JP2007229761A - Method, device, and program for predicting existence of wrinkle on material to be formed in press forming, and press forming method - Google Patents
Method, device, and program for predicting existence of wrinkle on material to be formed in press forming, and press forming method Download PDFInfo
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本発明は、プレス成形における被成形材の皺の発生の有無の予測方法、予測装置、予測プログラム、ならびにこれらで予測した結果に基づいてプレス成形条件を補償した上で、プレス成形を実際に行うプレス成形方法に関するものである。 The present invention actually performs press molding after compensating for press molding conditions based on a prediction method, a prediction device, a prediction program, and a result predicted by the prediction method of presence / absence of wrinkles of a molding material in press molding. The present invention relates to a press molding method.
金属板等のプレス成形においては、生産性の向上、コストの削減、及び開発期間の短縮を図るため、予め被成形材の成形性や欠陥の発生等を数値計算により予測することがある。更に、プレス成形用の型から離型して除荷後の被成形材のスプリングバックをも数値計算により予測することで、スプリングバック分を見越した型の形状にするなど、プレス成形条件を補償した上で、プレス成形を実際に行うようにすることもできる。いずれにしても、数値計算による解析は、プレス成形後の被成形材の形状を予測する上で重要であり、プレス成形後の被成形材の品質面、スプリングバック分のトリミングロスなどに伴う歩留面、あるいはスプリングバック分を矯正加工する工数面での改善を図る手立てとして有用であり、近年、予測精度の向上が図られている。 In press forming of a metal plate or the like, in order to improve productivity, reduce costs, and shorten the development period, the formability of the material to be formed, the occurrence of defects, and the like may be predicted in advance by numerical calculation. Furthermore, the press molding conditions are compensated by releasing the mold from the press mold and predicting the spring back of the material after unloading by numerical calculation, so that the shape of the mold allows for the spring back. In addition, press molding can be actually performed. In any case, numerical analysis is important for predicting the shape of the material after press forming, and the steps associated with the quality of the material after press forming, trimming loss for springback, etc. It is useful as a means to improve the man-hours for correcting the fixed surface or the spring back, and in recent years, the prediction accuracy has been improved.
ところで、本発明の対象とする、プレス成形後の被成形材の品質面の問題の一つに、特に重要なものとして、表面歪、皺、うねり等（以下、これら全てを単に皺と称す）の、プレス成形後の被成形材の表面が波打つ欠陥が発生する場合があるという問題があるが、こうした皺の発生は、たとえ僅かであっても製品価値を大いに損なうので、正確に予測して、可能な限りその発生を防止することが重要である。 By the way, surface distortion, wrinkles, waviness, etc. (hereinafter, all these are simply referred to as wrinkles) are particularly important as one of the problems of the quality of the molded material after press forming, which is the subject of the present invention. However, there is a problem that the surface of the material to be molded after press forming may be undulated. However, the occurrence of such wrinkles greatly damages the product value even if it is slight, so it can be accurately predicted. It is important to prevent its occurrence as much as possible.
従来、計算に時間がかかるスプリングバックをも数値計算により解析し、被成形材の最終形状を予測する場合にも、もちろん、皺の発生の有無を計算により予測する試みはなされてはいたが、計算にさらに多大な時間を要するため、効率の点で問題を有していた。
そのため、簡易な方法として、被成形材を挟圧した状態をシミュレーションし、シェーディングによって皺の発生の有無を判別したり、被成形材の厚み中心の最小主応力を算出し、そのコンター図に基づいて皺の発生の有無を判別したりする方法もある。
Conventionally, even when calculating the springback, which takes time to calculate, by numerical calculation and predicting the final shape of the material to be molded, of course, attempts have been made to predict the occurrence of wrinkles by calculation, Since much more time is required for the calculation, there is a problem in terms of efficiency.
Therefore, as a simple method, the state in which the material to be molded is clamped is simulated, the presence or absence of wrinkles is determined by shading, the minimum principal stress at the thickness center of the material to be molded is calculated, and the contour diagram is used. There is also a method for determining whether or not wrinkles have occurred.
また、特許文献１に記載されているように、プレス成形における下死点での被成形材の内部応力に基づいて、被成形材に作用している荷重の固有値解析を行うことで、固有モードである座屈モードを算出し、それに基づいて品質上の不具合の発生を予測するような方法もある。
さらに、特許文献２に記載されているように、板状の被成形材がその面方向に並んだ複数のシェル要素の集合体としてモデル化されたシェル要素モデルを用い、各シェル要素の厚み方向の応力を考慮した上で、各シェル要素の面内応力を算出することにより、板状の被成形材のプレス成形による変形を、高い精度で予測するような方法もある。
Further, as described in Patent Document 1, by performing eigenvalue analysis of the load acting on the molding material based on the internal stress of the molding material at the bottom dead center in press molding, an eigenmode is obtained. There is also a method for calculating the buckling mode and predicting the occurrence of a quality defect based on the buckling mode.
Furthermore, as described in Patent Document 2, using a shell element model that is modeled as an assembly of a plurality of shell elements in which plate-shaped workpieces are arranged in the surface direction, the thickness direction of each shell element There is also a method for predicting deformation due to press molding of a plate-shaped workpiece with high accuracy by calculating the in-plane stress of each shell element in consideration of the above stress.
あるいは、特許文献３に記載されているように、単位時間毎に算出される歪に応じて、さらに算出される相当応力と、材質が金属で板状の被成形材の加工硬化曲線から得られる相当応力との差を皺評価指数と定義し、これを計算することで、皺の発生の有無を予測し、さらに予測した結果と実際に被成形材をプレス成形した結果とで皺の高さを比較して、その精度を検証する方法などもある。
数値計算にて解析を実施して、その結果により、被成形材の皺の発生の有無を予測する最も簡易な方法として、シェーディングがある。しかしながら、シェーディングによって被成形材の皺の発生の有無を予測する場合、プレス成形における下死点に達する前に、被成形材に皺が発生するとしても、下死点に達すると、皺が押し潰されるような計算結果にしかならず、図８に示すようになるため、図９に示すように、下死点の例えば１ｍｍ手前の状態でなければ、被成形材の皺の発生の有無を予測できず、下死点に達した後、離型、除荷したときに再び被成形材に皺が発生することまでは、まずもって予測できなくなってしまう。 There is shading as the simplest method for performing analysis by numerical calculation and predicting the presence or absence of wrinkles of the molding material based on the result. However, when predicting the presence or absence of wrinkles on the molding material by shading, even if wrinkles occur on the molding material before reaching the bottom dead center in press molding, the wrinkles are pushed when the bottom dead center is reached. Since the calculation result is crushed and becomes as shown in FIG. 8, as shown in FIG. 9, the presence or absence of wrinkles of the molding material can be predicted unless the bottom dead center is, for example, 1 mm before. First, after reaching the bottom dead center, when the mold is released and unloaded, it is impossible to predict until wrinkles occur again in the molding material.
また、数値計算により得られた最小主応力に基づいて被成形材の皺の発生の有無を予測する場合、図１０に示すように、一様な圧縮応力と引張応力とが表示されるため、皺の形状をある程度までは判別できるものの、明瞭度が低く、皺の発生位置を特定しにくい。
また、特許文献１に記載された従来例にあっては、算出される固有値が、座屈解析における方程式やその解法に依存し、あるいはさらに材料特性の予測の正確さにも依存する場合があるため、開示されているような予測結果を容易に得られるとは言いがたい。
Further, when predicting the presence or absence of wrinkles of the molding material based on the minimum principal stress obtained by numerical calculation, as shown in FIG. 10, uniform compressive stress and tensile stress are displayed. Although the shape of the wrinkles can be discriminated to some extent, the clarity is low and it is difficult to identify the position where the wrinkles are generated.
Further, in the conventional example described in Patent Document 1, the calculated eigenvalue may depend on an equation in buckling analysis and its solution, or may further depend on accuracy of prediction of material properties. Therefore, it is difficult to say that a prediction result as disclosed is easily obtained.
また、特許文献２に記載された従来例にあっては、多大な計算時間とメモリ容量を必要とするため、やはり容易とはいえない。
また、上記特許文献３に記載された従来例にあっては、複雑な計算ロジックとなるため、やはり計算時間を要する。また、被成形材に発生すると予測される皺の高さによって予測精度の検証を行っているが、重要なのは皺の高さではなく、皺の発生の有無とその分布である。
本発明は、上記に説明されたような従来技術の諸問題に着目してなされたものであり、その課題は、容易な方法で、速やかに、且つ正確に、被成形材の皺の発生の有無を予測することにある。
In addition, the conventional example described in Patent Document 2 requires a great amount of calculation time and memory capacity, and is not easy.
Further, the conventional example described in Patent Document 3 requires complicated calculation logic because of the complicated calculation logic. Further, although the accuracy of prediction is verified based on the height of wrinkles predicted to occur in the material to be molded, what is important is not the height of wrinkles but the presence or absence of wrinkles and their distribution.
The present invention has been made by paying attention to the problems of the prior art as described above, and the problem is that the occurrence of wrinkles of the molding material is quickly and accurately performed in an easy manner. Presence or absence is to predict.
プレス成形用の型で挟圧した状態から被成形材を解放すると、被成形材には、残留応力によってスプリングバックが発生する場合が少なくないが、皺の発生もこれと同様の傾向がある。すなわち、プレス成形における下死点では、皺が押し潰されているため、わからなくなっているが、この状態から解放されると、被成形材の厚み方向の断面に分布をもっている残留応力によって曲げモーメントが発生するため、これによって被成形材に皺が発生する場合が出てくるのである。 When the material to be molded is released from a state of being clamped by a press molding die, the material to be molded often has a spring back due to residual stress, but the occurrence of wrinkles has the same tendency. In other words, at the bottom dead center in press molding, the wrinkles are crushed and are not understood. However, when released from this state, the bending moment is caused by the residual stress distributed in the cross section in the thickness direction of the material to be molded. As a result, wrinkles may occur in the material to be molded.
そこで、請求項１に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法は、プレス成形時に被成形材に皺が発生するか否かを予測するプレス成形における被成形材の皺の発生の有無の予測方法において、プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力を算出し、算出した曲げ応力を前記被成形材の厚み方向に沿って表面から裏面まで積分し、積分した曲げ応力と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測することを特徴としている。 Accordingly, the method for predicting the presence or absence of wrinkles in a material to be molded in press molding of the present invention according to claim 1 is a method for predicting whether or not wrinkles are generated in the material to be molded during press molding. In the method for predicting the presence or absence of wrinkles, a bending stress distributed in the same direction in a cross section in the thickness direction of the molding material is calculated at the bottom dead center in press molding, and the calculated bending stress is calculated in the thickness direction of the molding material. Is integrated from the front surface to the back surface, and the curvature radius or curvature of the molding material after unloading is estimated according to the integrated bending stress and the elastic modulus and thickness of the molding material, and the estimated curvature It is characterized by predicting whether wrinkles occur in the material to be molded during press molding according to the radius or curvature.
また、請求項２に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法は、プレス成形時に被成形材に皺が発生するか否かを予測するプレス成形における被成形材の皺の発生の有無の予測方法において、プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力を算出し、算出した曲げ応力を前記被成形材の表面から前記被成形材の厚みの１／３まで及び前記被成形材の裏面から前記被成形材の厚みの１／３まで積分し、積分した曲げ応力と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測することを特徴としている。 According to a second aspect of the present invention, there is provided a method for predicting the presence or absence of wrinkles in a material to be formed in press forming, wherein the material to be formed in press forming that predicts whether or not wrinkles occur in the material to be formed during press forming. In the method for predicting the presence or absence of wrinkles, a bending stress distributed in the same direction on the cross section in the thickness direction of the workpiece at the bottom dead center in press molding is calculated, and the calculated bending stress is calculated from the surface of the workpiece. Integrate up to 1/3 of the thickness of the molding material and 1/3 of the thickness of the molding material from the back surface of the molding material, depending on the integrated bending stress and the elastic modulus and thickness of the molding material Estimating the curvature radius or curvature of the molding material after unloading and predicting whether wrinkles will occur in the molding material during press molding according to the estimated curvature radius or curvature. It is said.
また、請求項３に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法は、プレス成形時に被成形材に皺が発生するか否かを予測するプレス成形における被成形材の皺の発生の有無の予測方法において、プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力のうち前記被成形材の表裏面の縁応力を算出し、算出した縁応力の表裏面差を算出し、算出した縁応力の表裏面差と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測することを特徴としている。 According to a third aspect of the present invention, there is provided a method for predicting the presence or absence of wrinkles in a material to be molded in press molding, wherein the material to be molded in press molding for predicting whether or not wrinkles are generated in the material during press molding. In the method for predicting the presence or absence of wrinkles, the edge stress on the front and back surfaces of the molding material is calculated among the bending stresses distributed in the same direction in the thickness direction cross section of the molding material at the bottom dead center in press molding, Calculate the front and back surface difference of the calculated edge stress, and according to the calculated front and back surface difference of the edge stress and the elastic modulus and thickness of the molding material, calculate the curvature radius or curvature of the molding material after unloading It is estimated, and whether or not wrinkles occur in the material to be molded during press molding is predicted according to the estimated radius of curvature or curvature.
さらに、請求項４に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法は、請求項１〜３の何れか一項に記載のプレス成形における被成形材の皺の発生の有無の予測方法において、前記曲率半径の絶対値がある一定の値以下であるとき、または前記曲率の絶対値がある一定の値以上であるときに、皺の発生が有ると予測することを特徴としている。 Furthermore, the prediction method of the presence or absence of the generation | occurrence | production of the wrinkle of the to-be-molded material in the press molding of this invention which concerns on Claim 4 is a generation | occurrence | production of the torn of the to-be-formed material in the press molding as described in any one of Claims 1-3. Predicting the presence of wrinkles when the absolute value of the radius of curvature is below a certain value or when the absolute value of the curvature is above a certain value. It is a feature.
さらに、請求項５に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法は、請求項１〜４の何れか一項に記載のプレス成形における被成形材の皺の発生の有無の予測方法において、前記曲率半径または前記曲率の大きさに応じて前記被成形材を色分けして画像表示することを特徴としている。
また、請求項６に係る本発明のプレス成形における被成形材の皺の発生の有無の予測装置は、請求項１〜５の何れか一項に記載のプレス成形における被成形材の皺の発生の有無の予測方法に従って、プレス成形時に前記被成形材に皺が発生するか否かを予測する手段を備えたことを特徴としている。
Furthermore, the prediction method of the presence or absence of the wrinkles of the molding material in the press molding of the present invention according to claim 5 is the generation of wrinkles of the molding material in the press molding according to any one of claims 1 to 4. In the method for predicting the presence or absence, the material to be molded is color-coded according to the radius of curvature or the magnitude of the curvature, and is displayed as an image.
Moreover, the prediction apparatus of the presence or absence of the generation | occurrence | production of the wrinkle of the to-be-molded material in the press molding of this invention which concerns on Claim 6 WHEREIN: Generation | occurrence | production of the torn of the to-be-formed material in the press molding as described in any one of Claims 1-5 According to a method for predicting the presence or absence of the material, there is provided means for predicting whether or not wrinkles are generated in the material to be molded during press molding.
また、請求項７に係る本発明のプレス成形における被成形材の皺の発生の有無の予測プログラムは、請求項１〜５の何れか一項に記載のプレス成形における被成形材の皺の発生の有無の予測方法に従って、プレス成形時に前記被成形材に皺が発生するか否かを予測することを特徴としている。
また、請求項８に係る本発明のプレス成形方法は、請求項１〜５の何れか一項に記載のプレス成形における被成形材の皺の発生の有無の予測方法に従って、プレス成形時に前記被成形材に皺が発生するか否かを予測し、予測した結果に基づいてプレス成形条件を補償した上で、プレス成形を実際に行うことを特徴としている。
Moreover, the prediction program of the presence or absence of the generation | occurrence | production of the wrinkles of the to-be-molded material in the press molding of this invention which concerns on Claim 7 WHEREIN: The generation | occurrence | production of the wrinkles of the to-be-formed material in the press molding as described in any one of Claims 1-5 In accordance with a method for predicting the presence or absence, whether or not wrinkles occur in the material to be molded at the time of press molding is predicted.
According to an eighth aspect of the present invention, there is provided a press molding method according to any one of the first to fifth aspects of the present invention. It is characterized by predicting whether or not wrinkles occur in the molding material, and actually performing press molding after compensating the press molding conditions based on the predicted result.
請求項１に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法によれば、プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力を算出し、算出した曲げ応力を前記被成形材の厚み方向に沿って表面から裏面まで積分し、積分した曲げ応力と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測するので、容易な方法で、速やかに、且つ正確に、被成形材の皺の発生の有無を予測することができる。 According to the method for predicting the presence or absence of wrinkles of a material to be molded in press molding of the present invention according to claim 1, bending stress distributed in the same direction in the cross section in the thickness direction of the material to be molded at the bottom dead center in press molding. And the calculated bending stress is integrated from the front surface to the back surface along the thickness direction of the material to be molded, and is unloaded according to the integrated bending stress and the elastic modulus and thickness of the material to be molded. Since the curvature radius or curvature of the material to be molded is estimated, and whether or not wrinkles occur in the material to be molded at the time of press molding according to the estimated curvature radius or curvature, quickly, in an easy manner, In addition, it is possible to accurately predict the presence or absence of wrinkles in the molding material.
また、請求項２に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法によれば、プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力を算出し、算出した曲げ応力を前記被成形材の表面から前記被成形材の厚みの１／３まで及び前記被成形材の裏面から前記被成形材の厚みの１／３まで積分し、積分した曲げ応力と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測するので、請求項１に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法と比較して、より速やかに皺の発生の有無を予測することができる。 Moreover, according to the prediction method of the presence or absence of the wrinkle of the to-be-molded material in the press molding of this invention which concerns on Claim 2, it distributes to the thickness direction cross section of the to-be-molded material in the same direction at the bottom dead center in press molding. The bending stress is calculated, and the calculated bending stress is integrated from the surface of the molding material to 1/3 of the thickness of the molding material and from the back surface of the molding material to 1/3 of the thickness of the molding material. In accordance with the integrated bending stress and the elastic modulus and thickness of the molding material, the curvature radius or curvature of the molding material after unloading is estimated, and during press molding according to the estimated curvature radius or curvature Since it is predicted whether or not wrinkles will occur in the material to be molded, compared with the prediction method for the presence or absence of wrinkles in the material to be molded in the press molding according to the first aspect of the present invention, the wrinkle is more quickly formed. Presence or absence of occurrence can be predicted.
また、請求項３に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法によれば、プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力のうち前記被成形材の表裏面の縁応力を算出し、算出した縁応力の表裏面差を算出し、算出した縁応力の表裏面差と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測するので、請求項１、２に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法と比較して、より速やかに皺の発生の有無を予測することができる。 Moreover, according to the prediction method of the presence or absence of the wrinkle of the to-be-molded material in the press molding of this invention which concerns on Claim 3, it distributes to the thickness direction cross section of the to-be-molded material in the same direction at the bottom dead center in press molding. Calculate the edge stress on the front and back surfaces of the molding material among the bending stress, calculate the front and back surface difference of the calculated edge stress, and calculate the difference between the front and back surfaces of the calculated edge stress and the elastic modulus and thickness of the molding material. Accordingly, the curvature radius or curvature of the molding material after unloading is estimated, and it is predicted whether wrinkles will occur in the molding material during press molding according to the estimated curvature radius or curvature. Compared with the prediction method of the presence or absence of wrinkles of the material to be molded in the press molding of the present invention according to claims 1 and 2, the presence or absence of wrinkles can be predicted more quickly.
さらに、請求項４に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法によれば、前記曲率半径の絶対値がある一定の値以下であるとき、または前記曲率の絶対値がある一定の値以上であるときに、皺の発生が有ると予測するので、皺の発生の有無を容易に予測することができる。
さらに、請求項５に係る本発明のプレス成形における被成形材の皺の発生の有無の予測方法によれば、前記曲率半径または前記曲率の大きさに応じて前記被成形材を色分けして画像表示するので、皺の発生の有無のみならず、その大きさや分布を、容易に把握することができる。
Furthermore, according to the method for predicting the presence or absence of wrinkles of the material to be molded in the press molding of the present invention according to claim 4, when the absolute value of the radius of curvature is less than a certain value, or the absolute value of the curvature When the value is equal to or greater than a certain value, the occurrence of wrinkles is predicted, so the presence or absence of wrinkles can be easily predicted.
Furthermore, according to the method for predicting the presence or absence of wrinkles of the material to be molded in the press molding of the present invention according to claim 5, the material to be molded is color-coded according to the radius of curvature or the size of the curvature. Since it is displayed, not only the presence or absence of wrinkles but also the size and distribution can be easily grasped.
また、請求項６に係る本発明のプレス成形における被成形材の皺の発生の有無の予測装置によれば、請求項１〜５の何れか一項に記載のプレス成形における被成形材の皺の発生の有無の予測方法に従って、プレス成形時に前記被成形材に皺が発生するか否かを予測する手段を備えたことで、前述したそれぞれの効果を得ることができる。
また、請求項７に係る本発明のプレス成形における被成形材の皺の発生の有無の予測プログラムによれば、請求項１〜５の何れか一項に記載のプレス成形における被成形材の皺の発生の有無の予測方法に従って、プレス成形時に前記被成形材に皺が発生するか否かを予測することで、前述したそれぞれの効果を得ることができる。
Moreover, according to the prediction apparatus of the presence or absence of the generation | occurrence | production of the wrinkle of the to-be-molded material in the press molding of this invention which concerns on Claim 6, the torn of the to-be-formed material in the press forming as described in any one of Claims 1-5. By providing means for predicting whether or not wrinkles occur in the material to be molded during press molding in accordance with a method for predicting whether or not the above has occurred, the respective effects described above can be obtained.
Moreover, according to the prediction program of the presence or absence of generation | occurrence | production of the wrinkle of the to-be-molded material in the press molding of this invention concerning Claim 7, the torn of the to-be-formed material in press forming as described in any one of Claims 1-5. According to the prediction method for the presence or absence of occurrence, whether or not wrinkles occur in the material to be molded at the time of press molding can obtain the respective effects described above.
また、請求項８に係る本発明のプレス成形方法は、請求項１〜５の何れか一項に記載のプレス成形における被成形材の皺の発生の有無の予測方法に従って、プレス成形時に前記被成形材に皺が発生するか否かを予測し、予測した結果に基づいてプレス成形条件を補償した上で、プレス成形を実際に行うことで、実際のプレス成形において、生産性の向上、コストの削減、及び開発期間の短縮を図れるとともに、品質面、歩留面、工数面での改善を図ることができる。 According to an eighth aspect of the present invention, there is provided a press molding method according to any one of the first to fifth aspects of the present invention. Predict whether or not wrinkles will occur in the molding material, compensate for the press molding conditions based on the predicted result, and actually perform press molding, improving productivity and cost in actual press molding And a development period can be shortened, and quality, yield and man-hours can be improved.
以下、本発明を実施するための最良の形態を図面に基づいて説明する。
図１は、プレス成形を行うようすについて、直接関係ないものを省略して示した概略図であり、ダイ１とホルダ２とで被成形材である金属の板材３を保持した状態で、パンチ４を押下することにより、ダイ１及びパンチ４のプレス面に沿って板材３がプレス成形される。このとき、板材３の流れは、ドロービード５によって調節される。なお、板材３は、一般的な冷延鋼板や熱延鋼板に限らず、めっき鋼板、ステンレス鋼板、アルミニウム板、アルミニウム合金板、マグネシウム板などの非鉄金属を用いてもよい。さらには、単板でもよいし、厚さや材質の異なる板材を接合したテーラードブランク材でもよい。このほか、金属以外の、例えばプラスチックや粘土などでもよい。
Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view in which press forming is omitted, omitting the items that are not directly related, and a die 4 and a holder 2 hold a metal plate 3 that is a material to be molded, and the punch 4 By pressing down, the plate material 3 is press-formed along the press surfaces of the die 1 and the punch 4. At this time, the flow of the plate 3 is adjusted by the draw bead 5. The plate material 3 is not limited to a general cold-rolled steel plate or hot-rolled steel plate, and non-ferrous metals such as a plated steel plate, a stainless steel plate, an aluminum plate, an aluminum alloy plate, and a magnesium plate may be used. Furthermore, a single plate may be sufficient and the tailored blank material which joined the board | plate material from which thickness and a material differ may be sufficient. In addition, other than metal, for example, plastic or clay may be used.
図２は、プレス成形時に、板材３の厚み方向断面に同方向に分布する引張及び圧縮の残留応力のようすを示している。ダイ１及びパンチ４によって板材３をプレス成形、すなわち挟圧していくと、板材３に皺が発生する場合があるが、下死点に達すると、皺は押し潰されてわからなくなってしまう。このとき、板材３の厚み方向断面には、正符号で示した引張応力と負符号で示した圧縮応力とが生じることになり、このような引張応力及び圧縮応力が曲げ応力となる。 FIG. 2 shows the tensile and compressive residual stresses distributed in the same direction on the cross section in the thickness direction of the plate 3 during press forming. When the plate material 3 is press-formed, that is, pinched with the die 1 and the punch 4, wrinkles may occur in the plate material 3, but when the bottom dead center is reached, the wrinkles are crushed and cannot be recognized. At this time, a tensile stress indicated by a positive sign and a compressive stress indicated by a negative sign are generated in the cross section in the thickness direction of the plate member 3, and such tensile stress and compressive stress become bending stresses.
図３は、除荷したときに、板材３の厚み方向断面に同方向に分布する曲げ応力のようすを示している。応力−歪曲線によって求まる応力をＡＯＡ′とし、幾何学的に発生する応力をＢＯＢ′とすると、皺の発生原因となる曲げ応力はＡＯＡ′とＢＯＢ′との差として求められるＣＯＣ′となる。
したがって、曲げモーメントをＭ、板材３の弾性係数をＥ、断面二次モーメント（断面慣性モーメントともいう）をＩとすると、図４に示すように、Ｍ、Ｉ、ならびに板材３の曲率κは、図中の数式によって表される。すなわち、板厚ｔにおいて中立面Ｓからの距離ηとそこでの微小部分の面積ｄＡを考え、曲げ応力σを板厚方向に沿って表面から裏面まで積分し、積分した曲げ応力と、板材３の弾性係数Ｅと板厚ｔとに応じて、除荷した後の板材３に発生する皺の曲率κを推定することができる。
FIG. 3 shows the bending stress distributed in the same direction on the cross section in the thickness direction of the plate 3 when unloaded. If the stress obtained from the stress-strain curve is AOA ′ and the geometrically generated stress is BOB ′, the bending stress causing the wrinkle is COC ′ obtained as the difference between AOA ′ and BOB ′.
Therefore, if the bending moment is M, the elastic modulus of the plate member 3 is E, and the secondary moment of section (also referred to as the moment of inertia of the cross section) is I, as shown in FIG. It is represented by the mathematical formula in the figure. That is, considering the distance η from the neutral surface S and the area dA of the minute portion at the thickness t, the bending stress σ is integrated along the thickness direction from the front surface to the back surface, and the integrated bending stress and the plate 3 The curvature κ of the wrinkles generated in the plate material 3 after unloading can be estimated according to the elastic coefficient E and the plate thickness t.
そして、曲率κから曲率半径ρを算出し（ρ＝１／κ）、この曲率半径ρの絶対値がある一定の値（例えば１０００ｍｍ）以下であるときに、皺の発生が有るものと予測する。もちろん、曲率κそのものをもって、その絶対値がある一定の値以上であるときに皺の発生が有るものと予測するようにしてもよい。
このように、除荷した後の板材３の曲率半径ρを板材のいたるところ、すなわち数値計算における各要素ごとに推定し、推定した曲率半径ρに応じてプレス成形における被成形材の皺の発生の有無を予測することで、容易な方法で、速やかに、且つ正確に、被成形材の皺の発生の有無を予測することができる。また、曲率半径ρの絶対値がある一定の値以下であるときに、皺の発生が有るものと予測するだけなので、皺の発生の有無を容易に予測することができる。
Then, the curvature radius ρ is calculated from the curvature κ (ρ = 1 / κ), and when the absolute value of the curvature radius ρ is equal to or smaller than a certain value (for example, 1000 mm), it is predicted that wrinkles are generated. . Of course, the curvature κ itself may be predicted to cause wrinkles when the absolute value is a certain value or more.
In this way, the curvature radius ρ of the plate material 3 after unloading is estimated everywhere in the plate material, that is, for each element in the numerical calculation, and generation of wrinkles of the material to be formed in press molding according to the estimated curvature radius ρ. By predicting the presence or absence, it is possible to predict the presence or absence of wrinkles of the molding material quickly and accurately by an easy method. In addition, when the absolute value of the radius of curvature ρ is equal to or less than a certain value, it is only predicted that wrinkles are generated, so that the presence or absence of wrinkles can be easily predicted.
図５は、曲率半径ρに応じて板材３を色分けして画像表示したものである。これにより、皺の発生の有無のみならず、その大きさや分布を、容易に把握することができる。
なお、曲げ応力σを板厚方向に沿って表面から裏面まで積分しなくても、表面から板厚の１／３まで及び裏面から板厚の１／３までを積分するだけでも、皺の発生の有無を予測するには十分である。この点は、そのようにした図６からも明らかである。この方法によれば、計算時間を短縮できるので、より速やかに皺の発生の有無を予測することができる。なお、図６は、曲率半径ρの代わりに曲率κに応じて板材３を色分けして画像表示したものである。
FIG. 5 shows the image of the plate 3 that is color-coded according to the radius of curvature ρ. As a result, it is possible to easily grasp not only the presence or absence of wrinkles but also the size and distribution thereof.
Even if the bending stress σ is not integrated from the front surface to the back surface along the plate thickness direction, wrinkles are generated only by integrating from the front surface to 1/3 of the plate thickness and from the back surface to 1/3 of the plate thickness. It is enough to predict the presence or absence. This point is also apparent from FIG. According to this method, since the calculation time can be shortened, it is possible to predict the occurrence of wrinkles more quickly. FIG. 6 shows the image of the plate 3 color-coded according to the curvature κ instead of the curvature radius ρ.
また、曲げ応力σの絶対値は中立面Ｓから最も離れた位置、すなわち表面または裏面で最大となるので、板材３の厚み方向断面に同方向に分布する曲げ応力σのうち表面の縁応力σtop_surfaceと裏面の縁応力σbottom_surfaceとが曲げモーメントＭに最も大きな影響を与えることになる。したがって、図７に示すように、これら縁応力の表裏面差を算出し、算出した縁応力の表裏面差と板材３の弾性係数Ｅと板厚ｔとに応じて、除荷した後の板材３の曲率κを推定するようにしてもよい。これによると、計算時間を更に短縮できるので、より速やかに皺の発生の有無を予測することができる。なお、縁応力は、板厚方向成分を無視して、最大主応力をもってこれに充てることなどもでき、この他にも、適宜工夫して、疑似相関的な指標を求め、代用するようにしてもよい。 Further, since the absolute value of the bending stress σ is maximized at a position farthest from the neutral plane S, that is, at the front surface or the back surface, the edge stress of the surface among the bending stress σ distributed in the same direction in the cross section in the thickness direction of the plate member 3. σ top_surface and back surface edge stress σ bottom_surface have the greatest influence on the bending moment M. Accordingly, as shown in FIG. 7, the difference between the front and back surfaces of the edge stress is calculated, and the plate material after unloading is calculated according to the calculated front and back surface difference of the edge stress, the elastic coefficient E of the plate material 3 and the plate thickness t. The curvature κ of 3 may be estimated. According to this, since the calculation time can be further shortened, it is possible to predict the occurrence of wrinkles more quickly. In addition, the edge stress can be assigned to the maximum principal stress by ignoring the component in the thickness direction. Also good.
以下、実施例について説明する。
表１は、実験に用いた材料の諸元を示している。
実験内容は、それぞれ５００ｍｍ角の冷延鋼板Ａ、及び高強度冷延鋼板Ｂ、Ｃを用い、プレス成形によってフロアパンを製作した。ホルダの圧力を３００ｋＮとし、シングルアクションでプレス成形を実施し、トリム（余肉除去成形）、及びリストライク（再プレス）は実施していない。また、ビードは設けず、潤滑は防錆油のみを使用した。
Examples will be described below.
Table 1 shows the specifications of the materials used in the experiment.
The experiment was conducted by using a 500 mm square cold-rolled steel sheet A and high-strength cold-rolled steel sheets B and C, and producing a floor pan by press molding. The pressure of the holder is 300 kN, press molding is performed with a single action, and trimming (removal removal molding) and re-striking (re-pressing) are not performed. Further, no beads were provided, and only rust preventive oil was used for lubrication.
表２は、本発明と従来例との比較結果を示している。
評価は、実験で得られた製品の皺を黙視で確認し、実際に皺が発生した部位に対して、計算で皺が発生すると予測した部位がどれだけ一致しているかを３段階で評価している。すなわち、予測した部位に実際に皺が発生していれば○、予測した部位に皺の兆候が見られれば△、予測した部位に皺が発生していなければ×としている。
Table 2 shows a comparison result between the present invention and the conventional example.
In the evaluation, the product wrinkles obtained in the experiment were confirmed silently, and the degree of coincidence between the part where the wrinkles actually occurred and the part predicted to be wrinkled in the calculation was evaluated in three stages. ing. That is, it is indicated as “◯” if a wrinkle actually occurs in the predicted part, “Δ” if a sign of wrinkle is seen in the predicted part, and “X” if no wrinkle occurs in the predicted part.
本発明と比較する従来例には、シェーディングによって予測する方法と、板厚中心の最小主応力を算出し、そのコンター図に基づいて予測する方法と、を採用している。また、本発明には、曲率κに応じて板材３を色分けして画像表示する方法と、曲率半径ρに応じて板材３を色分けして画像表示する方法と、を採用している。
また、本発明の方法と従来の手法の比較にあたり、ワークステーション６４ビット１ＣＰＵ（５５２ＭＨｚ）、２ＧＢメモリー、３６ＧＢハードディスクを使用した。解析用のデータとして自動車用外板部であるサイドパネルを用い、アダプティブを使用し、３０万メッシュ程度の鋼板のブランク（特性等は先の表１参照：冷延鋼板および高強度冷延鋼板０.７ｍｍ）を用いた。
The conventional example compared with the present invention employs a method of predicting by shading and a method of calculating the minimum principal stress at the center of the plate thickness and predicting based on the contour diagram. Further, the present invention employs a method of displaying images by color-coding the plate material 3 according to the curvature κ, and a method of displaying images by color-coding the plate material 3 according to the curvature radius ρ.
In comparison between the method of the present invention and the conventional method, a workstation 64-bit 1 CPU (552 MHz), 2 GB memory, and 36 GB hard disk were used. Using the side panel which is the outer plate part for automobiles as data for analysis, using adaptive, a steel plate blank of about 300,000 mesh (see Table 1 above for characteristics, etc .: cold-rolled steel sheet and high-strength cold-rolled steel sheet 0) 0.7 mm) was used.
本発明の方法との比較に用いた、各特許文献に示されている方法については、各特許文献より検討し、発明者自身が作製して用いた。本発明の方法では、シミュレーション解析をノンリニアペナルティ（ＮＬＰ）の陽解法により行った後に、皺をすばやく的確に判定するポスト処理をして、解析を行っている。この解析のしかたと実直に比較できるのが、特許文献１の方法であるため、特許文献１と比較してみた。 The method shown in each patent document used for comparison with the method of the present invention was examined from each patent document, and was prepared and used by the inventors themselves. In the method of the present invention, after simulation analysis is performed by an explicit method of non-linear penalty (NLP), post-processing for determining wrinkles quickly and accurately is performed for analysis. Since it is the method of Patent Document 1 that can be directly compared with this analysis method, it was compared with Patent Document 1.
その結果を表２に示す。この結果より、従来技術である特許文献１の方法は、軟鋼の冷延鋼板には適用可能であるが、高張力鋼板になるに従い、皺の判定が難しくなることがわかる。しかしながら、本発明の方法を用いた場合、問題なく皺の判定が可能となることがわかる。また、軟鋼の冷延鋼板を対象とした場合、特許文献１の方法でも、的確に皺を見出すことが可能であるものの、本発明の方法によれば、特許文献１の方法による計算時間に比較して、短時間で計算を行うことができ、本発明の有効性がわかった。 The results are shown in Table 2. From this result, it can be seen that the method of Patent Document 1 which is a prior art can be applied to a cold rolled steel sheet of mild steel, but it becomes more difficult to determine wrinkles as it becomes a high tensile steel sheet. However, when the method of the present invention is used, it can be seen that it is possible to determine wrinkles without problems. In addition, when a cold-rolled steel sheet of mild steel is targeted, the method of Patent Document 1 can accurately find defects, but according to the method of the present invention, it is compared with the calculation time by the method of Patent Document 1. Thus, the calculation can be performed in a short time, and the effectiveness of the present invention was found.
また、従来技術である特許文献２および特許文献３の方法による場合、本発明の方法による場合、それぞれの計算時間を比較すると、表３の結果が得られた。詳説しないが、内部の応力分布および歪について検討すると、それぞれほぼ同じような結果が得られており、そのため、計算時間で比較すると、本発明で用いているノンリニアペナルティ法が有利であることが分かる。この結果より、一般的な陽解法によるノンリニアペナルティ法による解析に、さらに本発明の方法を組み合わせることで、良好な結果を得られることもわかった。 In addition, in the case of the methods of Patent Document 2 and Patent Document 3 which are the prior art, and in the case of the method of the present invention, when the respective calculation times are compared, the results in Table 3 were obtained. Although not explained in detail, when the internal stress distribution and strain are examined, almost the same results are obtained, and therefore, it is understood that the nonlinear penalty method used in the present invention is advantageous when compared with the calculation time. . From this result, it was also found that an excellent result can be obtained by further combining the method of the present invention with the analysis by the general penalty method by the explicit method.
（１）Ａの素材を用いた比較
この場合、実際に、被成形材である板材に皺の発生は無く、どの予測方法も皺の発生が無いことを予測していたので、全ての方法が○となっている。
（２）Ｂの素材を用いた比較
シェーディングによって予測した場合、コーナ等の余肉が多く出るような部位では、予測した部位に実際に皺が発生しているものの、その他の部位では、実際に皺が発生している部位をシェーディングで確認することができなかったので、Ｂの素材を用いた場合には、適切な方法とはいえない。
(1) Comparison using A material In this case, there was actually no generation of wrinkles in the plate material being the molding material, and any prediction method predicted that there were no wrinkles. ○
(2) Comparison using the material of B When predicted by shading, wrinkles are actually generated in the predicted part in areas where there is a lot of excess corners, etc., but in other parts, Since the part where wrinkles are generated cannot be confirmed by shading, it is not an appropriate method when the material of B is used.
最小主応力によって予測した場合、予測した部位に実際に皺の兆候があるものの、不明瞭な部位もあり、充分な一致をみられなかったので、Ｂの素材を用いた場合には、十分な方法とはいえない。
曲率κまたは曲率半径ρによって予測した場合、予測した部位と実際に皺が発生している部位とが一致しており、Ｂの素材を用いた場合でも、正確な予測がなされているといえる。
When predicted by the minimum principal stress, the predicted part actually has signs of wrinkles, but there are also unclear parts, and there was not enough coincidence. It's not a method.
When predicted by the curvature κ or the curvature radius ρ, the predicted portion and the portion where wrinkles are actually generated match, and it can be said that accurate prediction is made even when the material of B is used.
（３）Ｃの素材を用いた比較
それぞれの予測結果は、Ｂの素材を用いた場合と同様である。
以上のように、本発明に係るプレス成形における被成形材の皺の発生の有無の予測方法によれば、従来の方法よりも正確に皺の発生の有無を予測することができ、実用的である。
したがって、本発明に係るプレス成形における被成形材の皺の発生の有無の予測方法に従って、プレス成形時に被成形材に皺が発生するか否かを予測する、予測手段を備えた予測装置や予測プログラムによれば、前述したそれぞれの効果を得ることができる。
(3) Comparison using C material Each prediction result is the same as when B material is used.
As described above, according to the method for predicting the presence or absence of wrinkles in a material to be molded in press molding according to the present invention, it is possible to predict the presence or absence of wrinkles more accurately than the conventional method, which is practical. is there.
Therefore, according to the prediction method for the presence or absence of wrinkles in the material to be molded in press molding according to the present invention, a prediction device or a prediction device equipped with a predicting means for predicting whether or not wrinkles are generated in the material during press molding According to the program, the above-described effects can be obtained.
また、本発明に係るプレス成形における被成形材の皺の発生の有無の予測方法に従って、プレス成形時に被成形材に皺が発生するか否かを予測し、予測した結果に基づいてプレス成形の条件を補償した上で、プレス成形を実際に行うようにすることで、実際のプレス成形において、生産性の向上、コストの削減、及び開発期間の短縮を図れるとともに、品質面、歩留面、工数面での改善を図ることができる。 Further, according to the method for predicting the presence or absence of wrinkles in the molding material in the press molding according to the present invention, whether or not wrinkles are generated in the molding material at the time of press molding is predicted. By actually performing press molding after compensating the conditions, in actual press molding, productivity can be improved, costs can be reduced, and the development period can be shortened. Improvements in man-hours can be achieved.
１ ダイ
２ ホルダ
３ 板材
４ パンチ
５ ドロービード
Ｓ 中立面
1 Die 2 Holder 3 Plate 4 Punch 5 Draw Bead S Neutral Surface
Claims (8)
プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力を算出し、算出した曲げ応力を前記被成形材の厚み方向に沿って表面から裏面まで積分し、積分した曲げ応力と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測することを特徴とするプレス成形における被成形材の皺の発生の有無の予測方法。 In the prediction method of the presence or absence of wrinkles of the molding material in press molding to predict whether wrinkles occur in the molding material during press molding,
Calculate the bending stress distributed in the same direction in the cross section in the thickness direction of the workpiece at the bottom dead center in press molding, and integrate the calculated bending stress from the front surface to the back surface along the thickness direction of the workpiece. The curvature radius or curvature of the molding material after unloading is estimated according to the bending stress and the elastic modulus and thickness of the molding material, and the molding material is subjected to press molding according to the estimated curvature radius or curvature. A method for predicting the presence or absence of wrinkles on a molding material in press molding, wherein wrinkles are predicted in the molding material.
プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力を算出し、算出した曲げ応力を前記被成形材の表面から前記被成形材の厚みの１／３まで及び前記被成形材の裏面から前記被成形材の厚みの１／３まで積分し、積分した曲げ応力と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測することを特徴とするプレス成形における被成形材の皺の発生の有無の予測方法。 In the prediction method of the presence or absence of wrinkles of the molding material in press molding to predict whether wrinkles occur in the molding material during press molding,
The bending stress distributed in the same direction in the cross section in the thickness direction of the molding material is calculated at the bottom dead center in press molding, and the calculated bending stress is reduced from the surface of the molding material to 1/3 of the thickness of the molding material. And from the back surface of the molding material to 1/3 of the thickness of the molding material, and the molding material after unloading according to the integrated bending stress and the elastic modulus and thickness of the molding material The curvature radius or curvature of the molding material is estimated, and whether or not wrinkles occur in the molding material during press molding according to the estimated curvature radius or curvature is predicted. Prediction method of occurrence.
プレス成形における下死点で前記被成形材の厚み方向断面に同方向に分布する曲げ応力のうち前記被成形材の表裏面の縁応力を算出し、算出した縁応力の表裏面差を算出し、算出した縁応力の表裏面差と前記被成形材の弾性係数と厚みとに応じて、除荷した後の当該被成形材の曲率半径または曲率を推定し、推定した曲率半径または曲率に応じてプレス成形時に前記被成形材に皺が発生するか否かを予測することを特徴とするプレス成形における被成形材の皺の発生の有無の予測方法。 In the prediction method of the presence or absence of wrinkles of the molding material in press molding to predict whether wrinkles occur in the molding material during press molding,
Calculate the edge stress of the front and back surfaces of the molding material among bending stresses distributed in the same direction in the thickness direction cross section of the molding material at the bottom dead center in press molding, and calculate the difference between the front and back surfaces of the calculated edge stress. The curvature radius or curvature of the molding material after unloading is estimated according to the difference between the front and back surfaces of the calculated edge stress and the elastic modulus and thickness of the molding material, and according to the estimated curvature radius or curvature. A method for predicting the presence or absence of wrinkles in a molding material in press molding, wherein whether or not wrinkles occur in the molding material during press molding is predicted.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010036239A (en) * | 2008-08-08 | 2010-02-18 | Honda Motor Co Ltd | Method for predicting occurrence of deformation |
| JP2018034176A (en) * | 2016-08-30 | 2018-03-08 | Ｊｆｅスチール株式会社 | Method for manufacturing press-molded product |
| JP2018108593A (en) * | 2017-01-05 | 2018-07-12 | Ｊｆｅスチール株式会社 | Spring-back amount prediction method |
| WO2023007875A1 (en) | 2021-07-30 | 2023-02-02 | Ｊｆｅスチール株式会社 | Wrinkling assessment indicator acquisition method, wrinkling assessment method, wrinkling assessment device, and wrinkling assessment program for press-formed part |
-
2006
- 2006-02-28 JP JP2006054127A patent/JP2007229761A/en active Pending
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010036239A (en) * | 2008-08-08 | 2010-02-18 | Honda Motor Co Ltd | Method for predicting occurrence of deformation |
| JP2018034176A (en) * | 2016-08-30 | 2018-03-08 | Ｊｆｅスチール株式会社 | Method for manufacturing press-molded product |
| JP2018108593A (en) * | 2017-01-05 | 2018-07-12 | Ｊｆｅスチール株式会社 | Spring-back amount prediction method |
| WO2023007875A1 (en) | 2021-07-30 | 2023-02-02 | Ｊｆｅスチール株式会社 | Wrinkling assessment indicator acquisition method, wrinkling assessment method, wrinkling assessment device, and wrinkling assessment program for press-formed part |
| KR20240025686A (en) | 2021-07-30 | 2024-02-27 | 제이에프이 스틸 가부시키가이샤 | Method for obtaining a wrinkle occurrence determination index for press molded products, wrinkle occurrence determination method, wrinkle occurrence determination device, and wrinkle occurrence determination program |
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