Apparatus and method of producing battery case

An apparatus for producing a battery case which has a tubular shape with a closed end and which houses an electricity-generating element, the apparatus including: a die assembly including a blanking die, a drawing die, a redrawing die and an ironing die which have respective die holes having mutually different sizes and which are immovably and coaxially arranged in series in the order of the sizes of the die holes; a first punch, a second punch and a third punch which are disposed coaxially with respect to the die assembly such that the first through third punches can be inserted into the corresponding die holes of the respective dies; and a moving mechanism which permits the first through third punches to be inserted into the corresponding die holes.

The present application is based on Japanese Patent Application No. 2005-150609 filed on May 24, 2005, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to an apparatus and a method of producing a battery case, and more particularly to improvements in an apparatus and a method of producing a battery case having a tubular shape with a closed end, by performing plural sorts of press working including DI (drawing and ironing) processing.

2. Discussion of Related Art

As well known, most of dry batteries and secondary batteries are constituted such that various sorts of electricity-generating elements suitable for the respective batteries are accommodated inside a metal battery case (battery can) having a tubular shape such as cylindrical or prismatic with one of its opposing ends closed. In each of such batteries, the battery case, as a shell body of the battery, needs to be light in weight and have a structure which withstands increased internal pressures during its use.

In view of the above, there is a recently proposed technique of producing a battery case by utilizing DI (drawing and ironing) processing capable of forming a metal tubular body having a small wall thickness and a sufficiently high degree of pressure withstanding strength, namely, by utilizing a press working method in which drawing and ironing are successively performed, as disclosed in WO00/69004, for instance.

Described more specifically, in the proposed technique, a drawing operation is initially performed on a plate-like metal material using a blanking die and a blanking punch, whereby a metal blank with a predetermined shape is obtained. The thus obtained metal blank is then subjected to a drawing operation using a drawing die and a drawing punch, thereby forming a tubular intermediate product having a closed end and a small depth. Subsequently, the intermediate product is subjected to DI processing wherein a plurality of redrawing operations and a plurality of ironing operations are successively performed using (i) a DI punch, (ii) a first die assembly (die mechanism) including a plurality of redrawing dies whose die holes have mutually different sizes and which are arranged in the order of the sizes of the die holes, and (iii) a second die assembly (die mechanism) including a plurality of ironing dies whose die holes have mutually different sizes and which are arranged in the order of the sizes of the die holes. Consequently, there is formed an intended battery case, which has a tubular shape having a closed end and a larger depth and a smaller wall thickness than the intermediate product. According to the proposed technique, it is possible to obtain, with high reliability, a battery case that is light in weight and has a structure that withstands increased internal pressure of the battery during its use.

In the proposed technique of producing the battery case, however, the step in which the plate-like metal material is formed into the intermediate product is carried out using a press machine exclusively for successively performing the blanking and the drawing, and thereafter the step in which the intermediate product is formed into the intended battery case is carried out using another press machine exclusively for performing the DI processing. Therefore, the proposed technique suffers from the following disadvantages.

Namely, where the battery case is produced according to the aforementioned conventional technique, space is needed for installing the two press machines. Further, in addition to the two press machines, a transfer device must be installed for transferring the intermediate product formed by one of the two press machines to the other. Thus, an enormous equipment investment is required, undesirably pushing up the cost of manufacture of the battery case.

SUMMARY OF THE INVENTION

The present invention has been made in the light of the situations described above. It is therefore an object of the invention to provide an apparatus and a method for producing, under industrially advantageous conditions at a reduced cost, a battery case obtained by performing plural types of press-working operations including the DI processing.

The above-indicated object of the invention may be attained according to a principle of the invention, which provides an apparatus for producing a battery case, which has a tubular shape with a closed end and which houses an electricity-generating element. The apparatus comprises a die assembly including: (i) a blanking die having a die hole with a predetermined size; (ii) a drawing die having a die hole whose size is smaller than that of the die hole of the blanking die; (iii) a redrawing die having a die hole whose size is smaller than that of the die hole of the drawing die, and (iv) an ironing die having a die hole whose size is smaller than that of the die hole of the redrawing die. The blanking die, the drawing die, the redrawing die and the ironing die are coaxially arranged in series in the order of the sizes of the die holes of the respective dies, such that the respective dies are inhibited from moving. A first punch is disposed coaxially with respect to the die assembly so as to be located on one side of the blanking die remote from the drawing die, such that the first punch can be inserted into the die hole of the blanking die and has a first accommodation hole that extends so as to be coaxial with the die hole of the blanking die. A second punch is accommodated coaxially in the first accommodation hole of the first punch such that the second punch can be advanced toward the blanking die. The blanking die is disposed so as to be insertable into the die hole of the drawing die as a result of the advancing movement thereof from the first accommodation hole, and the blanking die has a second accommodation hole that extends so as to be coaxial with the first accommodation holes. A third punch is accommodated coaxially in the second accommodation hole of the second punch such that the third punch can be advanced toward the blanking die and is disposed so as to be insertable sequentially into the die hole of the redrawing die and the die hole of the ironing die as a result of the advancing movement thereof from the second accommodation hole. A moving mechanism permits the inserting movement of the first punch into the die hole of the blanking die. The advancing movement of the second punch from the first accommodation hole and the advancing movement of the third punch from the second accommodation hole are to be performed independently of each other. With a plate-like metal material positioned between the blanking die and the first punch, the inserting movement of the first punch, the advancing movement of the second punch and the advancing movement of the third punch are carried out sequentially in order by the moving mechanism to sequentially perform: (i) a blanking operation by the first punch and the blanking die on the plate-like metal material so as to form a metal blank having a configuration that corresponds to the die hole of the blanking die; (ii) a drawing operation by the second punch and the drawing die on the metal blank so as to form a tubular intermediate product having a closed end and a predetermined depth; and (iii) a redrawing operation by the third punch and the redrawing die and an ironing operation by the third punch and the ironing die on the tubular intermediate product so as to form a tubular battery case as an end product having a closed end and a smaller wall thickness and a larger depth than the tubular intermediate product.

The present apparatus for producing a battery case constructed as described above includes the first punch for performing the blanking operation, the second punch for performing the drawing operation, and a third punch for successively or sequentially performing the redrawing operation and the ironing operation. Those three punches are assembled together such that the second punch is accommodated in the first accommodation hole formed in the first punch so as to be able to advance from the first accommodation hole and such that the third punch is accommodated in the second accommodation hole formed in the second punch so as to be able to advance from the second accommodation hole. The apparatus further has the die assembly including the blanking die, the drawing die, the redrawing die and the ironing die, those dies being assembled together. With the plate-like metal material positioned between the blanking die and the first punch, the moving mechanism initially permits the first punch to be inserted into the die hole of the blanking die, then permits the second punch to be inserted into the die hole of the drawing die as a result of the advancing movement thereof from the first accommodation hole, finally permits the third punch to be inserted sequentially into the die hole of the redrawing die and the die hole of the ironing die as a result of the advancing movement thereof from the second accommodation hole, whereby formation of the intermediate product from the plate-like metal material and formation of the battery case from the intermediate product are realized at one time in a series of steps. Therefore, a single piece of the present apparatus enables the intended battery case to be produced from the plate-like metal material with high reliability.

In the above-indicated apparatus according to the present invention, the die assembly includes the blanking die, the drawing die, the redrawing die and the ironing die, which dies are arranged in series in order so as to be inhibited from moving. Accordingly, in the series of steps in which the plate-like metal material is formed into the intermediate product and the intermediate product is formed into the battery case, the intermediate product is moved toward the redrawing die in accordance with the advancing movement of the second punch into the die hole of the drawing die, so that the intermediate product is positioned between the redrawing die and the third punch. Accordingly, the present apparatus permits speedy and reliable implementation of the DI processing in which the redrawing operation and the ironing operation are sequentially performed on the intermediate product, without a need of transferring the intermediate product by a separately provided transfer device as required in the conventional apparatus.

Therefore, unlike the conventional battery case producing apparatus using the two press machines, the battery case producing apparatus according to the present invention requires space for installing only single press machine. Further, the equipment for inserting the punches into the corresponding die holes of the dies is provided for only the single press machine. In addition, the conventionally required transfer device for transferring the intermediate product is eliminated.

In the battery case producing apparatus constructed according to the present invention, therefore, the battery case obtained by implementation of plural types of press working operations including the DI processing can be produced at reduced cost under industrially advantageous conditions. Consequently, the present apparatus attains high productivity and cost reduction of the battery case which is light in weight and has excellent pressure withstanding strength.

The present invention is preferably practiced at least in the following features.

(1) An apparatus for producing a battery case which has a tubular shape with a closed end and which houses an electricity-generating element comprises a die assembly including: (i) a blanking die having a die hole with a predetermined size; (ii) a drawing die having a die hole whose size is smaller than that of the die hole of the blanking die; (iii) a redrawing die having a die hole whose size is smaller than that of the die hole of the drawing die; and (iv) an ironing die having a die hole whose size is smaller than that of the die hole of the redrawing die, the blanking die. The drawing die, the redrawing die and the ironing die are coaxially arranged in series in the order of the sizes of the die holes of the respective dies, such that the respective dies are inhibited from moving. A first punch is disposed coaxially with respect to the die assembly so as to be located on one side of the blanking die remote from the drawing die, such that the first punch can be inserted into the die hole of the blanking die and the first punch has a first accommodation hole that extends so as to be coaxial with the die hole of the blanking die. A second punch is accommodated coaxially in the first accommodation hole of the first punch such that the second punch can be advanced toward the blanking die, is disposed so as to be insertable into the die hole of the drawing die as a result of the advancing movement thereof from the first accommodation hole, and has a second accommodation hole that extends so as to be coaxial with the first accommodation hole. A third punch is accommodated coaxially in the second accommodation hole of the second punch such that the third punch can be advanced toward the blanking die and is disposed so as to be insertable sequentially into the die hole of the redrawing die and the die hole of the ironing die as a result of the advancing movement thereof from the second accommodation hole. A moving mechanism permits the inserting movement of the first punch into the die hole of the blanking die, the advancing movement of the second punch from the first accommodation hole and the advancing movement of the third punch from the second accommodation hole to be performed independently of each other. With a plate-like metal material positioned between the blanking die and the first punch, the inserting movement of the first punch, the advancing movement of the second punch and the advancing movement of the third punch are carried out sequentially in order by the moving mechanism to sequentially perform: (i) a blanking operation by the first punch and the blanking die on the plate-like metal material so as to form a metal blank having a configuration that corresponds to the die hole of the blanking die; (ii) a drawing operation by the second punch and the drawing die on the metal blank so as to form a tubular intermediate product having a closed end and a predetermined depth; and (iii) a redrawing operation by the third punch and the redrawing die and an ironing operation by the third punch and the ironing die on the tubular intermediate product so as to form a tubular battery case as an end product having a closed end and a smaller wall thickness and a larger depth than the tubular intermediate product.

(2) The apparatus advantageously includes a first controller which controls the moving mechanism such that the inserting movement of the first punch. The advancing movement of the second punch and the advancing movement of the third punch are performed automatically and sequentially in order.

According to the above-indicated form (2), the series of steps of forming the intermediate product from the plate-like metal material and forming the battery case from the intermediate product are automated, thereby effectively enhancing the productivity of the battery case.

(3) The apparatus advantageously includes a second controller which controls the movements of the first punch, the second punch and the third punch such that the third punch is moved together with the second punch so that a leading end face of the third punch as seen in a direction of the advancing movement thereof is flush with a leading end face of the second punch as seen in a direction of the advancing movement thereof, until the tubular intermediate product is formed by the drawing operation performed by the second punch and the drawing die as a result of the advancing movement of the second punch from the first accommodation hole.

According to the above-indicated form (3), the third punch is prevented from being advanced from the second accommodation hole and therefore a portion of the metal blank is prevented from being deformed by the third punch, prior to formation of the intermediate product, in other words, prior to implementation of the drawing operation on the metal blank by the second punch and the drawing die. Therefore, the drawing operation on the metal blank can be implemented smoothly and stably. As a result, the intended battery case with a desired shape can be produced with high stability.

(4) In the apparatus according to the above form (1), the first punch is divided into a front section and a rear section as seen in a direction of the inserting movement thereof into the die hole of the blanking die, the front section and the rear section being assembled together so as to approach and separate relative to each other. The first punch is provided with a biasing device disposed between the front section and the rear section for applying biasing force to the front section and the rear section in a direction in which the front section and the rear section are separated away from each other. The metal blank is formed as a result of the inserting movement of the first punch into the die hole of the blanking die being gripped and held by and between the first punch and the drawing die based on the biasing force of the biasing device.

According to the above-indicated form (4), the front section of the first punch effectively functions as a blank holder for holding the metal blank when the drawing operation is performed on the metal blank by the second punch and the drawing die. Hence, the intermediate product formed by the drawing operation on the metal blank and accordingly the battery case to be obtained as the end product can be advantageously produced with stabilized quality without suffering from any faults or defects such as folds and wrinkles.

(5) A method of producing a battery case which has a tubular shape with a closed end and which houses an electricity-generating element, comprises a preparing step. The step includes preparing: (a) a die assembly including a blanking die having a die hole with a predetermined size, a drawing die having a die hole whose size is smaller than that of the die hole of the blanking die, a redrawing die having a die hole whose size is smaller than that of the die hole of the drawing die and an ironing die having a die hole whose size is smaller than that of the die hole of the redrawing die. The blanking die, the drawing die, the redrawing die and the ironing die being coaxially arranged in series in the order of the sizes of the die holes of the respective dies, such that the respective dies are inhibited from moving. The step further includes preparing (b) a first punch, which is disposed coaxially with respect to the die assembly so as to be located on one side of the blanking die remote from the drawing die, such that the first punch can be inserted into the die hole of the blanking die and which has a first accommodation hole that extends so as to be coaxial with the die hole of the blanking die. The step further includes preparing (c) a second punch which is accommodated coaxially in the first accommodation hole of the first punch such that the second punch can be advanced toward the blanking die, which is disposed so as to be insertable into the die hole of the drawing die as a result of the advancing movement thereof from the first accommodation hole, and which has a second accommodation hole that extends so as to be coaxial with the first accommodation hole. The step further includes preparing (d) a third punch which is accommodated coaxially in the second accommodation hole of the second punch such that the third punch can be advanced toward the blanking die and which is disposed so as to be insertable sequentially into the die hole of the redrawing die and the die hole of the ironing die as a result of the advancing movement thereof from the second accommodation hole. The method further includes a first process step in which a blanking operation by the first punch and the blanking die is performed on a plate-like metal material by inserting the first punch into the die hole of the blanking die with the plate-like metal material positioned between the blanking die and the first punch, thereby forming a metal blank having a configuration that corresponds to the die hole of the blanking die and in which the metal blank is moved toward the drawing die so as to be positioned between the second punch and the drawing die. The method further includes a second process step in which a drawing operation by the second punch and the drawing die is performed on the metal blank obtained in the first process step and positioned between the second punch and the drawing die, by advancing the second punch from the first accommodation hole so as to be inserted into the die hole of the drawing die, thereby forming a tubular intermediate product having a closed end and a predetermined depth and in which the tubular intermediate product is moved toward the redrawing die so as to be positioned between the third punch and the redrawing die. The method further includes a third process step in which a redrawing operation by the third punch and the redrawing die and an ironing operation by the third punch and the ironing die are sequentially performed on the tubular intermediate product obtained in the second process step and positioned between the third punch and the redrawing die, by advancing the third punch from the second accommodation hole so as to be inserted sequentially into the die hole of the redrawing die and the die hole of the ironing die, thereby forming a tubular battery case as an end product having a closed end and a smaller wall thickness and a larger depth than the tubular intermediate product.

In the battery case producing method according to the above-indicated form (5), the first process step of forming the metal blank from the plate-like metal material, the second process step of forming the intermediate product from the metal blank and the third process step of forming the intended battery case from the intermediate product are sequentially or consecutively carried out by using: (i) the first through the third punches which are assembled together such that the first through the third punches are coaxially arranged so as to be movable relative to each other; and (ii) the die assembly including the blanking die, the drawing die, the redrawing die and the ironing die, which dies are immovably arranged in series in order. Further, the metal blank formed by the blanking operation in the first process step is moved, in accordance with the movement of the first punch that performs the blanking operation, to a location where the drawing operation can be implemented in the second process step. Moreover, the intermediate product formed by the drawing operation in the second process step is moved, in accordance with the movement of the second punch that performs the drawing operation, to a location where the DI processing can be implemented in the third process step.

In the conventional method mentioned above, the step of forming the intermediate product from the plate-like metal material and the step of forming the battery case from the intermediate product by the DI processing are carried out using the two press machines and the transfer device for transferring the intermediate product between the two press machines, thereby producing the battery case. In contrast, in the present method according to the above-indicated form (5), the battery case can be produced at a time in the series of steps including the DI processing by using the single press machine equipped with the die assembly and the integrally assembled first through third punches. Thus, as compared with the conventional method, the present method can reduce the cost, the installation space and the like required for the equipment for producing the battery case more effectively.

Therefore, the present method according to the above-indicated form (5) permits advantageous production of the battery case that is light in weight and has a high degree of pressure withstanding strength, with excellent productivity and high economy.

DETAILED DESCRIPTION OF THE INVENTION

There will be explained in detail an apparatus and a method for producing a battery case according to the present invention by reference to the drawings.

Referring first toFIG. 1, there is schematically shown in vertical cross section an apparatus for producing a battery case for a secondary battery, constructed according to one embodiment of the present invention. The battery case to be produced has a cylindrical shape in which one of opposite ends is closed. InFIG. 1, the reference numeral10denotes a lower base which is a plate or block having a large thickness. There is disposed, above the lower base10, an upper base12which is a rectangular thick plate, such that the upper base12is opposed to the lower base10with a predetermined distance interposed therebetween. The upper base12is immovably supported by four long support posts14that extend upright from respective four corners of the lower base10. A die assembly16is fixed to the lower base10while a punch mechanism18is supported by the upper base12, thereby constituting the battery case producing apparatus according to the present invention.

Described more specifically, the die assembly16includes: five dies, i.e., a blanking die20, a drawing die22, a first redrawing die24, a second redrawing die26and an ironing die28; and a die holder30for holding those five dies20-28.

Each of the five dies20,22,24,26,28has a ring-like shape as a whole. The dies20,22,24,26,28have respective die holes32,34,36,38,40having mutually different sizes and formed through central portions of the respective dies20,22,24,26,28. Namely, the blanking die20has the largest ring-like shape among those five dies20,22,24,26,28and a die hole32defined by an inner circumferential surface thereof which is made as a cylindrical surface with a large diameter. In the blanking die20, an upper edge portion of the inner circumferential surface that defines the die hole32is formed as an outer blade33. The drawing die22has a ring-like shape smaller than the blanking die20and a die hole34defined by an inner circumferential surface thereof which is made as a cylindrical surface with a smaller diameter than the die hole32.

The first and second redrawing dies24,26and the ironing die28have ring-like shapes which are identical in size with each other and which are smaller than the drawing die22. The first and second redrawing dies24,26have respective die holes36,38defined by respective inner circumferential surfaces thereof each constituted by an upper tapered portion whose diameter gradually decreases in a downward direction as viewed inFIG. 1and a lower cylindrical portion whose diameter is smaller than that of the die hole34of the drawing die22. Further, the smallest inside diameter of the die hole38of the second redrawing die26is made smaller than the smallest inside diameter of the die hole36of the first redrawing die24. The ironing die28has a die hole40defined by an inner circumferential surface thereof which is tapered in the downward direction with the diameter gradually decreasing in the downward direction. The smallest inside diameter of the die hole40of the ironing die28is made smaller than the smallest inside diameter of the die hole38of the second redrawing die26.

In the present embodiment, therefore, the sizes of the die hole32of the blanking die20, the die hole34of the drawing die22, the die holes36,38of the first and second redrawing dies24,26and the die hole40of the ironing die28gradually decrease in this order.

The die holder30includes two thick-walled half-split members42a,42beach having a half-cylindrical shape. At an upper end portion of each of the half-split members42a,42b, there are formed: a lower shoulder surface44constituted by a half-annular surface with a small diameter and a large width; and an upper shoulder surface46constituted by a half-annular surface with a large diameter and a small width. Accordingly, the inner circumferential surface of each half-split member42a,42bis stepped at the upper end portion such that the diameter increases in two steps in the upward direction. At an axially middle portion of the inner circumferential surface of each half-split member42a,42b, there are formed three concave grooves48,50,52each having a rectangular cross section and extending continuously in the circumferential direction of each half-sprit member42a,42b. The three concave grooves48,50,52have the same depth and are spaced apart from each other by a predetermined spacing distance as viewed in the vertical direction ofFIG. 1. The two half-split members42a,42bare assembled so as to be butted together at respective cut or split surfaces thereof, thereby forming the die holder30having a thick-walled cylindrical shape as a whole.

At an upper open end portion of the thus formed cylindrical die holder30, there are provided an upper recess groove54and a lower recess56. The upper recess54is formed such that the upper shoulder surfaces46,46of the respective two half-split members42a,42bare connected to each other and has a large diameter and an annular bottom surface. The lower recess56is formed such that the lower shoulder surfaces44,44of the respective two half-split members42a,42bare connected to each other and has a small diameter and an annular bottom surface. The lower recess56is located right below the upper recess54. Further, the die holder30has, at an axially middle portion of the inner circumferential surface thereof, three circumferential grooves58,60,62which are respectively formed such that the three concave grooves48,50,52of the half-split member42aare respectively connected to the corresponding three concave grooves48,50,52of the half-split member42b. The three circumferential grooves58,60,62are spaced apart from each other by a suitable distance in the vertical direction ofFIG. 1.

Within the lower circumferential groove62which is located at the lowest position among the three circumferential grooves58,60,62, the ironing die28is accommodated with its outer peripheral portion held in contact, throughout the circumference thereof, with the side surfaces and the bottom surface of the lower circumferential groove62. Within the upper circumferential groove58which is located at the highest position among the three circumferential grooves58,60,62, the first redrawing die24is accommodated with its outer peripheral portion held in contact, throughout the circumference thereof, with the side surfaces and the bottom surface of the upper circumferential groove58. Within the intermediate circumferential groove60which is located between the upper and lower grooves58,62, the second redrawing die26is accommodated with its outer peripheral portion held in contact, throughout the circumference thereof, with the side surfaces and the bottom surface of the intermediate circumferential groove60.

Within the lower recess56of the die holder30, the drawing die22is accommodated with its outer circumferential surface and lower surface respectively held in contact, throughout the circumference thereof, with the inner circumferential surfaces and the lower shoulder surfaces44,44of the respective half-split members42a,42b. Within the upper recess54, the blanking die20is accommodated such that the outer circumferential surface of the blanking die20is held in contact, throughout the circumference thereof, with the inner circumferential surfaces of the half-split members42a,42band such that a radially outer portion of the lower surface of the blanking die20is held in contact with the upper shoulder surfaces46,46of the respective half-split members42a,42bwhile a radially inner portion of the lower surface thereof is held in contact with a radially outer portion of the upper surface of the drawing die22accommodated in the lower recess56.

Thus, the blanking die20, the drawing die22, the first redrawing die24, the second redrawing die26and the ironing die28are fixedly held by the die holder30such that the die holes32-40of the respective dies20-28are coaxially positioned in the inner hole of the die holder30.

Accordingly, in the present embodiment, the die assembly16is constituted as a unitary member in which the dies20,22,24,26,28are fixedly mounted on the die holder30such that the blanking die20, the drawing die22, the first redrawing die24, the second redrawing die26and the ironing die28are coaxially arranged in series in the order of the sizes of the die holes32,34,36,38,40of the respective dies20,22,24,26,28, i.e., in the order such that the sizes of the die holes32,34,36,38,40become smaller in the downward direction as seen inFIG. 1while the dies20,22,24,26,28are positioned horizontally. The thus constructed die assembly16is fitted, at the lower end portion of the die holder30thereof, in a circular fitting groove64provided at a central portion of the upper surface of the lower base10and fixed by bolts to the same10. Thus, the die assembly16is fixed to the lower base10so as to coaxially extend upright from the same10. A knockout66arranged to be movable in the vertical direction by a knockout device not shown is disposed such that the knockout66penetrates the central portion of the lower base10and coaxially extends into the inner hole of the die holder30of the die assembly16.

In the meantime, the punch mechanism18includes a blanking punch68as a first punch, a drawing punch70as a second punch, a DI punch72as a third punch, and a moving mechanism74for vertically moving the three punches68,70,72.

The blanking punch68generally has a cylindrical shape with a large thickness and a large diameter. The blanking punch68has an outside diameter that is determined such that the blanking punch68can be inserted into the die hole32of the blanking die20as shown inFIG. 3. The blanking punch68as the first punch has an inner hole functioning as a first accommodation hole76. A lower edge portion of the outer circumferential surface of the blanking punch68is made as an inner blade78.

The blanking punch68in the present embodiment is divided into two sections, i.e., a lower section80and an upper section82, which are connected by known connecting members such as connecting pins not shown, such that the lower and upper sections80,82can approach and separate relative to each other by a suitable distance in the vertical direction. Further, between the lower and upper sections80,82, a plurality of compression coil springs84as a biasing device are provided so as to be accommodated, in the preliminarily compressed state, in respective recesses formed at a plurality of locations in the circumferential direction on the surfaces of the lower and upper sections80,82that are opposed to each other. According to this arrangement, when a metal blank obtained by performing a blanking operation on a plate-like metal material is subjected to a drawing operation by the inner blade78of the blanking punch68and the outer blade33of the blanking die20as explained below, the outer peripheral portion of the metal blank is gripped and held by an between the lower section80of the blanking punch68and the drawing die22as shown inFIGS. 3 and 4, based on the biasing force of the compression coil springs84.

The drawing punch70generally has a columnar shape with a large diameter. The drawing punch70has an outside diameter that is determined such that drawing punch70can be inserted into the die hole34of the drawing die22as shown inFIGS. 4 and 5. There is formed, at a central portion of the drawing punch70, a second accommodation hole86that extends axially. The DI punch72generally has an elongate columnar shape and has an outside diameter that is determined such that the DI punch72can be inserted into the die hole40of the ironing die28through the die holes36,38of the first and second redrawing dies24,26as shown inFIGS. 6-8.

The thus constructed DI punch72is accommodated coaxially in the second accommodation hole86of the drawing punch70so as to be vertically movable. The drawing punch70in which the DI punch72is accommodated is accommodated, together with the DI punch72, coaxially in the first accommodation hole76of the blanking punch68so as to be vertically movable. In other words, the drawing punch70is fitted on the DI punch72and the blanking punch68is fitted on the drawing punch70, whereby these three punches68,70,72are disposed so as to be coaxial with each other and assembled together such that these three punches68,70,72are allowed to be moved relative to each other in the vertical direction.

The thus constructed assembly of the blanking punch68, the drawing punch70, and the DI punch72is inserted in a through hole88to be movable, wherein the through hole88is coaxially arranged with the die assembly16fixed to the lower base10and the through hole88has a large diameter. Owing to this, the blanking punch68, the drawing punch70, and the DI punch72are coaxially positioned above the die assembly16, which is fixed to the lower base10, so as to be able to move relative to each other in the axial direction.

In the present embodiment, the lower base10into which the three punches68,70,72are inserted has an upper surface on which are disposed side by side the moving mechanism74that cooperates with the three punches68,70,72to constitute the punch mechanism18and a controller90for controlling the operation of the moving mechanism74.

While not shown inFIG. 1, the moving mechanism74incorporates three drive sources such as hydraulic cylinders and electric motors. The three drive sources are electrically connected to the controller90. The blanking punch68, the drawing punch70and the DI punch72are connected, at respective upper portions thereof, to the respective three drive sources directly or indirectly via a motion converting mechanism such as a gear mechanism and a crank mechanism for converting a horizontally reciprocating movement of the hydraulic cylinders and a rotary movement of the electric motors into a vertically reciprocating movement. According to this arrangement, upon driving of the drive sources in the moving mechanism74, the blanking punch68, the drawing punch70and the DI punch72are moved in the vertical direction while being controlled independently of each other by the controller90.

Namely, in a state before the three drive sources in the moving mechanism74are driven, the blanking punch68, the drawing punch70and the DI punch72are positioned above the die assembly16so as to be placed at an upper stroke end of the vertical movement of the three punches68,70,72with lower end surfaces of the respective three punches68,70,72flush with each other, as shown inFIG. 1. Subsequently when one of the three drive sources in the moving mechanism74that is connected to the blanking punch68is driven by a predetermined amount under control of the controller90, the blanking punch68is moved downward, so that the lower end portion of the blanking punch68is inserted into the die hole32of the blanking die20as shown inFIG. 3.

Thereafter, when the two drive sources to which the drawing punch70and the DI punch72are respectively connected are driven in synchronism with each other by a predetermined amount under control of the controller90, the drawing punch70and the DI punch72are advanced from the first accommodation hole76of the blanking punch68as an integral unit. As a result, the punches70,72are moved downward, whereby the lower end portions of the respective punches70,72are inserted into the die hole34of the drawing die22as shown inFIGS. 4 and 5.

Subsequently when only the drive source to which the DI punch72is connected is driven by a predetermined amount under control of the controller90, the DI punch72is advanced from the second accommodation hole86of the drawing punch70. As a result, the DI punch72is moved downward, whereby the lower end portion of the DI punch72is inserted sequentially into the die holes36,38,40of the respective first redrawing die24, second redrawing die26and ironing die28and finally penetrate the die hole40, as shown inFIGS. 6-9.

Namely, owing to the operation of the moving mechanism74under control of the controller90, the inserting movement of the blanking punch68into the die hole32of the blanking die20, the insertion of the drawing punch70into the die hole34of the drawing die22as a result of the advancing movement of the drawing punch70from the first accommodation hole76, and the insertion of the DI punch72into the die holes36,38,40of the respective first redrawing die24, second redrawing die26and ironing die28as a result of the advancing movement of the DI punch72from the second accommodation hole86are performed automatically in sequence. In this instance, the downward movements of the punches68,70,72are controlled by the controller90such that the DI punch72and the drawing punch70are moved together with the respective lower end surfaces of the DI punch72and the drawing die22flush with each other, until the DI punch72is advanced from the second accommodation hole86. Thus, it is apparent that the controller90constitutes a first controller and a second controller.

A battery case is produced in the following manner, for instance, using the battery case producing apparatus constructed as described above.

Initially, a plate-like metal material92in the form of a thin flat plate is placed on the upper surface of the blanking die20while being in contact with a leading end face of the knockout66, so as to cover the entirety of the die hole32of the blanking die20, as shown inFIG. 2. As the plate-like metal material92, there may be suitably used an aluminum plate, an iron plate, a steel plate or the like. The plate-like metal material92is constituted by a material having a size sufficient for forming a single battery case or a strip-like material having a size large enough for forming a plurality of battery cases.

Next, as shown inFIG. 3, only the blanking punch68is moved downward based on the operation of the moving mechanism74controlled by the controller90and the lower end portion of the blanking punch68is inserted into the die hole32of the blanking die20, whereby the blanking operation is performed on the plate-like metal material92by the blanking punch68and the blanking die20. As a result, the plate-like metal material92is cut by the inner blade78of the blanking punch68and the outer blade33of the blanking die20so as to be formed into a metal blank94having a circular shape that corresponds to the die hole32of the blanking die20.

As the blanking punch68is moved downward, the thus formed metal blank94is moved downward, i.e., toward the drawing die22, together with the knockout66, so that the meal blank94is positioned between the drawing die22and the lower section80of the blanking punch68. In this state, the metal blank94is gripped and held, at its outer peripheral portion, by and between the lower end surface of the lower section80of the blanking punch68and the upper surface of the drawing die22, based on the biasing force of the compression coil springs84.

Subsequently, as shown inFIGS. 4 and 5, the drawing punch70and the DI punch72which is disposed in the second accommodation hole86of the drawing punch70are advanced (i.e., moved downward) from the first accommodation hole76of the blanking punch68as an integral unit based on the operation of the moving mechanism74controlled by the controller90, and the lower end portions of the punches70,72are inserted into the die hole34of the drawing die22, whereby the drawing operation is performed on the metal blank94by the drawing punch70and the drawing die22. As a result, there is formed a first intermediate product96which has a shallow cylindrical shape having a closed end and an outer circumferential surface that is made as a cylindrical surface corresponding to the inner circumferential surface of the die hole34of the drawing die22.

In this instance, because the outer peripheral portion of the metal blank94is gripped and held, based on the biasing force of the compression coil springs84, between the lower end surface of the lower section80of the blanking punch68and the upper surface of the drawing die22, the gripping or holding force with respect to the outer peripheral portion of the metal blank94acts on the metal blank94as a blank holder pressure or force during the drawing operation thereon. In addition, the drawing punch70and the DI punch72are moved downward as an integral unit, so that their lower end faces are made flush with each other. Accordingly, the drawing operation on the metal blank94can be performed with higher stability and more smoothly, thereby advantageously forming the first intermediate product96having the outer circumferential surface that well corresponds to the inner circumferential surface of the die hole34of the drawing die22, without suffering from any defects such as wrinkles.

As the drawing punch70and the DI punch72are integrally moved downward, the first intermediate product96is moved downward, i.e., toward the first redrawing die24, together with the knockout66, so that the first intermediate product96is positioned between the first redrawing die24and the lower end surfaces of the drawing punch70and the DI punch72while being supported by the knockout66.

Subsequently, as shown inFIGS. 6 and 7, the DI punch72is advanced (i.e., moved downward) from the second accommodation hole86of the drawing punch70based on the operation of the moving mechanism74controlled by the controller90, so that the lower end portion of the DI punch72is inserted successively into the die hole36of the first redrawing die24and the die hole38of the second redrawing die26that is smaller than the die hole36. Thus, the redrawing operation on the first intermediate product96is performed successively two times by the DI punch72and the first redrawing die24and by the DI punch72and the second redrawing die26. As a consequence, there is formed a second intermediate product98which has a stepped cylindrical shape having a closed end and a larger depth than the first intermediate product96, as shown inFIG. 7. In the second intermediate product98, the outer circumferential surface at its upper end portion is made as a cylindrical surface that corresponds to the inner circumferential surface of the die hole36of the first redrawing die24while the outer circumferential surface at its lower end portion is made as a cylindrical surface that corresponds to the inner circumferential surface of the die hole38of the second redrawing die26.

As the DI punch72is further moved downward, the second intermediate product98is moved downward, i.e., toward the ironing die28, together with the knockout66, so that the second intermediate product98is positioned between the ironing die28and the lower end surface of the DI punch72while being supported by the knockout66.

Thereafter, as shown inFIGS. 8 and 9, the DI punch72is further advanced (i.e., moved downward) from the second accommodation hole86of the drawing punch70based on the operation of the moving mechanism74controlled by the controller90, and the lower end portion of the DI punch72is inserted into the die hole40of the ironing die28, whereby the ironing operation is performed on the second intermediate product98by the DI punch72and the ironing die28. Consequently, there is formed a battery case100having a cylindrical shape which has a closed end and a smaller thickness and a larger depth than the second intermediate product98and whose outer circumferential surface is made as a cylindrical surface that corresponds to the inner circumferential surface of the die hole40of the ironing die28.

Subsequently, the blanking punch68, the drawing punch70and the DI punch72are raised so as to be placed at the upper stroke end shown inFIGS. 1 and 2by the operation of the moving mechanism74under control of the controller90while, on the other hand, the formed battery case100is removed from the DI punch72, whereby the intended battery case100is obtained.

In the present embodiment explained above, the operation of the moving mechanism74is controlled by the controller90to sequentially carry out: the first process step in which the plate-like metal material92is formed into the metal blank94by the blanking operation performed on the plate-like metal material92by the blanking punch68and the blanking die20; the second process step in which the metal blank94is formed into the first intermediate product96by the drawing operation performed on the metal blank94by the drawing punch70and the drawing die22; and the third process step in which the first intermediate product96is formed into the battery case100via the second intermediate product by performing the DI processing in which are sequentially carried out the two successive (two-stage) redrawing operations by the DI punch and the first and second redrawing dies24,26and the ironing operation by the DI punch72and the ironing die28. The first through the third process steps are carried out by the sequential working operation of moving the blanking punch68, the drawing punch70and the DI punch72downwards automatically and sequentially whereby the intended battery case100can be easily and efficiently produced from the plate-like metal material92.

In the present embodiment, the apparatus for producing the intended battery case100is constituted by a single apparatus in which the die assembly16, the punch mechanism18and the controller90are mounted on the integrally assembled lower base10and the upper base12. In contrast, the conventional system for producing the battery case100uses two apparatus, i.e., the apparatus which includes: a blanking die and a drawing die; a blanking punch and a drawing punch; and a moving mechanism for moving the punches so as to be inserted into corresponding die holes of the respective dies and which forms the first intermediate product96from the plate-like metal material92via the metal blank94, and the apparatus which includes: redrawing dies and ironing dies; a DI punch; and a moving mechanism for moving the DI punch so as to be inserted into die holes of the respective dies and which forms the battery case100from the first intermediate product96via the second intermediate product98. In the present arrangement, therefore, the space for disposing only the single apparatus for producing the battery case100is required, thereby effectively reducing the installation space for the battery case producing apparatus and accordingly the work area required for producing the battery case100.

Further, in the present embodiment, while the apparatus for producing the battery case100includes the punches68-72and the dies20-28the numbers of which are the same as those of the punches and dies in the conventional system for producing the battery case100using the two apparatus described above, the punches68-72are arranged to be moved so as to be insertable into the die holes32-40of the respective dies20-28by the single moving mechanism74. Accordingly, as compared with the conventional system in which the two moving mechanisms are used, the present apparatus using only the single moving mechanism advantageously assures reduced cost of the apparatus and accordingly reduced cost of manufacture of the battery case100.

In the course of formation of the battery case100, the metal blank94, the first intermediate product96and the second intermediate product98are automatically moved, by the advancing or inserting movements of the punches68-72into the corresponding die holes32-40of the dies20-28, to the respective locations where the drawing operation on the metal blank94, the redrawing operation on the first intermediate product96and the ironing operation on the second intermediate product98are performed, without using any special transfer device. Accordingly, the plurality of operations indicated above can be performed consecutively and smoothly.

Therefore, unlike the aforementioned conventional system for producing the battery case100using the two apparatus and the transfer device for transferring the intermediate product between the two apparatus, the present arrangement does not need such a transfer device, thereby attaining elimination of the installation space for the transfer device and the cost reduction.

According to the present embodiment, the intended battery case100can be automatically produced through the DI processing at a reduced cost under industrially advantageous conditions. As a result, the battery case100which is lightweight and has excellent pressure withstanding strength can be obtained with high productivity and at reduced cost.

When the drawing operation is performed on the metal blank94, the blank folding pressure acts on the outer peripheral portion of the metal blank94between the lower end surface of the lower portion80of the blanking punch68and the upper surface of the drawing die22on the basis of the biasing force of the compression coil springs84while, at the same time, the lower surfaces of the drawing punch70and the DI punch72are made flush with each other. Therefore, the metal blank94is formed, by the drawing operation, into the first intermediate product96which is free from defects such as wrinkles or folds and whose outer circumferential surface well corresponds to the inner circumferential surface of the die hole34of the drawing die22. Accordingly, the redrawing operations and the ironing operation to be subsequently performed on the first intermediate product96can be smoothly implemented with high stability, resulting in stable production of the intended battery case100with the desired shape.

While the presently preferred embodiment of the invention has been described in detail, for illustrative purpose only, it is to be understood that the present invention is not limited to the details of the illustrated embodiment, but may be otherwise embodied.

In the illustrated embodiment, the controller90controls the moving mechanism74such that the blanking punch68as the first punch, the drawing punch70as the second punch and the DI punch72as the third punch are sequentially and automatically moved downward so as to be inserted into the corresponding die holes32-40of the dies20-28. There may be provided for a switch mechanism or the like for moving the punches68-72downward, for instance, and the punches68-72may be arranged to be sequentially moved downward by manipulation of the switch mechanism by an operator.

The structure by which the punches68-72and the die assembly16are disposed or installed is not limited to that illustrated above.

The dies20-28may be otherwise mounted on the die holder30, provided that the dies are immovably and coaxially arranged in the order of the sizes of the respective die holes32-40.

Further, the numbers of the blanking die, the drawing die, the redrawing die and the ironing die are not particularly limited, provided that the die assembly16includes at least one blanking die which cooperates with the blanking punch68to perform the blanking operation on the plate-like metal material92, at least one drawing die which cooperates with the drawing punch70to perform the drawing operation on the metal blank94, at least one redrawing die which cooperates with the DI punch72to perform the redrawing operation on the first intermediate product96, and at least one ironing die which cooperates with the DI punch72to perform the ironing operation on the second intermediate product98.

The configuration of each of the punches68-72and the configuration of each of the die holes32-40of the respective dies20-28are not limited to those in the illustrated embodiment, but may be suitably changed depending upon the shape of the battery case100to be obtained. Where a battery case having an elliptical tubular shape with a closed end or a battery case having a prismatic tubular shape with a closed end is produced, for instance, each punch and each die hole are configured to have an elliptical shape or a rectangular shape.

While the apparatus and method for producing the battery case for the secondary battery has been described above as the preferred embodiment of the present invention, the principle of the invention is equally applicable to an apparatus and method for producing a battery case for a primary battery such as a dry battery.

It is to be understood that the present invention may be embodied with various other changes and modifications, which may occur to those skilled in the art, without departing from the scope of the invention defined in the appended claims.