JP6969133B2 - Molded body with stretch flange and its manufacturing method - Google Patents

Description

The present invention is a molded body having an stretched flange and a press molding method for manufacturing the molded body, and in particular, a molded body having an stretched flange that suppresses a decrease in plate thickness without changing the shape of the flange end. , And its manufacturing method.

For example, in the production of floor cross members of automobiles, a method of forming an stretch flange by press molding is known. Regarding the method of improving the formability of the stretch flange, for example, a method of improving the formability by the shape of the blank, a method of improving the properties of the stretch flange end face to improve the formability, and a method of dispersing the strain of the stretch flange end to improve the formability. Some suggestions have been made, such as how to improve it.

Patent Document 1 discloses a method and a manufacturing apparatus for a press-molded body made of a high-strength steel plate having an outward flange formed at an end portion in the longitudinal direction.

The invention described in Patent Document 1 has a substantially groove-shaped cross section having a groove bottom portion, a ridgeline portion, and a vertical wall portion without providing a notch in the flange or reducing the material yield, and has a substantially grooved cross section in the longitudinal direction. It is an object of the present invention to provide a method for manufacturing a molded body in which an outward flange is formed over a ridgeline portion, a groove bottom portion on both sides thereof, and a vertical wall portion among the end portions of the above.

The technique of Patent Document 1 improves the stretch flange formability by dispersing the strain concentration of the flange, but it is indispensable to change the molding site between the first step and the second step into two steps.

Patent Document 2 describes a portion on the boundary side with a deformed portion of the base and a deformed portion when press-molding a press-molded part in which a vertical wall portion having a curved portion that curves convexly toward the base is formed. A press forming method in which the outer part of the part is separately restrained and the part that becomes the vertical wall part of the deformed part is sheared and deformed in the plate surface to generate a material flow from the curved part to the part away from the curved part. Is disclosed.

In the technique of Patent Document 2, two restraint portions are required, and the movement of one restraint portion during press working becomes complicated.

In Patent Document 3, a step-shaped portion having a ridge line extending so as to surround the outer peripheral edge portion and being bent in the plate thickness direction is formed on the outer peripheral edge portion of the flange end to suppress stretch flange cracking, and the stretched flange molded product. The method of manufacturing has begun.

The technique of Patent Document 3 is indispensable to have two steps, that is, a step of forming a step-shaped portion and a step of forming a vertical wall portion and a flange portion.

Japanese Patent No. 5569661 International Publication No. 2016/031159 Japanese Patent No. 6052478

For example, as shown in FIG. 1, when a flange portion bent and molded along a concave outer peripheral portion is formed by press molding, the flange undergoes tensile deformation. In this case, since tensile stress acts on the flange during machining, the tensile stress is concentrated in the central portion of the concavely curved flange and tensile strain is generated, so that the plate thickness is reduced. When the decrease in plate thickness is large, there is a problem that machining cracks may occur at the flange end.

Consider a molded body shown in FIG. 1 (b) in which an extension flange portion (12) and a top plate portion (14) are formed on a blank (11) shown in FIG. 1 (a) by press molding. As an example of forming such an stretchable flange in press molding, as shown in FIG. 2, a stretchable flange is formed on a blank (21) by using a punch (22) and a die (23). The blank holder (24), along with the die (23), suppresses the blank (21), regulates the flow of material, and prevents the formation of wrinkles. The blank holder (24) does not necessarily have to be in close contact with the blank (21) and may have a gap. Using such a device, the stretch flange can be formed by pushing the blank (21) fixed with the die (23) by relatively moving the punch (22).

In the case of the molded body in which the stretch flange (12) and the top plate portion (14) shown in FIG. 1 (b) are formed, the top plate portion (14) has a concave outer peripheral portion recessed inward, and the concave outer peripheral portion is formed. The portion becomes a bending line (13). When forming the stretch flange portion (12), the direction of the line indicated by A, that is, the normal direction of the central portion of the flange end is compared with the line indicated by B, that is, the normal direction of the flange end. , Relative compression occurs. As a result, the plate thickness is reduced and cracks may occur at the end portion C, which is the central portion of the stretch flange portion (12), because the tensile strain is generally concentrated in the tangential direction of the flange.

FIG. 3 shows an increase / decrease in plate thickness when a molded body having an extension flange as shown in FIG. 1 (b) is formed by a conventional method. It can be seen that the plate thickness is greatly reduced near the center of the formed extension flange. This phenomenon is particularly likely to occur in a high-strength steel plate having a tensile strength of 590 MPa or more, and the tendency becomes more remarkable as the tensile strength increases.

In view of the above circumstances, the present invention can be formed in one step without changing the design shape of the molded body having an elongated flange that reduces the decrease in plate thickness due to the influence of compression deformation and the design shape of the flange, and relies on punching conditions. An object of the present invention is to provide a press molding method, which is a method for manufacturing a molded body having an unnecessary stretch flange.

The present inventors have diligently studied a method for improving formability by reducing a considerable strain applied to a flange end in a stretched flange formed by press forming. As a result, it has been found that the concentration of strain generated at the flange end can be alleviated by not inhibiting the out-of-plane deformation of the portion where the compressive deformation of the blank occurs.

The present invention has been further studied based on the above findings, and the gist thereof is as follows.

(1) An integrally molded body having a top plate portion having a concave outer peripheral portion whose outer peripheral portion is recessed inward, and a flange portion bent and molded along the concave outer peripheral portion. The top plate portion is further provided with a protrusion portion protruding from the surface of the flat plate.

(2) The molded body according to (1), wherein the protrusion is formed on the top plate portion in the minimum main strain direction in a region where strain is concentrated at the end of the extension flange.

(3) The molded body according to (1) or (2), wherein the protrusion is formed at a portion 20 mm or more away from a region where strain is concentrated at the end of the extension flange.

(4) The molded product according to any one of (1) to (3) above, which is made of a steel plate having a tensile strength of 590 MPa or more.

(5) The molded body according to any one of (1) to (4) above, which is a member for an automobile.

(6) Using a press molding apparatus equipped with a punch, a die, and a blank holder, a top plate portion having a concave outer peripheral portion whose outer peripheral portion is partially recessed inward from a flat molding material and the concave outer peripheral portion are formed. The top plate portion is a method for manufacturing a molded body having a flange portion bent and molded along the same direction, and the top plate portion is provided with a protrusion protruding out of the plane of the top plate portion. The blank holder or die is arranged between the die and the blank holder, and is provided with a step of forming an elongated flange by pressurizing and deforming the molding material by moving relative to the punch, and the blank holder or die is formed in the thickness direction of the molding material. A method for manufacturing a molded product, which comprises a space for inducing deformation and forming a protrusion on the top plate.

(7) The method for manufacturing a molded product according to (6), wherein the space is provided at a position corresponding to the minimum main strain direction in a region where strain is concentrated at the end of the extension flange.

(8) The method for producing a molded product according to (6) or (7) above, further comprising a step of removing the formed protrusions.

(9) In the step of removing the protrusion, the molding in which the protrusion is formed is formed by using a blank holder and a die having no space for inducing deformation of the molding material in the thickness direction and forming the protrusion. The press molding method according to (8) above, which is a step of reworking a body.

(10) In the step of removing the protrusion, the protrusion removing member induces deformation of the molding material provided on the blank holder or die in the thickness direction in the latter half of the relative movement to form the protrusion. The press molding method according to (8) above, which is a step of smoothing the formed protrusions by entering a space for smoothing.

(11) The press molding method according to (10), wherein the protrusion removing member is a member in which a part of a punch is extended.

According to the present invention, it is possible to form an elongated flange while suppressing a decrease in plate thickness while keeping the shape of the flange end to be formed.

It is a figure which shows an example of the molded body which has a stretch flange. It is a figure which shows the manufacturing method of the molded body which has a stretch flange by the prior art. It is a figure which shows the increase / decrease of the plate thickness at the time of forming a molded body which has a stretch flange by a conventional method. It is a figure which shows an example of the manufacturing method of the molded body which has an extension flange by the method of this invention. It is a figure which shows the increase / decrease of the plate thickness at the time of forming the molded body which has an extension flange by the method of this invention. It is a figure which shows the outline shape of the front pillar lower manufactured by this invention and the conventional method, (a) is the front pillar lower manufactured by the conventional method, (b) is the front pillar lower manufactured by the method of this invention. be. It is a figure which shows the outline of the collision model about the front pillar lower manufactured by this invention and the conventional method. It is a figure which shows the outline of the die, the blank, the blank holder, and the punch used in Example 1. FIG. It is a figure which shows the outline of the die, the blank, the blank holder, and the punch used in Example 2. FIG.

Hereinafter, an example of the embodiment for carrying out the present invention will be described with reference to the accompanying drawings.

In the press forming method of the present invention, for example, a blank is press-formed by a press forming apparatus provided with a punch and a die and a pad for pressing and restraining a blank (molding material) which is a flat plate such as a metal plate against the punch. An stretch flange is formed, and a molded body in which the top plate portion and the stretch flange portion are integrally molded is obtained. The top plate portion has a concave outer peripheral portion recessed inward, and the extension flange portion is formed by bending and molding the concave outer peripheral portion as a bending line. Here, integrally molded means that there is no joint portion by weld joint or mechanical joint.

More specifically, as shown in FIG. 4, a stretch flange is formed on the blank (41) by using a punch (42) and a die (43). The blank holder (44), together with the die (43), suppresses the blank (41), regulates the flow of material, and prevents the formation of wrinkles. The blank holder (44) does not necessarily have to be in close contact with the blank (41) and may have a gap. The press molding method of the present invention is characterized in that the blank holder (44) does not completely cover the blank (41) and is provided with a slit (45) as a space for allowing the material to flow in.

First, the blank (41) is sandwiched between the die (43) and the blank holder. Subsequently, the punch (42) and the die (43) are relatively moved to pressurize the blank (41) to form an extension flange. At this time, the punch (42) at the position corresponding to the slit (45) of the blank holder (44) is also shaped so as not to hinder the deformation of the blank (41).

In the example shown in FIG. 4, the stretch flange portion is formed so that the concave outer peripheral portion of the top plate portion becomes a bending line. Tensile strain centered on the tangential strain of the stretch flange end is concentrated in the central portion of the stretch flange, and compression deformation occurs in the minimum principal strain direction (generally the normal direction of the stretch flange end). At this time, since the deformation resistance of the blank (41) in the thickness direction is reduced in the slit (45) portion of the blank holder (44), it is possible to induce the deformation of the top plate portion out of the plane. .. Hereinafter, such free out-of-plane deformation is referred to as "free buckling".

In the example of FIG. 4, when the substantially fan-shaped blank (41) is pressed to form the extension flange portion and the top plate portion, the material flows in the radial direction of the center portion of the extension flange end having the slit (45). It will be easier to do. As a result, by increasing the amount of material inflow from the end of the stretch flange end, strain concentration in the central portion of the stretch flange end can be suppressed, and a decrease in the plate thickness at the stretch flange end can be suppressed.

The shape of the space is not limited to the slit as shown in FIG. For example, a blank holder may be provided with a circular space in a part thereof. Further, in the example of FIG. 4, the slit (45) is provided in the blank holder (44), but the same effect can be obtained by providing the slit (45) in the die (43). When the slit (45) is provided in the die (43), out-of-plane deformation is induced in the direction opposite to that provided in the blank holder (44).

FIG. 5 shows an increase / decrease in the plate thickness of a molded product having an stretch flange manufactured by using the press molding method of the present invention. The reduction rate of the plate thickness at the stretch flange end is 4.2%, which is smaller than the reduction rate of the plate thickness at the stretch flange end of the molded product manufactured by the conventional method (see FIG. 3). You can see that.

The press machine used in the present invention is not particularly limited, and a generally used press machine may be used.

Since the compression deformation is alleviated by the induction of free buckling, the line length increases in that direction, and as a result, a part of the top plate portion of the molded body after molding is deformed out of the plane. A protruding protrusion will be generated. Further, the top plate portion corresponding to the position where the protrusion is generated may be a recess. Depending on the intended use of the molded article, such protrusions may not be a problem. The present invention is particularly effective in such cases. Further, if the appearance is emphasized and the removal of the protrusion does not affect the intended use of the molded product, the protrusion may be removed by some method after molding.

Further, it is preferable that the position where such a protrusion is generated is a position where the influence on the extension flange is small. For example, when a steel plate having a plate thickness of about 0.5 to 3.0 mm is used as a material, the position of the protrusion is preferably a portion 20 mm or more away from the region where strain is concentrated at the end of the extension flange.

As a member that does not have a problem even if such a protrusion is generated, for example, a front pillar lower of an automobile member can be mentioned.

A collision model in which a front pillar lower is manufactured using a high-strength steel plate by the press forming method of the present invention and a conventional press forming method, the end portion is completely restrained, the impactor entry amount is 200 mm, and the speed is 15 km / h. When the amount of absorbed energy when the impactor approach amount was 120 mm was obtained by simulation, it was 4.2 × 10 ³ / J without protrusions and 4.7 × 10 ³ / J with protrusions.

From the above results, it can be confirmed that the presence or absence of protrusions does not adversely affect the absorption energy characteristics, which are the characteristics required for the front pillar lower. It is considered that the reason why the amount of absorbed energy is higher when there are protrusions is that the presence of the protrusions improves the resistance to out-of-plane deformation of the top plate of the front pillar lower.

FIG. 6 shows the outline of the front pillar lower. (A) is an outline of the front pillar lower produced by the conventional method, and (b) is an outline of the front pillar lower produced by the method of the present invention. The protrusion (61) is formed on the front side of the paper surface, and the extension flange portion is formed on the back side of the paper surface and is not shown.

FIG. 7 is a diagram showing an outline of the collision model used in the calculation for the front pillar lower shown in FIG.

When it is necessary to remove the protrusion of the top plate portion caused by the out-of-plane deformation due to a problem in appearance, for example, the protrusion can be removed by the method described below.

[1] Smooth the top plate surface by wrist-like

The protrusions on the top plate can be smoothed by wrist-like. Specifically, a member having a protrusion is reprocessed by using a die, a punch, and a blank holder having the same shape as that used for the flange molding character and having no slit. This makes it possible to smooth the protrusions. It is not necessary to rework the stretch flange portion as long as the protrusion can be smoothed for reworking.

[2] The blank surface is smoothed when the bottom dead center is reached by using the protrusion removing member.

In the latter half of the relative movement of the punch and the die, the protrusion removing member is provided in the blank holder or the die so as to induce deformation in the thickness direction of the blank and enter the space to form the protrusion on the top plate. It is also possible to smooth the top plate portion by gradually closing the space by moving the space to the blank holder or die provided with the space so that the protrusion removing member has the same height at the end of the relative movement. According to this method, it is also possible to induce out-of-plane deformation to generate protrusions and to smooth the generated protrusions in one step.

The protrusion removing member may be an independent movable member, but for example, a partially extended punch may be used. The extension portion of the punch shall be large enough to pass through the slit provided in the blank holder so that it will be at the same height as the blank holder surface when the bottom dead center is reached.

As a result, in the first half of molding, the blank can be deformed out of the plane. The deformed protrusion can be smoothed.

Comparing the above two methods, the method of [2] has the advantage that the flange surface can be smoothed in one step, but the deformation to the outside of the surface is suppressed in the latter half of the molding. Therefore, the effect of suppressing the decrease in the plate thickness at the end of the stretched flange is slightly smaller than that of the method of [1]. Which method to use may be determined by judging from the characteristics of the material used as the blank.

As described above, according to the present invention, it is possible to alleviate the compressive deformation of the molded product having an stretch flange manufactured by press molding using a general press machine, and as a result, the plate at the end of the stretch flange. The decrease in thickness can be reduced, and the effect of reducing cracks at the flange end is achieved. According to the present invention, it is possible to reduce the decrease in plate thickness even when a high-strength steel plate having a high tensile strength, preferably a tensile strength of 590 MPa or more, is used.

It is clear that by changing the shapes of the punch and the die, it is possible to manufacture a molded product having various shapes without being limited to the above-mentioned example of the molded product, and the deformation thereof is also included in the present invention. Needless to say.

Hereinafter, the present invention will be described in more detail with reference to examples. It goes without saying that the examples given below are examples of embodiments of the present invention, and the present invention is not limited by the following examples.

[Example 1]
A flange having an inclination angle of 60 ° with respect to the horizontal direction was formed on a substantially fan-shaped blank (980 MPa class high-strength steel plate, plate thickness 1.6 mm) by the following three methods.

(1) Using the punch, die, and blank holder shown in FIG. 8 (a), a flange was formed by a flange-up method which is a conventional technique.

(2) A flange was formed using the punch, die, and blank holder shown in FIG. 8 (b). At that time, since the blank holder has a slit, a protrusion was formed by out-of-plane deformation. In order to smooth the protrusions, the punches, dies, and blank holders shown in FIG. 8A were used for restlike to smooth the protrusions.

(3) A flange was formed using the punch, die, and blank holder shown in FIG. 8 (c). Since the blank holder has a slit, a protrusion is formed due to out-of-plane deformation, but a part of the punch is extended, and the extended part is at the same height as the blank holder surface at the bottom dead center during molding. Therefore, at the end of molding, the protrusions were smoothed.

The results are shown in Table 1.

No. which is a conventional flange-up method. In (1), the plate thickness was reduced by a maximum of 12.9% at the flange end, and cracks occurred at the flange end.

No. 1 which is the construction method of the present invention. In (2) and (3), the plate thickness reduction rate was smaller than that of the conventional method, and a molded product could be produced without cracking.

[Example 2]
A flange having an inclination angle of 90 ° in the horizontal direction was formed on a substantially fan-shaped blank (980 MPa class high-strength steel plate, plate thickness 1.6 mm) by the same three methods as in Example 1. In order to change the inclination angle of the flange from that of Example 1, a punch having a shape different from that of Example 1 was used as shown in FIGS. 9A to 9C. The results are shown in Table 2.

No. which is a conventional flange-up method. In (1), the plate thickness was reduced by up to 12.5% at the flange end, and cracks occurred at the flange end.

No. 1 which is the construction method of the present invention. In (2) and (3), the plate thickness reduction rate was smaller than that of the conventional method, and a molded product could be produced without cracking.

11 Blank 12 Stretched Flange 13 Bending Line 14 Top Plate 21 Blank 22 Punch 23 Dice 24 Blank Holder 41 Blank 42 Punch 43 Dice 44 Blank Holder 45 Slit 61 Protrusion 81 Dice 82 Blank 83 Blank Holder 84 Punch 91 Dice 92 Blank holder 94 punch

Claims (9)

It is an integrally molded body,
A top plate part having a concave outer peripheral part with a part of the outer circumference recessed inward,
It has a flange portion that is bent and molded along the concave outer peripheral portion.
The top plate portion further includes a protrusion protruding out of the surface of the top plate portion.
The protrusions along the normal direction of the center of the concave outer peripheral portion includes the normal line, the longitudinal direction as the normal direction, and characterized by being formed one on the top plate Molded body to be. The molded body according to claim 1, wherein the protrusion is formed at a portion 20 mm or more away from a region where strain is concentrated at the end of the flange portion. The molded product according to claim 1 or 2, wherein the molded product is made of a steel plate having a tensile strength of 590 MPa or more. The molded body according to any one of claims 1 to 3, which is a member for an automobile. Using a press forming apparatus equipped with a punch, a die, and a blank holder, a top plate portion having a concave outer peripheral portion whose outer peripheral portion is partially recessed inward from a flat molding material and bending along the concave outer peripheral portion. The top plate portion has a molded flange portion, and the top plate portion is a method for manufacturing a molded body that manufactures a molded body having a protrusion protruding out of the plane of the top plate portion.
The molding material is arranged between the die and the blank holder, and is provided with a step of forming a flange portion by pressurizing and deforming the molding material by moving it relative to the punch.
The blank holder or die has a space for inducing deformation of the molding material in the thickness direction and forming one protrusion on the top plate portion.
A method for manufacturing a molded product, wherein the space is provided along a normal direction of a central portion of the concave outer peripheral portion. The method for manufacturing a molded product according to claim 5, further comprising a step of removing the formed protrusions. In the step of removing the protrusion, the molding in which the protrusion is formed is performed by using a blank holder and a die that induces deformation of the molding material in the thickness direction and does not have a space for forming the protrusion. The method for manufacturing a molded product according to claim 6, wherein the process is a step of reprocessing the body. In the step of removing the protrusion, the protrusion removing member induces deformation of the molding material provided on the blank holder or die in the thickness direction in the latter half of the relative movement to form the protrusion. The method for manufacturing a molded product according to claim 6, wherein the step is a step of smoothing the formed protrusions by entering the space for the purpose. The method for manufacturing a molded product according to claim 8, wherein the protrusion removing member is a member in which a part of the punch is extended.

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