WO2024070061A1 - Method for manufacturing press-formed product - Google Patents

Method for manufacturing press-formed product Download PDF

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Publication number
WO2024070061A1
WO2024070061A1 PCT/JP2023/020982 JP2023020982W WO2024070061A1 WO 2024070061 A1 WO2024070061 A1 WO 2024070061A1 JP 2023020982 W JP2023020982 W JP 2023020982W WO 2024070061 A1 WO2024070061 A1 WO 2024070061A1
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press
die
formed product
springback
projection angle
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PCT/JP2023/020982
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French (fr)
Japanese (ja)
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裕之 田中
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Ｊｆｅスチール株式会社
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  • the present invention relates to a method for manufacturing a press-molded product that is curved when viewed from above and has at least a top plate portion and a vertical wall portion that continues from the top plate portion.
  • Automobile parts including parts of their structure, include press-formed products 1, which are curved when viewed from above and have at least a top plate portion 3 and a vertical wall portion 5 continuing from the top plate portion 3, as shown in Figure 3.
  • press-formed products if the die is moved to the bottom dead center and then released from the die, springback occurs, making the press-formed product prone to twisting.
  • the stress generated at the bottom dead center of forming increases due to the increased strength, and after release from the die, the large stress is released, making it prone to large twisting, which is problematic.
  • Patent Document 1 discloses a method of reducing the stress generated by providing through holes or grooves in a press-formed product.
  • paragraph [0004] of Patent Document 2 discloses a method of press-forming using a die that provides a twist angle in the opposite direction to springback.
  • Patent Document 1 creates through holes and grooves in the press molded product, resulting in a press molded product with a shape different from the target, which can lead to problems such as reduced rigidity when assembled to the vehicle body and difficulty in joining parts together.
  • the press molding method described in Patent Document 2 involves applying a twist angle to the die in only one direction, the opposite direction to springback, for press molding, which poses the problem that it is difficult to set the twist angle to be applied to the die.
  • the twist angle is too small, the twist that is springback cannot be fully eliminated, and if the twist angle is too large, twist in the opposite direction remains, so it is necessary to apply an appropriate twist angle, which is difficult.
  • the present invention has been made in consideration of the above problems, and its purpose is to provide a method for manufacturing a press-molded product that is curved when viewed from above and has at least a top plate portion and a vertical wall portion continuing from the top plate portion, and that can reduce shape errors caused by springback after demolding.
  • the manufacturing method of a press-molded product according to the present invention is a manufacturing method of a press-molded product that is curved when viewed from above, has at least a top plate portion and a vertical wall portion continuing from the top plate portion, and is manufactured by imparting a projection angle to a die in order to reduce an error from a target shape due to springback after demolding, and is characterized by comprising: a molding process of press-molding using a molding die imparted with a first projection angle such that a twist due to springback in the opposite direction (reverse twist) remains compared to the twist (positive twist) that occurs due to springback when press-molding is performed in one process without imparting a projection angle to the die; and a restriking process of press-molding the molded product molded in the molding process using a restriking die imparted with a second projection angle.
  • the manufacturing method of the press-formed product according to the present invention is characterized in that, in the invention (1) above, the first projection angle is greater than the one-step projection angle at which the twist due to springback when the press-formed product is press-formed in one step is equal to or smaller than a predetermined threshold value.
  • the manufacturing method of the press-formed product according to the present invention is the same as the invention (2) above, and is characterized in that a press forming analysis and a springback analysis of the press-formed product are performed in advance to determine the direction of twist due to springback and the one-step projection angle.
  • the manufacturing method of the press-formed product according to the present invention is the same as the invention (2) above, and is characterized in that the actual press-formation of the press-formed product is performed in advance to determine the direction of twist due to springback and the one-step projection angle.
  • the manufacturing method of the press-molded product according to the present invention is characterized in that, in any of the inventions (1) to (4) above, the first projection angle or the second projection angle is set as an inclination angle of the top plate molding surface portion of the widthwise cross section at the longitudinal end of the molding die or the restriking die, based on the top plate molding surface portion of the widthwise cross section at the longitudinal center of the molding die or the restriking die.
  • the manufacturing method of the press-molded product according to the present invention is characterized in that, in any of the inventions (1) to (5) above, the absolute value of the second projection angle in the restriking process is smaller than the absolute value of the first projection angle.
  • the manufacturing method of the press-molded product according to the present invention can sufficiently reduce the twisting, which is springback after demolding. As a result, there is no need to provide through holes or grooves, and the desired press-molded product shape is maintained, achieving the effect of being able to manufacture press-molded products with even better shapes than before.
  • the manufacturing method of the press-molded product according to the present invention has the effect of being able to manufacture press-molded products with sufficiently reduced springback using the same mold, even for blanks with different material strengths and variations in plate thickness and material quality.
  • FIG. 1 is an explanatory diagram of the die projection angle in the molding process and the restriking process in an example of the invention.
  • FIG. 2 is an explanatory diagram of the stress state at the bottom dead center of the forming process and the restriking process in an example of the invention.
  • FIG. 3 is an explanatory diagram of an example of a press-formed product to which the present invention is directed.
  • FIG. 4 is an explanatory diagram of the forming step and the restriking step according to the embodiment.
  • FIG. 5 is an explanatory diagram of the twist angle of a press-formed product.
  • FIG. 6 is an explanatory diagram of the die projection angle.
  • FIG. 7 is an explanatory diagram of the twist angle in a press-formed product after a forming process and a press-formed product after a restriking process in a conventional example.
  • FIG. 8 is an explanatory diagram of the stress state at the bottom dead center in the forming process and the restriking process in the conventional example.
  • FIG. 9 is an explanatory diagram of the die projection angle in the molding process and the restriking process in the comparative example.
  • FIG. 10 is an explanatory diagram of the stress state at the forming bottom dead center in the forming process and the restriking process in the comparative example.
  • FIG. 11 is an explanatory diagram of a press-formed product that is the subject of the examples (part 1).
  • FIG. 12 is an explanatory diagram of the press-formed product that was the subject of the embodiment (part 2).
  • the press-formed product 1 that is the subject of the present invention is curved when viewed from above, as shown as an example in Figure 3, and has a hat-shaped cross-section having at least a top plate portion 3, a vertical wall portion 5 continuing from the top plate portion 3, and a flange portion 7 at the lower end of the vertical wall portion 5.
  • the flange portion 7 is included, but the presence of the flange portion 7 is not essential.
  • the operation of the present invention will be explained using as an example the press-formed product 1 shown in Figure 3, which is formed using a 1470 MPa-class steel plate with a plate thickness of 1.0 mm as the blank 9.
  • the press-formed product 1 as shown in Figure 3 is formed in a forming process ( Figure 4(a)) and a restriking process (Figure 4(b)) as shown in Figure 4.
  • a blank 9 which is a metal plate
  • a forming die 15 is moved relatively to form a formed product 17 having a top plate portion 3, a vertical wall portion 5, and a flange portion 7.
  • the formed product 17 formed in the forming process is formed by a restriking punch 19 and a restriking die 21.
  • Figure 5(a) is a plan view of the press-formed product 1.
  • Figure 5(b) is a diagram showing the P-P cross section of the longitudinal center of the press-formed product 1 together with the forming surface of the longitudinal center of the restriking punch 19.
  • Figure 5(c) is a diagram showing the Q-Q cross section near the longitudinal end of the press-formed product 1 together with the forming surface of the longitudinal center of the restriking punch 19.
  • the twist angle of the molded product 17 and the press-molded product 1 is defined as the angle between the cross section of the top plate forming surface at the longitudinal center of the forming punch 13 and the restriking punch 19 and the cross section of the top plate forming surface at the longitudinal center of the forming punch 13 and the restriking punch 19, based on the cross section (see FIG. 5(b)).
  • the cross section of the top plate 3 at the longitudinal end is defined as the angle between the cross section of the top plate forming surface at the longitudinal center of the forming punch 13 and the restriking punch 19.
  • the angle is defined as a + (plus) value when it is shifted leftward (counterclockwise) on the page, with the outer side of the curve being the left and the inner side of the curve being the right, and a - (minus) value when it is shifted rightward (clockwise) on the page.
  • the die projection angle is defined as the angle of the cross section (S-S cross section) of the longitudinal end (for example, about 10 mm inside from the extreme end) (see Figs. 6(a) and (c)) based on the cross section (R-R cross section) (see Figs. 6(a) and (b)) of the longitudinal center of the top plate forming surface of the forming punch 13 and the restriking punch 19.
  • the die projection angle is defined as a + (plus) value when it rotates left (counterclockwise) on the page, with the outside of the curve on the left and the inside of the curve on the right, and a - (minus) value when it rotates right (clockwise) on the page.
  • FIG. 7 shows the Q-Q cross section (see FIG. 5) near the longitudinal end of the molded product 17A after the molding process (FIG. 7(a)) and the press-molded product 1A after the restrike process (FIG. 7(b)) of the conventional example.
  • the twist angle due to springback after the molding process remains negative, and is not corrected even in the restrike process and remains almost as it is.
  • the twist angle due to springback of the molded product 17A after the press molding process shown in FIG. 7(a) is -3.1 degrees.
  • the twist angle due to springback of the press-molded product 1A after restrike shown in FIG. 7(b) is -3.4 degrees.
  • FIG. 8 is a contour diagram of the analysis results.
  • Figure 8(a) is a diagram showing the stress distribution at the bottom dead center of the formed product 17A after the forming process.
  • Figure 8(b) is a diagram showing the stress distribution at the bottom dead center of the press-formed product 1A after the restriking process.
  • large compressive stress due to shrink flange deformation occurs in the outer flange parts 177A and 7A, and large tensile stress due to stretch flange deformation occurs in the inner flange parts 177A and 7A.
  • the one-step projection angle is an angle applied to the longitudinal end of the forming die so that the twist due to springback when the press-formed product is press-formed in one process is equal to or less than a predetermined threshold value.
  • the predetermined threshold value is the upper limit of the twist angle that is allowable for a press-formed product.
  • the one-step projection angle in this example is 6.0 degrees in the opposite direction to the twist due to springback with respect to the die of the target shape.
  • a one-step angle is provided in anticipation of springback during the forming process, so there is almost no twisting due to springback after the forming process, and when the part is formed using the restriking die 19B of the target shape in the restriking process, the part is shaped close to the target shape.
  • FIG. 10 is a contour diagram of the analysis results.
  • Figure 10(a) is a diagram showing the stress distribution at the bottom dead point of the formed product 17B after the forming process.
  • Figure 10(b) is a diagram showing the stress distribution at the bottom dead point of the press-formed product 1B after the restriking process.
  • the forming step and the restriking step are carried out as follows.
  • press forming is performed using a forming die 13C (see FIG. 1(a)) to which a first projection angle is imparted such that a twist (reverse twist) caused by springback in the opposite direction to the twist (positive twist) caused by springback when press forming is performed in one step without imparting a projection angle to the die remains.
  • the twist after springback is most reduced by setting the one-step projection angle to 6.0 degrees, so in order to leave the reverse twist, the first projection angle is made larger than 6.0 degrees.
  • the first projection angle of the S-S cross section in the longitudinal direction of the die is set to 8.0 degrees with respect to the R-R cross section at the center of the longitudinal direction of the die in FIG. 6.
  • the molded product 17C molded in the molding process is press molded using a restriking die 19C to which a second prospect angle that reduces the reverse twist is imparted.
  • the reverse twist remains due to springback, so in order to reduce this, as shown in FIG. 1(b), the mold is molded using a restriking die 19C to which a second prospect angle in the same direction as the springback is imparted (in this example, the angle of the S-S cross section near the end of the die in the longitudinal direction is -6.0 degrees with respect to the R-R cross section at the center of the die in the longitudinal direction of FIG. 6) to reduce the reverse twist, to obtain a target shape.
  • the absolute value of the second prospect angle in the restriking process is preferably smaller than the absolute value of the first prospect angle.
  • Figure 2 shows the stress distribution at the bottom dead center of the forming process, which was determined by FEM analysis of these forming and restriking processes.
  • Figure 2(a) in the forming process, in the longitudinal center of the formed product 17C, large compressive stress occurs in the outer flange portion 177C due to shrink flange deformation, and large tensile stress occurs in the inner flange portion 177C due to stretch flange deformation.
  • large tensile stress occurs on the outer side of the curve of the top plate portion 173C
  • large compressive stress occurs on the inner side of the curve of the top plate portion 173C.
  • FIG. 2(b) of the present invention Comparing FIG. 2(b) of the present invention with FIG. 10(b) of the comparative example, in the case of the present invention shown in FIG. 2(b), the compressive stress of the outer flange portion 7C and the tensile stress of the inner flange portion 7C are reduced more than in the comparative example. Furthermore, in the case of the present invention shown in FIG. 2(b), the tensile stress on the outer side of the curve of the top plate portion 3C and the compressive stress on the inner side of the curve of the top plate portion 3C are also reduced more than in the comparative example. That is, the stress distribution of the press-formed product 1C after the restriking process of FIG.
  • the present invention is not limited to this.
  • the present invention can also be applied to U-shaped cross-section parts that are curved when viewed from above and consist of a top plate and vertical wall portions on both sides, Z-shaped cross-section parts that consist of a vertical wall portion and a flange portion on only one side of the top plate, and L-shaped cross-section parts that consist of a top plate and a vertical wall portion on only one side. It can also be applied in cases where part of the press-molded product is curved.
  • the shape of the press-formed product 1 is a hat-shaped cross-sectional shape having a top plate portion 3, a vertical wall portion 5 continuing with the top plate portion 3, and a flange portion 7 continuing with the vertical wall portion 5, and the cross-sectional dimensions are as shown in FIG. 12.
  • the twist angle due to springback and the die projection angle are based on the cross section of the top plate forming portion at the center of the die longitudinal direction, with the outside of the curve being the left and the inside of the curve being the right, and the leftward rotation on the paper is a + (plus) value, and the rightward rotation on the paper is a - (minus) value.
  • the direction of twist (positive twist) due to springback was determined by molding using a die with no die projection angle. Furthermore, the one-step projection angle that can minimize twist due to springback in one step was determined to be 6.0 degrees. After that, the molding process and restriking process were carried out for each of the conventional example, comparative example, and invention example described above. The results are shown in Table 1.
  • Comparative examples No. 2-1 (1470 MPa class material) and No. 2-2 (980 MPa class material) have a one-step projection angle of 6.0 degrees in the forming process and a die projection angle of 0 degrees in the restriking process.
  • the torsion angle of the press-formed product 1A after restriking was reduced to 0.6 degrees in the case of No. 2-1 (1470 MPa class material), but was 2.0 degrees in the case of No. 2-2 (980 MPa class material), resulting in significant torsion due to springback.
  • the difference in torsion angle due to material strength after the restriking process was -1.4 degrees, which was greater than the difference between the conventional examples No. 1-1 and No. 1-2.
  • the first projection angle in the forming process was 7.0 degrees
  • the second projection angle in the restriking process was -2.0 degrees
  • the torsion angle of the press-formed product 1C after restriking was 0.3 degrees in the case of No. 3-1 (1470 MPa class material) and 0.6 degrees in the case of No. 3-2 (980 MPa class material), and the torsion due to springback was reduced.
  • the difference in the torsion angle due to the material strength after the restriking process was -0.3 degrees, and even though the material strength is significantly different between the 1470 MPa class material and the 980 MPa class material, the difference in the torsion angle due to the difference in material strength using the same die was small. Therefore, it was found that springback can be sufficiently reduced even when press forming is performed using different materials using the same die.
  • the first projection angle in the forming process was increased to 8.0 degrees, and the die projection angle in the restriking process was 0 degrees.
  • the twist angle of the press-formed product 1B after these restriking processes was 2.2 degrees for No. 4-1 (1470 MPa class material) and 3.4 degrees for No. 4-2 (980 MPa class material).
  • the difference in twist angle due to material strength after the restriking process was large at -1.2 degrees.
  • Inventive examples No. 5-1 (1470 MPa class material) and No. 5-2 (980 MPa class material) have a first projection angle of 8.0 degrees in the forming process and a second projection angle of -6.0 degrees in the restriking process.
  • the twist angle of the press-formed product 1C after restriking was 0.1 degrees for No. 5-1 (1470 MPa class material) and 0.2 degrees for No. 5-2 (980 MPa class material), and both 1470 MPa class material and 980 MPa class material were able to sufficiently reduce twist due to springback.
  • the difference in twist angle due to material strength after the restriking process was -0.1 degrees, and even though the material strength of the 1470 MPa class material and the 980 MPa class material was significantly different, the difference in twist angle due to the difference in material strength was small even when the same die was used. Therefore, it has been found that the present invention can sufficiently reduce springback even when press molding different materials using the same die.
  • the present invention can provide a method for manufacturing a press-molded product that can reduce shape errors caused by springback after demolding in a press-molded product that is curved when viewed from above and has at least a top plate portion and a vertical wall portion continuing from the top plate portion.

Abstract

The present invention relates to a method for manufacturing a press-formed product 1 that is curved in top view and has at least a top plate part 3 and a vertical wall part 5 continuous from the top plate part 3, the method reducing an error from a target shape due to springback of the press-formed product 1 after being released from a die. The method comprises: a forming step for performing press-forming using a forming die provided with a first prospective angle that introduces a torsion (reverse torsion) due to springback in a reverse direction to a torsion (normal torsion) that would be caused by springback if the press-forming were performed in a single step without providing the die with the prospective angle; and a restriking step for press-forming a formed product 17 formed in the forming step, using a restrike die provided with a second prospective angle for reducing the reverse torsion.

Description

プレス成形品の製造方法Manufacturing method of press-molded products
　本発明は、上面視で湾曲し、少なくとも、天板部と、天板部から連続する縦壁部とを有するプレス成形品の製造方法に関する。 The present invention relates to a method for manufacturing a press-molded product that is curved when viewed from above and has at least a top plate portion and a vertical wall portion that continues from the top plate portion.
　自動車の衝突安全性基準の厳格化により、車体の衝突安全性の向上が進む中で、二酸化炭素排出規制を受けて、燃費向上やＥＶ化のために車体の軽量化も必要とされている。これら車体の衝突安全性向上と軽量化とを両立させるために、車体構造部品への５９０ＭＰａ級以上の高強度鋼板（ハイテン材とも称する）の適用が進んでいる。 As automobile crash safety standards become stricter, the crash safety of car bodies is improving, but in response to carbon dioxide emission regulations, there is also a need to reduce the weight of car bodies to improve fuel efficiency and promote the shift to EVs. In order to achieve both improved crash safety and reduced weight of car bodies, the use of high-strength steel plates (also known as high-tensile steel) of 590 MPa class or higher is increasing for car body structural parts.
　自動車部品はその構造の一部を含めて、例えば、図３に示すように、上面視で湾曲し、少なくとも、天板部３と、天板部３から連続する縦壁部５とを備えたプレス成形品１がある。このようなプレス成形品をプレス成形する場合には、金型を成形下死点まで移動した後に離型するとスプリングバックが生じて、プレス成形品に捩れが生じやすい。特に、ハイテン材の場合には、高強度化によって成形下死点で発生する応力が大きくなり、離型後に大きな応力が解放されて、大きな捩れが発生しやすくなり問題である。 Automobile parts, including parts of their structure, include press-formed products 1, which are curved when viewed from above and have at least a top plate portion 3 and a vertical wall portion 5 continuing from the top plate portion 3, as shown in Figure 3. When press-forming such press-formed products, if the die is moved to the bottom dead center and then released from the die, springback occurs, making the press-formed product prone to twisting. In particular, with high tensile steel, the stress generated at the bottom dead center of forming increases due to the increased strength, and after release from the die, the large stress is released, making it prone to large twisting, which is problematic.
　このようなスプリングバックによる捩れを低減するための方法として、例えば、特許文献１には、プレス成形品に貫通孔または溝等を付与して発生する応力を低減する方法が開示されている。また、特許文献２の段落[０００４]には、スプリングバックと逆方向の捩れ角を付与した金型でプレス成形する方法が開示されている。 As a method for reducing such twisting due to springback, for example, Patent Document 1 discloses a method of reducing the stress generated by providing through holes or grooves in a press-formed product. Furthermore, paragraph [0004] of Patent Document 2 discloses a method of press-forming using a die that provides a twist angle in the opposite direction to springback.
特開２００７-２５３１７３号公報JP 2007-253173 A 特開２００７-１３０６７１号公報JP 2007-130671 A
　特許文献１に記載のプレス成形方法は、プレス成形品に貫通孔や溝を形成するため、目標とは異なる形状のプレス成形品となり、車体に組み付けた際に剛性が低下したり、部品同士を接合することが困難になったりするなどの課題があった。 The press molding method described in Patent Document 1 creates through holes and grooves in the press molded product, resulting in a press molded product with a shape different from the target, which can lead to problems such as reduced rigidity when assembled to the vehicle body and difficulty in joining parts together.
　また、特許文献２に記載のプレス成形方法では、スプリングバックと逆方向のみの一方向の捩れ角を金型に与えてプレス成形するため、金型に与える捩れ角の設定が難しいという課題がある。すなわち、捩れ角が小さすぎるとスプリングバックである捩れを十分解消できず、捩れ角が大きすぎると逆方向の捩れが残存してしまうため、適切な捩れ角を付与する必要があるが、これが難しい。 In addition, the press molding method described in Patent Document 2 involves applying a twist angle to the die in only one direction, the opposite direction to springback, for press molding, which poses the problem that it is difficult to set the twist angle to be applied to the die. In other words, if the twist angle is too small, the twist that is springback cannot be fully eliminated, and if the twist angle is too large, twist in the opposite direction remains, so it is necessary to apply an appropriate twist angle, which is difficult.
　さらに、同じ金型を用いて、材料強度の異なるブランクをプレス成形する場合や、プレス成形に供するブランクの材質や板厚等のばらつきがある場合には、以下のような問題がある。すなわち、従来の一方向のみの捩れ角を与えた同じ金型によりプレス成形しても、材料強度の違い、板厚や材質のばらつきによってスプリングバックの程度が異なり、プレス成形品のスプリングバックのばらつきが発生してしまう。 Furthermore, when blanks with different material strengths are press-formed using the same die, or when there is variation in the material or thickness of the blanks used for press forming, the following problems arise. That is, even when press forming is performed using the same die that has a conventional twist angle in only one direction, the degree of springback varies depending on the difference in material strength and the variation in thickness and material, resulting in variation in the springback of the press-formed product.
　本発明は、上記課題に鑑みてなされたものであって、その目的は、上面視で湾曲し、少なくとも、天板部と、天板部から連続する縦壁部とを有するプレス成形品における、離型後のスプリングバックによる形状誤差を低減できるプレス成形品の製造方法を提供することである。 The present invention has been made in consideration of the above problems, and its purpose is to provide a method for manufacturing a press-molded product that is curved when viewed from above and has at least a top plate portion and a vertical wall portion continuing from the top plate portion, and that can reduce shape errors caused by springback after demolding.
　上述した課題を解決し、目的を達成するために、
（１）本発明に係るプレス成形品の製造方法は、上面視で湾曲し、少なくとも、天板部と、天板部から連続する縦壁部とを有し、離型後のスプリングバックによる目標形状との誤差を低減するために、金型に見込み角を付与して製造されるプレス成形品の製造方法であって、金型に見込み角を付与せずに１工程でプレス成形した際にスプリングバックにより生ずる捩れ（正捩れ）と逆方向のスプリングバックによる捩れ（逆捩れ）が残存するような第１見込み角を付与した成形金型を用いてプレス成形する成形工程と、該成形工程で成形された成形品を第２見込み角を付与したリストライク金型を用いてプレス成形するリストライク工程と、を備えたことを特徴とするものである。 In order to solve the above problems and achieve the objectives,
(1) The manufacturing method of a press-molded product according to the present invention is a manufacturing method of a press-molded product that is curved when viewed from above, has at least a top plate portion and a vertical wall portion continuing from the top plate portion, and is manufactured by imparting a projection angle to a die in order to reduce an error from a target shape due to springback after demolding, and is characterized by comprising: a molding process of press-molding using a molding die imparted with a first projection angle such that a twist due to springback in the opposite direction (reverse twist) remains compared to the twist (positive twist) that occurs due to springback when press-molding is performed in one process without imparting a projection angle to the die; and a restriking process of press-molding the molded product molded in the molding process using a restriking die imparted with a second projection angle.
（２）本発明に係るプレス成形品の製造方法は、上記（１）の発明において、前記第１見込み角は、前記プレス成形品を１工程でプレス成形した際のスプリングバックによる捩れが所定の閾値以下となる１工程見込み角よりも大きいことを特徴とするものである。 (2) The manufacturing method of the press-formed product according to the present invention is characterized in that, in the invention (1) above, the first projection angle is greater than the one-step projection angle at which the twist due to springback when the press-formed product is press-formed in one step is equal to or smaller than a predetermined threshold value.
（３）本発明に係るプレス成形品の製造方法は、上記（２）の発明において、予め、前記プレス成形品のプレス成形解析およびスプリングバック解析を行って、スプリングバックによる捩れの方向と前記１工程見込み角を求めることを特徴とするものである。 (3) The manufacturing method of the press-formed product according to the present invention is the same as the invention (2) above, and is characterized in that a press forming analysis and a springback analysis of the press-formed product are performed in advance to determine the direction of twist due to springback and the one-step projection angle.
（４）本発明に係るプレス成形品の製造方法は、上記（２）の発明において、予め、前記プレス成形品の実プレス成形を行って、スプリングバックによる捩れの方向と前記１工程見込み角を求めることを特徴とするものである。 (4) The manufacturing method of the press-formed product according to the present invention is the same as the invention (2) above, and is characterized in that the actual press-formation of the press-formed product is performed in advance to determine the direction of twist due to springback and the one-step projection angle.
（５）本発明に係るプレス成形品の製造方法は、上記（１）乃至（４）のいずれかの発明において、前記第１見込み角又は前記第２見込み角は、前記成形金型又は前記リストライク金型の長手方向中央の幅方向断面の天板成形面部を基準として、前記成形金型又は前記リストライク金型の長手方向端部における幅方向断面の天板成形面部の傾斜角とすることを特徴とするものである。 (5) The manufacturing method of the press-molded product according to the present invention is characterized in that, in any of the inventions (1) to (4) above, the first projection angle or the second projection angle is set as an inclination angle of the top plate molding surface portion of the widthwise cross section at the longitudinal end of the molding die or the restriking die, based on the top plate molding surface portion of the widthwise cross section at the longitudinal center of the molding die or the restriking die.
（６）本発明に係るプレス成形品の製造方法は、上記（１）乃至（５）のいずれかの発明において、リストライク工程における第２見込み角の絶対値を、第１見込み角の絶対値より小さくしたことを特徴とするものである。 (6) The manufacturing method of the press-molded product according to the present invention is characterized in that, in any of the inventions (1) to (5) above, the absolute value of the second projection angle in the restriking process is smaller than the absolute value of the first projection angle.
　本発明に係るプレス成形品の製造方法は、離型後のスプリングバックである捩れを十分に低減できる。その結果、貫通孔や溝を付与する必要がなく、目標とするプレス成形品形状を保持して、従来に比べてさらに良好な形状を有するプレス成形品を製造することができるという効果を奏する。また、本発明に係るプレス成形品の製造方法は、材料強度の違いや、板厚や材質のばらつきのあるブランクであっても、同じ金型を用いてスプリングバックを十分低減したプレス成形品を製造できるという効果を奏する。 The manufacturing method of the press-molded product according to the present invention can sufficiently reduce the twisting, which is springback after demolding. As a result, there is no need to provide through holes or grooves, and the desired press-molded product shape is maintained, achieving the effect of being able to manufacture press-molded products with even better shapes than before. In addition, the manufacturing method of the press-molded product according to the present invention has the effect of being able to manufacture press-molded products with sufficiently reduced springback using the same mold, even for blanks with different material strengths and variations in plate thickness and material quality.
図１は、発明例における成形工程及びリストライク工程の金型見込み角の説明図である。FIG. 1 is an explanatory diagram of the die projection angle in the molding process and the restriking process in an example of the invention. 図２は、発明例における成形工程及びリストライク工程の成形下死点での応力状態の説明図である。FIG. 2 is an explanatory diagram of the stress state at the bottom dead center of the forming process and the restriking process in an example of the invention. 図３は、本発明が対象としているプレス成形品の一例の説明図である。FIG. 3 is an explanatory diagram of an example of a press-formed product to which the present invention is directed. 図４は、実施形態に係る成形工程とリストライク工程の説明図である。FIG. 4 is an explanatory diagram of the forming step and the restriking step according to the embodiment. 図５は、プレス成形品の捩れ角の説明図である。FIG. 5 is an explanatory diagram of the twist angle of a press-formed product. 図６は、金型見込み角の説明図である。FIG. 6 is an explanatory diagram of the die projection angle. 図７は、従来例における成形工程後の成形品及びリストライク工程後のプレス成形品における捩れ角の説明図である。FIG. 7 is an explanatory diagram of the twist angle in a press-formed product after a forming process and a press-formed product after a restriking process in a conventional example. 図８は、従来例における成形工程及びリストライク工程の成形下死点での応力状態の説明図である。FIG. 8 is an explanatory diagram of the stress state at the bottom dead center in the forming process and the restriking process in the conventional example. 図９は、比較例における成形工程及びリストライク工程の金型見込み角の説明図である。FIG. 9 is an explanatory diagram of the die projection angle in the molding process and the restriking process in the comparative example. 図１０は、比較例における成形工程及びリストライク工程の成形下死点での応力状態の説明図である。FIG. 10 is an explanatory diagram of the stress state at the forming bottom dead center in the forming process and the restriking process in the comparative example. 図１１は、実施例で対象としたプレス成形品の説明図である（その１）。FIG. 11 is an explanatory diagram of a press-formed product that is the subject of the examples (part 1). 図１２は、実施例で対象としたプレス成形品の説明図である（その２）。FIG. 12 is an explanatory diagram of the press-formed product that was the subject of the embodiment (part 2).
　以下に、本発明に係るプレス成形品の製造方法の実施形態について説明する。なお、本実施形態により本発明が限定されるものではない。 Below, an embodiment of the manufacturing method for press-molded products according to the present invention will be described. Note that the present invention is not limited to this embodiment.
　本発明が対象としているプレス成形品１は、図３に一例として示すように、上面視で湾曲し、少なくとも天板部３と、天板部３から連続する縦壁部５と、縦壁部５の下端にフランジ部７とを有するハット断面形状のものである。なお、図３に示す例では、天板部３と縦壁部５とに加えてフランジ部７を有しているが、フランジ部７を有することは必須ではない。以下、板厚１．０ｍｍの１４７０ＭＰａ級鋼板をブランク９として用いて成形された、図３に示すプレス成形品１を例に挙げて本発明の作用について説明する。 The press-formed product 1 that is the subject of the present invention is curved when viewed from above, as shown as an example in Figure 3, and has a hat-shaped cross-section having at least a top plate portion 3, a vertical wall portion 5 continuing from the top plate portion 3, and a flange portion 7 at the lower end of the vertical wall portion 5. Note that in the example shown in Figure 3, in addition to the top plate portion 3 and the vertical wall portion 5, the flange portion 7 is included, but the presence of the flange portion 7 is not essential. Below, the operation of the present invention will be explained using as an example the press-formed product 1 shown in Figure 3, which is formed using a 1470 MPa-class steel plate with a plate thickness of 1.0 mm as the blank 9.
　図３に示すようなプレス成形品１は、図４に示すように、成形工程（図４（ａ））とリストライク工程（図４（ｂ））とによって成形される。成形工程では、金属板であるブランク９をパッド１１と成形用パンチ１３とで押さえて、成形用ダイ１５を相対的に移動させて、天板部３と縦壁部５とフランジ部７とを有する成形品１７を成形する。そして、リストライク工程では、成形工程で成形された成形品１７をリストライク用パンチ１９とリストライク用ダイ２１とによって成形する。 The press-formed product 1 as shown in Figure 3 is formed in a forming process (Figure 4(a)) and a restriking process (Figure 4(b)) as shown in Figure 4. In the forming process, a blank 9, which is a metal plate, is pressed by a pad 11 and a forming punch 13, and a forming die 15 is moved relatively to form a formed product 17 having a top plate portion 3, a vertical wall portion 5, and a flange portion 7. Then, in the restriking process, the formed product 17 formed in the forming process is formed by a restriking punch 19 and a restriking die 21.
　リストライク後のプレス成形品１の形状、特に捩れ角について、図５に基づいて説明する。図５（ａ）は、プレス成形品１の平面図である。図５（ｂ）は、プレス成形品１の長手方向中央部のＰ－Ｐ断面をリストライク用パンチ１９の長手方向中央部の成形面と共に示した図である。図５（ｃ）は、プレス成形品１の長手方向端部近傍のＱ－Ｑ断面をリストライク用パンチ１９の長手方向中央部の成形面と共に示した図である。 The shape of the press-formed product 1 after restriking, particularly the twist angle, will be explained with reference to Figure 5. Figure 5(a) is a plan view of the press-formed product 1. Figure 5(b) is a diagram showing the P-P cross section of the longitudinal center of the press-formed product 1 together with the forming surface of the longitudinal center of the restriking punch 19. Figure 5(c) is a diagram showing the Q-Q cross section near the longitudinal end of the press-formed product 1 together with the forming surface of the longitudinal center of the restriking punch 19.
　図５に示すように、リストライク用パンチ１９の長手方向中央部の天板成形面の断面と、プレス成形品１の長手方向中央部のＰ－Ｐ断面の天板部３とを一致させた場合、長手方向端部近傍のＱ－Ｑ断面形状が、リストライク用パンチ１９の長手方向中央部の天板成形面の断面に対して時計回り（湾曲外側を左とし、湾曲内側を右とする紙面右回り）方向に回転している。これは、スプリングバックによってプレス成形品１が捩れていることを示している。 As shown in Figure 5, when the cross section of the top plate forming surface at the longitudinal center of the restriking punch 19 is aligned with the top plate portion 3 of the P-P cross section at the longitudinal center of the press-formed product 1, the Q-Q cross section shape near the longitudinal end rotates clockwise (rightwards on the page with the outer side of the curve being the left and the inner side of the curve being the right) relative to the cross section of the top plate forming surface at the longitudinal center of the restriking punch 19. This indicates that the press-formed product 1 is twisted due to springback.
　以下の説明では、成形品１７及びプレス成形品１の捩れ角を、成形用パンチ１３及びリストライク用パンチ１９の長手方向中央部の天板成形面の断面を基準とし（図５（ｂ）参照）、長手方向端部（本例では、最端部から１０ｍｍ程度中央寄り）の天板部３の断面が成形用パンチ１３及びリストライク用パンチ１９の長手方向中央部の天板成形面の断面と成す角度と定義する。そして、当該角度が湾曲外側を左とし、湾曲内側を右とする紙面左回り（反時計回り）にずれている場合を＋（プラス）の値とし、紙面右回り（時計回り）にずれている場合を－（マイナス）の値とする。 In the following explanation, the twist angle of the molded product 17 and the press-molded product 1 is defined as the angle between the cross section of the top plate forming surface at the longitudinal center of the forming punch 13 and the restriking punch 19 and the cross section of the top plate forming surface at the longitudinal center of the forming punch 13 and the restriking punch 19, based on the cross section (see FIG. 5(b)). The cross section of the top plate 3 at the longitudinal end (in this example, about 10 mm toward the center from the extreme end) is defined as the angle between the cross section of the top plate forming surface at the longitudinal center of the forming punch 13 and the restriking punch 19. The angle is defined as a + (plus) value when it is shifted leftward (counterclockwise) on the page, with the outer side of the curve being the left and the inner side of the curve being the right, and a - (minus) value when it is shifted rightward (clockwise) on the page.
　また、金型見込み角は、成形用パンチ１３及びリストライク用パンチ１９の天板成形面部の長手方向中央部の断面（Ｒ－Ｒ断面）（図６（ａ），（ｂ）参照）を基準とした、長手方向端部（例えば、最端部から１０ｍｍ程度内部）（図６（ａ），（ｃ）参照）の断面（Ｓ－Ｓ断面）の角度と定義とする。そして、金型見込み角が湾曲外側を左とし、湾曲内側を右とする紙面左回り（反時計回り）の場合を＋（プラス）の値とし、紙面右回り（時計回り）の場合を－（マイナス）の値とする。 The die projection angle is defined as the angle of the cross section (S-S cross section) of the longitudinal end (for example, about 10 mm inside from the extreme end) (see Figs. 6(a) and (c)) based on the cross section (R-R cross section) (see Figs. 6(a) and (b)) of the longitudinal center of the top plate forming surface of the forming punch 13 and the restriking punch 19. The die projection angle is defined as a + (plus) value when it rotates left (counterclockwise) on the page, with the outside of the curve on the left and the inside of the curve on the right, and a - (minus) value when it rotates right (clockwise) on the page.
　以下、従来例及び比較例の説明を通じて、本発明に至った経緯について説明する。
＜従来例＞
　従来例は、成形工程を行った後、同じ形状の金型でリストライクしていた。図７は、従来例の成形工程後（図７（ａ））の成形品１７Ａ及びリストライク工程後（図７（ｂ））のプレス成形品１Ａにおける長手方向端部近傍のＱ－Ｑ断面（図５参照）を示している。従来例では、図７に示す通り、成形工程後のスプリングバックによる捩れ角はマイナスのままであり、リストライク工程でも矯正されずにほぼそのまま残留する。図７（ａ）に示すプレス成形工程後の成形品１７Ａのスプリングバックによる捩れ角は、－３．１度である。図７（ｂ）に示すリストライク後のプレス成形品１Ａのスプリングバックによる捩れ角は、－３．４度である。 Hereinafter, the background to the invention will be described through explanations of conventional examples and comparative examples.
<Conventional Example>
In the conventional example, after the molding process, the press-molded product 17A was restrike with a die of the same shape. FIG. 7 shows the Q-Q cross section (see FIG. 5) near the longitudinal end of the molded product 17A after the molding process (FIG. 7(a)) and the press-molded product 1A after the restrike process (FIG. 7(b)) of the conventional example. In the conventional example, as shown in FIG. 7, the twist angle due to springback after the molding process remains negative, and is not corrected even in the restrike process and remains almost as it is. The twist angle due to springback of the molded product 17A after the press molding process shown in FIG. 7(a) is -3.1 degrees. The twist angle due to springback of the press-molded product 1A after restrike shown in FIG. 7(b) is -3.4 degrees.
　従来例における２工程（成形工程とリストライク工程）について有限要素法（ＦＥＭ）によるプレス成形解析を行った。図８は、解析結果のコンター図である。図８（ａ）は、成形工程後の成形品１７Ａの成形下死点における応力分布を示す図である。図８（ｂ）は、リストライク工程後のプレス成形品１Ａの成形下死点における応力分布を示す図である。図８に示されるように、成形品１７Ａ及びプレス成形品１Ａともに長手方向中央部には、外側のフランジ部１７７Ａ，７Ａに縮みフランジ変形による大きな圧縮応力が発生し、内側のフランジ部１７７Ａ，７Ａに伸びフランジ変形による大きな引張応力が発生する。また、天板部１７３Ａ，３Ａの湾曲外側に大きな引張応力が発生し、天板部１７３Ａ，３Ａの湾曲内側に大きな圧縮応力が発生する。また、成形品１７Ａ及びプレス成形品１Ａともに長手方向端部近傍では、前記の圧縮応力や引張応力は小さくなっている。 A press forming analysis was performed using the finite element method (FEM) for two processes (forming process and restriking process) in the conventional example. Figure 8 is a contour diagram of the analysis results. Figure 8(a) is a diagram showing the stress distribution at the bottom dead center of the formed product 17A after the forming process. Figure 8(b) is a diagram showing the stress distribution at the bottom dead center of the press-formed product 1A after the restriking process. As shown in Figure 8, in the longitudinal center of both the formed product 17A and the press-formed product 1A, large compressive stress due to shrink flange deformation occurs in the outer flange parts 177A and 7A, and large tensile stress due to stretch flange deformation occurs in the inner flange parts 177A and 7A. In addition, large tensile stress occurs on the outer side of the curve of the top plate parts 173A and 3A, and large compressive stress occurs on the inner side of the curve of the top plate parts 173A and 3A. In addition, in the vicinity of the longitudinal ends of both the formed product 17A and the press-formed product 1A, the compressive stress and tensile stress are small.
　従って、離型によりこれらの応力が解放されると、従来例では、これらの応力を駆動力として、長手方向端部に捩れが生じていたわけである。 Therefore, in the conventional example, when these stresses are released by demolding, these stresses act as a driving force to cause twisting at the longitudinal ends.
＜比較例＞
　比較例は、従来例で発生した捩れを解消するために、成形工程において長手方向中央部から長手方向端部に向かって、長手方向端部近傍（最端部から１０ｍｍ内部）にて、１工程見込み角を付与した成形金型（成形用パンチ１３Ｂ）を用いて成形し（図９（ａ）参照）、その後にリストライク工程で目標形状のリストライク金型（リストライク用パンチ１９Ｂ）で成形する（図９（ｂ）参照）。ここで、１工程見込み角とは、プレス成形品を１工程でプレス成形した際のスプリングバックによる捩れが、所定の閾値以下となるように、成形金型の長手方向端部に付与する角度である。また、所定の閾値とは、プレス成形品として許容できる捩れ角度の上限値のことである。本例の１工程見込み角は、目標形状の金型に対してスプリングバックの捩れと逆方向に６．０度である。 Comparative Example
In the comparative example, in order to eliminate the twist that occurred in the conventional example, in the forming process, a forming die (forming punch 13B) with a one-step projection angle is applied near the longitudinal end (10 mm inside from the end) from the longitudinal center to the longitudinal end (see FIG. 9(a)), and then in the restriking process, a restriking die (restriking punch 19B) of the target shape is used (see FIG. 9(b)). Here, the one-step projection angle is an angle applied to the longitudinal end of the forming die so that the twist due to springback when the press-formed product is press-formed in one process is equal to or less than a predetermined threshold value. In addition, the predetermined threshold value is the upper limit of the twist angle that is allowable for a press-formed product. The one-step projection angle in this example is 6.0 degrees in the opposite direction to the twist due to springback with respect to the die of the target shape.
　比較例においては、成形工程においてスプリングバックを見込んで１工程見込み角を付与しているので、成形工程後のスプリングバックによる捩れはほぼ発生せず、リストライク工程で目標形状のリストライク金型１９Ｂで成形すると、目標形状に近い形状となる。 In the comparative example, a one-step angle is provided in anticipation of springback during the forming process, so there is almost no twisting due to springback after the forming process, and when the part is formed using the restriking die 19B of the target shape in the restriking process, the part is shaped close to the target shape.
　比較例における成形工程とリストライク工程とについて、有限要素法（ＦＥＭ）によるプレス成形解析を行った。図１０は、解析結果のコンター図である。図１０（ａ）は、成形工程後の成形品１７Ｂの成形下死点における応力分布を示す図である。図１０（ｂ）は、リストライク工程後のプレス成形品１Ｂの成形下死点における応力分布を示す図である。図１０（ａ）に示されるように、比較例の場合、成形下死点では、成形品１７Ｂの長手方向中央部には、外側のフランジ部１７７Ｂに縮みフランジ変形による大きな圧縮応力が発生し、内側のフランジ部１７７Ｂに伸びフランジ変形による大きな引張応力が発生する。また、天板部１７３Ｂの湾曲外側に大きな引張応力が発生し、天板部１７３Ｂの湾曲内側に大きな圧縮応力が発生する。 A press molding analysis was performed using the finite element method (FEM) for the forming process and the restriking process in the comparative example. Figure 10 is a contour diagram of the analysis results. Figure 10(a) is a diagram showing the stress distribution at the bottom dead point of the formed product 17B after the forming process. Figure 10(b) is a diagram showing the stress distribution at the bottom dead point of the press-formed product 1B after the restriking process. As shown in Figure 10(a), in the comparative example, at the bottom dead point of the forming, a large compressive stress occurs in the outer flange portion 177B due to shrink flange deformation in the longitudinal center of the formed product 17B, and a large tensile stress occurs in the inner flange portion 177B due to stretch flange deformation. In addition, a large tensile stress occurs on the outer side of the curve of the top plate portion 173B, and a large compressive stress occurs on the inner side of the curve of the top plate portion 173B.
　成形工程における離型後には、スプリングバックが発生するが、１工程見込み角が従来例のスプリングバックとは逆方向のスプリングバックを生じさせるものであるため、スプリングバック後には、ほぼ目標形状となる。そのため、リストライク工程の成形下死点では、図１０（ｂ）に示されるように、発生応力は従来例より低減されており、リストライク工程の成形下死点後に離型すると、スプリングバックはほとんど発生せずに目標形状となるのである。 After demolding in the forming process, springback occurs, but because the one-step projection angle causes springback in the opposite direction to that of the conventional example, the target shape is almost reached after springback. Therefore, at the bottom dead center of the restriking process, as shown in Figure 10(b), the generated stress is reduced compared to the conventional example, and when the mold is released after the bottom dead center of the restriking process, there is almost no springback and the target shape is reached.
　しかしながら、リストライク工程の成形下死点において、外側のフランジ部７Ｂや天板部３Ｂの湾曲内側には圧縮応力が多少残留し、内側のフランジ部７Ｂや天板部３Ｂの湾曲外側には引張応力が残留して、十分に応力を低減するに至っていない。そのため、同じ金型を用いて、材料強度が異なるブランク９をプレス成形する場合や、材質や板厚等のばらつきがあるブランク９をプレス成形する場合には、リストライク工程の後、スプリングバックによる捩れが発生する場合があった。すなわち、比較例で示したように、成形工程のみで１工程見込み角を付与する方法では、材料強度の相違や材質や板厚等のばらつきによってプレス成形品１Ｂの残留応力の分布が異なる。その結果、同じ金型を用いたとしてもスプリングバックを十分低減できない場合があった。 However, at the bottom dead center of the restriking process, some compressive stress remains on the inside of the curve of the outer flange portion 7B and the top plate portion 3B, and tensile stress remains on the outside of the curve of the inner flange portion 7B and the top plate portion 3B, and stress is not sufficiently reduced. Therefore, when using the same die to press-form blanks 9 with different material strengths or blanks 9 with variations in material and plate thickness, twisting due to springback may occur after the restriking process. In other words, as shown in the comparative example, in the method of imparting a one-step projection angle only in the forming process, the distribution of residual stress in the press-formed product 1B differs depending on the difference in material strength and variations in material and plate thickness. As a result, there are cases where springback cannot be sufficiently reduced even when the same die is used.
　そこで、本発明においては、成形工程とリストライク工程とを以下のように行うこととした。
＜成形工程＞
　成形工程は、金型に見込み角を付与せずに１工程でプレス成形した際のスプリングバックにより生ずる捩れ（正捩れ）とは逆方向のスプリングバックによる捩れ（逆捩れ）が残存するような第１見込み角を付与した成形金型１３Ｃ（図１（ａ）参照）を用いてプレス成形する。比較例で示したように、本例では、１工程見込み角を６．０度にすることで、スプリングバック後の捩れが最も低減されるので、逆捩れを残存させるには、第１見込み角を６．０度よりも大きくする。具体的には、図１（ａ）の成形工程では、図６の金型長手方向中央部のＲ－Ｒ断面に対し、金型長手方向のＳ－Ｓ断面の第１見込み角を８．０度とする。 Therefore, in the present invention, the forming step and the restriking step are carried out as follows.
<Molding process>
In the forming process, press forming is performed using a forming die 13C (see FIG. 1(a)) to which a first projection angle is imparted such that a twist (reverse twist) caused by springback in the opposite direction to the twist (positive twist) caused by springback when press forming is performed in one step without imparting a projection angle to the die remains. As shown in the comparative example, in this example, the twist after springback is most reduced by setting the one-step projection angle to 6.0 degrees, so in order to leave the reverse twist, the first projection angle is made larger than 6.0 degrees. Specifically, in the forming process of FIG. 1(a), the first projection angle of the S-S cross section in the longitudinal direction of the die is set to 8.0 degrees with respect to the R-R cross section at the center of the longitudinal direction of the die in FIG. 6.
＜リストライク工程＞
　リストライク工程は、成形工程で成形された成形品１７Ｃを、前記逆捩れを低減する第２見込み角を付与したリストライク金型１９Ｃを用いてプレス成形する。成形工程の離型後には、スプリングバックによって逆捩れが残存しているので、これを低減するために図１（ｂ）に示すように、逆捩れを低減するためにスプリングバックと同方向の第２見込み角（本例では図６の金型長手方向中央部のＲ－Ｒ断面に対し、金型長手方向端部近傍のＳ－Ｓ断面の角度が－６．０度）を付与したリストライク金型１９Ｃで成形して、目標形状とする。なお、リストライク工程における第２見込み角の絶対値は、第１見込み角の絶対値よりも小さくすることが好ましい。 <Restriking process>
In the restriking process, the molded product 17C molded in the molding process is press molded using a restriking die 19C to which a second prospect angle that reduces the reverse twist is imparted. After the mold release in the molding process, the reverse twist remains due to springback, so in order to reduce this, as shown in FIG. 1(b), the mold is molded using a restriking die 19C to which a second prospect angle in the same direction as the springback is imparted (in this example, the angle of the S-S cross section near the end of the die in the longitudinal direction is -6.0 degrees with respect to the R-R cross section at the center of the die in the longitudinal direction of FIG. 6) to reduce the reverse twist, to obtain a target shape. Note that the absolute value of the second prospect angle in the restriking process is preferably smaller than the absolute value of the first prospect angle.
　これら成形工程及びリストライク工程をＦＥＭ解析して、成形下死点での応力分布を求めたものを図２に示す。図２（ａ）に示す通り、成形工程では、成形品１７Ｃの長手方向中央部には、外側のフランジ部１７７Ｃに縮みフランジ変形による大きな圧縮応力が発生し、内側のフランジ部１７７Ｃに伸びフランジ変形による大きな引張応力が発生する。また、天板部１７３Ｃの湾曲外側に大きな引張応力が発生し、天板部１７３Ｃの湾曲内側に大きな圧縮応力が発生する。 Figure 2 shows the stress distribution at the bottom dead center of the forming process, which was determined by FEM analysis of these forming and restriking processes. As shown in Figure 2(a), in the forming process, in the longitudinal center of the formed product 17C, large compressive stress occurs in the outer flange portion 177C due to shrink flange deformation, and large tensile stress occurs in the inner flange portion 177C due to stretch flange deformation. In addition, large tensile stress occurs on the outer side of the curve of the top plate portion 173C, and large compressive stress occurs on the inner side of the curve of the top plate portion 173C.
　図２（ｂ）に示す通り、リストライク工程のプレス成形品１Ｃの長手方向中央部では、外側のフランジ部７Ｃの圧縮応力、天板部３Ｃの湾曲外側の引張応力、内側のフランジ部７Ｃの引張応力、及び、天板部３Ｃの湾曲内側の圧縮応力ともに大幅に低減する。 As shown in Figure 2(b), in the longitudinal center of the press-formed product 1C in the restriking process, the compressive stress of the outer flange portion 7C, the tensile stress on the outer side of the curve of the top plate portion 3C, the tensile stress of the inner flange portion 7C, and the compressive stress on the inner side of the curve of the top plate portion 3C are all significantly reduced.
　本発明である図２（ｂ）と比較例である図１０（ｂ）とを比較すると、図２（ｂ）に示す本発明の場合は、外側のフランジ部７Ｃの圧縮応力、及び、内側のフランジ部７Ｃの引張応力が、比較例よりも低減する。さらに、図２（ｂ）に示す本発明の場合は、天板部３Ｃの湾曲外側の引張応力、及び、天板部３Ｃの湾曲内側の圧縮応力も、比較例よりも低減している。すなわち、本発明の図２（ｂ）のリストライク工程後のプレス成形品１Ｃの応力分布は、比較例の図１０（ｂ）に示すリストライク工程後のプレス成形品１Ｂの応力分布よりも、プレス成形品全体に応力が低減し、スプリングバックによる捩れを十分に低減できる。また、これと同時に、同じ金型を用いて、材料強度が異なるブランク９や材質や板厚等のばらつきがあるブランク９をプレス成形する場合でも、プレス成形品１Ｃに発生する応力を十分に低減できる結果、プレス成形品１Ｃのスプリングバックを低減できるわけである。 Comparing FIG. 2(b) of the present invention with FIG. 10(b) of the comparative example, in the case of the present invention shown in FIG. 2(b), the compressive stress of the outer flange portion 7C and the tensile stress of the inner flange portion 7C are reduced more than in the comparative example. Furthermore, in the case of the present invention shown in FIG. 2(b), the tensile stress on the outer side of the curve of the top plate portion 3C and the compressive stress on the inner side of the curve of the top plate portion 3C are also reduced more than in the comparative example. That is, the stress distribution of the press-formed product 1C after the restriking process of FIG. 2(b) of the present invention is lower in the entire press-formed product than the stress distribution of the press-formed product 1B after the restriking process of FIG. 10(b) of the comparative example, and the twist due to springback can be sufficiently reduced. At the same time, even when blanks 9 with different material strengths or blanks 9 with variations in material and plate thickness are press-formed using the same die, the stress generated in the press-formed product 1C can be sufficiently reduced, and the springback of the press-formed product 1C can be reduced.
　なお、上記はハット断面部品について説明したが、本発明はこれに限られるものではない。すなわち、上面視で湾曲し、天板とその両側の縦壁部とからなるコの字断面部品、天板部片側のみの縦壁部とフランジ部とからなるＺ字断面部品、及び、天板部と片側のみの縦壁部とからなるＬ字断面部品にも適用できる。また、プレス成形品の一部が湾曲しているような場合でも適用できる。 Note that while the above description is directed to hat-shaped cross-section parts, the present invention is not limited to this. In other words, the present invention can also be applied to U-shaped cross-section parts that are curved when viewed from above and consist of a top plate and vertical wall portions on both sides, Z-shaped cross-section parts that consist of a vertical wall portion and a flange portion on only one side of the top plate, and L-shaped cross-section parts that consist of a top plate and a vertical wall portion on only one side. It can also be applied in cases where part of the press-molded product is curved.
　本発明の効果を確認するため、板厚１．０ｍｍの１４７０ＭＰａ級鋼板と９８０ＭＰａ級鋼板とをブランク９として用いて、スプリングバックである捩れ角と、材料強度の相違による捩れ角の差とについて検討した。プレス成形品１の形状は、図１１に示すように、天板部３、天板部３に連続する縦壁部５、及び、縦壁部５に連続するフランジ部７を有するハット断面形状であり、断面寸法は図１２に示す通りである。なお、スプリングバックによる捩れ角、及び、金型見込み角は、上述したのと同様に、金型長手方向中央部の天板成形部の断面を基準として、湾曲外側を左とし、湾曲内側を右とする紙面左回りを＋（プラス）の値とし、紙面右回りを－（マイナス）の値とした。 In order to confirm the effect of the present invention, 1470 MPa class steel plate and 980 MPa class steel plate with a plate thickness of 1.0 mm were used as blanks 9 to study the twist angle due to springback and the difference in twist angle due to differences in material strength. As shown in FIG. 11, the shape of the press-formed product 1 is a hat-shaped cross-sectional shape having a top plate portion 3, a vertical wall portion 5 continuing with the top plate portion 3, and a flange portion 7 continuing with the vertical wall portion 5, and the cross-sectional dimensions are as shown in FIG. 12. As described above, the twist angle due to springback and the die projection angle are based on the cross section of the top plate forming portion at the center of the die longitudinal direction, with the outside of the curve being the left and the inside of the curve being the right, and the leftward rotation on the paper is a + (plus) value, and the rightward rotation on the paper is a - (minus) value.
　まず、金型見込み角を与えていない金型で成形してスプリングバックによる捩れ（正捩れ）の方向を求めた。さらに、１工程でスプリングバックによる捩れを極力低減できる１工程見込み角を求めると６．０度であった。その後、前述した従来例、比較例、及び、発明例のそれぞれの成形工程及びリストライク工程を実施した。その結果を、表１に示す。 First, the direction of twist (positive twist) due to springback was determined by molding using a die with no die projection angle. Furthermore, the one-step projection angle that can minimize twist due to springback in one step was determined to be 6.0 degrees. After that, the molding process and restriking process were carried out for each of the conventional example, comparative example, and invention example described above. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　従来例であるＮｏ．１―１（１４７０ＭＰａ級材）とＮｏ．１－２（９８０ＭＰａ級材）とは、成形工程及びリストライク工程ともに、金型見込み角を０度として、目標形状の金型をそのまま用いたものである。これらのリストライク後のプレス成形品１Ａの捩れ角は、それぞれ－３．４度及び－２．３度であって、スプリングバックによる捩れが大きく生じていた。また、リストライク工程後の材料強度による捩れ角の差は、－１．１度と大きかった。 In the conventional examples No. 1-1 (1470 MPa class material) and No. 1-2 (980 MPa class material), the die projection angle was set to 0 degrees in both the forming process and the restriking process, and the die of the target shape was used as is. The twist angles of these press-formed products 1A after restriking were -3.4 degrees and -2.3 degrees, respectively, and there was a large amount of twisting due to springback. In addition, the difference in twist angle due to material strength after the restriking process was large at -1.1 degrees.
　比較例であるＮｏ．２―１（１４７０ＭＰａ級材）とＮｏ．２－２（９８０ＭＰａ級材）とは、成形工程の１工程見込み角を６．０度とし、リストライク工程の金型見込み角を０度としたものである。これらのリストライク後のプレス成形品１Ａの捩れ角は、Ｎｏ．２―１（１４７０ＭＰａ級材）の場合に０．６度と捩れを低減できたが、Ｎｏ．２－２（９８０ＭＰａ級材）の場合に２．０度であってスプリングバックによる捩れが大きく生じていた。その結果、リストライク工程後の材料強度による捩れ角の差は－１．４度と、従来例のＮｏ．１－１とＮｏ．１－２との差よりも大きかった。 Comparative examples No. 2-1 (1470 MPa class material) and No. 2-2 (980 MPa class material) have a one-step projection angle of 6.0 degrees in the forming process and a die projection angle of 0 degrees in the restriking process. The torsion angle of the press-formed product 1A after restriking was reduced to 0.6 degrees in the case of No. 2-1 (1470 MPa class material), but was 2.0 degrees in the case of No. 2-2 (980 MPa class material), resulting in significant torsion due to springback. As a result, the difference in torsion angle due to material strength after the restriking process was -1.4 degrees, which was greater than the difference between the conventional examples No. 1-1 and No. 1-2.
　一方、発明例であるＮｏ．３―１（１４７０ＭＰａ級材）とＮｏ．３－２（９８０ＭＰａ級材）とは、成形工程の第１見込み角を７．０度とし、リストライク工程の第２見込み角を－２．０度としたものである。これらのリストライク後のプレス成形品１Ｃの捩れ角は、Ｎｏ．３―１（１４７０ＭＰａ級材）の場合に０．３度であり、Ｎｏ．３－２（９８０ＭＰａ級材）の場合に０．６度であり、スプリングバックによる捩れを低減できた。その結果、リストライク工程後の材料強度による捩れ角の差は－０．３度であって、材料強度が１４７０ＭＰａ級材及び９８０ＭＰａ級材と大きく異なるにも係わらず、同じ金型を用いて材料強度の相違による捩れ角の差はわずかであった。そのため、同じ金型を用いて材料が異なるプレス成形を行っても、十分にスプリングバックを低減できることがわかった。 On the other hand, in the invention examples No. 3-1 (1470 MPa class material) and No. 3-2 (980 MPa class material), the first projection angle in the forming process was 7.0 degrees, and the second projection angle in the restriking process was -2.0 degrees. The torsion angle of the press-formed product 1C after restriking was 0.3 degrees in the case of No. 3-1 (1470 MPa class material) and 0.6 degrees in the case of No. 3-2 (980 MPa class material), and the torsion due to springback was reduced. As a result, the difference in the torsion angle due to the material strength after the restriking process was -0.3 degrees, and even though the material strength is significantly different between the 1470 MPa class material and the 980 MPa class material, the difference in the torsion angle due to the difference in material strength using the same die was small. Therefore, it was found that springback can be sufficiently reduced even when press forming is performed using different materials using the same die.
　比較例であるＮｏ．４―１（１４７０ＭＰａ級材）とＮｏ．４－２（９８０ＭＰａ級材）とは、成形工程の第１見込み角を８．０度と大きくし、リストライク工程の金型見込み角を０度としたものである。これらのリストライク後のプレス成形品１Ｂの捩れ角は、Ｎｏ．４―１（１４７０ＭＰａ級材）の場合に２．２度であり、Ｎｏ．４－２（９８０ＭＰａ級材）の場合に３．４度であった。また、リストライク工程後の材料強度による捩れ角の差は－１．２度と大きかった。 In the comparative examples No. 4-1 (1470 MPa class material) and No. 4-2 (980 MPa class material), the first projection angle in the forming process was increased to 8.0 degrees, and the die projection angle in the restriking process was 0 degrees. The twist angle of the press-formed product 1B after these restriking processes was 2.2 degrees for No. 4-1 (1470 MPa class material) and 3.4 degrees for No. 4-2 (980 MPa class material). In addition, the difference in twist angle due to material strength after the restriking process was large at -1.2 degrees.
　発明例であるＮｏ．５―１（１４７０ＭＰａ級材）とＮｏ．５－２（９８０ＭＰａ級材）とは、成形工程の第１見込み角を８．０度とし、リストライク工程の第２見込み角を－６．０度としたものである。これらのリストライク後のプレス成形品１Ｃの捩れ角は、Ｎｏ．５―１（１４７０ＭＰａ級材）の場合に０．１度であり、Ｎｏ．５－２（９８０ＭＰａ級材）の場合に０．２度であり、１４７０ＭＰａ級材及び９８０ＭＰａ級材ともにスプリングバックによる捩れを十分低減できた。また、リストライク工程後の材料強度による捩れ角の差は－０．１度であって、材料強度が１４７０ＭＰａ級材及び９８０ＭＰａ級材と大きく異なるにも係わらず、同じ金型を用いても材料強度の相違による捩れ角の差はわずかであった。そのため、本発明によれば、同じ金型を用いて材料が異なるプレス成形を行っても、十分にスプリングバックを低減できることがわかった。 Inventive examples No. 5-1 (1470 MPa class material) and No. 5-2 (980 MPa class material) have a first projection angle of 8.0 degrees in the forming process and a second projection angle of -6.0 degrees in the restriking process. The twist angle of the press-formed product 1C after restriking was 0.1 degrees for No. 5-1 (1470 MPa class material) and 0.2 degrees for No. 5-2 (980 MPa class material), and both 1470 MPa class material and 980 MPa class material were able to sufficiently reduce twist due to springback. In addition, the difference in twist angle due to material strength after the restriking process was -0.1 degrees, and even though the material strength of the 1470 MPa class material and the 980 MPa class material was significantly different, the difference in twist angle due to the difference in material strength was small even when the same die was used. Therefore, it has been found that the present invention can sufficiently reduce springback even when press molding different materials using the same die.
　本発明は、上面視で湾曲し、少なくとも、天板部と、天板部から連続する縦壁部とを有するプレス成形品における、離型後のスプリングバックによる形状誤差を低減できるプレス成形品の製造方法を提供することができる。 The present invention can provide a method for manufacturing a press-molded product that can reduce shape errors caused by springback after demolding in a press-molded product that is curved when viewed from above and has at least a top plate portion and a vertical wall portion continuing from the top plate portion.
１　プレス成形品
３　天板部
５　縦壁部
７　フランジ部
９　ブランク
１１　パッド
１３　成形用パンチ
１５　成形用ダイ
１７　成形品
１９　リストライク用パンチ
２１　リストライク用ダイ
１Ａ　プレス成形品（従来例）
３Ａ　天板部
７Ａ　フランジ部
１Ｂ　プレス成形品（比較例）
３Ｂ　天板部
７Ｂ　フランジ部
１Ｃ　プレス成形品（発明例）
３Ｃ　天板部
７Ｃ　フランジ部
１３Ａ　成形用パンチ（従来例）
１３Ｂ　成形用パンチ（比較例）
１３Ｃ　成形用パンチ（発明例）
１７Ａ　成形品（従来例）
１７３Ａ　天板部
１７７Ａ　フランジ部
１７Ｂ　成形品（比較例）
１７３Ｂ　天板部
１７７Ｂ　フランジ部
１７Ｃ　成形品（発明例）
１７３Ｃ　天板部
１７７Ｃ　フランジ部
１９Ａ　リストライク用パンチ（従来例）
１９Ｂ　リストライク用パンチ（比較例）
１９Ｃ　リストライク用パンチ（発明例） Reference Signs List 1 Press-molded product 3 Top plate portion 5 Vertical wall portion 7 Flange portion 9 Blank 11 Pad 13 Molding punch 15 Molding die 17 Molded product 19 Re-striking punch 21 Re-striking die 1A Press-molded product (conventional example)
3A Top plate portion 7A Flange portion 1B Press-molded product (Comparative example)
3B Top plate portion 7B Flange portion 1C Press-molded product (example of the invention)
3C Top plate portion 7C Flange portion 13A Forming punch (conventional example)
13B Forming punch (comparative example)
13C Forming punch (example of invention)
17A Molded product (conventional example)
173A Top plate portion 177A Flange portion 17B Molded product (Comparative example)
173B Top plate portion 177B Flange portion 17C Molded product (example of the invention)
173C Top plate portion 177C Flange portion 19A Re-strike punch (conventional example)
19B Re-strike punch (comparison example)
19C Re-strike punch (example of invention)

Claims (7)

  1. 　上面視で湾曲し、少なくとも、天板部と、天板部から連続する縦壁部とを有するプレス成形品の製造方法であって、
    　金型に見込み角を付与せずに１工程でプレス成形した際にスプリングバックにより生ずる捩れ（正捩れ）と逆方向のスプリングバックによる捩れ（逆捩れ）が残存するような第１見込み角を付与した成形金型を用いてプレス成形する成形工程と、
    　該成形工程で成形された成形品を第２見込み角を付与したリストライク金型を用いてプレス成形するリストライク工程と、を備えたことを特徴とするプレス成形品の製造方法。     A method for manufacturing a press-formed product that is curved when viewed from above and has at least a top plate portion and a vertical wall portion continuing from the top plate portion,
    a forming process of press-forming using a forming die having a first projection angle such that a twist (positive twist) caused by springback when press-forming is performed in one step without a projection angle being imparted to the die and a twist (negative twist) caused by springback in the opposite direction remains;
    a restriking step of press-molding the molded product molded in the molding step using a restriking die having a second projection angle.
  2. 　前記第１見込み角は、前記プレス成形品を１工程でプレス成形した際のスプリングバックによる捩れが所定の閾値以下となる１工程見込み角よりも大きいことを特徴とする請求項１に記載のプレス成形品の製造方法。 The method for manufacturing a press-formed product according to claim 1, characterized in that the first projection angle is greater than a one-step projection angle at which twisting due to springback when the press-formed product is press-formed in one step is equal to or smaller than a predetermined threshold value.
  3. 　予め、前記プレス成形品のプレス成形解析およびスプリングバック解析を行って、スプリングバックによる捩れの方向と前記１工程見込み角を求めることを特徴とする請求項２に記載のプレス成形品の製造方法。 The method for manufacturing a press-formed product according to claim 2, characterized in that a press forming analysis and a springback analysis of the press-formed product are performed in advance to determine the direction of twist due to springback and the one-step projection angle.
  4. 　予め、前記プレス成形品の実プレス成形を行って、スプリングバックによる捩れの方向と前記１工程見込み角を求めることを特徴とする請求項２に記載のプレス成形品の製造方法。 The method for manufacturing a press-formed product according to claim 2, characterized in that the actual press-formed product is first press-formed to determine the direction of twist due to springback and the one-step projection angle.
  5. 　前記第１見込み角又は前記第２見込み角は、前記成形金型又は前記リストライク金型の長手方向中央の幅方向断面の天板成形面部を基準として、前記成形金型又は前記リストライク金型の長手方向端部における幅方向断面の天板成形面部の傾斜角とすることを特徴とする請求項１乃至４のいずれか一項に記載のプレス成形品の製造方法。 The method for manufacturing a press-molded product according to any one of claims 1 to 4, characterized in that the first projection angle or the second projection angle is set as an inclination angle of the top plate molding surface portion of the widthwise cross section at the longitudinal end of the molding die or the restriking die, based on the top plate molding surface portion of the widthwise cross section at the longitudinal center of the molding die or the restriking die.
  6. 　リストライク工程における第２見込み角の絶対値を、第１見込み角の絶対値より小さくしたことを特徴とする請求項１乃至４のいずれか一項に記載のプレス成形品の製造方法。 The method for manufacturing a press-formed product according to any one of claims 1 to 4, characterized in that the absolute value of the second projection angle in the restriking process is smaller than the absolute value of the first projection angle.
  7. 　リストライク工程における第２見込み角の絶対値を、第１見込み角の絶対値より小さくしたことを特徴とする請求項５に記載のプレス成形品の製造方法。 The method for manufacturing a press-formed product described in claim 5, characterized in that the absolute value of the second projection angle in the restriking process is smaller than the absolute value of the first projection angle.
PCT/JP2023/020982 2022-09-28 2023-06-06 Method for manufacturing press-formed product WO2024070061A1 (en)

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JP2022154725A JP2024048676A (en) 2022-09-28 2022-09-28 Manufacturing method of press-molded products

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