JP4808679B2 - Thin plate press die apparatus and press molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a press die apparatus and a press-forming method, capable of obtaining a press-formed product having excellent dimensional precision by accurately detecting a state of pressurization of a punch and a pad to a sheet at the time of press-forming. <P>SOLUTION: A press die apparatus, which performs press-forming of a sheet 5 through relative straight movements of a punch 1 and a die 3, is provided with a pad 2 for pressing the sheet 5 together with the punch 1. A strain measuring means 10 for measuring elastic strain generated in a normal direction of the sheet 5 is arranged inside near at least one of pressurizing faces 11, 21 of the punch 1 and the pad 2. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a press mold apparatus and a press molding method using a thin plate as a molding material, and in particular, in a press mold apparatus having a pad interlocked with a punch, the pressurizing force applied to the thin plate of the punch and the pad during press molding The present invention relates to a press mold apparatus and a press molding method capable of improving the dimensional accuracy by reducing the spring back and the like of the molded product by detecting.

  The press forming of a thin plate using a press die apparatus is widely used in the field of manufacturing automobile parts.

  When press-molding a thin plate, a spring back may occur when molding pressure is removed from the molded product, resulting in poor molding. Conventionally, in a press mold apparatus provided with a pad that presses a thin plate in conjunction with a punch, for example, when forming a hat-shaped molded product, it is known that spring back can be suppressed by the following method. . That is, at the time of initial pressurization, as shown in FIG. 2, the pad pressure is adjusted to be weak so that an appropriate gap is formed between the punch 1 receiving the bending resistance of the thin plate 5 and the pad 2, and the thin plate 5 is bent. In the bent state, the shoulder portion 12 of the punch 1 is bent at the point C of the thin plate 5. Thereafter, when the pressure is increased to the bottom dead center, as shown in FIG. 3, the thin plate 5 is pressed without being bent, so that a position different from the point C in FIG. 2 is bent. The molded product 50 molded in this way is less likely to cause a springback even if the applied pressure is removed due to the presence of a point C having a bend in the vertical wall portion.

  On the other hand, for example, when a molded product curved in the longitudinal direction is formed, as shown in FIG. It is preferable to mold first. In this case, if the vertical wall portion is formed first, the rigidity of the molded product is increased, and an extremely large force is required when bending in the longitudinal direction. For this reason, the spring back that warps in the longitudinal direction increases, and the dimensional accuracy deteriorates. Therefore, it is necessary to adjust the pad pressure to be high and press-mold in a state where the thin plate 5 is pressed between the punch 1 and the pad 2 without a gap. Thus, adjusting the pad pressure according to the shape of the molded product is important for improving the dimensional accuracy of the molded product.

  Conventionally, for example, Patent Document 1 discloses a method of suppressing spring back by providing a bending blade for applying a compressive force in a direction in which a residual stress of a molded product is removed. Patent Document 2 discloses an apparatus that controls the compression amount or press pressure in a slide by controlling the position of a cushion pad driven by a servo motor.

  Further, Non-Patent Document 3 discloses a technique in which a piezoelectric element is built in the vicinity of the shoulder portion of the die and the sliding characteristics of the thin plate are measured based on the compressive strain generated in the die shoulder.

JP 2005-88051 A JP 2006-326626 A Development of integrated high-strength steel sheet forming technology (development of mold friction sensor) ”, Proceedings of the 57th Joint Conference on Plastic Working (October 31 to November 2, 2006, Takaoka Chamber of Commerce and Industry Building) Published by Japan Society for Technology of Plasticity (October 17, 2006) pp. 165-166

  However, neither Patent Document 1 nor Patent Document 2 discloses a method for adjusting the pad pressure, and it is impossible to improve the dimensional accuracy of a molded product by adjusting the pad pressure as described above. In other words, the pad pressure for obtaining a molded article with high dimensional accuracy without causing a spring bag or the like differs depending on the device or the material of the thin plate, but depending on the devices disclosed in these Patent Documents 1 and 2. For example, the contact state between the thin plate and the mold during press molding cannot be detected to determine whether or not pressure is being applied in an appropriate state.

  Further, even when the frictional force between the die and the crease presser mold was measured as in Non-Patent Document 3, it was still impossible to know the contact state between the thin plate and the mold in the transfer / modeling portion.

  An object of the present invention is to provide a press mold apparatus and a press molding method capable of obtaining a press-molded product with excellent dimensional accuracy by accurately detecting the pressurization state to a thin plate by a punch and a pad during press molding. There is.

  In order to solve the above problem, according to the present invention, there is provided a press mold apparatus for press-molding a thin plate by relative linear movement of a punch and a die, comprising a pad for pressing the thin plate in conjunction with the punch, Provided is a press die apparatus characterized in that a strain measuring means for measuring elastic strain generated in the normal direction of the thin plate is disposed in the vicinity of the pressing surface of at least one of the punch and the pad. Is done.

  By providing the strain measuring means in the vicinity of the pressing surface of the punch or pad, it is possible to detect the strain caused by the reaction force of the compressive force applied from the punch or pad to the thin plate during press molding. Therefore, the contact state between the pressing surface and the thin plate can be accurately detected.

  In this press mold apparatus, the strain measuring means is, for example, a piezo element or a strain gauge.

  Further, according to the present invention, there is provided a press forming method of a thin plate using the press die device, wherein the pad pressure of the pad is previously set so that the strain measured by the strain measuring means falls within a predetermined range. There is provided a press molding method characterized by adjusting and press molding.

  Furthermore, in the press molding method of a thin plate using the press mold apparatus, when the strain measured by the strain measuring means exceeds a predetermined range or falls below a predetermined range, the press molding is temporarily interrupted. Thus, a press molding method is provided, wherein the pad pressure of the pad is adjusted so that the strain falls within a predetermined range, and then the press molding is restarted.

  Further, in the thin plate press forming method using the press mold apparatus, when the strain measured by the strain measuring means exceeds a predetermined range or falls below a predetermined range, it is determined that the forming is abnormal. A press molding method is provided.

  In addition, the pad pressure is adjusted so that the strain falls within a predetermined range from the start of pressurization to the thin plate until immediately before the press molding bottom dead center, and a predetermined gap is provided between the punch and the pad. May be formed. In this case, the spring back in the width direction of the vertical wall portion of the molded product can be suppressed.

  Further, at the start of pressurization to the thin plate, the vertical wall is formed after the pad pressure is adjusted so that the strain measured by the strain measuring means becomes a predetermined value or more, and the bottom surface of the molded product obtained by press molding is molded. You may make it shape | mold a part. In this case, the spring back in the longitudinal direction of the molded product can be suppressed.

  According to the present invention, it is possible to accurately detect the force acting on the thin plate from the punch or pad by measuring the strain in the normal direction of the thin plate generated near the pressing surface of the punch or pad. . That is, by detecting the contact state between the thin plate and the punch or the pad at the time of molding, it can be determined whether or not proper pressure is applied to the thin plate. Furthermore, by adjusting the pressurizing conditions according to the shape of the molded product, a spring-back is suppressed and a press-molded product with excellent dimensional accuracy is obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 to 3 are schematic explanatory views of a press die apparatus according to the first embodiment of the present invention. This press mold apparatus performs drawing while pressing a thin plate 5 with a punch 1 and a pad 2. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In the press mold apparatus of FIG. 1, a punch 1 is disposed on the upper side, and a pad 2 is disposed so as to face the tip of the punch 1. A die 3 is disposed below the punch 1, and a pad 2 is disposed in the cavity 30 of the die 3 so that the pressing load (pad pressure) to the punch 1 side can be adjusted.

  In such a press mold apparatus, first, as shown in FIG. 1, a thin plate 5 as a molding material is placed on the die 3 and the pad 2, and the punch 1 and the die 3 are moved relatively straight in the vertical direction. As the punch 1 and the die 3 move relative to each other, the thin plate 5 is drawn into the cavity 30 of the die 3 while being sandwiched between the punch 1 and the pad 2. In the present embodiment, the pad pressure is set low, and as shown in FIG. 2, when the punch 1 receives the bending resistance of the thin plate 5 at the initial pressurization, an appropriate gap is formed between the punch 1 and the pad 2. To be formed. Thereby, at the time of initial pressurization, the thin plate 5 is bent in a slightly bent state. After that, when the pressure is further increased and the bottom dead center is reached, the thin plate 5 is pressed in a tensioned state as shown in FIG. With this press mold apparatus, as shown in FIG. 4, a hat-shaped molded product 50 having one opened can be obtained. FIG. 4 is a view from the bottom side. In press forming, the punch 1 may be lowered or the die 3 may be raised.

  The strain measuring means 10 is provided to measure the strain generated in the normal direction of the thin plate 5 in the punch 1 and the pad 2 during the press molding. In the press die apparatus shown in FIGS. 1 to 3, the strain measuring means 10 </ b> A for measuring the strain generated in the normal direction of the thin plate 5, that is, the vertical direction in the figure, is provided inside the center of the punch 1. One strain measuring means 10B for measuring strain generated in the normal direction of the thin plate 5 is provided one by one in the center. Both strain measuring means 10A and 10B are provided in the vicinity of the pressurizing surfaces 11 and 21 of the punch 1 or the pad 2. By these strain measuring means 10A and 10B, it is possible to detect the strain caused by the reaction force of the compressive force applied from the punch 1 and the pad 2 to the thin plate 5 at the time of press molding.

  As the strain measuring means 10 provided inside the punch 1 and the pad 2 as described above, for example, a piezoelectric element or a strain gauge can be used. FIG. 5 shows an example of attachment of the measuring means 10 composed of such a piezo element or a strain gauge to the inside of the pad 2.

  As shown in FIG. 5, the strain measuring means 10B is inserted into the bottom of the hole formed in the pad 2 so that the strain measuring means 10B is disposed inside the pad 2, and then the hole is closed with a bolt 9. It has become. A lead wire 19 for taking out a detection signal from the strain measuring means 10B passes through the bolt 9 and is drawn to the outside. The strain measuring means 10B is preferably arranged at a position of a depth of about 4 to 30 mm from the pressure surface 21 on the surface of the pad 2.

  Thus, by providing the strain measuring means 10 for measuring the strain generated in the normal direction of the thin plate 5 inside the punch 1 and the pad 2, the pressing surface of the thin plate 5, the punch 1 and the pad 2 being molded. The contact state with 11 and 21 can be accurately detected. In the present embodiment, the pad pressure is adjusted so that the strain detection value by the strain measuring means 10A on the punch 1 side becomes small in order to appropriately form a gap between the punch 1 and the pad 2 at the time of initial pressurization. FIG. 6 is a graph showing the transition of the strain detection value by each strain measuring means 10A, 10B. Until the bottom dead center of the molding is reached, the thin plate 5 comes into contact with the central portion of the pad 2 and is pressed, and the thin plate 5 does not come into contact with the central portion of the punch 1, so that almost no distortion occurs. At this time, the shoulder 12 of the punch 1 is bent at a point C (FIG. 2) of the thin plate 5. After reaching the bottom dead center, the thin plate 5 is pressed against both the pressurizing surface 11 of the punch 1 and the pressurizing surface 21 of the pad 2 and is pressed without being bent. Therefore, the point C that is initially bent is positioned at an appropriate location on the vertical wall 51 in the molded product 50. In addition, since the detection value of distortion changes with the installation positions of the distortion measurement means 10, a reference value is appropriately set for each mold.

  By detecting the distortion caused by the reaction force of the compressive force applied to the thin plate 5 from the punch 1 and the pad 2, the contact state between the thin plate 5, the punch 1 and the pad 2 can be accurately grasped. Therefore, it can be determined whether proper pressurization is performed. As a result, in the present embodiment, the vertical wall portion 51 of the molded product 50 has a bend due to the initial pressurization, thereby suppressing the spring back and obtaining a press-molded product with excellent dimensional accuracy.

  Even after the press molding bottom dead center is reached, it is possible to determine whether the press molding is properly performed by detecting the strain by the strain measuring means 10. At this time, it is possible to prevent the thin plate 5 from breaking by setting an upper limit of the detection value and detecting an abnormality in the contact force. Furthermore, detection of contact force abnormality by setting an upper limit is also effective for detecting defects such as double blanks and wrinkle overlap.

  Further, for example, when the strain measured by the strain measuring means 10 during the press molding exceeds a predetermined range or falls below the predetermined range, it can be determined that the molding is abnormal. In such a case, when the next molding is performed, it is possible to cope by adjusting the pad pressure. Also, quality control during mass production, such as countermeasures by detecting defective products and correcting press conditions, can be facilitated by detecting molding abnormalities.

  Further, when the strain measured by the strain measuring means 10 during the press molding exceeds a predetermined range or falls below the predetermined range, the pad pressure is adjusted so that the strain falls within the predetermined range, so that Avoid occurrence.

  FIG. 7 is a schematic explanatory view of a press die apparatus according to the second embodiment of the present invention. In this embodiment, as shown in FIG. 8 (A), the convex portion 22 of the pressurizing surface 21 of the pad 2 and the concave portion 13 of the pressurizing surface 11 of the punch 1 open toward one side, and the concave portion 54 is formed on the bottom surface. The molded product 52 can be made. FIG. 8A is a view from the bottom side. Further, the molded product 52 in the present embodiment is curved in the longitudinal direction as shown in FIG.

  In the press mold apparatus, the arrangement of the punch 1, the pad 2, and the die 3 is the same as that shown in FIGS. The strain measuring means 10 is provided for measuring the strain generated in the normal direction of the thin plate 5 in the punch 1 and the pad 2 during press molding. In the press mold apparatus shown in FIG. 7, the strain measuring means 10 </ b> A for measuring the strain generated in the normal direction of the thin plate 5, that is, the vertical direction in the figure, is provided in the center of the concave portion 13 of the punch 1. One strain measuring means 10B for measuring the strain generated in the normal direction of the thin plate 5 is provided one by one inside the center of the portion 22. Both strain measuring means 10A and 10B are provided in the vicinity of the pressurizing surfaces 11 and 21 of the punch 1 or die 2. The strain measuring means 10 can detect a strain caused by a reaction force of a compressive force applied to the thin plate 5 from the concave portion 13 of the punch 1 and the convex portion 22 of the pad 2 during press molding. In this case, the strain measuring means 10 may be provided inside both the punch 1 and the pad 2 as shown in the figure, or may be provided only in one of them.

  In this embodiment, in order to mold the molded product 52 shown in FIG. 8, the pad pressure is set high, and the punch 1 and the pad 2 are in close contact with the thin plate 5 sandwiched from the initial pressurization. FIG. 9 is a graph showing the transition of the strain detection value by each strain measuring means 10A, 10B. Since the thin plate 5 is pressurized in a state where both the punch 1 and the pad 2 and the thin plate 5 are in contact with each other from the initial pressurization, both strains increase in proportion to the stroke. By being pressurized in this way, the curved shape of the molded product is molded first, the recessed portion 54 is transferred along the shape of the punch 1, and then the vertical wall portion 53 is molded. Thereby, the spring back of a curved surface is suppressed.

  Also in this case, the contact state between the thin plate 5 and the punch 1 and the pad 2 can be accurately grasped by detecting the distortion caused by the reaction force of the compressive force applied to the thin plate 5 from the punch 1 and the pad 2. Therefore, it can be determined whether the press molding is properly performed. As a result, the shape of the punch 1 is accurately modeled and transferred, and a press-molded product with excellent dimensional accuracy is obtained. In addition, the thin plate 5 can be prevented from being broken by setting an upper limit of the detection value and detecting a contact force abnormality. Furthermore, detection of contact force abnormality by setting an upper limit is also effective for detecting defects such as double blanks and wrinkle overlap.

  FIG. 10 is a schematic explanatory view of a press die apparatus according to the third embodiment of the present invention. The arrangement of the punch 1, the pad 2 and the die 3 is the same as in the first and second embodiments described above.

  In the present embodiment, two strain measuring means 10C are provided at the positions where the ridgelines of the molded product are formed, in the curvature radius direction of the curved surface, that is, in the oblique direction of the figure. As a result, the strain generated in the normal direction of the thin plate 5 is measured at the pad 2 at the position where the curved surface portion of the molded product is pressed. The strain measuring means 10 </ b> C is provided in the vicinity of the surface of the pad 2.

  By providing the strain measuring means 10C as shown in FIG. 10, the contact state between the thin plate 5 and the pad 2 at the time of press molding can be detected in detail and accurately, the press molding is properly performed, and the accurate shape is transferred. It is possible to form a molded product with excellent dimensional accuracy.

  The thin plate 5 was press-molded by the press die apparatus shown in FIGS. 1 to 3, and the strain ε was measured by the strain measuring means on the punch side and the pad side, and the dimension of the molded product was inspected. As shown in FIG. 1, a piezoelectric element is provided as a strain measuring means 10 in the vicinity of the pressure surfaces 11 and 21 inside the center of the punch 1 and inside the center of the pad 2 (each 5 mm from the surface). The strain ε generated in the normal direction of the thin plate 5 was measured.

  Table 1 was obtained as a result of examining the presence or absence of springback for the molded product 50 press-molded by the procedure of FIGS. In Table 1, the pad initial pressure indicates the pad pressure at the start of pressurization, and the pad end pressure indicates the pad pressure when the bottom dead center is reached. The values of the strain ε on the punch side and the pad side respectively showed values at the position of one half of the pressing stroke. The width W is the opening width W of the molded product 50 shown in FIG. 4, the design value is 65 mm, and an error of up to 1 mm is accepted. The thin plate was a high-strength steel plate having a thickness of 1.2 mm, and the design dimensions of the molded product were a height of 70 mm and a length in the longitudinal direction of 170 mm.

  As shown in Table 1, when the pad pressure was too low, a spring go was generated in which the width W was smaller than the design value, and when the pad pressure was too high, a spring back was generated. Further, the contact state of the punch and the pad with the thin plate due to the pad pressure appeared as the detected value of each strain.

  Next, based on the strain detection values of No. 2 to No. 4 that passed the quality standard among the results in Table 1, press molding was performed by performing online control, and Table 2 was obtained.

  As shown in Table 2, 6.1% defective products were generated when the control by strain was not performed, but when the control was performed, the defective rate decreased to 0.9%.

  The thin plate 5 was press-molded by the press mold apparatus shown in FIG. As shown in FIG. 7, a strain gauge is provided near the pressure surfaces 11 and 21 inside the center of the concave portion 13 of the punch 1 and inside the center of the convex portion 22 of the pad 2, as shown in FIG. 5 mm), and the strain generated in the normal direction of the thin plate 5 was measured. In this embodiment, since the punch 1 and the pad 2 are in close contact with each other with the thin plate 5 interposed therebetween, only the punch-side strain ε is detected.

  Table 1 was obtained as a result of examining the dimension of the warp h in the longitudinal direction of the molded product 52 press-molded by the method of FIG. The initial pad pressure indicates the pad pressure at the start of pressurization, and the final pad pressure indicates the pad pressure when the bottom dead center is reached. The value of the strain ε was a value at a position half the pressurizing stroke. The warpage is the warpage dimension h of the molded product 52 shown in FIG. 8, the design value is 48 mm, and an error of 1 mm is accepted. The thin plate was a high-strength steel plate having a thickness of 1.4 mm, and the design dimensions of the molded product were 90 mm in height, 100 mm in opening width, and 620 mm in length in the longitudinal direction.

  As shown in Table 3, when the pad pressure was low, springback occurred and the warp dimension h was reduced. The value of the strain ε indicating the contact state on the punch side is required to be 100 μm or more, for example, at the detection position of this embodiment.

  Next, on the basis of the strain detection values of No. 4 and No. 5 that passed the quality standards in Table 3, online control was performed to perform press molding, and Table 4 was obtained.

  As shown in Table 4, 3.9% of defective products were generated when control by strain was not performed, but no defective product was generated when control was performed.

  The thin plate 5 was press-molded by the above-described press mold apparatus of FIG. 7, and the strain ε was measured by the strain measuring means on the punch side and the pad side, and the dimensional inspection of the curvature radius R of the ridgeline of the molded product was performed. The type, position, and strain measuring direction of the strain measuring means 10 are the same as in the second embodiment, and in this embodiment, the strain ε at the bottom dead center is detected. The design value of the curvature radius R of the ridge 55 shown in FIG. 8 is 5 mm. As a result of press molding, Table 5 was obtained.

  As shown in Table 5, in the strain measuring means according to this example, when the detected value of the strain on the punch side and the pad side at the bottom dead center is at least 90 μm or more, the curvature radius of the ridge line becomes 5.0 mm, and the quality Passed the standards.

  The present invention can be applied to the field of press forming thin plates.

It is a schematic explanatory drawing of the press die apparatus concerning the 1st Embodiment of this invention, and has shown the state before a press. It is a schematic explanatory drawing of the press die apparatus concerning the 1st Embodiment of this invention, and has shown the state in the middle of a press. It is a schematic explanatory drawing of the press die apparatus concerning the 1st Embodiment of this invention, and has shown the state at the time of press completion. It is a perspective view of the molded article shape | molded by FIGS. 1-3. It is explanatory drawing of the attachment structure of the strain measurement means arrange | positioned inside a pad. It is a graph which shows the detected value of the distortion of the punch side at the time of press molding of FIGS. 1-3, and a pad side. It is a schematic explanatory drawing of the press die apparatus concerning the 2nd Embodiment of this invention, and has shown the state in the middle of a press. The molded product shape | molded by FIG. 7 is shown, (a) is a perspective view, (b) is a side view. It is a graph which shows the detected value of the distortion of the punch side at the time of press molding of FIG. 7, and a pad side. It is a schematic explanatory drawing of the press die apparatus concerning the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Punch 2 Pad 3 Die 5 Thin plate 10 Strain measuring means 11, 21 Pressurization surface 12 Shoulder part 13 Concave part 22 Convex part 30 Cavity 50,52 Molded product 51,53 Vertical wall part

Claims (7)

A press mold apparatus for press-molding a thin plate by a relative straight movement of a punch and a die,
A pad for pressing the thin plate in conjunction with the punch,
A press mold apparatus, wherein a strain measuring means for measuring an elastic strain generated in a normal direction of the thin plate is disposed in the vicinity of a pressing surface of at least one of the punch and the pad.   The press mold apparatus according to claim 1, wherein the strain measuring means is a piezo element or a strain gauge. A method for press-molding a thin plate using the press mold apparatus according to claim 1 or 2,
A press forming method, wherein the pad pressure of the pad is adjusted in advance so that the strain measured by the strain measuring means falls within a predetermined range. A thin plate press molding method using the press die apparatus according to claim 1 or 2,
When the strain measured by the strain measuring means exceeds a predetermined range or falls below the predetermined range, the press molding is temporarily stopped and the pad pressure of the pad is adjusted so that the strain falls within the predetermined range. A press molding method characterized by adjusting and then restarting the press molding. A thin plate press molding method using the press die apparatus according to claim 1 or 2,
A press forming method, wherein when the strain measured by the strain measuring means exceeds a predetermined range or falls below a predetermined range, it is determined that the forming is abnormal.   The pad pressure is adjusted so that the strain is within a predetermined range from the start of pressurization to the thin plate until immediately before the press molding bottom dead center, and a predetermined gap is formed between the punch and the pad. The press molding method according to claim 3, wherein the press molding method is performed.   Adjusting the pad pressure so that the strain becomes a predetermined value or more at the start of pressurization to the thin plate, and molding the bottom wall of the molded product obtained by press molding, and then molding the vertical wall portion The press molding method according to any one of claims 3 to 5.

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