JP2001210283A - Method of grooving bottom portion of battery can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the bottom thickness of a groove for an explosion-proof valve in a bottom portion of a battery can is changed with the fluctuation of the bottom dead point of a punch due to the thermal expansion of a sliding press. SOLUTION: A grooving method comprises a step of inserting a work W together with a punch 20 into a guide die 11 which is held ready at an upper end position while being energized by an energizing spring 14 having greater thrusting force than required clamping pressure. The bottom portion of the work is clamped with a grooving die protruded portion 10a having a set lower- end depth Hd from a guide die upper face 11b and a moving-down punch claming plane, and a punch positioning body 21 abuts to the guide die 11 at the same time when the punch claming plane comes from the guide die upper face 11b to a set insertion depth Hp. In this way, the punch 20 and the grooving die 10 are moved down to a bottom dead point while being positioned to form a groove of a set thickness Wt=Hd-Hp in the bottom portion of the work.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery bottom for a battery can, which is formed in a cylindrical shape with a bottom, and is pressed between a groove forming die of a lower die set and a punch of an upper die set to contact the bottom of the work. A groove processing method for the bottom of a battery can that presses a groove for an explosion-proof valve on the bottom of a work by using a groove processing die protrusion of the groove processing die that protrudes by a set height from the clamping base surface of the contacting groove processing die to the punch side. It is about.

[0002]

2. Description of the Related Art Lithium ion secondary batteries may explode when the internal pressure becomes excessive. Therefore, an explosion-proof valve is provided to prevent the explosion when the internal pressure reaches a set value. As the explosion-proof valve, for example, a groove is formed at the bottom of a battery can that accommodates and seals an electrode and an electrolyte solution disclosed in Japanese Patent Application Laid-Open No. 9-320549, when the internal pressure reaches a set value. It is known that the groove breaks to prevent an explosion. The groove for the explosion-proof valve is a groove to maintain the sealed state without breaking when the internal pressure is below the set value, and to break only when the internal pressure reaches the set value to prevent explosion, It is required to reduce the deviation of the groove bottom thickness.

However, in a press machine for manufacturing a battery can, a predetermined time has elapsed since the start of the operation until the temperature of a sliding portion of the machine is saturated, and the bottom dead center position of the punch due to thermal expansion of the press slide and the like. Fluctuates, the bottom thickness of the groove machined by being pressed between the die and the punch changes with this fluctuation, and the problem of exceeding the allowable value of the groove bottom thickness corresponding to the set value of the internal pressure described above occurs. is there.

In order to solve this problem, in the prior art, as a technique for keeping the groove bottom thickness within an allowable value, the groove bottom thickness machined on the bottom of the battery can is measured at an appropriate time and the allowable value is measured. A technique for adjusting the mold so that the groove bottom thickness falls within an allowable value when the value exceeds the value (hereinafter, referred to as conventional technique A) is known. In addition to the above, Japanese Patent Application Laid-Open No.
A technology disclosed in Japanese Patent No. 241699 (hereinafter, referred to as conventional technology B) is known.

The prior art B includes a hydraulic jack for extending and contracting the frame in the axial direction, a proportional electromagnetic pressure control valve for adjusting the pressure of the hydraulic pressure supplied to the hydraulic jack, and a displacement of the bottom dead center position for each stroke. The displacement of the bottom dead center position is controlled by controlling the proportional electromagnetic pressure control valve based on the slide displacement sensor and the detection signal from the slide displacement sensor, and changing the jack force of the hydraulic jack to expand and contract the frame in the axial direction. A press machine is provided with a bottom dead center position correcting device comprising a control means for correcting the bottom dead center position of the punch.

[0006]

According to the prior art A of the above-mentioned prior arts, when the bottom thickness of the groove formed in the bottom of the battery can is measured at an appropriate time, when the thickness exceeds an allowable value. In this case, it is necessary to stop the press machine and adjust the mold so that the groove bottom is within the allowable value. In particular, during the period of 1 to 2 hours immediately after the start of the start, the amount of change in the bottom dead center position is remarkable, and it is necessary to frequently stop the press machine, so that the productivity is low and it is difficult to maintain the quality. There was a problem.

Further, in the technique of forming a groove for an explosion-proof valve in the bottom of a battery can using the prior art B, the cost of providing a bottom dead center position correcting device in a press machine is required, and the manufacturing cost of the battery can is reduced. Not only is it expensive, but the increase in production speed is restricted. That is, the displacement of the bottom dead center position is corrected by controlling the proportional electromagnetic pressure control valve based on the detection signal from the slide displacement sensor and changing the jack force of the hydraulic jack to expand and contract the frame in the axial direction. There is a limit to the response speed of the bottom dead center position correction device.
If the production speed is increased during two hours, it is difficult to maintain the quality. Therefore, there is a problem that it is difficult to reduce manufacturing costs and improve productivity.

[0008] The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object:
The groove for the explosion-proof valve to be machined on the bottom of the battery can can be machined at a high speed without stopping the machine during manufacturing using a press machine with a simple configuration and its mold, within the allowable value Accordingly, it is an object of the present invention to provide a method for forming a groove in a bottom portion of a battery can, which can improve productivity and reduce manufacturing costs and can maintain quality.

[0009]

SUMMARY OF THE INVENTION In order to solve this problem, a method for forming a groove in a bottom of a battery can according to the present invention comprises: A grooved die protruding portion that is nipped by the grooved die and the punch of the upper die set, and protrudes from the grooved die pressing base surface of the grooved die that comes into contact with the work bottom by a set height to the punch side, and A method for pressing a groove for an explosion-proof valve at the bottom of a work with a set groove bottom thickness Wt by using a punch pressing surface, wherein a lower end surface of a punch position defining body which can be vertically reciprocated integrally with the punch is formed in advance. At the time of lowering, the insertion depth of the punch pressure surface defined by contacting the upper surface of the guide die fixed to the upper end of the movable die holder from the upper surface of the guide die is set to the set insertion depth Hp, and is movable. Groove that can move up and down in the die holder At the lower end position, the depth of the lower end position from the upper surface of the guide die to the apex of the grooved die projecting portion at the lower end position is set to the set lower end depth Hd = Hp + Wt, and the punch is lowered with the punch inserted in the work. The work is inserted together with the punch into the guide die which stands by at the upper end position while being urged upward by an urging member having a pressing force larger than a required clamping force capable of forming a groove in the work bottom at the groove processing die protrusion, In the guide die, the work bottom is squeezed by the groove machining die protrusion at the lower end position of the set lower end depth Hd and the descending punch squeezing surface, and the punch squeezing surface is moved from the guide die upper surface to the set insertion depth Hp. At the same time, the punch position defining body is brought into contact with the guide die so that a groove having a set groove bottom thickness Wt = Hd-Hp is formed at the work bottom, and the punch and the groove processing die are positioned at the bottom dead center. Until After being physically lowered, the punch and the punch position defining body are raised and the biasing member biases the guide die and the groove processing die upward, so that the bottom dead center position of the punch fluctuates. Also,
A groove having a set groove bottom thickness Wt is formed in the work bottom by press working.

According to the present invention, the bottom of the work is squeezed between the groove machining die projection located at the lower end position of the set lower end depth Hd in the guide die and the descending punch squeezing surface. When the punch reaches a set insertion depth Hp and the punch position defining body contacts the guide die at the same time, a groove having a set groove bottom thickness Wt = Hd-Hp is formed on the work bottom, and the punch and the groove processing are performed. Since the die and the bottom are integrally lowered to the bottom dead center position, even if the bottom dead center position of the punch fluctuates due to thermal expansion of a press slide or the like, a groove having a set groove bottom thickness Wt is formed at the work bottom. After that, the distance between the apex of the groove processing die protrusion and the punch pressing surface is maintained in a relative positional relationship equal to the set groove bottom thickness Wt, and the groove having the set groove bottom thickness Wt is stably formed on the work bottom. be able to.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG.
Is a longitudinal sectional view showing a state before the groove for the explosion-proof valve is formed in the work bottom (battery can bottom), and a state just before the work bottom is pressed. FIG. 2 is a view after the groove is formed in the work bottom. FIG. 3 is an enlarged vertical cross-sectional view showing a state in which the punch and the groove processing die are lowered to near the bottom dead center position. FIG. 3 is an enlarged vertical cross-sectional view of the work bottom, the groove processing die protrusion, and the punch pressure surface of FIG. FIG. 4 shows a positional relationship between a groove machining die and a punch for machining a groove with a set groove bottom thickness on a work bottom,
(A) shows the positional relationship between the punch position defining body and the punch pressing surface, (b) is an enlarged vertical sectional view showing the positional relationship between the guide die and the groove processing die protrusion, and FIG. 5 is a groove at the bottom. FIG. 2 is a longitudinal sectional view showing an example of a battery can in which is processed.

Prior to the description of the present invention, an outline of an apparatus for carrying out the present invention will be described. Fig. 1 shows a mold device for processing the groove for the explosion-proof valve on the bottom of the work (bottom of the battery can).
As shown in FIG. 1, a lower die set 1 is provided on a lower base 5 on a bolster (not shown) of a press machine, and an upper die set 2 is provided on an upper base 6 (not shown) which reciprocates up and down. ing.

The structure of the lower die set 1 is shown in FIGS.
As shown in (b), a groove forming die projection 1 for forming a groove Wg for an explosion-proof valve on a work bottom Wb of a work (battery can) W.
The groove forming die 10 is formed on the groove forming die clamping base surface 10b (see FIGS. 3 and 5), and the groove forming die 10 is vertically movably guided by a guide die hole 11a into which the work W is inserted. The guide die 11 to be fixed, and the guide die upper surface 11b of the guide die 11 is flush with the upper end surface, and is fixed to the upper center.
A movable die holder 12 that guides the grooving die 10 to be able to move up and down and that can also move up and down by itself, a bottom plate 13 that defines a lower end position of the grooving die 10 in the movable die holder 12, and the bottom plate 13. Springs 14 for urging the groove forming die 10 and the movable die holder 12 upward, and a spring holder 15 for accommodating the disc springs 14.
A lid 16 fixed to the upper end of the spring holder 15 to guide the bottom plate 13 movably up and down and to define a rising end thereof; and a fixing die holder 17 for accommodating these and defining a rising end position of the movable die holder 12. And a knockout 18 for moving the groove processing die 10 upward.

The groove forming die 10 has a die upper end 10c formed to have substantially the same body diameter as the work W and has a guide die hole 1 formed therein.
1a, the die base 10d is moved by the movable die holder 12
Can be moved up and down. The grooved die projecting portion 10a shown in FIG. 3 is formed so as to protrude from the grooved die pressing base surface 10b by a set height on the punch side (upper side in the drawing). The movable die holder 12 of the groove processing die 10
4B is positioned by contacting the bottom plate 13. At the lowered end position shown in FIG. 4B, the vertex position of the grooved die projecting portion 10a is set to the guide die upper surface 11b.
(The same plane as the upper end surface of the movable die holder 12) is set in advance so as to be separated by the set lower end depth Hd. Further, the rising end position of the groove processing die 10 is a position where the groove processing die clamping base surface 10b shown in FIG. 1 can discharge the processed work W corresponding to the guide die upper surface 11b,
Positioned by knockout 18.

The movable die holder 12 includes the stationary die holder 1.
7 so as to be vertically movable. The rising end position of the movable die holder 12 is urged upward by the disc spring 14 and is positioned by the jaw 17a of the stationary die holder 17 as shown in FIG. The lower end position is structurally positioned by the lower end surface of the movable die holder 12 abutting on the upper end surface of the lid 16, but during processing, as shown in FIG. It is defined by the bottom dead center position. Since the guide die 11 is fixed to the upper end so that the upper surface 11b of the guide die is flush with the upper surface of the movable die holder 12, the raised end position and the lowered end position are defined by the movable die holder 12. To move up and down.

A plurality of spring holders 15 capable of urging the groove forming die 10 with a pressing force larger than a required clamping force capable of forming the groove Wg on the work bottom Wb by the groove forming die projecting portion 10a shown in FIG. Of the disc spring 14 are stored. The plurality of disc springs 14 are connected to the bottom of the spring holder 15 and the bottom plate 13.
, And urges the movable die holder 12 together with the groove forming die 10 upward. And the spring holder 15
Is screwed to the lower end in the stationary die holder 17.
The stationary die holder 17 is fixed to the lower base 5.

Next, as shown in FIGS. 1 and 4A, the upper die set 2 has a punch pressing surface 20a formed at the lower end thereof for pressing the work bottom Wb in cooperation with the groove forming die 10. As shown in FIG. Punch 20, a punch position defining body 21 that presses the guide die 11 and the movable die holder 12 of the lower die set 1 downward, a punch holder 22 that houses and fixes the punch 20, and a liner 23. And an adjusting screw 24 for adjusting the position of the punch 20 in the vertical direction.

The lower end of the punch 20 is inserted into the guide die hole 11a of the guide die 11 when the press slide descends. At this time, the punch position defining body 2
1 also descends integrally, so that the punch position
After contacting the guide die 11 and the movable die holder 12, the punch 20 descends while maintaining a certain relationship with the guide die 11. That is, the amount by which the punch pressing surface 20a is inserted into the guide die hole 11a is determined in advance in FIG.
(A) Set insertion depth H from guide die upper surface 11b
p, the insertion depth H is set from the guide die upper surface 11b regardless of the position of the bottom dead center of the press slide.
It is defined that only p is inserted.

The punch holder 22 is located at a predetermined position on the upper base 6 which reciprocates up and down together with a press slide (not shown).
After the vertical position of the punch 20 is adjusted by the adjusting screw 24, the punch 20 is fixed together with the punch 20. The lower end surface of the punch position defining body 21 is formed so as to be in contact with the guide die 11 and the movable die holder 12, and is screwed to the punch holder 22 near the punch 20. The positional relationship of the punch pressing surface 20a with respect to the lower end surface of the punch position defining body 21 is set to the above-described set insertion depth Hp.

Then, the work bottom Wb is formed on the groove working die pressing base surface 10b of the groove descending die 10 urged by the disc spring 14 having a pressing force larger than a required holding force capable of working the groove Wg of the work W. The groove Wg is formed in the work bottom Wb by being pinched by the groove forming die protrusion 10a and the punch pinching surface 20a of the descending punch 20 (see FIG. 2).

The set groove bottom thickness Wt of this groove Wg shown in FIG.
The press slide is defined by defining the groove forming die projection 10a to the set lower end depth Hd shown in FIG. 4B and the punch pressing surface 20a to the set insertion depth Hp shown in FIG. 4A. Processing can be performed irrespective of the position of the bottom dead center.
That is, the set groove bottom thickness Wt is always the difference between the set lower end depth Hd of the grooved die projecting portion 10a and the set insertion depth Hp of the punch clamping surface 20a (set groove bottom thickness Wt = set lower end depth Hd). -Processing is performed at the set insertion depth Hp).

Next, a processing procedure for forming a groove Wg on the lower surface of the work bottom Wb according to the present invention will be described with reference to FIGS.

A work (battery can) W drawn deeper than a strip of a soft metal such as aluminum is transferred to a position below the punch 20 by a transfer means (not shown), and is moved together with the upper base 6 by lowering a press slide (not shown). 20,
It is assumed that the punch position defining body 21 is lowered and the punch 20 is in the state shown in FIG. In addition, the groove forming die 10 is provided with the completion of the processing of the previous work W,
It is assumed that the knockout 18 is raised by rotation of a knockout drive cam (not shown), the discharge of the previous work W is finished, and the knockout 18 is about to start lowering.

The groove forming die 10 is provided with a
0 is the guide die upper surface 11
The descent starts at a time until approaching b, and proceeds toward the descent end in the movable die holder 12 before the descent of the punch 20. That is, knockout 1 from the state shown in FIG.
As a result of the lowering of 8, only the groove forming die 10 is lowered, and the upper end thereof is immersed in the guide die hole 11a. The lower end position is positioned by contacting the bottom plate 13, and the vertex position of the groove machining die protrusion 10a at the lower end position is
The set lower end depth Hd is defined from the guide die upper surface 11b shown in FIG.

The work W is inserted into the guide die hole 11a by the punch 20 which descends slightly later than the groove forming die 10. Eventually, the lower end surface of the work bottom Wb comes into contact with the vertex of the grooved die protrusion 10a waiting at the lower end position in the movable die holder 12. Since the punch 20 further descends, the work bottom Wb is moved to the grooved die projecting portion 1.
0a and the punch pressing surface 20a, and as the punch 20 descends, the groove processing die protrusion 10a is formed on the work bottom Wb.
Bites into the pit, and a dent is formed in the bite (finally, the groove W
g) is processed.

As shown in FIG. 2, when the lower end surface of the punch position defining body 21 descending with the punch 20 abuts on the guide die upper surface 11b, the insertion amount from the guide die upper surface 11b to the punch clamping surface 20a is reduced. , The insertion depth Hp shown in FIG. At this time, since the vertex position of the grooved die protrusion 10a is defined by the set lower end depth Hd shown in FIG. 4B from the guide die upper surface 11b, the grooved die protrusion 10a is provided on the work bottom Wb. The groove Wg is formed by the punch pressurizing surface 20a with the groove bottom thickness Wt = set bottom depth Hd−set insertion depth Hp.

When the groove Wg is formed with the set groove bottom thickness Wt, the bottom wall thickness of the work bottom Wb is clamped by the groove machining die clamping base surface 10b and the punch clamping surface 20a. , Groove forming die clamping base surface 1 from guide die upper surface 11b
Due to the difference between the set depth up to 0b and the set insertion depth Hp of the punch clamping surface 20a, a bottom wall thickness is set.

The bottom dead center position of the punch 20 is such that if the lower end face of the punch position defining body 21 is in contact with the guide die upper surface 11b, a groove Wg having a set groove bottom thickness Wt is machined on the work bottom Wb. can do. However, due to thermal expansion of a press slide or the like, the punch 20
Since the bottom dead center position fluctuates, in actual machining, the lower dead center position is added to the position obtained by adding the above fluctuation to the lower position where the lower end surface of the punch position defining body 21 abuts on the guide die upper surface 11b. Set. Therefore, the punch 20
After the lower end surface of the punch position defining body 21 comes into contact with the guide die upper surface 11b, the lowering surface also descends.

After the lower end surface of the punch position defining body 21 contacts the guide die upper surface 11b as shown in FIG.
1 and the movable die holder 12 are pressed downward to the bottom dead center position of the punch 20 against the disc spring 14. During this time,
Groove processing die 10, guide die 11, movable die holder 12,
Since the components of the bottom plate 13, the punch 20, and the punch position defining member 21 are integrally lowered, the set lower end depth Hd of the grooved die projecting portion 10a shown in FIG.
The set insertion depth Hp of the punch pressure surface 20a shown in (b) is maintained.

Therefore, the position of the bottom dead center of the punch 20 is
Even if it fluctuates due to thermal expansion of a press slide or the like, the groove bottom thickness of the groove Wg formed in the work bottom Wb can maintain the set groove bottom thickness Wt.

When the press slide starts to rise from the bottom dead center position, the punch 20 and the punch position defining body 21 rise at the same time. With these rises, the grooving dies 10,
The guide die 11, the movable die holder 12, and the bottom plate 13 also
The stepped portion on the outer side near the upper end of the movable die holder 12 is raised by being urged by the disc spring 14 so that the stationary die holder 17 shown in FIG.
To the ascending end position in contact with the jaw 17a. During this time, the groove processing die 10 pushes the workpiece W upward by the groove processing die protrusion 10a and the groove processing die clamping base surface 10b while staying at the lower end position in the movable die holder 12.

Thereafter, when the movable die holder 12 reaches the rising end position, the punch position defining body 21 moves the guide die 11
And the movable die holder 12 and the punch 20
The punch pressing surface 20a moves away from the work bottom Wb and integrally moves upward toward the top dead center position. Immediately or immediately after the punch pressing surface 20a separates from the work bottom Wb, the groove forming die 10 is
Upward, and the groove processing die clamping base surface 10b is
The guide die is raised to a raised end position at the same level as the upper surface 11b.

After the groove forming die 10 reaches the rising end position and the punch 20 escapes from the inside of the work W, the work W is discharged by a discharge means (not shown) (or transferred by the transfer means). Then, in preparation for processing the next work W, the groove processing die 10 is knocked out 1.
8 together with the movable die holder 12 to the lower end position.

The present invention can be carried out by using a mold apparatus other than the above-described one. That is, the guide die 11,
In this embodiment, a spring is used as the urging member for urging the movable die holder 12, and the disc spring 14 is used. However, a coil spring may be used. Further, the present invention can be implemented by using a pneumatic actuator, a gas pressure actuator, a hydraulic actuator, or the like.

Further, in this embodiment, the variation of the position of the bottom dead center due to thermal expansion is absorbed by the biasing member of the lower die set 1. Even if a change in the point position is absorbed, the groove bottom thickness of the groove at the bottom of the work can be processed with the set groove bottom thickness. Specifically, for example, in FIG. 1, an urging member is provided between the liner 23 and the adjusting screw 24.

In the other lower die set 1, the disc spring 14 is removed, the guide die 11 is fixed in the stationary die holder 17 shown in FIG. 1, and the groove processing die 10 can be moved up and down by the knockout 18. By doing so, the groove bottom thickness of the groove at the bottom of the work can be processed with the set groove bottom thickness.

[0037]

As described above, the present invention has the following effects.

According to the present invention, the groove having the set groove bottom thickness is defined at the work bottom by contacting the punch position defining body with the guide die at the same time when the punch pressing surface reaches the set insertion depth. As a result, the punch and the groove forming die are lowered integrally to the bottom dead center position. Therefore, even if the bottom dead center position of the punch fluctuates due to thermal expansion of a press slide or the like, the set groove bottom thickness is set at the work bottom. After the groove is formed, the distance between the top of the groove processing die protrusion and the punch clamping surface is maintained in a relative positional relationship equal to the set groove bottom thickness, and the groove with the set groove bottom thickness is stabilized on the work bottom. Can be processed. Therefore, unlike the related art A, there is no need to stop the manufacturing apparatus during the production of the battery can, so that the productivity can be easily improved. Further, unlike the related art B, there is no need to provide a bottom dead center position correcting device, so that the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state before a groove for an explosion-proof valve is formed in a work bottom (battery can bottom) according to the present invention, wherein the work bottom is sandwiched by a descending punch and a standby groove processing die. FIG. 3 is a longitudinal sectional view showing the entire mold apparatus just before being pressed.

FIG. 2 is an explanatory view similarly showing a state after a groove is formed in a work bottom, and is lowered to near a bottom dead center position while maintaining a positional relationship between a punch and a groove processing die by a punch position defining body; It is the longitudinal cross-sectional view to which the principal part of the metal mold | die apparatus at the time of doing was expanded.

FIG. 3 is an enlarged longitudinal sectional view of a work bottom, a groove machining die protrusion, and a pressing surface of a punch in FIG. 2;

4A and 4B are explanatory views showing a positional relationship between a groove machining die and a punch for machining a groove with a set groove bottom thickness on a work bottom according to the present invention, wherein FIG. (B) is an enlarged vertical sectional view showing the positional relationship between the groove processing die protrusion at the lower end position in the guide die and the upper surface of the guide die.

FIG. 5 is an explanatory view showing an example of a battery can having a groove formed in a bottom portion according to the present invention, and is an enlarged longitudinal sectional view thereof.

[Explanation of symbols]

 Reference Signs List 1 lower die set 2 upper die set 10 groove processing die 10a groove processing die protrusion 10b groove processing die clamping base surface 11 guide die 11b guide die upper surface 12 movable die holder 13 bottom plate 14 disc spring 15 spring holder 17 stationary die holder 18 Knockout 20 Punch 20a Punch compression surface 21 Punch position defining body W Work Wb Work bottom Wg (Work) groove

Claims (1)

[Claims] 1. A groove of a grooved die that is pressed into a grooved die of a lower die set and a punch of an upper die set so that the bottom of the work for a battery can formed in a bottomed cylindrical shape is in contact with the bottom of the work. A groove for an explosion-proof valve is press-formed at a set groove bottom thickness Wt on a work bottom by a groove processing die protrusion protruding by a set height to the punch side from a processing die pressing base surface and a punch pressing surface of a punch. A method wherein the lower end surface of a punch position defining body which can be vertically reciprocated integrally with the punch is defined in advance by abutting on the upper surface of a guide die fixed to the upper end of a movable die holder. The insertion depth of the punch clamping surface from the upper surface of the guide die is set to the insertion depth Hp, and the groove processing die that can move up and down in the movable die holder is located at the lower end position. Lower end position up to Is set to the set lower end depth Hd = Hp + Wt, and the punch is lowered in a state where the punch is inserted into the work. A work is inserted together with a punch into the guide die that is waiting at the upper end position while being urged upward by the pressure urging member, and a groove forming die protrusion at the lower end position of the set lower end depth Hd in the guide die; The bottom of the work is squeezed by the descending punch squeezing surface, and the punch squeezing surface reaches the set insertion depth Hp from the upper surface of the guide die, and at the same time, the punch position defining body is brought into contact with the guide die to set the groove bottom on the work bottom. After the punch and the groove processing die are integrally lowered to the bottom dead center position while defining a groove having a thickness Wt = Hd-Hp, the punch and the punch position defining body are raised and urged. To the member That is, the guide die and the groove forming die are urged upward to press the groove having the set groove bottom thickness Wt on the work bottom even if the bottom dead center position of the punch fluctuates. A method for forming a groove on the bottom of a battery can.