JP7069998B2 - Manufacturing method and press forming device for automobile outer panel having concave embossed portion - Google Patents

Description

The present invention relates to a method for manufacturing an automobile outer panel having a concave embossed portion such as, for example, an automobile door outer, and a press forming apparatus.

Among the outer panel panels constituting the automobile, there is an outer panel having a concave embossed portion formed by overhanging, for example, as shown in FIG. 1. The concave embossed portion is usually formed by overhanging a blank with a press forming apparatus, but during press forming, the material flows toward the concave embossed portion. At the same time, as shown in FIG. 1, in the corner portion of the concave embossed portion seen from the side facing the concave embossed portion, there is uneven movement of the material in the circumferential direction of the corner portion, and the corner portion has a circumference. A directional compressive stress is generated. Therefore, a surface strain of several tens of microns to several hundreds of microns is generated on the design surface of the outer panel. In the example shown in FIG. 1, the position of the black circle mark in the figure corresponds to the above-mentioned corner portion, and surface strain is likely to occur.

When the outer panel on which the surface strain is generated is exposed to light, the surface strain appears on the appearance like a pattern, and the appearance quality standard of the product may not be satisfied. Such a problem of surface strain can occur not only in the door outer of an automobile but also in other outer panels of an automobile. In particular, when surface distortion occurs in the concave embossed portion of the outer panel such as a door or a back door, the appearance quality of the automobile body is significantly impaired.

Until now, the shape of the press die has been changed to suppress the occurrence of surface strain itself, and the surface strain has been corrected after press molding and before painting. And costly.
In recent years, there have been cases where high-strength steel plates have been adopted to reduce the weight of outer panels such as door outers and back door panels, but when such materials are applied, a great deal of cost is required to prevent surface strain. I need it.

As a conventional measure against surface strain, Patent Document 1 discloses an invention relating to a press forming method and a press forming apparatus for performing press forming using a draw press die having a movable punch having a concave portion and a die having a convex portion. ing. In the press molding method of Patent Document 1, the portion other than the recess is first press-molded, and then the recess is formed with a movable punch to reduce the inflow of material into the recess and ensure the surface quality of the recess. There is.

Further, in Patent Document 2, for the purpose of suppressing surface strain around the handle portion of the door outer, a press that reduces the coefficient of friction between the blank and the die by forming an oil film or optimizing the die material. The invention relating to the molding die is disclosed.

Japanese Unexamined Patent Publication No. 62-131737 Japanese Unexamined Patent Publication No. 2008-229637

The invention disclosed in Patent Document 1 needs to perform press molding using a movable punch while pressing the panel surface after molding the panel surface, which cannot be handled by a general press die. Therefore, in order to implement the molding method of Patent Document 1, there is a problem that a large cost is required when introducing the press molding apparatus.

Further, the invention disclosed in Patent Document 2 is a die for making the friction coefficient between the handle portion and the blank smaller than the friction coefficient between the portion other than the handle portion and the blank at the time of press molding, and is a lubricating oil. And it is necessary to change the mold material as appropriate and perform press molding. Therefore, it is necessary to optimize the optimum lubricating oil and mold material depending on the material strength of the material to be molded and the plating type, and it is difficult to stably suppress the surface strain. Further, in the press molding method of Patent Document 2, it is necessary to partially change the mold material, and there are problems such as securing an adjustment time and increasing the cost for that purpose.

As described above, in the conventional technique disclosed in Patent Documents 1 and 2, when manufacturing an automobile outer panel having a concave embossed portion, such as a door outer having a concave embossed portion, the surface is suppressed while suppressing the cost. It was difficult to stably suppress the strain.

The present invention has been made in view of the above circumstances, and when manufacturing an automobile outer panel having a concave embossed portion, the surface strain generated around the concave embossed portion is stably suppressed while suppressing the cost. The purpose is to do.

The cause of surface strain in the concave embossed part is
(I) Fluffing due to compressive stress in the circumferential direction due to the minute inflow of material from the peripheral edge of the concave embossed portion (particularly the corner portion described above).
(Ii) The swelling around the concave embossed part due to the bending moment,
It is thought to be in.

For this reason, with respect to the leaning due to the compressive stress in (i) above, it is possible to suppress the inflow of the material into the concave embossed portion as much as possible, that is, to apply tension to pull the material into the concave embossed portion side generated by press molding. By making it as small as possible, it is possible to suppress the occurrence of surface strain. In order to reduce this tension, the coefficient of friction of the convex portion of the mold in contact with the blank in the portion to be the concave embossed portion may be lowered.

Regarding the swelling around the concave embossed portion due to the bending moment in (ii) above, the contact range between the material being deformed and the mold should be as large as possible, that is, the material and the mold should be around the concave embossed portion. The surface strain can be reduced by making the contact state over. In order to maintain this contact state, it is sufficient to improve the attachment between the material and the mold.

One aspect of the present invention that solves the above problems based on the above findings is a method of manufacturing an automobile outer panel having a concave embossed portion, in which the press speeds are different from each other during press molding of the concave embossed portion. The concave embossed portion is formed by repeatedly switching between the first press speed and the second press speed, which are the speeds, and when the press speed is switched, the first press speed and the second press speed are used. It is characterized by switching so that the change in press speed between and is not a continuous change .

Another aspect of the present invention is a press forming apparatus for an automobile outer panel having a concave embossed portion, wherein the press speed is variable so as to change the press speed during press forming of the concave embossed portion. The press speed variable mechanism comprises a mechanism, and the press speed variable mechanism switches the press speed between a first press speed and a second press speed, which are different speeds from each other, and when the press speed is switched, the first press speed is switched. It is characterized in that the change in the press speed between the press speed of the above and the second press speed is switchable so as not to be a continuous change .

In the press molding according to one aspect of the present invention, by changing the press speed, which is a press molding condition, during the molding of the concave embossed portion, the tension for drawing the material into the concave embossed portion can be reduced, and the mold and the material can be further reduced. It is possible to improve the adhesion with and suppress the occurrence of surface strain. Further, since such press molding can be carried out with a structure simpler than that of the press molding apparatus disclosed in Patent Document 1 and Patent Document 2, the cost at the time of introducing the press molding apparatus can be suppressed. ..

According to the present invention, when manufacturing an automobile outer panel having a concave embossed portion, it is possible to stably suppress the surface strain generated around the concave embossed portion while suppressing the cost.

It is a side view which shows an example of the automobile outer panel having a concave embossed portion. It is a figure which shows the schematic structure of the press molding apparatus which concerns on one Embodiment of this invention. It is a top view which shows the shape of the punch in the Example of this invention. FIG. 3 is a cross-sectional view taken along the line AA in FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present specification and the drawings, the elements having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

As shown in FIG. 2, the press forming apparatus 1 of the present embodiment is provided with a punch 2 provided as a lower die, a die 3 provided as an upper die, and a die 3 on the side of the punch 2 so as to face the die 3. The blank holder 4 is provided. In the present embodiment, two blank holders 4 are arranged on the side of the punch 2 so as to sandwich the punch 2. A concave portion 5a is formed in the top portion 5 of the punch 2, and a convex portion 3a having a shape corresponding to the concave portion 5a of the punch top portion 5 is formed in a portion of the die 3 facing the punch top portion 5. At the time of press molding, a concave embossed portion is formed on the blank by the convex portion 3a of the die 3 and the concave portion 5a of the punch 2.

Further, the press forming apparatus 1 includes an elevating device (not shown) for elevating and lowering the die 3, an elevating device 6 for elevating and lowering the blank holder 4, and a control unit 10 for controlling the elevating speed of the die 3 and the blank holder 4. ing. Each elevating device of the die 3 and the blank holder 4 is provided with a drive unit (not shown) provided with a drive source such as a servomotor. The control unit 10 is configured to change the press speed, that is, the elevating speed of the die 3 and the blank holder 4 during press molding by sending a signal to the drive unit. Such a press forming apparatus 1 is, for example, a servo press machine, but is not limited to the servo press machine, as long as it is provided with a press speed variable mechanism configured to change the press speed during press forming. good.

The press forming apparatus 1 of this embodiment is configured as described above. In the present embodiment, the lower punch 2 is a fixed type and the upper die 3 is a movable type, but the punch 2 may be a movable type and the die 3 may be a fixed type. Further, the upper die may be punch 2 and the lower die may be die 3. Further, as for the convex portion and the concave portion on the mold side for forming the concave embossed portion on the blank, the convex portion may be formed on the punch 2 and the concave portion may be formed on the die 3. That is, the structure is not particularly limited as long as it has a structure in which at least one of the punch 2 and the die 3 moves up and down so that they can approach each other and the concave embossed portion can be formed.

Next, a method of manufacturing an automobile outer panel having a concave embossed portion in the present embodiment will be described.

First, the blank is fixed between the die 3 and the blank holder 4. At this time, of the surface (design surface) that appears on the appearance of the product and the surface that does not appear on the appearance (non-design surface) of the blank, the non-design surface is used. Fix the blank so that the surface side faces the punch 2 side. The blank is not limited to the steel plate, and may be another metal plate such as an aluminum alloy plate or a titanium alloy plate.

Subsequently, the upper die (die 3 in this embodiment) is lowered. Here, when the blank comes into contact with the convex portion 3a of the die 3, the blank is deformed so as to be pushed into the concave portion 5a of the punch top 5, and the material tends to move so as to be drawn into the concave portion 5a of the punch top 5. .. At this time, in the press forming method of the present embodiment, press forming is performed by changing the descending speed of the die 3, that is, the pressing speed.

When the press speed is high, the coefficient of friction between the convex portion 3a of the die 3 and the blank is low, but when the press speed is low, the coefficient of friction between the convex portion 3a and the blank is high. When this coefficient of friction is low, the tension generated by pulling the blank into the concave embossed portion during molding can be reduced. On the other hand, when the pressing speed is high (that is, when the coefficient of friction between the convex portion 3a and the blank is low), the swelling around the concave embossed portion due to the bending moment becomes large. Therefore, performing press molding while the press speed is high is an obstacle to reducing surface strain. On the other hand, in the present embodiment, by changing the press speed during press molding, the time in which the state becomes an obstacle to the reduction of such surface strain is reduced, and the blank and the die are well attached. The time to become increases. As a result, it is possible to suppress the swelling around the concave embossed portion due to the bending moment while reducing the tension generated by pulling the blank into the concave embossed portion. As a result, surface strain around the concave embossed portion can be suppressed.

The press speed is appropriately changed according to the type and hardness of the tool, the shape of the concave embossed portion, the material strength and plate thickness of the blank, the plating type, the plating thickness, and the like. Further, the press speed may be continuously changed or may be changed stepwise. For example, the press speed may be continuously increased and then continuously decreased, or continuously decreased and then continuously increased. Further, for example, the press speed may be increased stepwise and then gradually decreased, or may be gradually decreased and then gradually increased. In addition, continuous changes and gradual changes may be combined.

From the viewpoint of effectively suppressing the surface strain, it is preferable to repeatedly switch the press speed between the first press speed and the second press speed, which are different speeds from each other during press molding. From the viewpoint of effectively suppressing surface strain, the amount of change between the first press speed and the second press speed (absolute value of the difference between the first press speed and the second press speed) is 15 mm /. It is preferably sec or more, and more preferably 50 mm / sec or more. The upper limit of the amount of change between the first press speed and the second press speed is limited by the specifications of the press forming apparatus 1, but from the viewpoint of maintenance of the press forming apparatus 1, it may be 120 mm / sec or less. preferable.

The timing for changing the press speed is appropriately changed according to the type and hardness of the tool, the shape of the concave embossed portion, the material strength and plate thickness of the blank, the plating type, the plating thickness, and the like. It is preferable to change the pressing speed every time the die makes a stroke of 1 mm.

By lowering the die 3 to the bottom dead center while changing the press speed as described above, it is possible to manufacture an automobile outer panel having a concave embossed portion while suppressing surface strain.

According to the press molding method according to the present embodiment, it is possible to stably suppress surface strain, which is a problem in an automobile outer panel having a concave embossed portion such as a door outer. Further, since the press forming apparatus 1 as in the present embodiment does not have to have a complicated mold structure in performing the above press forming, the cost associated with the introduction of the press forming apparatus can be suppressed.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an example. It is clear that a person skilled in the art can come up with various modifications or amendments within the scope of the technical idea described in the claims, and of course, the technical scope of the present invention also includes them. It is understood that it belongs to.

A molding test was carried out simulating the door outer of an automobile. A 2000 kN servo press was used as the press forming apparatus. In the press forming apparatus of this embodiment, the punch of the lower die is a fixed type, and the die of the upper die is a movable type. The blank is a 340 MPa class baking hardened steel sheet (BH steel sheet) having a thickness of 0.70 mm and a square shape of 600 mm square.

FIG. 3 is a plan view of the punch 20 in this embodiment, and FIG. 4 is a sectional view taken along the line AA of FIG. The surface 20a of the punch 20 facing the die has a curved shape with a radius of curvature of 1200 mm in the cross section shown in FIG. 4, and a recess 21a is formed in the top portion 21 of the punch 20 as shown in FIG. Although not shown, the surface 20a facing the die of the punch 20 in the cross section orthogonal to the AA cross section is not curved but linear.

In this molding test, a panel having a concave embossed portion having a depth of 5 mm was formed by holding the blank with a die and a blank holder, applying a wrinkle pressing pressure of 50 tons, and then lowering the die. Further, in the molding test, the condition 1 in which the press speed during press molding was constant at 1 mm / sec (the first press speed in the present embodiment) and the press speed were set to 20 mm / sec (the second press in the present embodiment). It is carried out under the condition 2 that the speed is constant and the condition 3 that the press speed is repeatedly switched between the first press speed and the second press speed for each 1 mm stroke of the die.

Then, the surface of the panel after molding was polished with an oil grindstone, and the surface strain generated on the panel was quantitatively evaluated. Quantitative evaluation of surface strain was performed based on the amount of change in curvature around the concave embossed portion. The amount of change in the curvature is 3 with a gauge length of 50 mm when the longitudinal direction of the concave embossed portion, that is, the longitudinal direction L of the concave portion 21a of the punch 20 shown in FIG. 3 is in the vertical direction while facing the concave embossed portion. Using a point gauge, the strain at a position 15 mm below the concave embossed portion in a direction parallel to the longitudinal direction of the concave embossed portion was measured, and the strain was calculated based on the measurement result. The molding test results of the above conditions 1 to 3 are shown in Table 1 below.

Table 1 shows a comparison of the average values of the amount of change in curvature (1 / ρ) (δ) (maximum value of curvature-minimum value of curvature) under various conditions. The amount of change in curvature correlates with the unevenness of the panel surface, and the smaller the amount of change in curvature, the smaller the surface strain.

As shown in Table 1, the amount of change in curvature is smaller in condition 3 in which the press speed is changed during press molding, as compared with condition 1 and condition 2 in which the press speed during press molding is constant. A panel with good surface quality could be obtained. That is, by changing the press speed during press molding, it is possible to suppress the surface strain generated around the concave embossed portion.

INDUSTRIAL APPLICABILITY The present invention can be used for manufacturing an automobile outer panel having a concave embossed portion.

1 Press forming device 2 Punch 3 Dice 3a Convex part of die 4 Blank holder 5 Punch top 5a Concave part of punch top 6 Elevating device of blank holder 10 Control unit 20 Punch 20a Surface facing the die 21 Punch top 21a Recessed part of punch top L Longitudinal direction of punch recess

Claims (5)

It is a method of manufacturing an automobile outer panel having a concave embossed portion.
During the press forming of the concave embossed portion, the concave embossed portion is formed by repeatedly switching the press speed between the first press speed and the second press speed, which are different speeds from each other .
When switching the press speed, the outer panel of the automobile is characterized in that the change in the press speed between the first press speed and the second press speed is switched so as not to be a continuous change . Production method. The method for manufacturing an automobile outer panel according to claim 1 , wherein the amount of change between the first press speed and the second press speed is 15 mm / sec or more. A press forming device for an automobile outer panel having a concave embossed portion.
A press speed variable mechanism configured to change the press speed during press molding of the concave embossed portion is provided .
The press speed variable mechanism switches the press speed between the first press speed and the second press speed, which are different speeds from each other, and when the press speed is switched, the first press speed and the first press speed are switched. A press forming apparatus, characterized in that the change in the press speed between the second press speed and the second press speed is switchable so as not to be a continuous change . The press molding apparatus according to claim 3 , wherein the amount of change between the first press speed and the second press speed is 15 mm / sec or more. The press forming apparatus according to claim 3 or 4 , which is a servo press machine.

Images