JP2009023000A - Mold for press forming of metal plate and press forming method for metal plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold for press forming which stably generates a reverse bending deformed part by overrun even when a die shoulder radius is large, reduces a phenomenon such as a wall camber as much as possible, and can improve a dimensional accuracy of press forming of a metal plate as a result. <P>SOLUTION: A projecting part elongating in the direction of a die is formed at the region of the head of a punch corresponding to the part formed at the early period of forming, further, a recessed part is not formed at the die, and the punch-die clearance CL2 corresponding to the part formed at least immediately after the early period of press forming is set broader than the punch-die clearance CL1 corresponding to the part formed at the early period of press forming (CL1<CL2). Further, the thickness t (mm) of the metal plate to be formed and the clearances CL1, CL2 are set so as to satisfy prescribed relationships, respectively, and in a state where the forming of a vertical wall part is completed, overrun is generated at the metal plate, further, the overrun is amplified upon mold releasing, and reverse bending is generated at the formed metal plate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a die for press forming a metal plate such as a thin steel plate or an aluminum plate mainly applied to an automobile body and a press forming method using such a die. The present invention relates to a press molding die and a press molding method capable of reducing the occurrence of defective dimensional accuracy of a molded product due to elastic recovery after molding.

  In the automobile-related industry, the use of high-strength materials tends to increase due to increasing demands for vehicle body collision safety and environmental protection (improvement of fuel consumption through weight reduction). Many parts of an automobile body are generally manufactured by pressing a metal plate. However, when these parts are molded by press molding, the shape (dimensions) of the molded product changes from the design value due to the elastic recovery behavior after mold release (taken out from the mold after molding). In some cases, problems may occur during assembly and joining (mostly joining by spot welding). These defects are collectively referred to as dimensional accuracy defects, and various dimensional precision defects are known such as wall warp and angle change (for example, see Non-Patent Document 1).

  In recent years, from the viewpoints of weight reduction and stability of automobile bodies, there are increasing opportunities for automobile bodies to use higher strength steel sheets and aluminum sheets that are lighter than steel sheets but have a lower Young's modulus. The above dimensional accuracy defects have become a prominent problem.

  FIG. 1 is an explanatory view showing an external shape example of a hat channel member as an automobile part. As a main molding method of such a hat channel member, a drawing molding method as shown in FIG. 2 [FIG. And a bending method [FIG. 2 (b)].

  An example of poor dimensional accuracy when a hat channel member is molded using the mold (drawing mold) shown in FIG. 2A will be described with reference to FIG. FIG. 3 shows a product cross-sectional shape when a 980 MPa grade cold-rolled steel sheet (sheet thickness t: 1.2 mm) is formed. The shape after press forming [FIG. 3B] is the target. It can be seen that there is a large deviation from the dimensions. That is, when the design (target) shape (cross-sectional shape perpendicular to the axis) of the hat channel member is as shown in FIG. 3 (a), it is joined by spot welding or the like with other parts, and precise dimensional accuracy is obtained. The required flange surface has bounced up by 48 ° (this bounce angle is hereinafter referred to as “flange bounce angle θ”). This is considered to be the influence of both the angle change failure at the punch shoulder and the wall warp failure of the side wall [FIG. 3 (b)].

The generation mechanism of the wall warp generated in the side wall portion of the hat channel member is described according to the following mechanisms (1) to (3) (see Non-Patent Document 1).
(1) When the material (metal plate) passes through the die shoulder radius portion, it undergoes bending deformation.
(2) When this part flows into the side wall part from the die shoulder radius part, it is bent back and stretched in a straight line. At this time, a stress difference with a different sign is generated in the thickness direction in the side wall part. The bending moment due to this stress difference is inherent.
(3) When the molded product is released from the mold after molding, elastic recovery occurs so as to release this bending moment, resulting in warping.

  Various techniques have been proposed so far for reducing the wall warp phenomenon. As one of such techniques, a method using reverse bending in the die gap (between the die and the punch) is known (see Non-Patent Document 1). The mechanism of wall warp reduction when this method is applied is explained as follows.

  First, when passing through the die shoulder radius as in normal molding, it undergoes bending deformation, but when this part flows from the die shoulder radius into the side wall, the size of the die shoulder radius and the clearance (punch -Depending on the setting of the gap between the dies, a phenomenon may occur in which the material does not completely wrap around the shoulder radius of the die. This phenomenon is generally referred to as overrun, and the material that has flowed into the side wall portion due to this phenomenon undergoes bending opposite to the bending direction (generally referred to as reverse bending).

  Then, when the mold is released after molding, elastic recovery occurs so as to release this bending moment as in the normal molding. However, since the elastic recovery at this time works in the direction to cancel the reverse bending generated above, if the curvature of the reverse bending and the curvature generated by the elastic recovery become the same, they cancel each other out. Thus, the curvature of the side wall portion (= wall warp) can be made zero.

As a method of controlling the wall warp using the overrun, a method of appropriately controlling the die shoulder radius and the clearance has been conventionally known. However, such techniques require tight control of the die shoulder radius and clearance to eliminate any wall warpage. In particular, the die shoulder radius (rd) cannot be exhibited unless it is controlled to about rd / t (t: plate thickness) = 1.5 (see Non-Patent Document 1). Since the plate thickness t of the steel plate generally used for automobile structural parts is about 1 mm, in order to effectively exert the effect by the above technique, the die shoulder radius (rd) is set to about 1.5 mm. It will be indispensable.
"Press Forming Difficulty Handbook" 2nd edition (1997), pp. 175-196, Nikkan Kogyo Shimbun)

  However, when the die shoulder radius (rd) is decreased, there is a problem that the risk of cracking during molding is increased, and the tool is likely to be worn out, so that the tool needs to be frequently maintained. Since these problems can be said to be unstable factors in actual production, the above method has a drawback that it is difficult to apply to mass production.

  The present invention has been made under such circumstances, and the object thereof is to stably generate a reverse bending deformed portion due to overrun even when the die shoulder radius is large, and a phenomenon such as wall warp. Is to realize a press-molding die that can reduce the squeeze as much as possible and increase the dimensional accuracy at the time of press-molding a metal plate, and a press-molding method using such a die.

  The metal plate press-molding die of the present invention that has achieved the above object is a die for press-molding a metal plate having at least a punch and a die, and is formed at a site formed at the initial stage of molding. A convex portion extending in the die direction is formed in the corresponding punch head region, and no concave portion is formed in the die, and at least a punch-die clearance CL2 corresponding to a portion formed immediately after the initial press forming is formed. When the clearance CL1 is set wider than the punch-die clearance CL1 corresponding to the portion formed in the initial stage of press molding (CL1 <CL2) and the thickness of the metal plate to be formed is t (mm), the clearance CL1, CL2 is set so as to satisfy the following formulas (1) and (2) respectively, and in the state where the forming of the vertical wall portion is completed, an overrun is generated in the metal plate, and the die Wherein when the mold is to amplify overrun and has a gist in that to generate a reversely bent metal plate molded.

0.8 × t ≦ CL1 ≦ 1.2 × t (1)
CL2 ≧ CL1 + t (2)
In the metal mold | die of this invention, it is preferable to set so that CL1 = t (mm) may be satisfied.

  By press-molding a metal plate using the various press-molding molds as described above, a metal press-molded product having excellent dimensional accuracy can be obtained without causing inconvenience such as wall warp and angle change.

  The present invention is configured as described above, and even when the die shoulder radius rd is large, overrun is stably generated, and phenomena such as wall warp and angle change are reduced as much as possible. A press mold capable of increasing the dimensional accuracy during molding and a press molding method using such a mold have been realized.

  The present inventors have studied from various angles in order to solve the above problems. First, in order to effectively induce reverse bending deformation due to overrun even in a region where the die shoulder radius (rd) is large, the material that has passed through the die shoulder and flowed into the vertical wall (side wall) is molded. The idea that a mold having a space that can be greatly deformed between tools (between the die and the punch) at the time of release or mold release is obtained. As a result of further investigation based on such an idea, the present inventors have found that the above object can be achieved brilliantly by adopting the above configuration, and completed the present invention.

  The configuration, operation and effect of the present invention will be described with reference to the drawings. In the following description, for the sake of convenience of explanation, the case of drawing a hat channel member often used for parts of an automobile body as a member to be press-formed will be described. However, the member to be molded according to the present invention is originally such a hat channel. It is not limited to members, and the molding method is not limited to drawing, but can also be applied by changing the shape of the punch in bending molding (form molding) as shown in FIG. 2 (b), for example. It is.

  FIG. 4 is a schematic explanatory view showing a configuration example of the press-molding die of the present invention, in which 1 is a punch, 2 is a die, 3 is a blank holder, 4 is a metal plate, rd is a die shoulder radius, rp Indicates punch shoulder radius, and BHF indicates wrinkle holding force. In the mold of the present invention, as shown in FIG. 4, a punch-die clearance CL2 corresponding to at least a portion (lower portion of the punch 1 shown in FIG. 4) formed immediately after the initial molding is formed in the initial molding. Is set so as to be wider than the punch-die clearance CL1 corresponding to the region (upper portion of the punch 1 shown in FIG. 4) (CL1 <CL2). That is, in the press mold of the present invention, the convex portion 1a extending in the die direction is formed in the punch head region corresponding to the portion formed at the initial stage of molding so that the clearances CL1 and CL2 satisfy the above relationship. Is formed. Note that “formation initial stage” means a period from the start of press forming to the metal plate 4 until a certain time elapses.

  In the configuration shown in FIG. 4, the convex portion 1a is formed by a curved surface. However, the present invention is not limited to such a configuration. For example, as shown in FIG. 5A, a flat portion 1c is formed on a part of the convex portion 1b. With various shapes such as a mushroom-shaped cross section with a punch 1 and a punch 1 in which the length in the axial direction of the projection 1d is increased (that is, the molding time is increased) as shown in FIG. Can be adopted. In FIG. 5, “R5” means that the punch shoulder radius rp (or the radius of the curved surface at the tip of the convex portion 1d) is set to 5 mm.

  The structure of the mold in the present invention can achieve the effect as long as the clearances CL1 and CL2 satisfy the above relationship, but the structure is not limited to that shown in FIGS. For example, the clearance CL2 is configured to gradually widen from the part formed at the initial stage of molding to the part formed thereafter, or after the clearance CL2 is once widened immediately after the initial stage of molding so as to be closer to the clearance CL1. The object of the present invention can be achieved even if it is narrowly formed. In short, as long as at least the punch-die clearance CL2 corresponding to the portion formed immediately after the initial press forming and the punch-die clearance CL1 corresponding to the portion formed in the initial press forming satisfy the above relationship. It ’s good.

  As for the setting method of the clearances CL1 and CL2, various combinations are conceivable, and almost any combination is adopted, so that the result that the dimensional accuracy is improved as compared with the conventional mold is obtained. However, the present inventors have examined a combination of CL1 and CL2 that improves the dimensional accuracy most.

The present inventors use a 980 MPa class cold-rolled steel sheet (thickness t: 1.2 mm) and press-mold the hat channel member by the mold of the present invention shown in FIG. 4 (rp = 5 mm). The dimensional accuracy was investigated in relation to the clearances CL1 and CL2. At this time, the clearance CL1 was set to (1) t + 0.4 mm, (2) t + 0.2 mm, and (3) tmm, and the clearance CL2 was set to CL1 + 5 mm as a sufficiently large value. Other conditions were as follows. In addition, even when press molding (drawing) using the normal mold shown in FIG. 2A (clearance: t + 0.2 mm, t + 0.4 mm, t + 0.6 mm, t + 0.8 mm) investigated.
(Press molding conditions)
Die shoulder radius (rd): 5mm
Molding height H (FIG. 10 below): 67 mm
Blank size: width 250mm, depth 40mm

  FIG. 6 shows a cross-sectional shape when press molding is performed under each condition. In the case of press molding using the normal mold shown in FIG. 2 (a) (normal molding), the amount of dimensional accuracy such as “wall warp” was not different depending on the clearance, but the clearance was The cross-sectional shape at t + 0.8 mm was as shown in FIG. 3B, and both wall warp and angle change occurred, and the flange jump angle θ showed a large value of 48 °. .

  On the other hand, FIG. 6A shows the case where the clearance CL1 is set to (t + 0.4 mm). However, although the dimensional accuracy is greatly improved as compared with the normal molding, “wall warp” remains slightly. It was a situation. However, when the clearance CL1 was set to (t + 0.2 mm) [FIG. 6 (b)], the effects of wall warping and reverse warping were offset, and “wall warping” ≈0 could be realized. However, in this case, the flange still bounces due to a poor angle change at the punch shoulder.

  Further, when the clearance CL1 is reduced to t (equivalent to the plate thickness), the effect of overrun is strong and the side wall portion is warped inward [FIG. 6 (c)]. By offsetting the angle change, the flange jump angle θ = 0 ° could be realized. In addition, since the shape of the side wall part in this case is curving inward, it is different from the target shape.

  From these results, we could consider as follows. That is, if the clearance CL1 is finely adjusted within the range of t ≦ CL1 ≦ t + 0.2 (mm) depending on whether the shape of the side wall portion is important or the bounce of the flange surface is important, the optimum dimensional accuracy can be obtained. It turns out that it is obtained.

  The present inventors investigated the influence of the clearance CL1 on several materials while changing the clearance CL1 in the range of 0.8 t to 2.0 t. The conditions other than the material type and the plate thickness t at this time are the same as described above (thus, clearance CL2 = CL1 + 5 mm). The results are shown in Table 1 below. For each material, the optimum dimensional accuracy can be obtained by adjusting the clearance CL1 within the range of 0.8 × t ≦ CL1 ≦ 1.2 × t (mm). You can see that The reason why the lower limit of the clearance CL1 is set to 0.8 × t is that if the clearance CL1 becomes narrower than this, the plate thickness becomes too thin and the strength characteristics as a member may be deteriorated.

  By the way, when the mold shown in FIG. 4 is used and the clearance CL1 is set to (t + 0.2 mm), as shown in FIG. 6B, “wall warp” ≈0 can be realized. This is a situation where the flange spring still remains. Therefore, the present inventors also examined a method for reducing the flange jump angle θ as much as possible while realizing “wall warp” ≈0.

  As a result, as shown in FIG. 7, the flange jump angle θ can be made as small as possible by making the blank holder 3 stand by below the upper surface of the punch 1 at the start of molding (ΔH indicates the standby height in the figure). I understand. That is, in normal press molding, the metal plate 4 is generally held between the die 2 and the blank holder 3 and then the molding is started (see FIG. 9 to be described later for this procedure). If molding is started after the blank holder 3 is in the state shown in FIG. 7 at the start of molding, the change in punch shoulder angle can be reduced, and as a result, the flange jump angle θ can be reduced as much as possible. Therefore, when performing press molding using the mold of the present invention, the clearance CL1 is set to an appropriate range to realize “wall warp” ≈0, and the standby height ΔH shown in FIG. By providing and reducing the change in angle, it is possible to obtain a press-formed product with more excellent dimensional accuracy.

  The reason why the above-described effect can be obtained by starting press molding in the state shown in FIG. 7 could be considered as follows. That is, when the blank holder 3 is made to stand by below the upper surface of the punch at the start of molding, bending by the punch 1 and the die 2 acts on the metal plate 4 until the blank holder 3 and the die 3 approach each other. However, it is considered that overrun is more likely to occur as shown in FIG. 8 (partially enlarged view) because the material restraint due to the blank hold does not work during this bending. Therefore, the material (metal plate 4) is easily wound over a wide range of the punch shoulder (that is, the bending angle of the metal plate 4 becomes larger than 90 °), and the ideal 90 ° is obtained by the spring back after the mold release. It was thought that approached.

  Although the dimensional accuracy has been improved by the completion of the mold with the above configuration, it is not only the overrun at the time of molding that affects the dimensional accuracy but also the amplification of the overrun at the time of mold release. It was also found that reverse bending when passing through the punch shoulder (for example, the convex portion 1a in FIG. 4) also has an effect. Such a situation will be described with reference to the drawings.

  FIG. 9 is an explanatory view showing the state of the mold at the start of molding. First, as shown in FIG. 9A, the metal plate 4 is held between the die 2 and the blank holder 3 so that the tip of the punch 1 is in contact with the surface of the metal plate 4. Next, the die 2 is lowered while the metal plate 4 is sandwiched between the die and the blank holder, and the forming of the metal plate 4 is started by the operation of the punch 1 [FIG. Molding is performed by continuing to descend.

  FIG. 10 is an explanatory view showing a state (molding bottom dead center) in which the metal plate 4 is completely formed. In this state, the blank holder is lowered to the bottom, and the vertical wall portion of the metal plate 4 is Molding is completed (H in the figure indicates the molding height). In this state, overrun occurs in the vertical wall lower portion 4a of the metal plate 4.

  Subsequently, when the metal plate 4 which has been formed is released by raising the die 3 while being sandwiched between the die 2 and the blank holder 3, as shown in FIG. 11, the punch shoulder portion (convex portion 1a) is formed. ) Becomes a release resistance, and the overrun generated in the lower portion 4a of the vertical wall of the metal plate 4 is further amplified. When the die 2 is further raised (released), as shown in FIG. 12A, when the vertical wall lower portion 4a passes near the punch shoulder (convex portion 1a), the vertical wall lower portion Reverse bending occurs in the portion 4a. Under such circumstances, in the member after completely releasing the mold [FIG. 12B], the wall warp of the vertical wall portion is improved by the effect of the reverse bending. That is, as shown in FIGS. 6B and 6C, by controlling the reverse bending, it is possible to eliminate the wall warp or to make the wall warp.

  In the mold release shown in FIGS. 11 and 12, the case where the blank holder 3 also rises following the rise of the die 2 is shown. [The result shown in FIG. 6 is also assumed in this case. In some cases, the blank holder 3 is fixed (locked) at the bottom dead center of molding at the time of mold release and does not rise together with the die 2 at the time of mold release. Due to the productivity problem of press molding, it is relatively rare that the blank holder 3 is locked at the bottom dead center at the time of mold release, but if the mold is released with the blank holder 3 locked at the bottom dead center, the metal As shown in FIG. 13, the plate 4 is released from the mold and is in a wall warping state, and an overrun amplification effect at the time of mold release (see FIG. 11) and a reverse bending effect at the time of punch shoulder passage (see FIG. 12). ) Will not be demonstrated, and the wall warping improvement effect will be small.

On the other hand, as shown in FIG. 14, in the case of press-molding a member having a vertical wall portion that is inclined so that the vertical wall portion to be formed becomes lower (θ ₁ in the figure is the inclination of the vertical wall portion) Even if the blank holder 3 is lifted together at the time of mold release, the clearance between the punch shoulder and the die widens as the die 2 is lifted, and overrun as the material near the die shoulder approaches. In some cases, the amplification effect does not sufficiently occur, and the effects of the present invention may not be sufficiently exhibited. In other words, the wall warp is improved in the part where the clearance from the punch shoulder is narrow at the time of mold release, but the wall warp is slightly generated in the part where the clearance from the punch shoulder is wide at the time of release (the lower part of the vertical wall). It is easy to be in a state that is easy to do.

In order to solve the above problems, the present inventors have (1) that overrun and reverse bending deformation can be realized only during molding, and (2) the inclination angle of the vertical wall (θ ₁ shown in FIG. 14). Regardless of whether or not, overrun and reverse bending deformation can be realized over the entire length of the vertical wall, and further studies were made aiming at a mold structure that can satisfy the above requirements.

  As a result, it is configured to include a forming jig for forming the vertical wall portion of the metal plate while moving in synchronization with the die while maintaining the relative position with the die at the time of forming, and the forming jig is in the vicinity of the die shoulder. If the molding jig-die clearance CL4 is set to be wider (CL3 <CL4) than the molding jig-die clearance CL3 in the molding region other than the vicinity of the vicinity of the die shoulder, the above inconvenience is eliminated. It has been found that the dimensional accuracy during press forming of a metal plate can be further increased.

  FIG. 15 is a schematic explanatory view showing one configuration example of the press-molding die of the present invention made from the above viewpoint, and the basic configuration is similar to the configuration shown in FIG. Duplicate explanation is avoided by assigning the same reference numerals. In this configuration, a forming jig 10 for forming the vertical wall portion of the metal plate 4 (press-formed product) is integrally provided with the blank holder 3 on both inner sides (side facing the punch 1) of the blank holder 3. The projections 10a for molding the metal plate 4 from the inner side of the metal plate 4 are provided at the upper ends of the respective molding jigs 10. Since the molding jig 10 is moved in synchronization with the die while maintaining the relative position with the die during molding, the clearance between the molding jig (that is, the protrusion 10a) and the die 2 ( CL3) becomes constant. Further, the clearance CL4 between the forming jig 10 and the die 2 in the vicinity of the die shoulder is configured to be set wider than the clearance CL3 (that is, the clearance in the forming region other than the vicinity of the die shoulder). By adopting such a mold configuration, an overrun and reverse bending deformation action is further achieved by the forming jig 10 during press forming.

  FIG. 16 is a schematic explanatory view showing another configuration example of the press-molding die according to the present invention, and this configuration is applied when the vertical wall portion has an inclination angle, and other portions are as follows. The mold configuration is the same as that shown in FIG. The above-described effects of the present invention can also be achieved by adopting such a configuration.

  The clearances CL3 and CL4 are preferably set so as to satisfy the relationship of the following formulas (3) and (4) for the same reason as the clearances CL1 and CL2 (however, t Is the plate thickness). That is, each of the clearances CL3 and CL4 plays the role of (1) overrun induction, (2) overrun amplification, and (3) reverse bending addition, like the clearances CL1 and CL2. Further, as apparent from FIG. 23 described later, since the expressions (1) and (2) are not affected by the molding height H, even if the protrusion 10a shown in FIG. It can be considered that the same clearances as in the case of the punch shoulder 1a in FIG. 10 can be managed by the relationship of the equations (1) and (2) [that is, the equations (3) and (4)].

0.8 × t ≦ CL3 ≦ 1.2 × t (mm) (3)
CL4 ≧ CL3 + t (mm) (4)

  Therefore, when the mold configuration shown in FIGS. 15 and 16 is adopted, the effects of the present invention can be achieved only by defining the clearances CL3 and CL4 with an appropriate relationship without strictly defining the relationship between CL1 and CL2. Of course, even when such a configuration is adopted, the clearances CL1 and CL2 may be defined so as to satisfy the relationship of the above expressions (1) and (2). is there.

  The metal plate forming procedure when using a mold provided with a forming jig will be described with reference to the drawings. First, at the start of molding, as shown in FIG. 17A, the presence of the molding jig 10 prevents the metal plate 4 from being sandwiched between the die 2 and the blank holder 3. A predetermined space exists between the metal plate 4 and the metal plate 4. And by starting shaping | molding to the metal plate 4 with the die | dye 2, the metal plate 4 receives bending shaping | molding, but the blank holder 3 is still non-operating at this time [FIG.17 (b)]. Thereafter, the die 2 is lowered while the metal plate 4 is sandwiched between the die 2 and the blank holder 3 (the blank holder 3 also follows down), and the metal plate 4 is formed [FIG. c)].

  In the mold shown in FIGS. 15 and 16, by providing the forming jig 10, overrun and reverse bending are effectively generated with respect to the metal plate 4 at the time of forming. As shown in FIG. 7, at the start of molding using such a mold, the same action as that in the state where the blank holder 3 is made to stand by using a mold not provided with the molding jig 10 and molding is started is achieved (see FIG. 7). 8) The effect of reducing the flange jump angle is also exhibited.

By the way, if the clearances CL3 and CL4 are appropriately defined, the effects of the present invention can be achieved without strictly defining the clearances CL1 and CL2. Therefore, a mold design in which only the clearances CL3 and CL4 are provided if necessary. Is also possible. From this point of view, a modified example of the mold configured is shown in FIG. This mold is for manufacturing a molded product having an inclined vertical wall portion, but is formed with a vertical wall without the convex portion 1a on the upper portion of the punch 1, and is formed on the lower portion of the punch 1. Due to the relationship that the jig 10 enters, the molding surface of the die 2 is inclined. Then, by appropriately setting the clearance CL3, CL4 between mandrel 10 and the die 2 is for molding by the action of the forming jig 10 and the die 2 a vertical wall portion having an inclination angle theta _1. The effect of the present invention can also be achieved by such a mold.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the following examples are not intended to limit the present invention, and are appropriately modified within a range that can be adapted to the descriptions given above and below. All of this is included in the technical scope of the present invention.

[Example 1]
About dimensional accuracy when using a 980 MPa class cold rolled steel sheet (thickness t: 1.2 mm) and forming a hat channel member by press molding with the mold of the present invention shown in FIG. 4 (rp = 5 mm), The effect of changing the clearance CL2 was investigated. At this time, CL1 = t was used as the clearance CL1 in which the flange surface jump angle could be suppressed to 0 °. The clearance CL2 is changed in six ways: (1) CL1 + 0 mm, (2) CL1 + 0.5 mm, (3) CL1 + 1.7 mm, (4) CL1 + 2.8 mm, (5) CL1 + 3.9 mm, and (6) CL1 + 5 mm. It was. The other conditions (die shoulder radius rd, molding height H, wrinkle holding force, etc.) were the same as described above. In each of the above cases (1) to (6), the flange jump angle θ was as follows.

(Flange spring angle θ)
(1) 48 °, (2) 26.9 °, (3) 4.3 °, (4) -1.3 °, (5) -1.0 °, (6) -1.7 °
FIG. 19 shows the relationship between the difference between the clearances CL2 and CL1 (CL2−CL1: mm) and the flange jump angle θ, when the product cross-sectional shape during normal molding (CL2−CL1 = 0 mm) and CL2−CL1 = 5 mm. 20A and 20B are compared with each other in terms of product cross-sectional shapes. As is apparent from these results, it is understood that when CL2−CL1 ≧ t (ie, CL2 ≧ CL1 + t), the flange jump angle θ is stable in the vicinity of 0 °.

  In the same manner as described above, the same examination was performed using a 590 MPa class cold-rolled steel plate (plate thickness: 1.2 mm). As a result, the flange jump angle θ in each of the above cases (1) to (6) was as follows.

(Flange spring angle θ)
(1) 25.5 °, (2) 7.5 °, (3) -0.6 °, (4) -0.7 °, (5) 0.0 °, (6) -0.4 °
The relationship between the difference between the clearances CL2 and CL1 (CL2−CL1: mm) and the flange jump angle θ is shown in FIG. 21, and it can be seen that the same tendency as in FIG. 19 is observed.

  By the way, it is conceivable that the dimensional accuracy depends on several other influencing factors in the mold [molding height H (FIG. 10), die shoulder radius rd, punch head shape, etc.]. . The present inventors examined these factors and found that these factors do not significantly affect the effects of the present invention. Next, the results of these studies are shown.

  With respect to dimensional accuracy when a hat channel member is formed by press molding using the mold of the present invention shown in FIG. 4 using a 980 MPa class cold-rolled steel sheet (thickness t: 1.2 mm), the molding height The effect was investigated by changing the height H. The molding height H at this time is changed in the range of (1) 30 mm, (2) 40 mm, (3) 50 mm, (4) 60 mm, (5) 67 mm by changing the position of the bottom dead center of the die. It was.

  With respect to the clearances CL1 and CL2, in FIG. 19, the molding height H is the flange jump angle θ under the conditions of CL1 = t (mm) and CL2 = CL1 + 5 (mm) in which the flange jump angle θ≈0 ° can be realized. We investigated the impact on In FIG. 6B, the molding height H is given to the wall warp under the conditions of CL1 = t + 0.2 (mm) and CL2 = CL1 + 5 (mm) in which wall warp≈0 (mm) can be realized. The impact was investigated.

  FIG. 22 shows the relationship between the molding height H and the flange jump angle θ, and FIG. 23 shows the relationship between the molding height H and the wall curvature curvature ρ. The wall warp curvature ρ is a value represented by 1 / d when the warp radius is d. As is apparent from these results, the dimensional defect amount becomes large in the case of normal molding, but in the case of the present invention, it can be understood that the defect amount is small and the molding height H has no influence.

  With respect to the dimensional accuracy when a hat channel member is formed by press-molding using a 980 MPa class cold-rolled steel sheet (thickness t: 1.2 mm) and the mold of the present invention shown in FIG. The effect of changing rd was investigated. The die shoulder radius rd at this time was changed in the range of (1) 5 mm, (2) 10 mm, and (3) 15 mm (molding height H was 67 mm).

  FIG. 24 shows the relationship between the die shoulder radius rd and the flange jump angle θ. Even if the die shoulder radius rd is increased to 15 mm, the effect of the present invention can be maintained, and the flange jump angle θ≈0 can be realized. I understand that. On the other hand, when a conventional mold is used (normal molding), it can be seen that the influence of the die shoulder radius rd greatly affects the flange jump angle θ. That is, it can be seen that the die shoulder radius rd need not be controlled within a very narrow range by using the mold of the present invention.

As long as the relationship between the clearances CL1 and CL2 defined in the present invention is satisfied, the shape of the punch head is not particularly limited as described above, but the various head shapes shown in FIGS. The influence on the dimensional accuracy (flange spring angle θ) when a hat channel member was produced by press-forming a 440 MPa class cold-rolled steel plate (plate thickness t: 1.2 mm) with a punch was investigated. Other conditions at this time were as follows.
(Press molding conditions)
Clearance: CL1 = t (mm), CL2 = CL1 + 5 (mm)
Die shoulder radius rd: 5mm
Punch shoulder radius rp: 5mm
Molding height H (Fig. 10): 67mm
Blank size: width 250mm, depth 40mm
Wrinkle pushing force (BHF): 10KN

  The result is shown in FIG. 25 in comparison with the case of normal molding. As is clear from this result, although there is a slight difference depending on the shape of the punch head, in the case shown in FIGS. It can be seen that the effect of the present invention is sufficiently exhibited even in the shape. However, if the axial length in the convex part of the punch head (that is, the length of the part corresponding to the initial stage of molding) is increased [FIG. 5 (b)], the effect of the present invention is reduced. Therefore, it is necessary to set to an appropriate length.

  The appropriate clearances clarified above are set [CL1 = t (mm), CL2 = CL1 + 5 (mm)], and the 590 MPa class hot dip galvanized steel sheet (sheet thickness t: 1.4 mm) not used above is used. On the other hand, a hat channel member was produced by press forming (the other conditions were the same as above). As a result, it was confirmed that a hat channel member with good dimensional accuracy was formed.

[Example 2]
Dimensional accuracy when a hat channel member is formed by press-molding using a 780 MPa class cold-rolled steel sheet (plate thickness t: 1.2 mm) with the mold of the present invention shown in FIG. 4 (rp = 5 mm). Then, the standby height ΔH (FIG. 7) of the blank holder was changed (ΔH = 0 mm, 20 mm) to investigate the influence. The press molding conditions at this time are as follows.
(Press molding conditions)
Clearance: CL1 = t + 0.2 (mm), CL2 = CL1 + 5mm
Die shoulder radius rd: 5mm
Punch shoulder radius rp: 5mm
Molding height H (Fig. 10): 67mm
Blank size: width 250mm, depth 40mm
Wrinkle pushing force (BHF): 10KN
Standby height ΔH: 0 mm (without standby), 20 mm

  At this time, the dimensional accuracy when the hat channel member is formed by a normal procedure (see FIGS. 9 and 10) using a normal mold shown in FIG. 26 (the protrusion 1a is not formed on the upper portion of the punch). (Press forming conditions are the same as above except that the clearance CL = 1.5 mm). Moreover, in any case, the blank holder 3 was raised together at the time of mold release.

  FIG. 27 shows a product cross-sectional shape when press-molding with each mold. Of these, FIG. 27 (a) shows a case where molding is performed using a normal mold, and it is understood that the wall warp and the angle change remain large, and the flange jump angle θ is also increased. . On the other hand, FIG. 27 (b) shows a cross-sectional shape of the product when the mold of the present invention is used (standby height ΔH = 0 mm). However, although the angle change is large, the wall warpage and the flange jump angle θ are You can see that it is getting smaller. FIG. 27 (c) shows a state in which molding is started in a state where the blank holder is made to stand by using the mold of the present invention (standby height ΔH = 20 mm), but any change in the wall warp angle becomes small. It can be seen that the flange jump angle θ is further reduced.

[Example 3]
Using a 780 MPa class cold-rolled steel sheet (thickness t: 1.2 mm), the hat channel is press-molded by the mold shown in FIG. 4 and the mold shown in FIG. 15 (with the forming jig 10). Each case of the following (A) and (B) was investigated about the dimensional accuracy when the member was molded.
(A) When raising the blank holder together at the time of mold release (B) When fixing the blank holder at the bottom dead center at the time of mold release The common press molding conditions at this time are as follows.
(Press molding conditions)
Die shoulder radius rd: 5mm
Punch shoulder radius rp: 5mm
Molding height H (FIGS. 10 and 15): 67 mm
Blank size: width 250mm, depth 40mm
Wrinkle pushing force (BHF): 10KN

  The clearances CL1 and CL2 of the mold shown in FIG. 4 were set to CL1 = 1.2 mm (= plate thickness) and CL2 = CL + 5 mm, respectively. The mold clearances CL1 to CL4 shown in FIG. 15 were set to CL1 = 1.2 mm (plate thickness), CL2 = 15 mm, CL3 = 1.2 mm (plate thickness), and CL4 = CL3 + 3 mm. In the mold shown in FIG. 15, the height from the upper surface of the blank holder to the protrusion 10a was 11 mm, and the shoulder radius of the protrusion 10a was 3 mm.

  At this time, the dimensional accuracy when the hat channel member was formed by press molding in each of the cases (A) and (B) using the ordinary mold shown in FIG. The molding conditions are the same as above except that the clearance CL = 1.5 mm).

  As a result, when molding was performed using a normal mold, the wall warp and the angle change remained large in both of the above (A) and (B), and the flange jump angle θ was also large [the above-mentioned See FIG. 27 (a)].

  On the other hand, when the mold shown in FIG. 4 is used and molded under the condition (A), a molded product with improved wall warpage as shown in FIG. 28 is obtained. However, when the molding was performed under the condition (B), wall warp occurred and the shape shown in FIG. 27 (a) was obtained. Further, when the mold shown in FIG. 15 was used, the wall warp was improved in any of the cases (A) and (B), and a molded product as shown in FIG. 28 was obtained. .

[Example 4]
A 780 MPa class cold-rolled steel sheet (thickness t: 1.2 mm) is used and is press-molded by the mold shown in FIG. 14 and the mold shown in FIG. 16 (the vertical wall portion has an inclination angle). The dimensional accuracy when the channel member was molded was investigated.
The common press molding conditions at this time are as follows.
(Press molding conditions)
Die shoulder radius rd: 5mm
Punch shoulder radius rp: 5mm
Inclination angle θ ₁ : 3 °
Molding height H (FIGS. 14 and 16): 67 mm
Blank size: width 250mm, depth 40mm
Wrinkle pushing force (BHF): 10KN

  The clearances CL1 and CL2 of the mold shown in FIG. 14 were set to CL1 = 1.2 mm (plate thickness) and CL2 (the narrowest portion directly under the punch head) = CL1 + 5 mm, respectively. Further, the clearances CL1 to CL4 of the mold shown in FIG. 16 are CL1 = 1.2 mm (plate thickness), CL2 (the narrowest portion directly under the punch head) = 15 mm, CL3 = 1.2 mm (plate thickness), CL4 = CL3 + 3 mm. In the mold shown in FIG. 16, the height from the upper surface of the blank holder to the protrusion 10a was 11 mm, and the shoulder radius of the protrusion 10a was 3 mm.

At this time, it was also investigated dimensional accuracy at the shaping of the press-molded to the hat-channel member using conventional mold shown in FIG. 29 (those inclined angle theta ₁ of the vertical wall portion is 3 °) (press molding The conditions are the same as above except that the clearance CL = 1.5 mm). Moreover, the blank holder was raised together at the time of mold release after shaping | molding.

  FIG. 30 shows the cross-sectional shape of the product when it is press-molded with each mold. Of these, FIG. 30 (a) shows a case where molding is performed using a normal mold, and it is understood that the wall warp and the angle change remain large, and the flange jump angle θ is also increased. . On the other hand, FIG. 30B shows the product cross-sectional shape when the mold shown in FIG. 14 is used, but it can be seen that the wall warp is partially improved but greatly improved. FIG. 30C shows a product cross-sectional shape when the mold shown in FIG. 16 is used, and it can be seen that the wall warpage is improved over the entire length of the vertical wall.

  These results were obtained when the blank holder was raised together at the time of mold release, but when the mold shown in FIG. 16 was used, the blank holder was fixed at the bottom dead center at the time of mold release. Even if it exists, it has confirmed that the same result [FIG.30 (c)] was obtained.

It is explanatory drawing which shows the external appearance example of a hat channel member. It is a schematic explanatory drawing which shows the main shaping | molding methods of a hat channel member. It is a figure for demonstrating an example of a dimensional accuracy defect. It is a schematic explanatory drawing which shows one structural example of the press molding die of this invention. It is a schematic explanatory drawing which shows the various shapes of the metal mold | die of this invention. It is a schematic explanatory drawing which shows the product cross-sectional shape when it press-molds on the conditions which changed the clearance CL1. It is a figure explaining the state when starting shaping | molding in the state which waited for the blank holder. It is a figure explaining the overrun generation | occurrence | production situation when making a blank holder wait and forming. It is explanatory drawing which shows the state of the metal mold | die at the time of a shaping | molding start. It is explanatory drawing which showed the state (molding bottom dead center) which completed shaping | molding of the metal plate. It is a figure explaining the state in which the overrun which generate | occur | produced in the metal plate is further amplified. It is a figure explaining the state in which reverse bending generate | occur | produces in the lower part 4a of the metal plate 4. FIG. It is a figure explaining the state of a metal plate when releasing a blank holder in the state locked at the bottom dead center. It is explanatory drawing when the member of the shape inclined so that it may spread as the vertical wall part shape | molded becomes lower is press-formed. It is a schematic explanatory drawing which shows one structural example of the press molding die of this invention. It is a schematic explanatory drawing which shows the other structural example of the press molding die of this invention. It is a schematic explanatory drawing which shows the formation procedure of a metal plate when the metal mold | die provided with the shaping | molding jig | tool 10 is used. It is explanatory drawing which shows the metal mold | die modification which provided only clearance CL3 and CL4. It is the graph which showed the relationship of the difference of clearance CL2 and CL1, and flange bounce angle (theta) when shape | molding using a 980 MPa class cold-rolled steel plate. It is explanatory drawing which compared and showed the product cross-sectional shape at the time of setting to the product cross-sectional shape at the time of normal shaping | molding, and CL2-CL1 = 5mm. It is the graph which showed the relationship between the difference of clearance CL2 and CL1, and flange jump angle (theta) when shape | molding using a 590 mPa class cold-rolled steel plate. It is the graph which showed the relationship between shaping | molding height H and flange jump angle (theta). It is the graph which showed the relationship between shaping | molding height H and wall curvature curvature (rho). 6 is a graph showing a relationship between a die shoulder radius rd and a flange jump angle θ. It is the graph which showed the result of investigating the influence which the shape of a punch has on the flange jump angle θ. It is a schematic explanatory drawing which shows one structural example of a normal press molding die. It is a schematic explanatory drawing which shows the product cross-sectional shape when press-molding with each metal mold | die. It is explanatory drawing which shows the cross-sectional shape of the product by which the wall curvature was improved using the metal mold | die of this invention. It is a schematic explanatory drawing which shows the normal metal mold | die when shape | molding the product in which the vertical wall part inclined. It is a schematic explanatory drawing which shows the product cross-sectional shape when press-molding with each metal mold | die.

Explanation of symbols

1 Punch 2 Die 3 Blank holder 4 Metal plate 10 Molding jig 10a Projection rd Die shoulder radius rp Punch shoulder radius BHF Wrinkle holding force

Claims (3)

A mold having at least a punch and a die for press-molding a metal plate, and forming a convex portion extending in the die direction in a punch head region corresponding to a portion formed at the initial stage of molding, The die does not have a recess, and at least a punch-die clearance CL2 corresponding to a portion formed immediately after the initial press forming is greater than a punch-die clearance CL1 corresponding to a portion formed in the initial press forming. Set widely (CL1 <CL2) and set the clearances CL1 and CL2 to satisfy the following formulas (1) and (2) when the thickness of the metal plate to be formed is t (mm). In the state where the forming of the vertical wall portion is completed, an overrun is generated in the metal plate, and the overrun is amplified at the time of mold release, and the metal plate is bent backward. Metal plate press-molding die, characterized in that to generate.
0.8 × t ≦ CL1 ≦ 1.2 × t (mm) (1)
CL2 ≧ CL1 + t (mm) (2)   2. The metal plate press-molding die according to claim 1, which is set so as to satisfy CL1 = t (mm).   A metal plate press molding method, wherein the metal plate is press molded using the press molding die according to claim 1.

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