Manufacturing method for molded products
By adjusting the radius of curvature of corner wall portions during deep drawing, the method stabilizes mass production of rectangular tubular containers, preventing cracks and increasing their volume and depth, addressing the challenges of forming battery cases for electric vehicles.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2025-11-27
- Publication Date
- 2026-07-22
AI Technical Summary
Rectangular tubular containers used in battery cases for electric vehicles face challenges in forming a deep molding depth with a small radius of curvature at the corner walls, leading to cracks and reduced strength, which complicates mass production and increases costs.
The method involves adjusting the radius of curvature of the corner wall portions during deep drawing to prevent cracking by reducing it to a value that avoids wall cracking and increasing the molding depth, using a controlled deep drawing process.
This approach stabilizes mass production by preventing cracks at the corner walls, enhances the volume of the molded product, and allows for deeper drawing without equipment limitations, thus improving productivity and reducing defects.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a technique for manufacturing a rectangular tube-shaped molded product having a polygonal bottom surface by deep drawing. Deep drawing is performed by deep drawing process. The present invention relates to providing a method for manufacturing a molded product with improved deep drawing formability. The polygonal shape of the bottom surface is, for example, a rectangular shape. The polygonal shape is not limited to a rectangular shape, and other polygonal shapes such as a hexagonal shape are also applicable. That is, the rectangular tube shape in the present invention is not limited to a rectangular bottom surface.
Background Art
[0002] Deep drawing can form a vertical wall without a seam from a single metal plate. Therefore, deep drawing is still widely used in the manufacture of many parts. In recent years, from the perspective of carbon neutrality, battery electric vehicles have become popular. At this time, the application of rectangular tube deep drawing process is being considered for the manufacture of battery cases for mounting batteries. In this specification, the metal plate to be press-formed is also referred to as a blank. One of the requirements for such a battery case is to have a large capacity. By making the battery case have a large capacity, more batteries can be mounted on an electric vehicle.
[0003] Here, a rectangular tube-shaped container is a container having a polygonal bottom surface. For such a deep-drawn container with a polygonal bottom surface, several conventional forming methods for increasing its volume have been proposed. Patent Document 1 describes that during rectangular tube deep drawing, the punch pushing speed in the early stage of forming is increased, and the punch pushing speed in the later stage of forming is decreased. Patent Document 1 discloses that by controlling the punch pushing speed, the deep drawing formability can be improved. Furthermore, Patent Document 2 describes cutting out the corners of a rectangular blank so that the rectangular blank has a geometrically calculated shape. Patent Document 2 discloses that this reduces the radius of curvature of the corner wall portion of the rectangular tube part. [Prior art documents] [Patent Documents]
[0004] [Patent Document 1] Japanese Patent Publication No. 2009-90318 [Patent Document 2] Japanese Patent Application Publication No. 9-285825 [Overview of the project] [Problems that the invention aims to solve]
[0005] Rectangular tubular containers are used, for example, in battery cases for electric vehicles. Such rectangular tubular containers are preferably formed with a deep molding depth and a small radius of curvature at the corner walls. This is because such a shape is advantageous in terms of increasing battery capacity. However, forming such rectangular tubular containers is difficult. For example, cracks may occur at the ridges connecting the corner walls and the bottom surface, as shown in Figure 6, or at the walls above the corner walls. Containers with these cracks suffer a significant decrease in strength, leading to increased costs during mass production. In this specification, the ridge portion connecting the corner wall portion and the bottom portion is also referred to as the punch shoulder portion.
[0006] Here, cracking at the punch shoulder during molding is mainly influenced by the magnitude of the material flow resistance at the flange. A common countermeasure is to reduce the material flow resistance. Specifically, this involves corner cutting the four corners of the rectangular blank. However, if the corner cut is too large, the amount of material flowing into the corner wall decreases. In this case, the material may not be able to withstand the tensile stress in the molding direction that occurs in the corner wall during the later stages of molding. If the material cannot withstand this stress, wall cracking will occur in the corner wall. Furthermore, in order to stably mass-produce large-volume rectangular deep-drawn containers, it is preferable to implement crack prevention measures with a small number of work steps.
[0007] Furthermore, depending on the initial conditions during press forming, the material flow may be uneven during deep drawing. These initial conditions include the placement of the blank in the lower die and the condition of the press machine and die. Uneven material flow results in unevenness in the wrinkle-preventing force acting on the blank. This unevenness can lead to molding defects, such as cracks in the corner walls. It is necessary to reduce the probability of such cracks occurring in the corner walls and stabilize mass production.
[0008] The molding method described in Patent Document 1 involves changing the molding speed of a rectangular tube deep drawing according to the molding height in order to avoid wall cracking at the corner walls. However, such a molding method leads to a decrease in productivity for mass-produced parts. Furthermore, the method in Patent Document 1 requires the use of a press machine that can vary the molding speed at a desired timing during molding. Therefore, this method is subject to equipment limitations.
[0009] Furthermore, the method described in Patent Document 2 has the following problems. In other words, the optimal corner cutout shape differs depending on the mold shape and the size of the blank before cutting. Therefore, when changing the mold shape or the size of the blank before cutting, the cutout shape of the blank corners also needs to be changed. In addition, because the cutout shape of the blank corners is also special, the number of work steps required to create the blank may increase.
[0010] This invention focuses on the points mentioned above. The purpose of this invention is to simplify the crack prevention measures when wall cracks occur at the corner walls during the molding of rectangular tubular molded products, compared to conventional methods, and to enable the stable manufacture of molded products. [Means for solving the problem]
[0011] This invention focuses on increasing the volume of deep-drawn rectangular tubular molded products, and further stabilizing mass production while reducing the probability of wall cracking occurring during deep-drawing of parts.
[0012] To solve the problem, one aspect of the present invention is a method for manufacturing a molded product in the shape of a rectangular tube, having a polygonal base, vertical wall portions having straight wall portions continuous to each side of the base and corner wall portions connecting the left and right ends of adjacent straight wall portions, and flange portions continuous to the vertical wall portions, by deep drawing a blank made of a metal plate. In this method, if it is determined that wall cracking will occur at the corner wall portions when deep drawing is performed on a molded product of the target part shape, the radius of curvature of the corner wall portions of the target part shape is changed to a value smaller than the radius of curvature of the corner wall portions when it is determined that wall cracking will occur at the corner wall portions. [Effects of the Invention]
[0013] In one aspect of the present invention, when molding a rectangular tubular molded product, a simple measure is employed to prevent cracking at the corner wall, which occurs at the corner wall. This suppresses cracking at the corner wall, as stabilizes mass production. In other words, according to this aspect of the present invention, cracking at the corner wall can be avoided during mass production. Therefore, it is effective in stabilizing mass production. Further, according to the aspect of the present invention, the sharpening of the corner wall portion is effective in increasing the volume of the molded product. Furthermore, deep drawing molding becomes possible under the molding conditions in which the radius of curvature of the corner wall portion is reduced. Therefore, it is also possible to increase the molding depth as compared with before the change of the molding conditions. The molding depth corresponds to the height of the vertical wall portion.
Brief Description of the Drawings
[0014] [Figure 1] It is a perspective view illustrating a molded product according to an embodiment based on the present invention. [Figure 2] It is a view for explaining a mold used for deep drawing molding. [Figure 3] It is a top view of the punch seen from above. [Figure 4] It is a view for explaining the steps of this embodiment. [Figure 5] It is a view showing an example of the processing of the molding condition setting step. [Figure 6] It is a view showing typical cracks generated during square tube deep drawing. [Figure 7] It is a view for explaining the improvement of formability by changing the radius of curvature Rt of the corner wall portion. <000**********87>It is a view for explaining the blank shape. [Figure 9] It is a view for explaining the corner cut of the blank.
Mode for Carrying Out the Invention
[0015] Next, embodiments of the present invention will be described with reference to the drawings. Here, the drawings are schematic, and the sizes and length ratios of each part are different from the actual ones. Further, the embodiments shown below are examples of configurations for embodying the technical idea of the present invention. The technical idea of the present invention does not specify the material, shape, structure, etc. of the constituent parts as the following. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims. Furthermore, the dimensions shown in each figure are illustrative examples used to illustrate the embodiments, etc. These dimensions do not define the present invention in any way.
[0016] In this embodiment, we will explain using a rectangular tube deep-drawn molded product 1, which has a rectangular cross-section, as shown in Figure 1, as an example. Hereafter, this rectangular tube deep-drawn molded product 1 will also be referred to simply as molded product 1. However, the shape of the bottom surface portion 2 of the molded product 1 in this embodiment is not limited to a rectangular shape. It may be a hexagon or other polygonal shape.
[0017] As shown in Figure 1, the molded product 1 has a polygonal bottom portion 2, a vertical wall portion 3 continuous with the bottom portion 2, and a flange portion 4 continuous with the lower edge of the vertical wall portion 3. Figure 1 is a diagram showing the rectangular deep-drawn molded product 1 with the bottom portion 2 side facing upward. The vertical wall portion 3 comprises straight wall portions 3Aa and 3Ab continuous with each side 2a and 2b of the bottom portion 2, respectively, and a corner wall portion 3B. The corner wall portion 3B is the part that connects the left and right ends of two adjacent straight wall portions 3Aa and 3Ab. The surfaces formed by the two adjacent straight wall portions 3Aa and 3Ab face in different directions. The corner wall portion 3B is continuous with the vertices of the corners (ridges) of the bottom portion 2. The corners of the bottom portion 2 are rounded by deep drawing. These corners of the bottom portion 2 are formed by the punch shoulder portion.
[0018] The corner wall section 3B described above is a curved surface portion that has a predetermined radius of curvature along the left-right direction, centered on the vertical ridge extending vertically. This radius of curvature may be defined by the radius of curvature on the outer wall surface side of the corner wall section 3B or by the radius of curvature on the inner wall surface side. Furthermore, if the radius of curvature along the left-right direction of the corner wall section 3B changes, the radius of curvature of the corner wall section 3B may be determined by using the radius of curvature at the position of the vertical ridge or the average value of the overall radius of curvature. In other words, the radius of curvature can be determined and used according to a predetermined definition.
[0019] Here, deep drawing is performed by press working using a mold comprising a die 5, a blank holder 7, and a punch 8, as shown in Figure 2. Specifically, deep drawing is performed with the flange region of the blank 6, which will become the flange portion 4, pressed down by the die 5 and the blank holder 7. Subsequently, deep drawing is performed by moving the punch 8 in the pressing direction. The forming surface of the punch 8 is shaped to conform to the inner surfaces of the bottom portion 2 and the vertical wall portion 3 of the molded product 1. The forming depth of the deep drawing becomes the depth of the rectangular tube of the molded product 1.
[0020] The blank 6 made of a metal plate in this embodiment is, for example, made of a steel plate. From the viewpoint of rust prevention, the steel plate is preferably a plated steel plate. The blank 6 has, for example, a polygonal shape that follows the bottom surface 2, or a shape in which the corners of the polygonal shape are corner-cut. Furthermore, in this embodiment, when the contact surface between the punch 8 and the blank 6 is viewed from above, the forming surface at the top of the punch 8 preferably has a side length L of 100 mm or more, as shown in Figure 3. Also, the angle α between the adjacent straight wall portions 3Aa and 3Ab is preferably 90 degrees or more. In addition, the wrinkle-suppressing force of the blank holder 7 is preferably 10 tons or more.
[0021] "Manufacturing method for molded product 1" As shown in Figure 4, the manufacturing method of the molded product 1 in this embodiment comprises a molding condition setting step 20, a pressing step 21 for deep drawing, and a trimming step 22.
[0022] <Molding condition setting process 20> The molding condition setting step 20 performs a process to determine molding conditions that prevent wall cracking at the corner wall portion 3B when deep drawing the blank 6 into a molded product 1 with the target part shape. An example of the process in molding condition setting step 20 is shown in Figure 5. The process will be explained with reference to Figure 5.
[0023] First, in step S10, the molding conditions for deep drawing are set to manufacture molded product 1 with the target part shape. Next, in step S20, a forming analysis is performed using a known CAE analysis with a computer to form the blank into the target part shape by deep drawing under the forming conditions set in step S10. For example, a forming model corresponding to the blank model and the target part shape is generated, and a forming analysis of press forming is performed using that forming model. A springback analysis may also be performed in this forming analysis.
[0024] Next, in step 30, it is determined whether or not wall cracking occurs in the corner wall section 3B based on the results of the molding analysis. Furthermore, it is assumed that there are no defects in any part of the analyzed molded product 1 other than the corner wall portion 3B. If it is determined that no wall cracks have occurred in the corner wall section 3B, the process proceeds to step S40, and the current molding conditions are determined as the final molding conditions. On the other hand, if it is determined in step S30 that a wall crack has occurred at the corner wall section 3B, the process proceeds to step S50.
[0025] In step S50, multiple molding conditions are set for the molding conditions of the corner wall 3B where wall cracking occurred. Each of these multiple molding conditions is a molding condition in which the radius of curvature Rt of the corner wall 3B is smaller than the molding condition of the corner wall 3B where wall cracking occurred. It is assumed that the radii of curvature Rt of these multiple molding conditions are different from each other and are set in a stepwise manner, with the radii of curvature Rt decreasing in value. The radius of curvature Rt is the radius of curvature of the corner wall 3B in the arc direction. In addition, along with changing the radius of curvature of the corner wall section 3B to a smaller value, the height of the vertical wall section 3 may also be changed to a higher value as a molding condition.
[0026] In step S60, a molding analysis is performed for each molding condition to check whether wall cracks occur at the corner wall 3B. Additionally, it is checked whether cracks occur at the punch shoulder up to the molding depth set in step S10. In step S70, under the conditions that no wall cracking occurs at the corner wall portion 3B and no edge cracking occurs at the punch shoulder portion up to the molding depth set in step S10, the following is determined: That is, under the above conditions, the molding condition in which the radius of curvature Rt of the corner wall portion 3B is smallest is determined as the final molding condition.
[0027] Here, the processing flow shown in Figure 5 is an example of processing. For example, in step S50, the current radius of curvature Rt is reduced by a predetermined value. Subsequently, in step S60, a molding analysis may be performed on the modified molding conditions. Then, if the molding analysis shows that no edge cracking occurs at the punch shoulder up to the molding depth set in step S10, the process may be repeated, returning to step S50. In this case, if it is determined in step S60 that edge cracking occurs at the punch shoulder, the radius of curvature Rt set in the previous step may be used as the final radius of curvature Rt. The radius of curvature Rt set in the previous step is the radius of curvature at which no edge cracking occurs at the punch shoulder.
[0028] Subsequently, the maximum molding limit height Ht is determined under the molding conditions at the final radius of curvature Rt, so that no wall cracks occur in the corner wall portion 3B. Then, the determined molding limit height Ht may be set as the molding condition for the final molding conditions. The molding limit height Ht is the maximum molding depth. In this case, the molding height of the molded product 1 can also be increased. Of course, the final molding condition may be a molding depth that is greater than or equal to the molding depth set in step S10, but lower than the molding limit height Ht. In this process, the molding condition setting step 20 may also involve actually producing a molded product 1 to determine the final molding conditions.
[0029] <Pressing process 21> In the pressing process 21, a mold is manufactured using the molding conditions determined in the molding condition setting process 20. Then, using this mold, deep drawing is performed on the blank to produce a molded product 1 with the desired shape.
[0030] <Trimming process 22> In the trimming process 22, the flange portion of the molded product 1 produced in the pressing process 21 is cut for shaping to achieve the final product shape. The trimming process 22 is optional. During mass production, the processing will consist of the pressing process 21 and the trimming process 22. Once the molding conditions are determined, the molding condition setting process 20 will no longer be necessary.
[0031] (Operation and other functions) Deep drawing of rectangular tubular containers is difficult, and there is a risk of cracks 10 on the punch shoulder and cracks 9 on the corner wall 3B, as shown in Figure 6. The crack 10 on the punch shoulder is a ridge crack at the corner that is continuous with the corner wall 3B. According to this embodiment, when wall cracking occurs at the corner wall portion 3B during molding of the rectangular tubular molded product 1, the following measures are taken to prevent cracking: The radius of curvature Rt of the corner wall portion 3B is reduced to the extent that cracking 10 at the punch shoulder does not occur. According to this embodiment, wall cracking at the corner wall portion 3B can be suppressed by such a simple means. In other words, according to this embodiment, cracking at the corner wall portion 3B during mass production can be avoided with a simple process, which is effective in stabilizing mass production. Furthermore, according to this embodiment, the sharpening of the corner wall portion 3B has the effect of increasing the volume of the molded product. In addition, deep drawing becomes possible under molding conditions in which the radius of curvature Rt of the corner wall portion 3B is reduced. For this reason, in this embodiment, it is possible to increase the molding depth, that is, the molding height, compared to before the change in molding conditions.
[0032] <Reasons for crack suppression at corner wall section 3B> According to the inventor's considerations, the reason why the formability of deep drawing is improved by applying the present invention is as follows. Specifically, the reason why cracking at the corner wall portion 3B of the molded product 1, which has a polygonal rectangular tube shape at its bottom, is avoided by applying the present invention is as follows. In the following explanation, the boundary between the early and late stages of molding is the moment when the vertical wall portion of the molded product 1 is formed by the punch 8 and die 5 during deep drawing of a rectangular tube.
[0033] Wall cracks 9 in the corner wall section 3B occur when a large tensile strain is introduced in the forming direction during the later stages of forming, causing a decrease in plate thickness. Therefore, it can be inferred that the thicker the plate, i.e., the greater the compressive strain introduced in the circumferential direction when a large tensile strain is introduced during the later stages of forming, the following occurs. In this case, it is inferred that the occurrence of wall cracks during forming is delayed, and the material can be drawn deeper. As shown in Figure 7, if the forming height is the same, a smaller radius of curvature Rt of the corner wall section 3B causes the material to concentrate in the flange section 4. Therefore, a smaller radius of curvature Rt results in a thicker plate thickness within the corner wall section 3B. As a result, the occurrence of the concentration of plate thickness reduction, which is the cause of cracking, is delayed. This indicates that a smaller radius of curvature Rt of the corner wall section 3B allows for deeper drawing.
[0034] On the other hand, if the compressive deformation introduced in the flange portion 4 becomes excessive, a large load will be placed on the punch shoulder during the early stages of forming. This may cause cracking in the punch shoulder. The punch shoulder is the part that forms the ridge of the corner that is continuous with the corner wall portion 3B. In other words, if the resistance to material flow in the flange portion increases, the load on the punch shoulder increases. This is the reason why cracking occurs in the punch shoulder. The load on the punch shoulder is greatest at the end of the early stages of forming. Therefore, if cracking does not occur in the punch shoulder during the early stages of forming, cracking will not occur in the punch shoulder during the later stages of forming.
[0035] Based on the above, the radius of curvature Rt of the corner wall portion 3B is reduced to the limit of forming conditions that prevent punch shoulder cracking 10. This increases the circumferential compressive strain introduced in the flange portion 4. In other words, the thickness of the corner wall portion 3B increases. As a result, it can withstand the reduction in plate thickness due to tensile strain in the forming direction during the later stages of forming. Furthermore, it is thought that the forming depth can be increased. Here, the radius of curvature Rt of the corner wall portion 3B after the change in molding conditions is preferably 50% or less of the radius of curvature Rt of the corner wall portion 3B before the change in molding conditions. However, this is conditional on the absence of punch shoulder cracking 10. Furthermore, the lower limit of the radius of curvature Rt of the corner wall portion 3B after the change in molding conditions is preferably, for example, 5 mm or more.
[0036] (others) This disclosure may also take the following form: (1) Disclosure 1 is a method for manufacturing a molded product having a rectangular tube shape, which is produced by deep drawing a metal sheet, and which has a polygonal base, vertical wall portions having straight wall portions continuous with each side of the base and corner wall portions connecting the left and right ends of adjacent straight wall portions, and flange portions continuous with the vertical wall portions. If it is determined that wall cracking will occur at the corner wall portion when deep drawing is performed on a molded part with the target part shape, the radius of curvature of the corner wall portion of the target part shape is changed to a value smaller than the radius of curvature of the corner wall portion at which wall cracking was determined to occur. A method for manufacturing molded products. (2) Disclosure 2 involves changing the radius of curvature of the corner wall to a smaller value, and at the same time changing the height of the vertical wall to a higher value. A method for manufacturing the molded article described in Disclosure 1. (3) Disclosure 3 describes a deep drawing process in which, when a wall crack occurs at the corner wall under the molding conditions described above, the molding conditions are changed to conditions in which the radius of curvature of the corner wall is smaller than the molding conditions described above. A method for manufacturing a molded article as described in Disclosure 1 or Disclosure 2. (4) Disclosure 4 describes how, in response to the molding conditions under which wall cracking occurred at the corner wall, deep drawing is performed by changing to molding conditions in which the radius of curvature of the corner wall is smaller than the molding conditions under which wall cracking occurred. The only change to the molding conditions mentioned above is the radius of curvature of the corner wall. A method for manufacturing the molded article described in Disclosure 3. (5) Disclosure 5 states that the radius of curvature of the corner wall portion after changing the molding conditions shall be such that no cracks occur at the ridge portion connecting the corner wall portion and the bottom portion up to the molding depth before changing the molding conditions during deep drawing. A method for manufacturing a molded article as described in Disclosure 3 or Disclosure 4. [Examples]
[0037] Next, an example based on this embodiment will be described. The target part shape of the molded product 1 in this embodiment is a rectangular tube shape with a rectangular bottom portion 2, as shown in Figure 1. Furthermore, the test material used to construct the blank was a 0.8 mm thick, 270 MPa class hot-dip galvanized steel sheet.
[0038] The dimensions of the mold were as shown in Figure 2. Specifically, the top shape of punch 8 was set to 100 mm x 100 mm in plan view. The radius of the punch bottom edge was set to 12.5 mm. The radius of the punch bottom edge is the radius of the shoulder. A die 5 measuring 104.2 mm x 104.2 mm was used. Furthermore, the clearance at the corner wall portion 3B during deep drawing of the rectangular tube was set to 1.5 mm, and the flange portion 4 was formed without a bead.
[0039] Deep drawing was performed by varying the blank shape, wrinkle suppression force, die shoulder radius, and the radius of curvature Rt of the corner wall portion 3B, in addition to the molding conditions described above. Two types of shapes were set as the molding conditions for the blank shape. The two types of shapes are a 180 mm square as shown in Figure 8, and a shape in which the four corners of the square are corner-cut. The shape with the corner cuts was set so that the length C of the perpendicular from the vertex is 20 mm, as shown in Figure 9.
[0040] In addition, three different molding conditions were set to control wrinkle suppression: 10 tons, 15 tons, and 20 tons. Additionally, two molding conditions were set for the shoulder radius of die 5: 5 mm and 10 mm. Two molding conditions were also set for the radius of curvature Rt of corner wall section 3B: 10 mm and 25 mm. Then, under each molding condition, the depth relative to the upper surface of the flange portion 4 at the moment when a wall crack occurred in the corner wall portion 3B during molding was recorded as the molding limit depth. The molding limit depth is the limit molding height Ht.
[0041] The evaluation results are shown in Table 1. Table 1 shows the limit height Ht for molding under each molding condition.
[0042] [Table 1]
[0043] The following was found from Table 1: In other words, under each molding condition in which the corner cut, cushion pressure, and die shoulder radius were varied, the following similar results were obtained for all molding conditions. Specifically, under all molding conditions, the molding limit depth was deeper when the radius of curvature Rt of the corner wall 3B was 10 mm than when the radius of curvature Rt of the corner wall 3B was 25 mm. Furthermore, given the same molding depth, a smaller radius of curvature Rt of the corner wall 3B helps to avoid wall cracking at the corner wall 3B.
[0044] From this, for example, in a molded product 1 that was conventionally molded with a radius of curvature Rt: 25 mm for the corner wall portion 3B, if wall cracking occurs at the corner wall portion 3B, it can be corrected by changing the molding conditions as follows: That is, the target part shape is changed to a radius of curvature Rt: 10 mm for the corner wall portion 3B. This makes it possible to manufacture parts with a deep molding depth and sharp corner wall portions 3B. In other words, it becomes possible to increase the volume of the molded product 1. Furthermore, even if the molding depth does not change before and after changing the molding conditions, it becomes possible to produce molded products 1 in which wall cracking at the corner wall portion 3B is less likely to occur.
[0045] Here, under the conditions of die 5 shoulder radius: 5 mm, blank corner cut: 0, and wrinkle suppression force: 10 tons, the limiting molding depth was determined when the radius of curvature Rt was set to 5 mm in the first molding conditions listed in Table 1. It was confirmed that setting the radius of curvature Rt to 5 mm resulted in a deeper limiting molding depth than when the radius of curvature Rt was 10 mm. However, when the radius of curvature Rt was smaller than 5 mm, ridge cracking occurred at the punch shoulder before the molding depth reached the limiting molding depth at a radius of curvature Rt of 25 mm.
[0046] From the above, it was found that, in order to prevent wall cracking at corner wall section 3B, given the required volume of the container, it is preferable in this example to set the radius of curvature Rt to 5 mm as a molding condition. Furthermore, we gradually reduced the radius of curvature Rt in stages and, without changing any molding conditions other than the radius of curvature Rt and molding depth, we investigated the relationship between the radius of curvature Rt and the molding limit height Ht. As a result, we confirmed that when the radius of curvature Rt is 5 mm or more, the molding limit height Ht increases almost linearly as the radius of curvature Rt decreases.
[0047] Herein, the entire contents of Japanese Patent Application No. 2025-40566 (filed March 13, 2025), on which this application claims priority, constitute part of this disclosure by reference. While a limited number of embodiments have been described here with reference, the scope of the rights is not limited thereto, and modifications of each embodiment based on the above disclosure would be obvious to those skilled in the art. [Explanation of symbols]
[0048] 1 Molded product 2 Bottom part 3 Vertical wall section 3B Corner wall section 4. Flange section 5 Dies 6 Blank 7 Blank holder 8 punches 20 Molding condition setting process 21 Pressing process 22 Trim process Rt: Radius of curvature of corner wall
Claims
1. A method for manufacturing a rectangular tubular molded product, which has a polygonal base, vertical wall portions having straight wall portions continuous with each side of the base and corner wall portions connecting the left and right ends of adjacent straight wall portions, and flange portions continuous with the vertical wall portions, by deep drawing a metal sheet, If it is determined that wall cracking will occur at the corner wall portion when deep drawing is performed on a molded product with the target part shape, the radius of curvature of the corner wall portion of the target part shape is changed to a value smaller than the radius of curvature of the corner wall portion at which wall cracking was determined to occur. Both the target part shape described above and the part shape after changing the setting to a value smaller than the radius of curvature of the corner wall section described above are such that the contour shape of the corner wall section, as viewed from the bottom side, smoothly connects with the left and right ends of the straight wall section and consists only of a curved convex shape on the outside of the part. A method for manufacturing molded products.
2. In addition to changing the radius of curvature of the corner wall section to a smaller value, the height of the vertical wall section is changed to a higher value. A method for manufacturing a molded article as described in claim 1.
3. For molding conditions in which wall cracking occurred at the corner wall, deep drawing is performed by changing the molding conditions to ones that result in a smaller radius of curvature at the corner wall. A method for manufacturing a molded article as described in claim 1.
4. For molding conditions in which wall cracking occurred at the corner wall, deep drawing was performed by changing the molding conditions to ones that resulted in a smaller radius of curvature at the corner wall than the original molding conditions. The only change to the molding conditions mentioned above is the radius of curvature of the corner wall. A method for manufacturing a molded article as described in claim 1.
5. The radius of curvature of the corner wall after changing the molding conditions shall be such that no cracks occur at the ridge connecting the corner wall and the bottom surface up to the molding depth before changing the molding conditions during deep drawing. A method for manufacturing a molded article as described in claim 3 or claim 4.