JP7463179B2 - Manufacturing method for automobile door inner panel - Google Patents

Description

The present invention relates to a method for manufacturing an automobile door inner panel and an automobile door inner panel.

Generally, an automobile door comprises a door outer panel and a door inner panel. For example, as disclosed in FIG. 1 of Patent Document 1, the door inner panel has a step portion on its periphery, and the step portion has a stepped shape. Patent Document 1 discloses that the door inner panel having the above-mentioned shape is deep-drawn by pressing a steel plate (paragraph 0016 of Patent Document 1).

In recent years, there has been an increase in the use of aluminum alloys as materials for automobile door parts in order to reduce the weight of automobile bodies.

JP 2018-131106 A

However, aluminum alloy plate material has inferior formability to steel plate material. Therefore, when a door inner panel having a step portion as described above is deep-drawn by pressing the aluminum alloy plate material, cracks may occur in the step portion.

In order to form the door inner panel while preventing cracks from occurring in the step portion, it is possible to consider a method of deep drawing the door inner panel in stages, for example by performing multiple press processes (multiple deep drawing processes) on the aluminum alloy plate material. However, this method has the problem of increasing the number of steps in the manufacturing process, which increases the manufacturing costs.

The object of the present invention is to provide a technology for manufacturing an automobile door inner panel in which a door inner panel having a step is deep-drawn by pressing an aluminum alloy sheet material, which can prevent cracks from occurring in the step while suppressing an increase in the number of steps in the manufacturing process.

The provided manufacturing method is a manufacturing method for manufacturing an automobile door inner panel by pressing a plate-shaped blank material made of an aluminum alloy with a first mold and a second mold. The door inner panel has a step portion that constitutes at least a part of the peripheral portion of the door inner panel. The step portion is configured so that a first wall portion, a second wall portion, a third wall portion, and a fourth wall portion are successively arranged in this order in a stepped manner. The first mold and the second mold each have a first molding surface, a second molding surface, a third molding surface, and a fourth molding surface that are successively arranged in a stepped manner to form the first wall portion, the second wall portion, the third wall portion, and the fourth wall portion, respectively. The second molding surface and the third molding surface of the first mold constitute a recess. The second molding surface and the third molding surface of the second mold constitute a protrusion having a shape corresponding to the recess. The sum of the distance from the first boundary between the first molding surface and the second molding surface of the first mold to the second boundary between the second molding surface and the third molding surface of the first mold and the distance from the second boundary to the third boundary between the third molding surface and the fourth molding surface of the first mold, divided by the distance from the first boundary to the third boundary is equal to or less than the upper limit value preset based on the breaking limit of the blank. The manufacturing method includes a first step of contacting the first boundary with the blank while the blank is placed between the first mold and the second mold and the outer periphery of the blank is held, and a second step of contacting the third boundary with the blank at the same time as the fourth boundary between the second molding surface and the third molding surface of the second mold contacts the blank or before the fourth boundary contacts the blank by moving at least one of the first mold and the second mold in an approaching direction in which the first mold and the second mold approach each other.

In this manufacturing method, in the first and second steps, the first boundary of the first mold, the third boundary of the first mold, and the fourth boundary of the second mold contact the blank in the above-mentioned order, and the value obtained by dividing the total distance by the distance from the first boundary to the third boundary is equal to or less than the upper limit value that is preset based on the breaking limit of the blank. This makes it possible to suppress the occurrence of cracks in the step portion while suppressing an increase in the number of steps in the manufacturing process when the door inner panel having the step portion is deep-draw formed from the aluminum alloy blank by press working.

The first step may be a step of placing the blank material between the first and second dies, holding the outer periphery of the blank material, and moving at least one of the first and second dies in a direction in which the first and second dies approach each other, thereby bringing the first boundary portion into contact with the blank material.

The door inner panel provided is an automobile door inner panel made of an aluminum alloy. This door inner panel has a step portion constituting at least a part of the peripheral portion of the door inner panel, and the step portion is configured so that a first wall portion, a second wall portion, a third wall portion, and a fourth wall portion are arranged in a stepped manner in this order, and the door inner panel has a value obtained by dividing the total distance obtained by adding the distance from the first boundary portion between the first wall portion and the second wall portion to the second boundary portion between the second wall portion and the third wall portion and the distance from the second boundary portion to the third boundary portion between the third wall portion and the fourth wall portion by the distance from the first boundary portion to the third boundary portion, which is equal to or less than an upper limit value preset based on the breaking limit of the blank material.

As described above, the present invention provides a technology for manufacturing an automobile door inner panel in which a door inner panel having a step is deep-drawn by pressing an aluminum alloy sheet material, which can prevent cracks from occurring in the step while suppressing an increase in the number of steps in the manufacturing process.

1 is a perspective view showing an automobile door inner panel according to an embodiment of the present invention; 4 is a perspective view showing an outline of a press working device used in the manufacturing method of the door inner panel. FIG. 11 is a diagram showing the results of a simulation analysis of the distribution of strain occurring in the front edge portion of a door inner panel formed by press working. FIG. FIG. 2 is a schematic diagram for explaining the shapes of a punch and a die used in the manufacturing method. 3 is a schematic cross-sectional view showing a molding step in the manufacturing method. FIG. 3 is a schematic cross-sectional view showing a molding step in the manufacturing method. FIG. 3 is a schematic cross-sectional view showing a molding step in the manufacturing method. FIG. 3 is a schematic cross-sectional view showing a molding step in the manufacturing method. FIG. 11 is a diagram showing the results of a simulation analysis of the reduction rate of the thickness of a blank material in a region corresponding to a front edge portion of the door inner panel in a molding process of the manufacturing method. FIG. FIG. 2 is a diagram showing an example of a forming limit diagram of a blank material used in the manufacturing method. FIG. 13 is a schematic diagram for explaining a method of deriving an example of a mathematical formula used in designing the punch and the die. FIG. 13 is a schematic diagram for explaining a method of deriving an example of a mathematical formula used in designing the punch and the die. 7A to 7C are diagrams illustrating steps of a manufacturing method according to a modified example of the embodiment.

A preferred embodiment of the present invention will be described with reference to the drawings. Figure 1 is a perspective view showing an automobile door inner panel 100 according to this embodiment.

The door inner panel 100 is a component that constitutes a part of a side door for an automobile. The side door includes the door inner panel 100, a door outer panel (not shown) that is disposed on the outside of the door inner panel 100 in the vehicle width direction, and a plurality of reinforcing members (not shown) that are disposed between the door inner panel 100 and the door outer panel.

The letters and arrows "front," "rear," "up," "down," "outside," and "inside" shown appropriately in the drawings are directions based on the vehicle's fore-and-aft direction and vehicle width direction, and indicate the directions when the side door is in a state where the door opening of the vehicle body (not shown) is closed. The letters and arrows "outside" indicate the outside in the vehicle width direction, and the letters and arrows "inside" indicate the inside in the vehicle width direction.

As shown in FIG. 1, the door inner panel 100 includes a panel body 10 and a sash portion 15. The panel body 10 is a portion of the door inner panel 100 that is below the waistline WL (belt line). The sash portion 15 is a portion that is above the waistline WL and forms a window frame for holding the window glass together with a sash portion (not shown) of the outer panel. The sash portion 15 is not essential and may be omitted. The panel body 10 and the sash portion 15 may be integral or separate. Specifically, the panel body 10 and the sash portion 15 may be produced by press-molding a single blank material, or may be produced by press-molding a plurality of blank materials and then joining them together.

The panel body 10 includes a central portion 17 and a peripheral portion. The central portion 17 is a flat portion that spreads in the longitudinal direction and vertical direction of the vehicle and occupies most of the panel body 10, and has an inner side that faces inward in the vehicle width direction. The central portion 17 does not necessarily have to be entirely made of a flat plate, and may have some irregularities.

The peripheral portion is a portion that surrounds the central portion 17. The peripheral portion includes a front edge portion 11, a rear edge portion 12, a lower edge portion 13, and an upper edge portion 14.

The front edge portion 11 constitutes the front portion of the panel main body 10 in the door inner panel 100, and is formed so as to extend in the vertical direction from the upper end to the lower end of this front portion. The rear edge portion 12 constitutes the rear portion of the panel main body 10, and is formed so as to extend in the vertical direction from the upper end to the lower end of this rear portion. The lower edge portion 13 constitutes the lower portion of the panel main body 10, and is formed so as to extend in the vehicle longitudinal direction from the lower end of the front edge portion 11 to the lower end of the rear edge portion 12. The upper edge portion 14 constitutes the upper portion of the panel main body 10, and is formed so as to extend in the vehicle longitudinal direction from the upper end of the front edge portion 11 to the upper end of the rear edge portion 12.

The front edge portion 11 has a step portion 16 at least in a part thereof. In the embodiment shown in FIG. 1, the entire front edge portion 11 is constituted by the step portion 16. The step portion 16 includes a first wall portion 161, a second wall portion 162, a third wall portion 163, and a fourth wall portion 164, and these walls 161 to 164 are configured to be continuous in this order in a step-like manner. The first wall portion 161 and the second wall portion 162 are connected at a first bent portion B1 that constitutes the boundary between these walls 161 and 162. The second wall portion 162 and the third wall portion 163 are connected at a second bent portion B2 that constitutes the boundary between these walls 162 and 163. The third wall portion 163 and the fourth wall portion 164 are connected at a third bent portion B3 that constitutes the boundary between these walls 163 and 164.

The first wall portion 161 is located on the inside of the vehicle width direction and on the rear side of the vehicle front-rear direction relative to the second, third and fourth wall portions 162, 163 and 164. The first wall portion 161 is provided so as to extend in a band shape in the vertical direction in the front portion of the panel main body portion 10, and has an inner side surface S1 facing inward in the vehicle width direction. The direction in which this inner side surface S1 faces does not necessarily have to be parallel to the vehicle width direction, and may be slightly inclined with respect to the vehicle width direction. In the embodiment shown in FIG. 1, the first wall portion 161 is connected to the central portion 17 of the panel main body portion 10 via a step, but is not limited to this aspect. The first wall portion 161 may be connected to the central portion 17 without a step.

The second wall portion 162 is a portion formed so as to bend outward in the vehicle width direction relative to the first wall portion 161 at the first bend B1. The second wall portion 162 is provided so as to extend in a band shape in the vertical direction in the front portion of the panel main body portion 10, and has a front surface S2 facing forward in the vehicle longitudinal direction. The direction in which this front surface S2 faces does not necessarily have to be parallel to the vehicle longitudinal direction, and may be slightly inclined with respect to the vehicle longitudinal direction.

The second wall portion 162 has a door check arrangement portion, for example, in a portion surrounded by a dashed line II in FIG. 1. This door check arrangement portion is a portion for arranging components constituting a door check mechanism (not shown). Specifically, the door check arrangement portion may have, for example, a through hole for inserting a link member (rod-shaped member) (not shown) constituting the door check mechanism. The door check arrangement portion may also have, for example, an attachment portion for attaching a guide member (not shown) constituting the door check mechanism. The guide member is a member for guiding the link member while sliding on the surface of the link member in association with the opening and closing operation of the side door. Therefore, the second wall portion 162 needs to have a predetermined width in the vehicle width direction and a predetermined length in the vertical direction so that an area for providing the door check arrangement portion is secured.

The third wall portion 163 is a portion formed so as to bend forward in the vehicle longitudinal direction with respect to the second wall portion 162 at the second bend portion B2. The third wall portion 163 is provided so as to extend in a band shape in the vertical direction in the front portion of the panel main body portion 10, and has an inner surface S3 facing inward in the vehicle width direction. The direction in which this inner surface S3 faces does not necessarily have to be parallel to the vehicle width direction, and may be slightly inclined with respect to the vehicle width direction.

The third wall portion 163 has a seal arrangement portion. This seal arrangement portion is a portion for attaching a seal member (not shown). This seal member is a member for improving the sealability (airtightness) between the side door and a portion of the vehicle body that defines the door opening when the side door closes the door opening of the vehicle body. Therefore, the third wall portion 163 needs to have a predetermined width in the vehicle front-rear direction and a predetermined length in the vertical direction so that an area for providing the seal arrangement portion is secured.

The fourth wall portion 164 is a portion formed so as to bend outward in the vehicle width direction relative to the third wall portion 163 at the third bend B3. The fourth wall portion 164 is provided so as to extend in a band shape in the vertical direction in the front portion of the panel main body portion 10, and has a front surface S4 facing forward in the vehicle longitudinal direction. The direction in which this front surface S4 faces does not necessarily have to be parallel to the vehicle longitudinal direction, and may be slightly inclined with respect to the vehicle longitudinal direction.

The rear edge portion 12, the lower edge portion 13, and the upper edge portion 14 that constitute the peripheral portion may each have a step portion similar to the step portion 16 of the front edge portion 11, but the step portion is not essential for the rear edge portion 12, the lower edge portion 13, and the upper edge portion 14.

Figure 2 is a perspective view showing an outline of a press processing device used in the manufacturing method of the door inner panel 100. As shown in Figure 2, the press processing device includes a punch 31 (an example of a first die), a die 32 (an example of a second die), a blank holder 33, and a drive unit (not shown).

The punch 31 constitutes a male part of a press die. The punch 31 has a shape (convex shape) that corresponds to the shape of the outer surface of the door inner panel 100 in the vehicle width direction.

The die 32 constitutes the female part of the press die. The die 32 has a shape (concave shape) that corresponds to the shape of the inner surface of the door inner panel 100 in the vehicle width direction. The concave shape of the die 32 corresponds to the convex shape of the punch 31. The die 32 includes a die main body 32A and an outer periphery holding portion 32B. The die main body 32A is the part that constitutes the concave shape, and the outer periphery holding portion 32B is the part provided around the die main body 32A.

The blank holder 33 is a part for holding the outer periphery (held portion) of the blank piece 1. The blank holder 33 has a pressing surface 33S that faces the surface of the outer periphery holding portion 32B of the die 32. The blank holder 33 has a through hole 33a formed on the inside of the pressing surface 33S, which is large enough for the punch 31 to enter and exit.

The drive unit includes a die drive mechanism. This die drive mechanism operates to move at least one of the punch 31 and the die 32 in the approaching direction in which the punch 31 and the die 32 approach each other and in the opposite direction. Specifically, the die drive mechanism can displace at least one of the punch 31 and the die 32 in a stroke range between a separation position where the punch 31 and the die 32 are separated from each other and a mating position where the punch 31 and the die 32 are mated. Hereinafter, the mating position may be referred to as the bottom dead center.

In this embodiment, the die driving mechanism is configured to displace the die 32 downward in the approach direction and upward in the opposite direction to the approach direction, but is not limited to this aspect. The die driving mechanism may be configured to displace the punch 31 in the approach direction that brings the punch 31 closer to the die 32 and in the opposite direction, as in a modified example described below.

The drive unit may further include a holder drive mechanism. This holder drive mechanism operates to move the blank holder 33 in a direction parallel to the approach direction (downward in this embodiment) and in the opposite direction (upward in this embodiment). Specifically, the holder drive mechanism can displace the blank holder 33 in a stroke range between a position at an early stage of the forming process shown in FIG. 5 and a position at a final stage of the forming process shown in FIG. 8, which will be described later. Note that if the die drive mechanism is configured to be able to move both the die 32 and the blank holder 33, the holder drive mechanism can be omitted.

The blank material 1 is a plate-shaped material that has been punched or cut to a predetermined size for press processing using the press processing device. In this embodiment, an aluminum alloy plate material is used as the blank material 1. Examples of the aluminum alloy include, but are not limited to, 5000 series aluminum alloys, 6000 series aluminum alloys, and 7000 series aluminum alloys.

As shown in FIG. 2, in the press processing device according to this embodiment, the die 32 is disposed above the punch 31 and the blank holder 33. The punch 31 is supported by and fixed to a support member (not shown) included in the press processing device. The die 32 and the blank holder 33 are configured to be movable in the vertical direction relative to the punch 31 by the drive unit. However, the press processing device is not limited to the configuration according to this embodiment. For example, the press processing device may be configured such that the die 32 is disposed below or to the side of the punch 31 and the blank holder 33. The manufacturing method according to this embodiment will be described in detail below.

This manufacturing method includes an installation process, a holding process, and a forming process. The installation process is a process of installing the blank material 1 on the blank holder 33. The holding process is a process of holding the blank material 1 with the die 32 and the blank holder 33. The forming process is a process of forming the blank material 1 into the door inner panel 100 with the punch 31 and the die 32.

In the installation process, the die 32 is placed at a position above and away from the blank holder 33. In this installation process, the blank 1 is installed on the blank holder 33 so as to cover the through hole 33a of the blank holder 33. The blank 1 includes a central portion 1A, which is an area that blocks the through hole 33a of the blank holder 33 when installed on the blank holder 33, and an outer peripheral portion 1B that faces the pressing surface 33S of the blank holder 33.

In this installation process, the relative position of the blank holder 33 with respect to the punch 31 is preferably adjusted so that when the blank 1 is installed on the blank holder 33 in the installation process, at least a part of the upper surface of the punch 31 is in close proximity to or in contact with the lower surface of the central portion 1A of the blank 1. Specifically, in this embodiment, the relative position is adjusted so that the first forming surface 311, which is a part of the upper surface of the punch 31, is in close proximity to or in contact with the lower surface of the central portion 1A of the blank 1, as shown in FIG. 5, for example.

In the holding process, the die 32 is moved by the drive unit in a direction approaching the blank holder 33 (the approach direction). As a result, as shown in FIG. 5, the outer peripheral portion 1B of the blank 1 is sandwiched between the pressing surface 33S of the blank holder 33 and the surface (the lower surface in this embodiment) of the outer peripheral holding portion 32B of the die 32 with a predetermined pressing force. As a result, the blank 1 is held in a wrinkle-free state by the die 32 and the blank holder 33. At the time when this holding process is completed, the first forming surface 311 of the punch 31 is in proximity to or in contact with the lower surface of the center portion 1A of the blank 1.

After this holding step, the forming step described below is performed. The drive unit may move the die 32 and the blank holder 33 in the approaching direction during the holding step, temporarily stop the die 32 and the blank holder 33 when the holding step is completed (for example, the time shown in FIG. 5), and resume the movement of the die 32 and the blank holder 33 in the approaching direction at the start of the next forming step. The drive unit may also move the die 32 and the blank holder 33 in the approaching direction during the holding step, and continue the movement of the die 32 and the blank holder 33 in the approaching direction in the next forming step without stopping the die 32 and the blank holder 33 when the holding step is completed.

In the forming process, the die 32 and the blank holder 33 are moved relative to the punch 31 in the approach direction by the drive unit from the state shown in FIG. 5. As a result, the blank 1 is sandwiched between the punch 31 and the die 32 and begins to deform. Then, when the die 32 reaches the bottom dead center as shown in FIG. 8, the blank 1 is formed into the shape of the door inner panel 100.

Figure 3 shows the results of a simulation analysis of the distribution of strain occurring in the front edge portion 11 of the door inner panel 100 formed by deep drawing press processing. Figure 3 shows the analysis results of the distribution of the strain in the area surrounded by the dashed line II in Figure 1. Figure 3 shows that tensile strain occurs in the step portion 16 of the front edge portion 11 in the direction of the broken line arrow TS in Figure 3. For this reason, if the door inner panel 100 having the step portion 16 is deep drawn by pressing the aluminum alloy blank 1 using a conventional manufacturing method, there is a possibility that cracks will occur in the step portion 16.

Figure 3 also shows that almost no distortion occurs in the vertical direction in the step portion 16 of the leading edge portion 11. In other words, Figure 3 shows that in the press working, deformation in the step portion 16 of the leading edge portion 11 progresses in a plane strain state in which tensile strain occurs in the direction of the arrow TS, while almost no distortion occurs in the vertical direction.

The manufacturing method according to this embodiment can deep-draw the door inner panel 100 from the aluminum alloy blank 1 in a single deep drawing operation without causing cracks in the step portion 16 due to the tensile strain.

The following describes in detail the characteristics of the punch 31 and the die 32, mainly those of the portion for forming the step portion 16 of the front edge portion 11 of the door inner panel 100.

Figure 4 is a schematic diagram for explaining the shapes of the punch 31 and the die 32 used in the manufacturing method. Figure 4 shows the shapes of the punch 31 and the die 32 for forming the step portion 16 of the front edge portion 11. The approach direction arrow shown in Figure 4 indicates the direction in which the die 32 approaches the punch 31 in the forming process. The front-rear and inside-outside arrows shown in parentheses in Figure 4 indicate the directions when the side door including the door inner panel 100 formed by the punch 31 and the die 32 closes the door opening of the vehicle body.

Figures 5 to 8 are schematic cross-sectional views showing the forming steps of the manufacturing method. The positions of the cross sections in the cross-sectional views of Figures 5 to 8 are the positions shown by line V-V in the top diagram (diagram of the die 32) of Figure 2. Figure 5 shows an initial stage of the forming step that is performed after the holding step is completed. Specifically, Figure 5 shows the arrangement of the punch 31, die 32, blank holder 33, and blank 1 at the time when the holding step is completed and the time when the forming step is started. In this Figure 5, the blank 1 is held by the die 32 and the blank holder 33. Figure 8 shows the final stage of the forming step. Specifically, Figure 8 shows the arrangement of the punch 31, die 32, blank holder 33, and blank 1 at the time when the forming step is completed. As shown in Figures 5 to 8, in the forming process, the die 32 moves relative to the punch 31 from the position shown in Figure 5 in the approach direction (press direction), reaching the positions shown in Figure 6 and Figure 7 in that order, and finally reaching the mating position (bottom dead center) shown in Figure 8.

5, the punch 31 includes a central portion 310 and a peripheral portion located around the central portion 310. The peripheral portion has a portion corresponding to the front edge portion 11 of the door inner panel 100 as shown in FIGS. 4 and 5, and the portion has a first molding surface 311, a second molding surface 312, a third molding surface 313, and a fourth molding surface 314 that are continuous in a stepped manner. The die body portion 32A of the die 32 includes a central portion 320 and a peripheral portion located around the central portion 320. The peripheral portion of the die body portion 32A has a portion corresponding to the front edge portion 11 of the door inner panel 100, and the portion has a first molding surface 321, a second molding surface 322, a third molding surface 323, and a fourth molding surface 324 that are continuous in a stepped manner.

The first molding surface 311 and the second molding surface 312 of the punch 31 constitute a convex portion (first punch convex portion), and the first molding surface 321 and the second molding surface 322 of the die 32 constitute a concave portion (first die concave portion) having a shape corresponding to the first punch convex portion of the punch 31. The second molding surface 312 and the third molding surface 313 of the punch 31 constitute a concave portion (punch concave portion), and the second molding surface 322 and the third molding surface 323 of the die 32 constitute a convex portion (die convex portion) having a shape corresponding to the punch concave portion of the punch 31. The third molding surface 313 and the fourth molding surface 314 of the punch 31 constitute a convex portion (second punch convex portion), and the third molding surface 323 and the fourth molding surface 324 of the die 32 constitute a concave portion (second die concave portion) having a shape corresponding to the second punch convex portion of the punch 31.

In the following, the boundary between the first molding surface 311 and the second molding surface 312 of the punch 31 is referred to as the first boundary B11, the boundary between the second molding surface 312 and the third molding surface 313 of the punch 31 is referred to as the second boundary B12, and the boundary between the third molding surface 313 and the fourth molding surface 314 of the punch 31 is referred to as the third boundary B13. In addition, the boundary between the second molding surface 322 and the third molding surface 323 of the die 32 is referred to as the fourth boundary B14.

The first molding surface 311 of the punch 31 and the first molding surface 321 of the die 32 cooperate to form the first wall portion 161 of the step portion 16. The second molding surface 312 of the punch 31 and the second molding surface 322 of the die 32 cooperate to form the second wall portion 162 of the step portion 16. The third molding surface 313 of the punch 31 and the third molding surface 323 of the die 32 cooperate to form the third wall portion 163 of the step portion 16. The fourth molding surface 314 of the punch 31 and the fourth molding surface 324 of the die 32 cooperate to form the fourth wall portion 164 of the step portion 16.

The punch 31 and the die 32 are designed to satisfy the first and second conditions described below. The manufacturing method according to this embodiment uses the punch 31 and the die 32 designed as follows to form the door inner panel 100 having the step portion 16 from the aluminum alloy blank 1 in a single deep drawing operation, and can prevent cracks from occurring in the step portion of the formed door inner panel 100.

The first and second conditions described below are determined by the dimensions and angle of the punch 31, and the die 32 is designed to have a shape with dimensions and angles that correspond to the dimensions and angle of the punch 31.

[First condition]
The first condition is a condition that, among the first boundary portion B11 of the punch 31, the third boundary portion B13 of the punch 31, and the fourth boundary portion B14 of the die 32, a first process is performed in which the first boundary portion B11 comes into contact with the blank material 1, and then, at the same time as the fourth boundary portion B14 comes into contact with the blank material 1, or before the fourth boundary portion B14 comes into contact with the blank material 1, a second process is performed in which the third boundary portion B13 comes into contact with the blank material 1.

The first condition is expressed, for example, by the following formula (1):

In this formula (1), the dimensions H, H1, W, angle θ1, and angle θ2 are the values shown in FIG. 4. Specifically, the dimension H is the length in the approach direction (press direction) from the first boundary B11 of the punch 31 to the end E of the fourth forming surface 314 of the punch 31. This dimension H is the length corresponding to the dimension (vertical wall height) of the step portion 16 in the door inner panel 100 in the vehicle width direction. The end E is the intersection point where the extension line of the fourth forming surface 314 intersects with the extension line of the pressing surface 33S of the blank holder 33 in the state shown in the cross-sectional view of FIG. 8, that is, in the state where the punch 31 and the die 32 are arranged at the fitting position (bottom dead center).

The dimension H1 indicates the position of the third molding surface 313 of the punch 31. Specifically, the dimension H1 is the length in the approach direction from the second boundary portion B12 of the punch 31 to the end portion E of the punch 31. This dimension H1 is a length that can represent the position of the third wall portion 163 in the step portion 16 of the door inner panel 100 in the vehicle width direction.

In addition, the boundaries such as the first boundary B11, the second boundary B12, and the third boundary B13 may be formed not only by a sharp corner as shown in FIG. 4, but also by a curved portion having a curved shape. Even if the boundary is formed by a curved portion, if the radius of curvature is small (for example, the radius of curvature is 30 mm or less), the dimensions H and H1 can be set by regarding the boundary as having a shape like the sharp corner shown in FIG. 4. This also applies to the setting of the dimension W, the total distance L, and the distance _L0 described below. Since the effect of setting the dimensions as described above on the design of the punch 31 and the die 32 is small, even if the dimensions are set as described above, the door inner panel 100 can be deep-drawn from the blank 1 in one deep drawing without causing cracks in the step portion 16 by designing the punch 31 and the die 32 so that the first condition and the second condition described below are satisfied.

The dimension W indicates the width of the third molding surface 313 of the punch 31 (the width in the direction perpendicular to the approach direction). The dimension W corresponds to the width of the third wall portion 163 of the door inner panel 100 in the vehicle front-rear direction.

The angle θ1 is the angle of the fourth molding surface 314 of the punch 31. Specifically, the angle θ1 is the angle between the fourth molding surface 314 of the punch 31 and a straight line L1. The straight line L1 is a straight line that passes through the end E of the fourth molding surface 314, is perpendicular to the approach direction, and is parallel to the direction corresponding to the vehicle front-rear direction of the door inner panel 100.

The angle θ2 is the angle of the second forming surface 312 of the punch 31. The angle θ2 is the angle between the first forming surface 311 and the second forming surface 312 of the punch 31. Specifically, the angle θ2 is the angle between the first forming surface 311 and a virtual plane (dotted line L2 in FIG. 4) that extends the second forming surface 312 toward the die 32.

The first condition will be explained with reference to the specific examples shown in Figures 5 to 8.

The first step under this first condition is a step in which the first boundary portion B11 of the punch 31 comes into contact with the blank 1, as described above. This first step may be a step included in the holding step, or may be a step included in the forming step.

In this embodiment, as described above, the first forming surface 311 of the punch 31 is close to or in contact with the underside of the central portion 1A of the blank piece 1 at the time when the holding process shown in FIG. 5 is completed. Here, if the first boundary portion B11 of the punch 31 is in contact with the blank piece 1 at the time when the holding process is completed, the first process is included in the holding process. On the other hand, if the first boundary portion B11 of the punch 31 is close to the blank piece 1 but is not in contact with the blank piece 1 at the time when the holding process is completed, the first process is included in the forming process that is performed after the holding process.

As shown in FIG. 5, after the blank 1 is held by the die 32 and the blank holder 33 in the holding step, in the forming step, the drive unit moves the die 32 and the blank holder 33 in the approach direction (the press direction). As a result, the blank 1 held by the die 32 and the blank holder 33 also moves in the approach direction. In the initial stage of the forming step shown in FIG. 5, the first to fourth forming surfaces 321 to 324 (excluding the end E of the fourth forming surface 324) of the die 32 are not yet in contact with the blank 1. If the first boundary portion B11 of the punch 31 is not in contact with the blank 1 at the time when the holding step shown in FIG. 5 is completed, the die 32 and the blank holder 33 move in the approach direction from the initial stage of the forming step shown in FIG. 5 to perform the first step. In the first step, the first boundary portion B11 of the punch 31 comes into contact with the blank 1.

The second step is performed in the next stage of the forming step. In the second step, the die 32 and the blank holder 33 are further moved in the approach direction by the drive unit, so that the third boundary B13 of the punch 31 comes into contact with the blank 1 as shown in FIG. 6. When the third boundary B13 of the punch 31 comes into contact with the blank 1 in this second step, the bridge portion BR, which is a part of the blank 1, is positioned so as to bridge between the first boundary B11 and the third boundary B13. In other words, the bridge portion BR is supported at both ends by the first boundary B11 and the third boundary B13.

Note that "50 mm up from bottom dead center" in FIG. 6 means that the die 32 is 50 mm away from the bottom dead center when the punch 31 and die 32 are positioned at the bottom dead center where they fit together (as shown in FIG. 8). "20 mm up from bottom dead center" in FIG. 7 and similar descriptions in other figures also have the same meaning as above.

In the next stage of the forming process, the die 32 and blank holder 33 are further moved in the approaching direction by the drive unit, and the fourth boundary portion B14 of the die 32 comes into contact with the bridge portion BR of the blank piece 1 as shown in FIG. 7. This fourth boundary portion B14 comes into contact with the surface of the blank piece 1 opposite to the surface where the first and third boundaries B11, B13 come into contact. In addition, the fourth boundary portion B14 comes into contact with the middle portion of the bridge portion BR, i.e., the portion of the bridge portion BR between the two ends supported by the first and third boundaries B11, B13.

In the specific example shown in Figures 5 to 8, the third boundary portion B13 comes into contact with the blank piece 1 before the fourth boundary portion B14 comes into contact with the blank piece 1, but in the manufacturing method according to this embodiment, the third boundary portion B13 and the fourth boundary portion B14 may come into contact with the blank piece 1 at the same time.

At the final stage of the forming process, the die 32 and blank holder 33 are further moved in the approaching direction by the drive unit, and the die 32 reaches the bottom dead center (the mating position) as shown in FIG. 8, and the blank 1 is formed into the shape of the door inner panel 100.

[Second condition]
The second condition is a condition that the value obtained by dividing the total distance L obtained by adding the distance from the first boundary B11 to the second boundary B12 (in FIG. 4, the length from the first boundary B11 to the second boundary B12) and the distance from the second boundary B12 to the third boundary B13 (in FIG. 4, the length from the second boundary B12 to the third boundary B13 indicated by the symbol W) by the distance _L0 from the first boundary B11 to the third boundary B13 is equal to or less than an upper limit value preset based on the breaking limit of the blank material 1.

The second condition is expressed, for example, by the following formula (2). In the following formula (2), the upper limit is set to "A+1".

In this embodiment, A in formula (2) is set to the fracture limit value in a plane strain state as shown in the forming limit diagram shown in FIG. 10 described later, but is not limited to this form. A in formula (2) may be, for example, a value in which a safety factor is added to the fracture limit value. The fracture limit is the magnitude of strain on the forming limit line shown in FIG. 10.

Figure 9 shows the results of a simulation analysis of the reduction rate of the thickness of the blank material 1 in the region corresponding to the front edge 11 of the door inner panel 100 during the molding process of the manufacturing method. The position of the cross section in Figure 9 is a position on the V-V line in the top diagram of Figure 2 that includes the region corresponding to the front edge 11 of the door inner panel 100.

9, the cross section of the blank material 1 includes a portion (cross section) that is drawn as a straight line (broken line in the bottom drawing) spanning between the first boundary B11 and the third boundary B13 and extending diagonally downward to the right from the first boundary B11 toward the third boundary B13. This cross section is the portion indicated by the tip of the lead line with the symbol BR. In each of these three drawings, the blank material 1 is drawn three-dimensionally so as to extend in a planar manner in the depth direction from the cross section, and this portion (planar portion) that extends in the depth direction is shaded in a manner that corresponds to the range (Thinning (engineer value)) depicted on the left of FIG. As can be seen from the comparison of the shading of the planar portion and the range in the top and second figures in Figure 9, there is almost no distortion in the cross-sectional portion and planar portion of the blank material 1, i.e., there is almost no distortion in the bridge portion BR. Specifically, this is as follows:

The top diagram in Figure 9 shows a state in which, in the second step, the third boundary portion B13 of the punch 31 is in contact with the blank 1, the bridge portion BR of the blank 1 is positioned to bridge between the first boundary portion B11 and the third boundary portion B13, and the fourth boundary portion B14 of the die 32 is not yet in contact with the bridge portion BR of the blank 1.

The second figure from the top in Figure 9 shows the state when the punch 31 and the die 32 have come even closer to each other from the state shown in the top figure, and the fourth boundary portion B14 of the die 32 is about to come into contact with the bridge portion BR of the blank piece 1. The analysis results from the simulation shown in the top and second figures in Figure 9 show that there is almost no distortion in the bridge portion BR of the blank piece 1 at the time shown in these figures.

The bottom diagram in Figure 9 shows the state in which the punch 31 and the die 32 have come even closer to each other from the state shown in the second diagram, and the fourth boundary portion B14 of the die 32 has come into contact with the bridge portion BR of the blank piece 1, deforming the bridge portion BR. The analysis results from the simulation shown in the bottom diagram in Figure 9 indicate that distortion is beginning to occur in the bridge portion BR of the blank piece 1 at the time shown in this diagram.

9 shows that when the first boundary B11, the third boundary B13, and the fourth boundary B14 of the die 32 contact the blank 1 in an order that satisfies the first condition in the manufacturing method according to the present embodiment, the deformation of the bridge portion BR of the blank 1 progresses in a deformation form such as tensile bending. That is, when the bridge portion BR is supported at both ends by the first and third boundary portions B11 and B13 of the punch 31, the middle portion of the bridge portion BR is pressed by the fourth boundary portion B14 of the die 32, so that the bridge portion BR is deformed in a deformation form such as tensile bending in which the bridge portion BR is bent while being stretched. At this time, the portions of the blank 1 supported by the first and third boundary portions B11 and B13 (the both ends of the bridge portion BR) are suppressed from being displaced by the frictional force between the first and third boundary portions B11 and B13. Therefore, the amount of strain generated in the bridge portion BR corresponds to the change in length of the bridge portion BR (the change in the linear length of the bridge portion BR in the cross-sectional views of Figures 5 to 9).

Therefore, by designing the punch 31 and the die 32 so as to satisfy the first condition, the bridge portion BR of the blank 1 can be deformed in a deformation form such as tensile bending as described above in the forming process. If the bridge portion BR can be deformed in a deformation form such as tensile bending as described above, the behavior of the bridge portion BR in the forming process becomes simple. In other words, the allowable range of deformation of the bridge portion BR can be specified based on the relationship between the distance L ₀ (the length of the bridge portion BR before distortion occurs) and the total distance L (the length of the bridge portion BR after distortion occurs due to forming) (the second condition).

From the above, by designing the punch 31 and the die 32 so that the first and second conditions are satisfied, the door inner panel 100 can be drawn from the blank 1 without causing cracks in the bridge portion BR during the forming process. In other words, the manufacturing method according to this embodiment can provide design guidelines for preventing an increase in the number of steps in the manufacturing process and preventing cracks in the step portion 16, making it easier to design the punch 31 and the die 32.

Figure 10 is a diagram showing a schematic example of a forming limit diagram of the blank material used in the manufacturing method. Arrow A in Figure 10 indicates the fracture limit when the blank material 1 is deformed in a plane strain state. As described with reference to Figure 3, when the door inner panel 100 is deep-draw formed from the blank material 1 by press working, the deformation of the step portion 16 of the front edge portion 11 progresses in a plane strain state in which tensile strain occurs in the direction of the arrow TS in Figure 3 in the step portion 16 of the front edge portion 11, while almost no strain occurs in the vertical direction.

Therefore, the upper limit value in the second condition can be set based on the fracture limit A of the blank 1 in the plane strain state in FIG. 10. In other words, this fracture limit A is the value on the forming limit line in the graph shown in FIG. 10 when the minor strain is zero. This makes it even easier to design the punch 31 and the die 32.

The first and second conditions are satisfied by setting a number of parameters (the dimension H, the dimension H1, the width W, the angle θ1, and the angle θ2) to appropriate values, for example, as shown in FIG. 4.

Next, we will explain how to derive the above formula (1).

11 and 12 are schematic diagrams for explaining a method for deriving the formula (1). As shown in FIG. 11, in the forming process, the distance between the punch 31 and the die 32 at the timing when the third boundary portion B13 of the punch 31 contacts the blank piece 1 is Ap, and as shown in FIG. 12, in the forming process, the distance between the punch 31 and the die 32 at the timing when the fourth boundary portion B14 of the die 32 contacts the blank piece 1 is Ad.

Focusing on the distance of the portion enclosed in the dashed frame in FIG. 11, the following formula (3) holds based on the geometric relationship between the distance Ap and multiple parameters (the dimension H, the dimension H1, the width W, the angle θ1, and the angle θ2).

Transforming equation (3) gives us the following equation (4).

Next, when we focus on the distance in the portion enclosed by the dashed line frame in FIG. 12, the following formula (5) holds based on the geometric relationship between the distance Ad and multiple parameters (the dimension H, the dimension H1, the width W, the angle θ1, and the angle θ2).

Transforming equation (5) gives us the following equation (6).

Here, in order for the first condition to be satisfied, the following formula (7) must be satisfied.

By substituting the right-hand side of the above formula (4) and the right-hand side of the above formula (6) into the above formula (7) and rearranging, we obtain the following formula (1).

Next, we will explain how to derive the above formula (2).

In the forming process, the strain generated in the bridge portion BR of the blank 1 is expressed as a deformation amount relative to the original length _L0 . The condition showing that this deformation amount is equal to or less than the fracture limit value A in a plane strain state in the forming limit diagram shown in FIG. 10 is expressed by the following formula (8).

Transforming this equation (8) gives us the following equation (2).

[Modification]
The present invention is not limited to the above-described embodiment, but includes the following embodiments, for example.

(A) Regarding the Automobile Door In the above embodiment, the door inner panel 100 is a member constituting a part of the side door, but is not limited to this. The door inner panel may be a member constituting a part of an automobile door other than the side door, such as a rear door.

(B) Regarding the step portion In the above embodiment, the step portion 16 constitutes the front edge portion 11 of the door inner panel 100, but is not limited to this aspect. The step portion may constitute at least a part of the peripheral portion of the door inner panel. Specifically, the step portion may constitute, for example, the rear edge portion, the lower edge portion, or the upper edge portion.

(C) First and Second Molds In the above embodiment, the first mold (the punch 31) and the second mold (the die 32) are designed to satisfy the first and second conditions. However, the portion of the punch 31 and the die 32 designed to satisfy the first and second conditions does not have to correspond to the entire peripheral portion of the door inner panel 100, but may correspond to a part of the peripheral portion. In other words, it is sufficient that a portion that is likely to crack when deep-drawing is performed by the press working is selected as the part of the peripheral portion.

The portion of the punch 31 and the die 32 that is designed to satisfy the first and second conditions is, for example, a range having a vertical length including the cross section depicted in the cross-sectional views of Figures 5 to 9, and this range corresponds to the portion that is likely to crack when deep-drawing is performed by the press working.

(D) Regarding Formulas In the embodiment, the formula (1) is used as an example of a formula expressing the first condition that specifies the order in which the first boundary portion B11, the third boundary portion B13, and the fourth boundary portion B14 contact the blank piece 1 in the forming process. However, in the manufacturing method of the present invention, the formula expressing the first condition is not limited to the formula (1).

Similarly, in the embodiment, the formula (2) is used as an example of a formula expressing the second condition that specifies that the value obtained by dividing the total distance L by the distance _L0 is equal to or less than an upper limit value that is preset based on the fracture limit of the blank piece 1. However, in the manufacturing method of the present invention, the formula expressing the second condition is not limited to the formula (2).

(E) Relative Movement of Punch and Die In the above embodiment, the press working device is configured such that the punch 31 is fixed to the support member, and the die 32 can be moved in the approaching direction and the opposite direction by the drive unit, but is not limited to this aspect. The press working device may be configured such that the punch 31 can move in the approaching direction and the opposite direction, and the die 32 can move in the approaching direction and the opposite direction. Also, the press working device may be configured such that the die 32 is fixed to a support member (not shown), and the punch 31 can move relative to the die 32 in the approaching direction and the opposite direction.

The following is a specific description of a modified example in which the die 32 is fixed to the support member and the punch 31 is moved by the drive unit. Figure 13 is a diagram showing steps of a manufacturing method according to a modified example of the embodiment. In the manufacturing method according to the modified example shown in Figure 13, the die drive mechanism of the drive unit is configured to displace the punch 31 in the approach direction and in the direction opposite to the approach direction.

The holder drive mechanism of the drive unit operates to move at least one of the blank holder 33 and the die 32 in a direction in which the blank holder 33 and the die 32 approach each other and in the opposite direction. Specifically, the holder drive mechanism can displace at least one of the blank holder 33 and the die 32 in a stroke range between a separation position and a pressing position. The separation position is a position where the blank holder 33 and the die 32 are separated from each other. The pressing position is a position where the pressing surface 33S can press the blank 1 with the outer periphery 1B of the blank 1 interposed between the pressing surface 33S of the blank holder 33 and the surface of the outer periphery holding portion 32B of the die 32.

The manufacturing method according to this modified example includes an installation process, a holding process, and a forming process, similar to the above embodiment. The installation process is a process of installing the blank material 1 on the die 32. The holding process is a process of holding the blank material 1 by the die 32 and the blank holder 33. The forming process is a process of forming the blank material 1 into the door inner panel 100 by the punch 31 and the die 32.

In FIG. 13, the die 32 is drawn with the concave opening in the die body 32A facing upward, and the blank 1, the blank holder 33, and the punch 31 are drawn arranged so that they are stacked on top of the die 32 in that order, but the arrangement of these components is not limited to the arrangement shown in FIG. 13. In FIG. 13, these components are drawn in the above arrangement for convenience, so that the positional relationship between the punch 31, the die 32, the blank holder 33, and the blank 1 can be easily understood when explaining each process. Therefore, in this modified example, these components may be arranged upside down compared to FIG. 13, or may be arranged side by side.

In the installation process, as shown in the top diagram in FIG. 13, the blank 1 is installed on the die 32 so as to cover the die body portion 32A of the die 32. The blank 1 includes a central portion 1A, which is an area that faces the die body portion 32A when installed so as to cover the die body portion 32A, and an outer peripheral portion 1B that faces the outer peripheral holding portion 32B of the die 32.

In the holding process, the blank holder 33 is moved relatively toward the die 32 by the holder drive mechanism. As a result, as shown in the second diagram from the top in FIG. 13, the outer periphery 1B of the blank 1 is sandwiched between the pressing surface 33S of the blank holder 33 and the surface of the outer periphery holding portion 32B of the die 32 with a predetermined pressing force. As a result, the blank 1 is held in a wrinkle-free state by the die 32 and the blank holder 33. When this holding process is completed, the punch 31 is positioned away from the blank 1.

In the forming process, the punch 31 moves relative to the die 32 in the approach direction by the die drive mechanism, so that the punch 31 approaches or comes into contact with the blank 1 as shown in the third drawing from the top in FIG. 13 (for example, the early stage of the forming process as shown in FIG. 5). After that, the punch 31 moves further relative to the die 32 in the approach direction by the die drive mechanism, so that the blank 1 is sandwiched between the punch 31 and the die 32 and begins to deform (for example, the stage of the forming process as shown in FIG. 6 and FIG. 7). Then, the punch 31 reaches the bottom dead center as shown in the bottom drawing in FIG. 13, so that the blank 1 is formed into the shape of the door inner panel 100 (for example, the final stage of the forming process as shown in FIG. 8).

In this modified example, the punch 31 and the die 32 are also designed to satisfy the first and second conditions described above. In this modified example, the first step in the first condition, i.e., the step in which the first boundary portion B11 of the punch 31 comes into contact with the blank 1, is a step included in the forming step. In other words, the punch 31, which is positioned away from the blank 1 at the time the holding step is completed, moves in the approaching direction in the forming step, thereby performing the first step in which the first boundary portion B11 of the punch 31 comes into contact with the blank 1.

The second step is performed in the next stage of the forming step. In the second step, the punch 31 is further moved in the approach direction by the die driving mechanism of the driving unit, so that the third boundary B13 of the punch 31 comes into contact with the blank 1 (for example, the state shown in FIG. 6). When the third boundary B13 of the punch 31 comes into contact with the blank 1 in this second step, the bridge portion BR, which is a part of the blank 1, is positioned so as to bridge between the first boundary B11 and the third boundary B13. In other words, the bridge portion BR is supported at both ends by the first boundary B11 and the third boundary B13.

In the next stage of the forming process, the punch 31 is further moved in the approach direction by the die driving mechanism, and the fourth boundary portion B14 of the die 32 comes into contact with the bridge portion BR of the blank piece 1 (for example, the state shown in FIG. 7). Note that in this modified example, the third boundary portion B13 comes into contact with the blank piece 1 before the fourth boundary portion B14 comes into contact with the blank piece 1, but the third boundary portion B13 and the fourth boundary portion B14 may come into contact with the blank piece 1 simultaneously.

At the final stage of the forming process, the punch 31 is further moved in the approach direction by the die drive mechanism, and the punch 31 reaches the bottom dead center (engagement position) where it engages with the die 32, and the blank 1 is formed into the shape of the door inner panel 100 (for example, the state shown in Figure 8).

1 Blank 1B Outer periphery of blank 16 Step portion of inner panel 31 Punch (an example of a first die)
32 Die (an example of a second die)
100 Automobile door inner panel 161 First wall portion 162 of door inner panel Second wall portion 163 of door inner panel Third wall portion 164 of door inner panel Fourth wall portion 311 of door inner panel First forming surface 312 of punch Second forming surface 313 of punch Third forming surface 314 of punch Fourth forming surface 321 of die First forming surface 322 of die Second forming surface 323 of die Third forming surface 324 of die Fourth forming surface A of die Breaking limit B11 of blank material First boundary portion B12 of punch Second boundary portion B13 of punch Third boundary portion B14 of die Fourth boundary portion L of die Total distance L ₀ Distance from first boundary portion to third boundary portion

Claims (1)

A manufacturing method for manufacturing an automobile door inner panel by press-forming an aluminum alloy plate-shaped blank material with a first die and a second die, comprising:
The door inner panel has a step portion constituting at least a part of a peripheral portion of the door inner panel, and the step portion is configured such that a first wall portion, a second wall portion, a third wall portion, and a fourth wall portion are continuously arranged in this order in a stepped manner,
the first mold and the second mold each have a first molding surface, a second molding surface, a third molding surface, and a fourth molding surface which are continuous in a stepped manner in order to mold the first wall portion, the second wall portion, the third wall portion, and the fourth wall portion, respectively, the second molding surface and the third molding surface of the first mold constitute a recess, and the second molding surface and the third molding surface of the second mold constitute a protrusion having a shape corresponding to the recess,
a value obtained by dividing a total distance obtained by adding a distance from a first boundary between the first molding surface and the second molding surface in the first mold to a second boundary between the second molding surface and the third molding surface in the first mold and a distance from the second boundary to a third boundary between the third molding surface and the fourth molding surface in the first mold, by a distance from the first boundary to the third boundary is equal to or less than an upper limit value preset based on a breaking limit of the blank material,
The manufacturing method includes:
a first step of contacting the first boundary portion with the blank while the blank is placed between the first mold and the second mold and an outer periphery of the blank is held;
a second step of moving at least one of the first mold and the second mold in an approaching direction in which the first mold and the second mold approach each other, thereby bringing the third boundary portion into contact with the blank material at the same time as a fourth boundary portion between the second molding surface and the third molding surface of the second mold comes into contact with the blank material, or before the fourth boundary portion comes into contact with the blank material.

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