JP2006341295A - Method and device for predicting surface strain of press molded product - Google Patents
Method and device for predicting surface strain of press molded product Download PDFInfo
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本発明は、プレス成形品の面ひずみによる形状の不具合を予測・評価するためのプレス成形品の面ひずみ予測方法および装置に関するものである。 The present invention relates to a method and an apparatus for predicting surface strain of a press-formed product for predicting and evaluating a shape defect due to surface strain of the press-formed product.
近年、特に自動車など車両の軽量化を実現するため、ドアやフードなどの自動車アウター部品といったプレス成形品に高強度鋼板適用拡大が進められている。しかし高強度鋼板は、軟鋼板と比較してプレス成形後の弾性回復（スプリングバック）が大きく、成形品表面に面ひずみと呼ばれるミクロンオーダのゆがみが生じやすい性質がある。そして、成形品表面に生じた面ひずみは、自動車の外観品質を大きく低下させることから、製作現場では面ひずみを生じさせないように実物のプレス金型の形状修正を幾度となく繰り返している。 In recent years, in order to reduce the weight of vehicles such as automobiles, the application of high-strength steel sheets has been promoted to press-formed products such as automobile outer parts such as doors and hoods. However, a high-strength steel plate has a property that the elastic recovery (spring back) after press forming is larger than that of a mild steel plate, and distortion of micron order called surface strain is likely to occur on the surface of the molded product. And since the surface distortion produced on the surface of the molded product greatly deteriorates the appearance quality of the automobile, the shape correction of the actual press mold is repeated several times so as not to cause the surface distortion at the production site.
このような現場でのプレス金型形状修正作業を廃止ないしは軽減する必要性から、これまでにコンピュータシミュレーション技術を応用した種々の解析システムが開発され、金型設計段階で利用されている。 Due to the necessity of abolishing or mitigating such on-site press mold shape correction work, various analysis systems applying computer simulation technology have been developed and used at the mold design stage.
例えば、特許文献１に開示された技術がある。この技術は、成形プロセスおける成形面の形状不良評価において、成形すべき目標である基準形状データを与え、成形プロセスの数値解析シミュレーションにより、予測される成形後のワーク成形面に関するワーク形状データを求め、基準形状データから参照点を選択し、参照点に対応したワーク形状上の目標点との逸脱量により成形面の形状不良を評価するものである。 For example, there is a technique disclosed in Patent Document 1. This technology gives reference shape data, which is the target to be formed, in the shape defect evaluation of the forming surface in the forming process, and obtains the work shape data related to the predicted work forming surface after forming by numerical analysis simulation of the forming process. The reference point is selected from the standard shape data, and the shape defect of the molding surface is evaluated by the deviation amount from the target point on the workpiece shape corresponding to the reference point.
また、特許文献２に開示された技術もある。この技術は、板材から成形体を製造するプレス成形の数値シミュレーション結果に基づいて、プレス下死点での成形体の形状面に垂直に作用する面外偏差応力分布を取得し、その面外偏差応力分布に基づいて面ひずみを予測するものである。
しかしながら、上記特許文献１で開示されている技術では、高強度鋼板を用いた成形品の形状不良評価を精度良く行うことができない。すなわち、プレス成形後に弾性回復により発生する成形品表面にミクロンオーダの変形を正確に予測できないためである。 However, the technique disclosed in Patent Document 1 cannot accurately evaluate the shape defect of a molded product using a high-strength steel plate. In other words, it is because a micron-order deformation cannot be accurately predicted on the surface of a molded product generated by elastic recovery after press molding.
また、上記特許文献２で開示されている技術は、形状面に垂直に作用する面外偏差応力分布により面ひずみを予測する技術であるが、現状一般に行われているプレス成形シミュレーションでは、材料を垂直応力を０と仮定したシェル要素が適用されており、面外偏差応力を精度よく算出することは難しい。材料の垂直応力を考慮したソリッド要素で解析することも技術的には可能であるが、計算時間が膨大となり、現状では工業的な利用価値は小さいと言わざるおえない。 In addition, the technique disclosed in Patent Document 2 is a technique for predicting a surface strain by an out-of-plane deviation stress distribution acting perpendicularly to a shape surface. A shell element assuming that the normal stress is 0 is applied, and it is difficult to accurately calculate the out-of-plane deviation stress. Although it is technically possible to analyze with a solid element that takes into account the normal stress of the material, the calculation time becomes enormous and the industrial utility value is small at present.
また、高強度鋼板適用における面ひずみの検討においては、材料に発生する応力レベルが軟鋼板と比較して増大するため、面外偏差応力の絶対値レベルが変化する。面ひずみ発生の検討には、応力の周りとの不均一性を考慮に入れることが必要であり、そのため、材料置換等の検討において、特許文献２で提案されている面外偏差応力では面ひずみ発生の有無を合理的・定量的に判断することが困難である。 Further, in the study of surface strain in the application of high-strength steel sheets, the level of stress generated in the material increases as compared with that of mild steel sheets, so the absolute value level of out-of-plane deviation stress changes. It is necessary to take into account the non-uniformity around the stress in the study of the occurrence of surface strain. Therefore, in the study of material replacement, etc., the out-of-plane deviation stress proposed in Patent Document 2 is subject to surface strain. It is difficult to reasonably and quantitatively determine whether it has occurred.
さらに、上記特許文献１および特許文献２で開示されている技術では、板厚を考慮することができず、材料板厚の設計変更する検討ができないという問題がある。板厚が厚いほど面ひずみは発生しにくく、板厚が薄くなるほど面ひずみの度合いが大きくなることは一般的に知られた事実であり、面ひずみ予測において材料板厚の考慮は不可欠である。 Further, the techniques disclosed in Patent Document 1 and Patent Document 2 have a problem that the plate thickness cannot be taken into consideration and the design change of the material plate thickness cannot be considered. It is a generally known fact that surface strain is less likely to occur as the plate thickness is increased, and that the degree of surface strain is increased as the plate thickness is reduced. Therefore, it is indispensable to consider the material plate thickness in surface strain prediction.
本発明は、上記課題を解決するためになされたものであり、プレス成形品の面ひずみによる形状の不具合を精度良く予測・評価するためのプレス成形品の面ひずみ予測方法および装置を提供することを目的とする。 The present invention has been made to solve the above-described problems, and provides a press-molded product surface strain prediction method and apparatus for accurately predicting and evaluating shape defects due to surface strain of a press-formed product. With the goal.
本発明の請求項１に係る発明は、プレス成形品の成形過程の解析をおこなった後、パンチ下死点時の成形品各要素に発生する最小主応力値と板厚値を取得し、面ひずみ解析対象面に位置するすべての前記最小主応力値の平均値である平均最小主応力値を算出した後、該平均最小主応力値、前記最小主応力値、および前記板厚値を基にした評価値を算出し、該評価値の分布を３次元的に表示することにより面ひずみの発生位置および発生度合いを予測することを特徴とするプレス成形品の面ひずみ予測方法である。 The invention according to claim 1 of the present invention obtains the minimum principal stress value and the plate thickness value generated in each element of the molded product at the bottom dead center of the punch after analyzing the molding process of the press molded product, After calculating an average minimum principal stress value, which is an average value of all the minimum principal stress values located on the strain analysis target surface, based on the average minimum principal stress value, the minimum principal stress value, and the plate thickness value This is a method for predicting the surface strain of a press-molded product, wherein the evaluation value is calculated, and the generation position and the degree of the surface strain are predicted by displaying the distribution of the evaluation value three-dimensionally.
また本発明の請求項２に係る発明は、請求項１に記載のプレス成形品の面ひずみ予測方法において、前記評価値は、（最小主応力値−平均最小主応力値）／（A*板厚値2）、（ここで、Aは部品形状によって決定される定数である）、にて算出することを特徴とするプレス成形品の面ひずみ予測方法である。 The invention according to claim 2 of the present invention is the press-molded product surface strain prediction method according to claim 1, wherein the evaluation value is (minimum principal stress value−average minimum principal stress value) / (A * plate). Thickness value 2 ) (where A is a constant determined by the part shape).
さらに本発明の請求項３に係る発明は、パンチ下死点時の成形品各要素に発生する最小主応力値と板厚値を取得する成形過程解析データ取得手段と、面ひずみ解析対象面に位置するすべての前記最小主応力値の平均値である平均最小主応力値を算出する平均最小主応力値演算手段と、該平均最小主応力値、前記最小主応力値、および前記板厚値を基にした評価値を算出する評価値演算手段と、該評価値の分布を３次元的に表示する表示手段と、を備えることを特徴とするプレス成形品の面ひずみ予測装置である。 Further, the invention according to claim 3 of the present invention is a molding process analysis data acquisition means for acquiring a minimum principal stress value and a plate thickness value generated in each element of a molded product at the time of punch bottom dead center, and a surface strain analysis target surface. An average minimum principal stress value calculating means for calculating an average minimum principal stress value that is an average value of all the minimum principal stress values located; the average minimum principal stress value, the minimum principal stress value, and the plate thickness value; An apparatus for predicting surface distortion of a press-formed product, comprising: an evaluation value calculating unit that calculates an evaluation value based on the display unit, and a display unit that three-dimensionally displays the distribution of the evaluation value.
本発明では、最小主応力の周囲の平均値からの偏差という概念を用いた最小主応力偏差値という面ひずみ評価値を提案するようにしたので、材料強度の絶対レベルによらず定量的に精度良く面ひずみを予測することが可能である。さらに本発明で提案した最小主応力偏差値には板厚の影響も加味しており、素材板厚の影響も考慮した上で面ひずみの予測が可能である。 In the present invention, since the surface strain evaluation value called the minimum principal stress deviation value using the concept of deviation from the average value around the minimum principal stress is proposed, it is quantitatively accurate regardless of the absolute level of the material strength. It is possible to predict the surface strain well. Furthermore, the minimum principal stress deviation value proposed in the present invention takes into account the influence of the plate thickness, and the surface strain can be predicted in consideration of the influence of the material plate thickness.
以下、本発明について図面を参照して具体的に説明する。図１は、本発明に係る面ひずみ予測・評価するための処理手順例を示すフローチャートである。 Hereinafter, the present invention will be specifically described with reference to the drawings. FIG. 1 is a flowchart showing an example of a processing procedure for predicting and evaluating a surface strain according to the present invention.
本発明の実施にあたり、プレス成形過程の解析には、応力、歪、変形などを解析できるものであれば良く、コンピュータを用いたシミュレーション（CAE）または実験（例えば、歪ゲージを用いた解析など）を、目的に応じて使い分けることができる。以下の説明では、CAEの例として有限要素法による解析を例にフローチャートにそって説明してゆくものとする。 In carrying out the present invention, the press forming process may be analyzed as long as it can analyze stress, strain, deformation, etc., and simulation (CAE) using a computer or experiment (for example, analysis using a strain gauge) Can be used properly according to the purpose. In the following description, the analysis by the finite element method will be described as an example of CAE along the flowchart.
処理をスタート(Step100)すると、まず有限要素の定義を行い(Step101)、次のプレス成形過程の解析(Step102)の処理を行う。有限要素法による応力分布などのプレス成形解析が終了した後、面ひずみを解析する平面もしくは曲面を選択する(Step103)。ここでの解析面選択においては、コンピュータが判断して自動的に選択するか、解析者が製品形状を考慮してコンピュータの表示画面上で選択することも可能である。パンチ下死点での解析対象面に位置する各有限要素の最小主応力値S2 (Step104)および板厚データt(Step105)を、有限要素解析結果から取得する。 When the processing is started (Step 100), first, a finite element is defined (Step 101), and the next press forming process analysis (Step 102) is performed. After press forming analysis such as stress distribution by the finite element method is completed, a plane or curved surface for analyzing surface strain is selected (Step 103). In the analysis surface selection here, the computer can make a judgment and select automatically, or the analyst can select on the display screen of the computer in consideration of the product shape. The minimum principal stress value S2 (Step 104) and plate thickness data t (Step 105) of each finite element located on the analysis target surface at the punch bottom dead center are acquired from the finite element analysis result.
せん断応力がゼロである面に作用している垂直応力を主応力(principal stress)と呼び、このうち最小の主応力を最小主応力と呼ぶ。ある応力場［σij］=［Σ］が与えられたとき、主応力およびその作用する面は次のように決定できる。主応力の作用している面を表す面ベクトルをｎ(p)={ｎ(p) }(この方向は主応力方向［principal direction of stress］と呼ばれる)、主応力の大きさをｎ(p) とすると、主応力ベクトルは面ベクトルｎ(p) の方向に一致しσ(p)ｎ(p) と表される。従って、コーシーの関係式から次式（１）が成り立つ。
Σｎ(p) =σ(p)ｎ(p) あるいは ［Σ］{ｎ(p) }=σ(p) {ｎ(p) } ・・・・・（１）
上記σ(p) のうち最小の主応力が最小主応力であり、その大きさを最小主応力値と呼び、S2と表す（吉田総仁著、弾塑性力学の基礎、共立出版、pp36〜38参照）。
The normal stress acting on the surface where the shear stress is zero is called principal stress, and the minimum principal stress is called the minimum principal stress. When a certain stress field [σ ij ] = [Σ] is given, the principal stress and the surface on which it acts can be determined as follows. The surface vector representing the surface on which the main stress is applied is n (p) = {n (p) } (this direction is called the principal direction of stress), and the magnitude of the main stress is n (p ) and when the main stress vector is expressed as matching the direction of the plane vector n (p) σ (p) n (p). Therefore, the following equation (1) is established from the Cauchy relational expression.
Σn (p) = σ (p) n (p) or [Σ] {n (p) } = σ (p) {n (p) } (1)
Of the above σ (p) , the minimum principal stress is the minimum principal stress, and the magnitude is called the minimum principal stress value, which is expressed as S2. reference).
シェル要素で応力を計算する場合、板厚の表面、中央面、および裏面の最小主応力をそれぞれ計算することが可能である。本発明においては、板厚中央の最小主応力を採用したが、表面、中央面、および裏面の平均値や最大値を用いることも可能である。
図１の処理手順例を示すフローチャートの説明に戻り、Step106の後、解析対象面に位置する有限要素すべての最小主応力値S2を平均化して、平均最小主応力値S2aveを算出する(Step106)。そして、上記のデータから、以下の（２）式で定義される各有限要素の最小主応力偏差値S2devを算出する(Step107)。 S2dev = (S2 - S2ave ) / (A * t2 ) ・・・・・（２）
ここで、Aは部品形状によって決定される定数であり、例えば、対象の面が平面の場合には、A＝1.0〜2.0の範囲の値を、対象の面が曲率をもっている場合には、曲率の大きさに比例してA＝2.0〜10.0の範囲の値を用いればよい。
When calculating the stress in the shell element, it is possible to calculate the minimum principal stresses on the front, center and back surfaces of the plate thickness. In the present invention, the minimum principal stress at the center of the plate thickness is adopted, but it is also possible to use average values and maximum values of the front surface, the central surface, and the back surface.
Returning to the description of the flowchart showing the processing procedure example in FIG. 1, after Step 106, the average minimum principal stress value S2ave is calculated by averaging the minimum principal stress values S2 of all the finite elements located on the analysis target surface (Step 106). . Then, the minimum principal stress deviation value S2dev of each finite element defined by the following equation (2) is calculated from the above data (Step 107). S2dev = (S2-S2ave) / (A * t 2 ) (2)
Here, A is a constant determined by the part shape. For example, when the target surface is a plane, a value in the range of A = 1.0 to 2.0, and when the target surface has a curvature, the curvature is A value in the range of A = 2.0 to 10.0 may be used in proportion to the size of.
座屈理論の教えるところによれば、「座屈強度は板厚ｔの２乗に比例する」、すなわち、板厚が増せば増すほど板厚の２乗に比例して、座屈強度が増すというものである。座屈強度が増すと言うことは、面ひずみが生じにくくなることでもある。また、発明者らの研究により、「面ひずみ発生の原因は、最小主応力の不均一度合いに比例する」という知見も得ている。このような知見から本発明では、最小主応力値S2、平均最小主応力値S2aveおよび板厚ｔを基にした評価値すなわち最小主応力偏差値S2devを（２）式のように定義している。 According to the teaching of buckling theory, “the buckling strength is proportional to the square of the thickness t”, that is, as the thickness increases, the buckling strength increases in proportion to the square of the thickness. That's it. The fact that the buckling strength is increased also means that surface distortion is less likely to occur. Furthermore, the inventors have also obtained the knowledge that “the cause of surface strain is proportional to the degree of nonuniformity of the minimum principal stress”. Based on such knowledge, in the present invention, an evaluation value based on the minimum principal stress value S2, the average minimum principal stress value S2ave, and the sheet thickness t, that is, the minimum principal stress deviation value S2dev is defined as shown in Equation (2). .
算出した最小主応力偏差値S2devを３次元表示して、解析対象面における最小主応力偏差値の分布状態を３次元的に可視化する(Step108)。解析者は、この最小主応力偏差値の分布状態から、評価値の大小および分布密度を判断して、面ひずみの発生を予測する。さらに解析者は、最小主応力偏差値の分布状態と面ひずみの発生状況を過去に蓄積したデータベースを参照することにより、面ひずみの予測および対策方法を検討することも可能である。 The calculated minimum principal stress deviation value S2dev is displayed three-dimensionally, and the distribution state of the minimum principal stress deviation value on the analysis target surface is visualized three-dimensionally (Step 108). The analyst predicts the occurrence of surface strain by judging the magnitude and distribution density of the evaluation value from the distribution state of the minimum principal stress deviation value. Furthermore, the analyst can also examine a method for predicting the surface strain and a countermeasure method by referring to a database in which the distribution state of the minimum principal stress deviation value and the occurrence state of the surface strain are stored in the past.
図３は、本発明で提示した最小主応力偏差による面ひずみ評価の一例を示した図である。自動車用ドアアウターパネルのドア取手（中央上方部の白い楕円部分）部付近の面ひずみを評価したものであり、板厚0.7mmの2つの異なる引張強度を持つ鋼鈑での最小主応力偏差値分布を（ａ）および（ｂ）に、さらに（ｃ）には、要素ごとの最小主応力のヒストグラムを示したものである。 FIG. 3 is a diagram showing an example of surface strain evaluation based on the minimum principal stress deviation presented in the present invention. This is an evaluation of the surface strain near the door handle (white ellipse at the center upper part) of the outer door panel for automobiles, and the minimum principal stress deviation value in steel plates with two different tensile strengths with a thickness of 0.7 mm. The distributions are shown in (a) and (b), and (c) shows a histogram of the minimum principal stress for each element.
図中、（ａ）は引張強度270MPa、（ｂ）は引張強度390MPaの高強度鋼鈑のものであり、解析面の最小主応力偏差分布を、最小主応力偏差が負の値[−250（黒）]から正の値[250（白）]へと図中の濃淡で表している。（ａ）および（ｂ）の最小主応力偏差分布を見比べてみると、引張強度の高い（ｂ）の方が、引張強度の低い（ａ）のものより取手境界の濃淡の変化すなわち最小主応力偏差の変化が大きいことが分る。また、最小主応力平均値は、（ａ）145MPaおよび（ｂ）196MPaであり、最小主応力の絶対レベルも引張強度の高い（ｂ）の方が高くなっている。さらに、それぞれの最小主応力分布を、（ｃ）の最小主応力ヒストグラムで見てみると、両者の差がはっきり分る。すなわち、（ａ）と（ｂ）では、引張強度の低い（ａ）の方がピークが立っており平均を挟んで割合対称の形の分布であるのに対して、引張強度の高い（ｂ）はピークが低く、平均値(196MPa)より高いところに2
番目のピークの存在が確認できる。
In the figure, (a) is for a high strength steel plate with a tensile strength of 270 MPa, (b) is for a high strength steel plate with a tensile strength of 390 MPa, and the minimum principal stress deviation distribution on the analysis surface is a negative value [−250 ( The black and white in the figure shows the value from (black)] to a positive value [250 (white)]. Comparing the minimum principal stress deviation distributions of (a) and (b), the change in shading of the handle boundary, that is, the minimum principal stress, is higher for (b) with higher tensile strength than for (a) with lower tensile strength. It can be seen that the change in deviation is large. Moreover, the minimum principal stress average values are (a) 145 MPa and (b) 196 MPa, and the absolute level of the minimum principal stress is higher in (b) where the tensile strength is higher. Further, when each minimum principal stress distribution is viewed in the minimum principal stress histogram of (c), the difference between the two is clearly seen. That is, in (a) and (b), the lower tensile strength (a) has a higher peak and a distribution with a symmetrical shape across the average, whereas the higher tensile strength (b) Is 2 where the peak is low and higher than the average value (196 MPa).
The presence of the second peak can be confirmed.
図２は、本発明に係る面ひずみ予測装置の構成例を示す図である。面ひずみ予測装置は、大きくは一般のパソコン等の計算機と、この計算機に対して面ひずみ予測・評価を行わせるアプリケーションプログラムとで構成することができる。図１中、１は操作部、２は表示部、３は演算部、４は平均最小主応力値演算部、５は評価値演算部、６は入出力部、７は記憶部、および８はデータベースをそれぞれ示す。 FIG. 2 is a diagram illustrating a configuration example of the surface strain prediction apparatus according to the present invention. The surface strain prediction apparatus can be roughly composed of a computer such as a general personal computer and an application program that makes the computer perform surface strain prediction / evaluation. In FIG. 1, 1 is an operation unit, 2 is a display unit, 3 is a calculation unit, 4 is an average minimum principal stress value calculation unit, 5 is an evaluation value calculation unit, 6 is an input / output unit, 7 is a storage unit, and 8 is Each database is shown.
面ひずみ予測装置は、演算部３を備えており、この演算部３は、操作部１、表示部２、記憶部７、および入出力部６に対し動作指令を行うとともに、必要なデータや信号のやり取りを行っている。操作部１は解析者が動作を指示する部位であり、キーボード等の入力装置により構成される。表示部２はモニタ画面等の出力装置で構成され、計算結果、最小主応力偏差値分布等を表示する。記憶部７はメモリやハードディスク等の記憶装置から構成され、演算に必要な情報や、過去の最小主応力偏差値の分布状態および面ひずみの発生状況を蓄積したデータをデータベースなどの形で記憶を行うものである。 The surface strain prediction apparatus includes a calculation unit 3 that issues operation commands to the operation unit 1, the display unit 2, the storage unit 7, and the input / output unit 6 as well as necessary data and signals. We are exchanging. The operation unit 1 is a part where an analyst instructs an operation, and is configured by an input device such as a keyboard. The display unit 2 includes an output device such as a monitor screen, and displays a calculation result, a minimum principal stress deviation value distribution, and the like. The storage unit 7 is composed of a storage device such as a memory or a hard disk, and stores information necessary for calculation, data accumulated in the past distribution state of minimum principal stress deviation values and occurrence of surface strain in the form of a database or the like. Is what you do.
さらに、入出力部６はネットワーク入出力部や記録メディア入出力部から構成され、これにより、外部との情報のやり取りを行うことができる。入力される情報の例としては、例えば数値シミュレーションによるプレス成形過程の解析結果を利用する場合は、数値シミュレーションの結果を保持する装置から入力する成形体の形状特性データ、材料特性データ、シミュレーション結果などが挙げられる。実験による成形過程の解析結果を利用する場合にも、同様の情報が入力される。 Furthermore, the input / output unit 6 includes a network input / output unit and a recording medium input / output unit, and can exchange information with the outside. As an example of information to be input, for example, when using the analysis result of the press molding process by numerical simulation, the shape characteristic data, material characteristic data, simulation result, etc. of the molded body input from the device holding the numerical simulation result, etc. Is mentioned. The same information is also input when using the analysis result of the molding process by experiment.
演算部３には、平均最小主応力値演算部４と評価値演算部５が含まれている。平均最小主応力値演算部４は、入出力部６から入力された応力情報に基づいて最小主応力値および平均最小主応力値演算を行うことができる。なお、入出力部６を介さないで演算部３内部において数値シミュレーションも行う場合には、そのシミュレーション実行後得られた応力情報に基づいて最小主応力値および平均最小主応力値演算を行うことになる。 The calculation unit 3 includes an average minimum principal stress value calculation unit 4 and an evaluation value calculation unit 5. The average minimum principal stress value calculation unit 4 can calculate the minimum principal stress value and the average minimum principal stress value based on the stress information input from the input / output unit 6. In the case where a numerical simulation is also performed inside the calculation unit 3 without using the input / output unit 6, the minimum main stress value and the average minimum main stress value are calculated based on the stress information obtained after the execution of the simulation. Become.
評価値演算部５は、平均最小主応力値演算部４によって演算された最小主応力値および平均最小主応力値を入力して、評価値の計算を行う。評価値を求める一連の演算には、入出力部６から入力される成形体の形状特性データ、材料特性データ、シミュレーション結果などを適宜用いる。 The evaluation value calculation unit 5 inputs the minimum main stress value and the average minimum main stress value calculated by the average minimum main stress value calculation unit 4 and calculates the evaluation value. For a series of operations for obtaining the evaluation value, shape characteristic data, material characteristic data, simulation results, and the like of the molded body input from the input / output unit 6 are appropriately used.
また、記憶部７には、演算に必要な情報や評価値演算部５が評価値を演算する際に提供する対応関係情報のデータなどが格納される。対応関係情報は、評価値を面品質と対応づけるための情報であり、理論式や実験結果に基づいて予め与えられているものである。 Further, the storage unit 7 stores information necessary for calculation, data of correspondence information provided when the evaluation value calculation unit 5 calculates an evaluation value, and the like. The correspondence information is information for associating the evaluation value with the surface quality, and is given in advance based on a theoretical formula or an experimental result.
各種高強度鋼板( 強度レベル270MPa,340MPa,390MPa,および440MPaの4種で、板厚は0.7mmと同じ)を用いて、自動車用ドアアウターパネルの成形試験を実施するとともに、シミュレーションによる解析を行った。解析方法は、プレス成形過程の解析には市販の解析システム（ソルバー：LS-DYNA ver.970）を使用し、その後の面ひずみ予測には、本発明の手法を用いた。 Using various high strength steel plates (strength levels of 270MPa, 340MPa, 390MPa, and 440MPa, plate thickness is the same as 0.7mm), molding test of automobile door outer panel and analysis by simulation It was. As the analysis method, a commercially available analysis system (Solver: LS-DYNA ver. 970) was used for the analysis of the press forming process, and the method of the present invention was used for the subsequent surface strain prediction.
図４は、実験（ゼブラ表示）による面ひずみ評価を示す図である。白と黒の直線状ストライプをもった光源を塗装したプレス品に写し込む（ゼブラ表示）ことにより、面ひずみによる外観不良を評価するものである。写り込んだ平行線が歪んで見える場合、面ひずみが発生していると判断でき、ドア取手部での平行線の歪が確認できる。 FIG. 4 is a diagram showing surface strain evaluation by experiment (zebra display). By imprinting a light source with white and black linear stripes onto a pressed product (zebra display), the appearance defect due to surface distortion is evaluated. When the reflected parallel lines appear to be distorted, it can be determined that surface distortion has occurred, and the distortion of the parallel lines at the door handle can be confirmed.
さらに、図５は実験と本発明による面ひずみ評価結果の比較を示す図である。図は、左側に実験によるゼブラ表示と、右側に本発明で提案した最小主応力偏差の分布を、上から下へ強度レベル270MPa,340MPa,390MPa,および440MPaの4種高強度鋼板についての結果を、対比できるように示している。270MPaの鋼鈑では面ひずみが確認できなかったが、強度が増すにつれて面ひずみが出始めて、440MPaの鋼鈑では面ひずみが大きくなっていることが確認できる。本発明で提案した最小主応力偏差の分布も、上から下に行くにしたがって（強度が増すにつれて）濃淡の変化すなわち最小主応力偏差の変化が大きくなっている。図６には、材料強度が大きく異なる270MPaと440MPaについて、注目部分を拡大して詳細に示しており、440Mpaの強度が高い方が注目部分の最小主応力偏差の等高線が込み合っている様子を、より明確に確認することが出来る。 Further, FIG. 5 is a diagram showing a comparison between the experiment and the surface strain evaluation result according to the present invention. The figure shows the experimental zebra display on the left side, the distribution of the minimum principal stress deviation proposed in the present invention on the right side, and the results for the four high strength steel sheets with strength levels of 270 MPa, 340 MPa, 390 MPa, and 440 MPa from top to bottom. , So that it can be contrasted. Although the surface strain could not be confirmed with the 270 MPa steel plate, the surface strain began to appear as the strength increased, and it can be confirmed that the surface strain increased with the 440 MPa steel plate. Also in the distribution of the minimum principal stress deviation proposed in the present invention, the change in shading, that is, the change in the minimum principal stress deviation becomes larger from the top to the bottom (as the strength increases). In FIG. 6, the attention part is enlarged and shown in detail for 270 MPa and 440 MPa with greatly different material strengths, and the contour of the minimum principal stress deviation of the attention part is crowded when the strength of 440 MPa is higher. It can be confirmed more clearly.
このように、面ひずみの発生（実験によるゼブラ表示）と本発明で提案した評価値（最小主応力偏差）の分布は良く一致しており、面ひずみの発生位置と大きさを本発明により予測可能であることを示している。材料強度の異なる高強度鋼板を比較しているが、材料強度レベルによらず同一の基準で面ひずみを予測することも可能である。 Thus, the distribution of the surface strain (experience zebra display by experiment) and the distribution of the evaluation value (minimum principal stress deviation) proposed in the present invention are in good agreement, and the position and magnitude of the surface strain are predicted by the present invention. It shows that it is possible. Although high-strength steel sheets with different material strengths are compared, it is also possible to predict surface strain on the same basis regardless of the material strength level.
図７は、面ひずみに及ぼす取手深さの影響を検討した結果（実験）を示す図である。270MPaと440MPaの材料強度の鋼鈑を用いて、取手深さを０〜1４mmまで変化させたもの（10種類）を、ゼブラ表示させたものである。取手深さが深くなればなるほど、ゼブラ模様が歪んでいく様子が確認できる。さらに、図８(取手深さ0,4mm)および図９（取手深さ7,12mm）には、図６と同様に注目部分を拡大した、実験（ゼブラ表示）と本発明で提案した最小主応力偏差の分布の対比を示している。ここでも、面ひずみの発生と本発明で提案した評価値（最小主応力偏差）の分布は良く一致していることが確認できる。 FIG. 7 is a diagram showing a result (experiment) of examining the influence of the handle depth on the surface strain. Using steel plates with material strengths of 270MPa and 440MPa, the handle depth changed from 0 to 14mm (10 types) was displayed in zebra. It can be confirmed that the zebra pattern is distorted as the handle depth increases. 8 (handle depth 0,4 mm) and FIG. 9 (handle depth 7,12 mm) are the same as in FIG. It shows the contrast of the stress deviation distribution. Again, it can be confirmed that the occurrence of surface strain and the distribution of the evaluation value (minimum principal stress deviation) proposed in the present invention are in good agreement.
以上説明したように、本発明では最小主応力の周囲の平均値からの偏差という概念を用いた最小主応力偏差値という面ひずみ評価値を提案することにより、材料強度の絶対レベルによらず定量的に精度良く面ひずみを予測することが可能である。さらに本発明で提案した最小主応力偏差値には板厚の影響も加味しており、素材板厚の影響も考慮した上で面ひずみの予測が可能である。 As described above, the present invention proposes a surface strain evaluation value called the minimum principal stress deviation value using the concept of deviation from the average value around the minimum principal stress, thereby quantifying regardless of the absolute level of the material strength. Therefore, it is possible to predict the surface strain with high accuracy. Furthermore, the minimum principal stress deviation value proposed in the present invention takes into account the influence of the plate thickness, and the surface strain can be predicted in consideration of the influence of the material plate thickness.
１ 操作部
２ 表示部
３ 演算部
４ 平均最小主応力値演算部
５ 評価値演算部
６ 入出力部
７ 記憶部
８ データベース
DESCRIPTION OF SYMBOLS 1 Operation part 2 Display part 3 Calculation part 4 Average minimum principal stress value calculation part 5 Evaluation value calculation part 6 Input / output part 7 Storage part 8 Database
Claims (3)
前記評価値は、
（最小主応力値−平均最小主応力値）／（A*板厚値2）、（ここで、Aは部品形状によって決定される定数である）、
にて算出することを特徴とするプレス成形品の面ひずみ予測方法。 In the surface distortion prediction method of the press-formed product according to claim 1,
The evaluation value is
(Minimum principal stress value−average minimum principal stress value) / (A * plate thickness value 2 ), where A is a constant determined by the part shape,
A method for predicting the surface strain of a press-formed product, characterized by:
面ひずみ解析対象面に位置するすべての前記最小主応力値の平均値である平均最小主応力値を算出する平均最小主応力値演算手段と、
該平均最小主応力値、前記最小主応力値、および前記板厚値を基にした評価値を算出する評価値演算手段と、
該評価値の分布を３次元的に表示する表示手段と、
を備えることを特徴とするプレス成形品の面ひずみ予測装置。 Molding process analysis data acquisition means for acquiring a minimum principal stress value and a plate thickness value generated in each element of the molded product at the time of punch bottom dead center;
An average minimum principal stress value calculating means for calculating an average minimum principal stress value which is an average value of all the minimum principal stress values located on the surface subject to surface strain analysis;
An evaluation value calculation means for calculating an evaluation value based on the average minimum principal stress value, the minimum principal stress value, and the plate thickness value;
Display means for three-dimensionally displaying the distribution of the evaluation values;
An apparatus for predicting surface strain of a press-formed product, comprising:
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