JP5194982B2 - Press molding method and apparatus excellent in shape freezing property - Google Patents

Description

The present invention relates to spring back to reduce the press forming method and apparatus is excellent in shape fixability with improved dimensional accuracy of the parts hat-shaped cross-section beam which occurs in press forming a metal plate.

  Due to the demand for collision safety and weight reduction, the application of high-strength steel sheets to automobile bodies is progressing. These high-strength steel plates can increase the absorbed energy and strength at the time of collision without increasing the plate thickness. However, in the case of press working, a shape freezing defect called a springback occurs with an increase in the strength of the steel sheet, making it 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 the assembly work performed after molding. Therefore, countermeasures for shape freezing defects are particularly problematic for structural parts such as members and frames. .

  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, for bending angle changes and wall warpage, the stress distribution in the plate thickness direction is the driving force, and the rigidity is mainly determined by the plate thickness. Alternatively, if a beam with a height difference or a curved hat cross section is drawn in the longitudinal direction, wall warpage, ridge warpage (surface warpage), and twisting occur, but if the curvature of curvature is small, the rigidity of parts increases and the wall warpage decreases. In addition, it is known that there is a possibility that a difference in stress between the stretched flange deformed portion and the contracted flange deformed portion gives a torsional moment (for example, see Non-Patent Document 1).

  As a conventional countermeasure method for dimensional accuracy defects, a press molding method that uses a mold shape that is intentionally different from the product shape in anticipation of deformation so as to fit within a predetermined dimension after springback (for example, Patent Document 1, Patent Document 2, Non-Patent Document 1) is widely known. However, in this method, in order to obtain a desired mold shape, it is necessary to repeatedly correct the mold shape by machining several times to several tens of times, which requires a large number of man-hours and skilled skills, and costs There is a problem that it becomes higher. In addition, when trying to ensure dimensional accuracy with the expectation of the mold shape, it cannot be said that sufficient accuracy has been obtained for the accuracy prediction of the springback analysis using the widely used forming simulation. Trial-centered adjustment through trial and error is a heavy burden. Furthermore, many conventional springback countermeasures are for two-dimensional shape defects such as angle changes and wall sleds, and three-dimensional springs such as ridgeline sleds (plane sleds) and twists that are problematic for parts with complex shapes. There has been no suggestion of a countermeasure for back-up or a method for coping with these simultaneously.

  In addition, in press forming with a hat-shaped cross-sectional shape, as a press forming method that can prevent shape defects such as springback at the punch shoulder and wall warp at the punch side wall, curvature ρ of wall warp generated by press forming, wrinkle A relationship of ρ = F (BHF) is given to the pressing force BHF, and a wrinkle pressing force is applied so as to reduce the curvature based on this relationship, and the punching stroke is just before the bottom dead center after the start of molding. In the meantime, there has been proposed a press molding method in which a deflection is provided on a metal plate by a deflection adjusting device provided at the punch head and the deflection is eliminated at the bottom dead center (see, for example, Patent Document 3). . However, in this method, the movement of the material is restrained by the wrinkle presser, so that the residual stress of compression is introduced into the material by determining and pushing the slack of the punch head, resulting in a defective shape and twist of the punch bottom. There is. Furthermore, this method is for two-dimensional shape defects such as wall warpage of the beam beam section of the hat and changes in the angle of the ridge line, and measures against three-dimensional springback such as torsion and warping, or these can be performed simultaneously. No countermeasures have been proposed.

JP-A-8-243657 JP 2003-33828 A JP 2000-42635 A "Press Forming Difficulty Handbook 3rd Edition", published by Nikkan Kogyo Shimbun, March 30, 2007, pages 365-377

Therefore, in view of the above situation, the present invention performs press molding without correcting the mold shape, and three-dimensional shapes such as a two-dimensional shape defect such as an angle change due to a springback and a ridge line warp (surface warp). An object of the present invention is to provide a hat-shaped cross-section beam press-molding method and apparatus capable of preventing defects and obtaining a press-molded product and having excellent shape freezing property.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the relative displacement between the die and the punch from the start of molding is reduced when press-molding a part whose cross-sectional shape changes or a curved hat-shaped cross-sectional beam. Until it reaches zero, the pad position is controlled so that the relative displacement between the pad and the punch is within a predetermined range, and the sag of the metal plate, the workpiece, is controlled at the bottom of the punch. By forming the part shape while interlocking and controlling the pad and die so that there is no slack in the bottom, it is possible to prevent shape defects such as angle change due to springback and ridge warp (surface warpage), and excellent shape freezing property As a result, the present invention was completed.

  The gist of the present invention is as follows.

(1) Using a press forming device equipped with a punch and die and a pad that presses the metal plate of the workpiece in conjunction with the punch, the metal plate is formed into a hat-shaped cross-sectional shape by the relative linear movement of the punch and die. In the press molding method, the punch position, the die position, and the pad position are measured during press molding, the measured punch position zP [mm], the measured die position zD [mm], and the measured pad position zPad [mm]. ] Until the relative displacement of the die and the pad (zD-zPad) [mm] becomes zero from the start of molding until the relative displacement of the pad and the punch (zPad-zP) [mm] is 10 to 20 mm. A hat-shaped cross-section beam press excellent in shape freezing property, wherein the pad position zPad [mm] is controlled so as to be within the range and press-molded. Molding method.

(2) From the start of molding until the relative displacement (zD-zPad) between the die and the pad becomes zero, the pad position zPad [ mm], the pad and the die are interlocked so that there is no sagging of the punch bottom from the procedure after the procedure to the bottom dead center of the molding. The press-forming method of a hat-shaped cross-sectional beam excellent in shape freezing property as described in (1) above, comprising second means for forming into a part shape while controlling.

(3) Press forming of a hat-shaped cross-sectional beam excellent in shape freezing property as described in (1) or (2) above, wherein the punch and pad are driven by a hydraulic press or servo press Method.

(4) A press forming apparatus that includes a punch, a die, and a pad, and forms a metal plate into a hat-shaped cross-sectional shape by a relative linear movement of the punch and the die, and includes a pad that presses the metal plate in conjunction with the punch. A punch position measuring unit, a die position measuring unit, and a pad position measuring unit. The punch position zP [mm] measured by the punch position measuring unit, the die position zD [mm] measured by the die position measuring unit, and the pad position measuring. The pad position zPad [mm] based on the relative displacement (zD-zPad) [mm] of the die and pad and the relative displacement (zPad-zP) [mm] of the pad and punch from the pad position zPad [mm] measured by the part A hat-shaped cross-section beam press molding apparatus having excellent shape freezing property, comprising a pad position control unit for controlling the shape.

(5) The hat-shaped cross-section beam press molding apparatus with excellent shape freezing property according to (4) above, wherein the pad drive mechanism includes an electric servo motor.

  According to the present invention, the metal plate can be formed by controlling a predetermined amount of sag between the punch bottom and the pad, and the bending region is expanded by crushing the formed sag with the final pressing in the later stage of molding. Therefore, it balances the spring back of the vertical wall and the spring go and prevents two-dimensional shape defects such as angle changes and ridge line warpage (surface warpage), and is excellent in shape freezing without shape defects. A press-molded product can be obtained, and correction of the press die for avoiding a defective shape of the press-molded product as in the prior art becomes unnecessary.

  Hereinafter, the present invention will be described in detail.

  In a beam having a hat-shaped cross-sectional shape whose cross-sectional shape changes, in addition to a two-dimensional shape defect such as a wall warp or an opening, a ridge line warp (surface warp) and a twist occur simultaneously. Since such a three-dimensional shape defect has a complicated phenomenon, it is not easy to plan a countermeasure for solving the shape defect.

  FIG. 1 is a schematic view of a press-formed product of a side member having a hat-shaped cross-section, which is a member part of an automobile. Here, a specific example of shape freezing countermeasure according to the present invention will be described for the shape of FIG. 1 simulating a side member as an example of a shape defect due to press molding.

  First, an example in which a 1.4 mm-thick thin plate of a 980 MPa class high-tensile steel plate (High Ten) is press-formed into a hat-shaped cross-sectional shape in FIG. 1 by conventional foam forming will be described with reference to FIGS. 2 and 3. .

  FIG. 2 is a diagram showing an outline of a press molding apparatus, and FIG. 3 is a diagram for explaining a punch, die, and pad control method of a conventional foam molding method. 3A is a diagram showing the positional relationship of the punch, die, and pad in the z direction during press molding, and FIGS. 3B to 3D are schematic diagrams showing the positions of the punch, die, and pad during molding. FIG.

  As shown in FIG. 2, the press forming apparatus forms the thin plate 3 into a hat-shaped cross-sectional shape using a die 1, a pad 2, and a punch 4. In the conventional foam molding method, a punch 4 and a pad from the start of molding as shown in FIG. 3 (b) before the bottom dead center 40mm for a side member having a hat-shaped cross section having a height of 50 mm (see z direction in FIG. 1). 2, press the thin plate 3 to raise the punch 4 and the pad 2, press form, and as shown in FIG. 4 and the die 1 are used to continue press forming. Subsequently, as shown by the forming bottom dead center in FIG. The positional relationship in the z direction (see FIG. 1) of the punch (zP), die (zD), and pad (zPad) at the time of press molding is such that the punch (zP) position is the punch bottom position, and the die (zD) position is As shown in FIG. 3 (a), when the die position where the punch bottom is the bottom dead center and the pad (zPad) position are the positions of the surface facing the punch bottom, the respective z-direction positional relationships are as shown in FIG. In press molding, since the thin plate 3 is pressed by the punch 4 and the pad 2 and is pressed while the thin plate 3 is restrained from moving during the molding, z between the punch (zP) and the pad (zPad) from the start of molding to the end of molding. The direction distance is zero.

  When a hat cross-section beam having a height difference in the height direction (z direction in FIG. 1) is formed by this conventional method, the post-springback shape rather than the bottom dead center shape 12 as shown in FIG. The right side of 13 goes up in the z direction. This is because the restraint is eased by removing the molded product from the mold after molding, and the stress distribution at the bottom dead center of the molding becomes a driving force, and the part is elastically deformed to satisfy the new balance. In this case, the stress distribution in the thickness direction of the vertical wall portion becomes a driving force to open the vertical wall, cause the upper surface to bend, and facilitate warping.

  That is, the z-direction deflection in the yz plane of the convex ridge line 14 shown in FIG. 1 works to linearize the upper surface that is bent in the zx plane. At this time, since the three points on the left side of the convex ridge line are constrained in the z direction, a displacement in the z direction (surface warpage) is generated by a moment around the y axis. In the hat-shaped cross-sectional beam shape in which the cross-sectional shape changes, a warp occurs through the opening and bending of the vertical wall. FIG. 4 shows the state of warpage of the z-direction displacement distribution after springback when pressed by the conventional method. The numerical values in FIG. 4 indicate the z-direction displacement distribution in the state of warping.

  From such a point of view, the inventors have considered a springback mechanism and have come up with the idea that countermeasures against opening of the vertical wall are effective in suppressing warpage.

  Therefore, the present inventors have adopted a springback mechanism for a three-dimensional shape defect in which a ridge line warp (surface warp) occurs simultaneously in addition to such a two-dimensional shape defect such as a wall warp or an opening. As a result, the material at the bottom of the punch is controlled by controlling the pad position so that the relative displacement between the pad and the punch is within a predetermined range from the start of molding until the relative displacement between the die and the pad becomes zero. The method of forming into a part shape while controlling the pad and die so that there is no sag in the bottom of the punch from the bottom to the bottom dead center of the mold to solve the defective shape of the pressed product. The present invention has been found by finding it effective.

The present invention measures the punch position, the die position, and the pad position during press molding, and the positional relationship between the measured punch position zP [mm], the measured die position zD [mm], and the measured pad position zPad [mm]. However, until the relative displacement (zD-zPad) [mm] between the die and the pad becomes zero from the start of molding, the relative displacement (zPad-zP) [mm] between the pad and the punch is in the range of 10 to 20 mm. As described above, the position zPad [mm] of the pad is controlled, and the metal plate is press-molded into a hat-shaped cross-sectional shape by the relative linear movement of the punch and the die.

  According to the present invention, since the bending region is expanded by crushing the slack of the material generated between the punch bottom and the pad with the final pressing in the later stage of molding, the shape is poor by balancing the spring back and the spring go of the vertical wall You can get a vertical wall without.

  A case where a side member having a hat-shaped cross section having a height of 50 mm (see the z direction in FIG. 1) according to the present invention is press-molded will be specifically described.

  As shown in FIG. 2, the press forming apparatus forms a thin plate (metal plate) 3 into a hat-shaped cross-sectional shape using a die 1, a pad 2, and a punch 4.

  FIG. 5 is a diagram showing the positional relationship of the punch, die, and pad in the z direction during press molding of the present invention, and FIGS. 5B to 5E are schematic views showing the positions of the punch, die, and pad during molding. FIG.

  At the start of pressing, the pad 2 and the punch 4 are formed so that a slack 3 ′ is formed by sagging the thin plate 3 as a workpiece on the bottom of the punch 4 as shown in FIG. Relative displacement (zP-zPad) is controlled to be within a predetermined range, and then, as shown in FIGS. 5 (c) to 5 (e), the bottom dead center of 10 mm {see FIG. 5 (c)} and thereafter Molding into a part shape is performed while controlling the pad 2 and the punch 4 in an interlocked manner so as to eliminate the slack 3 ′ at the punch bottom {see FIGS. 5 (d) and 5 (e)}. In this way, a metal plate corresponding to the amount of sag is supplied from the punch bottom to the corner portion of the hat-shaped cross-sectional shape by press forming with a slack in the thin plate of the workpiece at the punch bottom, resulting in a defective shape The tensile residual stress and the compressive residual stress at the corners causing the occurrence of the offset are offset, and as shown in FIG. 6B, the spring back of the vertical wall and the spring go are balanced to reduce the wall opening, and at the same time, in the z direction. The sledding is greatly improved. FIG. 7 shows the state of warpage of the z-direction displacement distribution after springback according to the method of the present invention. The numerical values in FIG. 7 indicate the z-direction displacement distribution in the state of warping. According to the present invention, it can be seen that the value of the z-direction displacement distribution in the state of warpage is smaller than that in the state of warpage shown in FIG. That is, two-dimensional shape defects and three-dimensional shape defects are suppressed.

  The punches and pads can be driven by a hydraulic press or a servo press, and preferably formed by a servo press equipped with an electric servo motor. This is because the positions of the punch and the pad can be easily measured by detecting the rotational angular velocity of the electric servo motor.

  FIG. 5A shows the relative displacement between the die (zD) and the pad (zPad) and the relative displacement between the pad (zPad) and the punch (zP) in the press molding described above. At the position of the punch (zP), die (zD), and pad (zPad) in the z direction during press molding, the relative displacement (zD-zPad) of the die (zD) and the pad (zPad) is the bottom of the die and the pad. The relative distance between the upper part of the pad (zPad) and the punch (zP) (zPad-zP) means the relative distance between the lower part of the pad and the bottom of the punch. Here, the relative displacement of the pad (zPad) -punch (zP) is the amount of sag. When the amount of sag exceeds 20 mm, a so-called spring go occurs in which the vertical wall faces inward, and when the amount of sag is less than 10 mm, a so-called spring back is generated that opens the vertical wall. Therefore, it is necessary to control the relative displacement of the pad (zPad) -punch (zP) as the amount of sag to 10 to 20 mm.

  Next, the effect of the amount of material sag at the punch bottom on the amount of warpage (displacement in the z direction at the right end of the component in FIG. 7) will be described for the hat-shaped cross-section beam.

  The relative displacement between the pad and the punch was changed to 0 (conventional method in which the pad and the punch were brought into close contact during the molding), 5 mm, 10 mm, 20 mm, and 50 mm, and the amount of warpage after the spring back was investigated. The results are shown in FIG. 8 in the relationship between the relative displacement (zPad-zP) [mm] between the pad and the punch and the surface warp. As shown in FIG. 8, there is a correlation between the amount of sagging at the punch bottom and the amount of warpage. The larger the amount of sagging, the more the surface warpage is improved, but if the amount of sagging is too large, the right end is lowered. (Z direction minus is shown) It turns out that it becomes a spring go.

  In this way, by controlling the relative displacement between the pad and the punch to the optimum amount, it is possible to ensure the component dimensional accuracy (shape freezing accuracy), and the optimum amount of the relative displacement between the pad and the punch is in the range of 10 to 20 mm. It turned out to be within. Preferably it is 12 mm-18 mm.

  Next, a specific embodiment of pad position control in the press molding apparatus of the present invention will be described using the block diagram of the configuration of the pad control apparatus in FIG.

  The pad drive mechanism is composed of an electric servo motor 5 and a power transmission mechanism. The encoder 6 (pad position detection means) detects the rotational angular velocity of the electric servo motor, and the pad position is calculated by the pad position measuring unit 7 using the detected value. Further, the positions of the punch and die are also calculated by the punch position measuring unit and the die position measuring unit via the respective encoders.

  Here, a pad control method will be described along with an application example to a hat-shaped cross-section beam having a height difference.

  First, relative displacement (zD−) between the punch position zP [mm], the die position zD [mm], and the pad position zPad [mm] measured by the punch position measurement unit, the die position measurement unit, and the pad position measurement unit. zPad) [mm] and the relative displacement of the pad and punch (zPad−zP) [mm] are calculated. In the next step, if the die is at a position relatively higher than the pad (zD-zPad> 0), the pad position control unit is set so that zPad = zP + X [mm] (here, X is set to 10 [mm]). A position command signal is output from 10 to the servo amplifier 11, and a drive current is supplied from the servo amplifier 11 to the electric servomotor 5. If | zPad−zP | <Y [mm] (here, Y is set to 0.1 [mm]), the pad controller 10 moves to the servo amplifier 11 so as to approach zPad = zD [mm]. By outputting a position command signal and supplying a driving current from the servo amplifier 11 to the electric servomotor 5, the position of the pad is controlled.

  In the present invention, press forming can be performed by controlling the pad position to a predetermined position by the pad position control mechanism described above.

  In addition, the hydraulic press can control the position of the punch or die by adjusting the hydraulic pressure with a displacement meter that detects the position of the pad, die, or punch and a servo valve, and can perform pressing by pad position control as described above. .

  As described above, according to the present invention, a two-dimensional shape defect such as a change in angle due to a springback and a three-dimensional shape defect such as a ridge line warp (surface warp) can be prevented to obtain a press-formed product. .

It is a figure which shows the external appearance of the metal members which have a hat cross section from which cross-sectional shape changes. It is a schematic diagram which shows the external appearance of the forming tool which consists of a punch, die | dye, and a pad. It is a figure for demonstrating the control method of the punch of a conventional construction method, die | dye, and a pad. It is a figure which shows the z direction displacement distribution after the springback at the time of pressing with a conventional construction method. It is a figure for demonstrating the punch, die | dye, and pad control method of this invention construction method. It is a figure for demonstrating the two-dimensional shape defect (wall opening) of a conventional construction method and this invention construction method. It is a figure which shows z direction displacement distribution after the springback by this invention construction method. It is a figure which shows the relationship between pad control amount (relative displacement of a punch and a pad), and a surface curvature amount. It is a block diagram explaining the structure of a pad control apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Die 2 Pad 3 Thin board 3 'Slack 4 Punch 5 Electric servo motor 6 Encoder 7 Pad position measurement part 8 Punch position measurement part 9 Die position measurement part 10 Pad position control part 11 Servo amplifier 12 Bottom dead center shape 13 Shape after spring back 14 Convex ridge line

Claims (5)

A press that forms a metal plate into a hat-shaped cross-section beam by using a press forming device equipped with a punch and die and a pad that presses the metal plate of the workpiece in conjunction with the punch, by the relative linear movement of the punch and die. In the molding method, the punch position, the die position, and the pad position are measured during press molding, the measured punch position zP [mm], the measured die position zD [mm], and the measured pad position zPad [mm]. The relative position of the pad and punch (zPad-zP) [mm] is within the range of 10 to 20 mm until the relative displacement (zD-zPad) [mm] of the die and pad becomes zero from the start of molding. so as to press the hat-shaped cross-section beam which is excellent in shape fixability characterized by press-molding by controlling the position zPad [mm] of the pad Form method. From the start of molding until the relative displacement (zD-zPad) between the die and the pad becomes zero, the pad position zPad [mm] is set so that the relative displacement (zPad-zP) between the pad and the punch is in the range of 10 to 20 mm. The first means for forming the metal plate while sagging the punch bottom by controlling, and the pad and the die are controlled in conjunction so that there is no sagging of the punch bottom from the procedure to the bottom dead center of the forming. The method for press-forming a hat-shaped cross-sectional beam excellent in shape freezing property according to claim 1, further comprising a second means for forming into a part shape. 3. The press-forming method of a hat-shaped cross-sectional beam excellent in shape freezing property according to claim 1, wherein the punch and the pad are driven by a hydraulic press machine or a servo press machine. A press forming apparatus comprising a punch, a die and a pad, and forming a metal plate by relative linear movement of the punch and the die, comprising a pad for pressing the metal plate in conjunction with the punch, and a punch position measuring unit and a die position A punch position zP [mm] measured by the punch position measurement unit, a die position zD [mm] measured by the die position measurement unit, and a pad position zPad [measured by the pad position measurement unit]. a pad position control unit for controlling the pad position zPad [mm] based on the relative displacement (zD-zPad) [mm] of the die and the pad from the mm] and the relative displacement (zPad-zP) [mm] of the pad and the punch. A hat-shaped cross-section beam press-molding device having excellent shape freezing characteristics. The press-forming apparatus for a hat-shaped cross-sectional beam excellent in shape freezing property according to claim 4, wherein the pad drive mechanism includes an electric servo motor.

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