JP2004155005A - Resin fluid analyzing method and device for the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin fluid analyzing method which can seek a flow behavior such as the pressure, temperature, velocity, shear rate, shear stress or flow pattern of a resin in its flow process mainly in a plastic injection-molding field. <P>SOLUTION: In the resin fluid analyzing method comprising a pressure analyzing process for calculating a pressure applied to every part of a molded product at the time of resin packing and also a temperature analyzing process for calculating a temperature of said every part at the time of resin packing, with regard to an objective 2.5-dimensional thin-walled shell structure by plastic injection molding, the temperature-analyzing process calculates a heat conduction term δ(KδT/δz)δ/z in the sheet thickness direction in the energy equation represented by formula 1 as a heat flow rate α(T-T<SB>W</SB>) by deciding a heat transfer rate α based on a die wall surface temperature T<SB>W</SB>, the sheet thickness of a molded product and the heat conduction rate of the resin of this molded product. <P>COPYRIGHT: (C)2004,JPO

Description

μ：粘性係数、γ：せん断速度
ここで、板厚方向の温度分布を求めるためには、差分法或は有限要素法等の手法により、熱伝導項∂（Ｋ∂Ｔ／∂ｚ）／∂ｚについて面外方向、即ち板厚方向に自由度（節点或は要素分割が必要）を持つ離散化手法を適用する必要がある。このため、計算アルゴリズムが複雑化すると共に、計算コストが嵩むいう欠点があった。
本発明では、このような問題を解決するための解析手法として以下の式２に示すように、板厚方向への熱伝導項∂（Ｋ∂Ｔ／∂ｚ）／∂ｚを、金型壁面温度をＴ_ｗ として板厚と樹脂の熱伝導率による等価熱伝達率αによる熱流速項α（Ｔ−Ｔ_Ｗ ）として取り扱う。本手法によれば、前記熱伝導項∂（Ｋ∂Ｔ／∂ｚ）／∂ｚについて面外方向、即ち板厚方向に自由度を持つ離散化手法は必要がなく面内方向のみを考えれば良く、計算アルゴリズムを単純化させると共に、計算コストを大幅に削減できるメリットがある。
【０００８】
エネルギ方程式（本発明）
【０００９】
【数２】

α：等価熱伝達係数Ｔ_ｗ ：金型壁面温度
【発明の実施の形態】
プラスチック射出成形法のプロセスは、充填、保圧、冷却、取出し後の自然冷却という連続する過程から成り立っている。ここでは、充填過程における金型内圧力分布、温度分布の時間的変化及びメルトフロント進行状況のシミュレーションを行うことを目的とする。
先ず、最初に解析で用いる仮定について説明する。
１）非圧縮性粘性流体
溶融樹脂の粘弾性的な性質、並びに圧縮性は考慮しない。
２）クリープ流れ
溶融樹脂の速度は遅く、慣性力は粘性力との比較において無視する。
３）擬定常近似
流動過程の各時刻においては流れは定常として時間微分の項はゼロとする。
４）ヘルショー流れ
成形品は薄肉で、充填時の流れは厚み方向の速度分布を持たない。又、粘性力は流れと平行な面のみに作用する。
５）ハーゲンポアズイユ流れ
スプル・ランナ内の流れは、その軸方向の速度成分のみを持つ。
６）流入樹脂の初期樹脂温度、壁面温度は一定とする。
７）壁面で樹脂のスリップはないものとする。
８）キャビティの厚みに比較し、流動方向の広がりは十分大きいと仮定して、樹脂の熱の伝導は厚み方法のみを考える。
９）メルトフロント（流入樹脂先端）での圧力はゼロとする。
以上の仮定に基づき、流れと平行な面をｘ−ｙ平面、それと垂直にｚ軸とする２次元流れ（平板流れ）の場合の一般的な基礎方程式としては、次式のように表わされる。
【００１０】
【数３】

式３は連続の式、式４，５は運動方程式、式１はエネルギ式、式６は粘性式を表わす。
ここで、ｕ：ｘ方向速度、ｖ：ｙ方向速度、Ｐ：圧力、Ｔ：温度、μ：粘性、ρ：密度、ｃ：比熱、Ｋ：熱伝導率、γ：せん断速度、Ａ，Ｂ，Ｃ：粘性係数
尚、上記仮定に基づき運動方程式（式４，５）を板厚方向に積分し、連続の式（式３）に代入すると次式が得られる。
【００１１】
【数４】

ここで、Ｓはコンダクタンスとして定義され、次式で表わされる。
【００１２】
【数５】

式７に有限要素法を適用し、高次４角形シェル要素及び４角形シェル要素を縮合した３角形による離散化を適用すると、式７に対して次式のような代数マトリックスが得られる。
【００１３】
【数６】

ここで、［Ｋ］：係数マトリックス、｛Ｐ｝： 圧力マトリックス、｛Ｆ｝：右辺ベクトル
樹脂流入口における流量或は圧力境界条件、金型壁面における圧力勾配境界条件、メルトフロントにおける圧力境界条件を設定して計算することで、キャビティ内の圧力分布が得られる。
【００１４】
次に、各要素内での圧力勾配が計算され速度分布、せん断速度分布が計算され、式６により粘性が求まる。非ニュートン流体解析であり、この粘性が変化することで圧力、速度場が変化するので圧力の収束計算を行う必要がある。
【００１５】
本発明は、上記の基礎式に示すようなプラスチック射出成形における２．５次元薄肉シェル構造を対象とした樹脂流動解析方法において、温度計算に関るエネルギ方程式での板厚方向の熱伝導項∂（Ｋ∂Ｔ／∂ｚ）／∂ｚを、金型壁面温度をＴ_ｗ として板厚と樹脂の熱伝導率による熱伝達率αを考えることで平均熱流速α（Ｔ−Ｔ_Ｗ ）として計算することを特徴とする樹脂流動解析方法である。即ち、この場合、式１は以下に示す式２のように簡略化される。
【００１６】
【数７】

本手法によれば、前記熱伝導項∂（Ｋ∂Ｔ／∂ｚ）／∂ｚについて板厚方向に自由度を持つ離散化手法は必要がなく、計算アルゴリズムを単純化させると共に、計算コストを大幅に削減できるメリットがある。
式７で示した圧力解法と同様に、式２に対して有限要素法を適用すると次式のような代数マトリックスが得られる。
【００１７】
【数８】

ここで、［Ｃ］： 熱容量マトリックス、［Ｋ］： 熱伝導マトリックス
｛Ｔ｝： 温度マトリックス、｛Ｑ｝：熱流速マトリックス
式８の解法としては、数値解析上無条件安定となるクランク・ニコルソン法を用いる。
【００１８】
最後に本解析の全体のフローチャートを図１に示す。
【００１９】
先ず、最初にステップ１において解析の対象となる形状データや成形条件データ、圧力温度境界条件データ、各種解析制御パラメータ等を読込む。次に、ステップ２において、樹脂が指定した流入口から流れ始めて最終的に充填するまでの間を、複数の解析ステップに分割して取り扱うための解析ステップ数の設定を行う。本解析では樹脂の流動は非圧縮性を仮定しており、全解析ステップ数と解析対象となる成形品の全体積より１ステップ当りの樹脂充填量が決まることになる。ステップ３では、ステップ２において設定された解析ステップに基づき初期粘性（前期式６）、初期コンダクタンス（前期式８）等の初期計算を行う。
【００２０】
次に、ステップ４では、ＦＡＮ法（Ｆｌｏｗ Ａｎａｌｙｓｉｓ Ｎｅｔｗｏｒｋ Ｍｅｔｈｏｄ）等の方法により、ステップ２，３で計算しておいた１ステップでの樹脂充填量とコンダクタンスによりメルトフロント（樹脂流動先端部部分）の位置を決定する。そしてステップ５では、境界条件として流入口の部分において射出圧力の値或は射出速度の値を、メルトフロントにおいて圧力値を大気圧とすることで充填領域における圧力分布（前記式９）を求める。樹脂の粘性はせん断速度により変化するので、ステップ６において、この求まった圧力から圧力勾配、せん断速度、粘性値、コンダクタンスを修正しながら圧力の収束計算を行う。最終的に圧力が収束後、ステップ７で全充填領域での速度分布を計算する。この速度分布は、ステップ８での温度計算時に用いられる。
【００２１】
次に、ステップ８の温度計算の詳細について次に述べる。
【００２２】
ステップ１０では温度計算のための各種の初期解析パラメータの設定を行い、ステップ１１において板厚方向の壁面温度等の境界条件をとして考慮して、要素毎の熱伝導、熱容量、熱流速マトリックスを作成する。そして、充填領域全体の要素マトリックスを作成し、ステップ１４で全領域での温度分布（前記式１０）を求める。最終ステップ９において、本ステップにおける圧力、温度、せん断速度、速度、粘性、メルトフロント位置等の分布をポストプロセッサーに合せたフォーマットに変換し出力する。これらの操作をステップ２で設定した最終充填ステップまで繰返すことで解析を行うことができる。
以上示したように、本発明における温度解析法は、板厚方向の温度分布を面内方向のみの平均的な温度として計算する簡易的手法であるが、必要な解析精度を保ちつつ安定且つ高速に解析可能であり、充填解析に掛かる計算コストを大幅に削減できる。本手法は、特にウエルドライン予測等のフローパターン解析、充填圧力予測解析に非常に有効である。又、本提案における温度解析法は、充填解析に引続き行う保圧解析においても有効な方法である。
【００２３】
＜実施例１＞
以下、本発明の解析方法を用いて充填圧力の検証を行った実施例を以下に示す。
【００２４】
実験型として図２に示すような平板型を試作した。図中の▲１▼〜▲４▼の位置に圧力センサーを配置し、樹脂流動時の圧力を測定した。解析モデルは、図３に示すようにスプルー部をパイプ要素、その他の形状部分を４角形要素により分割を行った。
使用樹脂は、ＰＣ（ ポリカーボネート） のナチュラル材とガラス短繊維１０％含有材、成形条件は、樹脂温３２０℃、型温９０℃、流入流量３０ｃｍ^３ ／ｓｅｃである。
圧力センサー位置▲１▼〜▲４▼における圧力の時間的変化の計算結果と実験結果の比較を図４及び図５に示す。これらの図に示すように両者は良く一致している。
【００２５】
＜実施例２＞
次に、本発明の解析方法を用いて板厚が異なる偏肉平板を用いてフローパターンの比較検証を行った実施例を以下に示す。
形状及び要素分割図を図６及び図７に示す。この例では周辺部の板厚を１．５ｍｍに固定して、中央部の板厚（５０×３０ｍｍ）の部分を６種類変化（０．５〜３．０ｍｍ）させて検討を行った。
使用樹脂は、ＰＣ（ポリカーボネート）のナチュラル材で、成形条件は、樹脂温３００℃、型温１２０℃、流入流量３６．５５ｃｍ^３ ／ｓｅｃである。フローパターンの計算結果と実験結果の比較を図８に示す。板厚の変化に伴う流れの状態が良く一致していることが分かる。
【００２６】
＜実施例３＞
次に、本発明の解析方法を実際の製品である電子タイプライター・カセットケースに適用して流動バランス検討を行い、ゲート点数を削減し、成形品品質を向上させた事例について示す。
使用樹脂は、ＨＩ−ＰＳである。成形条件は、樹脂温２２０℃、型温４０℃、充填時間２ｓｅｃである。この成形品は、基本肉厚１．５ｍｍで中央部に１．０ｍｍの薄い肉厚個所が存在するので、当初４点ゲートにより成形を行っていた。しかしながら、図９に示すようにウエルドラインが中央部に生じてしまい、外観品質上及び強度上で問題が生じていた。
本発明の解析方法を適用して図１０に示す要素分割モデルを用い、この状況を実際に解析した時のフローパターンを図１１に示す。
【００２７】
ウエルドライン発生位置は良く一致した。そこで、ゲート点数、位置を変えて解析を行った結果、中央部１点ゲートで十分に成形可能であることが分かった。最終充填位置、ウエルドライン発生位置共に良く一致し、外観品質の向上が得られた他、ゲート点数削減に伴う金型製作費を削減することができた。
【００２８】
＜実施例４＞
もう一点、本発明の解析方法を実際の製品である中級機カメラ前カバー部品に適用してウエルドライン位置を予測した事例について示す。
【００２９】
使用樹脂はＰＣであり、成形条件は、樹脂温３１０℃、充填時間２．０ｓｅｃ、型温９０℃である。樹脂は成形品の撮影レンズが位置する中央部１点からディスクゲート方式で充填する。図１２はこの条件化でのフローパターンに関する解析結果である。図中に示す位置にウエルドラインが生じることが分かった。
【００３０】
図１３は実際の成形時においてショートショット試験により、ウエルドラインが生じる位置を検証したときの実成形品である。図に示すように両者は良く一致していることが分かる。
【００３１】
【発明の効果】
以上の説明で明らかなように、本発明によれば、熱伝導項∂（Ｋ∂Ｔ／∂ｚ）／∂ｚについて面外方向、即ち板厚方向に自由度を持つ離散化手法は必要がなく面内方向のみを考えれば良い。これにより計算アルゴリズムを単純化させると共に、計算コストを大幅に削減できるメリットがある。近年、製品のサイクル短縮化、製品機種の多様化、軽薄短小化が進み、製品設計、金型設計期間の短縮が従来にも増して要求され、ＣＡＥによる成形品不良現象予測技術に対する期待が非常に高くなってきている。本手法は簡易的ではあるが、特にウエルドライン予測等のフローパターン解析、充填圧力予測解析等、実用的に使用できる解析精度を有しており非常に有効である。又、本システムは、パソコン上でも非常に高速に動作するので、製品設計者、金型設計者がＣＡＤシステムにより設計作業中に容易に利用することができる。
【図面の簡単な説明】
【図１】解析フローチャートである。
【図２】平板形状を示す図である。
【図３】平板形状の要素分割モデルを示す図である。
【図４】圧力の計算結果と実験結果の比較（ポリカーボネートのナチュラル材の場合）を示す図である。
【図５】圧力の計算結果と実験結果の比較（ポリカーボネートのガラス繊維含有材の場合）を示す図である。
【図６】偏肉平板形状を示す図である。
【図７】偏肉平板形状の要素分割モデルを示す図である。
【図８】フローパターンの計算結果と実験結果の比較を示す図である。
【図９】電子タイプライター・カセットケース形状＆ウエルドラインを示す図である。
【図１０】電子タイプライター・カセットケース形状の要素分割モデルを示す図である。
【図１１】電子タイプライター・カセットケース形状のフローパターン解析結果を示す図である。
【図１２】中級機カメラ前カバー部品の解析モデル＆フローパターン解析結果を示す図である。
【図１３】中級機カメラ前カバーの実成形部品＆ウエルドライン位置を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an analysis method and apparatus for determining flow behavior such as pressure, temperature, speed, shear rate, shear stress or flow pattern of a resin in a resin flow process mainly in the field of plastic injection molding.
[0002]
[Prior art]
A resin flow analysis method for a 2.5-dimensional thin shell structure in plastic injection molding is widely practiced with commercial programs typified by Mold Flow and C-Mold. In the 2.5-dimensional resin flow analysis, a finite element analysis method in which each part inside the molded product cavity is mainly made of a triangular or quadrangular element is applied. A discretization method having a degree of freedom in the plate thickness direction, that is, a method of dividing the plate thickness into 5 to 10 layers and performing a calculation in consideration of the temperature distribution in the plate thickness direction is adopted.
[0003]
By the way, when a triangular element is used, the temperature calculation accuracy particularly concerning element characteristics such as advection term is complicated, and when a quadrilateral element is used, the formulation is complicated numerically. The computational cost to obtain is quite high. Also, recently, for example, as disclosed in Japanese Patent Application Laid-Open No. 8-99341, three-dimensional resin flow analysis and the like have been developed, and the creation of an analysis model has become easier by employing a voxel mesh division method using an orthogonal grid. However, in order to obtain the same accuracy as 2.5 dimensions, it is necessary to divide the mesh in the thickness direction, so the scale of the analysis model becomes large. At present, the calculation cost is considerably high, and it is used at a practical level. Needs more time.
On the other hand, the spread of 3D CAD has spread to the product design and mold design departments, and it has become possible to semi-automatically generate neutral surfaces from 3D product CAD data and semi-automatically perform mesh division. The time required to create an analysis model has been reduced. Further, the design and analysis of a computer using a personal computer (PC) having better operability has become practical from a conventional engineering workstation (EWS).
Under these circumstances, shortening of product cycles, diversification of product models, lightness, and shortening are further progressing, and shortening of product design and mold design periods is required more than ever before. Expectations for technology are becoming very high, and it is essential that product designers and mold designers directly conduct resin flow analysis. For this purpose, there is a demand for a high-speed analysis tool with a short analysis time while maintaining necessary analysis accuracy even during a short product or mold design period.
[0004]
[Problems to be solved by the invention]
According to the above method, there is no need for a discretization method having a degree of freedom in the out-of-plane direction, that is, the thickness direction, of the heat conduction term ∂ (K∂T / ∂z) / ∂z, and only the in-plane direction is considered. This has the advantage of simplifying the calculation algorithm and greatly reducing the calculation cost. Although this method is simple, it is very effective especially for flow pattern analysis such as weld line prediction and filling pressure prediction analysis.
[0005]
An object of the present invention is to provide a resin flow analysis method and apparatus capable of determining flow behavior such as pressure, temperature, speed, shear rate, shear stress, and flow pattern of a resin in a resin flow process mainly in the field of plastic injection molding. It is in.
[0006]
[Means for Solving the Problems]
In general, a mass conservation law, a motion equation, an energy equation, and a viscosity equation are required as basic equations in a resin flow analysis method for a 2.5-dimensional thin shell structure. Here, the energy distribution shown below is used for the temperature distribution in the flow direction and the thickness direction of the molded product.
Energy equation (general formula)
[0007]
(Equation 1)

μ: viscosity coefficient, γ: shear rate Here, in order to obtain the temperature distribution in the thickness direction, the heat conduction term ∂ (K∂T / ∂z) / ∂ is obtained by a method such as a difference method or a finite element method. For z, it is necessary to apply a discretization method having a degree of freedom in the out-of-plane direction, that is, the thickness direction (nodal points or element division is necessary). For this reason, there are drawbacks that the calculation algorithm becomes complicated and the calculation cost increases.
In the present invention, as an analysis method for solving such a problem, the heat conduction term 式 (K∂T / ∂z) / ∂z in the sheet thickness direction is calculated by using handling temperature as the T _w as heat flux term due equivalent heat transfer coefficient alpha by thermal conductivity of the plate thickness and the resin α (T-T _W). According to this method, there is no need for a discretization method having a degree of freedom in the out-of-plane direction, that is, in the thickness direction of the heat conduction term ∂ (K∂T / ∂z) / ∂z. The advantage is that the calculation algorithm can be simplified and the calculation cost can be greatly reduced.
[0008]
Energy equation (this invention)
[0009]
(Equation 2)

α: equivalent heat transfer coefficient _Tw : mold wall temperature [Embodiment of the invention]
The plastic injection molding process consists of a continuous process of filling, packing, cooling, and natural cooling after removal. Here, the purpose is to simulate the temporal change of the pressure distribution and the temperature distribution in the mold and the progress of the melt front in the filling process.
First, the assumptions used in the analysis will be described first.
1) The viscoelastic properties of the incompressible viscous fluid molten resin and the compressibility are not considered.
2) Creep flow The velocity of the molten resin is slow, and the inertial force is ignored in comparison with the viscous force.
3) At each time of the quasi-stationary approximate flow process, the flow is stationary and the term of the time derivative is zero.
4) The Hellsho flow molded product is thin and the flow during filling does not have a velocity distribution in the thickness direction. The viscous force acts only on the plane parallel to the flow.
5) Hagenpoiseuil flow The flow in the sprue runner has only its axial velocity component.
6) The initial resin temperature and the wall surface temperature of the inflow resin are constant.
7) There shall be no resin slip on the wall.
8) Assuming that the spread in the flow direction is sufficiently large compared to the thickness of the cavity, only the thickness method is considered for the heat conduction of the resin.
9) The pressure at the melt front (tip of the inflow resin) is set to zero.
Based on the above assumptions, a general basic equation in the case of a two-dimensional flow (flat plate flow) having a plane parallel to the flow on the xy plane and the z-axis perpendicular thereto is represented by the following equation.
[0010]
[Equation 3]

Equation 3 is a continuous equation, Equations 4 and 5 are equations of motion, Equation 1 is an energy equation, and Equation 6 is a viscosity equation.
Here, u: velocity in the x direction, v: velocity in the y direction, P: pressure, T: temperature, μ: viscosity, ρ: density, c: specific heat, K: thermal conductivity, γ: shear rate, A, B, C: Viscosity coefficient By integrating the equation of motion (Equations 4 and 5) in the thickness direction based on the above assumption and substituting it into the continuous equation (Equation 3), the following equation is obtained.
[0011]
(Equation 4)

Here, S is defined as conductance and is represented by the following equation.
[0012]
(Equation 5)

When the finite element method is applied to Equation 7, and discretization by a triangle obtained by condensing higher-order quadrangular shell elements and quadrangular shell elements is applied, an algebraic matrix such as the following equation is obtained for Equation 7.
[0013]
(Equation 6)

Here, [K]: coefficient matrix, {P}: pressure matrix, {F}: flow rate or pressure boundary condition at the resin inlet of the right side, pressure gradient boundary condition at the mold wall surface, and pressure boundary condition at the melt front. By setting and calculating, a pressure distribution in the cavity can be obtained.
[0014]
Next, the pressure gradient in each element is calculated, the velocity distribution and the shear velocity distribution are calculated, and the viscosity is obtained by Expression 6. Since this is a non-Newtonian fluid analysis, pressure and velocity fields change due to changes in this viscosity, so pressure convergence calculations must be performed.
[0015]
The present invention relates to a resin flow analysis method for a 2.5-dimensional thin shell structure in plastic injection molding as shown in the above basic formula, wherein a heat conduction term in a thickness direction in an energy equation relating to temperature calculation is obtained. (K∂T / ∂z) / ∂z and, calculated as the average thermal velocity α (T-T _W) by considering the heat transfer coefficient alpha by plate thickness and thermal conductivity of the resin mold wall temperature as T _w This is a resin flow analysis method. That is, in this case, Expression 1 is simplified as Expression 2 shown below.
[0016]
(Equation 7)

According to this method, there is no need for a discretization method having a degree of freedom in the thickness direction with respect to the heat conduction term ∂ (K∂T / ∂z) / ∂z, thereby simplifying the calculation algorithm and reducing the calculation cost. There is a merit that can be greatly reduced.
When the finite element method is applied to Equation 2 as in the case of the pressure solution shown in Equation 7, an algebraic matrix as shown in the following equation is obtained.
[0017]
(Equation 8)

Here, [C]: heat capacity matrix, [K]: heat conduction matrix {T}: temperature matrix, {Q}: heat flow rate matrix As a solution of Equation 8, the Crank-Nicholson method that is unconditionally stable in numerical analysis Is used.
[0018]
Finally, FIG. 1 shows an overall flowchart of this analysis.
[0019]
First, in step 1, shape data, molding condition data, pressure temperature boundary condition data, various analysis control parameters, and the like to be analyzed are read. Next, in step 2, the number of analysis steps for setting the number of analysis steps to be divided into a plurality of analysis steps from the time when the resin starts flowing from the designated inflow port until the resin is finally filled is set. In this analysis, the resin flow is assumed to be incompressible, and the resin filling amount per step is determined from the total number of analysis steps and the total volume of the molded article to be analyzed. In Step 3, initial calculations such as initial viscosity (Equation 6) and initial conductance (Equation 8) are performed based on the analysis step set in Step 2.
[0020]
Next, in step 4, by a method such as the FAN method (Flow Analysis Network Method) or the like, the melt front (resin flow tip portion) is calculated by the resin filling amount and conductance in one step calculated in steps 2 and 3. Determine the position. In step 5, as the boundary condition, the value of the injection pressure or the value of the injection speed at the inflow port and the value of the pressure at the melt front are set to the atmospheric pressure to obtain the pressure distribution (formula 9) in the filling region. Since the viscosity of the resin changes according to the shear rate, in step 6, the pressure convergence calculation is performed while correcting the pressure gradient, the shear rate, the viscosity value, and the conductance from the obtained pressure. After the pressure finally converges, in step 7, the velocity distribution in the entire filling region is calculated. This velocity distribution is used at the time of temperature calculation in step 8.
[0021]
Next, the details of the temperature calculation in step 8 will be described below.
[0022]
In step 10, various initial analysis parameters for temperature calculation are set, and in step 11, heat conduction, heat capacity, and heat flow velocity matrices are created for each element in consideration of boundary conditions such as wall temperature in the thickness direction. I do. Then, an element matrix of the entire filling region is created, and a temperature distribution (Equation 10) in the entire region is obtained in step 14. In the final step 9, the distribution of pressure, temperature, shear rate, speed, viscosity, melt front position, etc. in this step is converted into a format suitable for the post processor and output. The analysis can be performed by repeating these operations up to the final filling step set in step 2.
As described above, the temperature analysis method in the present invention is a simple method of calculating the temperature distribution in the thickness direction as an average temperature only in the in-plane direction, but it is stable and high-speed while maintaining the required analysis accuracy. And the calculation cost required for filling analysis can be greatly reduced. This method is very effective especially for flow pattern analysis such as weld line prediction and filling pressure prediction analysis. The temperature analysis method in the present proposal is also an effective method in the dwelling analysis performed subsequently to the filling analysis.
[0023]
<Example 1>
Hereinafter, examples in which the filling pressure was verified using the analysis method of the present invention will be described below.
[0024]
A flat plate type as shown in FIG. 2 was experimentally manufactured as an experimental type. Pressure sensors were arranged at positions (1) to (4) in the figure, and the pressure during resin flow was measured. In the analysis model, as shown in FIG. 3, a sprue portion was divided by a pipe element, and other shape portions were divided by a square element.
The resin used is a natural material of PC (polycarbonate) and a material containing 10% of short glass fibers. The molding conditions are a resin temperature of 320 ° C., a mold temperature of 90 ° C., and an inflow flow rate of 30 cm ³ / sec.
FIGS. 4 and 5 show a comparison between a calculation result of a temporal change in pressure at the pressure sensor positions (1) to (4) and an experimental result. As shown in these figures, the two agree well.
[0025]
<Example 2>
Next, examples in which flow patterns are compared and verified using uneven thickness flat plates having different thicknesses using the analysis method of the present invention will be described below.
FIGS. 6 and 7 show the shapes and the element division diagrams. In this example, the thickness of the peripheral portion was fixed to 1.5 mm, and the thickness of the central portion (50 × 30 mm) was changed by six types (0.5 to 3.0 mm) for examination.
The resin used is a natural material of PC (polycarbonate), and the molding conditions are a resin temperature of 300 ° C., a mold temperature of 120 ° C., and an inflow flow rate of 36.55 cm ³ / sec. FIG. 8 shows a comparison between the calculation result of the flow pattern and the experimental result. It can be seen that the state of the flow accompanying the change in the plate thickness is in good agreement.
[0026]
<Example 3>
Next, an example in which the analysis method of the present invention is applied to an electronic typewriter / cassette case, which is an actual product, to examine the flow balance, reduce the number of gate points, and improve the quality of a molded product will be described.
The resin used is HI-PS. The molding conditions are a resin temperature of 220 ° C., a mold temperature of 40 ° C., and a filling time of 2 seconds. Since this molded product had a basic thickness of 1.5 mm and a thin portion of 1.0 mm in the center, the molding was initially performed using a four-point gate. However, as shown in FIG. 9, a weld line was formed at the center, which caused problems in appearance quality and strength.
FIG. 11 shows a flow pattern when this situation is actually analyzed using the element division model shown in FIG. 10 by applying the analysis method of the present invention.
[0027]
Weld line occurrence positions agreed well. Therefore, as a result of performing analysis by changing the number of gate points and the position, it was found that a single point gate at the center can be sufficiently molded. Both the final filling position and the weld line generation position were in good agreement, and the appearance quality was improved, and the die manufacturing cost associated with the reduction in the number of gate points was able to be reduced.
[0028]
<Example 4>
Another example is shown in which the analysis method of the present invention is applied to an intermediate product camera front cover part as an actual product to predict a weld line position.
[0029]
The resin used is PC, and the molding conditions are a resin temperature of 310 ° C., a filling time of 2.0 sec, and a mold temperature of 90 ° C. The resin is filled by a disk gate method from one point at the center of the molded product where the taking lens is located. FIG. 12 shows an analysis result regarding the flow pattern under this condition. It was found that a weld line was generated at the position shown in the figure.
[0030]
FIG. 13 shows an actual molded product when a position where a weld line occurs is verified by a short shot test during actual molding. As shown in the figure, it can be seen that the two agree well.
[0031]
【The invention's effect】
As is apparent from the above description, according to the present invention, a discretization method having a degree of freedom in the out-of-plane direction, that is, the thickness direction of the heat conduction term ∂ (K∂T / ∂z) / ∂z is necessary. Only the in-plane direction need be considered. This has the advantage that the calculation algorithm can be simplified and the calculation cost can be significantly reduced. In recent years, the shortening of product cycles, the diversification of product models, the lightness, and the miniaturization have been progressing, and the shortening of product design and mold design periods has been required more than ever before. It is getting higher. Although this method is simple, it has analysis accuracy that can be used practically, such as flow pattern analysis such as weld line prediction and filling pressure prediction analysis, and is very effective. Further, since this system operates at a very high speed even on a personal computer, a product designer and a die designer can easily use the CAD system during a designing operation.
[Brief description of the drawings]
FIG. 1 is an analysis flowchart.
FIG. 2 is a view showing a flat plate shape.
FIG. 3 is a diagram showing a plate-shaped element division model.
FIG. 4 is a diagram showing a comparison between a calculation result of pressure and an experimental result (in the case of a natural material of polycarbonate).
FIG. 5 is a diagram showing a comparison between a calculation result of pressure and an experiment result (in the case of a glass fiber-containing material of polycarbonate).
FIG. 6 is a view showing an uneven thickness flat plate shape.
FIG. 7 is a view showing an element division model of an uneven thickness flat plate shape.
FIG. 8 is a diagram showing a comparison between a calculation result of a flow pattern and an experimental result.
FIG. 9 is a view showing an electronic typewriter / cassette case shape and weld line.
FIG. 10 is a view showing an element division model in the form of an electronic typewriter / cassette case.
FIG. 11 is a diagram showing a flow pattern analysis result of an electronic typewriter / cassette case shape.
FIG. 12 is a diagram showing an analysis model and a flow pattern analysis result of a cover part in front of an intermediate-class camera.
FIG. 13 is a view showing actual molded parts and weld line positions of the intermediate machine camera front cover.

Claims (2)

In a resin flow analysis device, which is intended for a 2.5-dimensional thin shell structure in plastic injection molding and has pressure analysis means for calculating the pressure at the time of filling each part of the molded product and temperature analysis means for calculating the temperature at the time of filling. ,
The temperature analysis means, heat conduction term ∂ the plate thickness direction of an energy equations (K∂T / ∂z) / ∂z, from the mold wall temperature T _W to the molded part thickness and thermal conductivity of the resin A resin flow analysis device comprising means for determining a heat transfer coefficient α and calculating the heat flow rate α ( _TTW ). In a resin flow analysis method having a temperature analysis method for calculating a pressure at the time of filling of each part of a molded product and a temperature analysis method for calculating a temperature at the time of filling, the method is intended for a 2.5-dimensional thin shell structure in plastic injection molding.
Said temperature analysis method, heat conduction term ∂ the plate thickness direction of an energy equations (K∂T / ∂z) / ∂z, from the mold wall temperature T _W to the molded part thickness and thermal conductivity of the resin A resin flow analysis method, wherein a heat transfer coefficient α is determined and calculated as a heat flow rate α (T−T _W ).

Images