JP7139665B2 - Manufacturing method and press forming apparatus for automobile outer panel having recessed portion - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of manufacturing an automobile outer panel having a partially concave shape, such as an automobile door outer, and a press forming apparatus.

Among skin panels that constitute automobiles, there are skin panels that have recessed embossed portions formed by overhanging, such as the door outer shown in FIG. 1 . The recessed embossed portion is usually formed by bulging a blank using a press molding device, and the material flows toward the recessed embossed portion during press molding. Along with this, at the corner of the recessed embossed portion viewed from the side directly facing the recessed embossed portion as shown in FIG. directional compressive stress occurs. For this reason, surface distortion of several tens of microns to several hundred microns occurs on the design surface of the outer panel. In the example shown in FIG. 1, the positions of the black circles in the drawing correspond to the corner portions described above, and surface distortion is likely to occur.

Further, in order to improve the exterior design of a recent automobile outer panel, a door outer having a plurality of character lines arranged as shown in FIG. 1 is adopted. An automobile outer panel having character lines of such convex portions has a component shape in which the space between adjacent character lines is recessed. During molding of such a part, as in the case of the recessed embossed portions described above, the material flows into the portions between adjacent character lines, so compressive stress is generated around these portions. Therefore, surface distortion occurs on the design surface even at such a portion.

When light hits a surface-distorted skin panel, the surface distortion appears as a pattern in the appearance, and the appearance quality standards of the product may not be met. Such a surface distortion problem is not limited to the outer door of an automobile, and can occur in other outer panels of the automobile as well. In particular, when surface distortion occurs on the design surfaces of outer panels such as side panels, front fenders, hoods, and back doors, the appearance quality of automobile bodies is significantly impaired.

Until now, changes in the shape of press dies to suppress the occurrence of surface distortion itself and correction work for surface distortion before painting after press molding have been performed, but countermeasures against surface distortion require a large amount of man-hours for correction. and costs.
In recent years, there are also examples of using high-strength steel sheets to reduce the weight of exterior panels such as door outer and back door panels, but when using such materials, countermeasures against surface distortion are very costly. I need it.

As a conventional countermeasure against surface distortion, Patent Document 1 discloses an invention related to a press forming method and a press forming apparatus that perform press forming using a drawing 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, parts other than the recesses are press-molded first, and then the recesses are formed with a movable punch, thereby reducing the amount of material flowing into the recesses and ensuring the surface quality of the recesses. there is

In addition, Patent Document 2 describes a press that reduces the friction coefficient between the blank and the mold by forming an oil film or optimizing the mold material for the purpose of suppressing surface distortion around the handle part of the door outer. An invention relating to a molding die is disclosed.

JP-A-62-131737 JP 2008-229637 A

The invention disclosed in Patent Document 1 requires press molding using a movable punch while pressing the panel surface after molding the panel surface, which cannot be done with a general press mold. For this reason, in order to carry out the press-molding method of Patent Document 1, there is a problem that a great amount of cost is required when introducing a press-molding apparatus.

Further, the invention disclosed in Patent Document 2 is a mold for making the coefficient of friction between a handle and a blank smaller than the coefficient of friction between a portion other than the handle and the blank during press molding. And it is necessary to perform press molding by appropriately changing the mold material. Therefore, it is necessary to optimize the lubricating oil and mold material that are most suitable for the material strength of the material to be molded and the type of plating, and it is difficult to stably suppress the surface distortion. Moreover, in the press molding method of Patent Document 2, it is necessary to partially change the material of the mold, and there are problems such as securing adjustment time for this and an increase in cost.

As described above, in the conventional techniques disclosed in Patent Documents 1 and 2, when manufacturing an automobile outer panel having a recessed portion such as a recessed embossed portion or a portion between character lines as shown in FIG. It was difficult to stably suppress the surface distortion while suppressing the cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. intended to

The cause of the surface distortion in the concave part is
(i) Thickening due to compressive stress in the circumferential direction due to minute inflow of material around the concave portion;
(ii) bulging around the recess due to bending moment;
It is considered to be in

For this reason, with regard to (i) thickness reduction due to compressive stress, the inflow of material into the recessed portion should be suppressed as much as possible. By making it smaller, it is possible to suppress the occurrence of surface distortion. In order to reduce this tension, it is necessary to improve the sliding characteristics of the protrusions of the mold that are in contact with the recessed portions of the blank, that is, to reduce the coefficient of friction of the protrusions of the mold corresponding to the recesses. good.

Regarding the swelling around the recessed embossed portion due to the bending moment of (ii) above, the contact range between the deforming material and the mold should be as large as possible, that is, the material and the mold should be in contact with the recessed embossed portion. Surface strain can be reduced by making contact over the entire area. In order to maintain this contact state, the material and the mold should be in good contact with each other.

One aspect of the present invention that solves the above problems based on the above knowledge is a method for manufacturing an automobile outer panel having a concave portion, wherein the concave portion is a concave embossed portion or an adjacent character line. When press-molding the recessed portion, the recessed portion is formed while vibrating the die, and the vibration frequency of the die during vibration is 3 Hz or more and 20 Hz or less, and the above Amplitude of the dice during vibration is characterized by being 1 μm or more .

In another aspect, one aspect of the present invention is a press molding apparatus for an automobile outer panel having a concave portion, the concave portion being a concave embossed portion or a portion between adjacent character lines, A vibrating device for vibrating the die is provided, and the vibrating device is configured to generate vibration with a vibration frequency of 3 Hz or more and 20 Hz or less and an amplitude of 1 μm or more .

In the press molding according to one aspect of the present invention, by vibrating the die when forming the concave portion, it is possible to reduce the compressive stress at the part where the surface distortion of the blank occurs, and furthermore, the mold and the material You can improve your relationship with As a result, it is possible to reduce the tension that draws the material into the recessed portion, suppress the swelling around the recessed embossed portion due to the bending moment, and suppress the occurrence of surface distortion. In addition, since such press molding can be performed with a simpler structure than the press molding apparatuses disclosed in Patent Documents 1 and 2, the cost for introducing the press molding apparatus can be reduced. .

Advantageous Effects of Invention According to the present invention, when manufacturing an automobile outer panel having a recessed portion, it is possible to stably suppress surface distortion that occurs around the recessed portion while suppressing costs.

1 is a side view showing an example of an automobile skin panel having recesses; FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the press molding apparatus which concerns on one Embodiment of this invention. FIG. 4 is a plan view showing the shape of the punch in the example of the present invention; 4 is a cross-sectional view taken along the line AA in FIG. 3; FIG.

An embodiment of the present invention will be described below with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

As shown in FIG. 2, the press molding apparatus 1 of this embodiment is an apparatus for forming a concave embossed portion, which is an example of a concave portion. A press forming apparatus 1 includes a punch 2 provided as a lower die, a die 3 provided as an upper die, and a blank holder 4 provided on the side of the punch 2 so as to face the die 3 . In this embodiment, two blank holders 4 are arranged on the sides of the punch 2 so as to sandwich the punch 2 therebetween. Further, in this embodiment, the die 3 and the blank holder 4 are configured to be vertically movable by a lifting mechanism (not shown). 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. As shown in FIG. During press molding, the convex portion 3a of the die 3 and the concave portion 5a of the punch 2 form a concave portion in the blank.

The press molding apparatus 1 includes a vibrating device 6 that vibrates the die 3 and a control section 10 that controls the operation of the vibrating device 6 . The control unit 10 sends a signal to the vibration device 6 so that the die 3 can be vibrated when forming the concave portion. Although the vibration device 6 is incorporated in the die 3 in the present embodiment, the installation method of the vibration device 6 is not particularly limited as long as the die 3 can be vibrated. As the vibrating device 6, for example, an ultrasonic vibrating device, a vibrating device using a hydraulic liner, or the like can be adopted, but the configuration of the device is not particularly limited as long as the die 3 can be vibrated.

The press molding apparatus 1 of this embodiment is configured as described above. Although the lower punch 2 is fixed and the upper die 3 is movable in this embodiment, the punch 2 may be movable and the die 3 fixed. Alternatively, the punch 2 may be the upper die and the die 3 may be the lower die. Moreover, as for the protrusions and recesses on the mold side for forming the recesses in the blank, the punch 2 may be formed with protrusions and the die 3 may be formed with recesses. In other words, the configuration is not particularly limited as long as at least one of the punch 2 and the die 3 moves up and down so that they can approach each other and the mold configuration is capable of molding the recessed portion.

Next, a method for manufacturing an automobile outer panel having a recessed portion according to the present embodiment will be described.

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

Subsequently, the upper mold (the 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 portion 5, and the material tries to move so as to be pulled into the concave portion 5a of the punch top portion 5. . At this time, in the press molding method of the present embodiment, press molding is performed while vibrating the die 3 .

By vibrating the die 3 in this manner, the compressive stress around the recessed portion can be reduced, and the material and the die can be more intimately connected. As a result, surface distortion around the concave portion can be suppressed.

The vibration conditions are appropriately changed according to the type and hardness of the tool, the shape of the concave portion, material strength and plate thickness of the blank, plating type and plating thickness, and the like. From the viewpoint of effectively suppressing surface strain, the vibration frequency is preferably 3 Hz or higher, more preferably 4 Hz or higher. Although the upper limit of the vibration frequency is limited by the specifications of the vibration device 6, it is preferably 20 Hz or less because wrinkles may occur when the vibration frequency is high. Also, from the viewpoint of effectively suppressing surface strain, the amplitude is preferably as large as possible, preferably 1 μm or more, more preferably 2 μm or more. By satisfying the conditions that the vibration frequency is 3 Hz or more, preferably 4 Hz or more and 20 Hz or less, and the amplitude is 1 μm or more, preferably 2 μm or more, the effect of suppressing surface distortion is further enhanced.

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

According to the press molding method according to the present embodiment, for example, it is possible to stably suppress the surface distortion that is a problem in automobile outer panels having concave portions such as doors, back doors, side panels, front fenders, and hoods. It becomes possible. In addition, the press molding apparatus 1 according to the present embodiment does not require a complicated mold structure when performing the above-described press molding, so the cost associated with the introduction of the press molding apparatus can be suppressed. In particular, in the press-molding apparatus 1 of this embodiment, the above-described press-molding can be performed simply by incorporating the vibrating device 6 into the die 3, so the apparatus structure does not become complicated.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an example. It is obvious that a person skilled in the art can conceive various modifications or modifications within the scope of the technical idea described in the claims, and these are also within the technical scope of the present invention. be understood to belong to

In the above-described embodiment, the concave embossed portion, which is an example of the concave-shaped portion, is the object to be molded. Surface strain can be suppressed by performing press molding.

A molding test simulating an automobile door outer was carried out. The recessed portions formed in this molding test are recessed embossed portions. A 2000 kN servo press machine was used as a press molding device. In the press molding apparatus of this embodiment, the punch of the lower die is fixed and the die of the upper die is movable. The blank was a 340 MPa grade bake hardening steel plate (BH steel plate) having a plate 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 cross-sectional view taken along line AA of FIG. A 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. Also, although not shown, the surface 20a of the punch 20 facing the die in the cross section perpendicular to the AA cross section is linear rather than curved.

In this forming test, the blank was held by the die and the blank holder, and after applying a wrinkle pressing pressure of 50 tons, the die was lowered to form a panel having a concave portion with a depth of 5 mm. Further, the forming test was conducted under condition 1 where the die was not vibrated during press forming and under condition 2 where the die was vibrated during press forming.

After the molding, the surface of the panel was polished with an oil grindstone, and the surface strain generated in the panel was quantitatively evaluated. Quantitative evaluation of surface strain was performed based on the amount of change in curvature around the concave portion. The amount of change in curvature is 3 mm with a gauge length of 50 mm when the longitudinal direction of the concave portion, that is, the longitudinal direction L of the concave portion 21a of the punch 20 shown in FIG. Using a point gauge, the strain in the direction parallel to the longitudinal direction of the concave portion was measured at a position 15 mm below the concave portion, and the strain was calculated based on the measurement results. Table 1 below shows the results of the molding test under Conditions 1 and 2 above.

Table 1 shows a comparison of average values of variation (δ) of curvature (1/ρ) (maximum value of curvature - minimum value of curvature) under various conditions. The amount of change in curvature is correlated 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, compared to condition 1 where the die is not vibrated during press forming, condition 2 where the die is vibrated during press forming has a smaller amount of change in curvature and a panel with good surface quality. I was able to get That is, by vibrating the die during press molding, it is possible to suppress the surface distortion that occurs around the concave portion.

INDUSTRIAL APPLICABILITY The present invention can be used in the manufacture of automotive skin panels having a concave shape.

1 Press forming device 2 Punch 3 Die 3a Convex part of die 4 Blank holder 5 Punch top part 5a Concave part of punch top part 6 Vibration device 10 Control part 20 Punch 20a Surface facing die 21 Punch top part 21a Concave part L of punch concave part longitudinal direction

Claims (3)

A method of manufacturing an automotive skin panel having a recessed feature, comprising:
The concave portion is a concave embossed portion or a portion between adjacent character lines,
forming the concave portion while vibrating the die when press-molding the concave portion;
a vibration frequency of the dice when vibrating is 3 Hz or more and 20 Hz or less ;
A method for manufacturing an automobile outer panel, wherein the amplitude of vibration of the die is 1 μm or more . A press molding apparatus for an automobile outer panel having a concave portion,
The concave portion is a concave embossed portion or a portion between adjacent character lines,
Equipped with a vibrating device that vibrates the dice,
The press molding apparatus, wherein the vibration device is configured to generate vibration with a vibration frequency of 3 Hz or more and 20 Hz or less and an amplitude of 1 μm or more . 3. A press molding apparatus according to claim 2 , wherein said vibration device is incorporated in said die.

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