Method for manufacturing formed product

Abstract

The present invention increases the volume of a rectangular tube-shaped deep-drawn product and reduces the probability of wall cracking occurring during deep-drawing of the component, thereby stabilizing mass production. Provided is a method for manufacturing a rectangular tube-shaped formed product (1) by deep-drawing a blank comprising a metal sheet, the formed product (1) having a polygonal bottom surface portion (2), a vertical wall portion (3) comprising straight wall portions (3Aa, 3Ab) continuous with each side of the bottom surface portion (2) and corner wall portions (3B) connecting adjacent edge portions of the straight wall portions in the left-right direction together, and a flange portion (4) continuous with the vertical wall portions (3), wherein, if it is determined that wall cracking will occur in the corner wall portions (3B) during deep-drawing of the formed product (1) having a target component shape, the setting of a radius of curvature (Rt) of the corner wall portions (3B) having the target component shape is changed to a value that is smaller than the radius of curvature of the corner wall portions (3B) when it is determined that wall cracking will occur in the corner wall portions (3B).

Description

Method for manufacturing molded article

[0001] The present invention relates to a technology for manufacturing a rectangular tubular molded article having a polygonal bottom portion by deep drawing. Deep drawing is performed by a deep drawing process. The present invention relates to providing a method for manufacturing a molded article with improved deep drawability. The polygonal shape of the bottom portion 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 targeted. That is, the rectangular tubular shape in the present invention is not limited to those having a rectangular bottom portion.

[0002] Deep drawing can seamlessly form a vertical wall from a single metal sheet. For this reason, deep drawing is still currently used in the manufacture of many components. In recent years, battery-powered electric vehicles have become widespread from the perspective of carbon neutrality. At this time, application of rectangular cylindrical deep drawing to the manufacture of battery cases for mounting batteries is being considered. In the present specification, a metal sheet to be press-formed is also referred to as a blank. One of the requirements for such a battery case is a large capacity. Increasing the capacity of the battery case allows more batteries to be mounted in an electric vehicle.

[0003] Here, a rectangular tubular container is a container having a polygonal bottom portion. Conventionally, several forming methods for increasing the volume of such a deep-drawn container having a polygonal bottom portion have been proposed. Patent Document 1 describes that, during rectangular cylindrical deep drawing, the punch pressing speed in the early stage of forming is increased, and the punch pressing speed in the late stage of forming is decreased. Patent Document 1 discloses that deep drawability is improved by controlling the punch pressing speed. Further, Patent Document 2 describes cutting out corner portions 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 a rectangular cylindrical component.

[0004] Japanese Unexamined Patent Application Publication No. 2009-90318 Japanese Unexamined Patent Application Publication No. Hei 9-285825

[0005] Rectangular tubular containers are used, for example, as 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 ridge connecting the corner wall and the bottom surface, as shown in Figure 6, or at the wall surface above the corner wall. Containers with these cracks suffer a significant decrease in strength, leading to increased costs during mass production. In this specification, the ridge connecting the corner wall and the bottom surface is also referred to as the punch shoulder.

[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, corner cutting is used to cut the four corners of the rectangular blank. However, if the amount of corner cutting 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 tension in the molding direction that occurs in the corner wall in the later stages of molding. If the material cannot withstand the 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 problem: the optimal notch shape at the corner differs depending on the mold shape and the size of the blank before notching. Therefore, when changing the mold shape or the size of the blank before notching, it is also necessary to change the notch shape at the blank corner. In addition, because the notch shape at the blank corner 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.

[0011] This invention focuses on increasing the volume of deep-drawn rectangular tube-shaped 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.

[0013] In one aspect of the present invention, when molding a rectangular tubular molded product, a simple method is employed to prevent cracking at the corner walls, by changing the radius of curvature of the corner walls. This suppresses cracking at the corner walls, thus preventing cracking during mass production. In other words, this method avoids cracking at the corner walls during mass production, thus contributing to the stabilization of mass production. Furthermore, this method increases the volume of the molded product by sharpening the corner walls. Additionally, deep drawing becomes possible under molding conditions with a smaller radius of curvature at the corner walls. Therefore, it becomes possible to increase the molding depth compared to before the change in molding conditions. The molding depth corresponds to the height of the vertical walls.

[0014] This is a perspective view illustrating a molded product according to an embodiment of the present invention. This is a diagram illustrating a die used for deep drawing. This is a top view of the punch seen from above. This is a diagram illustrating the process of this embodiment. This is a diagram illustrating an example of the process of setting the molding conditions. This is a diagram showing typical cracks that occur during deep drawing of a rectangular tube. This is a diagram illustrating improved moldability by changing the radius of curvature Rt of the corner wall. This is a diagram illustrating the blank shape. This is a diagram illustrating the corner cut of the blank.

[0015] Next, embodiments of the present invention will be described with reference to the drawings. Here, the drawings are schematic, and the size and length ratios of each component may differ from those of reality. Furthermore, the embodiments shown below are illustrative examples of configurations for realizing the technical concept of the present invention. The technical concept of the present invention does not limit the materials, shapes, and structures of the components to those described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims. Furthermore, the dimensions shown in each figure are example dimensions for illustrating the embodiments, etc. These dimensions do not define the present invention in any way.

[0016] In this embodiment, a rectangular tube deep-drawn molded product 1 with a rectangular cross-section, as shown in Figure 1, will be used as an example. Hereafter, this rectangular tube deep-drawn molded product 1 will also be simply referred to as molded product 1. However, the shape of the bottom portion 2 of the molded product 1 in this embodiment is not limited to a rectangular shape. Its shape 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 facing upwards. 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. 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 surfaces forming adjacent straight wall portions 3Aa and 3Ab is preferably 90 degrees or more. Furthermore, the wrinkle-suppressing force of the blank holder 7 is preferably 10 tons or more.

[0021] "Method for Manufacturing Molded Product 1" The method for manufacturing molded product 1 in this embodiment, as shown in Figure 4, comprises a molding condition setting step 20, a press step 21 for deep drawing, and a trim step 22.

[0022] <Molding Condition Setting Process 20> The molding condition setting process 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 of the target part shape. An example of the process of the molding condition setting process 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 a molded product 1 with the target part shape. Next, in step S20, a molding analysis is performed using a known computer-aided engineering (CAE) analysis to form the blank into the target part shape by deep drawing under the molding conditions set in step S10. For example, a molding model corresponding to the blank model and the target part shape is generated, and a molding analysis of press forming is performed using that molding model. A springback analysis may also be performed in the molding analysis.

[0024] Next, in step 30, it is determined whether or not wall cracking occurs at the corner wall portion 3B based on the results of the molding analysis. It is assumed that there are no defects in any part of the molded product 1 other than the corner wall portion 3B. If it is determined that no wall cracking occurs at the corner wall portion 3B, the process proceeds to step S40, where the current molding conditions are determined as the final molding conditions. On the other hand, if it is determined in step S30 that wall cracking occurs at the corner wall portion 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 has 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 has occurred. It is assumed that the radii of curvature Rt of these multiple molding conditions are different from each other and are set in stages, with the radii of curvature Rt decreasing in order. 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 3B to a smaller value, the height of the vertical wall 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 portion 3B. It is also checked whether cracks occur at the punch shoulder portion up to the molding depth set in step S10. In step S70, assuming that no wall cracks occur at the corner wall portion 3B and no edge cracks occur 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 at the molding conditions for 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 molding depth may be set to a molding depth greater than or equal to the molding depth set in step S10, and lower than the molding limit height Ht, as the final molding condition. Here, the molding condition setting step 20 may also be performed by actually manufacturing the 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, cutting is performed on the flange portion of the molded product 1 produced in the pressing process 21 to achieve the final product shape. The trimming process 22 is optional. Note that in mass production, the processing consists of the pressing process 21 and the trimming process 22. Once the molding conditions are determined, the processing in the molding condition setting process 20 becomes unnecessary.

[0031] (Operation and Others) Deep drawing of a rectangular tubular container is difficult, and there is a risk of cracks 10 on the punch shoulder and cracks 9 on the corner wall portion 3B, as shown in Figure 6. The crack 10 on the punch shoulder is a ridge crack at the corner portion that is continuous with the corner wall portion 3B. According to this embodiment, when a wall crack occurs at the corner wall portion 3B during the molding of the rectangular tubular molded product 1, the following measures are taken to prevent the crack: The radius of curvature Rt of the corner wall portion 3B is changed to be smaller, to the extent that the crack 10 on the punch shoulder does not occur. According to this embodiment, wall cracks at the corner wall portion 3B can be suppressed by such a simple means. In other words, according to this embodiment, cracks 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, sharpening the corner wall portion 3B has the effect of increasing the volume of the molded product. Moreover, deep drawing becomes possible under molding conditions in which the radius of curvature Rt of the corner wall portion 3B is reduced. Therefore, 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 suppressing cracking at corner wall portion 3B> According to the inventor's considerations, the reason why the formability of deep drawing is improved by applying the present invention is considered to be as follows. That is, the reason why cracking at the corner wall portion 3B of the molded product 1, which has a polygonal bottom surface and a rectangular tube shape, is avoided by applying the present invention is considered to be as follows. Here, in the following explanation, the boundary between the early molding stage and the late molding stage is the moment when the vertical wall portion of the molded product 1 is formed by the punch 8 and die 5 during rectangular tube deep drawing.

[0033] Wall cracks 9 at the corner wall portion 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, when a large tensile strain is introduced during the later stages of forming, the thicker the plate, i.e., the greater the compressive strain introduced in the circumferential direction, the following can be inferred. In this case, it can be 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 portion 3B causes the material to concentrate at the flange portion 4. Therefore, a smaller radius of curvature Rt results in a thicker plate thickness within the corner wall portion 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 portion 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 do not cause 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 considered that the forming depth can be increased. Here, it is preferable that the radius of curvature Rt of the corner wall portion 3B after changing the forming conditions is 50% or less of the radius of curvature Rt of the corner wall portion 3B before changing the forming conditions. However, this is conditional on the absence of punch shoulder cracking 10. Also, it is preferable that the lower limit of the radius of curvature Rt of the corner wall portion 3B after changing the forming conditions is, for example, 5 mm or more.

[0036] (Other) This disclosure may also take the following configurations: (1) Disclosure 1 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 metal sheet, wherein if it is determined that wall cracking will occur at the corner wall portions when a molded product of the target part shape is deep drawn, 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. (2) Disclosure 2 is the method for manufacturing a molded product as described in Disclosure 1, wherein in addition to changing the radius of curvature of the corner wall portions to a smaller value, the height of the vertical wall portions is also changed to a higher value. (3) Disclosure 3 is a method for manufacturing a molded article as described in Disclosure 1 or Disclosure 2, wherein, in the case of molding conditions in which wall cracking occurs at the corner wall portion, the molding conditions are changed to molding conditions in which the radius of curvature of the corner wall portion is smaller than the molding conditions in which wall cracking occurs at the corner wall portion, and deep drawing is performed. (4) Disclosure 4 is a method for manufacturing a molded article as described in Disclosure 3, wherein, in the case of molding conditions in which wall cracking occurs at the corner wall portion, the molding conditions are changed to molding conditions in which the radius of curvature of the corner wall portion is smaller than the molding conditions in which the molding conditions are changed, and the change in molding conditions is limited to the radius of curvature of the corner wall portion. (5) Disclosure 5 is a method for manufacturing a molded article as described in Disclosure 3 or Disclosure 4, wherein the radius of curvature of the corner wall portion after changing the molding conditions is 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.

[0037] Next, an embodiment 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. In addition, a 270 MPa class hot-dip galvanized steel sheet with a plate thickness of 0.8 mm was used as the test material to constitute the blank.

[0038] The dimensions of the mold were as shown in Figure 2. Specifically, the top shape of the 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. 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 radius of curvature Rt of the corner wall portion 3B, in accordance with the above molding conditions. Two types of blank shapes were set as molding conditions. The two types of shapes were a 180 mm square as shown in Figure 8, and a shape in which the four corners of the square were corner-cut. The shape of the corner cut was set so that the length C of the perpendicular from the vertex was 20 mm, as shown in Figure 9.

[0040] Furthermore, three molding conditions were set as wrinkle suppression forces: 10 tons, 15 tons, and 20 tons. In addition, two molding conditions were set as the shoulder radius of die 5: 5 mm and 10 mm. Two molding conditions were set as the radius of curvature Rt of corner wall portion 3B: 10 mm and 25 mm. For each molding condition, the depth relative to the upper surface of flange portion 4 at the moment when wall cracking occurred in 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]

[0043] The following findings are obtained from Table 1. That is, under each forming condition in which corner cut, cushion pressure and die shoulder radius are respectively changed, the same following result is obtained in all forming conditions. That is, in all forming conditions, the forming limit depth is greater under the forming condition where the curvature radius Rt of the corner wall portion 3B is 10 mm than under the forming condition where the curvature radius Rt of the corner wall portion 3B is 25 mm. In addition, it indicates that when the forming depth is the same, wall cracking at the corner wall portion 3B can be avoided if the curvature radius Rt of the corner wall portion 3B is smaller.

[0044] From this, it can be understood that, for example, when wall cracking occurs at the corner wall portion 3B in the molded product 1 conventionally molded with the curvature radius Rt of the corner wall portion 3B being 25 mm, the molded product may be manufactured by changing the molding conditions as follows, for example. That is, molding is performed after changing the shape of the target part to set the curvature radius Rt of the corner wall portion 3B to 10 mm. This enables manufacturing of parts with a large forming depth and sharp corner wall portions 3B. In other words, the volume of the molded product 1 can be increased. In addition, even when the forming depth does not change before and after changing the forming conditions, it is possible to produce the molded product 1 in which wall cracking at the corner wall portion 3B is less likely to occur.

[0045] Here, for the conditions where the shoulder radius of the die 5 is 5 mm, the corner cut of the blank is 0, and the wrinkling suppressing force is 10 ton, the forming limit depth when the curvature radius Rt is set to 5 mm was obtained for the first forming condition described in Table 1. It was confirmed that setting the curvature radius Rt to 5 mm provides a greater forming limit depth than when the curvature radius Rt is 10 mm. However, when the curvature radius Rt is made smaller than 5 mm, ridge line cracking occurs at the punch shoulder before the forming depth reaches the forming limit depth obtained when the curvature radius Rt is 25 mm.

[0046] From the above, it has been found that as a countermeasure against wall cracking at the corner wall portion 3B, it is preferable to set the radius of curvature Rt to 5 mm in this example as a molding condition in view of the requirement for the volume of the container.

[0047] The entire content of Japanese Patent Application No. 2025-40566 (filed on March 13, 2025), to which the present application claims priority, is incorporated herein by reference as part of the present disclosure. Although the description has been made with reference to a limited number of embodiments, the scope of rights is not limited thereto, and modifications of each embodiment based on the above disclosure are obvious to those skilled in the art.

[0048] 1 Molded product 2 Bottom surface portion 3 Vertical wall portion 3B Corner wall portion 4 Flange portion 5 Die 6 Blank 7 Blank holder 8 Punch 20 Molding condition setting step 21 Pressing step 22 Trimming step Rt Radius of curvature of corner wall portion

Claims

1. A method for manufacturing a molded product having a rectangular tube shape, comprising 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 metal sheet, wherein if it is determined that wall cracking will occur at the corner wall portions when deep drawing is performed on a molded product of a 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.

2. The method for manufacturing a molded product according to claim 1, wherein the radius of curvature of the corner wall portion is changed to a smaller value, and the height of the vertical wall portion is changed to a higher value.

3. A method for manufacturing a molded product according to claim 1 or claim 2, wherein, in response to a molding condition in which wall cracking occurs at the corner wall, the molding condition is changed to one in which the radius of curvature of the corner wall is smaller than the molding condition in which wall cracking occurred, and deep drawing is performed.

4. A method for manufacturing a molded product according to claim 1, wherein, in the case of molding conditions in which wall cracking occurs at the corner wall portion, deep drawing is performed by changing to molding conditions in which the radius of curvature of the corner wall portion is smaller than the molding conditions in which wall cracking occurred, and the change in molding conditions is limited to the radius of curvature of the corner wall portion.

5. The method for manufacturing a molded product according to claim 3 or claim 4, wherein the radius of curvature of the corner wall portion after changing the molding conditions is 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.

Images