Outer panel

Abstract

The present invention pertains to an outer panel having, on the outer surface thereof, a ridge line and a surface section adjacent to both sides of the ridge line, the panel thickness being less than 0.6 mm, the limit yield stress being 360 MPa or more, the surface section having an adjacent region adjacent to the ridge line and a separation region adjacent to the adjacent region on the opposite side from the ridge line, evaluation of surface properties between the adjacent region and the separation region is consistent.

Description

Technical Field

[0001] This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-083099 filed in Japan on May 20, 2022, the contents of which are incorporated herein by reference. Background Art

[0002] For automobile bodies, in addition to lightweighting and cost reduction to reduce CO2 emissions, there is a trend of also paying attention to design. For this reason, it is effective to use technologies that improve, suppress, and evaluate poor appearance quality that reduces design. Poor appearance quality includes, for example, surface strain equivalent to very small wrinkles, line deviation, etc. The so-called line deviation refers to the following poor appearance quality: when a blank is stamped to obtain a molded product with ridges, a local shape change occurs near the design line (characteristic line) represented by the ridge with relatively large curvature, and the shape change moves outside the design line and is visually observed as a line after painting.

[0003] Existing examples of countermeasures for line deviation include: optimizing the stamping direction, changing the flow balance of material into the mold, etc., so that the local shape changes produced in the early stage of stamping do not move outside the design line; even if they move outside the design line, they are suppressed to a level that is acceptable as appearance quality.

[0004] Patent document 1 discloses the following technology: in order to prevent the characteristic line from being formed by line deviation, the die is moved relative to the punch side, and the punch side elastic body protruding from the punch side forming surface of the forming panel surface and the die side elastic body protruding from the die side forming surface of the forming panel surface are brought into contact with the metal raw material plate. While the punch side elastic body and the die side elastic body are brought into contact with the metal raw material plate, the die is moved relative to the punch side to the forming bottom dead point, and the outer panel of the automobile is stamped while the punch side elastic body and the die side elastic body are flattened.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 6996605 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] According to the technology described in Patent Document 1, it is possible to prevent line deviation and form the target characteristic line without increasing the number of man-hours for press forming, but the device is complex.

[0010] However, if the outer panels are made thinner to reduce the weight of the vehicle body, dent resistance decreases. To maintain dent resistance even with thinner outer panels, high-strength materials can be used for the outer panels. However, it is generally believed that even with the same panel thickness, higher strength materials lead to more pronounced linear deviation.

[0011] Therefore, the present invention has been made in view of the above-mentioned problems, and an object thereof is to provide an outer panel having a character line, ensuring dent resistance and having an aesthetically pleasing appearance.

[0012] Means for solving problems

[0013] Focusing on the flow of material into the die during press forming, the inventors conducted in-depth research on the conditions that prevent linear deviation on the outer surface of the outer panel produced by press forming. As a result, they discovered that by reducing the plate thickness, the difference between the stress on the inner side of the bend and the stress on the outer side of the bend generated during press forming is reduced, thus suppressing the occurrence of localized plate thickness reduction and linear deviation.

[0014] The gist of the present invention, which has been accomplished based on the above findings, is as follows.

[0015] [1] An outer panel according to one embodiment of the present invention comprises a ridge line and face portions adjacent to the ridge line on both sides of the outer surface, wherein the panel thickness is less than 0.6 mm and the ultimate yield stress is 360 MPa or more, the face portions comprising adjacent regions adjacent to the ridge line on both sides of the ridge line and a separation region adjacent to the adjacent region on the side opposite to the ridge line, and the evaluation of the surface properties of the adjacent regions is consistent with the evaluation of the surface properties of the separation regions.

[0016] [2] In the outer panel described in [1] above, the adjacent region may be a strip-shaped region with a length of 20 mm in the arrangement direction of the separation region, and the separation region may be a strip-shaped region with a length of 20 mm in the arrangement direction of the adjacent region.

[0017] [3] In the outer panel described in [1] or [2] above, the evaluation may be based on the difference between the maximum value and the minimum value of the second-order differential coefficient of the shape of the outer surface in the cross section crossing the ridge line.

[0018] [4] In the outer panel described in [1] or [2] above, the curvature radius of the ridge line in a cross section perpendicular to the ridge line may be 20 mm or less.

[0019] [5] The outer panel described in [1] or [2] may include a plurality of ridge lines, wherein the ridge lines do not intersect with each other.

[0020] [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.

[0021] [7] The outer panel described in [1] or [2] may include a plurality of ridge lines, and two or more of the plurality of ridge lines may intersect.

[0022] [8] In the outer panel described in any one of [1] to [7] above, the outer panel may be made of steel.

[0023] [9] In the outer panel described in any one of [1] to [8] above, the thickness may be less than 0.5 mm, the ultimate yield stress may be greater than 590 MPa, and the curvature radius of the ridge line in the cross section perpendicular to the ridge line may be less than 10 mm.

[0024]

[10] In the outer panel described in any one of the above [1] to [9], the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient of the shape of the outer surface in the adjacent area and the separation area measured transversely to the above ridge line is less than 0.012 / mm.

[0025]

[11] In the outer panel described in any one of [1] to

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

[0026]

[12] In addition, another embodiment of the present invention is an outer panel having a ridge line and face portions adjacent to both sides of the ridge line on the outer surface, wherein the plate thickness is less than 0.6 mm, the ultimate yield stress is greater than or equal to 360 MPa, the face portions having adjacent areas adjacent to the ridge line on both sides of the ridge line, and a separation area adjacent to the adjacent area on the opposite side of the ridge line, and the difference ΔP / B between the maximum value and the minimum value of the second-order differential coefficient of the shape of the outer surface in the adjacent area measured by transversely crossing the ridge line is less than or equal to 0.012 / mm.

[0027] Effects of the Invention

[0028] As described above, according to the above aspect 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 DESCRIPTION OF THE DRAWINGS

[0029] Figure 1A This is a diagram showing an overview of press forming when line deviation occurs.

[0030] Figure 1B This is a diagram showing an overview of press forming when line deviation does not occur.

[0031] Figure 2This is a side view of an outer panel showing one embodiment of the present invention.

[0032] Figure 3 It is a perspective view showing another example of the outer panel of this embodiment.

[0033] Figure 4 This is a graph showing an example of the measurement results of the second-order differential coefficient of the shape of the outer surface where the line deviation is visually observed.

[0034] Figure 5 This is a graph showing an example of the measurement results of the second-order differential coefficient of the shape of the outer surface where no line deviation is visually observed.

[0035] Figure 6 It is a side view showing a modified example of the outer panel of this embodiment.

[0036] Figure 7 It is a diagram for explaining the conditions of the line deviation reproduction test.

[0037] Figure 8 This is a graph showing the relationship between the curvature radius R of the ridgeline and the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient of the surface shape of the test piece when the strength and thickness of the steel plate are changed. DETAILED DESCRIPTION

[0038] Before describing the outer panel of one embodiment of the present invention, Figure 1A as well as Figure 1B The mechanism of line deviation occurring in a stamped product during stamping of a forming characteristic line will be described. Figure 1A This is a diagram showing an overview of press forming when line deviation occurs. Figure 1B This is a diagram showing an overview of press forming when line deviation does not occur.

[0039] exist Figure 1A as well as Figure 1B In the embodiment, the die 21 is composed of an upper die 21 a and a lower die 21 b , and the blank 20 is sandwiched between the upper die 21 a and the lower die 21 b for press forming.

[0040] At the beginning of stamping, the blank 20 contacts the design characteristic line (not shown) on the die 21. The portion of the blank 20 that contacts the design characteristic line is called the initial contact portion 22. The die 21 is used for stamping, and as the characteristic line 23 (equivalent to the ridge line of the present invention) is formed, the initial contact portion 22 moves. In the case of line deviation, after the forming is completed, the initial contact portion 22 is located outside the R stop 24 of the characteristic line 23. This initial contact portion 22 is a portion where strain is introduced into the blank 20 at the beginning of stamping and the hardness becomes greater than that of other portions. Due to the hardness difference between the initial contact portion 22 and other portions, stress is concentrated near the initial contact portion 22, and the plate thickness near the initial contact portion 22 is locally reduced. In this portion, a depression is generated on the outer surface of the outer panel after stamping. This depression is a line deviation. If the initial contact portion 22 is located in a smooth area outside the R stop 24, the line deviation may sometimes be visually observed, and as a result, the aesthetics of the surface of the outer panel may sometimes be impaired. The outer surface refers to a surface that can be visually observed during normal use. For example, in an outer panel of a mobile object such as an automobile, the surface on the outer side of the vehicle is called the outer surface.

[0041] On the other hand, Figure 1B As shown, when the initial contact portion 22 between the blank 20 and the die 21 is located inside the R end 24 of the character line 23 at the completion of the stamping process, the character line 23 is curved, so the line deviation is not visually observed. As a result, the outer panel has an aesthetically pleasing appearance.

[0042] If the initial contact portion 22 is positioned inside the character line 23, the line deviation is not visually noticeable. However, the present inventors have studied how to prevent the line deviation from being visually noticeable even if the initial contact portion 22 is positioned outside the character line 23. As a result, they found that by reducing the plate thickness to less than 0.6 mm, an outer panel with a character line and an aesthetically pleasing appearance can be achieved.

[0043] Next, refer to Figure 2 as well as Figure 3 The outer panel of this embodiment will be described in detail. Figure 2 This is a side view of an outer panel according to one embodiment of the present invention. Figure 3 1 is a perspective view showing another example of an outer panel. In addition, in this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals and redundant descriptions are omitted.

[0044] The outer panel 100 of this embodiment has a ridgeline 101 and face portions 102 adjacent to both sides of the ridgeline on its outer surface. The panel thickness is less than 0.6 mm and the ultimate yield stress is 360 MPa or greater. The face portion 102 has adjacent regions Zn adjacent to the ridgeline 101, which serves as a characteristic line, on both sides of the ridgeline 101, and separation regions Zf adjacent to the adjacent regions Zn on the side opposite to the ridgeline 101. The evaluation of the surface properties of the adjacent regions Zn is consistent with the evaluation of the surface properties of the separation regions Zf. Figure 2 The outer panel 100 shown is the outer panel of the front door. Figure 3 The outer panel 100A shown is an outer panel of an engine hood.

[0045] As described later, the outer panel 100 is made of a material with an ultimate yield stress of 360 MPa or greater. The material used to construct the outer panel 100 is not particularly limited; for example, a steel plate with an ultimate yield stress of 360 MPa or greater can be used. As long as the steel plate has an ultimate yield stress of 360 MPa or greater, its chemical composition and metallurgical structure are not particularly limited. The outer panel 100 can be manufactured using galvanized steel sheet. Examples of galvanized steel sheet with an ultimate yield stress of 360 MPa or greater include JAC390W and JAC590Y, which comply with JFS A 3011:2020.

[0046] The thickness of the outer panel 100 is less than 0.6 mm. During stamping, compressive stress is generated on the inner side of the bend of the blank and tensile stress is generated on the outer side of the bend. However, when the thickness is thinner, the difference between the compressive stress on the inner side of the bend and the tensile stress on the outer side of the bend becomes smaller. In other words, the thinner the plate thickness, the more relaxed the stress concentration. Therefore, even if the hardness of the part in contact with the design characteristic line on the mold at the initial stage of stamping is greater than the hardness of other parts, if the plate thickness is less than 0.6 mm, the stress concentration on the initial contact part is also relaxed, and the generation of dents caused by the local reduction in plate thickness is suppressed. As a result, line deviation can be prevented. The plate thickness of the outer panel 100 is preferably less than 0.5 mm, and more preferably less than 0.4 mm.

[0047] The lower limit of the thickness of the outer panel 100 is not particularly limited, and the thickness can be set to 0.35 mm or more, for example. From the viewpoint of ensuring dent resistance, the thickness of the outer panel 100 is preferably 0.4 mm or more.

[0048] The thickness of the outer panel 100 is the thickness at a location visually observed as an external appearance, where the average radius of curvature is 500 mm or greater. The average radius of curvature is the average of the radii of curvature at the two principal curvatures that define Gaussian curvature. The thickness is measured on the surface 102, excluding any areas with significantly smaller radii of curvature. Examples of such areas include the peripheral edge of the outer panel 100 where the radius of curvature is reduced by hemming, areas with irregularities such as door handles, and ridges 101.

[0049] The ultimate yield stress of the outer panel 100 is 360 MPa or more. If the ultimate yield stress is 360 MPa or more, dent resistance can be ensured. In general outer panels, the higher the strength, the more likely it is to produce linear deviation. This is believed to be because, although strain is introduced into the blank by stamping, under the same degree of strain, the hardening amount of the high-strength material is further increased, and the hardness difference between the high-strength material and the non-deformed part becomes further increased. However, in the outer panel 100 of this embodiment, since the plate thickness is less than 0.6 mm, linear deviation can be suppressed as described above. 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.

[0050] The upper limit of the ultimate yield stress of the outer panel 100 is not particularly limited, and can be, for example, 1000 MPa or less. From the perspective of press forming properties, the ultimate yield stress of the outer panel 100 may be 700 MPa or less.

[0051] The ultimate yield stress of the outer panel 100 is measured by the following method: a test piece cut from a position visually observed as an appearance and having an average curvature radius of 500 mm or greater is subjected to a tensile test in accordance with JIS Z 2241:2011 to measure the ultimate yield stress.

[0052] The ridge line 101 is a portion that curves in one direction in the outer panel 100. The ridge line 101 curves so that the cross-sectional shape perpendicular to the extending direction is convex toward the vehicle outer side.

[0053] The radius of curvature R of the cross-sectional shape of the ridgeline 101 is not particularly limited; for example, the radius of curvature R can be set to be greater than 2.5 mm and less than 20 mm. Conventionally, if the radius of curvature R is less than 10 mm, linear deviation is likely to occur. However, in the outer panel 100 of this embodiment, linear deviation can be suppressed even if the radius of curvature R is less than 10 mm. On the other hand, if the ridgeline 101 bulges toward the vehicle exterior, a radius of curvature R of greater than 2.5 mm results in a relatively gently curved cross-sectional shape of the ridgeline 101, thereby minimizing damage to objects contacting the ridgeline 101 from the vehicle exterior. Therefore, if the ridgeline 101 bulges toward the vehicle exterior, the radius of curvature R is preferably greater than 2.5 mm.

[0054] The curvature radius R refers to the minimum curvature radius of the ridge 101 in a cross section perpendicular to the extending direction of the ridge 101. When the ridge 101 has different curvature radii along its extending direction, the minimum curvature radius in the cross section with the minimum curvature radius is defined as the curvature radius R. The curvature radius R is measured using a three-point gauge.

[0055] The shape of the ridge line 101 in a cross section perpendicular to the extending direction of the ridge line 101 is a shape having curvature, and can be, for example, a circular arc, an elliptical arc, or a parabola.

[0056] The outer panel 100 may include a plurality of ridge lines 101 . Figure 2 The outer panel 100, Figure 3 The outer panel 100A shows two ridge lines 101 .

[0057] The distance between at least two of the plurality of ridge lines 101 is not particularly limited and can be, for example, 20 mm or less or 10 mm or less. Because outer panel 100 suppresses line deviation, it is possible to create an outer panel with a design in which the distance between ridge lines 101 is reduced. In particular, even when the distance between two ridge lines 101 is 20 mm or less or 10 mm or less, an outer panel with clear ridge lines, as in a design pattern, can be obtained. Here, when the two ridge lines are not parallel, the distance between the two ridge lines 101 refers to their minimum value.

[0058] The face 102 is adjacent to both sides of the ridge line 101. For example, Figure 3 FIG. 1 shows a first surface portion 102A adjacent to ridgeline 101 and a second surface portion 102B adjacent to ridgeline 101 on the opposite side of first surface portion 102A. Surface portion 102 is a region flatter than ridgeline 101. Surface portion 102 is a planar surface or a curved surface having a larger radius of curvature than that of ridgeline 101. For example, surface portion 102 has a radius of curvature that is five times or greater than that of ridgeline 101.

[0059] The face 102 has an adjacent area Zn adjacent to the ridge line 101, and a separation area Zf adjacent to the adjacent area Zn on the opposite side of the ridge line 101. Line deviation is basically visually observed in the adjacent area Zn. The adjacent area Zn is, for example, a strip-shaped area with a length of 20 mm in the arrangement direction of the separation area Zf, and the separation area Zf is a strip-shaped area with a length of 20 mm in the arrangement direction of the adjacent area Zn. The adjacent area Zn and the separation area Zf are areas extending along the extension direction of the ridge line 101. Figure 3 , as adjacent regions Zn and separation regions Zf with respect to one ridge line 101 , adjacent region Zn1 and separation region Zf1 arranged on the first surface portion 102A, and adjacent region Zn2 ​​and separation region Zf2 arranged on the second surface portion 102B are shown.

[0060] In the face 102, the evaluation of the surface properties of the adjacent area Zn is consistent with the evaluation of the surface properties of the separating area Zf. As described above, line deviation is basically visually observed in the adjacent area Zn, but when a line deviation occurs at a large angle with the edge line 101, it is possible that the line deviation is visually observed in a posture that intersects the boundary line between the adjacent area Zn and the separating area Zf. Even in this case, the surface properties of the adjacent area Zn and the separating area Zf at a predetermined position in the longitudinal direction of the boundary line are different. Therefore, if the evaluation of the surface properties of the adjacent area Zn is consistent with the evaluation of the surface properties of the separating area Zf, it can be determined that the line deviation is suppressed. The evaluation of the surface properties is, for example, based on the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient of the shape of the outer surface in a cross section that intersects the edge line 101. Here, "intersects" means along a straight line that intersects the edge line 101 at an angle of 60 to 120 degrees.

[0061] exist Figure 4 、 Figure 5 2 is a graph showing an example of the measurement result of the second-order differential coefficient of the shape of the outer surface measured across the ridge line 101. Figure 4 This is a graph showing an example of the measurement results of the second-order differential coefficient of the shape of the outer surface where line deviation is visually observed. Figure 5 This is a graph showing an example of the measurement results of the second-order differential coefficient of the shape of the outer surface where no line deviation is visually observed. The horizontal axis is the X coordinate of the evaluation line, and the vertical axis is the second-order differential coefficient. The origin (zero) of the X coordinate corresponds to the position of the boundary between the adjacent area Zn and the separated area Zf. Figure 4 、 5 In the figure, the range of X coordinates from -20 to 0 mm corresponds to the adjacent area Zn, and the range of X coordinates from 0 to 20 mm corresponds to the separated area Zf. Figure 4As shown in FIG. 1 , in the outer surface where the line deviation is visually observed, the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient is large in the adjacent region Zn (range of -20 to 0 mm), and the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient is small in the separated region Zf (range of 0 to 20 mm). On the other hand, as Figure 5 As shown, in the outer surface where no line deviation is visually observed, the difference ΔP / B between the maximum value and the minimum value of the second-order differential coefficient is small in both the adjacent region Zn and the separated region Zf.

[0062] When the interval between adjacent ridges 101 is 40 mm, in the face 102 between adjacent ridges 101, the adjacent region Zn adjacent to one ridge 101 and the adjacent region Zn adjacent to the other ridge 101 are adjacent. In this case, the separation region Zf for one ridge 101 and the adjacent region Zn for the other ridge 101 largely overlap or coincide with each other. Alternatively, when the interval between adjacent ridges 101 is less than 40 mm, the face 102 between adjacent ridges 101 can be divided into two regions of equal width, each of which is defined as the adjacent region Zn and the separation region Zf.

[0063] In the outer panel 100, the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient of the outer surface shape in the adjacent region Zn, measured transversely to the ridgeline 101, is equal to or less than a predetermined threshold. Because the degree of line deviation required varies for each product, this threshold is determined for each product. Preferably, the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient in both the adjacent region Zn and the separated region Zf is equal to or less than the predetermined threshold.

[0064] In the outer panel 100 , more preferably, the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient of the outer surface shape in the adjacent region Zn and the separated region Zf measured transversely to the ridgeline 101 is 0.012 / mm or less.

[0065] As described above, line deviation can be understood as a localized reduction in thickness on the surface of the outer panel 100. However, according to the inventors' research, even if the height of the surface steps remains the same, sharp irregularities, i.e., significant changes in curvature, can sometimes be easily identified as poor appearance quality. Appearance quality defects, including line deviation, are evaluated based on the second-order differential coefficient representing the curvature of the surface shape. If the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient in the evaluation area is 0.012 / mm or less, line deviation is not visually observed in that evaluation area. Therefore, the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient in the evaluation area is preferably 0.012 / mm or less. The difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient is more preferably 0.010 / mm or less, and even more preferably 0.008 / mm or less. These are examples of evaluation reference values ​​and should be appropriately set depending on the quality level required of the outer panel's appearance performance.

[0066] The surface properties of the adjacent regions Zn and the separated regions Zf are evaluated based on whether an indicator representing the surface properties of each region is below an evaluation reference value. In this embodiment, the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient of the surface shape is used as an indicator representing the surface properties. The evaluation reference value is appropriately set according to the required quality level, as described above. In other words, in this embodiment, the surface properties of the adjacent regions Zn and the separated regions Zf are evaluated based on whether the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient of the surface shape of each region is below an evaluation reference value. Since line deviation occurs on either side of the edge line 101, if the evaluation of the adjacent regions Zn and the separated regions Zf on both sides of the edge line 101 is consistent, it can be determined that the appearance has been aesthetically pleasing, with the line deviation associated with the shaping of the edge line 101 suppressed.

[0067] It is preferred to use a non-contact laser shape measuring device to obtain shape data of the surface shape to be calculated for the second-order differential coefficient. In this embodiment, a laser microscope with high measurement accuracy is used to measure the surface shape of the outer panel 100. By using shape data with high measurement accuracy, the curvature of the surface shape can be appropriately reflected in the obtained second-order differential coefficient. In addition, when using a contact shape measuring device, the curvature of the surface shape may not be appropriately reflected in the second-order differential coefficient of the shape data due to the influence of mechanical measurement noise, etc. included in the shape data. In this case, in order to obtain data that appropriately reflects the curvature, it is also possible to filter the shape data to remove unnecessary components, or to calculate third-order differential coefficients or fourth-order differential coefficients of the shape data instead of the second-order differential coefficients.

[0068] Surface shape data is acquired by measuring the shape in a scanning direction transverse to the edge 101 of the outer panel 100. In this embodiment, shape measurement is performed at a single location in the longitudinal center of the edge 101. Second-order differential coefficients are calculated based on the acquired surface shape data. The difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficients in each range in the scanning direction corresponding to the adjacent region Zn and the separated region Zf is determined. The surface properties of each of the adjacent region Zn and the separated region Zf are evaluated based on whether the ΔP / B value in each range is below an evaluation reference value. In the outer panel 100 of this embodiment, these evaluations were all below the evaluation reference value, indicating consistent results.

[0069] Considering the potential for visually perceptible line deviations at the boundaries of adjacent regions Zn and separating regions Zf, it is preferable to perform shape measurements at multiple locations along the length of edge line 101, ensuring that the surface properties of adjacent regions Zn and separating regions Zf are consistently evaluated at all of these locations. These multiple locations should include at least the longitudinal center of edge line 101. For example, these locations may be dispersed throughout the longitudinal direction, including at the longitudinal ends, or concentrated in the longitudinal center. Because the appearance quality of the longitudinal center of a feature line significantly impacts the design impression, an exterior panel free of line deviation in this area is less likely to compromise its aesthetic appeal. Therefore, the absence of line deviation in the longitudinal center of edge line 101 is crucial for ensuring an aesthetically pleasing appearance.

[0070] In the manufacture of the outer panel of the present embodiment, a well-known stamping and forming device can be used. The technology applied to the outer panel of the present embodiment is the following technology: without introducing a complex mechanism for suppressing line deviation, line deviation is suppressed by stamping and forming a blank with a thinner plate thickness. Therefore, an outer panel with an aesthetically pleasing appearance can be produced by a stamping and forming device with a relatively simple structure. Of course, in order to further improve the appearance quality of the outer panel, the outer panel of the present embodiment can also be manufactured by a stamping and forming device with a complex mechanism. In the manufacture of the outer panel of the present embodiment, the plurality of ridges can also be formed so that the ridges intersect with each other. In addition, the plurality of ridges can also be formed so that the interval between at least two of the plurality of ridges (the shortest distance along the outer surface of the outer panel) is 20 mm. In addition, the plurality of ridges can also be formed so that two or more of the plurality of ridges intersect.

[0071] The present invention has been described above based on the preferred embodiments of the present invention, but the present invention is not limited thereto. The above is merely illustrative, and any method having substantially the same structure as the technical concept described in the scope of the patent claims of the present invention and having the same effect is included in the technical scope of the present invention.

[0072] For example, in the above embodiment, the case where the plurality of ridges 101 do not intersect is described, but the arrangement of the plurality of ridges 101 is not limited thereto. Figure 6 As shown, the ridge lines 101 may also intersect.

[0073] In addition, for example, Figure 2 、 Figure 3 as well as Figure 6 , two ridge lines 101 are shown, but the number of ridge lines 101 may be one or more than three. When three or more ridge lines 101 are provided, all ridge lines 101 may not intersect, or at least two ridge lines 101 among the plurality of ridge lines 101 may intersect.

[0074] For example, the thickness reduction can be used as an indicator of surface quality when evaluating surface properties. In this case, the surface properties of the adjacent region Zn are evaluated based on whether the thickness reduction in the adjacent region Zn is below the evaluation benchmark. Similarly, the surface properties of the adjacent region Zn are evaluated based on whether the thickness reduction in the separating region Zf is below the evaluation benchmark. If the evaluation results of the two are the same, it can be determined that the line deviation associated with ridgeline forming is suppressed. The evaluation benchmark can be determined based on the results of a sensory test related to visual observation of line deviation.

[0075] In addition, for example, Figure 2 as well as Figure 6 In the figure, an outer panel constituting a front door of a car is shown as an example of an outer panel. Figure 3 The outer panel of the hood is shown in the figure, but it is not limited to the front door and the hood. The outer panel of the present invention can also be applied to the rear door, the front fender, the rear fender, the roof or the tailgate.

[0076] The following describes an experimental example that led to the insight that became the beginning of the present invention. The insight is as follows: 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 generated during stamping becomes smaller, the occurrence of local plate thickness reduction is suppressed, and line deviation is suppressed.

[0077] Prepared are alloyed hot-dip galvanized steel sheets with a tensile strength of 270 MPa and a thickness of 0.7 mm, alloyed hot-dip galvanized steel sheets with a tensile strength of 590 MPa and a thickness of 0.4 mm, and alloyed hot-dip galvanized steel sheets with a tensile strength of 270 MPa and a thickness of 0.7 mm. Each test piece is a rectangle with a length of 500 mm in the rolling direction and a length of 60 mm in the width direction. Figure 7 As shown, the test piece is supported by two supports ( Figure 7The distance L between the centers of the two supports is 150 mm. The two ends of each test piece in the rolling direction are clamped by a chuck (not shown) and pulled in opposite directions to apply tension T1 to the test piece. With tension T1 applied to the test piece, a punch having an arc shape with a curvature radius R at the front end is pressed into the test piece with an indentation amount δ in such a way that the bending angle θ becomes 170°. Next, with tension T2 applied in the same direction as tension T1, the test piece is moved in one direction ( Figure 7 After moving in the direction indicated by s in the drawing, the punch is released. The magnitude of the tension T1 and T2 is set to s / YP=1.25. Here, s is the nominal stress, which is the value obtained by dividing the tension T1 or tension T2 by the width length of the test piece and the plate thickness. YP is the yield stress. Therefore, s / YP is a dimensionless number. The movement of the test piece simulates the flow of the material during stamping. The curvature radius R of the front end of the punch is 7mm, 10mm and 20mm. Figure 8 The results are shown in . Figure 8 This is a graph showing the relationship between the curvature radius R of the ridgeline and the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient of the surface shape of the test piece when the strength and thickness of the steel plate are changed. Figure 8 The "GA270, t=0.7" shown indicates the test results of alloyed hot-dip galvanized steel plates with a tensile strength of 270 MPa and a plate thickness of 0.7 mm, and the "GA590, t=0.4" indicates the test results of alloyed hot-dip galvanized steel plates with a tensile strength of 270 MPa and a plate thickness of 0.7 mm. The "GA270, t=0.4" indicates the test results of alloyed hot-dip galvanized steel plates with a tensile strength of 270 MPa and a plate thickness of 0.7 mm.

[0078] like Figure 8 As shown, it can be seen that the smaller the plate thickness, the smaller the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient. In addition, it can be seen that even when the tensile strength is 590 MPa, the difference ΔP / B between the maximum and minimum values ​​of the second-order differential coefficient can be reduced by reducing the plate thickness.

[0079] Explanation of symbols

[0080] 100, 100A, 100B: outer panels; 101: ridgeline; 102, 102A, 102B: face portions; Zn (Zn1, Zn2): adjacent regions; Zf (Zf1, Zf2): separation regions.

Claims

1. An outer panel having a ridgeline and surface portions adjacent to both sides of the ridgeline on an outer surface, wherein: The plate thickness is less than 0.6mm, and the ultimate yield stress is more than 360MPa. The face portion includes adjacent regions adjacent to the ridgeline on both sides of the ridgeline, and a separation region adjacent to the adjacent regions on the side opposite to the ridgeline. The evaluation of the surface properties of the adjacent region is consistent with the evaluation of the surface properties of the separated region.

2. The outer panel according to claim 1, wherein: The adjacent region is a strip-shaped region with a length of 20 mm in the arrangement direction of the separated region. The separation region is a strip-shaped region having a length of 20 mm in the arrangement direction of the adjacent regions.

3. The outer panel according to claim 1 or 2, wherein: The evaluation is based on the difference between the maximum value and the minimum value of the second-order differential coefficient of the shape of the outer surface in the cross section crossing the ridge line.

4. The outer panel according to claim 1 or 2, wherein: The curvature radius 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: The ridge lines are provided in plurality, and the ridge lines do not intersect 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: The ridge lines are provided in plurality, and two or more of the ridge lines intersect with each other.

8. The outer panel according to claim 1 or 2, wherein: The outer panels are made of steel.

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

10. The outer panel according to claim 3, wherein: The difference (ΔP / B) between the maximum value and the minimum value of the second-order differential coefficient of the shape of the outer surface in the adjacent region and the separated region measured across the ridgeline is 0.012 / mm or less.

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

12. An outer panel having a ridgeline and surface portions adjacent to both sides of the ridgeline on an outer surface, wherein: The plate thickness is less than 0.6mm, and the ultimate yield stress is more than 360MPa. The face portion includes adjacent regions adjacent to the ridgeline on both sides of the ridgeline, and a separation region adjacent to the adjacent regions on the side opposite to the ridgeline. A difference (ΔP / B) between a maximum value and a minimum value of a second-order differential coefficient of a shape of the outer surface in the adjacent region measured across the ridgeline is 0.012 / mm or less.

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