JP2007118014A - Press-forming method and press-forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a press-forming method and a press-forming apparatus by which stable local heating treatment is applied. <P>SOLUTION: By setting stress controlling stage after a drawing stage and before a trimming/piercing stage, residual stress is removed by applying the local heat treatment to a portion of a primary formed part W1 after the drawing stage. As die structure, electrodes 8a, 9a are oppositely disposed on a lower pad 5 and an upper pad 7 for pressurizing and restraining the primary formed part W1 and also an auxiliary electrode plate 15 is accompanied on the side of the electrode 9a on one side. After a part of the primary formed part W1 is made into the two-layer superposing state together with the auxiliary electrode plate 15, they are pressurized with the upper and lower electrodes 8a, 9a and, by supplying power between those electrodes 8a, 9a, the local heating treatment is performed by the principle of resistance welding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and apparatus for press-molding a molded product having a predetermined shape by subjecting a metal plate to drawing molding, and in particular, suppresses a dimensional accuracy defect of the molded product due to an elastic restoring force (so-called springback) after molding. Therefore, the present invention relates to a press molding method and a press molding apparatus that use local heat treatment together.

  Dimensional accuracy defects such as opening, warping, camber (ridge warping), and twisting that occur in a molded product after press molding such as drawing are caused by the elastic restoration of the plastically deformed molded product. It depends on the distribution of the stress remaining in the molded product. For this reason, various techniques for suppressing dimensional accuracy defects by controlling the stress of the causative part have been proposed. As one of the techniques, for example, Patent Document 1 discloses a press molding technique using a local heat treatment in combination. .

In the technique described in Patent Document 1, in a press die having a punch as a lower die and a die as an upper die movable up and down with respect to the punch, a so-called spring back is generated at the time of press molding. Immediately before the die reaches the bottom dead center, a plurality of heating electrodes elastically supported via springs are embedded in the punch shoulder on the mold side corresponding to the ridge line of the product and the concave groove corner of the die, respectively. The heating electrode is energized and heated along the ridge line portion of the molded product.
JP-A-7-155856

  In such a conventional technique, it is difficult to heat a limited part at a stable temperature because it is energized and heated in a so-called single sheet state, and the intended purpose can be sufficiently achieved. Not only cannot be performed, but the control of the heat affected zone tends to become unstable, which may lead to a decrease in strength of the entire molded product.

  In addition, since the path portion that linearly connects the adjacent electrodes is heated, it is difficult to cope with a molded product having a complicated shape, and a pair of elastically supported electrodes are attached from one side of the metal plate. Because of the pressing, not only the molded product that is a metal plate is likely to be distorted but also the contact state of the electrode is likely to be unstable. In particular, if a gap occurs in the electrode contact portion, sparks are generated, which is not preferable.

  The present invention has been made paying attention to such a problem, and an object of the present invention is to provide a press molding method and a press molding apparatus that can perform a particularly stable local heat treatment.

  The invention according to claim 1 is a method of press-restraining a metal plate with a metal mold consisting of upper and lower molds and press-molding a molded product having a predetermined shape, and the press-restraining force of the mold is applied. Applying a local heat treatment to the specific part of the molded product that is energized in the superposition direction in a state where two metal plates including the molded product itself are overlapped, the stress at the specific part It is characterized by adjusting.

  In this case, as described in claim 2, a primary molding step of press-molding a molded product having a predetermined shape by pressurizing and restraining a metal plate with an upper and lower mold, and a molded product after the primary molding In the secondary molding step, the same local heating treatment as described above is performed in the secondary molding step. Shall.

  Further, the molding in the primary molding step is performed cold as described in claim 3.

  As described in claim 4, the energization for heating is performed with a pair of electrodes facing each other in the polymerization direction between the two stacked metal plates, and according to claim 5, As described above, the specific portion is a portion where a residual stress that deforms the molded product by the elastic restoring force when the pressurizing restraint force of the mold is released is generated.

  In addition, as described in claim 6, it is desirable that an auxiliary metal plate to be superimposed on the molded product is attached to any one of the electrodes in advance.

  The invention described in claim 8 captures the technique described in claim 1 as a press molding apparatus, and molds a specific part of a molded product to which a pressure restraining force of a mold is applied. It is provided with an energizing heat treatment means for adjusting the stress at the specific part by applying a local heat treatment by energizing the two metal plates including the product itself in the overlapping direction. Features.

  Therefore, in at least the inventions described in claims 1 and 8, when a specific part of the molded product is heated by Joule heat based on the same principle as so-called spot welding, the elastic restoring force is released when the pressurizing restraint force of the mold is released. Residual stress that deforms the molded article by force is extremely small.

  According to the first and eighth aspects of the invention, since the two metal plates including the molded product itself are energized and heated in a state of being overlapped, stable local heat treatment, and consequently, the heating part Stable stress adjustment is possible. In other words, since the two metal plates are energized and heated in a state where the two metal plates are overlapped with each other, a very limited and clear portion such as a boundary portion between the metal plates can be locally heated, and the thermally affected portion is also limited. For this reason, it is very easy to control the heated part, and stable stress adjustment by heating can be performed.

  In addition, as described above, since it is a method of energizing and heating in a state where two metal plates are overlapped, it is possible to prevent the occurrence of sparks, and in particular when the electrode is used to energize the electrode By adjusting the shape to the shape of the heated part of the molded product, it is possible to adjust the stress by local heating in a complicatedly shaped part such as a phase part.

  FIG. 1 and the following drawings show a more specific embodiment of the present invention. As a panel component to be molded, for example, a center pillar of a so-called hat-shaped cross section as shown in FIG. This is referred to as a “molded product”).

  As shown in FIG. 2, such a molded product W has a tensile stress on the top wall T at the end of molding by the mold (at the bottom dead center of the press) and a compressive stress on the flanges F on both sides of the side wall S. The above-mentioned stresses are released when the molds are released from the constraint of the mold, so that the left and right side wall parts S including the flange part F jump up in a direction away from each other. Dimensional accuracy defects called as occur. In view of this, the above-described tensile stress and compressive stress, which are residual stresses, are actively controlled to prevent defective dimensional accuracy.

  As shown in FIG. 3, the molded product W is roughly formed through a draw process (drawing process) S1 which is a primary molding process, a stress control process S2 which is a secondary molding process, and a trim and piercing process S3. .

  In the draw step S1, as shown in FIG. 4, a flat blank B, which is a metal plate (steel plate) of a predetermined size, is prepared, and the punch 1 and the upper that constitute the lower mold together with the blank holder 3 are prepared. Using a die composed of a die 2 functioning as a die, for example, cold-drawing into a hat-shaped cross-sectional shape by single action molding of a transfer press to obtain a primary molded product W1.

  Next, in the case of normal press molding, in the primary molded product W1 in which a relatively large dimensional accuracy defect appears, as a secondary molding, the primary molded product W1 is used by a mold after allowing for an amount of deformation as a dimensional accuracy defect. In this embodiment, stress control by local heating processing is performed in the stress control step S2.

  FIG. 5 shows the stress control step S2 which is a secondary forming step, which is processed in synchronization with the forming cycle (upper die lowering → molding → upper die raising) in other steps in the transfer press described above. In this process, stress control of a specific part of the primary molded product W1 is performed using a mold composed of upper and lower molds. That is, while the upper pad 7 as the upper die fixed to the slide 6 is lowered and raised with respect to the lower pad 5 as the lower die on the bolster 4 at the same timing as other steps in the transfer press, as will be described later. In addition, local heating treatment is performed by energizing a specific part of the primary molded product W1.

  More specifically, as shown in FIG. 5, the primary molded product W <b> 1 is pressure-constrained with the lower pad 5 and the upper pad 7 in the same manner as in the conventional wrist-like process so as to impart the shape freezing property of the molded product W itself. Although it corrects, it does not correct by squeezing by the pressure restraint force conventionally, but in the part corresponding to the top wall part T and the flange part F of the molded product W of the upper pad 7 and the lower pad 5. For example, by burying cylindrical electrodes 8a, 8b and 9a, 9b in advance and energizing while pressing and restraining them from above and below across the top wall portion T and flange portion F from near the bottom dead center of the press, The top wall portion T and the flange portion F are locally heated by the same principle as so-called spot welding so that the tensile stress and the compressive stress, which are internal stresses of the top wall portion T and the flange portion F, are extremely small. Mashiku shall be removed or lost their stress.

  Therefore, as the lower pad 5 and the upper pad 7 constituting the mold, the primary molded product W1 which is deformed by a so-called spring back (elastic restoring force) after drawing and is not in a normal shape is a normal shape. It is sufficient to have a function as a so-called pad that only restrains and holds, i.e., suppresses the deformation of the elastic region, and is constituted by a so-called simple structure.

  In the trim and piercing process as the final process, as shown in FIG. 6, while the upper holder 11 as the upper mold descends and rises with respect to the punch 10 as the lower mold at the same timing as the other processes in the transfer press, Based on the meshing between the scrap cutter 12 and the punch 10 on the upper holder 11 side, the non-product portion region attached to the flange portion F of the primary molded product W1 is cut and removed as scrap Sc and, if necessary, the punch 10 Otherwise, the piercing hole processing is performed by meshing the piercing punch (not shown) and the button die, which are attached to the upper holder 11 in advance.

  7 and 8 show details of the D part of the mold in the stress control step shown in FIG. 5. As shown in FIGS. 7 and 8 in addition to FIG. 5, primary molding of the lower pad 5 and the upper pad 7 is performed. The heating electrodes 8a, 8b and 9a, 9b that are paired on the upper and lower sides of the top wall portion T and the flange portion F of the product W1 are opposed to each other so as to face each other. The electrodes 8a, 8b and 9a, 9b are connected to the secondary side of a power source (not shown).

  Of these plural sets of electrodes 8a, 8b and 9a, 9b, the lower electrodes 8a, 8b are elastically supported by the electrode holder 13 so as to be movable up and down. 5 is set so as to be flush with the upper surface of 5 or slightly projecting from it, but when the molded product W1 is pressed and restrained by the lower pad 5 and the upper pad 7, the lower electrodes 8a, 8b The front end surface of the first molded product W1 is flush with the lower surface of the primary molded product W1, that is, the top wall portion T and the lower surface of the flange portion F, and is in pressure contact with the lower surface of the primary molded product W1.

  On the other hand, of the plurality of sets of electrodes 8a, 8b and 9a, 9b, the upper electrodes 9a, 9b are elastically supported by the electrode holder 14 so as to be movable up and down. Even if it is set so that it is flush with the lower surface of the electrode or slightly less than that, when the upper and lower pads 5 and 7 press-restrain one molded product W1, the tip surfaces of the upper electrodes 9a and 9b Is flush with the upper surface of the auxiliary electrode plate 15, which will be described later, and the upper electrodes 9 a, 9 b are connected to the upper surface of the primary molded product W 1 via the auxiliary electrode plate 15, that is, the top wall portion T and The upper surface of the flange portion F is press-contacted.

  More specifically, as shown in FIGS. 7 and 8, an auxiliary metal plate having a plate thickness equivalent to the plate thickness of the primary molded product W1 as an auxiliary metal plate below each of the upper electrodes 9a and 9b and having conductivity. The electrode plates 15 are arranged in a horizontal state, and the auxiliary electrode plates 15 are elastically supported by the respective electrode holders 14 through elastic means 16 such as compression coil springs so as to be movable up and down. In addition, since the auxiliary electrode plate 15 functions as a part of the electrode as the name suggests and is used repeatedly, it is difficult to join the steel plate as the primary molded product W1 and is used in a high temperature environment. It is desirable to form with the material excellent in durability which can be endured.

  As is clear from the above description, the upper and lower electrodes 8a, 8b and 9a, 9b and the auxiliary electrode plate 15 form an energizing heat treatment means for local heat treatment. A combination of the upper and lower electrodes 8a and 9a and the combination of 8b and 9b is taken as one set, and a large number of electrodes having such a combination are arranged at a predetermined pitch along the longitudinal direction of the molded product W shown in FIG. It is installed side by side.

  Therefore, in the stress control step S2 having such a mold structure, as shown in FIG. 5, if the primary molded product W1 formed in the previous drawing step is placed on the lower pad 5 and positioned. For example, the upper pad 7 is lowered, and the primary molded product W1 is pressure-restrained by the upper and lower pads 5 and 7. That is, the deformation | transformation by the elastic restoring force in the top wall part T and the flange part F of the primary molded product W1 after draw molding is corrected, and it restrains and hold | maintains to a regular shape.

  At the same time as the lower pad 7 reaches the bottom dead center position, the lower electrodes 8a and 8b are pressed against the lower surface of the primary molded product W1, and the upper electrodes 9a and 9b are also attached to the auxiliary electrode plate 15. And is in pressure contact with the upper surface of the primary molded product W1. More specifically, the upper and lower electrodes 8a, 9a and 8b, 9b are added so that the top wall portion T and flange portion F of the primary molded product W1 and the auxiliary electrode plate 15 are in close contact with each other. In this state, current is passed between the upper and lower electrodes 8a and 9a and between 8b and 9b, and the top wall portion T and the flange portion F of the primary molded product W1 are applied by the principle of so-called resistance welding or spot welding. Apply local heat treatment. In this case, the auxiliary electrode plate 15 and the primary molded product W1 are placed in a so-called double-stacked state at the pressurization sites between the upper and lower electrodes 8a and 9a and between the upper and lower electrodes 8a and 9b. Since the current at the joint surface with the electrode plate 15 is reduced, the current-carrying area is small and the current density is high, the amount of heat generated by so-called Joule heat generation is increased compared to the case of only a single plate, and in particular the primary molded product. Efficient local heat treatment can be performed with the joint surface between W1 and the auxiliary electrode plate 15 as the center. Further, as described above, by energizing in a so-called two-layered state, a gap is not easily generated between the two, but a spark is not generated.

  Note that the heating conditions such as the voltage between the electrodes 8a and 9a and between the electrodes 8b and 9b and the welding current are such that the temperature is not less than the melting point and above the recrystallization temperature of the material forming the molded product W1 at the local heating site. Is adjusted in advance. In particular, in the present embodiment, as described above, since processing by a transfer press is premised, the pressurization restraint time and energization time between the upper and lower electrodes 8a, 9a and 8b, 9b are the upper and lower sides of the press. The voltage, current and the like are adjusted in advance as described above so that the target heating temperature is sufficiently obtained within that time. As a result, spatter does not scatter as in general spot welding.

  Thus, when the primary molded product W1 is subjected to the local heating treatment, the residual stress at the top wall portion T and the flange portion F of the primary molded product W1, which is the local heating portion, is remarkably reduced, and the shape freezing property of the so-called molded product W is reduced. Even if the pressure restraining force of the mold is subsequently released, deformation due to the elastic restoring force (so-called spring back) is greatly suppressed.

  As described above, according to the present embodiment, it is possible to perform a stable heat treatment at a locally extremely limited position in the molded product W, thereby significantly reducing the residual stress remaining in the molded product W. The deformation due to the elastic restoring force of the molded product W can be significantly suppressed.

  Further, when the heat treatment is locally applied to the curved surface portion or the like of the molded product W, it can be very easily handled by using the electrodes 8a, 8b and 9a, 9b according to the curved surface shape. It becomes like this.

The principal part perspective view which shows an example of the molded article which this invention makes a shaping | molding object. Explanatory drawing which shows the generation | occurrence | production situation of the tensile stress and the compressive stress accompanying the draw forming of the molded article shown in FIG. Schematic explanatory drawing which shows the shaping | molding procedure of the molded article shown in FIG. Cross-sectional explanatory drawing which shows the detail of the draw process shown in FIG. Cross-sectional explanatory drawing which shows the detail of the stress control process shown in FIG. Cross-sectional explanatory drawing which shows the detail of the trim piercing process shown in FIG. It is a figure which shows the detail of the D section shown in FIG. 5, Comprising: Explanatory drawing at the time of upper mold | type raise. It is a figure which shows the detail of the D section shown in FIG. 5, Comprising: Explanatory drawing at the time of upper mold | type lowering.

Explanation of symbols

1 ... Punch (lower mold)
2. Die (upper die)
3. Blank holder (lower mold)
5 ... Lower pad (lower mold)
7… Upper pad (upper mold)
8a, 8b ... Electrodes (electric heating treatment means)
9a, 9b ... Electrode (energization heat treatment means)
15 ... Auxiliary electrode plate as an auxiliary metal plate (electric heating treatment means)
16: Compression coil spring (elastic means)
B ... Blank material (steel plate)
F ... Flange part S ... Side wall part S1 ... Draw process S2 ... Stress control process S3 ... Trim and piercing process T ... Top wall part W ... Molded article (center pillar)
W1 ... Primary molded product

Claims (12)

A method of press-molding a molded product of a predetermined shape by pressurizing and restraining a metal plate with a mold composed of upper and lower molds,
Local heat treatment by energizing the specific direction of the molded product to which the pressure restraining force of the mold is applied, in the direction of polymerization in a state where two metal plates including the molded product itself are overlapped with each other Is applied to adjust the stress at the specific part. A primary molding step in which a metal plate is press-restrained with a mold composed of upper and lower molds and a molded product of a predetermined shape is press-molded,
A secondary molding step of correcting the molded product with the pressure restraint force of the mold in order to impart shape freezing property to the molded product after the primary molding;
Including
In the secondary forming step, with respect to a specific part of the molded product to which the pressure restraining force of the mold is applied, the two metal plates including the molded product itself are overlapped in the polymerization direction. The press molding method according to claim 1, wherein a local heat treatment is performed by energization to adjust a stress at the specific part. The press forming method according to claim 2, wherein the forming in the primary forming step is performed in a cold state.   The press molding method according to any one of claims 1 to 3, wherein electricity is passed through a pair of electrodes facing each other in the polymerization direction between the two metal plates superimposed.   5. The press molding according to claim 4, wherein the specific part is a part where a residual stress is generated that causes the molded product to be deformed by an elastic restoring force when the pressure restraining force of the mold is released. Method.   6. The press molding method according to claim 4, wherein an auxiliary metal plate to be overlaid with the molded product is attached to one of the electrodes in advance.   The press molding method according to any one of claims 1 to 6, wherein the local heat treatment is performed under a temperature condition such that a specific part of the molded product has a temperature higher than a recrystallization temperature and lower than a melting point. An apparatus for press-molding a molded product having a predetermined shape by pressurizing and restraining a metal plate with a mold composed of upper and lower molds,
Local heating treatment is performed by energizing in the polymerization direction in a state where two metal plates including the molded product itself are superimposed on a specific part of the molded product to which the pressure restraining force of the mold is applied. A press molding apparatus, comprising: an electric heating processing means for adjusting the stress at the specific portion.   The energization heat treatment means includes at least a pair of electrodes facing each other in the superposition direction across at least two superposed metal plates so as to energize in the superposition direction across the two superposed metal plates. The press molding apparatus according to claim 8, wherein the press molding apparatus is provided.   The said specific site | part is a site | part which generate | occur | produces the residual stress which deform | transforms a molded article with an elastic restoring force when the pressurization restraint force of a metal mold | die is cancelled | released. Press molding equipment.   The energization heat treatment means includes an auxiliary metal plate that is attached to one of the electrodes in advance and overlapped with the molded product in addition to the pair of electrodes. The press molding apparatus according to 10.   The local heat treatment by the energization heat treatment means is performed under a temperature condition in which a specific part of the molded product has a temperature higher than a recrystallization temperature and lower than a melting point. Press molding equipment.

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