produces a cylindrical body with a diameter of approximately 66 mm, which is easy to hold in the hand.

When the cylinders obtained through the drawing and ironing process using this existing equipment are formed into metal cups using the method described in Patent Document 1, the process involves drawing the cylinder, so the final cup shape will have a small diameter. To achieve the same volume as existing cylinders, the cup must be made long and narrow. In particular, because the bottom has the smallest diameter, there is a risk that the cup may tip over when placed on a table or the like. On the other hand, if an attempt is made to produce cups with a larger diameter, the drawing and ironing equipment would need to be extensively modified to one capable of forming large-diameter cylinders.

In the manufacturing method of the present invention, the cylindrical body is expanded, so the capacity can be adjusted by changing the height. Therefore, the drawing and ironing process can be the same as that used in existing beverage can manufacturing processes, making it economical to use existing beverage can manufacturing equipment as is.

In the method for manufacturing a metal cup of the present invention, the diameter expansion process preferably includes a step formation process in which one or more punches are used to form a step in the body of the cylindrical body, the diameter of which is larger at the opening end side than at the bottom side of the cylindrical body, and a shaping process in which one or more punches are used to expand the step and shape it into the tapered cylindrical portion.

When forming a tapered tube section on the body of a cylindrical tube with a bottom, if the taper angle is large, cracks are likely to occur if the tube is machined using a tapered punch from the beginning. For this reason, in this invention, a step is first formed in the step formation process, where the diameter at the open end is larger than the diameter at the bottom, and the step is then expanded to form the tapered tube section. This makes it less likely to crack, and as a result, a smoothly tapered surface can be formed.

In this case, the step forming process and the shaping process can be performed alternately multiple times.

Alternatively, after forming multiple step portions in the step forming process, the shaping process can be performed on each of these step portions individually or in batches.

In the method for manufacturing a metal cup of the present invention, the punch used in the step forming step may include a stepped punch that has a guide portion with a cylindrical outer surface connected to a forming portion with a larger diameter than the guide portion, and the guide portion of the stepped punch may be inserted into the cylindrical body first, thereby fitting the guide portion into the cylindrical body while the forming portion expands the diameter of the cylindrical body.

The guide portion of the stepped punch is inserted into the cylindrical body first, ensuring that the cylindrical body and the stepped punch are aligned, allowing the subsequent diameter expansion process using the forming portion to be carried out with high precision, resulting in the production of cups with high roundness.

In this case, a lower step is further formed near the bottom of the body of the metal cup, and the punch used in the step forming process further includes a lower step punch having a molding portion with a cylindrical outer surface. After forming an initial step near the bottom of the body using the stepped punch, the lower step punch is fitted into the initial step and the lower portion of the initial step is machined while expanding in diameter, thereby forming the lower step.

Because the lower step is formed at the very bottom of the cylinder, if a stepped punch with a guide were used to form it, there is a risk that the guide would come into contact with the inner bottom surface of the cylinder. For this reason, an initial step is first formed using a stepped punch at a position above the position where the lower step will be formed, and then the lower step punch is used to press the initial step position downward. The lower step punch can be designed without a guide, so even if it is brought close to the bottom to form the lower step, the bottom will not be deformed.

In the method for manufacturing a metal cup of the present invention, after the diameter expansion step, it is preferable to include a curling step in which the open end of the intermediate cylinder is folded back to form a curled portion. The curled portion at the open end improves the mouthfeel when the cup is placed on the lips.

In this case, the step forming process can be carried out in the diameter expansion process to form a straight upper cylindrical portion along the can axis direction at the open end of the intermediate cylindrical body. In the curling process, a forming tool is pressed against the open end of the intermediate cylindrical body in the can axis direction, so the load can be borne by the straight upper cylindrical portion, allowing the curled portion to be formed with high precision.

In other words, if the shape gradually expands from the bottom to the open end, it will deform significantly during the curl forming process, making it difficult to form accurately. Therefore, by forming a cylindrical portion at the open end and increasing its deformation strength, the curl can be formed more accurately without deforming the curled portion during the curl forming process.

The upper cylindrical portion should preferably be formed using an upper step punch. This is because this is the final processing step in the diameter expansion process, and if a stepped punch is used, there is a risk that the tapered portion formed in the previous step will be deformed by the guide portion.

This invention makes it possible to manufacture metal cups that are less prone to wrinkles or cracks on the outer surface and have a smoothly tapered body.

FIG. 1 is a front view of a metal cup manufactured by a manufacturing method according to an embodiment of the present invention, with half of the metal cup taken along a vertical cross section centered on the can shaft. FIG. 2 is a front view of a cylindrical body obtained in the drawing and ironing process, with half of the body being a vertical cross-sectional view centered on the can shaft. FIG. 10 is a vertical cross-sectional view of a main part showing a state where processing is being performed in a lower step forming step. FIG. 10 is a longitudinal cross-sectional view of a main part showing a state where processing is being performed in a step forming step. 5 is a longitudinal cross-sectional view of a main part showing a state in which processing is performed in a shaping step following the step forming step of FIG. 4. FIG. 6 is a longitudinal cross-sectional view of a main part showing a state in which processing is being performed in a step forming step following the shaping step of FIG. 5 . FIG. 10 is a cross-sectional view showing a state in which processing is performed with a curling tool in a curling step.

Below, an embodiment of the method for manufacturing a metal cup according to the present invention will be described with reference to the drawings.

As shown in Figure 1, the metal cup 1 manufactured by the manufacturing method of this embodiment is formed by press-forming a metal plate made of aluminum or an aluminum alloy into a bottomed, cylindrical shape. The diameter of the open end 3 is larger than the diameter of the bottom 2, and the cup has a tapered body 4 that gradually expands in diameter from the bottom 2 toward the open end 3. A curled portion 5 is formed at the open end 3 by rolling the end, including the edge, radially outward. The radial center of this metal cup 1 is the can axis C.

The bottom 2 has a shape that is made up of a concavely curved dome portion 6, an inner tapered wall portion 7 that is continuous with the outer edge of the dome portion 6 and gradually increases in diameter as it extends downward in the axial direction of the can, a rim portion 8 that is continuous with the outer edge of the inner tapered wall portion 7 and comes into contact with the ground when the metal cup 1 is placed on a table or the like, and a tapered rising portion 9 that runs from the outer edge of the rim portion 8 to the lowest end of the body portion 4.

The dome portion 6 is concave at its greatest distance from the tip of the rim portion 8 at a position on the can axis C. The rim portion 8 is formed in a ring shape around the can axis C, with a curved surface that convexly curves downward from the can axis C and makes contact with the ground at its most protruding position. The outermost edge of the rim portion 8 has a smaller diameter than the smallest diameter at the bottom end of the body portion 4, and this outermost edge of the rim portion 8 and the bottom end of the body portion 4 are connected by a rising portion 9.

The body 4 has a straight lower cylindrical section 11 and an upper cylindrical section 12 formed near the bottom 2 and the open end 3, respectively, that run parallel to the can axis C. A small lower step 13 is formed at the upper end of the lower cylindrical section 11, which continues from the bottom 2, and a small upper step 14 is also formed at the lower end of the upper cylindrical section 12, which continues from the curled section 5. A tapered tube section 15, whose diameter gradually increases from bottom to top, is formed between the upper end of the lower step 13 and the lower end of the upper step 14.

These dimensions are not necessarily limited, but are set, for example, as follows:
Diameter (outer diameter) D1 of curled portion: 75 mm or more and 100 mm or less Diameter D2 of ground contact portion: 45 mm or more and 60 mm or less Overall height H1: 80 mm or more and 180 mm or less Depth H2 of dome portion 6: 1 mm or more and 15 mm or less Diameter D3 of lower cylindrical portion 11: 50 mm or more and 70 mm or less Diameter D4 of upper cylindrical portion 12: 70 mm or more and 95 mm or less Height H3 from bottom surface to lower end of lower step portion 13: 8 mm or more and 25 mm or less Length H4 from upper end of curled portion 5 to upper end of upper step portion 14: 8 mm or more and 20 mm or less Angle θ of tapered tube portion 15 with respect to the horizontal plane: 80° or more and 85° or less

Next, we will explain the manufacturing method of this metal cup 1. The metal cup 1 is manufactured through a process that includes a cylinder-forming process in which a metal plate is drawn and ironed to form a bottomed, cylindrical cylinder 21; a diameter-expanding process in which, after the cylinder-forming process, multiple punches 40-43 with different outer diameters are pressed into the cylinder 21 from the open end 22 side using the punches 40-43 in ascending order of outer diameter, gradually expanding the diameter of the body 23 of the cylinder 21 from the bottom 2 side toward the open end 22 side to form a tapered cylinder portion 15 and form an intermediate cylinder 50; and a curling process in which a curled portion 5 is formed at the open end of the intermediate cylinder 50 formed in the diameter-expanding process. The processes will be explained below in order.

[Cylinder formation process]
The cylinder forming process includes a cup forming process (FIG. 2(a)) in which a plate made of aluminum or an aluminum alloy is punched and drawn to form a cup 25 that is shallower and has a larger diameter than the cylinder 21 to be formed in the next process, and a drawing and ironing process (FIG. 2(b)) in which the cup 25 is drawn and ironed to form a cylindrical cylinder 21 with a smaller diameter than the cup 25 and a predetermined height as shown in the figure, which has a bottom.

In this drawing and ironing process, the bottom 2 of the cylindrical body 21 is finished to the final shape of the bottom 2 of the metal cup 1, and has a dome portion 6, an inner tapered wall portion 7, a rim portion 8, and a tapered rising portion 9.

[Diameter expansion process]
The diameter expansion process consists of multiple steps, and by sequentially repeating a step formation process in which a step is formed in the body 23 of the cylindrical body 21, the diameter of which is larger on the opening end 22 side than on the bottom 2 side, and a shaping process in which the step is expanded and shaped into a tapered surface, the intermediate cylindrical body 50 shown in Figure 2 (c) is formed.

In this case, after the lower step forming process, which forms the lower step 13 at the bottom of the cylindrical body 21, there is the first step forming process, which forms a first step slightly above the lower step 13, the first shaping process, which shapes the first step, the second step forming process, which forms a second step near the top end of the shaping surface, the second shaping process, which shapes the second step, and so on. After the initial lower step is formed, the step forming process and the shaping process are alternately carried out, forming one step and shaping it to form the entire piece into a tapered shape. For example, the step forming process and the shaping process are each performed alternately 10 to 30 times.

Finally, at the top of the cylindrical body 21, an upper step formation process is carried out to form the upper step 14, thereby completing the diameter expansion process.

The details are explained below. Note that during this diameter expansion process, the shape of the cylindrical body 21 gradually changes, but the cylindrical body formed at the end of the diameter expansion process is referred to as the intermediate cylindrical body 50, and the cylindrical bodies formed in the steps up to that point will be described using the same reference numeral 21 as the cylindrical body used in the cylindrical body formation process.

(Step formation process)
As shown in Figures 3 to 6, the step forming process uses multiple stepped punches 40 to 42 of different diameters, two punches 43 for the lower step, and a punch for the upper step (the figures only show three stepped punches 40 to 42 of different diameters and one punch 43 for the lower step. Although the punch for the upper step has a different diameter, its external shape is the same as that of the punch for the lower step, so the explanation will be given with reference to the punch 43 for the lower step as necessary).

As shown in Figures 4 and 6 (also shown by two-dot chain lines in Figures 3 and 5), the stepped punches 40-42 are formed in a stepped shape with a guide portion 44 connected to a forming portion 45 that is larger in diameter than the guide portion 44, with the guide portion 44 located at the tip. The guide portion 44 is inserted into the cylindrical body 21 first, but the cylindrical body 21 is not formed by this guide portion 44; rather, it is used for centering with the cylindrical body 21.

The outer peripheral surface of the guide portion 44 of these stepped punches 40-42 is formed with a rounded chamfered surface 46 at the tip, and is formed from the outer peripheral end of the rounded chamfered surface 46 into a substantially straight cylindrical outer surface 47. The maximum diameter of the guide portion 44 of each stepped punch 40-42 is formed slightly smaller than the inner diameter of the opening of the cylindrical body 21 before the step is formed by that stepped punch 40-42.

The molding portion 45 is formed as a convex curved surface that protrudes radially outward from the cylindrical outer surface 47 of the guide portion 44, and its maximum diameter is larger than the diameter of the cylindrical outer surface 47 of the guide portion 44. The molding portion 45 then forms steps 51-53 (in Figures 3-6, steps at different molding locations are denoted by the reference numerals 51-53) that have a larger diameter on the open end 22 side than on the bottom 2 side of the cylindrical body 21.

As shown in Figure 3, the lower step punch 43 does not have a guide portion 44 like the stepped punches 40-42, and is a punch with the surface of the forming portion 48 extended to the tip, and the corners around the tip are chamfered into a convex arc shape. In Figure 3, the lower step punch 43 is formed in an unstepped shape. The upper step punch also has a different diameter, but like the lower step punch 43, it does not have a guide portion 44 like the stepped punches 40-42, and has a shape in which the surface of the forming portion (see symbol 48) extends to the tip.

The lower step punch 43 is formed with a diameter equal to or slightly smaller than the forming portion 45 of the stepped punch 40, which has the smallest diameter among the stepped punches 40-42, and the upper step punch is formed with a diameter equal to or slightly smaller than the maximum diameter of the shaping surface 65 of the shaping punch 61, which has the largest diameter among the shaping punches 61 used in the shaping process (the upper step punch is not shown in the illustration, but its shape is shown as a representative of the lower step punch 43, so please refer to this).

In addition, because the lower step punch 43 and upper step punch do not have a guide portion 44, the convex curved surface 48a of the forming portion 48 extends toward the tip, and its minimum diameter is smaller than the inner diameter of the cylinder before it is formed by the lower step punch 43 and upper step punch, respectively.

(Forming process)
In the shaping step, the steps 52, 53 formed in the step forming step are shaped into a smooth tapered surface. As shown in Figure 5, the shaping punch 61 used in this shaping step has a rounded chamfered surface 62 at its tip, and a tapered surface 63 that gradually widens from the tip to the rear continues from the rear end of the rounded chamfered surface 62, and a convex curved surface 64 with a large radius of curvature is formed on the rear end surface of the tapered surface 63. The region from the middle of the tapered surface 63 to the front half of the convex curved surface 64 forms a shaping surface 65.

In this case, the shaping surface 65, as indicated by the reference symbol 65a, is formed long in the distal direction so that shaping can be performed from a position sufficiently farther distally than the step 52 formed in the step forming process, while the rear end 65b of the shaping surface 65 is formed long enough to shaping to a position slightly behind the step 52, 53 formed in the step forming process.

Therefore, this shaping surface 65 is not a straight tapered surface, but rather a tapered surface having a convex curved surface 64 that curves so as to bulge slightly radially outward. This shape makes it possible to suppress elastic recovery (springback) when a wide area including the areas before and after the steps 52, 53 is pushed radially outward, ensuring that the body 23 of the cylindrical body 21 is formed into a tapered surface. Therefore, in this shaping process, the wide areas before and after the steps 52, 53 formed in the step forming process can be shaped into a smooth tapered shape.

In these step forming and shaping processes, the lower step 13, which is located at the bottom of the body 4, is formed first (Figure 3, lower step forming process). This lower step 13 is formed using the stepped punch 40 with the smallest diameter and a lower step punch 43, with the stepped punch 40 first forming a step 51 near the bottom 2 (this step is referred to as the initial step).

In this case, machining is performed at a position close to the bottom surface of the cylindrical body 21. If the stepped punch 40 were used to machine to a position close to the bottom 2, there is a risk that the guide portion 44 would collide with and deform the previously machined bottom 2. Therefore, the stepped punch 40 is used to machine to a position that does not reach the bottom 2. The state after machining with this stepped punch 40 is shown by the two-dot chain line in Figure 3.

Next, the lower step punch 43 is fitted into the cylindrical body 21, and the area below the initial step 51 formed by the stepped punch 40 is expanded in diameter while being machined so as to press the position of the initial step 51 downward, thereby forming the lower step 13. The lower step punch 43 is formed with an outer diameter that is the same as or slightly smaller than the forming portion 45 of the stepped punch 40, so it is fitted into the body 23 of the cylindrical body 21, the diameter of which has been expanded by the step 52, and is aligned with the body 23. Furthermore, because the lower step punch 43 does not have a guide portion 44, it can be brought closer to the bottom 2 than the stepped punch 40.

The area below the lower step 13 formed by the lower step punch 43 is where the outer surface of the cylindrical body 21 is held by the chuck 70 during the diameter expansion process, including the lower step formation process, and the lower cylindrical portion 11 is left straight rather than tapered.

Next, the second smallest diameter stepped punch 41 (explained in Figure 4 for convenience) forms the first step 52 slightly above the lower step 13 (not shown in Figure 4). At this time, the guide portion 44 of the stepped punch 41 is inserted into the large diameter portion of the lower step 13, aligning the punch 41 with the cylindrical body 21.

After forming this first step 52, the front and rear of the first step 52 are shaped into a smooth tapered shape by a shaping punch 61 (Figure 5). In this case, as mentioned above, the shaping surface 65 of the shaping punch 61 is not a straight tapered surface, but is formed as a curved surface that bulges slightly radially outward. This allows the step 52 formed in the previous process to be sufficiently expanded from the radially inward direction, effectively erasing any traces of it and forming a smooth tapered shape.

Then, after repeating this step forming process and shaping process the required number of times, finally, an upper step punch (not shown) is used to form the upper step 14 slightly below the open end 22 of the cylindrical body 21 (upper step forming process). Like the lower step punch 43, this upper step punch is a punch that does not have a guide portion and only has a forming portion 48.

This upper step-forming punch is formed with a diameter that is the same as or slightly smaller than the shaping surface 65 of the largest diameter shaping punch 61, so it fits easily into and is centered on the open end 22 of the previously formed cylindrical body 21. The top of the tapered surface shaped by the shaping punch 61 is then machined to form the upper step 14. Above the upper step 14 is a straight, cylindrical upper cylindrical portion 12' (see the two-dot chain line in Figure 7).

After forming this upper step 14, the upper cylindrical portion 12' is left straight, so no shaping process is carried out. However, if the upper step 14 were formed using stepped punches 41, 42, the tapered portion shaped in the previous shaping process would be deformed by the guide portion 44. Therefore, a punch without a guide portion 44 (an upper step punch) is used to prevent deformation of the lower portion of the upper step 14.

The tapered intermediate cylinder 51 formed through this series of diameter expansion processes has a straight lower cylindrical portion 11 near its bottom 2 that follows the can axis C, and an opening 22 is formed in the straight upper cylindrical portion 12'.

[Curling process]
After the diameter expanding step, the end portion including the edge of the upper cylindrical portion 12′ of the intermediate cylinder 50 is folded back radially outward and wound to form the curled portion 5. In this curling step, as shown in FIG. 7 , a plurality of curling tools 71 are used.

Each curling tool 71 is rotatable around an axis C1 that intersects the can axis C, and has a forming groove 72 along its circumferential direction. Each curling tool 71 is pressed against the open end of the intermediate cylinder 50 in the direction of the can axis C while rotating around the upper cylindrical portion 12', causing the forming groove 72 to expand and fold back the end portion, including the edge, of the upper cylindrical portion 12', forming the curled portion 5.

During this curling process, the curling tool 71 presses the tapered intermediate cylinder 50 in the direction of the can axis C. However, the open end of the intermediate cylinder 50 is formed by a straight upper cylindrical portion 12' that aligns with the can axis C. In addition, due to the work hardening effect achieved through the previous diameter expansion process, buckling and deformation are unlikely to occur.

The metal cup 1 manufactured in this manner has straight cylindrical sections 11, 12 of a certain length formed near the bottom 2 and open end 3, with most of the body 4 between them tapered, with the diameter gradually increasing from the bottom 2 to the open end 3. In this manufacturing method, steps 52, 53 with a larger diameter are formed on the open end 22 side of the cylindrical body 21 than on the bottom 2 side, and then the steps 52, 53 are repeatedly shaped to expand and taper, thereby forming the entire body 4 into a smooth tapered shape.

In this case, the metal material is pushed outward radially from the inner periphery, making it less likely to wrinkle. Furthermore, because the steps 52 and 53 are formed first and then tapered, cracks are less likely to occur compared to machining the material into a tapered shape without forming the steps 52 and 53. This allows for the formation of a smoothly tapered body portion 4.

The bottom 2 of this metal cup 1 is the same as the bottom 2 formed on the bottomed cylindrical tube 21 formed in the initial stage, with the portion above this bottom 2 being enlarged in diameter. Therefore, the process of forming the tube 21 (tube forming process) can be carried out using existing equipment for manufacturing beverage cans.

In addition, a curled portion 5 is formed at the opening 3, making it smooth to the touch.

In the above embodiment, the step forming process and the shaping process were repeated alternately in such a way that one step was formed in the diameter expansion process, this step was then shaped into a tapered surface, and then a new step was formed above it and shaped into a tapered surface as well. However, the step forming process may be performed multiple times to form multiple steps along the can axis C, and then these steps may be shaped one by one from the bottom side. It is also possible to shape two or more steps together.

In addition, the above embodiment can be modified as appropriate without departing from the spirit of the present invention.

C Can shaft 1 Metal cup 2 Bottom 3 Open end 4 Body 5 Curl 6 Dome 7 Inner tapered wall 8 Rim 9 Rising portion 11 Lower cylindrical portion 12 Upper cylindrical portion 13 Lower step 14 Upper step 15 Tapered tubular portion 21 Cylinder 25 Cups 41, 42 Stepped punch 43 Punch for lower step 44 Guide portion 45 Forming portion 47 Cylindrical outer surface 48 Forming portion 48a Convex curved surface 50 Intermediate tubular body 51 Step (initial step)
52, 53 Step portion 61 Shaping punch 63 Tapered surface 64 Convex curved surface 65 Shaping surface 70 Chuck portion 71 Curling tool 72 Forming groove

Claims (5)

A method for manufacturing a metal cup by press-forming a metal plate, comprising:
a drawing and ironing process for forming a cylindrical body with a bottom by drawing and ironing a metal plate;
a diameter expanding step in which, after the drawing and ironing step, a punch is pressed into the cylindrical body from the open end side to gradually expand the diameter of the body portion of the cylindrical body from the bottom side toward the open end side, thereby forming an intermediate cylindrical body having a tapered cylindrical portion;
and
The diameter expanding step includes:
a step forming step of forming a step in a barrel portion of the cylindrical body using one or more punches, the step having a diameter on the open end side of the cylindrical body that is larger than a diameter on the bottom side of the cylindrical body;
a shaping step of shaping the stepped portion into the tapered cylindrical portion while expanding the stepped portion using one or more of the punches;
the punch used in the step forming step includes a stepped punch having a guide portion having a cylindrical outer surface and a forming portion having a diameter larger than that of the guide portion, the punch being continuous with the guide portion;
The guide portion of the stepped punch is inserted into the cylindrical body first, thereby fitting the guide portion into the cylindrical body and expanding the diameter of the cylindrical body by the forming portion;
The punch used in the step forming step further includes a lower step punch having a forming portion with a cylindrical outer surface,
A method for manufacturing a metal cup, characterized in that an initial step is formed near the bottom of the body portion using the stepped punch, and then a lower step punch is fitted into the initial step and the lower part of the initial step is machined while expanding in diameter, thereby forming a lower step near the bottom of the body portion . 2. The method for manufacturing a metallic cup according to claim 1 , wherein in the diameter expanding step, the step forming step and the shaping step are alternately performed a plurality of times. 2. The method for manufacturing a metallic cup according to claim 1 , wherein after a plurality of steps are formed in the step forming step, the shaping step is carried out on these steps. 4. The method for manufacturing a metallic cup according to claim 1, further comprising a curling step of folding back the open end of the intermediate cylindrical body to form a curled portion after the diameter expanding step. 5. The method for manufacturing a metal cup according to claim 4 , wherein the step forming step is carried out in the diameter expanding step, thereby forming an upper cylindrical portion along the can axial direction at the open end of the intermediate cylindrical body.