JPH09237613A - Method for forming prismatic battery can - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To secure the wall thickness of a thick step portion by increasing the thickness of a square battery can having a thick step portion in the vicinity of an opening from a material sheet metal which is thinner than the wall thickness of the thick step portion. The present invention provides a molding method for uniformly drawing the wall thickness of a rectangular tube. SOLUTION: A material sheet metal is punched out into a disc-shaped blank and drawn into a cup-shaped bottomed cylindrical body, and the upper end portion of the bottomed cylindrical work is pressed by a punch 5 to form a tapered surface 3a of a die 3. And pressurize the cylindrical part to increase its wall thickness and draw-form. Subsequently, when the cylindrical portion is formed into an elliptical shape through the elliptical cross section, the corner-corresponding portion that is likely to be thickened in the downstream corner drawing step is thinned and ironed in advance, and is uniformly formed in the square drawing step. A square battery can is completed by drawing a thick-walled bottomed cylindrical portion, and performing steps such as step forming near the opening, upper corner drawing, and trimming.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a rectangular battery can having a bottomed rectangular tubular body having a thick step portion in the vicinity of an opening by pressing or the like.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Laid-Open No. 7-155883 and Japanese Patent Laid-Open No. 7-155 have been used as a method for locally increasing the wall thickness by pressing.
There is prior art published in No. 888. JP-A-7-15
In the prior art of No. 5883, an open flange portion 102 inclined by about 15 to 20 degrees is bent and formed on a general portion 101a of a sheet metal material 101 as shown in FIG. 18 (A), as shown in FIG. 18 (B). As shown in FIG. 2C, the opening flange portion 1
02 as it is pushed in the axial direction of the sheet metal material 101,
The thick portion 103 is formed by increasing the thickness only in the plate thickness direction.

In the prior art of Japanese Patent Laid-Open No. 7-155888, an intermediate punch 106 and an outer punch 107 are provided for a die 105 having a stepped portion 104 as shown in FIG.
And are lowered together and the flange is pushed in. The thickening portion 108A is formed by controlling the plastic flow direction of the material associated with this pressing by the stepped portion 104 and positively increasing the thickness of the flange portion 108 in the plate thickness direction.

[0004]

The method of pushing the flange portion to increase the wall thickness as described in the prior art requires at least one step of increasing the wall thickness. When a prismatic battery can with a deep bottomed rectangular tube is molded from a sheet metal material, it goes from the bottomed cylindrical body to an elliptical shape, an almost oval shape, and then gradually increases the major axis / minor axis ratio to form the final rectangle. It requires multiple draw forming steps to form a shape, and if more than one step is used only for thickening, the number of steps will increase and the die manufacturing cost will be high, and it will take time to adjust the die accordingly. I have a problem.

Further, in the method according to the prior art, since the wall-thickness flow for increasing the wall thickness causes an abrupt plastic flow in the direction perpendicular to the working axis of the indentation, as in the rectangular battery can according to the present invention, For workpieces with a relatively long plate length,
There is a problem that buckling and wrinkling are likely to occur, and that the shape and surface of the molded body are difficult to form smoothly.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to perform draw forming with thickening in a relatively early stage process, and to perform a subsequent redrawing process. In the subsequent square drawing process, the parts that are likely to become thick in the subsequent square drawing process are ironed so that buckling and wrinkles do not occur easily, and the finally formed bottomed rectangular tube part, thick stepped part and widened angle tube An object of the present invention is to provide a method for forming a prismatic battery can in which each part can be smoothly formed with a uniform wall thickness.

[0007]

In order to achieve the above object, a method for forming a rectangular battery can according to the present invention is a rectangular battery can having a bottomed rectangular tubular body having a thick step portion in the vicinity of an opening. A method of molding from a material with a plate thickness thinner than the wall thickness of the step,
The open end of the work formed in the bottomed cylindrical body is pressed in the axial direction of the cylinder to press and draw the cylindrical portion to perform draw-drawing, and the force applied in the compression direction due to the resistance at the press-drawing draws the material plate thickness. A thickening drawing step for thickening the wall thickness of the cylindrical portion, and drawing the thickened cylindrical portion into an elliptical cross-section while reducing the wall thickness around the corner formed in a substantially oval shape in the downstream step. A redrawing process for ironing to reduce the wall thickness, and a drawing process to draw the elliptical shape into an oval shape and reduce the wall thickness around the corner formed in the rectangular shape in the downstream process. The redrawing step, the first rectangular drawing step of drawing the substantially oval shape into a rectangular bottomed rectangular tube portion excluding the opening side from the thick step formed in the downstream step, and the vicinity of the opening Thick inside A step forming step for forming a portion, and a second angular drawing step for drawing an opening side from the thick step into a rectangular wide-angled tube section that is wider than the bottomed rectangular tube section. It comprises.

Further, in the thickening step, the opening end of the work formed on the bottomed cylindrical body is pressed in the axial direction of the cylinder to be pushed into the taper surface of the female die and between the taper surface and the opening end. This is a thickening and drawing step in which the cylindrical portion is pressed and drawn while being pressed, and the thickness of the cylindrical portion is made thicker than the material plate thickness by the force applied in the compression direction by the resistance at the time of the pressing and drawing.

As described above, in the relatively thickening step in the relatively early stage, the cylindrical portion formed in the bottomed cylindrical body is pressed to increase the thickness in the plate thickness direction and draw forming in the radial direction to increase the thickness. In order to obtain uniform wall thickness in each downstream process, the corners are formed in each downstream process during each redrawing process in which the formed cylindrical part is drawn into an oval shape through the process of drawing an elliptical shape. The thickness of the surrounding area becomes thin and ironed,
In the square drawing process, the square tube is square-drawn to a uniform thickness, and then in the step forming process, a thick step is formed near the opening. A prismatic battery can having is completed. Therefore, it is difficult to form a prismatic battery can having a deep bottomed rectangular tube and a thick step near the opening.
With a small number of processes, it is possible to form the bottomed rectangular tube portion, the thick-walled stepped portion, and the widened stepped portion to a uniform wall thickness, which reduces die manufacturing costs and reduces die adjustment costs including maintenance. Decrease.

Further, in the thickening drawing step, since the open end of the bottomed cylindrical body is pressed into the taper surface of the female die and the cylindrical portion is pressed while drawing, the taper angle of the taper surface is formed. With the relationship between the thickness increase amount of the cylindrical portion and the draw ratio can be easily set, the wall thickness flow for increasing the wall thickness and the diameter reducing flow for the draw are gradually plastically flowed by the action of the tapered surface, Even if the thickness increase ratio and the drawing ratio are set to be relatively large, buckling and wrinkling are less likely to occur in the molding process,
In addition, it is formed smoothly from the shape and surface of the molded body.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, an example of a work (square battery can) molded according to the embodiment of the present invention will be briefly described. 17 (a) is a top view of the prismatic battery can W, FIG. 17 (b) is a front sectional view seen from the long side, FIG. 17 (c) is a side sectional view seen from the short side, and FIG. 17 (d) is the same. (B), It is an enlarged view of the part enclosed with the dashed-dotted line of (c), ie, thick step d.

This prismatic battery can W is a prismatic case of a secondary battery used in, for example, a mini disk player, a portable personal computer, a portable telephone, etc., and has a deep section having a rectangular cross section with a thick step portion d interposed therebetween. The bottom-angled tubular portion and the widened-angled tubular portion that is wider than the bottomed-angled tubular portion are integrally formed above, and the sealing plate is placed on the thick-walled step d, and the widened-angled tubular portion is caulked. Is to be bent inward and sealed. FIG.
As shown in (d), the wall thickness t in the vicinity of the thick wall step portion d is thicker than the wall thickness t ′ of the rectangular tube portion in order to maintain the strength.

1 to 10 show from the drawing step of the first step (# 1) to the trimming step of the tenth step (# 10), and the front sectional views of the work shapes formed in the respective steps ( b), a cross-sectional view as seen from the direction of the arrow in the top view or (b), and a partially enlarged view of the thick step d in the eighth step (# 8) of FIG. 8 (c). It is shown by and. Further, FIGS. 12 to 16 are mold explanatory views of a vertical cross section viewed from the work short side of the process which is considered to be necessary for explaining the mold used in the 10 processes. Hereinafter, each step will be described step by step.

In the drawing and drawing step of the first step (# 1) shown in FIG. 1, a material (not shown) whose plate thickness is thinner than the thick step portion formed in the downstream step or thicker than the square tube portion or equivalent A circular blank Wa indicated by an imaginary line is punched from the sheet metal, and drawn into a cup-shaped bottomed cylindrical work Wb (FIG. 1).

In the thickening reduction step of the second step (# 2) shown in FIG. 2, the bottomed cylindrical workpiece Wb sent from the first step (# 1) is guided by the pressure punch 5 and the guide shown in FIG. Thickening drawing is performed by the punch 2 and the die 3. This thickening drawing will be described in more detail. The upper end surface 1a of the knockout 1 which is vertically movable and biased upward by a spring (not shown), and vertically movable in the center hole of the pressure punch 5 and downward by the spring 4. Lower end surface 2 of the guide punch 2 that is biased
The bottom part of the bottomed cylindrical work Wb sent by a is clamped at a position above the die 3, and the bottomed cylindrical work Wb is lowered toward the die 3 by lowering a slide (not shown).

When the lower end corner of the bottomed cylindrical work Wb comes into contact with the tapered surface 3a formed at the mouth of the die 3 at an angle suitable for thickening and drawing, the guide punch 2
Of the pressure punch 5 continues to descend, the lower end surface of the pressure punch 5 abuts the upper end of the bottomed cylindrical work Wb, and the pressure punch is moved downward by a slide (not shown). The taper surface 3 is formed in order from the lower end of the bottomed cylindrical work Wb by the pressing force from the upper end of the work of FIG.
Flowing downward along a, the outer peripheral surface of the guide punch 2 and the inner peripheral surface of the smallest diameter portion of the tapered surface 3a are used as guides to carry out pressing and throttling. At this time, the compressing force in the pressing direction acting on the cylindrical work Wb having a bottom between the lower end of the pressure punch 5 and the tapered surface 3a of the die 3 and the indentation resistance cause the cylindrical work Wb having a bottom. At the same time as the thickness of the portion is increased to a thickness corresponding to the thick step portion, the lower portion is drawn and formed into a bottomed cylindrical work Wc having a tapered portion on the upper portion.

In the third step (# 3) shown in FIG. 3, the upper tapered portion of the bottomed cylindrical work Wc is redrawn into a cylinder having the same diameter as the straight portion, and the cup-shaped bottomed cylindrical work is again formed. Mold to Wd.

In the fourth step (# 4) shown in FIG. 4, the cup-shaped bottomed cylindrical workpiece Wd sent from the third step (# 3) was formed into an elliptical cross section shown in FIG. Re-drawing is performed by the punch 6 and the die 7 having an elliptical shape whose cross section is larger than that of the punch 3 to form a bottomed cylindrical work piece We having an elliptical cylindrical cross section. At this time, the gap between the punch 6 and the die 7 has a characteristic that the peripheral plate thickness is concentrated and thickened in the corner portion in the later-described corner drawing step shown in FIG. The dimension of the portion corresponding to the short side portion b close to a and a is formed smaller than the dimension of the portion corresponding to the long side portion c whose thickness hardly changes.

Therefore, the bottomed cylindrical work piece We formed in the redrawing step of the fourth step (# 4) has a corner portion a in the later-described corner drawing step, as shown in the enlarged sectional view of the cylindrical portion of FIG. , A and parts a ′, b ′ formed on the short side part b are ironed to reduce the thickness of the bottomed cylindrical work piece We, and parts c ′, c ′ formed on the long side part c. A small amount of ironing or drawing is performed. That is, the parts a'and b'formed by ironing
In a state where the wall thickness is less than the wall thickness of the portion c ′ formed by drawing, an angular tube portion having a uniform wall thickness can be formed in the later-described corner drawing step. 8 is a knockout.

In the fifth step (# 5) shown in FIG. 5, FIG. 14 shows a bottomed cylindrical work piece We which is sent from the fourth step (# 4) and has an elliptical cross-section. A punch 9 having a substantially oval cross section and a die 10 having a substantially oval cross section having a substantially oval cross section are used for redrawing to have a thick inclined surface that can be opened toward the opening. A cylindrical bottomed workpiece Wf having a substantially oval cross section is formed. 11 is a knockout.

Also in this drawing process, the gap between the punch 9 and the die 10 at the part for forming the parts f, f corresponding to the corners where the surrounding meat is likely to concentrate in the later-described corner drawing process shown in FIG. Are formed to be smaller than the other portions, and the portions f of the bottomed cylindrical work Wf are formed to have a thinner wall thickness than the other portions.

In the sixth step (# 6) shown in FIG. 6, the bottomed cylindrical workpiece Wf sent from the fifth step (# 5) is redrawn by a punch and a die (not shown) to form an opening. A bottomed cylindrical work Wg having an elongated oval shape in which the cross-section of the cylindrical part having a thick inclined surface that is easy to open is formed.

Also in this drawing process, the gap between the punch (not shown) and the die for forming the parts g, g corresponding to the corners where the surrounding meat is likely to concentrate in the later-described corner drawing process shown in FIG. Are formed to be smaller than the other portions, and the portions g of the bottomed cylindrical work Wg are formed to have a thinner wall thickness than the other portions.

In the seventh step (# 7) shown in FIG. 7, the bottomed cylindrical work Wg sent from the sixth step (# 6) is processed into a rectangular shape having a rectangular cross section by a punch and a die (not shown). Square-drawing is performed to form a bottomed rectangular cylindrical work Wh having a thick inclined portion that can be opened toward the opening. The bottomed square tubular portion formed by the square drawing is processed in the above-described fourth step (#
4) to the sixth step (# 6), the uneven thicknesses formed in advance make the four sides and four corners of the short side portion b, the long side portion c, and the corner portion a uniform in thickness.

In the eighth step (# 8) shown in FIG. 8, the bottomed rectangular tubular work Wh sent from the seventh step (# 7) is
Step forming in which a stepped portion (not shown) is formed in a state in which the bottomed square tubular portion is supported from below by a die that holds the square tubular portion (not shown) and a notch out that holds the bottom portion against the action direction of the punch. A thick step portion d is formed at the inner boundary portion between the bottomed rectangular tube portion and the thick wall inclined portion by a punch for punching.

In the ninth step (# 9) shown in FIG. 9, from the thick step portion d of the bottomed rectangular tubular work Wi in which the thick step portion d sent in the eighth step (# 8) is formed. Also, the thick-walled inclined portion on the opening side is formed by square drawing by the punch 12 and the die 13 shown in FIG. 15 to form a widened rectangular tubular portion above the thick-walled step portion d, and the surplus portion is formed at the upper end. It is generated in the bottomed rectangular tubular work Wj having e, which is immediately before completion. 14 is a knockout.
Even in this upper corner drawing step, the uneven thickness formed in advance in the fourth step (# 4) provides a uniform wall thickness on the four sides and four sides.

In the tenth step (# 10) shown in FIG. 10, the punch 17 having the cutting edge formed on the lower outer peripheral edge and the die 16 having the cutting edge formed on the upper inner peripheral edge shown in FIG. Square bottomed cylindrical work W sent from 9th process (# 9)
A prismatic battery can W in which a thick step portion is formed between a bottomed rectangular tube portion and a widened rectangular tube portion that is wider than the bottomed rectangular tube portion is formed by trimming the excess thickness portion e at the upper end. Complete. Reference numeral 15 is a guide punch, and 18 is a knockout.

[0028]

EFFECTS OF THE INVENTION Since the method for forming a prismatic battery can of the present invention is constituted by the above-described forming method, the following effects can be obtained. In the thickening drawing process, the open end of the bottomed cylindrical work is pressed in the axial direction of the cylinder to increase the thickness of the cylindrical part and draw forming in the same process, and the thickened cylindrical part is drawn into an elliptical cross section. In the redrawing process that draws into an almost oval shape through the process described above, the wall thickness near the corners is thinned so that uniform thickness can be obtained in each downstream drawing process. , The thickness of the thick-walled stepped portion near the opening can be secured with a small number of steps, and the uneven thickness phenomenon that tends to occur in the corner drawing can be suppressed to obtain a uniform thickness, which reduces the die manufacturing cost. It becomes cheaper and the die adjustment cost including maintenance decreases.

Further, in the thickening drawing step, the open end of the bottomed cylindrical body is pressed into the tapered surface of the female die and the cylindrical portion is pressed while being pressed. Therefore, the tapered angle of the tapered surface is used to form the cylinder. It is possible to easily set the relationship between the amount of wall thickness increase and the drawing ratio, and the action of the tapered surface causes a plastic flow such as a wall thickness flow for increasing the wall thickness and a diameter reducing flow for the wall drawing to gradually increase the thickness increase ratio. Even if the drawing ratio is set to be relatively large, buckling and wrinkling are less likely to occur in the molding process, and the shape and surface of the molded body are formed smoothly.

[Brief description of drawings]

FIG. 1 is a shape explanatory view of a bottomed cylindrical work piece that has been drawn and drawn by a first step, in which (a) is a top view and (b) is a front sectional view.

2A and 2B are shape explanatory views of a bottomed cylindrical work piece that has been thickened by a second step, in which FIG. 2A is a top view and FIG. 2B is a front sectional view.

3A and 3B are shape explanatory views of a bottomed cylindrical work piece redrawn by the third step, in which FIG. 3A is a top view and FIG. 3B is a front sectional view.

FIG. 4 is a shape explanatory view of an elliptical bottomed cylindrical work piece redrawn by the fourth step, (a) is a top view,
(B) is a front sectional view.

5A and 5B are shape explanatory views of a substantially oval-shaped bottomed cylindrical work piece redrawn by the fifth step, where FIG. 5A is a sectional view taken along the arrow of FIG. is there.

6A and 6B are shape explanatory views of a slender, substantially oval-shaped bottomed cylindrical work piece redrawn by the sixth step, in which FIG. 6A is a sectional view taken along the arrow line in FIG. 6B, and FIG. Is.

7A and 7B are shape explanatory views of a bottomed rectangular cylindrical work piece that has been subjected to square drawing by a seventh step, wherein FIG. 7A is a sectional view taken along the arrow line in FIG. 7B, and FIG.

FIG. 8 is a view for explaining the shape of a bottomed cylindrical work piece that has been stepped by the eighth step, (a) is a cross-sectional view taken along the arrow of (b),
(B) is front sectional drawing, (c) is an enlarged view of the thick step part enclosed with the dashed-dotted line of (b).

9A and 9B are shape explanatory views of a bottomed rectangular tubular work formed by an upper angular drawing in a ninth step, FIG. 9A is a sectional view taken along the arrow of FIG. 9B, and FIG.

10A and 10B are explanatory views of a work shape of a prismatic battery can trimmed in a tenth step, in which FIG. 10A is a top view and FIG.

FIG. 11 is an enlarged view of FIG.

FIG. 12 is an explanatory diagram of a mold in the second step.

FIG. 13 is an explanatory diagram of a mold in a fourth step.

FIG. 14 is an explanatory diagram of a mold in a fifth step.

FIG. 15 is an explanatory diagram of a mold in a ninth step.

FIG. 16 is an explanatory diagram of a mold in the 10th step.

FIG. 17 is an explanatory diagram of a conventional method for increasing the local wall thickness by press working.

FIG. 18 is an explanatory view of a method of increasing the local wall thickness by press processing of the prior art.

[Explanation of symbols]

1,8,11,14,18 Knockout 2,15 Guide punch 3,7,10,13,16 Die 5,6,9,12,17 Punch Wa A blank punched from the material in the first step. Wb A bottomed cylindrical work piece formed by drawing in the first step. Wc A bottomed cylindrical work piece that has been thickened and drawn in the second step. Wd A bottomed cylindrical work piece redrawn in the third step. We The bottomed cylindrical work piece redrawn in the fourth step. Wf A bottomed cylindrical work piece redrawn in the fifth step. Wg A bottomed cylindrical work piece redrawn in the sixth step. Wh A bottomed rectangular cylindrical work piece formed by square drawing in the seventh step. Wi A bottomed rectangular cylindrical work piece having a step formed in the eighth step. Wj A bottomed rectangular cylindrical work piece just before completion, which has been formed by upper corner drawing in the ninth step. W A rectangular battery can completed by trimming in the 10th process.

[Procedure amendment]

[Submission date] July 19, 1996

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of drawings]

FIG. 1 is a shape explanatory view of a bottomed cylindrical work piece that has been drawn and drawn by a first step, in which (a) is a top view and (b) is a front sectional view.

2A and 2B are shape explanatory views of a bottomed cylindrical work piece that has been thickened by a second step, in which FIG. 2A is a top view and FIG. 2B is a front sectional view.

3A and 3B are shape explanatory views of a bottomed cylindrical work piece redrawn by the third step, in which FIG. 3A is a top view and FIG. 3B is a front sectional view.

FIG. 4 is a shape explanatory view of an elliptical bottomed cylindrical work piece redrawn by the fourth step, (a) is a top view,
(B) is a front sectional view.

5A and 5B are shape explanatory views of a substantially oval-shaped bottomed cylindrical work piece redrawn by the fifth step, where FIG. 5A is a sectional view taken along the arrow of FIG. is there.

6A and 6B are shape explanatory views of a slender, substantially oval-shaped bottomed cylindrical work piece redrawn by the sixth step, in which FIG. 6A is a sectional view taken along the arrow line in FIG. 6B, and FIG. Is.

7A and 7B are shape explanatory views of a bottomed rectangular cylindrical work piece that has been subjected to square drawing by a seventh step, wherein FIG. 7A is a sectional view taken along the arrow line in FIG. 7B, and FIG.

FIG. 8 is a view for explaining the shape of a bottomed cylindrical work piece that has been stepped by the eighth step, (a) is a cross-sectional view taken along the arrow of (b),
(B) is front sectional drawing, (c) is an enlarged view of the thick step part enclosed with the dashed-dotted line of (b).

9A and 9B are shape explanatory views of a bottomed rectangular tubular work formed by an upper angular drawing in a ninth step, FIG. 9A is a sectional view taken along the arrow of FIG. 9B, and FIG.

10A and 10B are explanatory views of a work shape of a prismatic battery can trimmed in a tenth step, in which FIG. 10A is a top view and FIG.

FIG. 11 is an enlarged view of FIG.

FIG. 12 is an explanatory diagram of a mold in the second step.

FIG. 13 is an explanatory diagram of a mold in a fourth step.

FIG. 14 is an explanatory diagram of a mold in a fifth step.

FIG. 15 is an explanatory diagram of a mold in a ninth step.

FIG. 16 is an explanatory diagram of a mold in the 10th step.

FIG. 17 is an explanatory view of the shape of the completed prismatic battery can,
(A) is a top view, (b) is a front sectional view seen from the long side,
(C) is a side sectional view seen from the short side, (d) is (b),
It is an enlarged view of the part surrounded by the dashed-dotted line (c).

FIG. 18 : Increase in local wall thickness due to conventional press working
It is explanatory drawing of a method.

[ Fig. 19 ] Similarly, local meat produced by press processing of the conventional technique
It is explanatory drawing of the thickness increasing method.

[Explanation of Codes] 1,8,11,14,18 Knockout 2,15 Guide punch 3,7,10,13,16 Die 5,6,9,12,17 Punch Wa Punched from material in the first step blank. Wb A bottomed cylindrical work piece formed by drawing in the first step. Wc A bottomed cylindrical work piece that has been thickened and drawn in the second step. Wd A bottomed cylindrical work piece redrawn in the third step. We The bottomed cylindrical work piece redrawn in the fourth step. Wf A bottomed cylindrical work piece redrawn in the fifth step. Wg A bottomed cylindrical work piece redrawn in the sixth step. Wh A bottomed rectangular cylindrical work piece formed by square drawing in the seventh step. Wi A bottomed rectangular cylindrical work piece having a step formed in the eighth step. Wj A bottomed rectangular cylindrical work piece just before completion, which has been formed by upper corner drawing in the ninth step. W A rectangular battery can completed by trimming in the 10th process.

Claims (2)

[Claims] 1. A method for forming a rectangular battery can having a bottomed rectangular tubular body having a thick-walled stepped portion near an opening from a material having a plate thickness smaller than that of the thickened walled portion, the method having a bottomed shape. The open end of the work formed on the cylindrical body is pressed in the axial direction of the cylinder to press and draw the cylindrical portion, and at the same time, the force applied in the compression direction due to the resistance at the time of the forced drawing of the cylindrical portion is larger than the material plate thickness. And a thickening step for thickening the wall thickness, and the thickened cylindrical portion is formed into an elliptical cross section and the wall thickness around the corner formed in a substantially oval shape in the downstream step is reduced. Redrawing step to perform ironing to reduce the thickness of the elliptical shape into an oval shape and to reduce the wall thickness around the corner formed in the rectangular shape in the downstream step. Process,
A first corner drawing step of drawing the above-mentioned substantially oval shape into a rectangular bottomed rectangular tube portion excluding the opening side from a thick step formed in a downstream step, and a thick step inside the vicinity of the opening. A step forming step for forming a portion, and a second angular drawing step for drawing an opening side from the thick step into a rectangular wide-angled tube section that is wider than the bottomed rectangular tube section. A method for forming a prismatic battery can, comprising: 2. The thickening and squeezing step according to claim 1,
The opening end of the work formed in the bottomed cylindrical body is pressed in the axial direction of the cylinder to be pushed into the female tapered surface, and the cylindrical portion between the tapered surface and the opening end is pressed while being pressed and drawn. The method for forming a prismatic battery can according to claim 1, which is a thickening and drawing step of increasing the wall thickness of the cylindrical portion to be thicker than the material plate thickness by a force applied in the compression direction due to resistance at the time of pressing and drawing.