Press molding method

Abstract

A press molding method according to the present invention comprises: a first molding step for press-molding an intermediate component 21 having an intermediate lateral side portion 23, an intermediate connection portion 25, and an intermediate longitudinal side portion 27; and a second molding step for molding the intermediate component 21 into a pressed component 1 having a target shape. The intermediate connection portion 25 and the intermediate longitudinal side portion 27 have the same shape as the target shape. Intermediate vertical wall sections 25w on both sides where the intermediate connection portion 25 is connected are each formed via an intermediate rounded part 29 having a larger radius of curvature than the target shape, and vertical walls are not present on the side where the intermediate connection portion 25 is not connected.

Description

Press forming method

[0001] The present invention relates to a press forming method for press forming a press part from a metal sheet, having a branch portion and a T-shaped portion to which a main portion is connected via a connection portion. The metal sheet may be a hot-rolled steel sheet, a cold-rolled steel sheet, or a surface-treated steel sheet that has undergone surface treatment (electro-galvanizing, hot-dip galvanizing, organic coating treatment, etc.), as well as a sheet made of various metals such as SUS, aluminum, and magnesium.

[0002] Due to the growing need for improved fuel efficiency through vehicle weight reduction and the desire to reduce manufacturing costs, the integration of multiple metal components into a single vehicle body is being considered. Integrating multiple metal components is expected to reduce weight by eliminating the need for joining materials between parts, and to reduce manufacturing costs by reducing the number of molds used in part production.

[0003] In particular, among automotive parts, there is growing interest in the integration of parts called door-rings 61 and rear members 63, as shown in black in Figure 8. A characteristic feature of the shape of these parts is that they have a hat-shaped cross section, as shown in Figure 9 for the door-ring 61, which has a horizontal side 3 and a vertical side 7 connected to the horizontal side 3 via a curved connecting part 5. In Figure 9, a dashed line is drawn at the boundary between the part constituting the T-shaped part 9 and the other parts to make the T-shaped part 9 easier to understand.

[0004] When such shaped automotive parts are integrally press-formed, forming defects such as fracture by stretch flange forming and wrinkles are likely to occur at the connection part, and these have been issues.

[0005] Conventionally, as a method for integrating parts, Patent Document 1 has proposed a method for manufacturing an integral part by casting aluminum. Also, as a method for avoiding fracture by stretch flange, Patent Document 2 has proposed a method of supplying a material by sliding the material located on the opposite side of the stretch flange forming part on the top portion of the part to avoid fracture by stretch flange.

[0006] International Publication No. 2022 / 031991, Patent No. 5168429

[0007] However, in the method of Patent Document 1, due to the limit of castability, the minimum plate thickness is about 3 mm, which is thicker than press parts and the weight is not reduced. Also, a device with a large clamping force is required, and it is difficult to reduce the manufacturing cost.

[0008] Also, in the method of Patent Document 2, since the blank as the material moves beyond the top portion, the amount of movement of the material varies greatly depending on the curved portion and other parts, and wrinkles are likely to occur on the top portion. Also, since the amount of movement of the material is large, when the part corresponding to the horizontal side of the T-shape is long, the material comes off the mold during the forming process, so there is a limit to the length of the horizontal side of the T-shape that can be formed.

[0009] The present invention has been made to solve the above problems, and an object thereof is to provide a press forming method capable of suppressing the occurrence of cracks and wrinkles in a press part having a T-shaped portion.

[0010] The press forming method according to the present invention is a method for press forming a press part having a T-shaped portion as a target shape, comprising: a first forming step of press forming an intermediate part; and a second forming step of press forming the intermediate part into the press part having the target shape, wherein the press part having the target shape is T-shaped having a horizontal side portion and a vertical side portion connected via a connecting portion, the horizontal side portion having a top plate portion, and on both sides of the top plate portion where the connecting portion is connected thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto thereto has a top plate portion, a curved vertical wall portion formed continuously with the top plate portion and curved from the horizontal side portion to the vertical side portion, and a curved flange portion formed continuously with the curved vertical wall portion The intermediate part has a portion, the vertical portion having a top plate portion, a vertical wall portion formed continuously with the top plate portion, and a flange portion formed continuously with the vertical wall portion, the intermediate part has a roughly T-shape in which the main portion of the intermediate product is connected via an intermediate horizontal portion (branch portion of intermediate product) and an intermediate connection portion (connection portion of intermediate product), the intermediate connection portion and the intermediate vertical portion are substantially the same shape as the target shape, the intermediate vertical wall portions on both sides of the intermediate horizontal portion to which the intermediate connection portion is connected are formed via an intermediate R portion (cross section curvature radius of intermediate product) with a larger curvature radius than the target shape, and there is no vertical wall on the side to which the intermediate connection portion is not connected.

[0011] The radius of curvature of the aforementioned intermediate R section should preferably be equal to the height of the vertical wall.

[0012] The first molding step is to form a constrained shape for restraining the flange portion of the intermediate part in the second molding step, and the second molding step is to form the constrained shape by pressing it with a pad.

[0013] The second molding step may involve forming a restraining shape for restraining the flange portion of the intermediate part using a pad.

[0014] According to the present invention, the occurrence of cracks and wrinkles in press-formed parts having a T-shaped portion can be suppressed. This enables the integration of metal component parts having a T-shaped portion through press forming, resulting in lighter parts and reduced manufacturing costs.

[0015] Figure 1 is an explanatory diagram of the press forming method of this embodiment, showing an intermediate part (Figure 1(a)) and a press part with the target shape (Figure 1(b)). Figure 2 is an explanatory diagram of the die for the first forming process in the embodiment (part 1). Figure 3 is an explanatory diagram of the die for the first forming process in the embodiment (part 2). Figure 4 is an explanatory diagram of the die for the second forming process in the embodiment (part 1). Figure 5 is an explanatory diagram of the die for the second forming process in the embodiment (part 2). Figure 6 shows the state of stretch flange cracking (Figure 6(a)) and wrinkles (Figure 6(b)) of the intermediate part in the embodiment. Figure 7 shows the state of stretch flange cracking (Figure 7(a)) and wrinkles (Figure 7(b)) of the press part with the target shape in the embodiment. Figure 8 is an explanatory diagram of an automobile part that is the subject of the present invention. Figure 9 is an excerpt of the door ring from the part shown in Figure 8. Figure 10 is an explanatory diagram of the T-shaped part that is the subject of the present invention. Figure 11 is an explanatory diagram of the target shape used in the explanation of the process leading to the invention (part 1). Figure 12 is an explanatory diagram of the target shape used in the explanation of the process leading to the invention (part 2). Figure 13 is an explanatory diagram of a conventional mold used in the explanation of the process leading to the invention (part 1). Figure 14 is an explanatory diagram of a conventional mold used in the explanation of the process leading to the invention (part 2). Figure 15 is a diagram showing the state of stretch flange cracking (Figure 15(a)) and wrinkles (Figure 15(b)) of a pressed part made with a conventional mold.

[0016] The press part 1 targeted by the present invention has a T-shaped portion 9, as shown in Figure 10, which consists of a horizontal portion 3 and a vertical portion 7 connected to the horizontal portion 3 via a curved connecting portion 5. First, each part constituting this T-shaped portion 9 will be described based on Figure 10. In this application, when the term "T-shaped portion" is used, it does not mean only an exact T shape in which the angle between the horizontal and vertical portions is a right angle, but rather any shape in which the horizontal and vertical portions are connected via a connecting portion. In this specification, when referring to the top plate portion, vertical wall portion, and flange portion, the letters "t", "w", and "f", respectively, are added after the numbers indicating each portion.

[0017] The horizontal portion 3 has a top plate portion 3t and a vertical wall portion 3w and a flange portion 3f formed continuously with the vertical wall portion 3w on the side to which the connecting portion 5 of the top plate portion 3t is connected. The side of the top plate portion 3t to which the connecting portion 5 is not connected also has a vertical wall portion 3w and a flange portion 3f. However, the T-shaped portion 9 targeted by the present invention also includes those to which the side of the side of the connection portion 5 is not connected has only a vertical wall portion 3w and no flange portion. In the following description, the side of the top plate portion 3t to which the connecting portion 5 is connected will simply be referred to as the "connecting portion side," and the side to which the connecting portion 5 is not connected will simply be referred to as the "unconnected portion side."

[0018] The connecting portion 5 is the area enclosed by the dashed line in Figure 10, and has a top plate portion 5t, curved vertical wall portions 5w formed on both sides of the top plate portion 5t and curving from the horizontal side portion 3 toward the vertical side portion 7, and a curved flange portion 5f formed continuously with the curved vertical wall portions 5w.

[0019] The vertical side portion 7 has a top plate portion 7t, vertical wall portions 7w formed on both sides of the top plate portion 7t, and flange portions 7f formed continuously with the vertical wall portions 7w.

[0020] <Background to the Invention> Before describing the embodiments, the background to the present invention will be explained. In considering a press forming method for the press part having the T-shaped portion 9 described above, the inventors first used press forming analysis using the finite element method to specifically examine the movement of material that causes molding defects.

[0021] Figure 11 shows a perspective view of the press part 1 under consideration, and Figure 12 shows a cross-sectional view of A-A in Figure 11, with dimensions of each part indicated in the figures. Figures 13 and 14 are explanatory diagrams of the conventional die 51 used in the analysis. The conventional die 51 is equipped with a punch 53, a pad 55, and a die 57, and the plate-holding load of the pad that holds the blank 11 was set to 10 tonf for crash forming. The analysis aimed to accurately identify the locations and places of stretch flange cracks and wrinkles by press forming the blank 11 in a single process using the conventional die 51. The material of the blank 11 is cold-rolled 980 MPa class high-tensile steel sheet with a thickness of 1.4 mm.

[0022] Figure 15 shows the contour plot of the analysis results. Figure 15(a) shows the analysis results regarding stretch flange cracking and indicates the state at the bottom dead center of molding. As shown in Figure 15(a), it was found that stretch flange cracking occurred at the flange end of the connecting portion 5, and that cracking was also a concern in the curved vertical wall portion 5w that is continuous with the curved flange portion 5f. Figure 15(b) shows the analysis results regarding wrinkles and indicates the shape 5 mm before the bottom dead center of molding. As shown in Figure 15(b), it was found that wrinkles occurred near the vertical edge portion 7 of the top plate portion 5t of the connecting portion 5.

[0023] From the analysis of the press forming process, it was found that among the forming defects, stretch flange cracks occur when the material is pulled into the curved vertical wall portion 5w during the forming of the curved portion of the connection 5. More specifically, the material at the end edge of the curved flange portion 5f, which is formed continuously with the curved vertical wall portion 5w, is pulled towards the curved vertical wall portion 5w and then pulled to both the left and right sides of the curved vertical wall portion 5w, causing the cracks to occur.

[0024] Furthermore, the cause of the wrinkles is thought to be as follows: On the non-connected side of the top plate portion 3t of the horizontal side portion 3, there is a vertical wall portion 3w that extends along the entire length of the horizontal side portion 3. Also, on the connected side of the horizontal side portion 3, as shown in Figure 10, there are vertical wall portions 3w on both sides of the connected portion 5, similar to the connected side. In other words, on both sides of the connected portion 5 on the top plate portion 3t of the horizontal side portion 3, there are vertical wall portions 3w on both sides of the top plate portion 5t.

[0025] However, in the region where the connection portion 5 is formed, there is a vertical wall portion 3w on the non-connection side of the top plate portion 3t, but there is no corresponding vertical wall portion 3w on the connection side, and instead there is a curved vertical wall portion 5w. Therefore, focusing on the top plate portion 3t, the amount of material movement is less in the region where the connection portion 5 is formed, especially in the region close to the vertical edge portion 7, than in other regions. Therefore, it is thought that the difference in the amount of material movement between these regions causes wrinkles to occur in the top plate portion 5t of the connection portion 5, especially in the part close to the vertical edge portion 7, where the amount of material movement is least.

[0026] From the above considerations, we have found that the following measures are effective in suppressing stretch flange cracking in the curved flange portion 5f and wrinkling in the top plate portion 5t. Specifically, to suppress stretch flange cracking, material movement in the curved flange portion 5f and the curved vertical wall portion 5w should be reduced. Also, to suppress wrinkling in the top plate portion 5t, the difference in the amount of material movement between the region where the connection portion 5 is formed and the other regions should be reduced. Specifically, the amount of material movement should be reduced in the region where the amount of material movement is large, i.e., the region other than the region where the connection portion 5 is formed.

[0027] To achieve these material movements, the present invention employs a two-step press forming process instead of a single-step one. In the first step, when forming the intermediate part 21, the amount of material movement in the area of ​​the intermediate top plate portion 23t of the intermediate horizontal portion 23, excluding the intermediate connection portion 25, is reduced from the viewpoint of suppressing wrinkle formation. In the second step, press forming is performed in a manner that reduces material movement in the curved flange portion 5f and the curved vertical wall portion 5w from the viewpoint of suppressing stretch flange cracking. The present invention is based on these findings, and specific embodiments will be described below.

[0028] [Embodiment] The press forming method according to this embodiment is a press forming method for a press part 1 having a T-shaped portion 9 as shown in Figure 10, and includes a first forming step of press forming an intermediate part 21 (see Figure 1(a)) having an intermediate horizontal portion 23, an intermediate connecting portion 25, and an intermediate vertical portion 27, and a second forming step of forming the intermediate part 21 into a press part 1 (see Figure 1(b)) which is the target shape. Figure 1(b) shows the state after trimming the unnecessary portion after forming. Each step will be described in detail below.

[0029] <First Molding Process> The first molding process is the process of molding the intermediate part 21. As shown in Figure 1(a), the intermediate part 21 has an intermediate horizontal side portion 23, an intermediate connecting portion 25, and an intermediate vertical side portion 27, and the intermediate connecting portion 25 and the intermediate vertical side portion 27 have the same shape as the target shape. When we say "same shape" here, it does not mean exactly the same shape, but includes cases such as when there is a gradually changing portion where the shape changes at the boundary between the intermediate connecting portion 25 and the intermediate horizontal side portion 23.

[0030] Furthermore, the intermediate top plate portion 23t of the intermediate horizontal portion 23 has an intermediate vertical wall portion 23w formed via an intermediate R portion 29 with a larger radius of curvature than the target shape, and an intermediate flange portion (flange wall of intermediate product) 23f formed continuously with the intermediate vertical wall portion 23w on the connection side. The intermediate flange portion 23f and the intermediate curved flange portion 25f also have a step shape 30. Moreover, the intermediate top plate portion 23t of the intermediate horizontal portion 23 does not have a vertical wall on the non-connection side.

[0031] In the example shown in Figure 1(a), the radius of curvature of the intermediate R section 29 is equal to the height of the vertical wall. Therefore, the entire intermediate vertical wall section 23w is the intermediate R section 29, and the entire structure has a curved shape.

[0032] The intermediate part 21 described above is produced using an intermediate molding die 31 consisting of a punch 33, a pad 35, and a die 37, as shown in Figures 2 and 3. The plate-holding load of the pad 35 is, for example, 10 tonf. The intermediate molding die 31 differs from the conventional die 51 shown in Figures 13 and 14 in the following three main points.

[0033] Firstly, in the first molding process, vertical walls are not formed on the non-connected side of the intermediate top plate portion 23t, so there is no die for forming vertical walls.

[0034] Secondly, the intermediate vertical wall forming sections 33w and 37w in the punch 33 and die 37, which form the intermediate vertical wall section 23w, have a large radius of curvature so that they can form an intermediate R section 29 with a larger radius of curvature than the target R section. In the example shown in Figure 1(a), the radius of curvature of the intermediate R section 29 is equal to the height of the vertical wall, so the intermediate R section 29 is formed by the intermediate vertical wall forming sections 33w and 37w in the punch 33 and die 37. In this example, the radius of curvature of the intermediate vertical wall forming sections 33w and 37w is 70 mm.

[0035] Thirdly, the intermediate flange forming sections 33f and 37 of the punch 33 and die 37, which form the intermediate flange sections 23f and 27f and the intermediate curved flange section 25f of the intermediate part 21, have stepped forming sections 33fs and 37f that form stepped shapes 30 with a height of 6 mm and a radius of curvature of 5 mm.

[0036] In the first molding process, the intermediate part 21 is formed without a vertical wall on the non-connecting side of the intermediate horizontal section 23, so the material is not pulled in that direction. Furthermore, the radius of curvature of the intermediate R section 29 is large, and more specifically, the entire shape is gently curved, so the amount of material movement is suppressed during the molding process of the intermediate vertical wall section 23w, and the difference in the amount of material movement between the area where the intermediate connection section 25 is formed and the area where the intermediate connection section 25 is formed is small. Therefore, no wrinkles occur in the intermediate top plate section 25t during the first molding process. Also, in the first molding process, because the radius of curvature of the intermediate R section 29 is large, no large tensile force is generated that pulls the intermediate curved flange section 25f and the intermediate curved vertical wall section 25w toward the intermediate horizontal section 23, so no cracks occur in the intermediate curved flange section 25f.

[0037] <Second Molding Process> The target shape mold 41 for the second molding process is equipped with a punch 43, a die 47, and a pad 45, as shown in Figures 4 and 5.

[0038] The second molding process involves press-forming the intermediate part 21 into the target shape of the press part 1 (see Figure 1(b)). Specifically, the intermediate part 21 is molded with a vertical wall portion 3aw and a flange portion 3af on the non-connecting side of the intermediate top plate portion 23t of the intermediate horizontal portion 23, and the intermediate R portion 29 of the intermediate part 21 is molded with a vertical wall portion 3w as the R portion with the radius of curvature of the target shape.

[0039] The second molding process involves press molding the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f while they are restrained. In this embodiment, since the stepped shape 30 is formed in the first molding process, the stepped shape 30 is pressed down with the pad 45 during the second molding process.

[0040] Since the intermediate connection portion 25 is already molded to the same shape as the target shape in the first molding process, there is virtually no material movement in that portion during the second molding process. Furthermore, since the intermediate vertical wall portion 23w is already formed on the connection portion side of the intermediate top plate portion 23t, there is also little material movement in that portion during the second molding process. As a result of these factors, no wrinkles occur in the top plate portion 5t of the connection portion 5 after the second molding process.

[0041] Furthermore, since the shape of the intermediate connection portion 25 is already formed to the target shape, the flange end of the intermediate connection portion 25 will not be pulled towards the intermediate curved vertical wall portion 25w and crack during the second molding process. In addition, during the second molding process, the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f are molded while restrained, so material movement is suppressed, and in this respect as well, the curved flange portion 5f of the connection portion 5 will not be pulled and crack.

[0042] As described above, according to this embodiment, no stretching flange cracks or wrinkles occur in either the first molding process or the second molding process.

[0043] In the above description, the case where the radius of curvature of the intermediate R portion 29 formed in the first molding step is the same as the height of the vertical wall portion 3w was shown. However, in the present invention, the radius of curvature of the intermediate R portion 29 only needs to be larger than the target shape, and includes cases where it is smaller than the height of the vertical wall. In this case, a planar intermediate vertical wall portion 23w exists continuously with the intermediate R portion 29.

[0044] Also, in the above description, the step shape 30 is given as an example of the restraining shape for restraining the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f. However, the restraining shape of the present invention is not limited to this, and any shape may be used as long as it can restrain the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f in the second molding step.

[0045] Further, in the above description, the restraining shape is formed on the intermediate flange portions 23f, 27f and the intermediate curved flange portion 25f in the first molding step. However, the present invention is not limited to this, and in the first molding step, the restraining shape may not be formed, and the portion may be restrained while forming the restraining shape by the pad 45 in the second molding step.

[0046] The target shape of FIG. 11 described above was simulated by analysis of the occurrence of elongation flange cracking and wrinkle when press-molded according to the example of the present invention. The molds for the first molding step and the second molding step are the same as those described in the embodiment.

[0047] The contour diagrams of the analysis results are shown in FIGS. 6 and 7. FIG. 6 shows the analysis results of the intermediate part 21. FIG. 6(a) shows the analysis results regarding elongation flange cracking and shows the state at the bottom dead center of molding. As shown in FIG. 6(a), elongation flange cracking does not occur at any location including the flange end of the intermediate connecting portion 25. Also, FIG. 6(b) shows the analysis results regarding wrinkles and shows the shape 5 mm before the bottom dead center of molding. As shown in FIG. 6(b), wrinkles do not occur at any location including the intermediate top plate portion 25t.

[0048] FIG. 7 shows the analysis results of the target shape. FIG. 7(a) shows the analysis results regarding elongation flange cracking and shows the state at the bottom dead center of molding. As shown in FIG. 7(a), elongation flange cracking does not occur at any location including the flange end of the connecting portion 5. Also, FIG. 7(b) shows the analysis results regarding wrinkles and shows the shape 5 mm before the bottom dead center of molding. As shown in FIG. 7(b), wrinkles do not occur at any location including the top plate portion 5t.

[0049] As described above, it has been confirmed that, according to the present invention, stretch flange cracks and wrinkles do not occur in either the intermediate part 21 or the press part 1 which has the target shape.

[0050] According to the present invention, it is possible to provide a press forming method that can suppress the occurrence of cracks and wrinkles in press parts having a T-shaped portion.

[0051] 1 Pressed part 3 Side section 3t Top section of side section 3w Vertical wall section of side section 3f Flange section of side section 5 Connection section 5t Top section of connection section 5w Curved vertical wall section of connection section 5f Curved flange section of connection section 7 Vertical section 7t Top section of vertical section 7w Vertical wall section of vertical section 7f Flange section of vertical section 9 T-shaped section 11 Blank 21 Intermediate part 23 Intermediate side section 23t Intermediate top section of intermediate side section 23w Intermediate vertical wall section of intermediate side section 23f Intermediate flange section of intermediate side section 25 Intermediate connection section 25t Intermediate top section of intermediate connection section 25w Intermediate curved vertical wall section of intermediate connection section 25f Intermediate curved flange section of intermediate connection section 27 Intermediate vertical section 27t Intermediate top section of intermediate vertical section 27w Intermediate vertical wall section of intermediate vertical section 27f Intermediate flange section of the intermediate vertical side 29 Intermediate R section 30 Stepped shape 31 Intermediate molding die 33 Punch 33w Intermediate vertical wall molding section 33f Intermediate flange molding section 33fs Stepped molding section 35 Pad 37 Die 37w Intermediate vertical wall molding section 37f Intermediate flange molding section 37fs Stepped molding section 41 Target shape die 43 Punch 45 Pad 47 Die 51 Conventional die 53 Punch 55 Pad 57 Die 61 Door ring 63 Rear member

Claims

1. A press forming method for press forming a press part having a T-shaped portion as a target shape, comprising: a first forming step of press forming an intermediate part; and a second forming step of press forming the intermediate part into the press part having the target shape, wherein the press part having the target shape is T-shaped having a horizontal side portion and a vertical side portion connected via a connecting portion, the horizontal side portion having a top plate portion, vertical wall portions and flange portions formed continuously with the vertical wall portions on both sides of the top plate portion where the connecting portion is connected, and at least a vertical wall portion on the side of the top plate portion where the connecting portion is not connected, the connecting portion having a top plate portion, a curved vertical wall portion formed continuously with the top plate portion and curved from the horizontal side portion to the vertical side portion, and a curved flange portion formed continuously with the curved vertical wall portion, the vertical side portion having a top plate portion, a vertical wall portion formed continuously with the top plate portion and a flange portion formed continuously with the vertical wall portion, and the intermediate part is A press forming method having a substantially T-shape with an intermediate horizontal portion and an intermediate vertical portion connected via an intermediate connecting portion, wherein the intermediate connecting portion and the intermediate vertical portion are substantially the same shape as the target shape, the intermediate vertical wall portions on both sides of the intermediate horizontal portion to which the intermediate connecting portion is connected are formed via an intermediate R portion with a larger radius of curvature than the target shape, and there is no vertical wall on the side not connected to the intermediate connecting portion.

2. The press molding method according to claim 1, wherein the radius of curvature of the intermediate R portion is equal to the height of the vertical wall.

3. The press molding method according to claim 1 or 2, wherein the first molding step is to form a restraining shape for restraining the flange portion of the intermediate part in the second molding step, and the second molding step is to press the restraining shape with a pad to form it.

4. The press molding method according to claim 1 or 2, wherein the second molding step involves forming a restraining shape for restraining the flange portion of the intermediate part with a pad.

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