Manufacturing method of rectangular cylindrical container with side walls of different thickness

Abstract

To provide a prismatic container which can be formed by a thin blank while reducing combinations of punches and dies and having one side wall thicker in plate thickness than the other side wall, and a method for manufacturing the same.SOLUTION: The method for manufacturing the prismatic container comprises: a first forming step S2 of drawing a blank to form a first intermediate container body; and a second forming step S3 of redrawing and ironing the first intermediate container body to form a second intermediate container body. The second forming step S3 includes a repeating step of further redrawing and ironing the second intermediate body. The second forming step S3 includes a step S31 of inserting a plate presser between a punch and a workpiece used in the first or repeating step and adjusting / holding a clearance between the plate presser and a die, and a pressing step S32 of regulating the radial movement of the workpiece and pressing the opening end of the workpiece in an axial direction.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a rectangular cylindrical container used, for example, in a battery case, and more specifically, to a method for manufacturing a rectangular cylindrical container in which the plate thickness of the short side wall differs from the plate thickness of the long side wall in the final product or intermediate molded product. [Background technology]

[0002] (Demand for square cylindrical containers) Lithium-ion secondary batteries are widely used as power sources for information and communication devices such as mobile terminals. Furthermore, as the spread of electric vehicles is desired as one of the measures to prevent global warming, the demand for large secondary batteries that can be installed in these vehicles is expected to increase. In particular, large, deep-bottomed metallic rectangular cylindrical containers are required as cases to store secondary batteries for electric vehicles.

[0003] (Challenge 1. Number of steps required to mold a deep-bottomed rectangular container) To mold a metal rectangular container, multiple drawing and ironing processes are usually required. In other words, to approximate the final container shape from the material (blank) shape, a forming die equipped with a pair of punches and dies with different shapes is required for each process, and the deeper the final container shape is (the greater the height), the more processes must be performed, i.e. the more forming dies must be prepared.

[0004] (Issue 2. Weight and loss of materials) In addition, in the conventional drawing and ironing process, which requires multiple steps, a heavy blank with an original thickness that is significantly thicker than the final thickness is required to obtain the final thickness of the final product shape. This means fewer material options and higher material costs. For example, there will always be ends (losses) of blanks that are not used in the final product shape, but the greater the thickness of the blank, the greater the loss of material and material costs.

[0005] (Issue 3. Demand for rectangular containers with different thicknesses) Recently, there has also been an increasing demand for rectangular tubular containers in which the thickness of one side wall is different from that of the other side wall. For example, there is a demand for the thickness of the short side wall to be thicker than that of the long side wall in order to reduce the weight of the battery case while increasing its mechanical strength. To meet this demand using conventional technology, additional drawing and ironing processes would be required for the side walls that should be thinner, and it is expected that this would require more processes than molding a rectangular tubular container with uniform thickness on all side walls.

[0006] (Challenge 4. Suppression of wrinkles, cracks, and thickness variations) Even when drawing cylindrical containers, which have a simpler shape and are easier to form than rectangular containers, small elements in the workpiece expand and contract in the axial and radial directions depending on the location, making it easy for wrinkles and cracks to occur during forming. Furthermore, when focusing on the thickness of a side wall when processing a workpiece, it is unavoidable that the shoulder (punch shoulder) close to the punch (bottom surface) is thin and the shoulder (die shoulder) close to the die (away from the bottom surface) is thick. Thus, there is a demand for a method of forming rectangular containers that is less prone to wrinkles and cracks and that achieves uniform thickness on each side wall.

[0007] (Prior art related to issues 1 and 2) In relation to problem 1, Patent Document 1 discloses a method for manufacturing a rectangular tubular container with the aim of reducing the number of steps. However, since it is necessary to prepare a blank with a thickness 2.7 to 3.5 times larger than the thickness of the final processed product, problem 2 is not resolved at all. Furthermore, Patent Document 1 does not disclose a technology for manufacturing a rectangular tubular container having side walls with different thicknesses on the short and long sides.

[0008] (Prior art related to issue 3) In relation to problem 3, Patent Document 2 discloses a method for manufacturing a rectangular battery can in which the thickness of the short side wall is made thicker than the thickness of the long side wall. This prior art requires a first step of obtaining a substantially elliptical first intermediate container body from a blank, a second step of forming a second intermediate container body having a cross-sectional shape with a smaller minor axis / major axis ratio than the cross-sectional shape of the first intermediate container body, and a third step of continuously performing DI processing, which combines drawing and ironing, on this second intermediate container body in one go. Patent Document 2 discloses a manufacturing device that performs multiple drawing processes and then finally performs ironing.

[0009] (Number of punch and die combinations) At first glance, the manufacturing method disclosed in Patent Document 2 appears to be a simple technique consisting of only the first to third steps. However, ironing cannot be performed immediately after drawing (first step), and a re-drawing process (second step) is required that is not intended to adjust the plate thickness. In addition, in the second and third steps, multiple dies (four dies per step in the attached drawings) are provided for one punch. Therefore, the total number of combinations of punches and dies required for all of the first to third steps is as much as nine, which is not necessarily a simple method.

[0010] (Blanks to be procured) The manufacturing method disclosed in Patent Document 2 is a technique for forming both the short side wall and the long side wall while gradually reducing the thickness after forming from the thickness before one process, similar to Patent Document 1. Therefore, it is necessary to procure a blank having an original thickness that is much greater than the thickness of the relatively thicker side in the final product shape.

[0011] (Thickness difference achievable with prior art) In the embodiment disclosed in Patent Document 2, even if a total of nine dies are used, the thickness difference of the final product is only 0.02 mm (= short side thickness 0.17 mm - long side thickness 0.15 mm), and even if this is compared with the final thinner thickness (long side thickness 0.15 mm), it is only about 13%. And, even to obtain a battery can with this slight thickness difference, it is necessary to procure a blank with an original thickness of 0.4 mm, which is about 2.35 times larger than the short side thickness. In addition, in this conventional technology, since the bottom side wall is not subjected to DI processing, the bottom thickness remains thick, which will cause another problem of the weight of the final product being heavy.

[0012] In this way, if an attempt is made to further increase the target thickness difference using conventional technology, the original thickness of the blank will also increase as the thickness of the short side walls increases, and the amount of waste material (loss) not used in forming the blank will also increase in proportion to the increase in the original thickness. In contrast, if a new molding technology for rectangular cylindrical containers could be found that would maintain the final thickness (for example, the thickness of the side walls that should be thick) at almost the same thickness as the original thickness, or even make it thicker than the original thickness, then the blanks that need to be procured would need to be made of extremely thin plate-like material.

[0013] (How to set thickness difference and number of dies required) In order to achieve a thickness difference between side walls using the prior art disclosed in Patent Document 2, it is necessary to apply a relatively high ironing rate to the side wall to be thinned and a relatively low ironing rate to the side wall to be thickened. One side wall processed at a higher ironing rate is more likely to crack or break, while the other side wall processed at a lower ironing rate has a large variation in thickness after forming. As such, since it is not possible to set an excessively large difference in ironing rate in one operation (one die stage), the only way to increase the thickness difference is to increase the number of die stages set in the DI processing machine, which increases the manufacturing cost of the device in addition to the loss of blank material described above.

[0014] (Prior art related to issue 4) In relation to problem 4, Patent Document 3 discloses a method for forming a stainless steel rectangular tubular container with good shape and uniform thickness of the side wall by performing redrawing and ironing in a continuous process up to the final process, omitting the annealing process in the intermediate process. In addition, a cylindrical plate holder that surrounds the outer periphery of the punch and is placed between the workpiece and the punch to suppress wrinkles during the redrawing process is disclosed.

[0015] However, the technology in Patent Document 3 is a warm working technique, and the die and punch must be heated with a heater or the like. This makes the manufacturing equipment complicated and increases costs. Furthermore, this warm working technique requires that the temperatures of the workpiece and the die be kept constant throughout the process, so other processes such as redrawing and ironing must be carried out continuously and all at once, and forming cannot be interrupted between processes.

[0016] In addition, the technology of Patent Document 3, like Patent Documents 1 and 2, is a processing method in which the thickness of the blank is gradually reduced from its original thickness, and since a thin material cannot be used for the blank, it cannot solve Problem 2. Moreover, Patent Document 3 does not mention at all the technology of Problem 2, which is to create a large difference in thickness between side walls.

[0017] As such, no matter which conventional processing technology is used or how these technologies are combined, it is difficult to simultaneously solve all of the above problems 1 to 4, and a new molding technology for rectangular tubular containers is desired. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] JP 2019-166527 A [Patent Document 2] Patent No. 4119612 [Patent Document 3] JP 2009-113059 A Summary of the Invention [Problem to be solved by the invention]

[0019] The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing a square tubular container in which the side walls have different thicknesses in the final product or intermediate molded product (for example, a square tubular container in which the thickness of the short side wall of the cross-sectional shape is thicker than the thickness of the long side wall).

[0020] Furthermore, the present invention aims to provide a method for manufacturing a rectangular tubular container that can be formed from a thin plate-like blank and that can increase the difference in plate thickness between the side walls while reducing the number of punch and die combinations required for forming.

[0021] After extensive research, the inventors focused on the sheet holder that had been used to prevent wrinkles in the workpiece during conventional redrawing and ironing processes, and discovered that all of the above-mentioned problems could be solved at once by adding a mechanism for thickening the side walls of the workpiece to this sheet holder and adjusting the ironing rate for each side wall within a prescribed range, thereby completing the present invention.

[0022] The inventors also discovered that by making the thickness of each side wall in an intermediate molded product different, and then performing additional processing to make the thickness of each side wall uniform, it is possible to produce a square tubular container having side walls with the same thickness in the final product while reducing the number of steps compared to conventional processing methods. [Means for solving the problem]

[0023] That is, the present invention has, for example, the following configurations and features. (Aspect 1) A method for manufacturing a rectangular cylindrical container having first and second side walls with different thicknesses, comprising the steps of: A step of preparing a plate-shaped metal blank as a workpiece; a first forming step of forming a container body having an elliptical cross-sectional shape by drawing the workpiece; a second forming step in which the workpiece that has completed the first forming step is simultaneously subjected to redrawing and ironing to form a container body having a height greater than that of the workpiece immediately before forming and a cross-sectional shape having a smaller minor axis / major axis ratio than that of the cross-sectional shape of the workpiece immediately before forming; Including, The second forming step includes a repeating step of simultaneously subjecting the formed workpiece to redrawing and ironing, The second forming step includes a pressing step in which a body part of a plate holder is inserted between the punch used in the first or repeated step and the workpiece, while a clearance is maintained between the punch and the die to restrict radial movement of the workpiece to be formed, and a compressive force is applied in the axial direction to the upper opening end of the workpiece using a pressing part of the plate holder, In the second molding step, a first clearance in a first side wall that is to be relatively thick among the clearances is defined as C1, and a second clearance in a second side wall that is to be relatively thin is defined as W1, If the thicknesses of the first and second side walls just before forming are t1 and t2, (1) C2 <C1であり、 (2) 0.65 <C1 / t1≦1.25 (3) 0.65≦C2 / t2≦1.00 Set it so that all the conditions above are met. A method for manufacturing a rectangular cylindrical container comprising the steps of: (Aspect 2) The method for producing a rectangular tubular container according to aspect 1, wherein the compressive force is 0.25 to 1.1 in terms of a yield stress ratio of the material used per unit area. (Aspect 3) In the second molding process, (4) the first and second clearances C1 and C2 are set so as to satisfy 0.2≦(C1-C2) / C2. 3. The method for producing a rectangular tubular container according to claim 1 or 2. (Aspect 4) In the second forming step, by setting the first clearance C1 so as to fall within the range of (2’) 1.00 < C1 / t1 ≤ 1.25, while increasing the plate thickness t1’ of the first side wall immediately after forming as compared to the plate thickness t1 of the first side wall immediately before forming, (3’) by setting the second clearance C2 so as to fall within the range of 0.65 ≤ C2 / t2 < 1.00, the plate thickness t2’ immediately after forming is decreased with respect to the plate thickness t2 of the second side wall immediately before forming, A method for manufacturing a square tube container according to any one of Aspects 1 to 3, characterized by the above. (Aspect 5) After the second forming step, further including a third forming step of performing re-drawing and ironing on at least one of the first and second side walls so as to equalize the plate thicknesses of the first and second side walls with each other, A method for manufacturing a square tube container according to any one of Aspects 1 to 4, characterized by the above. (Aspect 6) The cross-sectional shape of the square tube container is rectangular, The first side wall is a short side wall, and the second side wall is a long side wall, A method for manufacturing a square tube container according to any one of Aspects 1 to 5, characterized by the above. (Aspect 7) The square tube container is for a battery case, A method for manufacturing a square tube container according to any one of Aspects 1 to 6, characterized by the above 。 [Effect of the Invention]

[0024] According to the manufacturing method of the present invention, including re-drawing and ironing on the workpiece, the plate presser inserted between the punch and the workpiece not only restricts the radial deformation of the workpiece during processing, but also continuously applies a force to compress the workpiece in the axial direction with respect to the open end of the workpiece. As a result, more material can be more reliably introduced by the clearance on at least one side wall side in one step, so that the plate thickness of the side wall can be maintained to be almost the same as the original plate thickness of the blank.

[0025] Furthermore, in a preferred embodiment of the present invention, the thickness of the side wall to be thickened can be made larger than the original thickness of the blank. In other words, a thin plate material having an original thickness smaller than the thickness of the relatively thick side wall of the final product or intermediate molded product can be used as the blank of the present invention. This is a groundbreaking breakthrough that has not been achieved in the prior art in this field.

[0026] In addition, if the clearance ratio (C1 / C2) is set large in the preferred embodiment of the present invention, a large thickness difference can be obtained by one redrawing and ironing process. Therefore, even if the final target thickness difference is large, a much smaller number of processes (combinations of dies and punches) is required compared to the prior art.

[0027] Furthermore, according to the manufacturing method of the present invention, the clearance is regulated both radially and axially, so that wrinkles on the side wall surface and variations in plate thickness after molding can be suppressed more than the capabilities of conventional techniques. [Brief description of the drawings]

[0028] [Figure 1] 4 shows changes in the shape of a workpiece in each step of the manufacturing method of the present invention. [Diagram 2] FIG. 2 is a longitudinal sectional view of a blank and a diagram showing the change in the cross-sectional shape of a workpiece after each process of the present invention, superimposed thereon. [Diagram 3] 1 is a diagram showing a cross-sectional structure of a rectangular tubular container formed by the manufacturing method of the present invention. [Figure 4] 1 is a flowchart showing each step of a manufacturing method of the present invention. [Diagram 5] FIG. 4 is a schematic view showing a second molding device (molding die) that can be used in the production method of the present invention. [Figure 6] FIG. 4 is a diagram showing the structure of the plate holder of the present invention used in the second step. [Figure 7] 13A to 13C are diagrams illustrating the processing mechanism for each side wall in the second step. [Figure 8]1A and 1B are conceptual diagrams for explaining the difference in processing capacity (number of steps, change in plate thickness of each side wall) between the conventional technology and the present invention. [Figure 9] 1(a) is an image diagram for explaining the difference in processing capacity between the conventional technology and the present invention, and FIG. 1(b) is an experimental result showing the change in plate thickness on each side wall when processing using the forming device of the embodiment. [Figure 10] 1A to 1C are diagrams showing the appearances of a prototype and a defective product manufactured using the manufacturing method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention will be described below based on the embodiments shown in the drawings, but the present invention is not limited to the specific embodiments described below. In addition, the same reference numerals are used for the same or corresponding parts in each drawing. EXAMPLES

[0030] Figure 1 shows the shape of the workpiece W (hereinafter, also referred to as "work") in each step of the manufacturing method of the present invention. Each view in the upper row (a) of Figure 1 shows a plan view of the workpiece W, each view in the middle row (b) is a vertical cross section of the workpiece W (its long side wall) (a cross section cut along line BB in the corresponding plan view in the upper row), and each view in the lower row (c) is a vertical cross section of the workpiece W (its short side wall) (a cross section cut along line CC in the corresponding plan view in the upper row).

[0031] The diagrams in the leftmost column of figures in Fig. 1 (n=0 in the figure) show the workpiece W (i.e., blank BL) before forming. The diagrams in the column immediately to the right of that (n=1 in the figure) show the workpiece W (W1) after it has been subjected to drawing (first forming process S2 described below). The diagrams in the third column from the left (n=2 in the figure) show the workpiece W (W2) after it has been subjected to the first redrawing and ironing process (second forming process S3 described below). The diagrams in the rightmost column of figures (n=3 in the figure) show the workpiece W (W3) after it has been subjected to the second redrawing and ironing process.

[0032] Fig. 2(a) is a vertical cross-sectional view showing a blank BL, and Fig. 2(b) is a diagram showing the cross-sectional shapes of a workpiece W immediately after each process of the present invention, superimposed on each other, where n indicates the number of processes.

[0033] (Square cylindrical container after molding) FIG. 3 shows the cross-sectional structure of a rectangular tubular container SC (more specifically, the cross-sections of the short side wall and the long side wall) formed by the manufacturing method of the present invention. FIG. 3(a) is a perspective view in which the first and second side walls SW1 and SW2 are partially broken so that the inside of the rectangular tubular container SC after final forming can be seen. FIG. 3(b) is a view of FIG. 3(a) seen from the direction of the arrow B in the figure, and FIG. 3(c) is a view of FIG. 3(a) seen from the direction of the arrow C in the figure. As can be seen from these figures, the rectangular tubular container SC has first and second side walls SW1 and SW2 with different thicknesses t1' and t2', and in the illustrated example, the thickness t1' of the first side wall SW1, which is the short side wall, is greater than the thickness t2' of the second side wall SW2, which is the long side wall.

[0034] (Production method of the present invention) Each step of the manufacturing method of the present invention will be described with reference to the flow chart of Fig. 4. First, a plate-shaped metal blank BL is prepared as a workpiece W (step S1). This plate-shaped blank BL may be made of, for example, aluminum or stainless steel, but is not necessarily limited to these. The thickness and shape of the blank BL are derived and determined by calculating backwards from the final product shape to gradually determine the shape to be formed before the previous process.

[0035] (First forming process: drawing) Next, the blank BL is subjected to drawing to form a first intermediate container body W1 having an elliptical cross-sectional shape (first forming step S2). For the shape of the first intermediate container body W1 after forming, please refer to the workpiece W1 shown in Figure 1 and Figure 2 (b) where n = 1. In this first forming step S2, the first intermediate container body W1 can be formed from the blank BL using, for example, a known press forming die.

[0036] (Second forming process: redrawing and ironing) Thereafter, the first intermediate container body W1 is simultaneously subjected to redrawing and ironing to form a second intermediate container body W2 having a height greater than that of the first intermediate container body W1 and a cross-sectional shape with a smaller minor axis / major axis ratio than that of the cross-sectional shape of the first intermediate container body W1 (second forming step S3). In this second forming step S3, for example, the second intermediate container body W2 can be formed from the workpiece W (first intermediate container body W1) using a second forming device 1 of the present invention described later. For the shape of the second intermediate container body W2 after forming, please refer to the workpiece W2 shown in FIG. 1 and FIG. 2(b) where n=2.

[0037] (Repeated redrawing and ironing processes) The second molding step S3 preferably includes a step S3B for determining whether the dimensions of the molded second intermediate container body W2 have reached a target dimension (for example, a dimension (deep drawing degree) at which the third forming step S4, restriking step S5, and trimming step S6 described below can be started). If the target dimension has not been reached, a repeat step of carrying out the second molding step S3 is performed again. On the other hand, if the target dimension has been reached, the second molding step S3 is terminated and the process proceeds to the next step S4.

[0038] (Adjusting and maintaining clearance) It should be noted that the second forming step S3 uses a unique sheet holder 2 (see also Figs. 5 and 6) that is original to the present invention. This sheet holder 2 has a body portion 2a that is inserted between the punch 3 used in the first or repeated step and the workpiece W, and adjusts and maintains the clearances C1, C2 between the outer periphery of the punch 3 (specifically, the punch body) and the inner periphery of the die 4 (step S31).

[0039] (Restriction of radial deformation and axial pressure) 5 and 6, in addition to the main body 2a, the plate holder 2 is also formed with a push-in portion 2b on the outer periphery of the main body 2a. The main body 2a is used to restrict the radial movement (deformation) of the first intermediate container body W1 (the second intermediate container body W2 immediately before forming in the case of the repeating process) which is the work W, and at the same time, the push-in portion 2b is used to restrict the radial movement (deformation) of at least the first side wall SW1 of the work W (both side walls SW1 and SW2 in the drawing). o A compressive force F is applied to the side walls SW1 and SW2 in the axial direction (pressing step S32). By applying the compressive force F, the plate thicknesses t1' and t2' of the side walls SW1 and SW2 after forming are increased from the bottom (punch shoulder) to the upper end opening W o is uniform throughout.

[0040] (Molding conditions in the second molding process) More specifically, when the first clearance in the first side wall SW1, which should be relatively thick, of the above-mentioned clearances C1, C2 is taken as C1, the second clearance in the second side wall SW2, which should be relatively thin, is taken as C2, and the plate thicknesses of the first and second side walls SW1, SW2 immediately before forming are taken as t1, t2, the clearances are set to satisfy the following conditions (1) to (3).

[0041] (Adding clearance difference) (1) C2 <C1である。 Since C1 and C2 both become the thicknesses t1' and t2' of the first and second side walls SW1 and SW2 after forming, this condition means that the thickness t1' of the first side wall SW1 after each forming step of the second forming process S3 will be greater than the thickness t2' of the second side wall SW2.

[0042] (Setting the squeezing rate for each side wall) (2) 0.65 <C1 / t1≦1.25であり、かつ、 (3) 0.65≦C2 / t2≦1.00.

[0043] Here, C1 / t1 (or C2 / t2) indicates the degree of deformation (i.e., the ironing rate) of the plate thickness t1' (or t2') after forming relative to the plate thickness t1 (or t2) before forming in the first side wall SW1 (or the second side wall SW2). Incidentally, when the ironing rate is set in the range of 0.65 to 1, it means that the workpiece W is processed with "relatively strong ironing", and when the ironing rate is set in the range of 1 to 1.25, it means that the workpiece W is processed with "relatively light ironing".

[0044] (When increasing the thickness of one side wall and decreasing the thickness of the other side wall) Furthermore, it is also possible to make the thickness t1' of the first side wall SW1 after forming thicker than the thickness t1 immediately before forming, while making the thickness t2' of the other side wall SW2 after forming thinner than the thickness t2 before forming. If this forming process is desired, the following preferable conditions are set.

[0045] (2')1.00 <C1 / t1≦1.25であり、かつ、 (3') 0.65≦C2 / t2<1.00.

[0046] By setting these preferred conditions, the first side wall SW1 is processed with "relatively light ironing" while a compressive force F is applied thereto, so that the thickness t1' after forming is greater than the thickness t1 before forming. On the other hand, the second side wall SW2 is processed with "relatively strong ironing" while a compressive force F is applied thereto, so that the thickness t2' after forming is smaller than the thickness t2 before forming. By executing these preferred conditions once or repeatedly, it is possible to increase the thickness t1' after forming of the first side wall SW1 not only to the thickness t1 immediately before forming, but also to the original thickness t0 of the blank BL at the start of forming.

[0047] (When making a difference in plate thickness while thinning both sides) When each squeezing rate is set in the range of 0.65 to 1.00 (provided that C2 < C1), relatively strong squeezing processes are applied to both the first and second side walls SW1 and SW2. As a result, the wall thicknesses t1' and t2' on both sides are thinned, but the reduction rate of the wall thickness t1' of the first side wall SW1 after forming is lower than that of the wall thickness t2' of the second side wall SW2.

[0048] (Setting of wall thickness difference) In addition, in the second forming step S3, it is further preferable to set the first and second clearances C1 and C2 so as to satisfy (4) 0.2 ≦ (C1 - C2) / C2. As a result, a large wall thickness difference (the wall thickness t1' of the first side wall SW1 - the wall thickness t2' of the second side wall SW2) can be ensured in one forming in the second forming step S3. Therefore, the number of forming times (that is, the combination of the punch 3 and the die 4) can be significantly reduced compared with the prior art.

[0049] (Compression force in the pressing step) In addition, the axial compression force F to be applied to the workpiece W by the plate presser 2 of the present invention depends on the material of the workpiece W. Therefore, when expressed by the yield stress ratio of the material used per unit area, the compression force F is 0.25 to 1.1, preferably 0.5 to 0.8. When the compression force F is less than the lower limit of this preferred range, the thickening effect cannot be sufficiently obtained. On the other hand, when it exceeds the upper limit, as shown in Fig. 10(b), forming defects such as buckling deformation of the side walls SW1 and SW2 of the workpiece W occur. For example, when the material of the workpiece W is an aluminum alloy, its yield stress (0.2% proof stress) is 100 N / m 2 Therefore, an actual compression force F per unit area from the plate presser 2 to the workpiece W of 25 to 110 N / m 2 should be applied.

[0050] (Completion of the second forming step) By performing the processing of the second forming step S3 once or repeatedly, if the dimensions of the formed second intermediate container body W2 are within the target range in the determination step S3B, the second forming step S3 is terminated.

[0051] (Third molding process) According to the method of the present invention, after the second forming step S3, at least one of the first and second side walls SW1 and SW2 may be subjected to redrawing and ironing, as described below, as necessary, so as to make the final (formed) thicknesses of the first and second side walls SW1 and SW2 uniform (third forming step S4). For example, only the first side wall SW1, which has been thickened in the second forming step S3, may be subjected to redrawing and ironing in this step S4, and its thickness t1' may be ironed (thickness reduction treatment) to be the same as the thickness t2' of the relatively thin second side wall SW2. Alternatively, in this step S4, the thickness t1' of the relatively thick first side wall SW1 may be significantly reduced, while the thickness t2' of the relatively thin second side wall SW2 may be slightly reduced, so that the thicknesses t1' and t2' of the two side walls SW1 and SW2 are the same.

[0052] (Restriking process and trimming process) After the second forming step S3 or the third forming step S4 is completed, a step of adjusting the shape of the workpiece W may be performed (restriking step S5). As a further finishing step, it is preferable to cut and remove the end (excess portion) of the workpiece W (trimming step S6). o During this processing, the elongation (deformation) is restricted by the plate clamp 2, making it easy to obtain the target dimensional accuracy, and therefore the loss of material to be trimmed can be made extremely small.

[0053] (Apparatus for manufacturing rectangular cylindrical containers of the present invention) Next, an apparatus for manufacturing the rectangular cylindrical container SC of the present invention will be described. First, in the first drawing process S2, a bottomed hollow container body (first intermediate container body W1) having a substantially elliptical cross section is formed from a plate-shaped metal blank BL using a known press molding die (not shown) equipped with a pair of punch and die.

[0054] (Second molding device for performing the second molding step or the third molding step) The redrawing and ironing process S3 performed after the above-mentioned first forming process (drawing process) S2 is performed, for example, by using a second forming device (forming die) 1 shown in FIG. 5. This forming die 1 forms the workpieces W2 and W3 shown in FIG. 1 and FIG. 2. The above-mentioned second forming process S3 is performed by using this device 1. For example, one side wall SW1 of the first intermediate container body W1 is redrawn and ironed in the range of "relatively light ironing", and at the same time, the other side wall SW2 is redrawn and ironed in the range of "relatively strong ironing". In addition, by changing the combination of the die 4, punch 3, and plate holder 2 and setting them in the device 1, it is possible to repeatedly perform the redrawing and ironing process on the formed second intermediate container body W2 the number of times that the combination is set. It is also possible to perform the third forming process S4 by using the second forming device 1.

[0055] (Outline of the second molding device) The second molding device 1 is broadly composed of an upper mold 10 and a lower mold 11. The upper mold 10 is provided with an upper mold plate 10a, and a solid cylindrical punch 3 extends downward from the upper mold plate 10a. On the other hand, the lower mold 11 is provided with a lower mold plate 11a, and a die 4 is installed on the lower mold plate 11a and extends upward. The die 4 has an opening 5 formed in the center to receive the punch 3 and the workpiece W. The opening 5 contains a back pressure plate 7 that can be biased by a back pressure spring 6. When the workpiece W descends to a predetermined position, the back pressure plate 7 abuts against the lower surface of the workpiece W and applies an upward pushing force (back pressure) to the workpiece W being processed. The configurations of the upper mold 10 and the lower mold 11 may be interchanged.

[0056] (Board clamp structure) It should be noted that the upper die 10 is further provided with a plate holder 2, which is a feature of the present invention. As shown in Figs. 5 and 6, the plate holder 2 includes a main body 2a that can be inserted between the workpiece W and the punch 3, and a pressing portion 2b that protrudes from the main body 2a in the outer circumferential direction. The pressing portion 2b may be provided separately on the main body 2a. For example, in the example shown in Fig. 5, the main body 2a is provided with a first pressing spring 8a that connects the upper die plate 10a to the upper end of the main body 2a, and the pressing portion 2b is provided with a second pressing spring 8b that connects the upper die plate 10a to the upper surface of the pressing portion 2b.

[0057] In this embodiment, the push-in portion 2b and the main body portion 2a move separately and independently, and each presses each portion of the workpiece W. The main body portion 2a is divided into a tip portion 2a1 arranged on the lower side and a base portion 2a2 arranged on the upper side, and the push-in portion 2b is movably provided on the main body portion 2a near the middle between them.

[0058] At least the tip 2a1 of the main body 2a has a shape and dimensions that allow it to be inserted into the annular gap G between the outer periphery of the punch 3 and the inner periphery of the workpiece W, and by inserting this main body 2a into the annular gap G during the second forming step S3, the workpiece W is reliably supported from the inner periphery side of the workpiece W, preventing the occurrence of wrinkles and cracks in each part of the workpiece W. In other words, it can be said that the main body 2a supports and reinforces the workpiece W in the radial or circumferential direction during the above step S3.

[0059] On the other hand, the pushing portion 2b is located at the upper end opening (upper end surface) W of the workpiece W. o and presses in the workpiece W. That is, during step S3, the pressing portion 2b applies a compressive force F in the downward (axial) direction to the workpiece W while restricting the workpiece W from being deformed (stretched) in the upward direction.

[0060] As a modified example, the pressing portion 2b may be integrally formed with the main body portion 2a. In this case, it is not necessary to provide separate pressure springs connecting the upper mold plate 10a and the pressing portion 2b (or the main body portion 2a), and a single pressure spring may be sufficient.

[0061] By using the plate retainer 2 with such a unique configuration, with its main body portion 2a, while reliably restricting the radial deformation of the workpiece W passing through the clearances C1 and C2 between the die 4 and the punch 3, at the same time, with its pressing portion 2b, by applying a compressive force F to the upper end opening W of the workpiece W o it becomes possible to press the workpiece W in the axial direction.

[0062] (Processing mechanism) Using each figure of FIG. 7, the processing mechanism for the first and second side walls SW1 and SW2 during the second forming step S3 will be described. In this illustration, the case where the plate thickness t1' of the first side wall SW1 is made thicker than the plate thickness t1 before forming and the plate thickness t2' of the second side wall SW2 is made thinner than the plate thickness t2 before forming will be described. The dashed-dotted line shown in each figure of FIG. 7 is the center line O of the punch 3, and since the punch 3 and its peripheral members are axisymmetric with respect to the center line O, only one side of the axis is shown.

[0063] (State of the first side wall before forming) FIG. 7(a) is a diagram for explaining the processing mechanism in the first side wall SW1 (the side wall to be thickened) in the second forming step S3. The left and right figures respectively show the punch 3 and the die 4 before and after forming. The symbol t1 shown in FIG. 7(a) is the plate thickness of the first side wall SW1 before forming, and the symbol t3 is the plate thickness of the corner portion immediately before bending at the shoulder of the punch 3. The symbol C1 is the clearance for the first side wall SW1. Note that the symbol t1' is the plate thickness of the first side wall SW1 after forming, and the symbol t3' is the plate thickness of the corner portion immediately after forming.

[0064] At this stage, in the previous process, the workpiece W (W1) has also been subjected to drawing forming, and since the degree of deformation of its corner portion is large, t3 < t1. However, the workpiece W (the first side wall SW1) is constantly subjected to a compressive force F from the pressing portion 2b, and since the material (thickness) is collected in the clearance C1 and thickens, the clearance C1 can be set to be larger than the plate thickness t3 of the corner portion before forming and the plate thickness t1 before forming (that is, C1 > t1 > t3). In other words, it can be said that the first side wall SW1 is ironed in the range of "relatively light ironing" (ironing rate).

[0065] (State of the first side wall after forming) If ironing and ironing processes are performed under the above set conditions, t3 < t1 < t1'. This is because the clearance C1 becomes the plate thickness t1' after forming of the first side wall SW1 (∵ C1 = t1'), and the plate thickness t1' can be made thicker than the plate thickness t1 before forming.

[0066] (State of the second side wall before forming) It is a diagram explaining the processing mechanism in the second side wall SW2 (the side wall to be thinned) in the second forming step S3 of Fig. 7(b). The left and right diagrams show the punch 3 and the die 4 before and after forming, respectively. The symbol t2 shown in Fig. 7(b) is the plate thickness of the second side wall SW2 before forming, and the symbol t4 is the plate thickness of the corner part immediately before bending at the shoulder of the punch 3. The symbol C2 is the clearance for the second side wall SW2. Note that the symbol t2' is the plate thickness of the second side wall SW2 after forming, and the symbol t4' is the plate thickness of the corner part immediately after forming.

[0067] Regarding the second side wall SW2, since ironing forming has been performed in the previous process, t4 < t2. However, unlike the case of the first side wall SW1, the second side wall SW2 is subjected to ironing and ironing processes with the above-mentioned "relatively light ironing", so the clearance C2 for the second side wall SW2 can be set to be thinner than the plate thickness t4 of the corner part (that is, C2 < t4 < t2).

[0068] (State of the second side wall after forming) If ironing and ironing processes are performed under the above set conditions, t2' < t4 < t2. This is because the clearance C2 becomes the plate thickness t2' after forming of the second side wall SW2 (∵ C2 = t2'), and the plate thickness t2' can be made thinner than the plate thickness t2 before forming.

[0069] Moreover, the plate thickness t2' after forming can be made thinner than the plate thickness t4' of the corners after forming. This means that by using the compressive force F by the pressing portion 2b, while keeping the thickness of the corners and the bottom periphery of the second side wall SW2 at a predetermined level or more, the plate thickness t2' of the body portion above them can be made thinner than the plate thickness t2 before forming.

[0070] This is a major advantage over conventional technology. In conventional technology, the area around the shoulder of punch 3, both on the thickening side and the thinning side, receives a larger tensile stress than punch 3 during forming, and therefore becomes thinner than the body part of the workpiece W, making it the area most susceptible to breakage. However, since the plate thicknesses t3' and t4' around the corners can be made thicker than the plate thicknesses t1 and t2 of the body part just before forming, breakage during processing is less likely to occur.

[0071] FIG. 8(a) is a diagram for comparing and explaining the number of processes, the plate thicknesses of each side wall, and the plate thickness difference when the conventional technology and the present invention (when the plate thickness t1 on one side is increased and the plate thickness t2 on the other side is decreased) are carried out. In the present invention, the upper end opening W o Since the workpiece W can be formed while being pressed into the workpiece W, for example, it is possible to increase the thickness of one side wall SW1 while decreasing the thickness of the other side wall SW2.

[0072] Here, if we follow the change in the plate thickness t1 of the first side wall SW1 in Figure 8(a), it becomes thinner than the original plate thickness t0 of the blank BL in the first forming process S2. However, from the second forming process S3 onwards, since a plate clamp 2 with a pressing portion 2b is used, the plate thickness t1' after forming can be reliably made larger than the original plate thickness t0 by the initial processing or repeated processing.

[0073] Furthermore, in the second forming step S3, a compressive force F is obtained by the pushing portion 2b, so that a large difference in the ironing rate can be provided between the processing of the first side wall SW1 and the processing of the second side wall SW2, and therefore the number of steps (the number of combinations of the punch 3 and the die 4 (the number of dies)) required to achieve a desired thickness difference can be significantly reduced. In the illustrated example, the number of steps in the conventional technology is eight in total, whereas the number of steps in the present invention is three in total.

[0074] On the other hand, FIG. 8(b) is a diagram for comparing and explaining the number of steps, the thickness of each side wall, and the thickness difference when the conventional technology and the present invention (when the thicknesses t1 and t2 on both sides are thinned) are implemented. Even in this case, for the same reason as in FIG. 8(a), a large difference in the ironing rate can be given between the processing of the first side wall SW1 and the processing of the second side wall SW2, so that the number of steps for achieving the desired thickness difference can be significantly reduced. In the embodiment of FIG. 8(b), it can be seen that the thickness t1 of the first side wall SW1 remains almost the same as or slightly thinner than the original thickness t0 of the blank throughout the entire processing, whereas the thickness t2 of the second side wall SW2 becomes rapidly thinner after the second forming step S3. As described above, during forming, the thicknesses t3' and t4' near the corners of the workpiece W can be secured to be larger than the thicknesses t1 and t2 of the body part immediately before forming, so that an extremely thin clearance C2 (thickness t2' after forming) can be set in one process.

[0075] FIG. 9(a) is a diagram for comparing and explaining the number of steps, the thickness and thickness difference of each side wall when the present invention (the case where the third forming process S4 is performed after the second forming process S3 to make the thickness of each side wall of the final shape uniform) is performed with the conventional technology. In the example of this figure, in the second forming process S3, only the thickness t1' of the first side wall SW1 is increased, while the thickness t2' of the second side wall SW2 is maintained almost constant, but in the third forming process S4, an additional process is performed by redrawing and ironing only the first side wall SW1 so that its thickness t1' becomes the same as the thickness t2'. According to such a preferred embodiment of the present invention, although the number of steps increases by one by performing the additional third forming process S4, it becomes possible to manufacture a final product (a rectangular cylindrical container) having side walls with the same thickness, and the number of steps to reach the final shape is still smaller than that of the conventional technology.

[0076] (Prototype and verification of plate thickness difference) A square tubular container SC was actually prototyped using the manufacturing apparatus 1 of the present invention. Figure 9(b) shows the changes in thickness t1', t2' of the side walls SW1, SW2 of the work W during the prototype. As shown in Figure 9(b), a blank BL having an original thickness t0 = 1.5 mm was used to process the work W in a total of three steps (one first forming step S2 and two second forming steps S3). In the first side wall SW1, the final thickness was t1' = 2.0 mm, which was 0.5 mm larger than the original thickness t0 of the blank BL. On the other hand, in the second side wall SW2, the final thickness was t2' = 1.1 mm, which was 0.4 mm smaller than the original thickness t0.

[0077] In other words, the thickness difference of the final product (t1'-t2') is 0.9 mm, which is approximately 82% of the final thinner thickness (t2'=1.1 mm).Compared to the thickness difference (approximately 13%) in the embodiment of Patent Document 2 mentioned above, it can be seen that a significant difference has been achieved in the thicknesses t1', t2' of the first and second side walls SW1, SW2.

[0078] (Appearance of prototype) Fig. 10(a) shows a square tube container SC (prototype) actually molded using the manufacturing method of the present invention. Note that a portion of the square tube container SC was cut away before photographing to make the internal structure of the container easier to see. Meanwhile, Fig. 10(b) shows an example of a defective product. Specifically, it shows the molded state (an example in which buckling deformation has occurred) when the workpiece W is subjected to a force exceeding the upper limit of the preferred range of the compressive force F described above by the plate holder 2 during the second molding step S3. [Industrial Applicability]

[0079] According to the manufacturing method of the present invention, the workpiece is subjected to redrawing and ironing processes, and the presser inserted between the punch and die not only restricts the radial deformation of the workpiece during processing, but also continuously applies a compressive force in the axial direction to the open end of the workpiece. This allows more material to be introduced more reliably into the clearance on at least one side wall in one process, so that the thickness of the side wall can be maintained at a level almost the same as the original thickness of the blank.

[0080] Furthermore, in a preferred embodiment of the present invention, the thickness of the side wall to be thickened can be made greater than the original thickness of the blank. In other words, a thin plate material having an original thickness smaller than the thickness of the relatively thick side wall of the final product or intermediate molded product can be used as the blank of the present invention. This is a groundbreaking breakthrough that has not been achieved in the prior art in this field.

[0081] In addition, if the clearance ratio (C1 / C2) is set large in the preferred embodiment of the present invention, a large thickness difference can be obtained by one redrawing and ironing process. Therefore, even if the final target thickness difference is large, a much smaller number of processes (combinations of dies and punches) is required compared to the prior art.

[0082] Furthermore, according to the manufacturing method of the present invention, the clearance is regulated both radially and axially, so that wrinkles on the side wall surface and variations in plate thickness after molding can be suppressed more than the capabilities of conventional techniques.

[0083] As described above, the present invention has extremely high industrial applicability and industrial utility. [Explanation of symbols]

[0084] 1. Second molding device (molding die) 2 Board Holder 2a, 2a1, 2a2: Main body of plate holder, tip of main body, base of main body 2b Pressing part of plate holder 3 Punch 4 Dice 5 Opening 6,7 Back pressure spring, back pressure plate 8a, 8b 1st and 2nd compression springs 10, 10a Upper mold, upper mold plate 11,11a Lower mold, lower mold plate BL Blank C1, C2 Clearance for first and second side walls F Compressive force by plate holder G Annular gap O center line SC Square tube container SW1,SW2 1st and 2nd side walls t0 Original thickness of blank t1, t1': Thickness of the first side wall before and after forming t2, t2': Thickness of the second side wall before and after forming t3, t3': Thickness of the corner of the first side wall before and after forming t4, t4' Thickness of the corner of the second side wall before and after forming W, W1, W2, W3: Workpieces (workpieces) after each forming process, 1st and 2nd intermediate container bodies W o Top opening of workpiece

Claims

1. A method for manufacturing a rectangular cylindrical container having first and second side walls with different thicknesses, comprising the steps of: A step of preparing a plate-shaped metal blank as a workpiece; a first forming step of drawing the workpiece to form a container body having an elliptical cross-sectional shape; a second forming step in which the workpiece that has completed the first forming step is simultaneously subjected to redrawing and ironing to form a container body having a height greater than that of the workpiece immediately before forming and a cross-sectional shape having a smaller minor axis / major axis ratio than that of the cross-sectional shape of the workpiece immediately before forming; Including, The second forming step includes a repeating step of simultaneously subjecting the formed workpiece to redrawing and ironing, The second forming step includes a pressing step in which a body part of a plate holder is inserted between the punch used in the first or repeated step and the workpiece, while a clearance is maintained between the punch and the die to restrict radial movement of the workpiece to be formed, and a compressive force is applied in the axial direction to the upper opening end of the workpiece using a pressing part of the plate holder, In the second molding step, the first clearance in the first side wall that should be relatively thick among the clearances is set to C １ and the second clearance at the second side wall, which should be relatively thin, is W １ year, Plate thickness t of the first and second side walls just before forming １ , t ２ In this case, (1) C ２ <C １ and (2)0.65<C １ / t １ ≦1.25 (3)0.65≦C ２ / t ２ ≦1.00 Set it so that all the conditions above are met. A method for manufacturing a rectangular cylindrical container comprising the steps of:

2. 2. The method for manufacturing a rectangular tubular container according to claim 1, wherein the compressive force is 0.25 to 1.1 in terms of a yield stress ratio of the material used per unit area.

3. In the second molding step, (4) 0.2≦(C １ -C ２ ) / C ２ First and second clearances C are set to satisfy １ , C ２ Set The method for manufacturing a rectangular tubular container according to claim 1 or 2.

4. In the second molding step, (2') 1.00<C １ / t １ First clearance C is set to be within the range of ≦1.25 １ By setting the thickness t of the first side wall immediately before forming, １ In comparison, the thickness t of the first side wall immediately after forming １ While increasing ' (3') 0.65≦C ２ / t ２ Second clearance C to be in the range of <1.00 ２ By setting the thickness t of the second side wall just before forming, ２ In contrast, the plate thickness immediately after forming is t ２ ' to reduce, The method for manufacturing a rectangular tubular container according to any one of claims 1 to 3.

5. The method further includes a third forming step of performing a redrawing process and an ironing process on at least one of the first and second side walls so as to make the plate thicknesses of the first and second side walls uniform after the second forming step. The method for manufacturing a rectangular tubular container according to any one of claims 1 to 4.

6. The cross-sectional shape of the rectangular tubular container is rectangular, The first side wall is a short side wall and the second side wall is a long side wall. The method for manufacturing a rectangular tubular container according to any one of claims 1 to 5.

7. The rectangular cylindrical container is for a battery case. The method for manufacturing a rectangular tubular container according to any one of claims 1 to 6.

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