Outer panel

Abstract

This outer panel has, on the outer surface thereof, a ridgeline and plane sections adjacent to each side of the ridgeline. The outer panel has a plate thickness of less than 0.6 mm and an ultimate yield stress of 360 MPa or more. The plane sections each include: an adjacent section which is adjacent to the ridgeline; and a separated region which is adjacent to the adjacent section on the side opposite the ridgeline. The results of evaluating surface characteristics are consistent between the adjacent region and the separated region.

Description

[Technical Field]

[0001] The present invention relates to an outer panel. This application claims priority to Japanese Patent Application No. 2022-083099, filed on May 20, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] In addition to weight reduction and cost reduction aimed at reducing CO2 emissions, there is a growing trend toward placing importance on design when it comes to automobile bodies. To achieve this, technologies that can improve, suppress, and evaluate appearance quality defects that detract from design are effective. Examples of appearance quality defects include surface distortions and line misalignment, which are equivalent to very small wrinkles. Line misalignment occurs when a blank is press-formed to obtain a molded product with ridges. This localized shape change occurs near the design line (character line), which is represented by a ridge with a relatively large curvature. This shape change moves outside the design line, resulting in an appearance defect that remains visible as a line even after painting.

[0003] Conventional countermeasures for line misalignment include optimizing the press direction or changing the balance of material flow into the mold to prevent local shape changes that occur in the early stages of press forming from moving outside the design line, or keeping any movement outside the design line to a level that is acceptable in terms of appearance quality.

[0004] Patent Document 1 discloses a technology for press-forming an automotive outer panel by moving the die relatively toward the punch side to prevent line misalignment and form a character line, bringing a punch-side elastic body that protrudes from the punch-side forming surface portion that forms the panel surface portion and a die-side elastic body that protrudes from the die-side forming surface portion that forms the panel surface portion into contact with a metal blank, and moving the die relatively toward the punch side to the forming bottom dead center while the punch-side elastic body and die-side elastic body are kept in contact with the metal blank, and crushing the punch-side elastic body and die-side elastic body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent No. 6996605 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology described in Patent Document 1 is said to be able to prevent line misalignment and form the desired character line without increasing the number of steps in press molding, but the equipment required is complex.

[0007] However, when the outer panel is thinned to reduce the weight of the automobile body, its dent resistance decreases. To maintain dent resistance even when the outer panel is thinned, it is possible to use a high-strength material for the outer panel. However, it is generally said that the higher the strength of the material, the more pronounced the line misalignment becomes, even with the same plate thickness.

[0008] The present invention has been made in consideration of the above problems, and has an object to provide an outer panel having character lines, which ensures dent resistance and has a beautiful appearance. [Means for solving the problem]

[0009] The inventors of the present invention have focused on the flow of material into the mold during press forming and have conducted extensive research into the conditions under which misalignment does not occur on the outer surface of the outer panel manufactured by press forming. As a result, they have discovered that by reducing the plate thickness, the difference between the stress on the inside and outside of the bend that occurs during press forming is reduced, thereby preventing localized reductions in plate thickness and preventing misalignment.

[0010] The gist of the present invention, which was completed based on the above findings, is as follows. [1] An outer panel according to one embodiment of the present invention has a ridge line on its outer surface and surface portions adjacent to both sides of the ridge line, the panel thickness being less than 0.6 mm and the ultimate yield stress being 360 MPa or more, the surface portions having an adjacent region adjacent to the ridge line and a spaced region adjacent to the adjacent region on the opposite side of the ridge line on both sides of the ridge line, and the evaluation of the surface texture of the adjacent region and the evaluation of the surface texture of the spaced region are consistent. [2] In the outer panel described in [1] above, the adjacent region may be a strip-shaped region having a length of 20 mm in the direction aligned with the spaced region, and the spaced region may be a strip-shaped region having a length of 20 mm in the direction aligned with the adjacent region. [3] In the outer panel described in [1] or [2] above, the evaluation may be based on the difference between the maximum and minimum values of the second derivative of the shape of the outer surface in a cross section crossing the ridge line. [4] In the outer panel described in [1] or [2] above, the radius of curvature of the ridge line in a cross section perpendicular to the ridge line may be 20 mm or less. [5] The outer panel according to the above [1] or [2] may have a plurality of ridge lines, and the ridge lines may not intersect with each other. [6] In the outer panel described in [5] above, the interval between at least two of the plurality of ridge lines may be less than 20 mm. [7] The outer panel according to the above [1] or [2] may have a plurality of ridge lines, and two or more of the plurality of ridge lines may intersect with each other. [8] The outer panel according to any one of the above [1] to [7] may be made of steel. [9] The outer panel described in any one of [1] to [8] above may have a plate thickness of 0.5 mm or less, an ultimate yield stress of 590 MPa or more, and a radius of curvature of the ridge line in a cross section perpendicular to the ridge line of 10 mm or less.

[10] The outer panel described in any one of [1] to [9] above may have a difference ΔP / B between the maximum and minimum values of the second derivative of the shape of the outer surface in the adjacent region and the separated region measured across the ridge line, both of which may be 0.012 / mm or less.

[11] In the outer panel according to any one of the above [1] to

[10] , the evaluation may be based on an amount of reduction in plate thickness.

[12] In addition, another aspect of the present invention provides an outer panel having a ridge line on its outer surface and surface portions adjacent to both sides of the ridge line, the panel thickness being less than 0.6 mm, and the ultimate yield stress being 360 MPa or more, the surface portions having an adjacent region adjacent to the ridge line and a spaced region adjacent to the adjacent region on the opposite side of the ridge line on both sides of the ridge line, and the difference ΔP / B between the maximum and minimum values of the second derivative of the shape of the outer surface in the adjacent region measured across the ridge line is 0.012 / mm or less. [Effects of the Invention]

[0011] As described above, according to the above aspects of the present invention, it is possible to provide an outer panel having a character line, ensuring dent resistance and having a beautiful appearance. [Brief explanation of the drawings]

[0012] [Figure 1A] FIG. 10 is a diagram showing an outline of press forming when line misalignment occurs. [Figure 1B] FIG. 1 is a diagram showing an outline of press forming when no line misalignment occurs. [Figure 2] FIG. 2 is a side view of an outer panel according to one embodiment of the present invention. [Figure 3] FIG. 10 is a perspective view showing another example of the outer panel according to the embodiment. [Figure 4] FIG. 10 is a graph showing an example of measurement results of the second derivative of the shape of the outer surface where line deviation is visually recognized. [Figure 5] FIG. 10 is a graph showing an example of the measurement results of the second derivative of the shape of the outer surface where no line deviation is visible. [Figure 6] FIG. 10 is a side view showing a modified example of the outer panel according to the embodiment. [Figure 7] FIG. 10 is a diagram for explaining the conditions of a line deviation reproduction test. [Figure 8] FIG. 1 is a graph showing the relationship between the radius of curvature R of the ridgeline and the difference ΔP / B between the maximum and minimum values of the second derivative of the surface shape of the test specimen when the strength and thickness of the steel plate are changed. DETAILED DESCRIPTION OF THE INVENTION

[0013] Prior to describing an outer panel according to one embodiment of the present invention, the mechanism of line misalignment that occurs in a press-formed product during press forming to form a character line will be described with reference to Figures 1A and 1B. Figure 1A is a diagram illustrating an overview of press forming when line misalignment occurs. Figure 1B is a diagram illustrating an overview of press forming when line misalignment does not occur.

[0014] 1A and 1B, a mold 21 is composed of an upper mold 21a and a lower mold 21b, and a blank 20 is sandwiched between the upper mold 21a and the lower mold 21b and press-molded. In the early stages of press forming, the blank 20 comes into contact with a design character line (not shown) on the die 21. The portion of the blank 20 that comes into contact with the design character line is called the initial contact portion 22. As pressing by the die 21 progresses and the forming of the character line 23 (corresponding to the ridge line in the present invention) progresses, the initial contact portion 22 moves. If line misalignment occurs, after forming is complete, the initial contact portion 22 will be located outside the R end 24 of the character line 23. This initial contact portion 22 is a portion where strain is introduced into the blank 20 in the early stages of press forming, making it harder than other portions. Because a difference in hardness occurs between the initial contact portion 22 and other portions, stress concentrates near the initial contact portion 22, and the plate thickness near this initial contact portion 22 is locally reduced. In this portion, a depression occurs on the outer surface of the outer panel after press forming. This depression is line misalignment. If the initial contact portion 22 is located in a smooth area outside the R stop 24, the line misalignment may be visible, which may result in a loss of aesthetic appeal to the surface of the outer panel. The outer surface is the surface that is visible during normal use. For example, in the outer panel of a moving body such as an automobile, the surface facing the outside of the vehicle is called the outer surface. 1B, when the initial contact point 22 between the blank 20 and the mold 21 is located inside the R end 24 of the character line 23 at the completion of press forming, the misalignment is not visible because the character line 23 is curved. As a result, the outer panel has a beautiful appearance.

[0015] If the initial contact portion 22 is arranged inside the character line 23, the misalignment will not be visible, but the inventors have studied ways to prevent the misalignment from being visible even if the initial contact portion 22 is arranged outside the character line 23. As a result, they have found that by making the plate thickness less than 0.6 mm, it is possible to create an outer panel with a character line and a beautiful appearance.

[0016] Next, the outer panel according to this embodiment will be described in detail with reference to Figures 2 and 3. Figure 2 is a side view of the outer panel according to one embodiment of the present invention. Figure 3 is a perspective view showing another example of the outer panel. Note that in this specification and drawings, components having substantially the same functional configuration are designated by the same reference numerals, and redundant description will be omitted.

[0017] The outer panel 100 according to this embodiment is an outer panel having a ridge line 101 on its outer surface and surface portions 102 adjacent to both sides of the ridge line, with a plate thickness of less than 0.6 mm and an ultimate yield stress of 360 MPa or more, and the surface portions 102 have an adjacent region Zn adjacent to the ridge line 101, which is a character line, and a separated region Zf adjacent to the adjacent region Zn on the opposite side of the ridge line 101, on both sides of the ridge line 101, and the evaluation of the surface texture of the adjacent region Zn and the evaluation of the surface texture of the separated region Zf are consistent. The outer panel 100 shown in Fig. 2 is a front door outer panel, and the outer panel 100A shown in Fig. 3 is a hood outer panel.

[0018] As will be described later, the outer panel 100 is made of a material having an ultimate yield stress of 360 MPa or more. There are no particular limitations on the material that makes up the outer panel 100, and for example, a steel plate having an ultimate yield stress of 360 MPa or more can be used. As long as the steel plate has a yield stress of 360 MPa or more, there are no particular limitations on its chemical composition or metal structure. The outer panel 100 may be manufactured using a galvanized steel plate, and examples of galvanized steel plates having an ultimate yield stress of 360 MPa or more include JAC390W and JAC590Y that comply with JFS A 3011:2020.

[0019] The outer panel 100 has a thickness of less than 0.6 mm. During press forming, compressive stress occurs on the inside of the blank bent and tensile stress occurs on the outside of the bent portion. However, when the plate thickness is thin, the difference between the compressive stress on the inside of the bent portion and the tensile stress on the outside of the bent portion becomes smaller. In other words, the thinner the plate thickness, the less stress concentration there is. Therefore, even if the portion that contacts the design character line on the die at the beginning of press forming is harder than other portions, a plate thickness of less than 0.6 mm reduces stress concentration at the initial contact point, thereby suppressing the occurrence of dents due to localized thickness reduction. As a result, line misalignment can be prevented. The outer panel 100 preferably has a thickness of 0.5 mm or less, more preferably 0.4 mm or less.

[0020] There is no particular lower limit to the thickness of the outer panel 100, and the thickness can be, for example, 0.35 mm or more. From the viewpoint of ensuring dent resistance, the thickness of the outer panel 100 is preferably 0.4 mm or more.

[0021] The thickness of the outer panel 100 is the thickness at a position that is visible externally and further at a position where the mean radius of curvature is 500 mm or more. The mean radius of curvature is the average of the two principal curvatures that define the Gaussian curvature. The thickness is measured at the surface portion 102, excluding areas where the radius of curvature is significantly small. Examples of areas where the radius of curvature is significantly small include the peripheral edge of the outer panel 100 where the radius of curvature is small due to hemming, areas with irregularities such as door handles, and ridges 101.

[0022] The ultimate yield stress of the outer panel 100 is 360 MPa or more. A ultimate yield stress of 360 MPa or more ensures dent resistance. In general, the higher the strength of an outer panel, the more likely it is that misalignment occurs. This is thought to be because, while strain is introduced into the blank during press forming, high-strength materials have a greater hardening amount for the same amount of strain, resulting in a greater difference in hardness from the non-deformed portion. However, the outer panel 100 according to this embodiment has a thickness of less than 0.6 mm, which, as described above, can suppress misalignment. Therefore, the ultimate yield stress of the outer panel 100 is 360 MPa or more. The ultimate yield stress is preferably 440 MPa or more, and more preferably 590 MPa or more.

[0023] The upper limit of the ultimate yield stress of the outer panel 100 is not particularly limited, and may be, for example, 1000 MPa or less. From the viewpoint of formability in press molding, the ultimate yield stress of the outer panel 100 may be 700 MPa or less.

[0024] The ultimate yield stress of the outer panel 100 is measured by the following method: A test piece is cut out from a position that is visible externally and further from a position where the mean radius of curvature is 500 mm or more, and a tensile test is performed using a method in accordance with JIS Z 2241:2011 to measure the ultimate yield stress.

[0025] The ridge line 101 is a portion curved in one direction in the outer panel 100. The ridge line 101 is curved so that the shape of a cross section perpendicular to the extending direction thereof is convex toward the vehicle exterior.

[0026] The radius of curvature R of the cross-sectional shape of the ridgeline 101 is not particularly limited, and can be, for example, 2.5 mm or more and 20 mm or less. Conventionally, a radius of curvature R of 10 mm or less has been prone to misalignment, but the outer panel 100 according to this embodiment can suppress misalignment even when the radius of curvature R is 10 mm or less. On the other hand, when the ridgeline 101 is convex toward the vehicle exterior, a radius of curvature R of 2.5 mm or more gives the ridgeline 101 a relatively gently curved cross-sectional shape, thereby suppressing damage to a contact body that comes into contact with the ridgeline 101 from the vehicle exterior. Therefore, when the ridgeline 101 is convex toward the vehicle exterior, it is preferable that the radius of curvature R be 2.5 mm or more.

[0027] The radius of curvature R refers to the smallest radius of curvature of the ridge line 101 in a cross section perpendicular to the extension direction of the ridge line 101. If the ridge line 101 has different radii of curvature in its extension direction, the smallest radius of curvature in the cross section with the smallest radius of curvature is taken as the radius of curvature R. The radius of curvature R is measured using a three-point gauge.

[0028] The shape of the ridge line 101 in a cross section perpendicular to the direction in which the ridge line 101 extends is a shape having curvature, and can be, for example, a circular arc, an elliptical arc, or a parabola.

[0029] A plurality of ridge lines 101 may be provided on the outer panel 100. Two ridge lines 101 are shown on the outer panel 100 in Fig. 2 and the outer panel 100A in Fig. 3.

[0030] The distance between at least two of the multiple ridge lines 101 is not particularly limited and can be, for example, 20 mm or less, or 10 mm or less. Since the outer panel 100 is one in which misalignment is suppressed, it is possible to design an outer panel with a small distance between the ridge lines 101. In particular, even if the distance between the two ridge lines 101 is 20 mm or less or 10 mm or less, an outer panel with clear ridge lines as designed can be obtained. Here, if the two ridge lines are not parallel, the distance between the two ridge lines 101 refers to the minimum value.

[0031] The surface portions 102 are adjacent to both sides of the ridge line 101. For example, FIG. 3 shows a first surface portion 102A adjacent to the ridge line 101 and a second surface portion 102B adjacent to the opposite side of the first surface portion 102A. The surface portion 102 is a flat area compared to the ridge line 101. The surface portion 102 is a flat surface or a curved surface having a larger radius of curvature than the radius of curvature of the ridge line 101. For example, the surface portion 102 has a radius of curvature that is five times or more the radius of curvature of the ridge line 101.

[0032] The surface portion 102 has an adjacent region Zn adjacent to the ridge line 101 and a separated region Zf adjacent to the adjacent region Zn on the opposite side of the ridge line 101. Line misalignment is primarily visible in the adjacent region Zn. The adjacent region Zn is, for example, a strip-shaped region having a length of 20 mm in the direction of alignment with the separated region Zf, and the separated region Zf is also a strip-shaped region having a length of 20 mm in the direction of alignment with the adjacent region Zn. The adjacent region Zn and the separated region Zf are regions extending in the extension direction of the ridge line 101. In FIG. 3, the adjacent region Zn1 and the separated region Zf1 arranged on the first surface portion 102A, and the adjacent region Zn2 and the separated region Zf2 arranged on the second surface portion 102B are shown as the adjacent region Zn and the separated region Zf for one ridge line 101.

[0033] In the surface portion 102, the evaluation of the surface texture of the adjacent region Zn and the evaluation of the surface texture of the separated region Zf are consistent. As described above, line misalignment is generally visible in the adjacent region Zn. However, if a line misalignment occurs at a large angle with the ridge line 101, line misalignment may be visible in a position that intersects with the boundary line between the adjacent region Zn and the separated region Zf. Even in this case, the surface textures of the adjacent region Zn and the separated region Zf at a predetermined position in the longitudinal direction of the boundary line will be different. Therefore, if the evaluation of the surface texture of the adjacent region Zn and the evaluation of the surface texture of the separated region Zf are consistent, it can be determined that line misalignment is suppressed. The evaluation of the surface texture is based, for example, on the difference ΔP / B between the maximum and minimum values of the second derivative of the shape of the outer surface in a cross section that intersects with the ridge line 101. Here, "intersects" means along a straight line that forms an angle of 60 to 120 degrees with the ridge line 101.

[0034] 4 and 5 show graphs illustrating an example of the measurement results of the second-order derivatives of the shape of the outer surface measured across the ridge line 101. FIG. 4 is a graph illustrating an example of the measurement results of the second-order derivatives of the shape of an outer surface where line misalignment is visible. FIG. 5 is a graph illustrating an example of the measurement results of the second-order derivatives of the shape of an outer surface where line misalignment is not visible. The horizontal axis represents the X-coordinate of the evaluation line, and the vertical axis represents the second-order derivative. The origin (zero) of the X-coordinate corresponds to the boundary position between the adjacent region Zn and the separated region Zf. Therefore, in FIGS. 4 and 5, the range of X-coordinates from -20 to 0 mm corresponds to the adjacent region Zn, and the range of X-coordinates from 0 to 20 mm corresponds to the separated region Zf. On the outer surface where line misalignment is visible, as shown in FIG. 4, the difference ΔP / B between the maximum and minimum values of the second-order derivatives is large in the adjacent region Zn (range from -20 to 0 mm), and the difference ΔP / B between the maximum and minimum values of the second-order derivatives is small in the separated region Zf (range from 0 to 20 mm). On the other hand, on the outer surface where no line misalignment is visible, as shown in FIG. 5, the difference ΔP / B between the maximum and minimum values of the second derivative is small in both the adjacent region Zn and the separated region Zf.

[0035] When the distance between adjacent ridgelines 101 is 40 mm, in the surface portion 102 between the adjacent ridgelines 101, the adjacent region Zn adjacent to one ridgeline 101 and the adjacent region Zn adjacent to the other ridgeline 101 are in contact. In this case, the separated region Zf for one ridgeline 101 overlaps or coincides with a large portion of the adjacent region Zn for the other ridgeline 101. Note that when the distance between adjacent ridgelines 101 is less than 40 mm, the surface portion 102 between the adjacent ridgelines 101 can be divided into two regions of the same width, and each region can be designated as the adjacent region Zn and the separated region Zf.

[0036] In the outer panel 100, the difference ΔP / B between the maximum and minimum values of the second derivative of the shape of the outer surface in the adjacent region Zn measured across the ridge line 101 is equal to or less than a predetermined threshold. Since the degree of line misalignment required for each product differs, the threshold is determined for each product. It is preferable that the difference ΔP / B between the maximum and minimum values of the second derivative in both the adjacent region Zn and the separated region Zf is equal to or less than a predetermined threshold. In the outer panel 100, it is more preferable that the difference ΔP / B between the maximum and minimum values of the second derivative of the shape of the outer surface in the adjacent region Zn and the separated region Zf measured across the ridge line 101 is 0.012 / mm or less. As described above, misalignment can be understood as a localized reduction in the thickness of the outer panel 100 surface. However, according to the inventors' investigations, even if the step height of the surface shape is the same, if the surface shape has sharp irregularities, i.e., if the curvature changes significantly, it may be easily recognized as an appearance quality defect. Appearance quality defects, including misalignment, are evaluated based on the second-order derivative, which represents the curvature of the surface shape. If the difference ΔP / B between the maximum and minimum values of the second-order derivative in the evaluation target area is 0.012 / mm or less, misalignment is not visually recognized in the evaluation target area. Therefore, the difference ΔP / B between the maximum and minimum values of the second-order derivative in the evaluation target area is preferably 0.012 / mm or less. The difference ΔP / B between the maximum and minimum values of the second-order derivative is more preferably 0.010 / mm or less, and even more preferably 0.008 / mm or less. These are examples of evaluation criteria, which are set appropriately depending on the quality level required for the appearance performance of the outer panel.

[0037] The surface texture of the adjacent region Zn and the separated region Zf is evaluated based on whether an index indicating the surface texture for each region is equal to or less than an evaluation reference value. In this embodiment, the difference ΔP / B between the maximum and minimum values of the second-order derivative of the surface shape is used as the index indicating the surface texture, and the evaluation reference value is set appropriately according to the required quality level, as described above. That is, in this embodiment, the surface texture of the adjacent region Zn and the separated region Zf is evaluated based on whether the difference ΔP / B between the maximum and minimum values of the second-order derivative of the surface shape for each region is equal to or less than the evaluation reference value. Since line deviation occurs on either side of the ridge line 101, if it can be confirmed that the evaluations of the adjacent region Zn and the separated region Zf are consistent for both sides of the ridge line 101, it can be determined that the line deviation caused by the shaping of the ridge line 101 is suppressed and the appearance is beautiful.

[0038] The shape data of the surface shape, from which the second-order derivative is calculated, is preferably obtained using a non-contact laser shape measurement device. In this embodiment, the surface shape of the outer panel 100 is measured using a laser microscope with high measurement accuracy. Using shape data with high measurement accuracy allows the curvature of the surface shape to be appropriately reflected in the obtained second-order derivative. However, when a contact-type shape measurement device is used, the curvature of the surface shape may not be appropriately reflected in the second-order derivative of the shape data due to influences such as mechanical measurement noise contained in the shape data. In such cases, in order to obtain data that appropriately reflects the curvature, unnecessary components may be removed by filtering the shape data, or the third or fourth order derivative of the shape data may be calculated instead of the second-order derivative.

[0039] The surface shape data is acquired by measuring the shape in a scanning direction that crosses the ridge line 101 of the outer panel 100. In this embodiment, the shape is measured at one position in the center portion of the ridge line 101 in the longitudinal direction. A second-order derivative is calculated from the obtained surface shape data, and the difference ΔP / B between the maximum and minimum values of the second-order derivative in each range in the scanning direction corresponding to the adjacent region Zn and the separated region Zf is determined. The surface texture of each of the adjacent region Zn and the separated region Zf is evaluated based on whether ΔP / B in each range is equal to or less than an evaluation reference value. In the outer panel 100 of this embodiment, all of these evaluations are equal to or less than the evaluation reference value, and the evaluations are consistent.

[0040] Considering the possibility that misalignment of the character line at the boundary between the adjacent region Zn and the separated region Zf may be visible, it is preferable to measure the shape at multiple positions along the ridge line 101 and ensure that the surface texture evaluations of the adjacent region Zn and the separated region Zf at all of these positions are consistent. The multiple positions include at least a position in the longitudinal center of the ridge line 101. For example, these positions may be distributed throughout the entire longitudinal direction, including positions at the longitudinal ends, or may be concentrated in the longitudinal center. Because the appearance quality of the longitudinal center of the character line has a significant impact on the impression of the design, an outer panel without misalignment in this area is less likely to detract from the aesthetic impression. Therefore, ensuring that the ridge line 101 is free of misalignment in the longitudinal center is important for ensuring an aesthetically pleasing appearance.

[0041] A known press-forming apparatus may be used to manufacture the outer panel according to this embodiment. The technology applied to the outer panel according to this embodiment is a technology that suppresses misalignment by press-forming a thin blank without introducing a complex mechanism for suppressing misalignment. Therefore, an outer panel with a beautiful appearance can be manufactured using a press-forming apparatus with a relatively simple configuration. Of course, to further improve the appearance quality of the outer panel, the outer panel according to this embodiment may also be manufactured using a press-forming apparatus with a complex mechanism. In manufacturing the outer panel according to this embodiment, the multiple ridgelines may be formed so that the ridgelines do not intersect with each other. Alternatively, the multiple ridgelines may be formed so that the distance between at least two of the multiple ridgelines (the shortest distance along the outer surface of the outer panel) is 20 mm. Alternatively, the multiple ridgelines may be formed so that two or more of the multiple ridgelines intersect with each other.

[0042] Although the present invention has been described above based on preferred embodiments thereof, the present invention is not limited thereto. The above is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.

[0043] For example, in the above-described embodiment, the case where the multiple ridge lines 101 do not intersect has been described, but the arrangement of the multiple ridge lines 101 is not limited to this. For example, as shown in FIG. 6, the ridge lines 101 may intersect.

[0044] 2, 3, and 6 show two ridge lines 101, but the number of ridge lines 101 may be one, or three or more. When three or more ridge lines 101 are arranged, all of the ridge lines 101 do not have to intersect, or at least two of the multiple ridge lines 101 may intersect.

[0045] Furthermore, for example, the evaluation of the surface texture may use the amount of thickness reduction as an index of the surface texture. In this case, the surface texture of the adjacent region Zn is evaluated based on whether the amount of thickness reduction in the adjacent region Zn is equal to or less than the evaluation standard, and similarly, the surface texture of the adjacent region Zn is evaluated based on whether the amount of thickness reduction in the separated region Zf is equal to or less than the evaluation standard. If the evaluation results for both are the same, it can be determined that the line misalignment associated with the forming of the ridge line has been suppressed. The evaluation standard may be determined based on the results of a sensory test on the visual recognition of the line misalignment.

[0046] Furthermore, for example, Figures 2 and 6 show the outer panel of a front door that constitutes an automobile as an example of an outer panel, and Figure 3 shows the outer panel of a hood, but the outer panel of the present disclosure may be applied not only to the front door and the hood, but also to the rear door, front fender, rear fender, roof, or tailgate.

[0047] Below, we will explain the test examples that led to the discovery that is the basis of the present invention, namely, that by reducing the plate thickness, the difference between the stress on the inside of the bend and the stress on the outside of the bend that occurs during press forming is reduced, the occurrence of localized reductions in plate thickness is suppressed, and line misalignment is suppressed.

[0048] Test specimens were prepared from a galvannealed steel sheet having a tensile strength of 270 MPa and a thickness of 0.7 mm, a galvannealed steel sheet having a tensile strength of 590 MPa and a thickness of 0.4 mm, and a galvannealed steel sheet having a tensile strength of 270 MPa and a thickness of 0.7 mm. Each test specimen was in the form of a strip measuring 500 mm in the rolling direction and 60 mm in the width direction. As shown in Figure 7, the test specimen (blank in Figure 7) was supported by two supports. The distance L between the centers of the two supports was 150 mm. Both ends of each test specimen in the rolling direction were clamped by chucks (not shown) and pulled in opposite directions to apply a tension T1 to the test specimen. With tension T1 acting on the test specimen, a punch having an arc-shaped tip with a curvature radius R was pressed into the test specimen by a penetration depth δ so that the bending angle θ was 170°. Next, the test specimen was moved in one direction (the direction indicated by s in Figure 7) while applying tension T2 in the same direction as tension T1, and then the punch was released. The magnitudes of tensions T1 and T2 were set so that s / YP = 1.25. Here, s is the nominal stress, calculated by dividing tension T1 or T2 by the width direction length and thickness of the test specimen. YP is the yield stress. Therefore, s / YP is a dimensionless number. This test specimen movement simulated the material flow during press forming. The radius of curvature R of the punch tip was 7 mm, 10 mm, and 20 mm. The results are shown in Figure 8. Figure 8 is a graph showing the relationship between the radius of curvature R of the ridgeline and the difference ΔP / B between the maximum and minimum values of the second derivative of the surface shape of the test specimen when the strength and thickness of the steel sheet were changed. In FIG. 8 , "GA270, t=0.7" indicates the test results for a galvannealed steel sheet having a tensile strength of 270 MPa and a thickness of 0.7 mm, "GA590, t=0.4" indicates the test results for a galvannealed steel sheet having a tensile strength of 270 MPa and a thickness of 0.7 mm, and "GA270, t=0.4" indicates the test results for a galvannealed steel sheet having a tensile strength of 270 MPa and a thickness of 0.7 mm.

[0049] As shown in Figure 8, it was found that the thinner the plate thickness, the smaller the difference ΔP / B between the maximum and minimum values of the second derivative. It was also found that even when the tensile strength is 590 MPa, it is possible to reduce the difference ΔP / B between the maximum and minimum values of the second derivative by reducing the plate thickness. [Explanation of symbols]

[0050] 100, 100A, 100B outer panel 101 Ridgeline 102, 102A, 102B surface section Zn(Zn1,Zn2) adjacent region Zf(Zf1,Zf2) Separation area

Claims

1. An outer panel having a ridge line on its outer surface and surface portions adjacent to both sides of the ridge line, The plate thickness is less than 0.6 mm, and the ultimate yield stress is 360 MPa or more; the surface portion includes an adjacent region adjacent to the ridge line and a spaced region adjacent to the adjacent region on the opposite side of the ridge line, on both sides of the ridge line; An outer panel, wherein the evaluation of the surface texture of the adjacent region and the evaluation of the surface texture of the separated region are consistent.

2. the adjacent region is a strip-shaped region having a length of 20 mm in a direction aligned with the spaced region, The outer panel according to claim 1 , wherein the spaced region is a strip-shaped region having a length of 20 mm in a direction aligned with the adjacent region.

3. 3. The outer panel according to claim 1, wherein the evaluation is based on a difference between a maximum value and a minimum value of a second derivative of the shape of the outer surface in a cross section that intersects the ridge line.

4. The outer panel according to claim 1 or 2, wherein a radius of curvature of the ridge line in a cross section perpendicular to the ridge line is 20 mm or less.

5. The outer panel according to claim 1 or 2, wherein a plurality of the ridge lines are provided, and the ridge lines do not intersect with each other.

6. The outer panel according to claim 5 , wherein the interval between at least two of the plurality of ridge lines is less than 20 mm.

7. The outer panel according to claim 1 or 2, wherein a plurality of the ridge lines are provided, and two or more of the plurality of ridge lines intersect with each other.

8. 3. The outer panel according to claim 1 or 2, which is made of steel.

9. 9. The outer panel according to claim 8, wherein the panel has a thickness of 0.5 mm or less, an ultimate yield stress of 590 MPa or more, and a radius of curvature of the ridge line in a cross section perpendicular to the ridge line is 10 mm or less.

10. 4. The outer panel according to claim 3, wherein a difference ΔP / B between the maximum and minimum values of the second derivative of the shape of the outer surface in the adjacent region and the separated region measured across the ridge line is 0.012 / mm or less.

11. The outer panel according to claim 1 or 2, wherein the evaluation is based on an amount of reduction in plate thickness.

12. An outer panel having a ridge line on its outer surface and surface portions adjacent to both sides of the ridge line, The plate thickness is less than 0.6 mm, and the ultimate yield stress is 360 MPa or more; the surface portion includes an adjacent region adjacent to the ridge line and a spaced region adjacent to the adjacent region on the opposite side of the ridge line, on both sides of the ridge line; an outer panel, wherein a difference ΔP / B between the maximum and minimum values of the second derivative of the shape of the outer surface in the adjacent region measured across the ridge line is 0.012 / mm or less.

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