JP2017217661A - Manufacturing method of closed cross-section structure member and upper die for o forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a closed cross-section structural member capable of suppressing buckling upon O forming when forming the closed cross-section structural member according to UO forming from high-strength and thin-wall material.SOLUTION: A manufacturing method of a closed cross-section structural member includes: a U forming process of providing a U formed article having a pair of lateral walls according to press forming using a punch and a die; a preforming process of deforming the U formed article provided according to the U forming process such that end parts of the pair of lateral walls get near to each other and, thereby, providing a preformed article which causes extension lines of the pair of lateral walls to intersect each other in a cross-section view on at least a part of axial directions and has not a part of a shape protruded to the inner surface side in a cross-sectional view on all parts of the axial directions; and an O forming process of setting the preformed article provided by the preforming process onto a lower die, holding the preformed article between the lower die and an upper die and providing an O formed article of which shapes of the outer surface side are shapes along forming surfaces of the upper die and the lower die.SELECTED DRAWING: Figure 4A

Description

  The present invention relates to a method for manufacturing a closed cross-section structural member and an upper mold for O molding.

  Conventionally, so-called UO molding is known as a method of molding a tube (see, for example, Patent Document 1). UO molding is a method in which a single plate material is first molded into a U-shaped product having a U-shaped cross section, and then the U-shaped product is sandwiched between upper and lower molds to form a closed cross-section structural member (O molded product). is there. UO forming is mainly used for the production of line pipes used for transportation of petroleum and the like, and is performed using a thick steel plate having a thickness of 6 mm or more as a raw material.

International Publication No. 2005/063418

  By the way, in recent years, in order to reduce the weight of an automobile in consideration of global environmental problems, it has been desired to apply a closed cross-section structure member manufactured from a high-strength and thin material to the body of the automobile.

  However, when a closed cross-section structural member is formed from a high-strength and thin material by UO molding, there is a problem that it is difficult to obtain a desired shape. Specifically, when the U molded product is sandwiched between the upper and lower molds (in the case of O molding), the side wall of the U molded product may buckle, and as a result, the shape along the molding surface of the upper and lower molds may be It may not be obtained.

  Here, as described in Patent Document 1, as a countermeasure, C molding (C press) may be performed before U molding. However, when a thin plate is used as a material, there are problems in the following points.

That is, when obtaining a U-shaped product from a thin plate, it is usually performed by press molding using a die and a punch die from the viewpoint of productivity. When the press molding method is drawing, the side wall is bent and stretched at the shoulder of the die, and the shape obtained by C molding disappears. When the press molding method is bending molding, the shape obtained by the C molding disappears if all of the side walls are pushed between the die and the punch. Further, as shown in FIG. 12, even if the vicinity of the end of the side wall is not pushed between the die 164 and the punch 162 so that the shape obtained by the C molding remains, the portion that has exited the die shoulder 164A is O Bending in the opposite direction to forming (O-press) may cause unintended buckling.
In other words, if press molding, which is usually performed with a thin material, is used for U molding, the effect of C molding is lost, or a molded portion by C molding hinders O molding.

  Accordingly, the present disclosure provides a method for manufacturing a closed cross-section structural member that can suppress buckling during O molding when the closed cross-section structural member is molded from a high-strength and thin material by UO molding. With the goal.

  A manufacturing method of a closed cross-section structural member that solves the above problems includes a U molding step for obtaining a U molded product having a pair of side walls by press molding using a punch and a die, and a U molded product obtained by the U molding step. , The ends of the pair of side walls are deformed so as to approach each other, and the extension lines of the pair of side walls intersect in a cross-sectional view in at least a part of the axial direction, and in a cross-sectional view in the entire axial direction. A preforming step for obtaining a preformed part having no convex portion on the inner surface side, and a preformed product obtained by the preforming step are set in a lower mold and sandwiched between upper molds, and the shape on the outer surface side is An O molding step of obtaining an O molded product having a shape along the molding surface of the upper mold and the lower mold.

  As described above, according to the manufacturing method of the closed cross-section structural member according to the present disclosure, when the closed cross-section structural member is formed by UO molding from a high-strength and thin material, buckling during O molding is suppressed. can do.

It is a perspective view which shows the raw material steel plate of this embodiment. It is a perspective view which shows the U molded product of this embodiment. It is a perspective view which shows the preformed product of this embodiment. It is a perspective view which shows O molded product of this embodiment. It is the figure seen from the apparatus axial direction which shows the state by which the raw steel plate was set to the U press apparatus of this embodiment. It is the figure seen from the apparatus axial direction which shows the state which shape | molded the U molded product with the U press apparatus of this embodiment. It is a cross-sectional view which shows the preformed product of this embodiment. It is the figure seen from the apparatus axial direction which shows the state by which the U molded product was set to the preforming apparatus of this embodiment. It is the figure seen from the apparatus axial direction which shows the state which shape | molded the preform by the preforming apparatus of this embodiment. It is the figure seen from the apparatus axial direction which shows the state by which the U molded product was set to the preforming apparatus of another form. It is the figure seen from the apparatus axial direction which shows the state which shape | molded the preform by the preforming apparatus of another form. It is the figure seen from the apparatus axial direction which shows the state at the moment when a preformed article was set in the O press apparatus of this embodiment, and the upper mold | type contacted a pair of edge part of a preformed article. It is the figure seen from the apparatus axial direction which shows the state in the middle of O shaping | molding by the O press apparatus of this embodiment. It is the figure seen from the apparatus axial direction which shows the state which shape | molded O molded article with the O press apparatus of this embodiment. It is a figure which shows the O shaping | molding process which concerns on the comparative example 1, and is a figure which shows the state in the moment when the upper mold | type contacted a pair of edge part of the U molded product which is a workpiece. It is a figure which shows a mode that the side wall of the workpiece was buckled in the O shaping | molding process which concerns on the comparative example 1. FIG. It is a cross-sectional view showing a preformed product according to Comparative Example 2. It is a figure which shows a mode that the side wall of the workpiece was buckled in the O shaping | molding process which concerns on the comparative example 2. FIG. It is a cross-sectional view showing a preformed product according to a modification. It is a cross-sectional view showing a preformed product according to a modification. It is a cross-sectional view showing a preformed product according to a modification. It is a cross-sectional view showing a U molded product according to a modification. FIG. 10B is a cross-sectional view showing a preformed product obtained by preforming the U molded product shown in FIG. 10A. FIG. 10B is a cross-sectional view showing an O-shaped product obtained by O-molding the preform shown in FIG. 10B. It is a cross-sectional view showing a U molded product according to a modification. It is a cross-sectional view showing a preformed product obtained by preforming the U molded product shown in FIG. 11A. It is a cross-sectional view which shows O molded product obtained by carrying out O molding of the preformed product shown to FIG. 11B. When U molding is performed by press molding using a die and a punch die after C molding, the end portion of the side wall is not pushed between the die and the punch so that the shape obtained by C molding remains. It is a figure which shows the deformation | transformation state in a case.

  Hereinafter, the manufacturing method of the closed cross-section structural member which concerns on embodiment is demonstrated. In the manufacturing method of a closed cross-section structural member, as shown in FIGS. 1A to 1D, a U-shaped product 20 is formed from a raw steel plate 10 (U-shaped), and a preformed product 30 is formed from the U-shaped product 20 (preliminary). Molding), an O molded product 40 as a “closed cross-section structural member” is molded from the preform 30 (O molding).

-U molding process-
(U molded product 20)
The U molded product 20 will be described with reference to FIGS. 1B and 2B. 1B indicates the width direction of the U molded product 20, arrow A indicates the upper side of the U molded product 20, and arrow L indicates the axial direction of the U molded product 20.

  FIG. 2B shows a cross section obtained by cutting the U molded product 20 along a plane orthogonal to the axial direction (that is, a cross section of the U molded product 20). As shown in this figure, the U molded product 20 has an open cross-sectional structure opened upward (that is, a structure having a U-shaped cross section). Specifically, it is configured to include a pair of side walls 22 that extend in the vertical direction and are opposed in the width direction, and a bottom wall 24 that connects the lower portions of the pair of side walls 22. The shape of the bottom wall 24 is a substantially semicircular cross-sectional shape opened upward. Hereinafter, the upper end portion of the pair of side walls 22 is referred to as “a pair of end portions 26”.

  In order to simplify the drawing, FIG. 1B shows a U-shaped product 20 having the same cross-sectional shape regardless of the position in the axial direction. However, the U-shaped product 20 depends on the position in the axial direction. The cross-sectional shape may be different.

(U press device 60)
A U press device 60 for forming the U molded product 20 will be described with reference to FIGS. 2A and 2B. In these drawings, the arrow W is the apparatus width direction of the U press apparatus 60, the arrow A is the apparatus upper side of the U press apparatus 60, and the direction perpendicular to the paper surface is the apparatus axial direction of the U press apparatus 60. And the apparatus width direction of the U press apparatus 60 and the width direction of the U molded product 20 match, the apparatus vertical direction of the U press apparatus 60 and the vertical direction of the U molded article 20 match, and the U press The apparatus axial direction of the apparatus 60 and the axial direction of the U molded product 20 coincide with each other.

  The U press device 60 includes a punch 62 that constitutes the upper portion of the U press device 60 and a die 64 that constitutes the lower portion of the U press device 60. Further, the U press device 60 includes a pair of blank holders 66 positioned on both sides in the device width direction.

  The punch 62 has a molding surface corresponding to the shape on the inner surface side of the U molded product 20. The die 64 has a molding surface corresponding to the shape of the outer surface side of the U molded product 20. By changing the shape of the molding surface of the punch 62 and the die 64 depending on the position in the apparatus axial direction, the U molded product 20 having a different cross-sectional shape depending on the position in the axial direction can be formed.

  The pair of blank holders 66 are located on the outer side in the apparatus width direction from the molding surface of the die 64 and above the die 64. As a result, as shown in FIG. 2A, the material steel plate 10 set on the die 64 can be pressurized from the vertical direction of the apparatus by the die 64 and the blank holder 66.

  A moving device (not shown) is connected to the punch 62, and the moving device is constituted by a hydraulic device, an electric drive device, or the like. As a result, the punch 62 is configured to be movable in the vertical direction of the apparatus (the direction in which it is in contact with and away from the die 64) by the moving device.

(U molding process)
A U forming process in which U forming is performed on the material steel plate 10 by the U press device 60 will be described.

  First, as shown in FIG. 2A, the raw steel plate 10 is installed (set) on the die 64. And the blank holder 66 and the die | dye 64 pressurize the part of the width direction both ends of the raw steel plate 10. FIG.

  In addition, although the tensile strength of the raw steel plate 10 is not specifically limited, For example, 440 Mpa or more is preferable. More preferably, it is 780 MPa or more, or 980 Mpa or more. Moreover, the plate | board thickness of the raw material steel plate 10 is although it does not specifically limit, Preferably it is 0.6 mm or more and 3.6 mm or less, More preferably, it is 2.3 mm or more and 3.6 mm or less.

  Next, in a state where the blank steel plate 10 and the die 64 are pressurized, the punch 62 is moved relative to the die 64 relative to the die 64 by the moving device.

  And as FIG. 2B shows, the U molded article 20 is shape | molded by moving the punch 62 to a bottom dead center.

―Pre-molding process―
Next, the preforming process will be described. In the preforming step, the U-shaped product 20 is deformed to obtain the preformed product 30.

(Pre-formed product 30)
A preform 30 is shown in FIGS. 1C and 3. In these figures, the arrow W is the width direction of the preform 30, the arrow A is the upper side of the preform 30, and the arrow L is the axial direction of the preform 30. In addition, the direction orthogonal to the paper surface of FIG. 3 coincides with the axial direction of the preform 30.

  As shown in FIG. 3, the preform 30 has an open cross-sectional structure opened upward and has a pair of side walls 32, as with the U-shaped product 20. However, one (left side in the figure) of the pair of side walls 32 is inclined inward in the width direction (right side in the figure) toward the end 36. Further, the other side wall 32 (right side in the figure) is inclined inward in the width direction (left side in the figure) toward the end portion 36. In other words, the pair of side walls 32 are both inclined obliquely upward inside (upward and in the width direction) so that the end portions 36 approach each other.

  As a result, assuming a virtual line (extension line IL, see FIG. 3) in which the pair of side walls 32 are extended from the end portions 26, the extension lines IL intersect each other. Further, as shown in FIG. 3, in the cross section of the preform 30, the distance D <b> 1 between the pair of end portions 36 is smaller than the dimension (inner dimension) D <b> 2 in the width direction of the preform 30. It has become.

As shown in FIG. 3, the preform 30 does not have a convex portion on the inner surface 30 </ b> A side of the preform 30 in a cross-sectional view.
For example, the preformed product 130 according to the comparative example 2 shown in FIG. 8A has a part (concave portion 38) having a convex shape on the inner surface 130A side of the preformed product 130 in a cross-sectional view. In other words, the preformed product 130 according to the comparative example 2 has the concave portion 38 having a convex shape on the inner surface 130 </ b> A side of the preformed product 130 in a cross-sectional view.
On the other hand, the preform 30 of the present embodiment does not have the convex recess 38 on the inner surface 30A side of the preform 130 in a cross sectional view.

(Pre-molding process)
Next, as a specific method of preforming, a first preforming method and a second preforming method will be described.

The first preforming method will be described with reference to FIGS. 4A and 4B.
In the first preforming method, the preforming apparatus 70 shown in FIG. 4A is used. The preforming device 70 is configured to include a jig 72 to which the U-shaped product 20 is fixed and a pair of biasing tools 74 for applying a processing force for preforming.

  First, the bottom wall 24 of the U molded product 20 is fixed to the jig 72. This fixing is performed, for example, by providing a fixing hole (not shown) in the bottom wall 24 of the U molded product 20 and inserting a pin (not shown) protruding from the jig 72 into the fixing hole. In addition, as the jig 72, a lower mold 94 of an O press device 90 described later may be used as it is. In short, it is only necessary to fix a portion (bottom wall 24) between the vertical walls 24 that is not pre-formed so that the U-shaped product does not wobble and interfere with the pre-forming.

  Next, the bending tool 74 is disposed on the outside in the width direction of the pair of side walls 22. Each of the bending tools 74 has a processing surface 74A that contacts the U-shaped product 20 and applies a processing force. The processing surface 74A is inclined upward in the apparatus (in an oblique direction toward the inside of the apparatus and upward of the apparatus) as it goes inward in the apparatus width direction.

  Then, as shown in FIG. 4A, each of the pair of bending tools 74 is moved inward in the width direction. Thereby, 74 A of process surfaces contact the pair of side wall 22 of the U molded product 20, and the processing force to the width direction inner side is added. And a pair of side wall 22 deform | transforms inside, and the preform 30 is shape | molded (refer FIG. 4B).

  The moving direction of the pair of bending tools 74 is not limited to the above-described inner side in the width direction, and may be a direction including a component on the inner side in the width direction. For example, the moving direction of the pair of bending tools 74 may be an oblique direction that faces inward and downward in the width direction. Further, the processing surface 74A of the bending tool 74 is not limited to the inclined surface as described above, and may be a vertical surface extending in the vertical direction of the apparatus.

The second preforming method will be described with reference to FIGS. 5A and 5B.
The second preforming method is performed by a preforming apparatus 80 shown in FIG. 5A. The pre-forming device 80 includes a jig 82 on which the U-shaped product 20 is set, and a punch 84 disposed above the jig 82. A moving device (not shown) is connected to the punch 84, and the moving device is constituted by a hydraulic device, an electric drive device, or the like. Accordingly, the punch 84 is configured to be movable in the vertical direction of the apparatus (direction in which the jig 82 is in contact with and separated from the jig 82) by the moving device.

  The punch 84 has a pair of processed surfaces 84A. The pair of processed surfaces 84 </ b> A is positioned above the pair of end portions 26 of the U molded product 20 set on the jig 82. Each of the pair of processed surfaces 84A is inclined upward in the apparatus (in an oblique direction toward the inside of the apparatus and upward of the apparatus) toward the inside in the apparatus width direction. A pad 86 is provided in the center of the punch 84 in the apparatus width direction. Note that the inclination angle and the specific shape of the pair of processed surfaces 84A are set so that buckling does not occur in the preforming step.

  First, as shown in FIG. 5A, the U molded product 20 is set on the jig 82, and the bottom wall 24 of the U molded product 20 is pressed and clamped by the jig 82 and the pad 86. Then, the punch 84 is moved downward in the apparatus. Since the pair of end portions 26 of the U-shaped product 20 are positioned below the processing surface 84A of the punch 84, the processing surface 84A contacts the pair of end portions 26. Since the processing surface 84A is inclined upward in the apparatus as it goes inward in the apparatus width direction, when the punch 84 continues to move downward in the apparatus, a processing force inward in the apparatus width direction is applied to the pair of end portions 26. Thereby, a pair of side wall 22 of the U molded product 20 deform | transforms inside, and the preform 30 is shape | molded (refer FIG. 5B).

  In the preforming process, it is not always necessary to apply a processing force to the entire side wall 22 of the U-shaped product 20 in the axial direction (perpendicular to the paper surface in FIGS. 5A and 5B). That is, the U molded product 20 may be deformed by applying a processing force to a part of the side wall 22 of the U molded product 20 in the axial direction. In this case, in the U-shaped product 20, a portion to which a processing force is applied (a part in the axial direction) and a peripheral portion thereof are deformed by the processing force, and deformation may not occur in other portions. The molded product thus obtained is also included in the “preformed product” of the present disclosure. That is, in the “pre-formed product” of the present disclosure, the extension lines IL of the pair of side walls 32 do not need to intersect each other in the cross-sectional view in the entire axial direction, and a pair in the cross-sectional view in at least a part of the axial direction. The extension line IL of the side wall 32 may be crossed. This is because, if the extension lines IL intersect each other in a cross-sectional view in at least a part of the axial direction, the effect of suppressing buckling during O molding, which will be described later, is exhibited to a certain extent.

―O-molding process―
(O molded product 40)
The O molded product 40 will be described with reference to FIGS. 1D and 6C. 1D is the width direction of the O molded product 40, the arrow A is the upper side of the O molded product 40, and the arrow L is the axial direction of the O molded product 40.

  As shown in these drawings, in the O molded product 40, portions 46 (a pair of joining end portions 46) corresponding to the pair of end portions 36 of the preformed product 30 are in abutment with each other. Thereby, the O molded product 40 has a closed cross-sectional structure with a cross-sectional shape whose cross-sectional shape is closed. Specifically, the O molded product 40 of the present embodiment has a closed cross-sectional structure with a circular cross-sectional shape. The pair of joining end portions 46 do not need to be in complete contact with each other, and those having a slight opening between the pair of joining end portions 46 are also included in the “O molded product” or “closed cross-section structural member”. .

  In order to simplify the drawing, FIG. 1D shows an O molded product 40 having the same closed cross-sectional shape (circular shape) regardless of the axial position, but the axial position of the cross section is shown. Therefore, the cross-sectional shape may be different (for example, a circular cross-section having a different diameter depending on the position in the axial direction).

(O press device 90)
An O press apparatus 90 for forming the O molded product 40 will be described with reference to FIG. 6A. In this figure, the arrow W is the apparatus width direction of the O press apparatus 90, the arrow A is the apparatus upper side of the O press apparatus 90, and the direction perpendicular to the paper surface is the apparatus axial direction of the O press apparatus 90. The device width direction of the O press device 90 and the width direction of the O molded product 40 are matched, and the device vertical direction of the O press device 90 and the vertical direction of the O molded product 40 are matched. The apparatus axial direction of the apparatus 90 and the axial direction of the O molded product 40 are coincident.

  As shown in FIG. 6A, the O press device 90 includes an upper die 92 that constitutes the upper portion of the O press device 90 and a lower die 94 that constitutes the lower portion of the O press device 90. Has been.

  The upper mold 92 has a molding surface 92A corresponding to the shape of the upper outer surface side of the O molded product 40, and the lower mold 94 is molded corresponding to the shape of the lower outer surface side of the O molded product 40. It has a surface 94A. That is, the shape obtained by combining the shape of the molding surface 92A of the upper mold 92 and the shape of the molding surface 94A of the lower mold 94 is a shape corresponding to the shape of the entire O molded product 40 on the outer surface 40B side.

  The upper die 92 is connected to a moving device (not shown), and the moving device is constituted by a hydraulic device, an electric drive device, or the like. Thereby, the upper mold 92 is configured to be movable in the vertical direction of the apparatus (direction in which the lower mold 94 is in contact with and separated from) by the moving device.

  Further, the upper mold 92 has a pair of inclined surfaces 92B on the outer side in the apparatus width direction of the molding surface 92A. Both of the pair of inclined surfaces 92B are formed continuously from the outer end portion of the molding surface 92A in the apparatus width direction, and are inclined downward in the apparatus width direction (lower die 94 side) toward the outer side in the apparatus width direction. Is desirable. On the other hand, the lower mold 94 preferably includes an inclined surface 94B having a shape that comes into contact with the inclined surface 92B of the upper mold 92 when the upper mold 92 is moved downward by the moving device.

  Since the inclined surface 92B of the upper die 92 is inclined downward in the apparatus width direction toward the outside in the apparatus width direction, the following effects can be obtained. That is, in the process of moving the upper die 92 to the lower side of the apparatus, even if the end portion 36 of the preform 30 is in contact with the inclined surface 92B outside the apparatus than the molding surface 92A, the upper mold 92 is inclined. The end portion 36 is guided to the inside of the apparatus by the inclined surface 92B and easily enters the molding surface 92A. Note that the inclination angles of the inclined surfaces 92B and 94B are preferably 45 ° or more with respect to the horizontal. That is, when the cross-sectional shape of the molding surface 92A is semicircular, it is desirable that the angle formed by the outer end portion of the molding surface 92A and the inclined surface 92B is larger than 135 °.

(O molding process)
The O molding process performed on the preform 30 by the O press device 90 will be described with reference to FIGS. 6A to 6C.

  First, the preform 30 is set on the lower mold 94. In this state, the bottom wall 34 of the preform 30 is disposed on the molding surface 94A of the lower mold 94. Then, the pair of end portions 36 of the preform 30 are in a state of protruding upward from the lower mold 94. As a method of setting the preform 30 on the lower mold 94, for example, a fixing hole (not shown) is provided in the bottom wall 34 of the preform 30 and a pin protruding from the lower mold 94 is omitted in this fixing hole (not shown). There is a way to insert.

  Next, in this state, the upper die 92 disposed above the lower die 94 is moved downward. FIG. 6A shows a state at the moment when the pair of end portions 36 of the preform 30 contacts the forming surface 92A of the punch 84. When the upper die 92 is further moved downward, the pair of end portions 36 of the preform 30 approach each other along the molding surface 92A of the upper die 92 (see FIG. 6B). Then, as shown in FIG. 6C, when the upper mold 92 moves to the bottom dead center, the pair of joining end portions 46 are brought into contact with each other. Thereby, the O molded product 40 having a shape along the molding surfaces 92A and 94A of the upper die 92 and the lower die 94 is formed.

  Finally, the pair of end portions 46 of the O molded product 40 are joined to each other by welding or the like, thereby completing the manufacture of the closed cross-section structural member.

<Action and effect>
The operation and effect of the present embodiment will be described in comparison with Comparative Example 1 and Comparative Example 2.

  The method for forming the closed cross-sectional structure of Comparative Example 1 proceeds to the O forming step after the U forming step without passing through the pre-forming step.

  As shown in FIG. 7A, in Comparative Example 1, the workpiece to be subjected to the O molding process is a U molded product 20. The pair of side walls 22 of the U-shaped product 20 extends in the vertical direction (the vertical direction of the O press device 90, that is, the mold clamping direction). Therefore, when the upper die 92 of the O press device 90 is moved downward and the molding surface 92A of the upper die 92 contacts the end portion 26 of the U-molded product 20, the side wall 22 extends to the side wall 22. Compressive load in the direction to act (compressive stress occurs). The side wall 22 may be buckled by this compressive load, and as a result, as shown in FIG.

  The molding method of the closed cross-section structure of Comparative Example 2 is the same as the present embodiment in that it proceeds to the O molding process after the U molding process, but the preforming process obtained by the preforming process. The shape of the product is different from the present embodiment.

  FIG. 8A shows a preform 130 obtained by the preforming process according to Comparative Example 2. As shown in this figure, in the preformed product 130 according to the comparative example 2, the extension lines IL at the pair of end portions 26 cross each other in the cross-sectional shape as in the present embodiment. However, the preformed product 130 according to the comparative example 2 has a part (concave portion 38) having a convex shape on the inner surface 130A side of the preformed product 130 in a cross-sectional view. In other words, the preformed product 130 has a concave portion 38 having a convex shape on the inner surface 130A side of the preformed product 130 in a cross-sectional view.

  When O molding is performed using this preformed product 130, the workpiece is bent to the inner surface side starting from the recess 38, and the shapes along the molding surfaces of the upper die 92 and the lower die 94 are formed as shown in FIG. 8B. There is a high possibility that it will not be obtained.

  In contrast to Comparative Example 1 and Comparative Example 2, according to the manufacturing method of the closed cross-section structural member of the present embodiment, the workpiece to be subjected to the O molding step is the preform 30, and the preform 30 is crossed. There is no convex concave portion on the inner surface 30A side of the preform 30 in plan view. For this reason, a bending load in the direction along the molding surface is likely to act on the side wall 32 of the workpiece (pre-formed product 30) subjected to the O molding process. Therefore, according to the manufacturing method of the closed cross-section structural member of the present embodiment, the buckling of the side wall 32 is suppressed as compared with Comparative Example 1 and Comparative Example 2 described above, and an O molded product having a desired shape is obtained. It becomes easy and the yield is good.

(Supplementary explanation of the embodiment)
In addition, as shown in FIG. 3, the preform 30 of the above-described embodiment is configured such that most of the pair of side walls 32 are inclined inward in the width direction toward the end portion 36. However, the preformed product obtained by the preforming process may be a preformed product having a shape as shown in FIGS. 9A, 9B, and 9C.

  9A, only the vicinity of the end portion 36 of the pair of side walls 32 is inclined inward in the width direction toward the end portion 36. Thus, even if only the vicinity of the end portion 36 is inclined, there is an effect of suppressing buckling in the O molding process.

  9B and 9C, only one side wall 32 of the pair of side walls 32 (the right side in the figure) is inclined inward in the width direction toward the end portion 36. Specifically, in the preform 30 shown in FIG. 9B, most of one side wall 32 is inclined, and the preform 30 shown in FIG. Only the vicinity is inclined. Even in these modes, there is an effect of suppressing buckling in the O molding step as compared with a mode in which the pre-molding step is not performed (Comparative Example 1).

  In the above-described embodiment, as shown in FIG. 2B, the bottom wall 24 of the U-shaped product 20 has a substantially semicircular cross-sectional shape opened upward. "" Is not limited to this, and may be, for example, the U molded product 20 shown in FIGS. 10A and 11A.

  10A, a U-shaped product 20 shown in FIG. 10A has a pair of ridge lines 23 formed at the lower ends of a pair of side walls 22 extending in the vertical direction, and has a substantially flat plate shape that connects the pair of ridge lines 23 in the width direction. The bottom wall 24 is formed. In this case, the lower mold 94 of the O press device 90 used in the O molding process may have a molding surface having a shape corresponding to the bottom wall 24 and the ridge line portion 23 of the U molded product 20. In this case, as shown in FIG. 10C, an O molded product 40 having a ridge line portion 43 is obtained. As can be seen from the above description, the closed cross-section structural member that can be formed by the “method for manufacturing a closed cross-section structure member” of the present disclosure is not limited to a closed cross-section structure member having a circular cross section.

  Further, in the U molded product 20 shown in FIG. 11A, the lengths of the pair of side walls 22 in the vertical direction are different. When forming a closed cross-section structural member from such a U-shaped product 20, only the longer side wall 22 of the pair of side walls 22 (the right side in the figure) is the upper die 92 (see FIGS. 6A and 6B). ) From the molding surface 92A. And the closed side cross-section structural member (refer FIG. 11C) can be obtained because the longer side wall 22 deform | transforms along the molding surface of the upper mold | type 92. FIG. In this case, in the pre-forming step, as shown in FIG. 11B, if the pre-forming step is performed so as to obtain a pre-formed product 30 in which only the longer side wall 22 (right side in the drawing) is inclined, the O forming step The occurrence of buckling can be suppressed.

  9A, FIG. 9B, FIG. 9C, FIG. 10B, and FIG. 11B, the preform 30 has a virtual line (extension line) in which a pair of side walls 32 are extended from the end portions 36. IL), the extension lines IL intersect each other. Further, in these pre-formed products 30, the width direction distance D <b> 1 between the pair of end portions 36 is smaller than the width-direction dimension (internal size) D <b> 2 of the pre-formed product 30 in the cross-sectional view. Yes.

  In the above-described embodiment, the pair of side walls 22 of the U-shaped product 20 extends in the vertical direction (the vertical direction of the O press device 90), but the U-shaped product of the present disclosure is not limited thereto. . For example, the side wall 22 of the U molded product may be slightly inclined outward in the width direction toward the end portion 26.

20 U molded product 22 Side wall 26 End 30 Pre-formed product 30A Inner surface 32 Side wall 36 End portion IL Side wall extension 38 Recess 40 O Molded product 40B Outer surface 74 Bending tool 74A Work surface 84 Upper die 84A Work surface 92 Upper die ( O Mold upper mold)
92A Molding surface 92B Inclined surface 94 Lower mold 94A Molding surface W Axial direction

Claims (6)

A method for producing a closed-section structural member,
A U molding step of obtaining a U molded product having a pair of side walls by press molding using a punch and a die;
The U molded product obtained by the U molding step is deformed so that the ends of the pair of side walls are close to each other,
It is possible to obtain a pre-formed product in which the extension lines of the pair of side walls intersect in a cross-sectional view in at least a part of the axial direction and do not have a convex-shaped portion on the inner surface side in a cross-sectional view in the entire axial direction. Molding process;
The preformed product obtained by the preforming process is set in a lower mold and sandwiched between upper molds,
An O-molding step of obtaining an O-molded product having a shape on the outer surface side along the molding surfaces of the upper mold and the lower mold;
A method for manufacturing a closed cross-section structural member. In the preforming process,
Deforming both of the pair of side walls of the U-shaped product;
The manufacturing method of the closed cross-section structural member of Claim 1. The preforming process includes:
The U-shaped product is fixed, and the pair of bending tools are each moved in a direction including a component on the inner side in the width direction.
The manufacturing method of the closed cross-section structural member of Claim 2. The preforming process includes:
The U-shaped product is fixed, and a punch having a pair of processing surfaces disposed above the pair of end portions of the fixed U-shaped product is moved downward.
The manufacturing method of the closed cross-section structural member of Claim 2. An upper mold for O molding,
A molding surface having a semicircular cross-sectional shape;
An inclined surface formed continuously from the outer end of the molding surface;
With
The angle formed by the outer end of the molding surface and the inclined surface is greater than 90 °,
Upper mold for O molding. The angle formed by the outer edge of the molding surface and the inclined surface is greater than 135 °,
The upper mold for O molding according to claim 5.

Images