Methods for manufacturing parts using press molding.

Abstract

DEPCT68 The method of manufacturing press-formed parts according to this invention includes the shape-receiving step. Reference pressed part for shape acceptance; Reference pressed part shape acceptance step 5; Acceptance step. Wave-shaped blank forming part shape for pressed part acceptance. Waveform blank sheet, 9-step input quantity deviation of the input. The amount of deviation between the reference part shape 5 and the pressed part shape. Wave-shaped blank sheet forming process (9 steps), blank sheet pressing and shaping process. The deflected waveform represents the periodic load of a pressed blank part. The waveform deviates over a period of 13 steps, receiving the quantity of the second deviation. The input represents the amount of deviation between the reference part shape 5 of the pressed part and the part shape. The 13-step wave-shaped blank forming press identifies the necessary components. Countermeasures involving the identification of necessary components of countermeasures, procedures for providing submission forms. The output of the forming process includes extension forms 23 and 27 for actual tooling and forming procedures. The actual pressing of the forming operation using the actual tools provided. Filing formats 23 and 27;

Description

Manufacturing method for press-molded products

[0001] The present invention relates to a method for manufacturing a press-formed product that reduces the influence of shape variations of a blank obtained by press-forming a press-formed product using a blank taken from a metal plate having shape variations.

[0002] While stricter automobile crash safety standards are improving the crash safety of automobile bodies, recent carbon dioxide emission regulations are also urging vehicle weight reduction to improve fuel efficiency. In order to achieve both crash safety performance and vehicle weight reduction, metal plates with even higher strength than before are being used in vehicle bodies.

[0003] Conventionally, actual metal plates from which blanks for press-formed products are cut are not completely flat but have a corrugated shape (shape variation). Therefore, actual blanks cut from metal plates are also not necessarily flat and may have shape variation.

[0004] If a metal plate having such shape variations is used as a blank and press-formed into a vehicle body part, there is a risk that the shape variations will affect the press-formed product obtained after press-forming, causing it to deviate from the target dimensional accuracy.

[0005] As a technique for sorting out press-molded products that deviate from a target dimensional accuracy after press molding, for example, Patent Documents 1 and 2 are disclosed. In addition, Patent Documents 3 and 4 disclose a technique for providing unevenness to the surface of a press molding die.

[0006] JP 62-047504 A JP 2019-002834 A JP 2020-127959 A JP 3-077728 A

[0007] The techniques disclosed in Patent Documents 1 and 2 compare the shapes of press-formed products after press forming to identify areas with poor dimensional accuracy. The techniques disclosed in Patent Documents 1 and 2 do not identify which areas of the press-formed product are susceptible to the shape variation of the blank before press forming, making it difficult to take measures.

[0008] Furthermore, blanks used in press forming are obtained by punching or shearing from metal sheets such as steel sheets. Therefore, when multiple blanks are obtained from a metal sheet with shape variations, the blanks will have different uneven areas depending on the extraction position, even if they are obtained from the same metal sheet. Therefore, to reduce the impact of blank shape variations, measures must be taken that take into account the differences in shape variations between individual blanks.

[0009] The technology disclosed in Patent Document 3 provides irregularities on the surface of a die to retain oil between the die and the blank during press forming, thereby suppressing friction between the die and the blank and facilitating forming. Furthermore, the technology disclosed in Patent Document 4 provides irregularities on the surface of a die to enable the production of metal sheets with high design quality. Therefore, the technologies disclosed in Patent Documents 3 and 4 do not reduce the effects of blank shape variations, which is the objective of the present invention.

[0010] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a method for manufacturing a press-formed product that reduces the influence of shape variation of a blank in a press-formed product that is press-formed using a blank taken from a metal plate having shape variation.

[0011] In order to solve the above-mentioned problems and achieve the object, (1) a manufacturing method of a press-formed product according to the present invention is a method for reducing the influence of shape variation of a blank in a press-formed product press-formed using a blank taken from a metal plate having shape variation, the method including: a reference press-formed product shape acquisition step of performing press-forming analysis when a flat blank model having a flat shape is press-formed with a predetermined die model, and acquiring the shape of the press-formed product after demolding as a reference press-formed product shape; a corrugated blank press-formed product shape acquisition step of generating a corrugated blank model having a waveform of a predetermined wavelength and a predetermined amplitude corresponding to the shape variation, and performing press-forming analysis when the generated corrugated blank model is press-formed with the predetermined die model, and acquiring the shape of the press-formed product after demolding as a corrugated blank press-formed product shape; a first deviation amount acquisition step of comparing the reference press-formed product shape with the corrugated blank press-formed product shape and determining a portion where the two shapes deviate and the amount of deviation; and a first deviation amount acquisition step of generating a period-shifted corrugated blank model having a waveform that has the same amplitude and wavelength as the waveform in the corrugated blank model but a waveform that is shifted in period. Alternatively, a plurality of types of period-deviation wave-shaped blank press-formed product shapes are generated, and the generated period-deviation wave-shaped blank model is used to perform press forming analysis when press-forming is performed with the predetermined die model, and the press-formed product shape after demolding is acquired as a period-deviation wave-shaped blank press-formed product shape; a second deviation amount acquisition step is used to compare the reference press-formed product shape with one or more types of period-deviation wave-shaped blank press-formed product shapes, and determine the portions where the two shapes deviate and the amount of deviation; and a second deviation amount acquisition step is used to acquire a portion where the reference press-formed product shape and one or more types of period-deviation wave-shaped blank press-formed product shapes deviate from each other and the amount of deviation. The method is characterized by comprising: a step of identifying areas requiring countermeasures, which identifies areas of the press-molded product corresponding to areas where a deviation amount has occurred and areas where a deviation amount exceeding a threshold has occurred in the second deviation amount acquisition step, as areas requiring countermeasures; a convex pattern imparting step of imparting a convex pattern to the areas requiring countermeasures or to the areas that mold the areas requiring countermeasures and their surroundings in the upper and lower dies of the actual die that molds the press-molded product; and an actual press molding step of press-molding the blank using the upper and lower dies to which the convex pattern has been imparted.

[0012] (2) The manufacturing method of a press-formed product according to the present invention is characterized in that, in the invention described in (1) above, the first deviation amount acquisition step acquires as the deviation amount the difference between the springback amount of a specified portion in the reference press-formed product shape and the springback amount of the same portion of the reference press-formed product shape in the corrugated blank press-formed product shape, and the second deviation amount acquisition step acquires as the deviation amount the difference between the springback amount of a specified portion in the reference press-formed product shape and the springback amount of the same portion of the reference press-formed product shape in the periodic offset corrugated blank press-formed product shape.

[0013] (3) The method for manufacturing a press-molded product according to the present invention is the invention described in (1) or (2) above, wherein the convex pattern is composed of a plurality of convex portions formed at predetermined intervals on a flat or curved surface, and the vertical and horizontal lengths A of the convex portions are set to be 3 mm or more and 50 mm or less, and the distance between adjacent convex portions is set to be 1.2 A or more and 2.0 A or less, the convex pattern imparting step imparts the convex pattern to the upper mold and the lower mold so that the convex portions of the upper mold face the flat or curved surface of the lower mold, and the convex portions of the lower mold face the flat or curved surface of the upper mold, and the actual press-molding step presses the blank so that the distance between the lower surfaces of the convex portions of the upper mold and the upper surfaces of the convex portions of the lower mold at the bottom dead center of molding is 0.1 t or more and 0.5 t or less when molding the blank having a plate thickness t (mm).

[0014] The method for manufacturing a press-formed product according to the present invention takes into consideration differences in shape variation among individual blanks, identifies areas in the press-formed product that are significantly affected by shape variation of the blank, and takes measures to address those areas, thereby reducing the impact of shape variation of the blank. As a result, the method for manufacturing a press-formed product according to the present invention makes it possible to manufacture press-formed products with good dimensional accuracy, and can produce press-formed products with good dimensional accuracy with a high yield, even when using blanks taken from metal sheets with shape variation.

[0015] FIG. 1 is an explanatory diagram of each step of a method for manufacturing a press-formed product according to an embodiment. FIG. 2 is an external view of a part that is the subject of the embodiment. FIG. 3 is an explanatory diagram of a flat blank model. FIG. 4 is a diagram showing a reference press-formed product shape analyzed by press forming using the flat blank model of FIG. 3 and the amount of change from the bottom dead center at each location of the shape. FIG. 5 is an explanatory diagram of a corrugated blank model. FIG. 6 is a diagram showing a corrugated blank press-formed product shape analyzed by press forming using the corrugated blank model of FIG. 5 and the amount of change from the bottom dead center at each location of the shape. FIG. 7 is a diagram showing a first deviation amount when comparing the reference press-formed product shape of FIG. 4 with the corrugated blank press-formed product shape of FIG. 6. FIG. 8 is an explanatory diagram of a period-shifted corrugated blank model having a wave shape with the same amplitude and wavelength as the wave shape in the corrugated blank model of FIG. 5 but with a wave period shifted by a quarter wavelength. FIG. 9 is a diagram showing a period-shifted corrugated blank press-formed product shape analyzed by press forming using the period-shifted corrugated blank model of FIG. 8 and the amount of change from the bottom dead center at each location of the shape. FIG. 10 is a diagram showing the second deviation amount when comparing the reference press-formed product shape of FIG. 4 with the period-shifted corrugated blank press-formed product shape of FIG. 9 . FIG. 11 is a diagram showing the ranges of the first deviation amount and the second deviation amount shown in FIGS. 7 and 10 in correspondence with the target shape. FIG. 12 is an explanatory diagram of a convex pattern imparted to a die. FIG. 13 is a diagram showing a reference press-formed product shape analyzed by press-forming using a die model to which a convex pattern is imparted, and the amount of deviation from the bottom dead center at each portion of the shape. FIG. 14 is a diagram showing a corrugated blank press-formed product shape analyzed by press-forming using a die model to which a convex pattern is imparted, and the amount of deviation from the bottom dead center at each portion of the shape. FIG. 15 is a diagram showing the first deviation amount when comparing the reference press-formed product shape of FIG. 13 with the corrugated blank press-formed product shape of FIG. 14 . Fig. 16 is a diagram showing the shape of a blank press-formed product with a periodic deviation wave shape obtained by press-forming analysis using a die model with a convex pattern, and the amount of deviation from the bottom dead center of forming at each portion of the shape. Fig. 17 is a diagram showing the second deviation amount when comparing the reference press-formed product shape of Fig. 13 with the blank press-formed product shape of Fig. 16.FIG. 18 is a diagram showing the ranges of the first deviation amount and the second deviation amount shown in FIGS. 15 and 17 in correspondence with the target shape. FIG. 19 is an explanatory diagram of a period-shifted corrugated blank model having a corrugated shape with the same amplitude and wavelength as the corrugated blank model of FIG. 5 but with a period shifted by 1 / 2 wavelength. FIG. 20 is a diagram showing the shape of a period-shifted corrugated blank press-formed product analyzed by press forming using the period-shifted corrugated blank model of FIG. 19 and the amount of deviation from the bottom dead center at each portion of the shape. FIG. 21 is a diagram showing the second deviation amount when comparing the reference press-formed product shape of FIG. 4 with the period-shifted corrugated blank press-formed product shape of FIG. 20. FIG. 22 is a diagram showing the ranges of the first deviation amount and the second deviation amount shown in FIGS. 7 and 21 in correspondence with the target shape. FIG. 23 is a diagram showing the shape of a period-shifted corrugated blank press-formed product analyzed by press forming using a die model with a convex pattern and the amount of deviation from the bottom dead center at each portion of the shape. Fig. 24 is a diagram showing the second deviation amount when comparing the reference press-formed product shape of Fig. 13 with the period-shifted wave-shaped blank press-formed product shape of Fig. 23. Fig. 25 is a diagram showing the ranges of the first deviation amount and the second deviation amount shown in Fig. 15 and Fig. 24 in correspondence with the target shape.

[0016] Hereinafter, an embodiment of the method for manufacturing a press-formed product according to the present invention will be described, but the present invention is not limited to the embodiment.

[0017] The method for manufacturing a press-formed product according to the embodiment is a method for reducing the influence of blank shape variations on a press-formed product when a blank taken from a metal plate having shape variations (unevenness) is used for press forming, such as form forming or draw forming. Specifically, as shown in FIG. 1 , the method for manufacturing a press-formed product according to the embodiment includes a reference press-formed product shape acquisition step S1 to an actual press forming step S15. In this embodiment, each component will be described in detail below using an example in which the press-formed product 1 shown in FIG. 2 is press-formed as a target shape. Note that, in this embodiment, a blank made of a 1.5 GPa-class steel plate with a plate thickness of 1.2 mm and a corresponding blank model are used, but the present invention is not limited thereto.

[0018] <Reference press-formed product shape acquisition step> The reference press-formed product shape acquisition step S1 is a step in which a press forming analysis is performed with a predetermined die model using a flat blank model 3 as shown in Fig. 3, and the shape of the press-formed product after demolding is acquired as the reference press-formed product shape. Note that the "press forming analysis" in this description includes an analysis for acquiring the shape at the bottom dead center of forming and an analysis for acquiring the shape after demolding, i.e., after springback.

[0019] The flat blank model 3 is a blank model that has been conventionally used in general press forming analysis, and has a flat shape without any irregularities.

[0020] Press forming analysis is usually performed using CAE analysis such as the finite element method (FEM). Press forming includes form forming and draw forming, but in this embodiment, form forming will be described as an example.

[0021] FIG. 4 is a diagram showing the reference press-formed product shape 5 after demolding based on press molding analysis. In FIG. 4, the amount of change from the bottom dead center of the press is indicated by numerical values ​​and color shading. The amount of change is the value obtained by subtracting the height of the corresponding portion of the shape at the bottom dead center from the height of each portion of the press-formed product shape after demolding and springback after press molding, in the press-forming direction. This corresponds to the amount of springback in the press-forming direction. When the height difference (amount of change) is + (plus), the shape becomes more convex than the bottom dead center shape. When the height difference (amount of change) is - (minus), the shape becomes more concave than the bottom dead center shape. In FIG. 4, the color of the portion that becomes more concave than the bottom dead center shape is lighter, and the color of the portion that becomes more convex is darker. The numbers shown in FIG. 4 indicate that + indicates the amount of change in the convex direction (toward the page) and - indicates the amount of change in the concave direction (toward the page), and are in mm.

[0022] In this example, as shown in FIG. 4 , the change in the left end (region A) of the reference press-formed product shape 5 was 1.06 mm. The left end (region B) of the top plate portion of the reference press-formed product shape 5 was 0.63 mm. The longitudinal center (region C) of the reference press-formed product shape 5 was 6.02 mm. The right end (region D) of the lower flange portion of the reference press-formed product shape 5 was 1.10 mm. The right end (region E) of the reference press-formed product shape 5 was −2.61 mm.

[0023] <Step for acquiring the shape of a wavy blank press-formed product> Step S3 for acquiring the shape of a wavy blank press-formed product is a step in which the same press forming analysis as step S1 for acquiring the shape of a reference press-formed product is performed using a blank model corresponding to the shape variation of the metal plate, and the shape of the press-formed product after demolding is acquired.

[0024] In the corrugated blank press-formed product shape acquisition step S3, a corrugated blank model 7 having a shape corresponding to the shape variation of the metal plate is first generated. Fig. 5(a) is a diagram showing an example of the corrugated blank model 7, and the specific shape will be described below.

[0025] The corrugated blank model 7 shown in FIG. 5(a) is a blank model having a corrugated shape with a predetermined wavelength and a predetermined amplitude. The shading in FIG. 5(a) represents the concave and convex shapes, with the darker areas being convex toward the front of the page and the lighter areas being concave toward the back of the page. FIG. 5(b) shows FIG. 5(a) as viewed from the direction of the white arrow, and FIG. 5(c) is a partially enlarged view of FIG. 5(a). The example shown in FIG. 5 has a plate thickness of 1.2 mm, a waveform amplitude of 5.0 mm (±2.5 mm), and a wavelength (see FIG. 5(d)) of 320 mm. The start and end positions of the corrugated shape set in the blank do not need to be at the edges of the metal plate. FIG. 5(e) is a diagram emphasizing the corrugated shape of FIG. 5(a).

[0026] The corrugated blank model 7 may be generated based on the measurement results obtained by measuring the shape of an actual blank sampled from a predetermined position on a metal plate having a shape variation. For example, the corrugated blank model 7 may be generated by measuring the shape of the actual blank using a three-dimensional shape measuring device such as a laser distance meter and using a representative wavelength and amplitude in the measurement results.

[0027] Next, in the corrugated blank press-formed product shape acquisition step S3, press forming analysis is performed using the corrugated blank model 7 when press-forming is performed using the same predetermined die model as in the reference press-formed product shape acquisition step S1. The press-formed product shape after demolding is then acquired as the corrugated blank press-formed product shape 9. FIG. 6 is a diagram showing the corrugated blank press-formed product shape 9 obtained by press forming analysis. The colors and values ​​shown in FIG. 6 are the same as those in FIG. 4. In this example, as shown in FIG. 6, the change in the left end (region A) of the corrugated blank press-formed product shape 9 was 1.37 mm. The left end (region B) of the top plate portion of the corrugated blank press-formed product shape 9 was 0.72 mm. The longitudinal center (region C) of the corrugated blank press-formed product shape 9 was 6.02 mm. The right end (region D) of the lower flange portion of the corrugated blank press-formed product shape 9 was 0.96 mm. The right end (region E) of the corrugated blank press-formed product shape 9 was -2.11 mm.

[0028] <First deviation amount acquisition step> The first deviation amount acquisition step S5 is a step of comparing the reference press-formed product shape 5 (Figure 4) with the corrugated blank press-formed product shape 9 (Figure 6) to determine the areas where the two shapes deviate and the amount of deviation (first deviation amount).

[0029] In this embodiment, the press-formed product shape at the bottom dead center of the press is used as the reference shape, and the change (springback amount) in each portion of the press-formed product shape after demolding from the reference shape is calculated. The difference in the change amounts of the two press-formed product shapes is calculated as the deviation amount. That is, the first deviation amount calculated in the first deviation amount acquisition step S5 is the value obtained by subtracting the change amount ( FIG. 4 ) in the reference press-formed product shape 5 using a flat blank model from the change amount ( FIG. 6 ) in the corrugated blank press-formed product shape 9 using a blank model with shape variations. Therefore, when the first deviation amount is + (plus), the corresponding portion of the corrugated blank press-formed product shape 9 has a convex shape compared to the reference press-formed product shape 5. On the other hand, when the first deviation amount is − (minus), the corresponding portion of the corrugated blank press-formed product shape 9 has a concave shape compared to the reference press-formed product shape 5.

[0030] FIG. 7 is a diagram showing the first deviation amount determined as described above. As shown in FIG. 7, the first deviation amount between the corrugated blank press-formed product shape 9 and the reference press-formed product shape 5 was 0.31 mm at the left end (region A). The first deviation amount was 0.09 mm at the left end (region B) of the top plate portion. The first deviation amount was 0.00 mm at the longitudinal center (region C). The first deviation amount was −0.14 mm at the right end (region D) of the lower flange portion. The first deviation amount was 0.50 mm at the right end (region E).

[0031] <Step for acquiring the shape of a period-shifted wave-shaped blank press-molded product> Step S7 for acquiring the shape of a period-shifted wave-shaped blank press-molded product is a step for performing the same press molding analysis as step S1 for acquiring the shape of a reference press-molded product using a wave-shaped blank model having a shape different from that of the wave-shaped blank model 7, and acquiring the shape of the press-molded product after demolding.

[0032] In the period-deviated corrugated blank press-formed product shape acquisition step S7, first, a period-deviated corrugated blank model 11 is generated, which has a corrugated shape with the same wavelength and amplitude as the corrugated shape in the corrugated blank model 7 but with a shifted period. Fig. 8 is a diagram showing an example of the period-deviated corrugated blank model 11, and the specific shape will be described below.

[0033] The example shown in Figure 8(a) is a blank model having a periodic waveform with a predetermined wavelength and a predetermined amplitude, and the shading in Figure 8(a) represents the waveform. Figure 8(b) shows the state when Figure 8(a) is viewed from the direction of the white arrow, and Figure 8(c) is a partially enlarged view of Figure 8(a). The example shown in Figure 8 has a plate thickness of 1.2 mm, and the amplitude and wavelength of the waveform are the same as those of the waveform-shaped blank model 7 in Figure 5, but the waveform period is shifted to the right of the paper by 1 / 4 wavelength compared to the waveform-shaped blank model 7 (see Figures 8(d) and 8(e)).

[0034] Next, in the period-distortion corrugated blank press-formed product shape acquisition step S7, press forming analysis is performed using the period-distortion corrugated blank model 11 and the same predetermined die model as in the reference press-formed product shape acquisition step S1. The press-formed product shape after demolding is then acquired as the period-distortion corrugated blank press-formed product shape 13. FIG. 9 is a diagram illustrating the period-distortion corrugated blank press-formed product shape 13. The colors and values ​​shown in FIG. 9 are the same as those in FIGS. 4 and 6 . In this example, as shown in FIG. 9 , the change in the left end (region A) of the period-distortion corrugated blank press-formed product shape 13 was 1.64 mm. The change in the left end (region B) of the top plate portion of the period-distortion corrugated blank press-formed product shape 13 was 0.83 mm. The change in the longitudinal center (region C) of the period-distortion corrugated blank press-formed product shape 13 was 6.13 mm. The change in the right end (region D) of the lower flange portion of the period-distortion corrugated blank press-formed product shape 13 was 1.41 mm. The change in the right end portion (area E) of the period-shifted wave-shaped blank press-formed product shape 13 was −2.96 mm.

[0035] The second deviation amount acquisition step S9 is a step of comparing the reference press-formed product shape 5 with the periodically-shifted wave-shaped blank press-formed product shape 13 to determine the deviation portions and deviation amounts (second deviation amounts) between the two shapes. The method of determining the second deviation amount is the same as the method described in the first deviation amount acquisition step S5, and therefore will not be described here.

[0036] FIG. 10 is a diagram showing the second deviation amount when comparing the reference press-formed product shape 5 ( FIG. 4 ) with the periodically offset corrugated blank press-formed product shape 13 ( FIG. 9 ). As shown in FIG. 10 , the second deviation amount between the periodically offset corrugated blank press-formed product shape 13 and the reference press-formed product shape 5 was 0.58 mm at the left end (region A). The second deviation amount was 0.20 mm at the left end (region B) of the top plate portion. The second deviation amount was 0.11 mm at the longitudinal center (region C). The second deviation amount was 0.31 mm at the right end (region D) of the lower flange portion. The second deviation amount was −0.35 mm at the right end (region E).

[0037] <Step for identifying areas requiring countermeasures> Step S11 for identifying areas requiring countermeasures is a step for identifying areas of the press-molded product 1 corresponding to areas where a first deviation amount exceeding a threshold value occurred in step S5 for acquiring first deviation amount and areas where a second deviation amount exceeding a threshold value occurred in step S9 for acquiring second deviation amount as areas requiring countermeasures.

[0038] For example, when multiple press-formed products are stacked and joined to assemble members of a vehicle body, if there is a large deviation in the shapes of the press-formed products (particularly in flange portions, etc.), it becomes difficult to join the press-formed products together, and measures may be required. Therefore, in this embodiment, parts that are expected to be significantly affected by shape variations in the blank (large deviations) are identified as parts requiring measures, and measures to reduce the effects can be taken.

[0039] 11 is a diagram showing both the first deviation amount (see FIG. 7 ) obtained in the first deviation amount obtaining step S5 and the second deviation amount (see FIG. 10 ) obtained in the second deviation amount obtaining step S9, in correspondence with the target shape of the press-formed product 1. As shown in FIG. 11 , the deviation amount was 0.31 mm to 0.58 mm at portion A. The deviation amount was 0.09 mm to 0.20 mm at portion B. The deviation amount was 0.00 mm to 0.11 mm at portion C. The deviation amount was −0.14 mm to 0.31 mm at portion D. The deviation amount was −0.35 mm to 0.50 mm at portion E.

[0040] For example, if the threshold value in step S11 for identifying a portion requiring countermeasure is set to ±0.15 mm, the portions where a deviation amount exceeding the threshold value occurs are portion A, portion B, portion D, and portion E. Therefore, in step S11 for identifying a portion requiring countermeasure, these portions are identified as portions requiring countermeasure.

[0041] In this embodiment, as a measure to reduce the influence of shape variations of the blank, a convex pattern is imparted to a portion of the actual die that forms the above-mentioned portion requiring countermeasures, and press forming is performed using the actual die. The convex pattern is imparted to the corresponding portion of each of the upper die and the lower die that constitute the actual die. Fig. 12 is a diagram showing an example of a convex pattern imparted to the actual die. The shape of this convex pattern will be described.

[0042] Fig. 12(a) is a side view of the protruding pattern 23 of the upper mold 21 and the protruding pattern 27 of the lower mold 25 at the bottom dead center of molding. Fig. 12(b) is a view taken along the arrows CC in Fig. 12(a). In Fig. 12(b), the position of the opposing protruding pattern 27 of the lower mold 25 is indicated by a dashed line. As shown in Figs. 12(a) and 12(b), the protruding patterns 23, 27 of this embodiment are composed of a plurality of protruding portions 23a, 27a (protruding portion groups) formed at predetermined intervals on the flat or curved surface of the surface of the upper mold 21 or the lower mold 25.

[0043] The shape of the tip surface of the convex portions 23a, 27a is a square with a side length of A (mm). Such convex portions 23a, 27a are arranged vertically and horizontally at a predetermined distance B (mm) to form regular convex patterns 23, 27. By providing convex patterns 23, 27 as shown in Figure 12 to the portions of the upper mold 21 and the lower mold 25 that will form the areas requiring countermeasures, the convex portions 23a, 27a can be press-formed while suppressing shape variations in the areas requiring countermeasures, thereby reducing the effects of shape variations in the blank.

[0044] The size (length and width) A of the tip surface of the protrusions 23a, 27a is preferably 3 mm or more and 50 mm or less. If the size A of the tip surface of the protrusions 23a, 27a is less than 3 mm, shape variations (wave shapes) of the blank may remain in the press-formed product after press forming, reducing the effectiveness. Also, if the size A of the tip surface of the protrusions 23a, 27a is more than 50 mm, the size will protrude from the top plate portion, flange portion, etc. of the mold, and the wide surface of the tip of the protrusion will press the blank, resulting in a molding similar to that without the protrusions, which is ineffective.

[0045] Furthermore, the distance B between adjacent convex portions is preferably 1.2 A or more and 2.0 A or less relative to the size A of the tip surface of the convex portions 23 a, 27 a. If the distance B (mm) between adjacent convex portions is less than 1.2 A or more than 2.0 A, shape variations (wave shapes) of the blank may remain in the press-formed product after press-forming, which is not preferable.

[0046] 12 are merely examples and do not limit the form of the protruding pattern of the present invention. For example, the shape of the tip surface of the protrusions may be rectangular or circular.

[0047] 12(a) and 12(b), the convex patterns 23 imparted to the upper mold 21 and the convex patterns 27 imparted to the lower mold 25 are preferably arranged so that their convex portions do not face each other. That is, when the convex patterns 23, 27 are imparted to the upper mold 21 and the lower mold 25, the convex patterns 23, 27 are preferably arranged so that the convex portions 23a of the upper mold 21 face the flat surface 25a (or curved surface) of the lower mold 25 and the convex portions 27a of the lower mold 25 face the flat surface 21a (or curved surface) of the upper mold 21.

[0048] Furthermore, when forming a blank with a thickness t (mm), the distance d between the lower surface of the convex portion 23a of the upper die 21 and the upper surface of the convex portion 27a of the lower die 25 at the bottom dead center of forming is preferably 0.1t or more and 0.5t or less. This allows new alternating minute strains to be imparted to the portions of the blank surface that correspond to the areas requiring countermeasures when a blank with shape variations is sandwiched between the upper die 21 and the lower die 25. As a result, these strains mitigate the shape variations in the areas requiring countermeasures, making it easier to suppress the effects of the shape variations in the blank.

[0049] If the distance d is less than 0.1t, the amount of strain will be too large, causing the shape of the tip end faces of the protrusions 23a and 27a to be clearly transferred to the surface of the press-formed product after press forming, which is not preferable. Also, if the distance d is more than 0.5t, the amount of strain will be insufficient, reducing the effect of mitigating shape variations in the blank, which is not preferable.

[0050] In this embodiment, the effects of press molding using the upper mold 21 and the lower mold 25 having the protruding patterns 23, 27 were confirmed by press molding analysis, and will be described below.

[0051] In the press molding analysis described below, the tip surface shape of the convex portions 23a, 27a was set to a 3 mm square (A = 3 mm), and the distance B between adjacent convex portions was set to 4.5 mm. The convex pattern 23 of the upper mold 21 and the convex pattern 27 of the lower mold 25 were provided so that the convex portions did not face each other. Specifically, as shown in FIG. 12(b), the positions of the convex portions 23a of the upper mold 21 and the convex portions 27a of the lower mold 25 were set so as to be offset from each other in the horizontal and vertical directions of the paper. Note that the positional relationship between the convex portions of the upper mold and the convex portions of the lower mold is not limited to this, and they may be offset only in the horizontal or vertical direction of the paper.

[0052] Furthermore, the distance d between the lower surface of the protrusion 23a of the upper die 21 and the upper surface of the protrusion 27a of the lower die 25 at the bottom dead center of forming was set to 0.36 mm. As described above, the thickness t of the blank in this embodiment is 1.2 mm, so the relationship between the distance d and the thickness t of the blank is d = 0.3t.

[0053] In this embodiment, the above-mentioned convex patterns 23, 27 were applied to portions of the predetermined die model used in the press molding analysis described above that correspond to the portions requiring countermeasures. Then, in this embodiment, the die model (hereinafter referred to as the "die model with convex patterns") was used to perform analyses similar to those performed in step S1 to step S9 to obtain the reference press-formed product shape. The amounts of change and deviation in the following description were determined using the same methods as those shown in FIGS. 4 to 11.

[0054] Fig. 13 is a diagram showing a reference press-formed product shape 31 obtained by performing press-forming analysis on the flat blank model 3 (see Fig. 3) using the convex-pattern-imparted die model. Note that Fig. 13 shows a region (strain-imparted region 33) to which distortion is imparted by the convex patterns 23, 27 of the convex-pattern-imparted die model, shaded (the same applies to Figs. 14 to 18).

[0055] As shown in Fig. 13, when press forming analysis was performed using a convex pattern-imparted mold model, the amount of change in portion A of the reference press-formed product shape 31 was 1.29 mm. The amount of change in portion B of the reference press-formed product shape 31 was 0.07 mm. The amount of change in portion C of the reference press-formed product shape 31 was 6.50 mm. The amount of change in portion D of the reference press-formed product shape 31 was 2.10 mm. The amount of change in portion E of the reference press-formed product shape 31 was 1.80 mm.

[0056] FIG. 14 is a diagram showing a corrugated blank press-formed product shape 35 obtained by performing press-forming analysis on the corrugated blank model 7 (see FIG. 5) using a convex pattern-imparting mold model. As shown in FIG. 14, the change in portion A of the corrugated blank press-formed product shape 35 was 1.45 mm. The change in portion B of the corrugated blank press-formed product shape 35 was 0.12 mm. The change in portion C of the corrugated blank press-formed product shape 35 was 6.50 mm. The change in portion D of the corrugated blank press-formed product shape 35 was 2.03 mm. The change in portion E of the corrugated blank press-formed product shape 35 was 2.05 mm.

[0057] FIG. 15 is a diagram showing the first deviation amount determined by comparing the reference press-formed product shape 31 ( FIG. 13 ) with the corrugated blank press-formed product shape 35 ( FIG. 14 ). As shown in FIG. 15 , the first deviation amount between the reference press-formed product shape 31 and the corrugated blank press-formed product shape 35 when press-forming analysis was performed using a convex pattern-imparting mold model was 0.16 mm at region A. The first deviation amount was 0.05 mm at region B. The first deviation amount was 0.00 mm at region C. The first deviation amount was −0.07 mm at region D. The first deviation amount was 0.25 mm at region E.

[0058] FIG. 16 shows a periodic-deviated corrugated blank press-formed product shape 37 obtained by press-forming analysis of the periodic-deviated corrugated blank model 11 (see FIG. 8) using a convex-pattern-imparting mold model. As shown in FIG. 16, the change in portion A of the periodic-deviated corrugated blank press-formed product shape 37 was 1.58 mm. The change in portion B of the periodic-deviated corrugated blank press-formed product shape 37 was 0.17 mm. The change in portion C of the periodic-deviated corrugated blank press-formed product shape 37 was 6.60 mm. The change in portion D of the periodic-deviated corrugated blank press-formed product shape 37 was 2.26 mm. The change in portion E of the periodic-deviated corrugated blank press-formed product shape 37 was 1.63 mm.

[0059] FIG. 17 is a diagram showing the second deviation amount determined by comparing the reference press-formed product shape 31 ( FIG. 13 ) with the period-shifted corrugated blank press-formed product shape 37 ( FIG. 16 ). As shown in FIG. 17 , the second deviation amount between the reference press-formed product shape 31 and the period-shifted corrugated blank press-formed product shape 37 was 0.29 mm at portion A. The second deviation amount was 0.10 mm at portion B. The second deviation amount was 0.10 mm at portion C. The second deviation amount was 0.16 mm at portion D. The second deviation amount was −0.17 mm at portion E.

[0060] FIG. 18 is a diagram showing both the first deviation amount in FIG. 15 and the second deviation amount in FIG. 17 in relation to the target shape. As shown in FIG. 18, the first deviation amount and the second deviation amount were 0.16 mm to 0.29 mm at portion A. The first deviation amount and the second deviation amount were 0.05 mm to 0.10 mm at portion B. The first deviation amount and the second deviation amount were 0.00 mm to 0.10 mm at portion C. The first deviation amount and the second deviation amount were −0.07 mm to 0.16 mm at portion D. The first deviation amount and the second deviation amount were −0.17 mm to 0.25 mm at portion E. The deviation amounts in FIG. 18 are reduced compared to the deviation amounts before the countermeasures were implemented, as shown in FIG. 11. Therefore, it was confirmed that using a convex pattern-imparting mold model is effective in reducing the influence of blank shape variations.

[0061] <Convex Pattern Imparting Step> The convex pattern imparting step S13 is a step of imparting the convex patterns 23 and 27 described in FIG. 12 to the actual mold. The convex patterns 23 and 27 may be imparted to the surface of the actual mold by laser processing or etching. The convex patterns 23 and 27 are imparted to the countermeasure-requiring portions of the upper mold 21 and the lower mold 25 of the actual mold, or to the countermeasure-requiring portions and the portions that mold the periphery of the countermeasure-requiring portions. In this case, as described in FIG. 12, it is preferable that the convex portion 23a of the upper mold 21 faces the flat surface 25a or the curved surface of the lower mold 25, and the convex portion 27a of the lower mold 25 faces the flat surface 21a or the curved surface of the upper mold 21. Here, the convex patterns 23 and 27 similar to those of the convex pattern imparting mold model used in the press molding analysis described in FIGS. 13 to 18 were imparted to the actual mold.

[0062] <Actual Press-Forming Step> The actual press-forming step S15 is a step of press-forming an actual blank using the upper die 21 and the lower die 25 to which the convex patterns 23, 27 have been imparted in the convex pattern imparting step S13. As described above, in the actual press-forming step S15, it is preferable to perform press-forming so that the distance d between the lower surface of the convex portion 23 a of the upper die 21 and the upper surface of the convex portion 27 a of the lower die 25 at the bottom dead center of forming is 0.1 t or more and 0.5 t or less (t (mm) is the plate thickness of the blank).

[0063] When an actual blank having shape variations was press-formed using an actual die having the convex patterns 23, 27, the shape of the press-formed product after press forming was less affected by the shape variations of the blank, as in the analysis result of FIG. 18 , and good dimensional accuracy was obtained.

[0064] As described above, according to this embodiment, it is possible to identify areas of the blank that are significantly affected by shape variations and take appropriate measures, thereby making it possible to stably obtain press-formed products with good dimensional accuracy. Note that in this embodiment, multiple blank model patterns are generated assuming blanks with shape variations, and the deviation amount for each case is calculated to identify areas requiring measures, so that differences in shape variations that occur between individual actual blanks are taken into consideration.

[0065] Although only one type of period-deviation corrugated blank model was generated in the above example, multiple types of period-deviation corrugated blank models may be generated. In this case, the waveforms of the period-deviation corrugated blank models should be set to have different periods (the wavelength and amplitude should be common to the corrugated blank model and all period-deviation corrugated blank models). By increasing the number of blank model patterns that simulate blanks with shape variations, it is possible to more specifically consider the differences in shape variations that occur between individual actual blanks.

[0066] In the above description, the deviation amount between the two press-formed product shapes was calculated by the difference in the amount of change (springback amount) from the bottom dead center in the press-forming direction. However, this is not limited to this. For example, in the present invention, the deviation amount may be calculated by subtracting the height of each portion of one press-formed product shape after release (springback) from the height of each portion of the other press-formed product shape after release (springback) in the press-forming direction. However, in this case, a fixed point common to the two press-formed product shapes must be set, and the deviation amount may vary depending on how the fixed point is selected. In this regard, comparing the change amounts based on the shape at the bottom dead center, which is constant regardless of whether the blank shape changes, as in the present embodiment, is preferable because it allows the deviation amount to be calculated accurately and easily.

[0067] Furthermore, although the present embodiment has been described taking the case of foam molding as an example, draw molding may also be used.

[0068] In addition, by using upper and lower molds with a convex pattern, a concave-convex pattern may be formed on the press-molded product after press molding. In such a case, after the actual press molding step S15, a restriking process may be further provided in which the press-molded product with the concave-convex pattern formed is re-pressed to flatten the concave-convex pattern. By flattening the concave-convex pattern in the restriking process, strain is applied to the area where the concave-convex pattern is formed and its surrounding area, causing work hardening and further improving rigidity. This makes it possible to suppress the wave shape (shape fluctuation) remaining in the press-molded product, thereby improving dimensional accuracy.

[0069] In order to confirm the effects of the present invention, the method for manufacturing a press-molded product described with reference to FIG. 1 was carried out. In this example, the press-molded product 1 shown in FIG. 2 was used as the target shape, as in the embodiment. Furthermore, the molding for CAE analysis in this example was foam molding, as in the embodiment. The amount of change and the amount of deviation in this example were determined by the same method as in the embodiment.

[0070] First, in this example, the reference press-formed product shape acquisition step S1 was performed using a flat blank model 3 (see FIG. 3 ) as in the embodiment. When the flat blank model 3 was subjected to press forming analysis using a predetermined die model, the amount of change in the reference press-formed product shape 5 was as follows: That is, as described in FIG. 4 , the amount of change was 1.06 mm at portion A, 0.63 mm at portion B, 6.02 mm at portion C, 1.10 mm at portion D, and −2.61 mm at portion E.

[0071] In this example, the corrugated blank press-formed product shape acquisition step S3 was performed using the corrugated blank model 7 (see FIG. 5 ) as in the embodiment. When the corrugated blank model 7 was subjected to press-forming analysis using a predetermined die model, the amount of change in the corrugated blank press-formed product shape 9 was as follows: That is, as described in FIG. 6 , the amount of change was 1.37 mm at portion A, 0.72 mm at portion B, 6.02 mm at portion C, 0.96 mm at portion D, and −2.11 mm at portion E.

[0072] Furthermore, in this example, in the first deviation amount acquisition step S5, the reference press-formed product shape 5 ( FIG. 4 ) was compared with the corrugated blank press-formed product shape 9 ( FIG. 6 ) to determine the deviation amounts (first deviation amounts) between the two shapes. As described with reference to FIG. 7 , the first deviation amounts were 0.31 mm at portion A, 0.09 mm at portion B, 0.00 mm at portion C, −0.14 mm at portion D, and 0.50 mm at portion E.

[0073] Next, in this example, in the period-deviated corrugated blank press-formed product shape acquisition step S7, a corrugated blank model having a shape different from that of the corrugated blank model 7 was generated. Then, in this example, press forming analysis was performed using the same predetermined die model as above, and the shape of the press-formed product after demolding was acquired. As a corrugated blank model having a shape different from that of the corrugated blank model 7, the period-deviated corrugated blank model 11 described in FIG. 8 was used in the embodiment, but in this example, a period-deviated corrugated blank model 41 shown in FIG. 19 was used. The specific shape of the period-deviated corrugated blank model 41 is described below.

[0074] The example shown in Figure 19 is a blank model having a periodic waveform with a predetermined wavelength and a predetermined amplitude, and the shading in Figure 19(a) represents the concaves and convexes. Figure 19(b) shows the state when Figure 19(a) is viewed from the direction of the white arrow, and Figure 19(c) is a partially enlarged view of Figure 19(a). The example shown in Figure 19 has a plate thickness of 1.2 mm, and the amplitude and wavelength of the concaves and convexes are the same as those of the corrugated blank model 7 in Figure 5, but the period of the waveform is shifted to the right of the paper by 1 / 2 wavelength compared to that of the corrugated blank model 7 (see Figures 19(d) and 19(e)).

[0075] FIG. 20 shows a period-distorted corrugated blank press-formed product shape 43 obtained by performing press-forming analysis on the period-distorted corrugated blank model 41 of FIG. 19 using a predetermined die model. As shown in FIG. 20, when performing press-forming analysis using a predetermined die model, the change in portion A of the period-distorted corrugated blank press-formed product shape 43 was 0.85 mm. The change in portion B of the period-distorted corrugated blank press-formed product shape 43 was 0.88 mm. The change in portion C of the period-distorted corrugated blank press-formed product shape 43 was 5.95 mm. The change in portion D of the period-distorted corrugated blank press-formed product shape 43 was 0.86 mm. The change in portion E of the period-distorted corrugated blank press-formed product shape 43 was -2.64 mm.

[0076] Furthermore, in this example, in the second deviation amount acquisition step S9, the reference press-formed product shape 5 ( FIG. 4 ) was compared with the periodic-delayed wave-shaped blank press-formed product shape 43 ( FIG. 20 ) to determine the deviation amount (second deviation amount). As shown in FIG. 21 , the second deviation amounts between the periodic-delayed wave-shaped blank press-formed product shape 43 and the reference press-formed product shape 5 were −0.21 mm at portion A, 0.25 mm at portion B, −0.07 mm at portion C, −0.24 mm at portion D, and −0.03 mm at portion E.

[0077] 22 is a diagram showing both the first deviation amount ( FIG. 7 ) obtained in first deviation amount obtaining step S5 and the second deviation amount ( FIG. 21 ) obtained in second deviation amount obtaining step S9, in correspondence with the press-formed product 1 (target shape). As shown in FIG. 22 , the deviation amounts before the countermeasures were taken were −0.21 mm to 0.31 mm at portion A, 0.09 mm to 0.25 mm at portion B, −0.07 mm to 0.00 mm at portion C, −0.24 mm to −0.14 mm at portion D, and −0.03 mm to 0.50 mm at portion E.

[0078] Here, for example, if the threshold value in step S11 for identifying a portion requiring countermeasure is set to ±0.15 mm, the portions where a deviation amount exceeding the threshold value occurs are portion A, portion B, portion D, and portion E. Therefore, these portions are identified as portions requiring countermeasures.

[0079] In this example as well, as a measure to reduce the influence of the shape variation of the blank, the protruding patterns 23, 27 explained in Fig. 12 were applied to the surface of the actual die corresponding to the above-mentioned portion requiring the measure. In this example, the effect thereof was confirmed by press forming analysis, and will be explained below.

[0080] In the press forming analysis described below, the tip surface shape of the convex portions 23a and 27a was a 3 mm square (A = 3 mm), and the distance B between adjacent convex portions was 4.5 mm. The convex pattern 23 of the upper die 21 and the convex pattern 27 of the lower die 25 were provided so that the convex portions 23a and 27a did not face each other. Specifically, as shown in FIG. 12(b), the positions of the convex portions 23a of the upper die 21 and the convex portions 27a of the lower die 25 were set to be offset from each other in the horizontal and vertical directions of the drawing. The distance d between the lower surface of the convex portion 23a of the upper die 21 and the upper surface of the convex portion 27a of the lower die 25 at the bottom dead center of forming was 0.36 mm. The blank thickness t in this example was 1.2 mm, as in the embodiment, so the relationship between the distance d and the blank thickness t was d = 0.3t.

[0081] In this embodiment, the above-mentioned convex patterns 23, 27 were applied to areas corresponding to areas requiring countermeasures in a specified mold model, and an analysis similar to the reference press-molded product shape acquisition step S1 to the second deviation amount acquisition step S9 was performed using the mold model (mold model with convex patterns applied).

[0082] When the flat blank model 3 (see FIG. 3 ) was subjected to press forming analysis using the convex pattern-imparted mold model, the amount of change in the reference press-formed product shape 31 was 1.29 mm at portion A, as described in FIG. 13 . The amount of change in the reference press-formed product shape 31 was 0.07 mm at portion B. The amount of change in the reference press-formed product shape 31 was 6.50 mm at portion C. The amount of change in the reference press-formed product shape 31 was 2.10 mm at portion D. The amount of change in the reference press-formed product shape 31 was 1.80 mm at portion E.

[0083] When the corrugated blank model 7 (see FIG. 5) was subjected to press forming analysis using a convex pattern-imparting mold model, the change in the corrugated blank press-formed product shape 35 was 1.45 mm at region A, as described in FIG. 14 . The change in the corrugated blank press-formed product shape 35 was 0.12 mm at region B. The change in the corrugated blank press-formed product shape 35 was 6.50 mm at region C. The change in the corrugated blank press-formed product shape 35 was 2.03 mm at region D. The change in the corrugated blank press-formed product shape 35 was 2.05 mm at region E.

[0084] The first deviation amount obtained by comparing the reference press-formed product shape 31 ( FIG. 13 ) with the corrugated blank press-formed product shape 35 ( FIG. 14 ) was 0.16 mm at portion A, as described in FIG. 15 . The first deviation amount was 0.05 mm at portion B. The first deviation amount was 0.00 mm at portion C. The first deviation amount was −0.07 mm at portion D. The first deviation amount was 0.25 mm at portion E.

[0085] FIG. 23 shows a periodic-distortion-waveform blank press-formed product shape 51 obtained by performing press-forming analysis on the periodic-distortion-waveform blank model 41 (see FIG. 19 ) using a convex-pattern-imparting mold model. As shown in FIG. 23 , when a convex-pattern-imparting mold model was used, the change in region A of the periodic-distortion-waveform blank press-formed product shape 51 was 1.19 mm. The change in region B of the periodic-distortion-waveform blank press-formed product shape 51 was 0.20 mm. The change in region C of the periodic-distortion-waveform blank press-formed product shape 51 was 6.44 mm. The change in region D of the periodic-distortion-waveform blank press-formed product shape 51 was 1.98 mm. The change in region E of the periodic-distortion-waveform blank press-formed product shape 51 was 1.82 mm.

[0086] FIG. 24 is a diagram showing the second deviation amount determined by comparing the reference press-formed product shape 31 ( FIG. 13 ) with the periodic-shifted wave-shaped blank press-formed product shape 51 ( FIG. 23 ). As shown in FIG. 24 , the second deviation amount between the reference press-formed product shape 31 and the periodic-shifted wave-shaped blank press-formed product shape 51 when a convex-pattern-imparting mold model was used was −0.10 mm at region A. The second deviation amount was 0.13 mm at region B. The second deviation amount was −0.06 mm at region C. The second deviation amount was −0.12 mm at region D. The second deviation amount was 0.02 mm at region E.

[0087] FIG. 25 is a diagram showing both the first deviation amount in FIG. 15 and the second deviation amount in FIG. 24 in relation to the press-formed product 1 (target shape). As shown in FIG. 25, when a convex pattern-imparting die model was used, the deviation amount was −0.10 mm to 0.16 mm at portion A. The deviation amount was 0.05 mm to 0.13 mm at portion B. The deviation amount was −0.06 mm to 0.00 mm at portion C. The deviation amount was −0.12 mm to −0.07 mm at portion D. The deviation amount was 0.02 mm to 0.25 mm at portion E. The deviation amounts in FIG. 25 are significantly smaller than the deviation amounts before the countermeasures were taken, as shown in FIG. 22. Therefore, it was confirmed that imparting a convex pattern to a die corresponding to the portions requiring countermeasures has the effect of reducing the effects of shape variations in the blank.

[0088] Therefore, in the convex pattern imparting step S13, convex patterns 23, 27 similar to the convex pattern imparting die model were imparted to the surface of an actual die. Specifically, the convex patterns 23, 27 were imparted to the countermeasure-requiring portion in this example, or to a portion of the die that molds the countermeasure-requiring portion and its periphery. Then, in the actual press-forming step S15, an actual blank with shape variation was press-formed using the actual die to which the convex patterns 23, 27 were imparted. Note that the actual blank used was a 1.5 GPa-class steel plate with a plate thickness of 1.2 mm, which corresponds to the blank model described above.

[0089] In this example, the shape of the press-formed product press-formed in the actual press-forming step S15 was less affected by the shape variation of the blank, as in the analysis results of FIG. 25, and good dimensional accuracy was obtained.

[0090] The present invention can provide a method for manufacturing a press-formed product that reduces the influence of shape variations in the blank.

[0091] 1 Press-formed product (target shape) 3 Flat blank model 5 Reference press-formed product shape (using a predetermined die model) 7 Wave-formed blank model 9 Wave-formed blank press-formed product shape (using a predetermined die model) 11 Periodically offset wave-formed blank model 13 Periodically offset wave-formed blank press-formed product shape (using a predetermined die model) 21 Upper die 21a Plane 23 Convex pattern (upper die) 23a Convex portion 25 Lower die 25a Plane 27 Convex pattern (lower die) 27a Convex portion 31 Reference press-formed product shape (using a convex pattern-imparting die model) 33 Strain-applied region 35 Wave-formed blank press-formed product shape (using a convex pattern-imparting die model) 37 Periodically offset wave-formed blank press-formed product shape (using a convex pattern-imparting die model) 41 Periodically offset wave-formed blank model (Example) 43 Periodically offset wave-formed blank press-formed product shape (using a predetermined die model) 51 Periodically shifted wave-shaped blank press-formed product shape (using a mold model with a convex pattern)

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