JP4378011B2 - Mold design equipment and mold shape design method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily perform the optimization design of a mold shape by performing highly accurate shape simulation of the mold shape within a short period. SOLUTION: Various data becoming determination factors of a mold shape are inputted (S1) and temperature distribution is calculated (S2) and shrink strain considering the relaxation of stress is calculated on the basis of the temperature distribution and the calculation result is stored (S3) and, further, an operation result is displayed (S4) and the deviation with a design shape is calculated (S5). This process is repeated a proper number of times and the optimum molding condition is selected to be stored (S6). Thereafter, the error of the design value of an analyzing model with the operation result is calculated (S7) and the nodal point on the surface of a mold is corrected by error quantity in an anti-shrink direction (S8). Subsequently, the operation of the temperature distribution and the calculation of shrink strain are performed according to the optimum molding condition (S9, S10) and the shape deviation with the design shape is calculated (S11) and, when the shape deviation comes into an allowable range, the shape data is outputted as a mold manufacturing dimension (S12→S13).

Description

ここで、Ｑは発熱量、ｔは時間、x、y、zは各座標成分を夫々示している。
【００３５】
数式（２）を有限要素法により離散化し、ガラーキン法により積分した後、全要素を加算し、さらに時間につき差分すると数式（３）が得られる。
【００３６】
｛（［Ｋ］／２）＋（［Ｃ］／Δｔ）｝・｛φ（ｔ＋Δｔ）｝
＝｛（−［Ｋ］／２）＋（［Ｃ］／Δｔ）｝・｛φ（ｔ）｝＋｛Ｆ｝ …（３）
ここで、［Ｋ］＝Σ［ｋ］、［Ｃ］＝Σ［ｃ］、｛Ｆ｝＝Σ｛ｆ｝であり、［ｋ］は熱伝導マトリックス、［ｃ］は熱容量マトリックス、｛ｆ｝は熱流束ベクトル、｛φ（ｔ）｝は節点温度ベクトル、Δｔは時間刻みを示している。
【００３７】
そして、｛φ（ｔ）｝は初期値として与えられるので、｛φ（ｔ＋Δｔ）｝を逐次算出することができ、これにより温度分布を算出することができる。
【００３８】
次いで、ステップＳ３では応力緩和を考慮しながらステップＳ２で得られた温度分布に基づいて収縮歪みεを算出する。
【００３９】
ここで、応力緩和とは、成形品に一定の歪みを加えた場合、成形材料の粘弾性特性により時間の経過と共に成形品に発生する応力σが低下してゆく現象をいう。そして、粘弾性材料における応力―歪み式は、一般に、履歴積分形式で表現され、応力緩和を考慮した場合、最終的には数式（４）で表わされる。
【００４０】
【数２】

ここで、ｔ_mは時刻、ｈは時間ステップ（＝ｔ_m−ｔ_m-1）、Δσ（ｔ_m）は時刻ｔ_mにおける応力の増分、Δε（ｔ_m）は時刻ｔ_mにおける歪みの増分を示す。また、Ｇ（０）は時間「０」における緩和弾性係数、Ｇ（ｎ）は時間ｎにおける緩和弾性係数を示し、図４の緩和弾性特性マップを検索し、さらに温度シフトファクタＡ（Ｔ）を加味して算出される。
【００４１】
また、αⁿ（ｈ）、βⁿ（ｈ）は数式（５）、（６）で表わされる。
【００４２】
【数３】

尚、λは緩和係数である。
【００４３】
したがって、このようにして時間と温度の変化率に応じて応力−歪み関係を算出することができ、冷却時間や冷却温度の差に起因して生じ得る収縮歪みが評価され、その演算結果が演算結果記憶部３ｂに記憶される。
【００４４】
次いで、ステップＳ４では、前記演算結果を光学面（球面）の面精度として表示部４に表示する。
【００４５】
図５はステップＳ４で表示された光学面であって、解析対象であるレンズを或る特定の「Ｒ」に設定したときの干渉縞を示している。このシミュレーション結果により、図中、Ａ部で示すように、成形条件を上述した初期値に設定して射出成形を行った場合は、光学面上で縞が大きく曲がり、所謂「クセ」が顕著に発生する。また、図５では示されていないが測定時のＲを変更することにより干渉縞が変化することが確認され、したがって所謂「Ｒズレ」も発生していると考えられる。
【００４６】
そして、続くステップＳ５では設計形状と演算結果記憶部３ｂに記憶されている形状との偏差を算出し、その算出結果を演算結果記憶部３ｂに記憶すると共に、ステップＳ６で形状偏差が最適か否かを判断する。今回ループ（第１回目）では、上述したように「Ｒズレ」と「クセ」が発生しているため、最適成形条件ではないと判断し、再びステップＳ１に戻り、圧力条件及び冷却条件を再入力する。
【００４７】
すなわち、Ｒズレは収縮量で決定されるため成形条件の変更では対応することが困難であるため、ステップＳ１では、クセ量に着目し、該クセ量を小さくすることを目的として成形条件を変更する。本実施の形態では、一次冷却水温度を１１６℃に上げ、他の条件は前回と同一条件（成形圧力８５ＭＰａ、一次冷却時間１０分、二次冷却水温度８０℃、二次冷却時間８分）に設定し、斯かる成形条件をデータ入力部１に入力する。そして、ステップＳ２、ステップＳ３で上述と同様の処理を繰り返し、ステップＳ４で図６に示すように、第２回目の演算結果を表示部４に表示する。
【００４８】
次いで、再計算された演算結果形状と設計形状との形状誤差を演算して演算結果記憶部３ｂに記憶する。そして、ステップＳ６では形状誤差が最適か否かを判断する。図６は、図５に比べてクセ量は減少しているものの「０」にはなっていないため、再度ステップＳ１に戻り、成形条件を変更して上述の処理を繰り返す。今回、すなわち第３回目は一次冷却水温度のみを例えば１１８℃に設定し直し、他の条件を前回と同一条件（成形圧力８５ＭＰａ、一次冷却時間１０分、二次冷却水温度８０℃、二次冷却時間８分）に設定し、斯かる成形条件をデータ入力部１に再入力し、再度ステップＳ２、ステップＳ３の処理ステップを実行し、ステップＳ４で第３回目の演算結果を表示部４に表示する。
【００４９】
そして、図４〜図６の面精度から明らかなように第２回目の成形条件（図５）が設計形状と演算結果の偏差が最小となり、最適であることが分かる。従って、ステップＳ６では３つの成形条件から第２回目の成形条件（圧力条件及び冷却条件）、すなわち、成形圧力８５MＰａ、射出温度２６０℃、一次冷却水温度１１６℃、一次冷却時間１０分、二次冷却水温度８０℃二次冷却時間８分を最適成形条件として選択し、該最適成形条件を最適成形条件記憶部３ｃに記憶する。尚、このとき、有限要素分割された解析モデルの節点の移動するベクトル、すなわち収縮方向と大きさ（収縮量）等の演算形状データが最適条件記憶部３ｃに記憶される。
【００５０】
次に、上述したＲズレを補正すべく、ステップＳ７に進み、各節点の収縮ベクトルの方向と大きさの設計値と演算結果との誤差を収縮誤差量演算部２ｅで算出する。
【００５１】
図８は解析に使用したメッシュ図であって、５は固定金型、６が可動金型、７はレンズであり、固定金型５及び可動金型６には急冷用冷却管８と徐冷用冷却管９が設けられ、該急冷用冷却管８と徐冷用冷却管９とでレンズ７を冷却している。
【００５２】
図９は上記メッシュ図のレンズ近傍を拡大した要部拡大図であって、成形されたレンズ７の表面が収縮によって両金型５、６から離れていることを表わしている。
【００５３】
図１０は金型形状と成形品であるレンズの表面形状との関係を示した図であって、１０は金型表面を構成する有限要素メッシュの節点、１１は成形材料が射出されて金型キャビティに充填されたときに節点１０と同一座標のレンズ表面を構成する有限要素メッシュの節点である。射出充填された成形材料は、充填当初は金型キャビティ内壁と接触しているが、冷却が進行するにしたがって収縮し金型内壁表面を滑りながら分離していき、最終的には図１０の節点１１に示すように金型形状よりも小さな形状に成形される。すなわち、充填当初は金型表面を構成する節点１０にあったレンズ表面の節点は符号１１に示す位置に移動し、矢印Ｄに示すように、節点１０から節点１１の方向を指し示す収縮ベクトルが得られる。つまり、金型を設計する際に設定した収縮率が正確であれば節点１０の位置がレンズの設計形状になっているが。実際には収縮率を正確に設定することは困難であり、誤差量としての収縮ベクトルＤが算出され、斯かる誤差量が形状誤差量演算部２ｅで得られる。
【００５４】
次に、ステップＳ８に進み、形状誤差量だけ反収縮方向に金型表面の節点を補正する。
【００５５】
すなわち、図１１において、点線１２はレンズ６の所望設計形状、５ａは固定金型５の表面形状、６ａはレンズ６の現時点における表面形状、１３はレンズ６の表面における有限要素メッシュの節点、１４は固定金型５の表面における有限要素メッシュの節点、１５は節点１４と節点１３とを結ぶ収縮ベクトルＤと所望設計形状１２の交差点であり、次回演算での目標座標となる。１６は前記収縮ベクトルＤと反対方向に収縮量Ａだけ移動させた座標であり、次回演算時の金型形状を示している。すなわち、成形によってレンズ６が収縮した収縮量は節点１４と節点１３との距離、すなわち収縮ベクトルに合致すると、設計形状との形状誤差を規格内とするために、交差点１５と節点１３との距離である収縮量Ａだけに収縮ベクトルＤの反対方向の延長線上に固定金型５の形状線を移動させ、新しい解析モデルの形状１７を決定する。また、可動金型７とレンズ６についても同様の処理を行う。
【００５６】
このようにして求めた金型形状に解析モデルを修正して、再度最適条件記憶部３ｃに記憶されている成形条件にしたがって温度分布の演算（ステップＳ９）、応力緩和を考慮した収縮歪みを時間と温度に応じて算出し（ステップＳ１０）、設計形状と成形レンズとの形状偏差を算出する（ステップＳ１１）。そして、斯く算出された形状偏差が所定の規格内にあるか否かを判断し、その答が否定（Ｎｏ）のときはステップＳ８に戻って上述した処理を繰り返す一方、ステップＳ１１の答が肯定（Ｙｅｓ）、例えば、０．１μm以下の場合はステップＳ１３で理想の金型形状が得られたとして出力し、処理を終了する。
【００５７】
このように本実施の形態によれば、冷却時間や冷却サイクルの相違を考慮して金型形状の最適化をシミュレーションすることができるので、試験用金型を製作して成形作業を行わなくとも短期間で高精度な金型形状を決定することができる。
【００５８】
【発明の効果】
以上説明したように本発明によれば、時間の経過と共に変化する緩和弾性特性を考慮して収縮歪みを評価し、成形条件を決定し、且つ成形品の収縮状態に対応して金型の形状を補正しているので、試験用金型を製作することなく所望の高精度な金型形状を有する金型の最適設計を容易に短期間で行うことができる。
【００５９】
また、実際に金型を製作する前に精度予測、設備能力の予測を行うことができるので、機械的な仕上げ作業の繰り返しである金型の補正作業を行う必要がなくなり、経済的にも時間的にも多大な負荷軽減が可能となる。
【図面の簡単な説明】
【図１】本発明に係る金型形状設計装置のブロック構成図である。
【図２】本発明に係る金型形状の設計方法の処理手順を示すフローチャートである。
【図３】ＰＶＴデータより得られる線膨張係数マップである。
【図４】緩和弾性係数の特性図である。
【図５】第１の成形条件でシミュレートして得られる光学面の干渉縞を示す例である。
【図６】第２の成形条件でシミュレートして得られる光学面の干渉縞を示す例である。
【図７】第３の成形条件でシミュレートして得られる光学面の干渉縞を示す例である。
【図８】解析メッシュ図である。
【図９】解析メッシュの要部拡大図である。
【図１０】金型形状と成形されたレンズの表面形状の関係を示す説明図である。
【図１１】解析モデルの形状補正を説明する説明図である。
【符号の説明】
１ データ入力部（入力手段）
２ａ 温度分布演算部（温度分布算出手段）
２ｂ 収縮歪み演算部（演算形状データ算出手段）
２ｅ 収縮誤差量演算部（収縮誤差量算出手段）
２ｄ 形状偏差評価部（最適成形条件選択手段）
２ｆ データ補正部（形状補正手段）
３ａ 入力データ記憶部（緩和弾性特性作成手段）
３ｃ 最適条件記憶部（最適化条件記憶手段）
４ 表示部（表示手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mold design apparatus and a mold shape design method. More specifically, a flow analysis of a molding material is performed by a finite element method using CAE (Computer Aided Engineering: “computer aided technology”). The present invention relates to a mold design apparatus for optimizing a shape and a mold shape design method.
[0002]
[Prior art]
In recent years, precision parts such as a plastic lens as an optical element have been manufactured by using a molding method such as an injection molding method, an injection compression molding method, or a compression molding method.
[0003]
When a molding die for manufacturing this type of optical element is manufactured, it is anticipated that the molding material will shrink due to temperature changes and the like, and the shrinkage rate is calculated from a desired dimension (design dimension) of the molded product. After manufacturing a test mold with a large cavity size and optimizing molding conditions such as injection temperature and injection time, the molded product is manufactured by performing the predetermined molding process using the test mold. Then, measure the dimensions of each part of the molded product that has been molded to calculate the amount of error from the desired shape, and then correct the cavity size of the test mold so that it increases in the anti-shrinkage direction by the amount of error. As a result, a molding die for use in actual molding was manufactured. For this reason, in the case of precision parts with strict requirements, such as lenses for single-lens reflex cameras, it is often impossible to satisfy the required dimensions with a single mold correction process, and the required dimensions are satisfied. Until then, a series of steps of molding process → dimension measurement of molded article → calculation of error amount → mold correction process was repeated.
[0004]
Therefore, as a technique that can reduce such a mold correction process, the shape regression curve of the molded product and its molding surface is obtained based on the actual measurement data of the molded product, and the shrinkage amount of the molding material is calculated from these, There has already been proposed a mold shape design apparatus which obtains a new shape regression curve capable of correcting / absorbing a shape error of a molded product based on the shrinkage amount, and creating NC data from the shape regression curve. (For example, JP-A-5-96572; hereinafter referred to as “first prior art”).
[0005]
According to the first prior art, when the shrinkage amount can be accurately predicted, useless mold correction work is not required, and the mold design and development period can be greatly shortened. The cost required to manufacture the mold can be greatly reduced.
[0006]
Further, as another conventional technique, the time point at which the melt phase of the molding material in the mold is disconnected is specified, and the temperature distribution at that time point is set as the initial temperature, until the molded product reaches a uniform room temperature. There has already been proposed a molding process simulation system in which thermal stress distortion is analyzed by a finite element method using a temperature change as a thermal load, and a molding shape distortion, that is, a deformation amount is calculated (for example, Japanese Patent Publication No. 6-22840). Hereinafter referred to as “second prior art”).
[0007]
According to the second prior art, the temperature distribution at a specific location of the mold is the flow stop temperature, or the temperature distribution at the time when the melting phase such as the solidification temperature and the glass transition temperature is disconnected is set as the initial temperature, The initial temperature is subdivided from the temperature at which the molded product is taken out, and the temperature-dependent physical property data (linear expansion coefficient α, specific heat c, thermal conductivity k, etc.) corresponding to the temperature range within the subdivided minute temperature range. Is used to calculate the thermal stress strain, and the cumulative total of the thermal stress strain is calculated as the amount of deformation in the final total temperature range, so that the molding material and mold can be obtained prior to the production of the actual machine. It is possible to evaluate the influence of structure and molding conditions on molding shape distortion. Therefore, it is not necessary to design the mold shape by trial and error, greatly reducing the time and cost required for the development and design of new molds. can do Conceivable.
[0008]
[Problems to be solved by the invention]
However, in the first prior art, since a shape regression curve is obtained based on actually measured data of a molded product, a test mold is manufactured before manufacturing a molding die for manufacturing a molded product having a desired size. There is a problem that the development period becomes longer and the development cost becomes higher.
[0009]
That is, today, the life cycle of products has also been shortened, so that a significant reduction in the development period required from the design stage to the completion of the product is required. However, in the first conventional technology, a test mold is used. After manufacturing, the test mold is used to manufacture a molded product, and the dimensions of each part of the molded product manufactured with the test mold are optimized after the molding conditions are optimized so that stable molding is possible. Since the shape regression curve is obtained based on the measurement data, the work process is complicated, the development period takes a long time, and the development cost increases.
[0010]
In the second prior art, the deformation analysis of the molded product is performed on the assumption that the entire molded product is uniformly cooled from the initial temperature to the removal temperature of the molded product. Since the relationship with time is not taken into account, there is a problem that the analysis result is the same even if the cooling gradient and the molding cycle are greatly different, and the analysis result does not necessarily match the actual phenomenon.
[0011]
That is, for example, when cooling a molded product from 250 ° C. to 90 ° C., time is not taken into account in the cooling process, and therefore the second prior art requires 100 hours even if it is cooled in 1 second. Even when cooled, the same analysis result can be obtained. That is, in the second prior art, for example, when the gate portion of the molded product reaches the solidification temperature, the solidification temperature is analyzed as the initial temperature. However, even in the same molded product, the temperature at the gate portion and other parts is analyzed. There is variation in the distribution (there may be a part at a temperature of 150 ° C. or a part at a temperature of 90 ° C. in the molded product), and the thermal stress strain is calculated based on the temperature difference from the initial temperature to room temperature and the linear expansion coefficient. Therefore, the same thermal stress strain can be obtained even when cooling is performed in 1 second or even when cooling is performed for 100 hours. On the other hand, as an actual phenomenon, the internal temperature difference decreases with time due to internal conduction while the entire molded product is cooled to room temperature, and therefore, when cooled in 1 second and when cooled over 100 hours. Then there will be a big difference in the final shape.
[0012]
That is, even if the initial temperature and the final temperature are the same, the deformation amount of the molded product varies greatly depending on the cooling history and pressure history such as the length of the cooling time and the magnitude of the cooling gradient. For this reason, even if the thermal stress distortion analysis is performed without considering the concept of time as in the second prior art, it does not coincide with the actual phenomenon. Therefore, the distortion of the molded product is predicted in advance and desired. There is a problem that it is difficult to manufacture a mold capable of obtaining the molded product.
[0013]
Furthermore, in the second prior art, the thermal stress strain is calculated from the difference between the initial temperature and the removal temperature of the molded product, or the entire molded product becomes a uniform temperature (for example, room temperature) after the molded product is taken out. The thermal stress strain is calculated from the temperature difference up to and therefore the analysis is based on the premise that the entire molded product is cooled uniformly, so the temperature distribution of the initial temperature (regardless of the cooling history after the initial temperature ( Thermal stress strain is calculated by the temperature difference.
[0014]
However, high-precision optical elements used in single-lens reflex cameras, video tape recorders (VTRs), or laser beam printers often require an optical functional surface shape transfer accuracy of 1 μm or less. In an optical element having severe conditions, local sink marks of several μm are important in performance. Therefore, in the second conventional technique based on the premise that the whole contracts uniformly, a desired highly accurate shape prediction is performed. There was a problem that it was difficult.
[0015]
The present invention has been made in view of such problems, and a mold that can easily perform optimization design of a mold shape by performing a highly accurate shape simulation of the mold shape in a short period of time. It is an object to provide a design apparatus and a mold shape design method.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the mold designing apparatus according to the present invention performs a flow analysis of a molding material using a computer-aided technology prior to the production of a mold for manufacturing a molded product by performing a molding method. , A mold design device for optimal design of molds, Design shape The input means for inputting data, molding conditions and data required for molding, and the relationship between processing time and stress relaxation This is a relaxation elastic property obtained by processing the data measured in the viscoelasticity test, and constitutes the viscoelasticity data together with a temperature shift factor indicating the dependence of temperature change on the viscoelasticity. Relaxation elastic properties of solid physical property test below glass transition temperature and melt physical property test above glass transition temperature By converting and connecting two types of data and drawing a continuous curve within the range from room temperature to injection molding temperature A relaxation elastic characteristic creating means to be created; a temperature distribution calculating means for calculating a temperature distribution of the analytical model based on the molding condition; a calculation result of the temperature distribution calculating means and a relaxation elastic characteristic of the analytical model; Optimum molding is performed by calculating the relationship between shrinkage strain and stress and calculating the calculation shape data of the analysis model, and repeatedly calculating the calculation shape data by the calculation shape data calculation means an appropriate number of times. Optimal molding condition selection means for selecting conditions, and the calculation shape data calculation means Calculated shape data calculated by And said Design shape A contraction error amount calculation unit that calculates a contraction error amount that is an error from data, and a shape correction unit that corrects calculation shape data based on a calculation result of the contraction error amount calculation unit. .
[0017]
In addition, the mold shape design method according to the present invention performs a flow analysis of a molding material using a computer-aided technology prior to the production of a mold for manufacturing a molded product by applying a molding method, This is a mold shape design method for optimal design of a mold, and the analysis model to be analyzed Design shape Shows the input step for inputting data, molding conditions and data required for molding, and the relationship between machining time and stress relaxation. This is a relaxation elastic property obtained by processing the data measured in the viscoelasticity test, and constitutes the viscoelasticity data together with a temperature shift factor indicating the dependence of temperature change on the viscoelasticity. Relaxation elastic properties of solid physical property test below glass transition temperature and melt physical property test above glass transition temperature By converting and connecting two types of data and drawing a continuous curve within the range from room temperature to injection molding temperature A relaxation elastic property creating step to create, a temperature distribution calculating step to calculate a temperature distribution of the analytical model based on the molding condition, and a shrinkage strain and stress of the analytical model based on the temperature distribution and the relaxed elastic property. A calculation shape data calculation step for calculating a calculation shape data of the analysis model, and an optimum molding condition selection for selecting the optimum molding condition of the calculation shape data by repeating the calculation of the calculation shape data an appropriate number of times Steps, Calculated in the calculation shape data calculation step The calculated shape data and the Design shape It includes a contraction error amount calculating step for calculating a contraction error amount that is an error with data, and a shape correcting step for correcting calculation shape data based on the contraction error amount.
[0018]
Other features of the present invention will become apparent from the following embodiments of the present invention.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 is a block configuration diagram showing an embodiment of a mold designing apparatus according to the present invention. The mold designing apparatus includes a data input unit 1 for inputting various design shape data and physical property value data, An arithmetic control unit 2 that performs various arithmetic processes for shape optimization based on the input data input to the data input unit 1 and controls the entire apparatus, and an arithmetic result that is arithmetically processed by the arithmetic control unit 2 And a display unit 4 for displaying individual calculation results. A shape simulation by CAE is performed by using a finite element method to optimally design a mold shape.
[0021]
The calculation control unit 2 performs a heat conduction analysis based on the input data input to the data input unit 1 and calculates a temperature distribution. The calculation result of the temperature distribution calculation unit 2a and the data input unit 1 The contraction strain calculation unit 2b that calculates the contraction strain due to thermal contraction based on the viscoelasticity data input to, the design shape data input by the data input unit 1, and the shape of the calculation result calculated by the contraction strain calculation unit 2b A shape deviation calculating unit 2c for calculating a deviation from the data, a shape deviation evaluating unit 2d for evaluating a calculation result of the shape deviation calculating unit 2c, and a direction and a contraction amount (design) of the contraction vector of each node in the finite element method analysis A contraction error amount calculation unit 2e that calculates an error from the value) and a data correction unit 2f that corrects shape data in the direction opposite to the direction of the contraction vector by the contraction amount as necessary.
[0022]
The storage unit 3 also stores an input data storage unit 3a for storing input data input to the data input unit 1, and various calculation results such as calculated temperature distribution, shrinkage distortion, shape deviation, and shrinkage error amount. It has an operation result storage unit 3b for storing, and an optimum condition storage unit 3c for storing optimum analysis conditions such as molding conditions used for analysis when the shape error is optimized.
[0023]
Next, a mold shape design method in the case where a plastic lens (hereinafter simply referred to as “lens”) as an optical element is manufactured by injection molding is an axially symmetric three-dimensional model having an optical axis as a symmetric surface. Detailed description.
[0024]
FIG. 2 is a flowchart showing an embodiment of the processing procedure of the mold shape designing method. In the present embodiment, RAMAX manufactured by Woodeholm is used as the mold material, and PMMA (polymethyl methacrylate) is used as the molding material.
[0025]
In step S1, the shape data of the molded product, the constraint condition, the pressure condition, the cooling condition, the physical property data, and the P (pressure) -V (specific volume) -T (temperature) data (determining factors of the mold shape (cavity shape) Input data such as state change data) and viscoelasticity data is input from the data input unit 1.
[0026]
That is, first, in order to be able to handle the system by the finite element method, the entire shape is divided into fine regions to create elements, and the node coordinates, node numbers, element numbers, etc. that express the mold shape or molded product shape Enter shape data. In this embodiment, in order to increase the efficiency by reducing the number of operations, dimension data larger than the design dimension by the shrinkage rate of the molding material (PMMA) is input as the mold dimension. Specifically, the mold dimension is inputted with data of 1.006 times the design dimension and stored in the input data storage unit 3a.
[0027]
Next, a predetermined constraint condition necessary for the calculation of the finite element analysis is input, and further, a pressure condition and a cooling condition as initial values for optimizing the processing condition of the forming process are input, and the input data storage unit 3a is input. Remember. In the present embodiment, the molding pressure is 85 MPa as the initial value of the pressure condition, the injection temperature is 260 ° C., the primary cooling water temperature is 114 ° C., the primary cooling time is 10 minutes, and the secondary cooling water temperature is the initial value of the cooling condition. Is set to 80 ° C. and the secondary cooling time is set to 8 minutes. The pressure condition and the cooling condition are input as initial values to the data input unit 1 and stored in the input data storage unit 3a. In actual injection molding, when the secondary cooling is completed, the molded product is taken out from the mold and air-cooled to room temperature (for example, 20 ° C.).
[0028]
Next, temperature-dependent physical property data of the molding material and the mold material is input and stored in the input data storage unit 3a. Specifically, for the molding material (PMMA), the thermal conductivity k is 2.09 × 10. ^-Four W / (m · K), specific heat c is 1.66 J / (kg · K), density ρ is 1.15 × 10 ^Three kg / m ^Three And the thermal conductivity k of the mold material (RAMAX manufactured by Woodeholm) is 2.28 × 10 ^-2 W / (m · K), specific heat c is 0.46 J / (kg · K), density ρ is 7.78 × 10 ^Three kg / m ^Three Therefore, these physical property data are input to the data input unit 1 and stored in the input data storage unit 3a.
[0029]
Next, PVT data of the molding material is input. Since the linear expansion coefficient α is expressed by Equation (1), the linear expansion coefficient α is calculated based on the PVT data to create a linear expansion coefficient map α (P, T), and the linear expansion coefficient map α (P, T) is stored in the input data storage unit 3a.
[0030]
α = (dV / dT) _P / V (1)
FIG. 3 is a linear expansion coefficient map α (P, T) stored in the input data storage unit 2a, where the horizontal axis is the temperature T (° C.) and the vertical axis is the linear expansion coefficient α (K ^-1 ), And the characteristics in the figure show the linear expansion coefficient α (K) at each temperature (° C.) when the pressure is 40 MPa, 80 MPa, 120 MPa, 160 MPa, 200 MPa, and 240 MPa, respectively. ^-1 ).
[0031]
Further, viscoelasticity data is input to the data input unit 1. Viscoelasticity data consists of relaxation elastic characteristics obtained by processing data measured with a viscoelasticity tester and a temperature shift factor A (T) indicating the dependence of temperature change on viscoelasticity. These viscoelasticity data are input. It is stored in the data storage unit 3a. Specifically, the relaxation elastic properties are obtained by converting and connecting two types of data, a solid physical property test below the glass transition temperature and a melt physical property test above the glass transition temperature, and injection molding from room temperature (for example, 20 ° C.). By drawing a continuous curve within a temperature range (for example, 300 ° C.), as shown in FIG. 4, for example, the relaxation elastic characteristic (time t to relaxation elastic modulus G (t)) at a reference temperature of 90 ° C. The relaxation elastic characteristics are created and stored as a master curve in the input data storage unit 3a, thereby making it unnecessary to set the initial solidification state from the melting temperature region to the solidification region. The temperature shift factor A (T) is also obtained for each temperature based on the data measured by the viscoelasticity tester described above.
[0032]
Next, in step S2, a known heat conduction analysis is performed to obtain a temperature distribution.
[0033]
That is, it is known that a non-stationary nonlinear heat conduction equation is generally expressed by Equation (2).
[0034]
[Expression 1]

Here, Q is the calorific value, t is the time, and x, y, and z are the respective coordinate components.
[0035]
Formula (2) is discretized by the finite element method, integrated by Galerkin method, all elements are added, and further, the difference with respect to time gives Formula (3).
[0036]
{([K] / 2) + ([C] / Δt)} · {φ (t + Δt)}
= {(− [K] / 2) + ([C] / Δt)} · {φ (t)} + {F} (3)
Here, [K] = Σ [k], [C] = Σ [c], {F} = Σ {f}, [k] is a heat conduction matrix, [c] is a heat capacity matrix, {f} Is a heat flux vector, {φ (t)} is a nodal temperature vector, and Δt is a time step.
[0037]
Since {φ (t)} is given as an initial value, {φ (t + Δt)} can be calculated sequentially, and thereby the temperature distribution can be calculated.
[0038]
Next, in step S3, the shrinkage strain ε is calculated based on the temperature distribution obtained in step S2 while considering stress relaxation.
[0039]
Here, stress relaxation refers to a phenomenon in which when a certain strain is applied to a molded product, the stress σ generated in the molded product decreases with time due to the viscoelastic characteristics of the molding material. The stress-strain formula in the viscoelastic material is generally expressed in a hysteresis integral format, and finally, expressed in formula (4) when stress relaxation is taken into consideration.
[0040]
[Expression 2]

Where t _m Is the time, h is the time step (= t _m -T _m-1 ), Δσ (t _m ) Is time t _m Stress increment at Δε (t _m ) Is time t _m The distortion increment at. G (0) indicates the relaxation elastic coefficient at time “0”, G (n) indicates the relaxation elastic coefficient at time n, and the relaxation elastic characteristic map of FIG. 4 is searched, and the temperature shift factor A (T) is further calculated. Calculated with consideration.
[0041]
Α ⁿ (H), β ⁿ (H) is expressed by equations (5) and (6).
[0042]
[Equation 3]

Note that λ is a relaxation coefficient.
[0043]
Therefore, the stress-strain relationship can be calculated according to the rate of change of time and temperature in this way, shrinkage strain that can be caused by the difference in cooling time and cooling temperature is evaluated, and the calculation result is calculated. The result is stored in the result storage unit 3b.
[0044]
Next, in step S4, the calculation result is displayed on the display unit 4 as the surface accuracy of the optical surface (spherical surface).
[0045]
FIG. 5 shows the interference pattern when the lens to be analyzed is set to a specific “R”, which is the optical surface displayed in step S4. From this simulation result, as shown by part A in the figure, when injection molding is performed with the molding conditions set to the initial values described above, the stripes are greatly bent on the optical surface, and so-called “habit” is prominent. appear. Further, although not shown in FIG. 5, it is confirmed that the interference fringes change by changing R at the time of measurement. Therefore, it is considered that so-called “R deviation” also occurs.
[0046]
In step S5, a deviation between the design shape and the shape stored in the calculation result storage unit 3b is calculated. The calculation result is stored in the calculation result storage unit 3b. In step S6, whether the shape deviation is optimal. Determine whether. In the current loop (the first time), as described above, “R deviation” and “peculiarity” occur, so it is determined that the molding conditions are not optimal, and the process returns to step S1 again, and the pressure condition and the cooling condition are restored. input.
[0047]
That is, since the R deviation is determined by the shrinkage amount, it is difficult to cope with it by changing the molding conditions. In step S1, paying attention to the habit amount, the molding condition is changed for the purpose of reducing the habit amount. To do. In this embodiment, the primary cooling water temperature is raised to 116 ° C., and the other conditions are the same as the previous one (molding pressure 85 MPa, primary cooling time 10 minutes, secondary cooling water temperature 80 ° C., secondary cooling time 8 minutes). And the molding conditions are input to the data input unit 1. Then, the same processing as described above is repeated in step S2 and step S3, and the second calculation result is displayed on the display unit 4 in step S4 as shown in FIG.
[0048]
Next, a shape error between the recalculated calculation result shape and the design shape is calculated and stored in the calculation result storage unit 3b. In step S6, it is determined whether or not the shape error is optimal. In FIG. 6, the amount of habit is reduced compared with FIG. 5 but not “0”. Therefore, the process returns to step S <b> 1 again, the molding conditions are changed, and the above processing is repeated. This time, that is, in the third time, only the primary cooling water temperature is reset to 118 ° C., for example, and the other conditions are the same as the previous one (molding pressure 85 MPa, primary cooling time 10 minutes, secondary cooling water temperature 80 ° C., secondary Cooling time 8 minutes), such molding conditions are re-input to the data input unit 1, the processing steps of step S2 and step S3 are executed again, and the third calculation result is displayed on the display unit 4 in step S4. indicate.
[0049]
As can be seen from the surface accuracy of FIGS. 4 to 6, it can be seen that the second molding condition (FIG. 5) has the smallest deviation between the design shape and the calculation result, and is optimal. Therefore, in step S6, from the three molding conditions, the second molding condition (pressure condition and cooling condition), that is, molding pressure of 85 MPa, injection temperature of 260 ° C., primary cooling water temperature of 116 ° C., primary cooling time of 10 minutes, secondary cooling. A cooling water temperature of 80 ° C. and a secondary cooling time of 8 minutes are selected as optimum molding conditions, and the optimum molding conditions are stored in the optimum molding condition storage unit 3c. At this time, the vector in which the nodes of the analysis model divided by the finite element are moved, that is, the calculation shape data such as the contraction direction and size (contraction amount) is stored in the optimum condition storage unit 3c.
[0050]
Next, in order to correct the above-described R deviation, the process proceeds to step S7, and an error between the direction of the contraction vector and the design value of the magnitude of each node and the calculation result is calculated by the contraction error amount calculation unit 2e.
[0051]
FIG. 8 is a mesh diagram used for analysis, in which 5 is a fixed mold, 6 is a movable mold, and 7 is a lens. The fixed mold 5 and the movable mold 6 are provided with a quenching cooling pipe 8 and a slow cooling. A cooling pipe 9 is provided, and the rapid cooling cooling pipe 8 and the slow cooling cooling pipe 9 cool the lens 7.
[0052]
FIG. 9 is an enlarged view of a main part in which the vicinity of the lens in the mesh diagram is enlarged, and shows that the surface of the molded lens 7 is separated from both molds 5 and 6 by contraction.
[0053]
FIG. 10 is a diagram showing the relationship between the mold shape and the surface shape of the lens, which is a molded product, wherein 10 is a node of a finite element mesh constituting the mold surface, and 11 is a mold after the molding material is injected. It is a node of a finite element mesh that forms a lens surface having the same coordinates as the node 10 when the cavity is filled. The injection-filled molding material is in contact with the inner wall of the mold cavity at the beginning of filling, but shrinks as the cooling proceeds and separates while sliding on the inner wall surface of the mold. As shown in FIG. 11, it is formed into a shape smaller than the mold shape. That is, the nodal point on the lens surface which was at the nodal point 10 constituting the mold surface at the beginning of the filling is moved to the position indicated by reference numeral 11, and as shown by the arrow D, a contraction vector indicating the direction from the nodal point 10 to the nodal point 11 is obtained. It is done. In other words, if the shrinkage rate set when designing the mold is accurate, the position of the node 10 is the design shape of the lens. Actually, it is difficult to set the shrinkage rate accurately, and a shrinkage vector D as an error amount is calculated, and such an error amount is obtained by the shape error amount calculation unit 2e.
[0054]
Next, the process proceeds to step S8, where the nodes on the mold surface are corrected in the anti-shrinkage direction by the shape error amount.
[0055]
That is, in FIG. 11, a dotted line 12 indicates a desired design shape of the lens 6, 5 a indicates a surface shape of the fixed mold 5, 6 a indicates a current surface shape of the lens 6, and 13 indicates a node of a finite element mesh on the surface of the lens 6. Is the node of the finite element mesh on the surface of the fixed mold 5, and 15 is the intersection of the contraction vector D connecting the node 14 and the node 13 and the desired design shape 12, which will be the target coordinates in the next calculation. Reference numeral 16 denotes coordinates moved by the contraction amount A in the direction opposite to the contraction vector D, and shows the mold shape at the next calculation. That is, when the amount of contraction of the lens 6 due to molding matches the distance between the node 14 and the node 13, that is, the contraction vector, the distance between the intersection 15 and the node 13 is set so that the shape error with the design shape is within the standard. The shape line of the fixed mold 5 is moved to the extension line in the opposite direction of the shrinkage vector D only by the shrinkage amount A, and the shape 17 of the new analysis model is determined. The same process is performed for the movable mold 7 and the lens 6.
[0056]
The analytical model is corrected to the mold shape thus obtained, and the temperature distribution is calculated again in accordance with the molding conditions stored in the optimum condition storage unit 3c (step S9), and the shrinkage strain considering the stress relaxation is timed. And the temperature according to the temperature (step S10), and the shape deviation between the design shape and the molded lens is calculated (step S11). Then, it is determined whether or not the calculated shape deviation is within a predetermined standard. If the answer is negative (No), the process returns to step S8 to repeat the above-described processing, while the answer to step S11 is affirmative. (Yes), for example, in the case of 0.1 μm or less, it is output in step S13 that an ideal mold shape has been obtained, and the process is terminated.
[0057]
As described above, according to the present embodiment, the optimization of the mold shape can be simulated in consideration of the difference in cooling time and cooling cycle, so that it is not necessary to manufacture the test mold and perform the molding operation. A highly accurate mold shape can be determined in a short period of time.
[0058]
【The invention's effect】
As described above, according to the present invention, the shrinkage strain is evaluated in consideration of the relaxation elastic characteristics that change with the passage of time, the molding conditions are determined, and the shape of the mold corresponding to the contracted state of the molded product. Therefore, the optimum design of a mold having a desired highly accurate mold shape can be easily performed in a short period of time without producing a test mold.
[0059]
In addition, accuracy and equipment capacity can be predicted before the mold is actually manufactured, so there is no need to perform mold correction, which is a repetition of mechanical finishing operations, and it is economically time-consuming. In particular, the load can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram of a mold shape designing apparatus according to the present invention.
FIG. 2 is a flowchart showing a processing procedure of a mold shape designing method according to the present invention.
FIG. 3 is a linear expansion coefficient map obtained from PVT data.
FIG. 4 is a characteristic diagram of relaxation elastic modulus.
FIG. 5 is an example showing interference fringes on an optical surface obtained by simulating under a first molding condition.
FIG. 6 is an example showing interference fringes on an optical surface obtained by simulating under a second molding condition.
FIG. 7 is an example showing interference fringes on an optical surface obtained by simulating under a third molding condition.
FIG. 8 is an analysis mesh diagram.
FIG. 9 is an enlarged view of a main part of an analysis mesh.
FIG. 10 is an explanatory diagram showing a relationship between a mold shape and a surface shape of a molded lens.
FIG. 11 is an explanatory diagram illustrating shape correction of an analysis model.
[Explanation of symbols]
1 Data input section (input means)
2a Temperature distribution calculation unit (temperature distribution calculation means)
2b Contraction strain calculation unit (calculation shape data calculation means)
2e Shrinkage error amount calculation unit (shrinkage Error amount Calculation means)
2d Shape deviation evaluation part (optimum Molding Condition selection means)
2f Data correction unit (shape correction means)
3a Input data storage unit (relaxation elastic property creation means)
3c Optimal condition storage unit (optimum Conversion Condition memory means )
4 Display section (display means)

Claims (18)

A mold design device that performs the flow analysis of molding materials using computer-aided technology and performs the optimal design of the mold prior to the production of the mold for manufacturing the molded product by applying the molding process method,
An input means for inputting design shape data of an analysis model to be analyzed, molding conditions and data required for molding;
A relaxation elastic characteristics obtained by processing the data measured by the shown viscoelastic test the relationship between the processing time and the stress relaxation, constituting a viscoelastic data with temperature shift factor showing the dependence of the temperature changes in the viscoelasticity relaxation elastic properties, combined tie by converting the two types of data below the glass transition temperature solid physical testing and the glass transition point or higher melt property test, draw a continuous curve in the range of an injection molding temperature from room temperature to Relaxation elastic property creating means to create by,
Temperature distribution calculating means for calculating a temperature distribution of the analysis model based on the molding conditions;
Calculation shape data calculation means for calculating the relationship between the shrinkage strain and stress of the analysis model based on the calculation result of the temperature distribution calculation means and the relaxation elastic characteristics, and calculating calculation shape data of the analysis model;
Optimum molding condition selection means for selecting the optimum molding condition by repeating calculation shape data calculation by the calculation shape data calculation means an appropriate number of times;
Shrinkage error amount calculating means for calculating a shrinkage error amount that is an error between the calculated shape data and the design shape data calculated by the calculated shape data calculating means;
A mold design apparatus comprising: a shape correction unit that corrects calculation shape data based on a calculation result of the shrinkage error amount calculation unit. Calculating shape data calculated by the previous SL calculating shape data calculating means, mold design apparatus according to claim 1, characterized in that it is calculated by adding the temperature shift factor. Optimization condition storage means for storing the optimum molding conditions selected by the optimum molding condition selection means,
The shape correction means corrects the mold shape for shrinkage by the shrinkage error amount, and
The mold design apparatus according to claim 1, wherein calculation shape data is calculated under the optimum molding conditions for the shrinkage corrected mold shape. A judgment means for judging whether the calculated shape data corrected by the shape correction means is within an allowable range with respect to the design shape data of the analysis model;
4. The apparatus according to claim 1, further comprising: a mold shape determining unit that determines the calculation shape data as a mold shape when the determination unit determines that the calculated shape data is within the allowable range. The mold design apparatus according to any one of the above.   5. The mold design apparatus according to claim 1, further comprising modeling means for modeling by dividing the mesh to be analyzed by a finite element method.   The mold design apparatus according to claim 1, wherein the temperature distribution calculation unit calculates a temperature change of the analysis model in a minute time according to a time history.   The mold design apparatus according to any one of claims 1 to 6, further comprising display means for visually displaying the calculated shape data.   The mold design apparatus according to any one of claims 1 to 7, wherein the analysis model is an optical element.   9. The mold design apparatus according to claim 1, wherein the molding method includes an injection molding method, a compression molding method, and an injection compression molding method. This is a mold shape design method that performs the flow analysis of molding materials using computer-aided technology and performs the optimal design of the mold prior to the production of the mold for manufacturing the molded product by applying the molding method. And
An input step for inputting design shape data of an analysis model to be analyzed, molding conditions, and data required for molding,
A relaxation elastic characteristics obtained by processing the data measured by the shown viscoelastic test the relationship between the processing time and the stress relaxation, constituting a viscoelastic data with temperature shift factor showing the dependence of the temperature changes in the viscoelasticity relaxation elastic properties, combined tie by converting the two types of data below the glass transition temperature solid physical testing and the glass transition point or higher melt property test, draw a continuous curve in the range of an injection molding temperature from room temperature to a relaxation elastic properties creating step of creating, by,
A temperature distribution calculating step for calculating a temperature distribution of the analysis model based on the molding conditions;
A calculation shape data calculation step of calculating a relationship between the shrinkage strain and stress of the analysis model based on the temperature distribution and relaxation elastic characteristics, and calculating calculation shape data of the analysis model;
Optimal molding condition selection step of selecting the optimum molding condition of the calculated shape data by repeating the calculation of the calculated shape data an appropriate number of times;
A shrinkage error amount calculating step for calculating a shrinkage error amount which is an error between the calculated shape data and the design shape data calculated in the calculated shape data calculating step;
A mold shape design method comprising: a shape correction step of correcting the calculated shape data based on the shrinkage error amount. Before SL arithmetic shape data, a method of designing a die shape according to claim 10, wherein the calculating in consideration of the temperature shift factor. The optimum molding conditions are stored, and the mold shape is subjected to shrinkage correction by the shrinkage error amount, and
The mold shape design method according to claim 10 or 11 , wherein calculation shape data is calculated under the optimum molding condition for the shrinkage corrected mold shape. Determining whether the corrected calculation shape data is within an allowable range with respect to the design shape data of the analysis model;
The mold shape according to any one of claims 10 to 12 , wherein when the calculated shape data is determined to be within the allowable range, the calculated shape data is determined as a mold shape. Design method. A method of designing a die shape according to any one of claims 10 to 13, characterized in that modeled mesh division to simulate analyzed by the finite element method. The temperature distribution, a method of designing a die shape according to any one of claims 10 to 14, and calculates the temperature change of the analytical model in short time according to the time history. A method of designing a die shape according to any one of claims 10 to 15, characterized in that visual display unit to display the calculation shape data. The method for designing a mold shape according to any one of claims 10 to 16 , wherein the analysis model is an optical element. The forming method is injection molding, compression molding, and a method of designing a die shape according to any one of claims 10 to 17, characterized in that it comprises an injection compression molding method.

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