JP5890654B2 - Press forming method - Google Patents

Description

  The present invention relates to a press molding method of a hat cross-sectional shape part used for a vehicle body structural part of various transport machines such as automobiles, and more particularly to a technique for adjusting a wall opening amount after press molding.

  Platform integration is progressing in order to shorten the development period of new models and reduce automobile manufacturing costs. A platform is a chassis that consists of a mainframe with no body. By using a common platform, various types of suspensions, engines, and transmissions can be combined to create a variety of vehicles. As a result, an enormous number of parts and systems constituting the platform can be shared, and the number of parts can be reduced, and manufacturing costs such as die costs and parts inventory management costs can be greatly reduced. Furthermore, by using a common platform, derivative vehicles can be developed in a short period of time, thereby reducing development costs.

  However, it is not easy to satisfy various requirements such as collision safety, rigidity, and durability for all the developed models consisting of a common platform. In the vehicle body design that assumes the same part shape in order to share the mold, it is necessary to select the optimal material strength and thickness for each part according to the required performance for each developed vehicle. In order to share a press die on a common platform, it is necessary to press metal materials having different plate thicknesses or different strengths using the same press molding apparatus and the same press die. However, if the strength and thickness of the material are different, the size of the shape freezing defect called spring back that occurs when the molded product is taken out from the mold after molding changes, and it becomes difficult to ensure the dimensional accuracy of the parts. This shape freezing defect not only significantly impairs the appearance quality of the final product, but also causes welding defects in assembly operations performed after molding. Therefore, when pressing different plate thicknesses or different metal materials with the same press molding equipment and the same press mold, it is necessary to develop press processing technology that can obtain parts with the same dimensional accuracy regardless of the plate thickness and strength of the material. It is.

[Conventional technology]
Shape freezing failure is classified into angle change, wall warpage, twist, ridge line warpage (surface warpage), and punch bottom shape freezing failure depending on the phenomenon. In either case, after removing the molded product from the mold after molding, or by trimming unnecessary parts, the residual stress becomes the driving force by relaxing the restraint, and the part is elastically deformed (spring) to satisfy the new balance Back) occurs. For example, in the wall opening, the stress distribution in the plate thickness direction becomes a driving force, and the rigidity is mainly determined by the plate thickness. Alternatively, when a beam with a height difference or a curved hat cross section is drawn in the longitudinal direction, wall warpage and ridge line warpage and twisting occur, but if the curvature of curvature is small, the part rigidity increases, and the wall warpage decreases, and It is known that the difference in stress between the stretched flange deformed part and the contracted flange deformed part may give a torsional moment.

As a conventional countermeasure method for poor dimensional accuracy, a method of intentionally using a mold shape that is different from the product shape in anticipation of deformation so as to be within a predetermined dimension after springback is widely used. However, in order to ensure dimensional accuracy with the prospect of the mold shape, it is necessary to have a mold that allows for a springback for each material strength and thickness. The number of molds cannot be reduced, and the manufacturing cost reduction effect cannot be obtained.
On the other hand, as a method for reducing the springback, a method has been studied in which the vertical wall tension is increased by stepped drawing of a hat cross-section part, thereby reducing the amount of wall opening (for example, Patent Documents 1 and 2). It is not easy to make the stress distribution in the plate thickness direction uniform while avoiding the danger of the plate, and it is not possible to secure the specified dimensional accuracy for materials with different plate thickness and strength by controlling the wall opening Difficult and impractical.

JP 2004-344925 A JP 2004-31413 A

  Therefore, an object of the present invention is to provide a method for press-molding thin metal plates having different plate thicknesses or different material strengths using the same press-forming apparatus.

As a result of intensive studies, the present inventors have determined that when a metal material having a different plate thickness or different strength is pressed into a press-formed product having a hat cross-sectional shape using the same press-molding apparatus and the same press mold, As a method for controlling the opening amount, the inventors have conceived various aspects of the invention described below.
[1] A plurality of press forming apparatuses each including a punch, a die, and a pad that is located at a position facing the punch bottom surface of the punch and can hold a metal thin plate as a workpiece together with the punch. The workpieces having different thicknesses are sequentially press-molded into press-formed products having a hat cross-sectional shape,
The clearance between the punch and the die is set to a clearance when press-molding the workpiece having the thickest plate thickness among the plurality of workpieces having different plate thicknesses,
When press-molding a workpiece having the thickest thickness, the workpiece is pressed against the punch by the pad between the start of molding and the bottom dead center until the punch is pressed against the punch bottom surface. Press-molded with the workpiece in contact with the press-molded product,
Adjust the clearance between the pad and the punch between the start of molding and just before the bottom dead center when press-molding a workpiece that is thinner than the thickest workpiece. in between the punch and the first step for relatively moving the punch while slack workpiece bottom immediately below with respect to the die, the punch after the first step and up to the bottom dead center A second step of pressing the workpiece against the punch by the pad to eliminate sagging of the workpiece immediately below the bottom surface of the punch, and press-molding to form the press-molded product, Method.
[2] A plurality of press forming apparatuses including a punch, a die, and a pad that is located at a position facing the punch bottom surface of the punch and can hold a metal thin plate as a workpiece together with the punch. The workpieces of different material strengths are sequentially press-molded into press-formed products having a hat cross-sectional shape,
The clearance between the punch and the die when pressing the workpieces having different material strengths is constant,
When a workpiece having the lowest material strength is press-molded, the workpiece is pressed against the punch by the pad between the start of molding and the bottom dead center until the punch is pressed against the punch bottom surface. Press-molded with the workpiece in contact with the press-molded product,
When press-molding a workpiece with higher material strength than the workpiece with the lowest material strength , adjust the clearance between the pad and the punch between the start of molding and just before the bottom dead center in between the punch and the first step for relatively moving the punch while slack workpiece bottom immediately below with respect to the die, the punch after the first step and up to the bottom dead center A press forming method , wherein the work material is pressed against the punch by the pad to perform the press forming by the second step of eliminating the sag immediately below the bottom surface of the punch.

  According to the present invention, it is possible to control a wall opening amount of a press-formed product generated at the time of mold release after press forming, and thereby, by using the same press mold, metal thin plates having different plate thicknesses and different material strengths can be controlled in a predetermined manner. It can be press-molded with dimensional accuracy. As a result, it is possible to manufacture parts constituting a common platform for automobiles that simultaneously satisfy the weight reduction and the collision performance while suppressing the manufacturing cost.

FIG. 1 is a perspective view showing an external appearance of a press-formed product having a hat shape in sectional view. It is process drawing explaining the conventional press molding method. It is process drawing explaining the press molding method which is embodiment of this invention. It is process drawing explaining the press molding method which is embodiment of this invention. It is a cross-sectional schematic diagram which shows the press-molded product press-molded in the Example. It is a graph which shows the relationship between the wall opening amount of the press-molded product press-molded in the Example, and plate | board thickness. It is a graph which shows the relationship between the amount of wall opening of the press-molded product press-molded in the Example, and the amount of slack at the time of press molding. It is a graph which shows the relationship between the amount of wall opening of the press molded product press-molded in the Example, and the pad pressing force at the time of press molding. It is a graph which shows the relationship between the amount of wall opening of the press-molded product press-molded in the Example, and the tensile strength of a board.

  Hereinafter, a press molding apparatus and a press molding method to which the present invention is applied will be described in detail with reference to the drawings. In the drawings used in the following description, in order to make the features easy to understand, the portions that become the features may be schematically shown for convenience, and the dimensional ratios of the portions are not always the same as the actual ones. In addition, the materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto, and can be appropriately modified and implemented without departing from the scope of the invention. .

In the present embodiment, as an example of a press-formed product, a specific example of countermeasures against shape freezing failure according to the present invention will be described for a press-formed product 100 having a hat cross-sectional shape simulating a side member shown in FIG.
The press-formed product 100 shown in FIG. 1 includes a top wall portion 100a, a pair of vertical wall portions 100c and 100c connected to both ends in the width direction of the top wall portion 100a via bent portions 100b, and vertical wall portions 100c and 100c. Flange portions 100d and 100d connected to one end in the width direction are provided.

First, an example of press-molding the press-formed product 100 having the hat cross-sectional shape of FIG. 2A to 2C are schematic views showing the positional relationship among the punch 4, the die 1 and the pad 3 during press molding.
The press molding apparatus shown in FIG. 2 mainly includes a punch 4 attached to the upper holder, a die 1 supported by the lower holder, and a pad 3 supported by the lower holder and connected to the gas cylinder 3a. ing. A gas cylinder 4a is connected to the punch 4 so that the punch 4 can be raised and lowered.

In the press molding apparatus having the above structure, first, as shown in FIG. 2A, the metal thin plate 2 is disposed on the die 1 and the pad 3, the punch 4 is lowered, and the punch bottom surface 4b of the punch 4 and the pad 3 The thin metal plate 2 is sandwiched between the two.
Subsequently, as shown in FIG. 2 (b), the pad 3 and the punch 4 are moved to the bottom dead center while interlocking with the pad 3 and the punch 4 while the metal thin plate 2 is sandwiched between the pad 3 and the punch 4, so that FIG. As shown in FIG. 5, the press molded product 100 having a hat cross-sectional shape is formed.

Thereafter, when the press-formed product 100 is taken out from the mold, as shown in FIG. 5, the plate thickness direction stress distribution of the bent portion 100b becomes a driving force to cause a wall opening. This wall opening is caused by the result of elastic deformation according to the rigidity determined by the thickness of the metal thin plate and the part shape, as the stress distribution in the thickness direction acts as a bending moment. Therefore, in the press-molded product obtained by press-molding thin metal plates with different plate thicknesses using the same die with the same press-molding device, the press-molded product composed of thin metal plates has a low part rigidity, so The opening amount ΔW increases.
Further, in a press-molded product obtained by press-molding metal thin plates having different material strengths, the bending moment that is the driving force of the springback increases as the strength of the metal thin plate increases, and the wall opening amount ΔW increases. The wall opening amount ΔW is a difference between the maximum width W of the vertical wall portions 100c immediately after being processed by the mold and the maximum width W ′ of the vertical wall portions 100c after being taken out of the mold. .

  Therefore, as a result of intensive studies to solve the above-mentioned problems, the inventors have made a method of press-forming metal thin plates having different plate thicknesses or different material strengths using the same press-forming apparatus, and in particular, adjusting the amount of wall opening after press forming. The method was found and the present invention was completed. Below, the press molding method of this invention which press-forms a metal thin plate in hat cross-sectional shape is demonstrated using FIG.

  First, a press forming method for press forming a plurality of metal thin plates (workpieces) having different plate thicknesses will be described. In this press forming method, as shown in FIG. 3A, a metal thin plate, which is a workpiece, is pressed together with the punch 14 at a position facing the punch 14, the die 11, and the punch bottom surface 14 b of the punch 14. A press molding apparatus including a pad 13 that can be used is used. The punch 14 is attached to the upper holder, the die 11 is supported by the lower holder, and the pad 13 is supported by the lower holder via the gas cylinder 13a. A gas cylinder 14a is connected to the punch 14, and the punch 14 can be raised and lowered.

  Next, the clearance between the punch 14 and the die 11 when the punch 14 is at the bottom dead center is determined by pressing the workpiece having the thickest thickness among the workpieces having different thicknesses. Set to clearance. Specifically, the clearance is set to the thickness of the workpiece having the largest thickness.

When the workpiece having the thickest thickness is press-formed, the metal thin plate 2 is disposed on the die 11 and the pad 13 as shown in FIG. The thin metal plate 2 is sandwiched between the punch bottom surface 14 b and the pad 13.
Subsequently, as shown in FIG. 3B, with the metal thin plate 2 held between the pad 13 and the punch 14, in other words, the pad 13 and the punch 14 are held while the metal thin plate 2 is in contact with the punch bottom surface 14b. While being interlocked, it is lowered to the bottom dead center and formed into a press-formed product 100 having a hat cross-sectional shape as shown in FIG. In order to lower the pad 13 and the punch 14 to the bottom dead center while keeping the metal thin plate 2 in contact with the punch bottom surface 14b, for example, the pad 13 is always pressed against the punch bottom surface 14b by the pad 13. What is necessary is just to control the pressing amount of the metal thin plate by gas cylinder 13a.

  On the other hand, when press-molding a workpiece having a thickness smaller than that of the thickest workpiece, the metal thin plate 2 is set in the press-molding apparatus in the same manner as in FIG. As a first step, as shown in FIG. 4A, the punch 14 is moved with respect to the die 11 while slacking the workpiece immediately below the punch bottom surface 14 b from the start of molding to just before the bottom dead center. Move relative. That is, by adjusting the pressing force of the gas cylinder 13a, the punch 14 is moved relative to the die 11 in a state where the clearance between the pad 13 and the punch bottom surface 14b is larger than the plate thickness of the workpiece. Further, the amount of slack of the thin metal plate can be adjusted by the clearance between the pad 13 and the punch bottom surface 14b.

Next, as shown in FIG. 4B, as the second step, the slack of the thin metal plate 2 immediately below the bottom surface 14b of the punch 14 from the first step until the bottom dead center is formed. Is solved. Specifically, for example, the metal thin plate 2 immediately below the punch bottom surface 14b is pressed against the punch bottom surface 14b by the pad 13. In this way, the press-molded product 100 that has been press-molded is obtained by sequentially performing the first and second steps.
In order to sag the metal thin plate 2 immediately below the punch bottom surface 14b or to press the metal thin plate 2 immediately below the punch bottom surface 14b against the punch bottom surface 14b, the amount of pressing against the metal thin plate 2 may be controlled by the gas cylinder 13a.

  In the second step, the bending area is expanded by supplying the slack of the thin metal plate 2 generated between the pad 13 and the punch 14 to the vertical wall portion 100c immediately before the bottom dead center. The wall opening amount ΔW of the vertical wall portion 100c can be adjusted by balancing the spring back and the spring go. Thereby, when the metal thin plates having different plate thicknesses are sequentially press-formed by the same press forming apparatus, the wall opening amount ΔW after press forming can be adjusted, and the metal thin plate 2 having different plate thicknesses is press-formed. It is possible to secure the same amount of wall opening.

  Further, as another example of the press molding method of the present invention, by using the same press molding apparatus, by sequentially molding a plurality of workpieces of different material strength into a press molded product with a hat cross-sectional shape, It is possible to adjust the wall opening amount ΔW after press molding. The material strength here can be exemplified by, for example, the tensile strength of a thin metal plate.

In this case, the clearance between the punch 14 and the die 11 when the punch 14 is at the bottom dead center is constant regardless of a plurality of workpieces having different material strengths. Specifically, the clearance is set to the same dimension as the plate thickness of the workpiece.
Then, when press-molding a workpiece made of a thin metal plate having the lowest material strength, a metal is formed on the punch bottom 14b after the punch 14 reaches the bottom dead center after the molding starts, as in the case of FIG. A press-formed product 100 is formed by press molding in a state where the thin plate is in contact.

  In addition, when press-molding a work material having a material strength higher than that of the work material having the lowest material strength, as in the case of FIG. 4, a punch is performed between the start of forming and immediately before the bottom dead center. The first step of moving the punch 14 relative to the die 11 while slacking the thin metal plate directly under the bottom surface 14b, and the punch bottom surface 14b between the first step and the subsequent steps until the bottom dead center of the molding. The second step of eliminating the sag immediately below is press-molded to obtain a press-molded article 100.

  In the second step, the bending area is expanded by supplying the slack of the thin metal plate 2 generated between the pad 13 and the punch 14 to the vertical wall portion 100c immediately before the bottom dead center. The wall opening amount ΔW of the vertical wall portion 100c can be adjusted by balancing the spring back and the spring go. As a result, when the metal thin plates having different material strengths are sequentially press-molded with the same press molding apparatus, the wall opening amount ΔW after press molding can be adjusted, and when the metal thin plates with different material strengths are press-molded. It is possible to secure the same amount of wall opening.

Hereinafter, the present invention will be specifically described based on examples.
As the metal thin plate, a high strength steel plate having a thickness of 1.2 mm, 1.4 mm, 1.6 mm and a tensile strength of 590 MPa was prepared. First, a press-formed product having a hat cross-sectional shape as shown in FIG. 5 was manufactured by conventional foam molding shown in FIG. The clearance between the punch and the die was 1.6 mm based on the thickest material. FIG. 6 shows the result of the wall opening amount ΔW before and after the spring back defined in FIG. 5. It can be seen that the wall opening amount ΔW increases as the plate thickness decreases. As can be seen from this, when metal thin plates with different plate thicknesses are press-formed with the same mold, the wall opening amount ΔW greatly changes due to the spring back, and it is not easy to ensure the same dimensional accuracy. Recognize.

  Next, it press-molded by the method of this invention shown in FIG.3 and FIG.4 using the same metal thin plate as the above. Here, the pressing force of the pad 13 is changed to 2, 5, 15, 20, and 30 kN by adjusting the gas cylinder 13a, and the clearance between the punch 14 and the pad 13 and the wall opening amount ΔW of the press-molded product after the springback are performed. Was actually measured.

FIG. 7 shows the relationship between the slack amount c [mm] obtained by subtracting the plate thickness from the clearance between the punch 14 and the pad 13 and the wall opening amount ΔW [mm], and FIG. 7 shows the pad pressing force f [kN] and the wall opening amount ΔW. The relationship of [mm] is shown in FIG. As shown in FIG. 7, there is a correlation between the sag amount c and the wall opening amount ΔW, and it can be seen that the wall opening amount ΔW decreases as the sag amount c increases regardless of the plate thickness. Further, it can be seen that by adjusting the sag amount c, it is possible to ensure a dimensional accuracy equivalent to the wall opening amount ΔW of the workpiece when press-molding by the conventional method (actual value where the sag amount is 0 in FIG. 7).
Further, from FIG. 8, when the pressing force of the pad 13 is controlled, the amount of sag c changes, and when pressing is performed by the conventional method by setting the optimal pressing force (30 kN with a high pad pressing force in FIG. 8). It can be seen that a dimensional accuracy equivalent to the wall opening amount ΔW of the workpiece of (actually measured value) can be secured.

  Further, in FIG. 9, conventional foam molding (pad 13 and punch) is applied to a high strength steel plate having a thickness of 1.2 mm and a tensile strength of 590 MPa class, and a high strength steel sheet having a thickness of 1.2 mm and a tensile strength of 780 MPa class. 14 shows a result when the press pressing is performed by adjusting the pressing force of the pad 13 to a plate thickness of 30 kN) and the pressing force of the pad 13 to 5 kN to ensure a slack between the pad 13 and the punch 14. As shown in FIG. 9, it can be seen that the same dimensional accuracy can be secured by the present invention even for materials having different strengths.

  2 ... Metal thin plate (workpiece), 11 ... Die, 13 ... Pad, 14 ... Punch, 14a ... Punch bottom surface, 100 ... Press-formed product.

Claims (2)

A plurality of different plates using a press forming apparatus comprising a punch, a die, and a pad that is positioned opposite the punch bottom surface of the punch and can hold a metal thin plate as a workpiece together with the punch. It is a method of press-molding thick workpieces sequentially into a press-molded product with a hat cross-sectional shape,
The clearance between the punch and the die is set to a clearance when press-molding the workpiece having the thickest plate thickness among the plurality of workpieces having different plate thicknesses,
When press-molding a workpiece having the thickest thickness, the workpiece is pressed against the punch by the pad between the start of molding and the bottom dead center until the punch is pressed against the punch bottom surface. Press-molded with the workpiece in contact with the press-molded product,
Adjust the clearance between the pad and the punch between the start of molding and just before the bottom dead center when press-molding a workpiece that is thinner than the thickest workpiece. in between the punch and the first step for relatively moving the punch while slack workpiece bottom immediately below with respect to the die, the punch after the first step and up to the bottom dead center A second step of pressing the workpiece against the punch by the pad to eliminate sagging of the workpiece immediately below the bottom surface of the punch, and press-molding to form the press-molded product, Method. A plurality of different materials using a press forming apparatus comprising a punch, a die, and a pad that is positioned opposite to the punch bottom surface of the punch and can hold a metal thin plate as a workpiece together with the punch. It is a method of press-molding a strong work material sequentially into a press-molded product with a hat cross-sectional shape,
The clearance between the punch and the die when pressing the workpieces having different material strengths is constant,
When a workpiece having the lowest material strength is press-molded, the workpiece is pressed against the punch by the pad between the start of molding and the bottom dead center until the punch is pressed against the punch bottom surface. Press-molded with the workpiece in contact with the press-molded product,
When press-molding a workpiece with higher material strength than the workpiece with the lowest material strength , adjust the clearance between the pad and the punch from the start of molding until just before the bottom dead center. wherein between up to bottom dead center from said a first step for relatively moving the punch relative to the die while slack workpiece immediately below the punch bottom, the punch after the first step Te A press forming method , wherein the work material is pressed against the punch by the pad and the second step of eliminating the sag just below the bottom surface of the punch is press formed into the press formed product.

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