WO2023032369A1 - Method for acquiring press forming limit line - Google Patents

Method for acquiring press forming limit line Download PDF

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Publication number
WO2023032369A1
WO2023032369A1 PCT/JP2022/021878 JP2022021878W WO2023032369A1 WO 2023032369 A1 WO2023032369 A1 WO 2023032369A1 JP 2022021878 W JP2022021878 W JP 2022021878W WO 2023032369 A1 WO2023032369 A1 WO 2023032369A1
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deformation
thin metal
forming
metal plate
thickness
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PCT/JP2022/021878
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French (fr)
Japanese (ja)
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祐太 仮屋▲崎▼
健太郎 佐藤
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Ｊｆｅスチール株式会社
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Publication of WO2023032369A1 publication Critical patent/WO2023032369A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/28—Investigating ductility, e.g. suitability of sheet metal for deep-drawing or spinning

Definitions

  • the present invention relates to cracking (
  • the present invention relates to a press forming limit line acquisition method for obtaining a forming limit diagram for determining the presence or absence of fracture.
  • Patent Document 2 A method for calculating the forming limit of cracks at (sheet edge) is disclosed (Patent Document 2).
  • FLD forming limit diagram
  • Non-Patent Document 1 a forming limit diagram
  • FLD can be obtained by a simple molding test, and in the press molding process of press-molded products using thin metal plates (blanks) printed with scribed circles and various dot patterns, scribed circles
  • blades thin metal plates
  • scribed circles By measuring the strain distribution in the thin metal plate based on the change in the print shape such as the dot pattern, it can be easily applied to determine the presence or absence of cracks in the actual press-molded product.
  • many commercial CAE (Computer Aided Engineering) solvers are also equipped with a function to determine the presence or absence of cracks by FLD using the results obtained from press forming simulation.
  • the presence or absence of cracks can be determined by FLD only for cracks that occur along a certain deformation path in draw forming and stretch forming.
  • the deformation path changes from compressive deformation to tensile deformation during press forming, the forming limit is different from the case of deformation along a constant deformation path, so it is not possible to determine the presence or absence of cracks by FLD.
  • the combination of the deformation patterns (compression deformation, tensile deformation) of the primary path and the secondary path, or the deformation from the primary path A myriad of deformation paths are possible due to differences in strain distribution ratios that change to secondary paths.
  • the present invention has been made to solve the above problems, and its object is to determine whether or not cracking occurs at a portion where the deformation path of the thin metal plate changes from compressive deformation to tensile deformation during the press forming process of the thin metal plate.
  • a press-forming limit line acquisition method is a method for obtaining a forming limit line for determining whether or not a crack occurs at a portion where a deformation path of a thin metal plate changes from compressive deformation to tensile deformation in press-forming of a thin metal plate.
  • a basic forming test in which the metal sheet is deformed along the deformation path is performed under various forming conditions, and the deformation path in the metal sheet is evaluated for the various forming conditions.
  • a basic forming test process to acquire the presence or absence of cracking in the part where the deformation changes from compression deformation to tensile deformation, and FEM analysis (finite element analysis) for the analysis target of the basic forming test of the metal sheet under the various forming conditions is performed, and based on the FEM analysis step of calculating the change in the thickness of the metal thin plate, and the change in the thickness of the metal thin plate calculated in the FEM analysis step, the compression of the deformation path for the various forming conditions
  • a maximum thickness increment, which is the amount of change in the thickness of the metal sheet until it reaches the maximum thickness in deformation, and a change from compressive deformation to tensile deformation in the deformation path, and the metal sheet is A crack determination parameter acquiring step of obtaining a relative thickness decrement, which is a change in plate thickness from the maximum plate thickness to the minimum plate thickness, as a forming crack estimation parameter; The presence or absence of cracks obtained for the various forming conditions in the basic forming test step and the crack determination parameters
  • the thin metal plate is preferably deformed along the deformation path by drawing the thin metal plate.
  • the various forming conditions are set by changing the shape of the thin metal plate or the blank holder pressure applied to the thin metal plate in the drawing process of the thin metal plate. do it.
  • the presence or absence of cracks in the thin metal plate obtained by a basic forming test in which the thin metal plate is deformed along a deformation path that changes from compressive deformation to tensile deformation and the crack determination parameter by FEM analysis for the basic forming test.
  • FIG. 1 is a flowchart for explaining the flow of processing in the press forming limit line acquisition method according to the embodiment of the present invention.
  • FIG. 2 shows a change in thickness of the thin metal plate at a portion where the deformation path of the thin metal plate changes from compressive deformation to tensile deformation, and determination of the presence or absence of cracking in the press forming limit line acquisition method according to the embodiment of the present invention.
  • 4 is a graph for explaining the maximum plate thickness increase amount and the relative plate thickness decrease amount obtained as crack determination parameters.
  • FIG. 3 is a diagram illustrating an example of a mold for drawing a thin metal plate into a rectangular cylindrical container with a bottom as a basic forming test in the embodiment and examples of the present invention ((a) perspective view).
  • FIG. 4 is a diagram for explaining a portion where the deformation path changes from compressive deformation to tensile deformation when a thin metal plate is drawn into a square tube-shaped columnar container with a bottom.
  • FIG. 5 is a diagram for explaining the shape and dimensions of the thin metal plate used in the embodiments and examples of the present invention.
  • FIG. 6 shows the presence or absence of crack generation determined by a basic forming test in which a thin metal plate is drawn into a rectangular cylindrical columnar container with a bottom in the example, and the maximum plate obtained as a crack determination parameter by FEM analysis of the basic forming test.
  • FIG. 4 is a graph showing results plotted on a two-dimensional coordinate plane in association with the amount of increase in thickness and the amount of relative thickness decrease, and a forming limit line created based on the plotted distribution of presence or absence of cracking.
  • FIG. 7 is a diagram illustrating an example of a mold for drawing a thin metal plate into a cylindrical container with a bottom as a basic forming test in Examples ((a) perspective view, (b) parallel to the forming direction). Cross-sectional view, (c) Cross-sectional view perpendicular to the molding direction).
  • FIG. 7 is a diagram illustrating an example of a mold for drawing a thin metal plate into a cylindrical container with a bottom as a basic forming test in Examples ((a) perspective view, (b) parallel to the forming direction). Cross-sectional view, (c) Cross-sectional view perpendicular to the molding direction).
  • FIG. 7 is a diagram illustrating an example of a mold for drawing a thin metal plate into a cylindrical container with
  • the inventors diligently studied the reason why the forming limit is different when the deformation path of the thin metal plate changes from compressive deformation to tensile deformation during press forming compared to when deformation follows a constant deformation path. Then, we focused on the fact that if the amount of deformation due to compressive deformation in the primary path is large, material cracks (fractures) are likely to occur even if the amount of deformation due to tensile deformation in the subsequent secondary path is small. In the primary path, work hardening due to compressive deformation affects the material's ductility and other deformation characteristics (damage), and subsequent tensile deformation in the secondary path causes cracks to easily occur. We presumed the mechanism that it occurs.
  • the amount of compressive deformation due to compressive deformation in the primary path and the amount of tensile deformation due to tensile deformation in the secondary path are each expressed as the true strain (thickness change amount) in the sheet thickness direction of the thin metal sheet. thought to express.
  • FIG. 2 is a diagram schematically showing changes in plate thickness when a thin metal plate is deformed along a deformation path that changes from compressive deformation to tensile deformation.
  • the vertical axis represents the reduction in thickness given by the true strain (-ln (thickness after deformation/thickness before deformation)) in the thickness direction of the thin metal sheet on the deformation path that changes from compressive deformation to tensile deformation.
  • thickness reduction ratio the horizontal axis is the elapsed time from the start of deformation of the metal sheet.
  • the true strain in compressive deformation and tensile deformation is obtained as the amount of compressive deformation and the amount of tensile deformation, respectively.
  • the idea was to determine the presence or absence of cracks in thin plates.
  • a press-forming limit line acquisition method is a method for determining whether or not a crack occurs at a portion where a deformation path in a thin metal plate changes from compressive deformation to tensile deformation in press-forming of a thin metal plate.
  • a limit line is obtained, and as shown in FIG. 1, a basic forming test step S1, an FEM analysis step S3, a crack determination parameter acquisition step S5, a crack determination parameter plotting step S7, and a forming limit line creation step. and S9.
  • a basic forming test is performed in which the thin metal plate is deformed along a deformation path that changes from compression deformation to tensile deformation under various forming conditions. This is a step of obtaining whether or not cracks have occurred in the portion that changes to deformation.
  • metal is formed using a tool of press forming 1 equipped with a punch 3, a die 5 and a blank holder 7, as illustrated in FIG.
  • a basic forming test is performed by drawing a thin plate (not shown).
  • the drawing process involves pressing the punch 3 into the die hole portion 5a of the die 5 while holding the edge of the metal sheet between the die 5 and the blank holder 7, thereby pulling the metal sheet toward the center and flattening it. It refers to forming a rectangular tubular columnar container 11 with a bottom from a thin metal plate. FIG. 4 shows a 1/4 area around the corner portion 11a of the columnar container 11 with the bottom.
  • the thin metal plate In the drawing process for forming the thin metal plate into the bottomed columnar container 11 using the die 1, the thin metal plate is first drawn toward the die hole portion 5a by the punch 3, so that the thin metal plate moves toward the die hole portion 5a. , and undergoes compression deformation along the circumferential direction of the outer edge of the die hole portion 5a.
  • the portion of the thin metal sheet that has undergone compressive deformation is subjected to tensile deformation when it is pushed into the die hole portion 5a in contact with the punch shoulder portion 3a, and is also subjected to tensile deformation after being drawn into the die hole portion 5a.
  • the corner portion 11a of the bottomed columnar container 11 and the side wall portion 15 around it are molded along a deformation path that changes from compressive deformation to tensile deformation.
  • Various forming conditions in the basic forming test include the shape and dimensions of the metal sheet, the wrinkle holding force of the metal sheet by the blank holder, and the lubricated conditions (lubricating oil ( The type of lubricating oil, viscosity coefficient, supply amount, addition of extreme pressure additive, etc.), bead-shape given to the thin metal plate, etc. can be changed and set appropriately. good.
  • the forming conditions can be easily changed by changing the shape of the metal sheet or the wrinkle holding force applied to the metal sheet by the blank holder 7. can do.
  • the radius of the punch shoulder part (shoulder part of a punch) 3a is R12 mm
  • the radius of the die part of the die shoulder part (shoulder part of a die) 5b is R12 mm.
  • the corner radius of the corner portion 11a was set to R25 mm.
  • a steel sheet of 980 MPa class with a thickness of 1.4 mm was used as a test material.
  • Various forming conditions in the basic forming test were set by changing the wrinkle-holding force in the range of 5 to 20 tonf.
  • Table 1 shows the forming conditions (shape, size and wrinkle pressing force of the metal sheet) in the basic forming test for drawing the metal sheet 21 shown in FIG. show.
  • the FEM analysis step S3 is a step of performing FEM analysis for various forming conditions with the basic forming test of the metal thin plate as the analysis target, and calculating changes in the plate thickness of the metal thin plate.
  • the FEM analysis in the FEM analysis step S3 is for a basic forming test in which the metallic mold 1 shown in FIG.
  • the molding conditions in the FEM analysis step S3 are the same molding conditions as the basic molding test in the basic molding test step S1.
  • Fig. 2 shows an example of calculation by FEM analysis of changes in the plate thickness of a portion of a thin metal plate that changes from compressive deformation to tensile deformation.
  • the thickness of the thin metal sheet increases and reaches the maximum thickness hc in the process of compressive deformation, and decreases in the process of tensile deformation after compressive deformation.
  • the minimum value of plate thickness in tensile deformation is expressed as minimum plate thickness ht.
  • the change in thickness of the thin metal plate is calculated in the FEM analysis step S3 as shown in FIG.
  • the true strain ⁇ compression in compressive deformation given by the above formula (1) is calculated as the maximum plate thickness increase
  • the maximum plate thickness hc and the minimum plate thickness ht in tensile deformation is calculated as a relative plate thickness reduction amount.
  • the maximum plate thickness increase amount and the relative plate thickness decrease amount calculated in this manner are acquired as crack determination parameters.
  • Table 1 shows the maximum plate thickness increase calculated as a crack determination parameter for each forming condition by FEM analysis of a basic forming test in which the thin metal plate 21 shown in FIG. and the results of the amount of relative plate thickness reduction.
  • the crack determination parameter plotting step S7 includes the presence or absence of cracks obtained for various molding conditions in the basic molding test step S1, and the various molding conditions in the crack determination parameter acquisition step S5. and the crack determination parameter, and plotted on two-dimensional coordinates with the maximum plate thickness increase amount and the relative plate thickness decrease amount as respective axes.
  • the plots marked with ⁇ indicate that cracks did not occur in the basic forming test step S1
  • the plots marked with x indicate that cracks occurred in the basic forming test step S1.
  • the forming limit line creation step S9 is based on the distribution of the presence or absence of crack generation plotted on the two-dimensional coordinates in the crack determination parameter plotting step S7, and the portion where the thin metal plate deforms along the deformation path that changes from compressive deformation to tensile deformation. This is a step of creating a forming limit line that distinguishes whether or not cracks occur.
  • the forming limit line may be created, for example, by fitting a functional expression that approximates the boundary between cracking and non-cracking in the crack determination parameter.
  • the forming limit line can be formulated as a high-dimension (eg, cubic) inverse function.
  • a crack determination parameter indicating the occurrence of a crack is extracted, and a high-order inverse function is assumed as a forming limit line that smoothly connects the extracted crack determination parameters. Then, the forming limit line can be created by determining the coefficient of the inverse function so that the sum of squared error of the inverse function assumed to be the extracted crack determination parameter is minimized.
  • the press-forming limit line acquisition method it is possible to obtain a forming limit line for determining whether or not cracks occur in a thin metal plate that is deformed along a deformation path that changes from compressive deformation to tensile deformation. can. Then, by using the forming limit line obtained by the press forming limit line acquisition method, cracks can be generated based on the change in plate thickness at the part where the deformation path that changes from compressive deformation to tensile deformation occurs in the press forming process. It is possible to determine the presence/absence and establish press molding conditions that enable stable press molding.
  • the press forming limit line acquisition method was to perform drawing using the die 1 shown in FIG. 3 as a basic forming test for thin metal plates.
  • the thin metal plate is compressively deformed in the direction along the outer edge of the die hole portion 5a, and then tensilely deformed in the direction in which the thin metal plate is pushed into the die hole portion 5a.
  • the direction of compressive deformation in the secondary path does not match the direction of tensile deformation in the secondary path.
  • the basic molding test in the basic molding test step S1 is not limited to a uniaxial compression-tension test in which the compression direction and the tension direction are the same.
  • a drawing process in which the pulling directions do not match may also be used.
  • the forming conditions can be changed by changing the inflow resistance of the metal flow toward the die hole 5a (see FIG. 3) of the thin metal plate.
  • the molding conditions it is possible to change the maximum plate thickness increase amount due to compressive deformation and the relative plate thickness decrease amount due to tensile deformation.
  • the size of the thin metal plate is increased in order to set the forming condition to increase the inflow resistance of the material flow toward the die hole portion 5a of the thin metal plate.
  • the die shoulder radius of the die shoulder 5b is smaller than the plate thickness of the thin metal plate, thickness reduction due to tensile deformation after compressive deformation will occur. is abruptly accelerated and leads to cracking, it is not possible to properly determine whether or not cracking has occurred. Therefore, the die shoulder radius of the die 5 is preferably several times or more the thickness of the thin metal plate.
  • the mold 1 shown in FIG. 3 was used to form a rectangular container
  • the mold 31 shown in FIG. 7 was used to form a cylindrical container.
  • the crack determination parameter acquisition step S5 obtains the true strain ⁇ compression in compressive deformation given by the formula (1) as the maximum plate thickness increase, and the true strain ⁇ given by the formula (2)
  • the tension after compression was obtained as the amount of relative thickness reduction.
  • the maximum plate thickness increase amount and the relative plate thickness decrease amount obtained as crack determination parameters are, for example, the nominal strain converted from the true strain in compressive deformation and tensile deformation after compressive deformation,
  • the true strain in the plate thickness direction in compressive deformation may be positive, and the true strain in the plate thickness direction in tensile deformation may be calculated as negative.
  • the above explanation is the result when the 980 MPa class steel plate was used as the test material for the thin metal plate, but the present invention does not limit the material strength and thickness of the thin metal plate.
  • the material is not limited to a steel plate, but may be another metal sheet.
  • a metal sheet was drawn into a cylindrical columnar container with a bottom (not shown) using a mold 31 shown in FIG. Determination was made using the forming limit line (Fig. 6) obtained by the basic forming test in which drawing was performed into a rectangular tube shape described in the mode.
  • a steel plate with a tensile strength of 980 MPa and a thickness of 1.4 mm was used as the test material for the thin metal plate, and the thin metal plate 21 having the shape and dimensions shown in Fig. 5 was used.
  • the die 31 includes a punch 33, a die 35, and a blank holder 37.
  • the punch shoulder radius of the punch shoulder portion 33a is R12 mm
  • the die shoulder radius of the die shoulder portion 35b is R5 mm.
  • the wrinkle pressing force by the blank holder 37 was set to 5 tonf.
  • Table 2 shows the presence or absence of cracks obtained by drawing a cylindrical columnar container with a bottom, and the results of crack determination parameters (maximum plate thickness increase and relative plate thickness decrease) obtained by FEM analysis.
  • the press forming limit in the process of press forming a thin metal plate, can be obtained to determine the presence or absence of cracks at the portion where the deformation path of the thin metal plate changes from compressive deformation to tensile deformation.
  • a line acquisition method can be provided.

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Abstract

A method for acquiring a press forming limit line according to the present invention comprises: a step (S1) for conducting a basic forming test to acquired the presence or absence of occurrence of cracking in a place of a thin metal sheet where a deformation path transitions from compression deformation to tension deformation; a step (S3) for calculating a sheet thickness change amount in the basic forming test on the thin metal sheet by means of FEM analysis; a step (S5) for determining, from the calculated sheet thickness change amount, the maximum sheet thickness increase amount in the thin metal sheet under compression deformation and a relative sheet thickness decrease amount in the thin metal sheet under tension deformation following the compression deformation, as cracking determination parameters; a step (7) for plotting the presence or absence of occurrence of cracking, in association with the cracking determination parameters on a two-dimensional coordinate system; and a step (S9) for generating a forming limit line that sectionalizes the presence or absence of occurrence of cracking on the basis of the distribution of the plotted presence or absence of occurrence of cracking.

Description

プレス成形限界線取得方法Press forming limit line acquisition method
　本発明は、金属薄板（metal　sheet）のプレス成形加工（press　forming）において、金属薄板の変形経路（deformation　path）が圧縮変形（compressive　deformation）から引張変形（tensile　deformation）に変化する部位における割れ（fracture）発生の有無を判定するための成形限界線（forming　limit　diagram）を求めるプレス成形限界線取得方法に関する。 In the press forming of a metal sheet, the present invention relates to cracking ( The present invention relates to a press forming limit line acquisition method for obtaining a forming limit diagram for determining the presence or absence of fracture.
　近年のエネルギー・地球環境問題への対応として、自動車の燃費向上を目的とした車体（automotive　body）の軽量化（weight　reduction）と衝突安全性（collision　safety）への要求が高まっている。これらの要求に応えるため、車体の軽量化を目的とした高強度鋼板（high-strength　steel　sheet）の適用拡大が進んでいる。そして、衝突性能（crash　worthiness）と車体の軽量化を両立させるべく、高張力鋼板を様々な形状の自動車部品に成形する技術の開発が一層求められている。また、先進各国がガソリン車の撤廃目標を掲げるなど、動力の転換も急速に進んでおり、特に電気自動車へのシフトが顕著である。電気自動車はバッテリーを車体に積む必要がある。このため、今後、バッテリーケースのような金属薄板を深絞り（deep　drawing）加工した自動車部品の需要が急増する可能性があり、このような需要に対応するプレス成形技術の開発が急務である。 In recent years, as a response to energy and global environmental issues, there is a growing demand for weight reduction and collision safety of automotive bodies aimed at improving fuel efficiency. In order to meet these demands, the application of high-strength steel sheets is being expanded to reduce the weight of vehicle bodies. In order to achieve both crash worthiness and vehicle weight reduction, there is a growing demand for the development of technology for forming high-strength steel sheets into automobile parts of various shapes. In addition, advanced countries have set goals for the abolition of gasoline vehicles, and the shift to power is progressing rapidly, and the shift to electric vehicles is particularly noticeable. Electric vehicles require batteries to be installed in the vehicle. For this reason, it is possible that the demand for automotive parts such as battery cases that are made by deep drawing thin metal sheets will increase rapidly in the future, and there is an urgent need to develop press molding technology to meet such demand.
　プレス成形時の最も大きな課題として、プレス成形過程において発生する割れが挙げられる。一般的に、プレス成形時に割れを生じさせるプレス成形の形態は、曲げ変形（bending　deformation）、伸びフランジ変形（stretch　flange　forming）、絞り変形（drawing　deformation）及び張出変形（bulging　deformation）の４種に分類できる。そして、これらのプレス成形の形態において、割れ発生の有無を予め判定する技術がいくつか提案されている。例えば、曲げ変形における割れ発生を判定する方法として、Ｖ曲げ試験（V-bending　test）の割れ発生時における曲げ外側表面におけるひずみ（strain）量から曲げ変形による割れを判定する方法が開示されている（特許文献１）。また、伸びフランジ変形における割れ発生を判定する方法として、穴広げ試験（hole　expansion　test）後のせん断縁（sheared　edge）近傍におけるひずみ勾配（strain　gradient）から、伸びフランジ（stretch　flange）部の板縁（sheet　edge）における割れの成形限界を算出する方法が開示されている（特許文献２）。 The biggest issue during press forming is the cracking that occurs during the press forming process. In general, there are four forms of press forming that cause cracks during press forming: bending deformation, stretch flange forming, drawing deformation, and bulging deformation. can be classified into In addition, several techniques have been proposed for determining in advance whether or not cracks have occurred in these forms of press molding. For example, as a method for determining the occurrence of cracks due to bending deformation, a method of determining cracks due to bending deformation from the amount of strain (strain) on the outer surface of the bend when cracking occurs in a V-bending test is disclosed. (Patent Document 1). In addition, as a method for determining the occurrence of cracks in stretch flange deformation, from the strain gradient near the sheared edge after the hole expansion test, the sheet edge of the stretch flange A method for calculating the forming limit of cracks at (sheet edge) is disclosed (Patent Document 2).
　さらに、絞り変形及び張出変形における割れ発生の判定には、成形限界線図（Forming　Limit　Diagram；FLD）が広く利用されている（非特許文献１）。FLDは簡易な成形試験で得ることができるうえ、スクライブドサークル（scribed　circle）や各種ドットパターンを印字した金属薄板（ブランク（blank））を用いたプレス成形品のプレス成形加工において、スクライブドサークルやドットパターン等の印字形状の変化に基づいて金属薄板におけるひずみ分布を測定することで、実際のプレス成形品での割れ発生の有無の判定に容易に適用することができる。また、多くの商用のCAE（Computer　Aided　Engineering）ソルバー（solver）にも、プレス成形シミュレーション（press　forming　simulation）で求めた結果を用いてFLDにより割れ発生の有無を判定する機能が実装されている。 Furthermore, a forming limit diagram (FLD) is widely used to determine the occurrence of cracks in drawing deformation and bulging deformation (Non-Patent Document 1). FLD can be obtained by a simple molding test, and in the press molding process of press-molded products using thin metal plates (blanks) printed with scribed circles and various dot patterns, scribed circles By measuring the strain distribution in the thin metal plate based on the change in the print shape such as the dot pattern, it can be easily applied to determine the presence or absence of cracks in the actual press-molded product. In addition, many commercial CAE (Computer Aided Engineering) solvers are also equipped with a function to determine the presence or absence of cracks by FLD using the results obtained from press forming simulation.
特開２０１３－１２８９５６号公報JP 2013-128956 A 特開２００９－２０４４２７号公報JP 2009-204427 A
　しかしながら、FLDにより割れ発生の有無を判定することができるのは、絞り成形や張出成形において一定の変形経路で生じる割れである。プレス成形中に変形経路が圧縮変形から引張変形へと変化する場合においては、一定の変形経路で変形する場合とは成形限界が異なるため、FLDにより割れ発生の有無を判定することができない。また、実際のプレス成形品のプレス成形において変形経路が一次経路から二次経路へと変化する場合、一次経路と二次経路それぞれの変形パターン（圧縮変形、引張変形）の組み合わせや、一次経路から二次経路へと変化するひずみ分配比の違いにより、無数の変形経路が考えられる。このため、変形経路が一定の簡易な成形試験に基づいて作成したFLDを用いて割れ発生の有無を判定するのには限界があった。さらに、プレス成形加工において金属薄板の圧縮変形中にしわ（wrinkles）が発生すると、しわの発生する箇所とその周囲の応力（stress）が変化する。このため、発生したしわによる成形限界への影響も考慮する必要があるが、FLDではこのような影響を考慮することはできなかった。 However, the presence or absence of cracks can be determined by FLD only for cracks that occur along a certain deformation path in draw forming and stretch forming. When the deformation path changes from compressive deformation to tensile deformation during press forming, the forming limit is different from the case of deformation along a constant deformation path, so it is not possible to determine the presence or absence of cracks by FLD. In addition, when the deformation path changes from the primary path to the secondary path in the press molding of an actual press-formed product, the combination of the deformation patterns (compression deformation, tensile deformation) of the primary path and the secondary path, or the deformation from the primary path A myriad of deformation paths are possible due to differences in strain distribution ratios that change to secondary paths. For this reason, there is a limit to judging the presence or absence of cracks using an FLD prepared based on a simple molding test with a fixed deformation path. Furthermore, when wrinkles are generated during compressive deformation of the metal sheet in the press forming process, the stress at the location where the wrinkles are generated and the surrounding area changes. For this reason, it is necessary to consider the influence of generated wrinkles on the forming limit, but it was not possible to consider such an influence with FLD.
　特に、実際の自動車車体部品（automotive　part）のように複雑な形状のプレス成形の絞り加工（drawing）によるプレス成形において変形経路が圧縮変形から引張変形に転じる場合、一次経路での圧縮変形時の圧縮変形量が大きいと、その後の二次経路での引張変形量が小さい場合でも割れが発生し易くなり、FLDを用いて適切な割れ発生の有無を判定ができない場合があった。 In particular, when the deformation path changes from compression deformation to tensile deformation in press forming by drawing of press forming of complicated shapes like actual automotive parts, during compression deformation in the primary path If the amount of compressive deformation is large, cracking is likely to occur even if the amount of tensile deformation in the subsequent secondary path is small, and it may not be possible to appropriately determine the presence or absence of cracking using FLD.
　本発明は、以上の問題を解決すべくなされたものであり、その目的は、金属薄板のプレス成形過程において、金属薄板の変形経路が圧縮変形から引張変形に変化する部位の割れの発生の有無を判定する成形限界線を求めることが可能なプレス成形限界線取得方法を提供することにある。 The present invention has been made to solve the above problems, and its object is to determine whether or not cracking occurs at a portion where the deformation path of the thin metal plate changes from compressive deformation to tensile deformation during the press forming process of the thin metal plate. To provide a press forming limit line acquisition method capable of obtaining a forming limit line for judging
　本発明に係るプレス成形限界線取得方法は、金属薄板のプレス成形加工において、前記金属薄板の変形経路が圧縮変形から引張変形に変化する部位の割れ発生の有無を判定するための成形限界線を求めるものであって、前記金属薄板を前記変形経路で変形させる基礎成形試験（basic　forming　test）を種々の成形条件（forming　condition）で行い、該種々の成形条件について、前記金属薄板における前記変形経路が圧縮変形から引張変形に変化する部位の割れ発生の有無を取得する基礎成形試験工程と、前記金属薄板の前記基礎成形試験を解析対象とするＦＥＭ解析（finite　element　analysis）を前記種々の成形条件について行い、前記金属薄板の板厚の変化を算出するＦＥＭ解析工程と、該ＦＥＭ解析工程において算出した前記金属薄板の板厚の変化に基づいて、前記種々の成形条件について、前記変形経路の圧縮変形において前記金属薄板が最大板厚に至るまでの板厚の変化量である最大板厚増加量（maximum　thickness　increment）と、前記変形経路において圧縮変形から引張変形へと変化して前記金属薄板が最大板厚から最小板厚に至るまでの板厚の変化量である相対板厚減少量（relative　thickness　decrement）と、を割れ判定パラメータ（forming　clack　estimation　parameter）として求める割れ判定パラメータ取得工程と、前記基礎成形試験工程において前記種々の成形条件について取得した割れの発生の有無と、前記割れ判定パラメータ取得工程において前記種々の成形条件について求めた割れ判定パラメータと、を関連付けて、前記最大板厚増加量及び前記相対板厚減少量を各軸とする二次元座標（two-dimensional　coordinate）上にプロットする割れ判定パラメータプロット工程と、該二次元座標上にプロットした割れ発生の有無の分布に基づいて、前記変形経路で前記金属薄板が変形する部位の割れ発生の有無を区分する成形限界線を作成する成形限界線作成工程と、を含む。 A press-forming limit line acquisition method according to the present invention is a method for obtaining a forming limit line for determining whether or not a crack occurs at a portion where a deformation path of a thin metal plate changes from compressive deformation to tensile deformation in press-forming of a thin metal plate. A basic forming test in which the metal sheet is deformed along the deformation path is performed under various forming conditions, and the deformation path in the metal sheet is evaluated for the various forming conditions. A basic forming test process to acquire the presence or absence of cracking in the part where the deformation changes from compression deformation to tensile deformation, and FEM analysis (finite element analysis) for the analysis target of the basic forming test of the metal sheet under the various forming conditions is performed, and based on the FEM analysis step of calculating the change in the thickness of the metal thin plate, and the change in the thickness of the metal thin plate calculated in the FEM analysis step, the compression of the deformation path for the various forming conditions A maximum thickness increment, which is the amount of change in the thickness of the metal sheet until it reaches the maximum thickness in deformation, and a change from compressive deformation to tensile deformation in the deformation path, and the metal sheet is A crack determination parameter acquiring step of obtaining a relative thickness decrement, which is a change in plate thickness from the maximum plate thickness to the minimum plate thickness, as a forming crack estimation parameter; The presence or absence of cracks obtained for the various forming conditions in the basic forming test step and the crack determination parameters obtained for the various forming conditions in the crack determination parameter acquisition step are associated, and the maximum plate thickness increase amount And a crack determination parameter plotting step of plotting on two-dimensional coordinates with the relative plate thickness reduction amount as each axis, and based on the distribution of the presence or absence of crack generation plotted on the two-dimensional coordinates, and a forming limit line creating step for creating a forming limit line for determining whether or not a crack is generated in a portion where the thin metal plate is deformed along the deformation path.
　前記基礎成形試験工程は、前記金属薄板を絞り加工することにより該金属薄板を前記変形経路で変形させるとよい。 In the basic forming test step, the thin metal plate is preferably deformed along the deformation path by drawing the thin metal plate.
　前記基礎成形試験工程は、前記金属薄板の絞り加工において、前記金属薄板の形状、又は、前記金属薄板に付与するしわ押さえ力（blank　holder　pressure）を変更することにより、前記種々の成形条件を設定するとよい。 In the basic forming test step, the various forming conditions are set by changing the shape of the thin metal plate or the blank holder pressure applied to the thin metal plate in the drawing process of the thin metal plate. do it.
　本発明においては、金属薄板を圧縮変形から引張変形へと変化する変形経路で変形させる基礎成形試験により取得した金属薄板における割れ発生の有無と、基礎成形試験を対象とするＦＥＭ解析により割れ判定パラメータとして求めた圧縮変形における金属薄板の最大板厚増加量及び引張変形における相対板厚減少量と、を関連付けて二次元座標上にプロットし、該プロットした割れ発生の有無の分布に基づいて割れ発生の有無を区分する成形限界線を作成することで、金属薄板における変形経路が圧縮変形から引張変形に変化する部位の割れ発生の有無を判定する成形限界線を求めることができる。 In the present invention, the presence or absence of cracks in the thin metal plate obtained by a basic forming test in which the thin metal plate is deformed along a deformation path that changes from compressive deformation to tensile deformation, and the crack determination parameter by FEM analysis for the basic forming test. The maximum plate thickness increase amount of the thin metal plate in compressive deformation and the relative plate thickness decrease amount in tensile deformation obtained as are plotted on a two-dimensional coordinate, and crack generation is based on the plotted distribution of the presence or absence of crack generation. By creating a forming limit line that distinguishes the presence or absence of, it is possible to obtain a forming limit line that determines the presence or absence of cracking at a portion where the deformation path of the thin metal sheet changes from compressive deformation to tensile deformation.
図１は、本発明の実施の形態に係るプレス成形限界線取得方法における処理の流れを説明するフロー図である。FIG. 1 is a flowchart for explaining the flow of processing in the press forming limit line acquisition method according to the embodiment of the present invention. 図２は、本発明の実施の形態に係るプレス成形限界線取得方法において、金属薄板の変形経路が圧縮変形から引張変形にする部位における金属薄板の板厚の変化と、割れ発生の有無を判定する割れ判定パラメータとして求める最大板厚増加量及び相対板厚減少量と、を説明するグラフである。FIG. 2 shows a change in thickness of the thin metal plate at a portion where the deformation path of the thin metal plate changes from compressive deformation to tensile deformation, and determination of the presence or absence of cracking in the press forming limit line acquisition method according to the embodiment of the present invention. 4 is a graph for explaining the maximum plate thickness increase amount and the relative plate thickness decrease amount obtained as crack determination parameters. 図３は、本発明の実施の形態と実施例において、基礎成形試験として金属薄板を角筒状の底付き柱状容器に絞り加工する金型の一例を説明する図である（（ａ）斜視図、（ｂ）成形方向に平行な断面図、（ｃ）成形方向に直交する断面図）。FIG. 3 is a diagram illustrating an example of a mold for drawing a thin metal plate into a rectangular cylindrical container with a bottom as a basic forming test in the embodiment and examples of the present invention ((a) perspective view). , (b) cross-sectional view parallel to the forming direction, (c) cross-sectional view perpendicular to the forming direction). 図４は、金属薄板を角筒状の底付き柱状容器に絞り加工した場合において、変形経路が圧縮変形から引張変形に変化する部位を説明する図である。FIG. 4 is a diagram for explaining a portion where the deformation path changes from compressive deformation to tensile deformation when a thin metal plate is drawn into a square tube-shaped columnar container with a bottom. 図５は、本発明の実施の形態及び実施例において用いた金属薄板の形状及び寸法を説明する図である。FIG. 5 is a diagram for explaining the shape and dimensions of the thin metal plate used in the embodiments and examples of the present invention. 図６は、実施例において、金属薄板を角筒状の底付き柱状容器に絞り加工する基礎成形試験により求めた割れ発生の有無を、基礎成形試験のＦＥＭ解析により割れ判定パラメータとして求めた最大板厚増加量及び相対板厚減少量に関連付けて二次元座標平面上にプロットした結果と、プロットした割れ発生の有無の分布に基づいて作成した成形限界線と、を示すグラフである。FIG. 6 shows the presence or absence of crack generation determined by a basic forming test in which a thin metal plate is drawn into a rectangular cylindrical columnar container with a bottom in the example, and the maximum plate obtained as a crack determination parameter by FEM analysis of the basic forming test. 4 is a graph showing results plotted on a two-dimensional coordinate plane in association with the amount of increase in thickness and the amount of relative thickness decrease, and a forming limit line created based on the plotted distribution of presence or absence of cracking. 図７は、実施例において、基礎成形試験として金属薄板を円筒状の底付き容器に絞り加工する金型の一例を説明する図である（（ａ）斜視図、（ｂ）成形方向に平行な断面図、（ｃ）成形方向に直交する断面図）。FIG. 7 is a diagram illustrating an example of a mold for drawing a thin metal plate into a cylindrical container with a bottom as a basic forming test in Examples ((a) perspective view, (b) parallel to the forming direction). Cross-sectional view, (c) Cross-sectional view perpendicular to the molding direction). 図８は、実施例において、金属薄板を円筒状に絞り加工する基礎成形試験により求めた割れ発生の有無と、実施の形態において金属薄板を角筒状に絞り加工する基礎成形試験とＦＥＭ解析により求めた成形限界線と、を示すグラフである。FIG. 8 shows the presence or absence of cracking obtained by a basic forming test in which a thin metal plate is drawn into a cylindrical shape in the example, and the basic forming test and FEM analysis in which the thin metal plate is drawn into a square tube in the embodiment. It is a graph showing the obtained forming limit line.
＜発明に至った経緯＞
　本発明の実施の形態に係るプレス成形限界線取得方法について説明するに先立ち、本発明を着想するに至った経緯を説明する。 <Circumstances leading to the invention>
Prior to explaining the press forming limit line acquisition method according to the embodiment of the present invention, the circumstances leading to the idea of the present invention will be explained.
　発明者らは、プレス成形中に金属薄板の変形経路が圧縮変形から引張変形へと変化する場合においては、一定の変形経路で変形する場合とは成形限界が異なる原因について鋭意検討した。そして、一次経路での圧縮変形による変形量が大きいと、その後の二次経路での引張変形による変形量が小さくても材料割れ（crack）（破断（fracture））が発生しやすいことに着目し、一次経路では圧縮変形による加工硬化（work　hardening）が影響して材料の延性（ductility）等の変形特性が低下し（ダメージを受け）、その後の二次経路での引張変形により容易に割れが発生する、とのメカニズムを推定した。そこで、一次経路での圧縮変形による圧縮変形量と、二次経路での引張変形による引張変形量、のそれぞれを、金属薄板の板厚方向の真ひずみ（true　strain）（板厚変化量）で表すことを想到した。 The inventors diligently studied the reason why the forming limit is different when the deformation path of the thin metal plate changes from compressive deformation to tensile deformation during press forming compared to when deformation follows a constant deformation path. Then, we focused on the fact that if the amount of deformation due to compressive deformation in the primary path is large, material cracks (fractures) are likely to occur even if the amount of deformation due to tensile deformation in the subsequent secondary path is small. In the primary path, work hardening due to compressive deformation affects the material's ductility and other deformation characteristics (damage), and subsequent tensile deformation in the secondary path causes cracks to easily occur. We presumed the mechanism that it occurs. Therefore, the amount of compressive deformation due to compressive deformation in the primary path and the amount of tensile deformation due to tensile deformation in the secondary path are each expressed as the true strain (thickness change amount) in the sheet thickness direction of the thin metal sheet. thought to express.
　図２に、金属薄板を圧縮変形から引張変形へと変化する変形経路で変形させた場合の板厚の変化を模式的に表した図を示す。図２において、縦軸は圧縮変形から引張変形へと変化する変形経路での金属薄板の板厚方向の真ひずみ（-ln（変形後板厚／変形前板厚））で与えられる板厚減少率（thickness　reduction　ratio）、横軸は金属薄板の変形開始からの経過時間である。このとき、（i）一次経路での圧縮変形による板厚方向の真ひずみεcompressionと、（ii）二次経路での引張変形による板厚方向の真ひずみεtension　after　compressionは、それぞれ、式（１）及び式（２）で与えられる。 FIG. 2 is a diagram schematically showing changes in plate thickness when a thin metal plate is deformed along a deformation path that changes from compressive deformation to tensile deformation. In Fig. 2, the vertical axis represents the reduction in thickness given by the true strain (-ln (thickness after deformation/thickness before deformation)) in the thickness direction of the thin metal sheet on the deformation path that changes from compressive deformation to tensile deformation. thickness reduction ratio, the horizontal axis is the elapsed time from the start of deformation of the metal sheet. At this time, (i) the true strain ε compression in the thickness direction due to compressive deformation in the primary path and (ii) the true strain ε tension after compression in the thickness direction due to tensile deformation in the secondary path are given by the formula ( 1) and equation (2).
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　そして、圧縮変形と引張変形それぞれにおける真ひずみを圧縮変形量及び引張変形量として求め、これらの変形量に基づいて圧縮変形から引張変形に変化する変形経路で金属薄板を変形させたときの当該金属薄板における割れ発生の有無を判定することを着想した。 Then, the true strain in compressive deformation and tensile deformation is obtained as the amount of compressive deformation and the amount of tensile deformation, respectively. The idea was to determine the presence or absence of cracks in thin plates.
　しかし、金属薄板を圧縮変形から引張変形に変化する変形経路で変形させる成形試験により金属薄板における割れの発生の有無を求めることはできても、当該変形経路における金属薄板の圧縮変形による最大板厚（maximum　thickness）hc及び引張変形による最小板厚（minimum　thickness）htを直接実測することは困難である。 However, although it is possible to determine the presence or absence of cracks in a thin metal sheet by a forming test in which the thin metal sheet is deformed along a deformation path that changes from compressive deformation to tensile deformation, the maximum thickness of the thin metal sheet due to compressive deformation along the deformation path It is difficult to directly measure the (maximum thickness) hc and the minimum thickness (minimum thickness) ht due to tensile deformation.
　そこで、圧縮変形から引張変形に変化する変形経路での金属薄板の変形を再現したＦＥＭ（Finite　Element　Method；有限要素法）解析を行い、金属薄板における圧縮変形から引張変形に変化する部位に相当する要素の板厚の変化を算出し、該算出した板厚の変化から最大板厚及び最小板厚を求めることとした。 Therefore, FEM (Finite Element Method) analysis was performed to reproduce the deformation of the metal sheet along the deformation path that changes from compressive deformation to tensile deformation. A change in the plate thickness of the element is calculated, and the maximum plate thickness and the minimum plate thickness are obtained from the calculated plate thickness change.
　本発明は、上記の検討に基づいてなされたものであり、以下、本発明の実施の形態について説明する。 The present invention has been made based on the above studies, and the embodiments of the present invention will be described below.
＜プレス成形限界線取得方法＞
　本発明の実施の形態に係るプレス成形限界線取得方法は、金属薄板のプレス成形加工において、金属薄板における変形経路が圧縮変形から引張変形に変化する部位の割れ発生の有無を判定するための成形限界線を求めるものであって、図１に示すように、基礎成形試験工程Ｓ１と、ＦＥＭ解析工程Ｓ３と、割れ判定パラメータ取得工程Ｓ５と、割れ判定パラメータプロット工程Ｓ７と、成形限界線作成工程Ｓ９と、を含む。以下、上記の各工程について説明する。 <Method for obtaining press forming limit line>
A press-forming limit line acquisition method according to an embodiment of the present invention is a method for determining whether or not a crack occurs at a portion where a deformation path in a thin metal plate changes from compressive deformation to tensile deformation in press-forming of a thin metal plate. A limit line is obtained, and as shown in FIG. 1, a basic forming test step S1, an FEM analysis step S3, a crack determination parameter acquisition step S5, a crack determination parameter plotting step S7, and a forming limit line creation step. and S9. Each of the above steps will be described below.
≪基礎成形試験工程≫
　基礎成形試験工程Ｓ１は、金属薄板を圧縮変形から引張変形に変化する変形経路で変形させる基礎成形試験を種々の成形条件で行い、種々の成形条件について、金属薄板における変形経路が圧縮変形から引張変形に変化する部位の割れ発生の有無を取得する工程である。 ≪Basic molding test process≫
In the basic forming test step S1, a basic forming test is performed in which the thin metal plate is deformed along a deformation path that changes from compression deformation to tensile deformation under various forming conditions. This is a step of obtaining whether or not cracks have occurred in the portion that changes to deformation.
　本実施の形態では、図３に例示するような、パンチ（punch）３とダイ（die）５とブランクホルダー（blank　holder）７とを備えた金型（tool　of　press　forming）１を用いて金属薄板（図示なし）を絞り加工する基礎成形試験を行う。 In this embodiment, metal is formed using a tool of press forming 1 equipped with a punch 3, a die 5 and a blank holder 7, as illustrated in FIG. A basic forming test is performed by drawing a thin plate (not shown).
　絞り加工とは、金属薄板の端部をダイ５とブランクホルダー７とにより挟持しながらパンチ３をダイ５のダイ穴部（die　hole　portion）５ａに押し込むことで金属薄板を中央に引き寄せて、平らな金属薄板から角筒状の底付き柱状容器１１を成形することをいう。なお、図４は、底付き柱状容器１１におけるコーナー部（corner　portion）１１ａを中心とした1/4の領域を表示したものである。 The drawing process involves pressing the punch 3 into the die hole portion 5a of the die 5 while holding the edge of the metal sheet between the die 5 and the blank holder 7, thereby pulling the metal sheet toward the center and flattening it. It refers to forming a rectangular tubular columnar container 11 with a bottom from a thin metal plate. FIG. 4 shows a 1/4 area around the corner portion 11a of the columnar container 11 with the bottom.
　金型１を用いて金属薄板を底付き柱状容器１１に成形する絞り加工においては、まず、金属薄板がパンチ３によりダイ穴部５ａに向けて引き込まれるため、金属薄板はダイ穴部５ａに向かって流動し、ダイ穴部５ａの外縁周方向に沿って圧縮変形を受ける。そして、金属薄板における圧縮変形を受けた部位は、パンチ肩部３ａに接してダイ穴部５ａに押し込まれることで引張変形を受け、ダイ穴部５ａへの引き込み後においても引張変形を受ける。その結果、底付き柱状容器１１のコーナー部１１ａとその周辺における縦壁部（side　wall　portion）１５は、圧縮変形から引張変形へと変化する変形経路で成形される。 In the drawing process for forming the thin metal plate into the bottomed columnar container 11 using the die 1, the thin metal plate is first drawn toward the die hole portion 5a by the punch 3, so that the thin metal plate moves toward the die hole portion 5a. , and undergoes compression deformation along the circumferential direction of the outer edge of the die hole portion 5a. The portion of the thin metal sheet that has undergone compressive deformation is subjected to tensile deformation when it is pushed into the die hole portion 5a in contact with the punch shoulder portion 3a, and is also subjected to tensile deformation after being drawn into the die hole portion 5a. As a result, the corner portion 11a of the bottomed columnar container 11 and the side wall portion 15 around it are molded along a deformation path that changes from compressive deformation to tensile deformation.
　基礎成形試験における種々の成形条件は、金属薄板の形状及び寸法、ブランクホルダーによる金属薄板のしわ押さえ力、金属薄板におけるダイとブランクホルダーにより挟持される部位の潤滑条件（lubricated　conditions）（潤滑油（lubricating　oil）の種類、粘度（viscosity　coefficient）、供給量、極圧添加剤（extreme　pressure　additive）の添加等）、金属薄板に付与するビード形状（bead-shape）等を変更して適宜設定すればよい。 Various forming conditions in the basic forming test include the shape and dimensions of the metal sheet, the wrinkle holding force of the metal sheet by the blank holder, and the lubricated conditions (lubricating oil ( The type of lubricating oil, viscosity coefficient, supply amount, addition of extreme pressure additive, etc.), bead-shape given to the thin metal plate, etc. can be changed and set appropriately. good.
　特に、図３に示す金型を用いて絞り加工する基礎成形試験では、金属薄板の形状、又は、ブランクホルダー７により金属薄板に付与するしわ押さえ力を変更することで、容易に成形条件を変更することができる。 In particular, in the basic forming test in which drawing is performed using the die shown in FIG. 3, the forming conditions can be easily changed by changing the shape of the metal sheet or the wrinkle holding force applied to the metal sheet by the blank holder 7. can do.
　本実施の形態では、パンチ肩部（shoulder　part　of　a　punch）３ａのパンチ肩半径（radius　of　shoulder　part）をR12mm、ダイ肩部（shoulder　part　of　a　die）５ｂのダイ肩半径（radius　of　die　part）をR5mm、コーナー部１１ａのコーナー半径をR25mmとした。そして、金属薄板には、板厚1.4mm、980MPa級（MPa-class）の鋼板（steel　sheet）を供試材とし、図５に示す形状及び寸法の金属薄板２１を用い、また、ブランクホルダー７によるしわ押さえ力は5～20tonfの範囲で変更して、基礎成形試験における種々の成形条件を設定した。 In this embodiment, the radius of the punch shoulder part (shoulder part of a punch) 3a is R12 mm, and the radius of the die part of the die shoulder part (shoulder part of a die) 5b is R12 mm. ) was set to R5 mm, and the corner radius of the corner portion 11a was set to R25 mm. As the thin metal plate, a steel sheet of 980 MPa class with a thickness of 1.4 mm was used as a test material. Various forming conditions in the basic forming test were set by changing the wrinkle-holding force in the range of 5 to 20 tonf.
　表１に、図５に示す金属薄板２１を角筒状の底付き柱状容器１１に絞り加工する基礎成形試験における成形条件（金属薄板の形状・寸法及びしわ押さえ力）と、割れ発生の有無を示す。 Table 1 shows the forming conditions (shape, size and wrinkle pressing force of the metal sheet) in the basic forming test for drawing the metal sheet 21 shown in FIG. show.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
≪ＦＥＭ解析工程≫
　ＦＥＭ解析工程Ｓ３は、金属薄板の基礎成形試験を解析対象とするＦＥＭ解析を種々の成形条件について行い、金属薄板の板厚の変化を算出する工程である。 <<FEM analysis process>>
The FEM analysis step S3 is a step of performing FEM analysis for various forming conditions with the basic forming test of the metal thin plate as the analysis target, and calculating changes in the plate thickness of the metal thin plate.
　本実施の形態において、ＦＥＭ解析工程Ｓ３におけるＦＥＭ解析は、図３に示す金型１を用いて金属薄板を角筒状の底付き柱状容器１１に絞り加工する基礎成形試験を解析対象とする。そして、ＦＥＭ解析工程Ｓ３における成形条件は、基礎成形試験工程Ｓ１における基礎成形試験と同じ成形条件とする。 In the present embodiment, the FEM analysis in the FEM analysis step S3 is for a basic forming test in which the metallic mold 1 shown in FIG. The molding conditions in the FEM analysis step S3 are the same molding conditions as the basic molding test in the basic molding test step S1.
　図２に、金属薄板における圧縮変形から引張変形に変化する部位の板厚の変化をＦＥＭ解析により算出した一例を示す。図２に示すように、圧縮変形する過程では金属薄板の板厚が増加して最大板厚hcに達し、圧縮変形後に引張変形する過程では板厚が減少する。ここで、引張変形における板厚の最小値を最小板厚htと表記する。 Fig. 2 shows an example of calculation by FEM analysis of changes in the plate thickness of a portion of a thin metal plate that changes from compressive deformation to tensile deformation. As shown in FIG. 2, the thickness of the thin metal sheet increases and reaches the maximum thickness hc in the process of compressive deformation, and decreases in the process of tensile deformation after compressive deformation. Here, the minimum value of plate thickness in tensile deformation is expressed as minimum plate thickness ht.
　ＦＥＭ解析工程Ｓ３は、基礎成形試験工程Ｓ１において割れの発生の有無を取得した金属薄板の部位に相当する要素の板厚の変化を算出する。 In the FEM analysis process S3, the change in the plate thickness of the element corresponding to the portion of the thin metal plate for which the presence or absence of cracking was obtained in the basic forming test step S1 is calculated.
≪割れ判定パラメータ取得工程≫
　割れ判定パラメータ取得工程Ｓ５は、ＦＥＭ解析工程Ｓ３において算出した金属薄板の板厚の変化に基づいて、種々の成形条件について、変形経路の圧縮変形において金属薄板が最大板厚hcに至るまでの板厚の変化量である最大板厚増加量と、変形経路において圧縮変形から引張変形へと変化して金属薄板が最大板厚hcから最小板厚htに至るまでの板厚の変化量である相対板厚減少量と、を割れ判定パラメータとして求める工程である。 ≪Crack determination parameter acquisition process≫
In the crack determination parameter acquisition step S5, based on the change in the thickness of the thin metal plate calculated in the FEM analysis step S3, the thickness of the thin metal plate until the thin metal plate reaches the maximum thickness hc in compressive deformation along the deformation path is obtained for various forming conditions. The maximum thickness increase amount, which is the amount of change in thickness, and the relative It is a step of obtaining the plate thickness reduction amount as a crack determination parameter.
　ＦＥＭ解析工程Ｓ３において図２に示すように金属薄板の板厚の変化が算出されている場合、割れ判定パラメータ取得工程Ｓ５は、金属薄板の初期の板厚h0と圧縮変形での最大板厚hcとを用いて、前述した式（１）により与えられる圧縮変形での真ひずみεcompressionを最大板厚増加量として算出し、最大板厚hcと引張変形での最小板厚htとを用いて、前述した式（２）により与えられる圧縮変形後の引張変形での真ひずみεtension　after　compressionを相対板厚減少量として算出する。そして、このように算出した最大板厚増加量と相対板厚減少量とを割れ判定パラメータとして取得する。 When the change in thickness of the thin metal plate is calculated in the FEM analysis step S3 as shown in FIG. Using and, the true strain ε compression in compressive deformation given by the above formula (1) is calculated as the maximum plate thickness increase, and using the maximum plate thickness hc and the minimum plate thickness ht in tensile deformation, The true strain ε tension after compression in tensile deformation after compressive deformation given by the above equation (2) is calculated as a relative plate thickness reduction amount. Then, the maximum plate thickness increase amount and the relative plate thickness decrease amount calculated in this manner are acquired as crack determination parameters.
　前記した表１に、図５に示す金属薄板２１を角筒状の底付き柱状容器１１に絞り加工する基礎成形試験のＦＥＭ解析により、各成形条件について割れ判定パラメータとして算出した最大板厚増加量及び相対板厚減少量の結果を示す。 Table 1 shows the maximum plate thickness increase calculated as a crack determination parameter for each forming condition by FEM analysis of a basic forming test in which the thin metal plate 21 shown in FIG. and the results of the amount of relative plate thickness reduction.
≪割れ判定パラメータプロット工程≫
　割れ判定パラメータプロット工程Ｓ７は、図６に一例として示すように、基礎成形試験工程Ｓ１において種々の成形条件について取得した割れの発生の有無と、割れ判定パラメータ取得工程Ｓ５において種々の成形条件について求めた割れ判定パラメータと、を関連付けて、最大板厚増加量及び前記相対板厚減少量を各軸とする二次元座標上にプロットする工程である。 ≪Crack determination parameter plotting process≫
As shown in FIG. 6 as an example, the crack determination parameter plotting step S7 includes the presence or absence of cracks obtained for various molding conditions in the basic molding test step S1, and the various molding conditions in the crack determination parameter acquisition step S5. and the crack determination parameter, and plotted on two-dimensional coordinates with the maximum plate thickness increase amount and the relative plate thickness decrease amount as respective axes.
　図６において、〇印のプロットは、基礎成形試験工程Ｓ１において割れ発生無しを、×印のプロットは基礎成形試験工程Ｓ１において割れ発生有りを示す。 In FIG. 6, the plots marked with ◯ indicate that cracks did not occur in the basic forming test step S1, and the plots marked with x indicate that cracks occurred in the basic forming test step S1.
≪成形限界線作成工程≫
　成形限界線作成工程Ｓ９は、割れ判定パラメータプロット工程Ｓ７において二次元座標上にプロットした割れ発生の有無の分布に基づいて、圧縮変形から引張変形に変化する変形経路で金属薄板が変形する部位の割れ発生の有無を区分する成形限界線を作成する工程である。 ≪Forming limit line creation process≫
The forming limit line creation step S9 is based on the distribution of the presence or absence of crack generation plotted on the two-dimensional coordinates in the crack determination parameter plotting step S7, and the portion where the thin metal plate deforms along the deformation path that changes from compressive deformation to tensile deformation. This is a step of creating a forming limit line that distinguishes whether or not cracks occur.
　図６に、割れ判定パラメータプロット工程Ｓ７において二次元座標上にプロットした割れ判定パラメータの分布に基づいて作成した成形限界線の一例を示す。 FIG. 6 shows an example of a forming limit line created based on the distribution of crack determination parameters plotted on two-dimensional coordinates in the crack determination parameter plotting step S7.
　成形限界線は、例えば、割れ判定パラメータにおいて、割れ発生有りと割れ発生なしとの境界を近似する関数式をフィッティングにより求めて作成してもよい。 The forming limit line may be created, for example, by fitting a functional expression that approximates the boundary between cracking and non-cracking in the crack determination parameter.
　本発明が対象としている、変形経路が圧縮変形から引張変形に変化する成形形態における割れは、最大板厚増加量が大きい場合には相対板厚減少量の限界値は低く、逆に、最大板厚増加量が小さい場合には相対板厚減少量の限界値は大きくなる。したがって、成形限界線は、高次（high　dimension）（例えば三次）の逆関数（inverse　function）として定式化することができる。 Cracking in a forming mode in which the deformation path changes from compression deformation to tensile deformation, which is the object of the present invention, has a low limit value for the relative plate thickness decrease when the maximum plate thickness increase is large, and conversely, the maximum plate thickness When the amount of increase in thickness is small, the limit value of the amount of relative thickness decrease is large. Therefore, the forming limit line can be formulated as a high-dimension (eg, cubic) inverse function.
　具体的には、割れ判定パラメータプロット工程Ｓ７においてプロットした割れ判定パラメータのうち割れ発生有りの割れ判定パラメータを抽出し、抽出した割れ判定パラメータを滑らかに結ぶ成形限界線として高次の逆関数を仮定し、抽出した割れ判定パラメータと仮定した逆関数の誤差二乗和（sum　of　squared　error）が最小になるように逆関数の係数を決定することにより、成形限界線を作成すればよい。 Specifically, among the crack determination parameters plotted in the crack determination parameter plotting step S7, a crack determination parameter indicating the occurrence of a crack is extracted, and a high-order inverse function is assumed as a forming limit line that smoothly connects the extracted crack determination parameters. Then, the forming limit line can be created by determining the coefficient of the inverse function so that the sum of squared error of the inverse function assumed to be the extracted crack determination parameter is minimized.
　成形限界線より上の領域にプロットされた割れ判定パラメータはすべて割れ発生有りでなければならないため、割れ発生有りと割れ発生なしの境界付近、すなわち、割れ発生有りの割れ判定パラメータのうち、各最大板厚増加量における最小の相対板厚減少量の割れ判定パラメータのプロットを抽出する。 Since all the crack determination parameters plotted in the area above the forming limit line must have cracks, near the boundary between cracks and no cracks, that is, among the crack determination parameters with cracks, each maximum Extract a plot of the crack determination parameter for the minimum relative thickness decrease in thickness increase.
　図６に示す成形限界線は、式（３）に示す三次の逆関数を仮定して作成したものであり、式（３）中の各係数の値は、a=2.1×10-10、b=8.9×10-12、c=2.0、d=0、e=0.01である。 The forming limit line shown in FIG. 6 was created assuming a cubic inverse function shown in formula (3), and the values of each coefficient in formula (3) are a = 2.1 × 10 -10 , b =8.9×10 −12 , c=2.0, d=0, e=0.01.
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　以上、本実施の形態に係るプレス成形限界線取得方法によれば、圧縮変形から引張変形へと変化する変形経路で変形される金属薄板の割れ発生の有無を判定する成形限界線を求めることができる。そして、プレス成形限界線取得方法により求めた成形限界線を用いることで、プレス成形過程において、圧縮変形から引張変形へと変化する変形経路が生じる部位の板厚の変化に基づいて割れの発生の有無を判定することができ、安定してプレス成形可能なプレス成形条件を確立することができる。 As described above, according to the press-forming limit line acquisition method according to the present embodiment, it is possible to obtain a forming limit line for determining whether or not cracks occur in a thin metal plate that is deformed along a deformation path that changes from compressive deformation to tensile deformation. can. Then, by using the forming limit line obtained by the press forming limit line acquisition method, cracks can be generated based on the change in plate thickness at the part where the deformation path that changes from compressive deformation to tensile deformation occurs in the press forming process. It is possible to determine the presence/absence and establish press molding conditions that enable stable press molding.
　本実施の形態に係るプレス成形限界線取得方法は、金属薄板の基礎成形試験として図３に示す金型１を用いて絞り加工を行うものであった。このような金属薄板の絞り加工においては、ダイ穴部５ａの外縁に沿った方向に圧縮変形し、その後、ダイ穴部５ａに金属薄板が押し込まれる方向に引張変形しているため、一次経路での圧縮変形の方向と、二次経路での引張変形の方向とが一致していない。 The press forming limit line acquisition method according to the present embodiment was to perform drawing using the die 1 shown in FIG. 3 as a basic forming test for thin metal plates. In the drawing of such a thin metal plate, the thin metal plate is compressively deformed in the direction along the outer edge of the die hole portion 5a, and then tensilely deformed in the direction in which the thin metal plate is pushed into the die hole portion 5a. The direction of compressive deformation in the secondary path does not match the direction of tensile deformation in the secondary path.
　金属薄板における圧縮変形から引張変形へと変化する変形経路で変形する部位の割れは、一次経路での圧縮変形による加工硬化と、その後の二次経路での引張変形が関係すると考えられる。このため、本発明に係るプレス成形限界線取得方法での基礎成形試験は前述した絞り加工のように、一次経路での圧縮方向と、二次経路での引張方向とを必ずしも一致させる必要はない。 It is thought that the cracking of the portion of the thin metal plate that is deformed along the deformation path from compressive deformation to tensile deformation is related to work hardening due to compressive deformation in the primary path and subsequent tensile deformation in the secondary path. For this reason, in the basic forming test in the press forming limit line acquisition method according to the present invention, it is not necessary to match the compression direction in the primary path and the tensile direction in the secondary path, as in the drawing process described above. .
　そのため、基礎成形試験工程Ｓ１における基礎成形試験は、圧縮方向と引張方向が一致する単軸圧縮引張試験（uniaxial　compression-tension　test）に限らず、本実施の形態で述べたように、圧縮方向と引張方向が一致しない絞り加工でもよい。 Therefore, the basic molding test in the basic molding test step S1 is not limited to a uniaxial compression-tension test in which the compression direction and the tension direction are the same. A drawing process in which the pulling directions do not match may also be used.
　もっとも、金属薄板の面内で圧縮変形から引張変形に反転する単軸圧縮引張試験では、金属薄板の圧縮変形中に座屈（buckling）が発生するため、金属薄板に付与できる圧縮変形量は狭い範囲に留まる。これに対し、絞り加工では、金属薄板を圧縮変形させる一次経路において大きな圧縮変形量を付与することができ、また、その後の二次経路においても大きな引張変形を与えることができる。これにより、絞り加工による基礎成形試験では、圧縮変形における最大板厚増加量と圧縮変形後の引張変形における相対板厚減少量とを広い範囲で求めることができる。このため、割れ発生の有無を区分する成形限界線を広い範囲で作成することができ、成形限界線の精度を高めるとともに適用可能な成形条件を広範囲とすることができる。 However, in a uniaxial compression-tension test in which compression deformation is reversed to tensile deformation in the plane of the metal sheet, buckling occurs during compression deformation of the metal sheet, so the amount of compressive deformation that can be imparted to the metal sheet is narrow. stay in range. On the other hand, in the drawing process, a large amount of compressive deformation can be imparted in the primary path of compressive deformation of the thin metal sheet, and a large tensile deformation can be imparted in the subsequent secondary path. As a result, in the basic forming test by drawing, it is possible to determine the maximum plate thickness increase in compressive deformation and the relative plate thickness decrease in tensile deformation after compressive deformation in a wide range. Therefore, it is possible to create a wide range of forming limit lines for determining the presence or absence of crack generation, thereby improving the accuracy of the forming limit lines and widening the applicable forming conditions.
　絞り加工による基礎成形試験では、金属薄板のダイ穴部５ａ（図３参照）に向かう材料流動（metal　flow）の流入抵抗（inflow　resistance）を変更することで、成形条件を変更することができる。そして、成形条件を変更することで、圧縮変形による最大板厚増加量と引張変形による相対板厚減少量とを変更することができる。 In the basic forming test by drawing, the forming conditions can be changed by changing the inflow resistance of the metal flow toward the die hole 5a (see FIG. 3) of the thin metal plate. By changing the molding conditions, it is possible to change the maximum plate thickness increase amount due to compressive deformation and the relative plate thickness decrease amount due to tensile deformation.
　例えば、金型１を用いて金属薄板を絞り加工する基礎成形試験において、金属薄板のダイ穴部５ａに向かう材料流動の流入抵抗を高くする成形条件とするには、金属薄板の寸法を大きくする、ブランクホルダー７によるしわ押さえ力を大きくする、金属薄板とダイ５及びブランクホルダー７との摩擦係数（friction　coefficient）が高い潤滑条件とする、金属薄板にビード形状を付与する、等を行えばよい。 For example, in a basic forming test for drawing a thin metal plate using the die 1, the size of the thin metal plate is increased in order to set the forming condition to increase the inflow resistance of the material flow toward the die hole portion 5a of the thin metal plate. , increasing the wrinkle pressing force by the blank holder 7, setting lubrication conditions with a high friction coefficient between the metal thin plate and the die 5 and the blank holder 7, giving the metal thin plate a bead shape, etc. .
　そして、材料流動の流入抵抗を高くする成形条件では、金属薄板のダイ穴部５ａに向かう流動が抑制されることで、金属薄板におけるダイ穴部５ａの外縁周方向の圧縮変形が緩和されるので、最大板厚増加量は小さくなる。さらに、ダイ穴部５ａに引き込まれる材料流動が減少することで、絞り加工による金属薄板の引張変形が大きくなり、相対板厚減少量は大きくなる。 Under molding conditions that increase the inflow resistance of the material flow, the flow of the thin metal plate toward the die hole portion 5a is suppressed, so that the compressive deformation of the thin metal plate in the circumferential direction of the outer edge of the die hole portion 5a is alleviated. , the maximum plate thickness increase becomes smaller. Furthermore, since the material flow drawn into the die hole portion 5a is reduced, the tensile deformation of the thin metal plate due to the drawing process is increased, and the relative plate thickness reduction amount is increased.
　金属薄板の絞り加工では、フランジ部にしわが発生すると当該発生したしわが過剰な絞り力（drawing　force）を誘発して金属薄板の破断（割れ）の原因となる可能性がある。このような金属薄板の割れは、本発明で対象とする圧縮変形から引張変形へと変形経路が変化する部位での割れとは異なるため、割れ発生の有無を適正に判定することができない。そのため、金属薄板の絞り加工により基礎成形試験を行う場合においては、図３に示すように、ブランクホルダー７を用いてしわの発生を防ぐことが好ましい。 In the drawing process of thin metal sheets, if wrinkles occur in the flange, the generated wrinkles may induce excessive drawing force and cause breakage (cracking) of the thin metal sheet. Since such cracks in the thin metal plate are different from cracks at a portion where the deformation path changes from compressive deformation to tensile deformation, which is the object of the present invention, it is impossible to properly determine whether or not cracks have occurred. Therefore, when a basic forming test is performed by drawing a thin metal plate, it is preferable to use a blank holder 7 to prevent the generation of wrinkles, as shown in FIG.
　図３に示すような金型１により絞り加工する場合、ダイ肩部５ｂのダイ肩半径が金属薄板の板厚に比べて小さいと、圧縮変形後の引張変形での板厚減少（thickness　reduction）が急激に促進されて割れに至るので、割れ発生の有無の適正な判定を行うことができない。そのため、ダイ５のダイ肩半径は、金属薄板の板厚の数倍以上とするのが好ましい。 When drawing is performed using the die 1 as shown in FIG. 3, if the die shoulder radius of the die shoulder 5b is smaller than the plate thickness of the thin metal plate, thickness reduction due to tensile deformation after compressive deformation will occur. is abruptly accelerated and leads to cracking, it is not possible to properly determine whether or not cracking has occurred. Therefore, the die shoulder radius of the die 5 is preferably several times or more the thickness of the thin metal plate.
　絞り加工試験では、前述した図３に示す金型１を用いて角筒の容器を成形するものに限らず、図７に示すような金型３１を用いて円筒の容器を成形するものであってもよい。 In the drawing test, the mold 1 shown in FIG. 3 was used to form a rectangular container, and the mold 31 shown in FIG. 7 was used to form a cylindrical container. may
　上記の説明において、割れ判定パラメータ取得工程Ｓ５は、一例として、式（１）で与えられる圧縮変形での真ひずみεcompressionを最大板厚増加量として求め、式（２）で与えられる真ひずみεtension　after　compressionを相対板厚減少量として求めるものであった。もっとも、本発明において、割れ判定パラメータとして求める最大板厚増加量及び相対板厚減少量は、例えば、圧縮変形及び圧縮変形後の引張変形における真ひずみから変換される公称ひずみ（nominal　strain）や、圧縮変形での板厚方向の真ひずみをプラスとし、引張変形での板厚方向の真ひずみをマイナスとして算出したものであってもよい。 In the above description, the crack determination parameter acquisition step S5, as an example, obtains the true strain ε compression in compressive deformation given by the formula (1) as the maximum plate thickness increase, and the true strain ε given by the formula (2) The tension after compression was obtained as the amount of relative thickness reduction. However, in the present invention, the maximum plate thickness increase amount and the relative plate thickness decrease amount obtained as crack determination parameters are, for example, the nominal strain converted from the true strain in compressive deformation and tensile deformation after compressive deformation, The true strain in the plate thickness direction in compressive deformation may be positive, and the true strain in the plate thickness direction in tensile deformation may be calculated as negative.
　上記の説明は、980MPa級鋼板を金属薄板の供試材とした場合の結果であるが、本発明は、金属薄板の材料強度（material　strength）や板厚を限定するものではなく、金属薄板の材質（material）についても鋼板に限らず、その他の金属材料（metal　sheet）であってもよい。 The above explanation is the result when the 980 MPa class steel plate was used as the test material for the thin metal plate, but the present invention does not limit the material strength and thickness of the thin metal plate. The material is not limited to a steel plate, but may be another metal sheet.
　本発明に係るプレス成形限界線取得方法の作用効果を検証する実験及び解析を行ったので、以下、これについて説明する。 Experiments and analyzes were conducted to verify the effects of the press forming limit line acquisition method according to the present invention, which will be described below.
　本実施例では、図７に示す金型３１を用いて金属薄板を円筒状の底付き柱状容器（図示なし）に絞り加工し、円筒状の底付き柱状容器における割れ発生の有無を、実施の形態で説明した角筒状に絞り加工する基礎成形試験により求めた成形限界線（図６）を用いて判定した。 In this example, a metal sheet was drawn into a cylindrical columnar container with a bottom (not shown) using a mold 31 shown in FIG. Determination was made using the forming limit line (Fig. 6) obtained by the basic forming test in which drawing was performed into a rectangular tube shape described in the mode.
　金属薄板には引張強度980MPa級、板厚1.4mmの鋼板を供試材とし、前述した図５に示す形状及び寸法の金属薄板２１を用いた。 A steel plate with a tensile strength of 980 MPa and a thickness of 1.4 mm was used as the test material for the thin metal plate, and the thin metal plate 21 having the shape and dimensions shown in Fig. 5 was used.
　金型３１は、パンチ３３と、ダイ３５と、ブランクホルダー３７と、を備えたものであり、パンチ肩部３３ａのパンチ肩半径をR12mm、ダイ肩部３５ｂのダイ肩半径をR5mmとした。また、ブランクホルダー３７によるしわ押さえ力は5tonfとした。 The die 31 includes a punch 33, a die 35, and a blank holder 37. The punch shoulder radius of the punch shoulder portion 33a is R12 mm, and the die shoulder radius of the die shoulder portion 35b is R5 mm. Also, the wrinkle pressing force by the blank holder 37 was set to 5 tonf.
　まず、金型３１を用いて金属薄板２１を絞り加工した円筒状の底付き柱状容器における割れ発生の有無を、図５に示す金属薄板２１の各形状及び寸法について取得した。 First, the existence or non-existence of cracks in a cylindrical container with a bottom formed by drawing the thin metal plate 21 using the metal mold 31 was obtained for each shape and size of the thin metal plate 21 shown in FIG.
　次に、図５に示す形状及び寸法の各金属薄板２１について、金型３１を用いて絞り加工するＦＥＭ解析を行い、圧縮変形から引張変形へと変化する変形経路で変形される部位である円筒状の底付き柱状容器の縦壁部における最大板厚増加量及び相対板厚減少量を割れ判定パラメータとして取得した。 Next, for each thin metal plate 21 having the shape and dimensions shown in FIG. The maximum plate thickness increase and the relative plate thickness decrease in the vertical wall portion of the cylindrical container with a bottom were obtained as crack determination parameters.
　表２に、円筒状の底付き柱状容器の絞り加工により取得した割れ発生の有無と、ＦＥＭ解析により求めた割れ判定パラメータ（最大板厚増加量及び相対板厚減少量）の結果を示す。 Table 2 shows the presence or absence of cracks obtained by drawing a cylindrical columnar container with a bottom, and the results of crack determination parameters (maximum plate thickness increase and relative plate thickness decrease) obtained by FEM analysis.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　そして、絞り加工により取得した割れ発生の有無を、ＦＥＭ解析により求めた割れ判定パラメータと関連付けて、図８に示すように、最大板厚増加量及び相対板厚減少量を二軸とする二次元座標平面上にプロットした。 Then, the presence or absence of crack generation obtained by drawing is associated with the crack determination parameter obtained by FEM analysis, and as shown in FIG. plotted on the coordinate plane.
　さらに、前述した実施の形態で説明した金属薄板を角筒状の底付き柱状容器１１に絞り加工する基礎成形試験について求めた成形限界線（図６）を、図８に示す割れ発生の有無をプロットした二次元座標上に表示した。 Furthermore, the forming limit line (FIG. 6) obtained in the basic forming test for drawing the thin metal plate described in the above-described embodiment into the square cylindrical columnar container 11 with the bottom, and the presence or absence of crack generation shown in FIG. It is displayed on the plotted two-dimensional coordinates.
　図８に示すように、金属薄板を角筒状の底付き柱状容器１１に絞り加工する基礎成形試験について求めた成形限界線を用いても、円筒状の底付き柱状容器に絞り加工する場合における割れ発生の有無を精度良く判定できることが示され、本発明の有効性が実証された。 As shown in FIG. 8, even if the forming limit line obtained in the basic forming test for drawing a thin metal plate into a rectangular cylindrical columnar container 11 with a bottom is used, there is no difference in the case of drawing into a cylindrical columnar container with a bottom. It was shown that the presence or absence of crack generation can be determined with high accuracy, proving the effectiveness of the present invention.
　本発明によれば、金属薄板のプレス成形過程において、金属薄板の変形経路が圧縮変形から引張変形に変化する部位の割れの発生の有無を判定する成形限界線を求めることが可能なプレス成形限界線取得方法を提供することができる。 According to the present invention, in the process of press forming a thin metal plate, the press forming limit can be obtained to determine the presence or absence of cracks at the portion where the deformation path of the thin metal plate changes from compressive deformation to tensile deformation. A line acquisition method can be provided.
　１　金型
　３　パンチ
　３ａ　パンチ肩部
　５　ダイ
　５ａ　ダイ穴部
　５ｂ　ダイ肩部
　７　ブランクホルダー
　１１　底付き柱状容器
　１１ａ　コーナー部
　１３　底部（bottom　portion）
　１５　縦壁部
　１７　フランジ部（flange　portion）
　２１　金属薄板
　３１　金型
　３３　パンチ
　３３ａ　パンチ肩部
　３５　ダイ
　３５ａ　ダイ穴部
　３５ｂ　ダイ肩部
　３７　ブランクホルダー 1 Die 3 Punch 3a Punch Shoulder 5 Die 5a Die Hole 5b Die Shoulder 7 Blank Holder 11 Columnar Container with Bottom 11a Corner 13 Bottom Portion
15 vertical wall portion 17 flange portion
21 Metal Sheet 31 Mold 33 Punch 33a Punch Shoulder 35 Die 35a Die Hole 35b Die Shoulder 37 Blank Holder

Claims (3)

  1. 　金属薄板のプレス成形加工において、前記金属薄板の変形経路が圧縮変形から引張変形に変化する部位の割れ発生の有無を判定するための成形限界線を求めるプレス成形限界線取得方法であって、
    　前記金属薄板を前記変形経路で変形させる基礎成形試験を種々の成形条件で行い、該種々の成形条件について、前記金属薄板における前記変形経路が圧縮変形から引張変形に変化する部位の割れ発生の有無を取得する基礎成形試験工程と、
    　前記金属薄板の前記基礎成形試験を解析対象とするＦＥＭ解析を前記種々の成形条件について行い、前記金属薄板の板厚の変化を算出するＦＥＭ解析工程と、
    　該ＦＥＭ解析工程において算出した前記金属薄板の板厚の変化に基づいて、前記種々の成形条件について、前記変形経路の圧縮変形において前記金属薄板が最大板厚に至るまでの板厚の変化量である最大板厚増加量と、前記変形経路において圧縮変形から引張変形へと変化して前記金属薄板が最大板厚から最小板厚に至るまでの板厚の変化量である相対板厚減少量と、を割れ判定パラメータとして求める割れ判定パラメータ取得工程と、
    　前記基礎成形試験工程において前記種々の成形条件について取得した割れの発生の有無と、前記割れ判定パラメータ取得工程において前記種々の成形条件について求めた割れ判定パラメータと、を関連付けて、前記最大板厚増加量及び前記相対板厚減少量を各軸とする二次元座標上にプロットする割れ判定パラメータプロット工程と、
    　該二次元座標上にプロットした割れ発生の有無の分布に基づいて、前記変形経路で前記金属薄板が変形する部位の割れ発生の有無を区分する成形限界線を作成する成形限界線作成工程と、
    　を含む、プレス成形限界線取得方法。     A press forming limit line acquisition method for obtaining a forming limit line for determining the presence or absence of cracking at a portion where a deformation path of the thin metal plate changes from compressive deformation to tensile deformation in press forming of a metal sheet, comprising:
    A basic forming test in which the metal sheet is deformed along the deformation path is performed under various forming conditions, and whether or not cracks occur in the portion of the metal sheet where the deformation path changes from compressive deformation to tensile deformation for the various forming conditions. A basic molding test process to obtain
    an FEM analysis step of performing an FEM analysis with the basic forming test of the thin metal plate as an analysis target for the various forming conditions, and calculating a change in the thickness of the thin metal plate;
    Based on the change in the thickness of the thin metal plate calculated in the FEM analysis process, the amount of change in the thickness of the thin metal plate until the thin metal plate reaches the maximum thickness in the compression deformation of the deformation path for the various forming conditions A certain maximum plate thickness increase amount, and a relative plate thickness decrease amount that is the plate thickness change amount from the maximum plate thickness to the minimum plate thickness of the thin metal plate as the deformation path changes from compressive deformation to tensile deformation. A crack determination parameter acquisition step of obtaining , as a crack determination parameter;
    By associating the presence or absence of cracks obtained for the various forming conditions in the basic forming test step with the crack determination parameters obtained for the various forming conditions in the crack determination parameter acquisition step, the maximum plate thickness increase a crack determination parameter plotting step of plotting the amount and the relative plate thickness reduction amount on two-dimensional coordinates with each axis;
    a forming limit line creating step of creating a forming limit line that distinguishes whether or not a crack occurs in a portion where the thin metal plate is deformed along the deformation path, based on the distribution of presence or absence of crack occurrence plotted on the two-dimensional coordinates;
    A method for obtaining a press forming limit line, comprising:
  2. 　前記基礎成形試験工程は、前記金属薄板を絞り加工することにより該金属薄板を前記変形経路で変形させる、請求項１に記載のプレス成形限界線取得方法。 The press-forming limit line acquisition method according to claim 1, wherein the basic forming test step deforms the thin metal plate along the deformation path by drawing the thin metal plate.
  3. 　前記基礎成形試験工程は、前記金属薄板の絞り加工において、前記金属薄板の形状、又は、前記金属薄板に付与するしわ押さえ力を変更することにより、前記種々の成形条件を設定する、請求項２に記載のプレス成形限界線取得方法。 3. The basic forming test step sets the various forming conditions by changing the shape of the thin metal plate or the wrinkle holding force applied to the thin metal plate in the drawing of the thin metal plate. The press forming limit line acquisition method described in .
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JP2011141237A (en) * 2010-01-08 2011-07-21 Nippon Steel Corp Method and for system predicting breakage, program and recording medium
JP2011147949A (en) * 2010-01-20 2011-08-04 Nippon Steel Corp Method and device for deciding breakage in press forming simulation of sheet
JP2012166252A (en) * 2011-02-16 2012-09-06 Jfe Steel Corp Method of creating forming limit diagram in press forming, method of predicting crack, and method of manufacturing pressed part

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* Cited by examiner, † Cited by third party
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JP2011141237A (en) * 2010-01-08 2011-07-21 Nippon Steel Corp Method and for system predicting breakage, program and recording medium
JP2011147949A (en) * 2010-01-20 2011-08-04 Nippon Steel Corp Method and device for deciding breakage in press forming simulation of sheet
JP2012166252A (en) * 2011-02-16 2012-09-06 Jfe Steel Corp Method of creating forming limit diagram in press forming, method of predicting crack, and method of manufacturing pressed part

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