JP3650338B2 - Mold design method and apparatus, and extrusion die and core design method and apparatus - Google Patents

Description

を演算することが望ましい。樹脂物性は非線形粘弾性モデルとして与えられることが望ましく、例としてGiesekusモデルで記述した。ここで、溶融樹脂の流れる方向にｚ軸をとり、動径方向をｒ軸とした。また、応力σと速度ｖは、以下のように各成分に分けて表した。
【数２】

樹脂物性パラメータは緩和モードｊに対する緩和時間λ_jと弾性率Ｇ_jである。なお、Giesekusモデルでは易動度因子（mobility factor）と呼ばれる非線形パラメータαを要する。
【００１４】
本発明の第二の観点によると、押出ダイとコアとの間のギャップを通して溶融樹脂を押し出してパリソンを形成するときの溶融樹脂の形状変化をシミュレートする第一の手段と、押し出されたパリソンに対する金型の型締めおよびパリソン内への圧縮空気の吹き込みによる溶融樹脂の形状変化をシミュレートする第二の手段と、金型内で溶融樹脂が固化して得られた成形品を高温状態で金型から取り出した後にその成形品に冷却により生じる熱変形をシミュレートする第三の手段と、前記第一ないし前記第三の手段のシミュレーション結果から、所望の形状の成形品が得られるような金型、押出ダイおよびコアの形状を決定する第四の手段とを備えたことを特徴とする金型、押出ダイおよびコアの設計装置が提供される。
【００１５】
【発明の実施の形態】
本発明実施例の金型設計方法を図１および図２を参照して説明する。
【００１６】
ブロー成形は、図１に示すように、押出ダイとコアとの間のギャップを通して溶融樹脂を押し出してパリソンを形成する押出工程（Ｐ１）と、押し出されたパリソンに対して金型を型締する型締工程（Ｐ２）と、パリソン内へ圧縮空気を吹き込む吹込工程（Ｐ３）と、金型内で溶融樹脂を固化させる冷却工程（Ｐ４）と、得られた成形品を金型から取り出す型開工程（Ｐ５）とを含む。本発明では、成形品を高温状態で金型から取り出すため、成形品に冷却により熱変形が生じる。
【００１７】
本発明では、図２に示すように、これらの各工程をシミュレートする。すなわち、動的粘弾性データ（Ｄ１）およびその他の樹脂物性（Ｄ２）から樹脂物性データを作成し（Ｓ１）、成形条件（Ｄ３）を付加して押出工程（Ｐ１）における溶融樹脂の形状変化をシミュレートする（Ｓ２、以下「押出シミュレーション」という）。次に、金型のキャビティ形状に関するデータおよび金型配置（Ｄ４）からパリソンのＦＥＭデータを作成し（Ｓ３）、吹込条件および樹脂物性のデータ（Ｄ５）から、型締工程（Ｐ２）および吹込工程（Ｐ３）における溶融樹脂の形状変化をシミュレートする（Ｓ４、以下「型締−吹込シミュレーション」という）。続いて、冷却工程（Ｐ４）および型開工程（Ｐ５）後の成形品の熱変形をシミュレートする（Ｓ５、以下「冷却−熱変形シミュレーション」という）。これらのシミュレーション結果から、所望の形状の成形品が得られるような金型、押出ダイおよびコアの形状を決定する（Ｓ６）。
【００１８】
押出シミュレーションでは、押出ダイとコアの間のギャップを通過する溶融樹脂の流れを流体の発達流れ方程式で演算し、ギャップを通過したときに溶融樹脂がもつ歪みを与えてそのギャップを通過した後の溶融樹脂の挙動を伸長弾性回復方程式で演算する。発達流れ方程式および伸長弾性回復方程式については後述する。
【００１９】
金型の形状、特にキャビティの形状を決定するには、金型キャビティの形状をパラメータとして冷却-熱変形シミュレーションを繰り返し、所望の最終形状を得る。また、押出ダイおよびコアの形状、特にそれらにより形成されるギャップの形状（図３参照）を決定するには、押出シミュレーション、型締−吹込シミュレーションを用いて、成形品の肉厚分布が所望の分布となるような形状を決定する。
【００２０】
表１に示すように、コア径φ１６ｍｍに対し、成形条件Ａはダイをφ１９ｍｍ（ａ＝ｂ）の円とし、成形条件Ｂはダイを１９．２ｍｍ（ａ）×１９．０ｍｍ（ｂ）の楕円とし、成形条件Ｃはダイを１９．４ｍｍ（ａ）×１９．０ｍｍ（ｂ）の楕円とした。ここで、ａ、ｂは図３のように定義している。また、成形サイクルは１６．６秒、パリソン長は２５５ｍｍ、樹脂温度は２００°Ｃ、ブロー圧は０．５７ＭＰａとした。これにより、表２と図４（ａ）ないし（ｃ）のプロットに示すような成形結果を得た。図には実線でシミュレーション結果を併記している。
【表１】

【表２】

【００２１】
図４の実線のように得られたシミュレーション結果の中から所望の肉厚分布に近似するものを選択し、押出ダイおよびコアの形状を選定する。通常は、正面および背面と側面の肉厚がほぼ等しくなるように選ぶ。金型キャビティ形状は、この肉厚分布のもとで冷却-熱変形シミュレーションを行ったときに、目的の成形品形状となるように設計される。
【００２２】
押出ダイおよびコアの選定をした後、金型キャビティ形状の設計に先立って、熱変形が相似変形に近くなるような、より望ましい押出ダイおよびコアの形状を求めることもできる。これを図５および図６を参照して説明する。図５はダイおよびコアの構成およびその間のギャップΔａ、Δｂを示す。ギャップΔａは成形品の側面の肉厚に対応し、Δｂは成形品の正面または背面の肉厚に対応する。図６は形状を求める手順を示す。
【００２３】
図６に示すように、先に選定した押出ダイおよびコアを初期形状とし（Ｓ１１）、押出シミュレーションと型締-吹込シミュレーションにより成形品の肉厚分布を求める（Ｓ１２）。この成形品肉厚分布を用いて冷却-熱変形シミュレーションを行い、変形後の成形品形状を求める（Ｓ１３）。成形品の変形が相似変形に近いかどうかを判断し（Ｓ１４）、相対的に成形品の正面および背面が膨らんでいる場合には図５に示したΔａ／Δｂを小さくし、へこんでいる場合にはΔａ／Δｂを大きくする（Ｓ１５）。以下、Ｓ１１ないしＳ１５を相似変形に近づくまで繰り返す。
【００２４】
本発明の金型、押出ダイおよびコアの設計方法は、図７に示す設計装置により実行される。この装置は、押出ダイとコアとの間のギャップを通して溶融樹脂を押し出してパリソンを形成するときの溶融樹脂の形状変化をシミュレートする押出シミュレーション部１と、押し出されたパリソンに対する金型の型締めおよびパリソン内への圧縮空気の吹き込みによる溶融樹脂の形状変化をシミュレートする型締-吹込シミュレーション部２と、金型内で溶融樹脂が固化して得られた成形品を高温状態で金型から取り出した後にその成形品に冷却により生じる熱変形をシミュレートする冷却-熱変形シミュレーション部３と、これらのシミュミレーション結果から、熱変形が相似変形に近づくような押出ダイおよびコアの形状と所望の形状の成形品が得られるような金型形状を決定する形状設計部4とを備える。形状設計部４は、押出シミュレーション、型締-吹込シミュレーション、冷却-熱変形シミュレーションを繰り返し行うことにより、金型、押出ダイおよびコアの形状を設計する。
【００２５】
この装置はまた、読取装置５を備え、ＣＤ−ＲＯＭ６などの記録媒体に書き込まれたプログラムを読み取り、これをコンピュータに装填することにより、コンピュータを本発明の金型、押出ダイおよびコアの設計装置として動作させることができる。
【００２６】
当該シミュレーションの流れを図２に戻って説明する。樹脂物性の測定データとして貯蔵および損失弾性率、もしくは粘度を与えると、設計者が設定した任意の個数の緩和時間に対して対応する弾性率が計算される。得られた緩和時間と弾性率のセットに樹脂の非線形性を表すパラメータを加えて、樹脂物性データが作成される。
【００２７】
図８は樹脂物性データの求め方の一例を示す。この図において、貯蔵弾性率と損失弾性率の実測値をそれぞれ●と▲で示す。貯蔵弾性率Ｇ'(ω)、損失弾性率Ｇ"(ω)は、
【数３】

と表される。Ｍは緩和モードの個数で、この実施例では11モードとっている。貯蔵弾性率、損失弾性率の実測値を用いて、最小二乗法により緩和時間λ_jに対する弾性率Ｇ_jを決定する。図８中の実線は、このようにして得られたλ_j、Ｇ_jを上式に代入して計算したものである。
【００２８】
導出された樹脂物性データに成形条件を併せてパリソン形成の計算が行われる。この計算は、図９に示すように、三つの部分に分けて行われる。
（１）図３に示した押出ダイ内を溶融樹脂が流れる部分は発達流れ方程式が用いられ、上述した数１の式により計算が行われる。これにより、ダイ内法線応力σ_{j ｉ}、γ_{j ｉ}が与えられる。数１では添え字ｉを省いているが、このｉはパリソンを重量一定の各要素に分割したときの各要素の番号である。ダイ内歪みε_dは後述するように与えられる。ここで求めたσ_{j ｉ}、γ_{j ｉ}と、別途与えられるε_dとは、続く伸長弾性回復方程式の初期値として用いられる。
（２）押出ダイから流出する部分は、伸長弾性回復方程式が用いられ、
【数４】

として計算が行われる。ここでＮ₁はダイ内で発生する第一法線応力差で、数１で求めたσ_i、γ_iからＮ_１＝γ_i−σ_iで与えられる。ν_eは溶融樹脂のダイからの押出速度で、ｔ_iは押し出し開始から要素ｉが押し出されるのに要した時間である。また、ρは溶融樹脂の密度、ｇは重力加速度を表す。数４より押出直後の法線応力σ_ji、γ_ji、歪みε_iが与えられる。また、
（３）パリソンが垂れ下がる部分については、ドローダウン／スウェル方程式が用いられ、
【数５】

として、計算が行われる。ここで求められた歪みε_iをもとに、要素ｉの形状と肉厚が決められる。各要素を併せて、パリソン全体の形状と肉厚分布が決められる。なお、前出のダイ内歪みε_dは数５により得られるパリソン長さが目標長と合うように決める。これは通常、数１、数４および数５を繰り返し計算することにより決められる。
【００２９】
このようにして導出されたパリソン形状およびパリソン肉厚分布から、金型に関するデータや要素分割方法の情報を併せてパリソンのＦＥＭデータが作成される。このパリソンＦＥＭデータに対して型締-吹込シミュレーションが実行され、さらに、冷却-熱変形シミュレーションが実行される。これらのシミュレーションの結果、熱変形が相似変形に近づくように押出ダイおよびコアが設計され、所望の形状の成形品が得られるように金型設計が行われる。
【００３０】
【発明の効果】
以上説明したように、本発明によれば、試作を行うことなく金型や押出ダイおよびコアの設計をコンピュータ上の成形工程のシミュレーションにより行うことができる。
【図面の簡単な説明】
【図１】ブロー成形工程のフローを示す図。
【図２】本発明実施例の金型、押出ダイおよびコアの設計方法のフローを示す図。
【図３】押出ダイおよびコアの形状を示す図。
【図４】成形後の肉厚の実測値と対応するシミュレーション結果を示す図。
【図５】ダイおよびコアの構成およびその間のギャップΔa、Δbを示す図。
【図６】熱変形が相似変形に近くなるような押出ダイおよびコアの形状を求める手順のフローを示す図。
【図７】本発明実施例の設計装置の要部ブロック構成図。
【図８】貯蔵弾性率および損失弾性率の一例を示す図。
【図９】パリソン形成シミュレーションの基礎方程式の適用箇所を示す図。
【符号の説明】
１ 押出シミュレーション部
２ 型締−吹込シミュレーション部
３ 冷却−熱変形シミュレーション部
４ 形状設計部
５ 読取装置
６ ＣＤ−ＲＯＭ[0001]
BACKGROUND OF THE INVENTION
The present invention is used in the design of plastic product molds or the design of extrusion dies and cores.
[0002]
[Prior art]
A plastic molding method is widely used in which a plastic melted at a high temperature is extruded into a tube shape, sandwiched between molds, and blown into a tube to be inflated. In this conventional example, a tube-shaped molten plastic (parison) is disposed at an intermediate position of a divided mold, and the mold is closed. In this state, when air is blown into the molten plastic, the molten plastic comes into close contact with the inner wall of the mold and exhibits the same shape as the inner wall of the mold. By maintaining this state while blowing high-pressure air in the mold, the plastic is cooled and solidified to obtain a molded product having the same shape as the mold. After cooling and solidification, when the mold is opened, the molded product is taken out.
[0003]
For example, in the case where a molded product is a container (bottle) for filling and selling a liquid, a standard resin temperature for opening a mold is usually about 50 ° C. This cooling takes 10 seconds or more. In order to realize a lower production cost, it is a problem to shorten the time required for cooling.
[0004]
However, if the cooling time is shortened and the mold is opened to a high temperature, the high temperature molten plastic contracts greatly and causes nonlinear deformation. As a result, unlike the target molded product shape, the cooling time could not be shortened.
[0005]
Therefore, the inventors simulated the deformation behavior using the finite element method, and created the mold shape in consideration of the deformation in advance, so that the desired molded product shape can be obtained even at high temperature removal. A mold design method and apparatus have been invented (see Patent No. 2955509, Patent No. 2975503).
[0006]
In this mold design method, the initial shape of a molded product immediately after being taken out from the die is subjected to a thermal deformation simulation for the deformation that occurs after being taken out from the die, and the shape deformed by this simulation and the target molded product shape. A difference is calculated, the difference is compared with a threshold value, and when the difference exceeds the threshold value, the initial shape is changed based on the difference.
[0007]
[Problems to be solved by the invention]
In this mold design method, an optimal mold shape is obtained so as to obtain a desired molded product shape by simulating how a given initial shape changes due to heat shrinkage. However, the thickness distribution of the molded product is obtained by actually making a test mold. Therefore, a plurality of prototypes are required until one mold is completed, which is disadvantageous in terms of cost and time. In addition, in order to obtain a desired molded product thickness distribution, it is necessary to prototype a plurality of parison extrusion die cores.
[0008]
The present invention has been carried out against this background, and it is an object of the present invention to provide a mold, an extrusion die, and a core design method and apparatus that do not require trial manufacture of a mold, an extrusion die, and a core. And
[0009]
[Means for Solving the Problems]
According to a first aspect of the present invention, a first step of simulating a molten resin shape change when extruding a molten resin through a gap between an extrusion die and a core to form a parison, and an extruded parison The second step of simulating the mold change of the molten resin due to mold clamping and the injection of compressed air into the parison, and the molded product obtained by solidifying the molten resin in the mold at high temperature A molded product having a desired shape can be obtained from the third step of simulating thermal deformation caused by cooling of the molded product after removal from the mold and the simulation results of the first to third steps. And a fourth step of determining the shape of the mold, the extrusion die and the core, and a method for designing the mold, the extrusion die and the core is provided.
[0010]
The first step includes a step of determining a parison shape and a parison wall thickness distribution by giving parameters of a shape of a gap between an extrusion die and a core and a resin physical property, and the second step includes clamping a die against the parison. And a deformation prediction by blowing to obtain a thickness distribution in a shape along the cavity of the mold, and the third step performs a shrinkage prediction for the obtained thickness distribution. The fourth step may include a step of obtaining a mold shape from which a molded product having a desired shape is obtained from a result of the shrinkage prediction.
[0011]
In addition, the first step includes a step of obtaining a parison shape and a parison thickness distribution by giving parameters of a shape of a gap between the extrusion die and the core and a resin physical property, and the second step. The step includes a step of performing deformation prediction by mold clamping and blowing with respect to the parison to obtain a wall thickness distribution in a shape along the cavity of the mold, and the fourth step includes the mold of the mold. The step of evaluating the thickness distribution in the shape along the cavity by its strength and stability against thermal deformation, and determining the shape of the extrusion die and core so as to obtain the optimum thickness distribution based on the evaluation It can also be included.
[0012]
The step of obtaining the parison shape and the parison thickness distribution includes calculating a flow of the molten resin that passes through the gap between the extrusion die and the core by a development flow equation of a nonlinear viscoelastic fluid, and when passing through the gap It is preferable to include a step of calculating the behavior of the molten resin after passing through the gap by applying the strain of the molten resin with an elongation elastic recovery equation.
[0013]
That is, as a development flow of molten resin,
[Expression 1]

It is desirable to calculate The resin physical properties are preferably given as a non-linear viscoelastic model, and are described by the Giesekus model as an example. Here, the z axis is taken in the direction in which the molten resin flows, and the radial direction is taken as the r axis. Further, the stress σ and the velocity v are expressed separately for each component as follows.
[Expression 2]

The resin property parameters are relaxation time λ _j and elastic modulus G _j for relaxation mode j. Note that the Giesekus model requires a non-linear parameter α called a mobility factor.
[0014]
According to a second aspect of the present invention, a first means for simulating molten resin shape change when extruding molten resin through a gap between an extrusion die and a core to form a parison, and an extruded parison A second means of simulating the mold change of the molten resin due to mold clamping against the mold and blowing of compressed air into the parison, and the molded product obtained by solidification of the molten resin in the mold at high temperature From the simulation results of the third means for simulating thermal deformation caused by cooling of the molded product after removal from the mold and the simulation results of the first to third means, a molded product having a desired shape can be obtained. A mold, an extrusion die, and a core design apparatus, comprising: a mold, an extrusion die, and a fourth means for determining the shape of the core are provided.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
A mold design method according to an embodiment of the present invention will be described with reference to FIGS.
[0016]
In blow molding, as shown in FIG. 1, an extrusion process (P1) in which a molten resin is extruded through a gap between an extrusion die and a core to form a parison, and a mold is clamped against the extruded parison. Clamping step (P2), blowing step (P3) for blowing compressed air into the parison, cooling step (P4) for solidifying the molten resin in the mold, and mold opening for removing the obtained molded product from the mold And (P5). In the present invention, since the molded product is removed from the mold at a high temperature, the molded product is thermally deformed by cooling.
[0017]
In the present invention, each of these steps is simulated as shown in FIG. That is, resin physical property data is created from the dynamic viscoelasticity data (D1) and other resin physical properties (D2) (S1), and molding conditions (D3) are added to change the shape of the molten resin in the extrusion step (P1). Simulate (S2, hereinafter referred to as "extrusion simulation"). Next, the FEM data of the parison is created from the data on the cavity shape of the mold and the mold arrangement (D4) (S3), and the mold clamping process (P2) and the blowing process from the blowing condition and resin physical property data (D5) The shape change of the molten resin in (P3) is simulated (S4, hereinafter referred to as “clamping-blowing simulation”). Subsequently, thermal deformation of the molded product after the cooling step (P4) and the mold opening step (P5) is simulated (S5, hereinafter referred to as “cooling-thermal deformation simulation”). From these simulation results, the shapes of the mold, the extrusion die and the core are determined so as to obtain a molded product having a desired shape (S6).
[0018]
In the extrusion simulation, the flow of the molten resin passing through the gap between the extrusion die and the core is calculated by the fluid development flow equation, and after passing through the gap, the molten resin is strained and passes through the gap. The behavior of the molten resin is calculated by the stretch elastic recovery equation. The development flow equation and the stretch elastic recovery equation will be described later.
[0019]
In order to determine the shape of the mold, particularly the shape of the cavity, the cooling-thermal deformation simulation is repeated using the shape of the mold cavity as a parameter to obtain a desired final shape. Further, in order to determine the shape of the extrusion die and the core, particularly the shape of the gap formed by them (see FIG. 3), the thickness distribution of the molded product is desired by using an extrusion simulation and a mold-clamping / blowing simulation. Determine the shape to be distributed.
[0020]
As shown in Table 1, with respect to the core diameter of 16 mm, the molding condition A is a circle of φ19 mm (a = b), and the molding condition B is an ellipse of 19.2 mm (a) × 19.0 mm (b). In the molding condition C, the die was an ellipse of 19.4 mm (a) × 19.0 mm (b). Here, a and b are defined as shown in FIG. The molding cycle was 16.6 seconds, the parison length was 255 mm, the resin temperature was 200 ° C., and the blow pressure was 0.57 MPa. Thereby, the molding results as shown in Table 2 and the plots of FIGS. 4A to 4C were obtained. In the figure, the simulation results are also shown with solid lines.
[Table 1]

[Table 2]

[0021]
From the simulation results obtained as indicated by the solid line in FIG. 4, the one that approximates the desired thickness distribution is selected, and the shapes of the extrusion die and the core are selected. Normally, the thickness is selected so that the thickness of the front, back, and side is almost equal. The mold cavity shape is designed so as to have a desired molded product shape when a cooling-thermal deformation simulation is performed under this wall thickness distribution.
[0022]
After selecting the extrusion die and core, prior to designing the mold cavity shape, a more desirable extrusion die and core shape can be determined so that thermal deformation is close to similar deformation. This will be described with reference to FIGS. FIG. 5 shows the die and core configurations and the gaps Δa, Δb between them. The gap Δa corresponds to the thickness of the side surface of the molded product, and Δb corresponds to the thickness of the front surface or the back surface of the molded product. FIG. 6 shows a procedure for obtaining the shape.
[0023]
As shown in FIG. 6, the previously selected extrusion die and core are set to the initial shape (S11), and the thickness distribution of the molded product is obtained by the extrusion simulation and the mold-clamping-blowing simulation (S12). A cooling-thermal deformation simulation is performed using the thickness distribution of the molded product, and the shape of the molded product after deformation is obtained (S13). When it is determined whether the deformation of the molded product is close to a similar deformation (S14), and when the front and back surfaces of the molded product are relatively swollen, Δa / Δb shown in FIG. Is increased by Δa / Δb (S15). Thereafter, S11 to S15 are repeated until approaching similar deformation.
[0024]
The mold, extrusion die and core design method of the present invention is executed by a design apparatus shown in FIG. This apparatus includes an extrusion simulation unit 1 for simulating a change in shape of a molten resin when a molten resin is extruded through a gap between an extrusion die and a core to form a parison, and a mold clamping for the extruded parison. And mold clamping-blowing simulation section 2 for simulating changes in the shape of the molten resin due to the injection of compressed air into the parison, and a molded product obtained by solidifying the molten resin in the mold from the mold at a high temperature. The cooling-thermal deformation simulation unit 3 for simulating the thermal deformation caused by cooling of the molded product after removal, and the results of these simulations indicate the shape and desired shape of the extrusion die and core so that the thermal deformation approaches the similar deformation And a shape design unit 4 that determines a mold shape so as to obtain a molded product having the following shape. The shape design unit 4 designs the shapes of the mold, the extrusion die, and the core by repeatedly performing extrusion simulation, mold clamping-blowing simulation, and cooling-thermal deformation simulation.
[0025]
This apparatus also includes a reading device 5, reads a program written on a recording medium such as a CD-ROM 6, and loads the computer into the computer, thereby allowing the computer to design the mold, extrusion die and core of the present invention. Can be operated as
[0026]
The simulation flow will be described with reference to FIG. When storage and loss elastic modulus or viscosity is given as measurement data of resin physical properties, the elastic modulus corresponding to an arbitrary number of relaxation times set by the designer is calculated. A parameter representing the nonlinearity of the resin is added to the obtained set of relaxation time and elastic modulus to create resin physical property data.
[0027]
FIG. 8 shows an example of how to obtain resin property data. In this figure, the measured values of storage elastic modulus and loss elastic modulus are indicated by ● and ▲, respectively. The storage elastic modulus G ′ (ω) and the loss elastic modulus G ″ (ω) are
[Equation 3]

It is expressed. M is the number of relaxation modes, and 11 modes are used in this embodiment. Storage modulus, using measured value of the loss modulus, to determine the elastic modulus G _j for relaxation time lambda _j by the least squares method. The solid lines in FIG. 8 are calculated by substituting λ _j and G _j obtained in this way into the above equation.
[0028]
The parison formation is calculated by combining the derived resin property data with the molding conditions. This calculation is performed in three parts as shown in FIG.
(1) The development flow equation is used for the portion where the molten resin flows in the extrusion die shown in FIG. 3, and the calculation is performed by the above-described equation (1). As a result, in-die normal stresses σ _{j i} and γ _{j i} are given. And omitting the number 1 suffix i, this i is the number of each element when dividing the parison to each element of Weight a constant. The in-die strain ε _d is given as will be described later. Σ _{j i} , γ _{j i} obtained here and ε _d given separately are used as initial values of the subsequent stretch elastic recovery equation.
(2) The stretched elastic recovery equation is used for the part flowing out from the extrusion die,
[Expression 4]

Is calculated as follows. Here, N ₁ is a first normal stress difference generated in the die, and is given by N ₁ = γ _i −σ _i from σ _i and γ _i obtained in Equation ₁ . ν _e is the extrusion speed of the molten resin from the die, and t _i is the time required for the element i to be extruded from the start of extrusion. Ρ represents the density of the molten resin, and g represents the acceleration of gravity. From Equation 4, normal stresses σ _ji and γ _ji and strain ε _i immediately after extrusion are given. Also,
(3) For the part where the parison hangs, the drawdown / swell equation is used,
[Equation 5]

As the calculation is performed. The shape and thickness of the element i are determined based on the strain ε _i obtained here. Together with each element, the shape and thickness distribution of the entire parison are determined. The intra-die strain ε _d is determined so that the parison length obtained by Equation 5 matches the target length. This is usually determined by repeatedly calculating Equation 1, Equation 4, and Equation 5.
[0029]
From the parison shape and the parison thickness distribution thus derived, the parison FEM data is created together with the data on the mold and the information on the element dividing method. A mold-clamping simulation is performed on the parison FEM data, and a cooling-thermal deformation simulation is further performed. As a result of these simulations, the extrusion die and the core are designed so that the thermal deformation approaches the similar deformation, and the mold is designed so as to obtain a molded product having a desired shape.
[0030]
【The invention's effect】
As described above, according to the present invention, a mold, an extrusion die, and a core can be designed by a simulation of a molding process on a computer without performing a prototype.
[Brief description of the drawings]
FIG. 1 is a diagram showing a flow of a blow molding process.
FIG. 2 is a diagram showing a flow of a method for designing a mold, an extrusion die and a core according to an embodiment of the present invention.
FIG. 3 is a view showing shapes of an extrusion die and a core.
FIG. 4 is a diagram showing a simulation result corresponding to an actual measurement value of the thickness after molding.
FIG. 5 is a diagram showing a configuration of a die and a core and gaps Δa and Δb therebetween.
FIG. 6 is a diagram showing a flow of a procedure for obtaining the shape of an extrusion die and a core such that thermal deformation is close to similar deformation.
FIG. 7 is a block diagram of a main part of a design apparatus according to an embodiment of the present invention.
FIG. 8 is a diagram showing an example of storage elastic modulus and loss elastic modulus.
FIG. 9 is a diagram showing an application location of a basic equation for parison formation simulation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Extrusion simulation part 2 Clamping-blow simulation part 3 Cooling-thermal deformation simulation part 4 Shape design part 5 Reader 6 CD-ROM

Claims (4)

A first step of simulating the shape change of the molten resin when the molten resin is extruded through a gap between the extrusion die and the core to form a parison;
A second step of simulating the mold change of the extruded parison and the shape change of the molten resin due to the injection of compressed air into the parison;
A third step of simulating thermal deformation caused by cooling of the molded product after the molded product obtained by solidifying the molten resin in the mold is removed from the mold at a high temperature;
The simulation results of the first to the third step, seen including a fourth step of determining a desired mold shape as the molded article is obtained in the shape,
The first step includes a step of obtaining a parison shape and a parison thickness distribution by giving parameters of a shape of a gap between an extrusion die and a core and a resin physical property;
The second step includes a step of performing deformation prediction by mold clamping and blowing with respect to the parison to obtain a thickness distribution in a state along the cavity of the mold,
The third step includes a step of performing shrinkage prediction for the obtained thickness distribution,
The fourth step includes a step of obtaining a mold shape so as to obtain a molded product having a desired shape from the result of the shrinkage prediction.
In the mold design method,
The step of obtaining the parison shape and the parison thickness distribution comprises:
Calculating the flow of the molten resin passing through the gap between the extrusion die and the core with a developmental flow equation of a nonlinear viscoelastic fluid;
A step of calculating the elastic behavior of the molten resin after passing through the gap by applying the strain of the molten resin when passing through the gap,
A mold design method characterized by comprising : A first step of simulating the shape change of the molten resin when the molten resin is extruded through a gap between the extrusion die and the core to form a parison;
A second step of simulating the mold change of the extruded parison and the shape change of the molten resin due to the injection of compressed air into the parison;
A third step of simulating thermal deformation caused by cooling of the molded product after the molded product obtained by solidifying the molten resin in the mold is removed from the mold at a high temperature;
A fourth step of determining the shapes of the extrusion die and the core so as to obtain a molded product having a desired shape from the simulation results of the first to third steps;
Including
The first step includes a step of obtaining a parison shape and a parison thickness distribution by giving parameters of a shape of a gap between an extrusion die and a core and a resin physical property;
The second step includes a step of performing deformation prediction by mold clamping and blowing with respect to the parison to obtain a thickness distribution in a state along the cavity of the mold,
In the fourth step, the thickness distribution in a state along the cavity of the mold is evaluated, and the shape of the extrusion die and the core that provides the optimum thickness distribution is obtained based on the evaluation. Including steps
In the extrusion die and core design method,
The step of obtaining the parison shape and the parison thickness distribution comprises:
Calculating the flow of the molten resin passing through the gap between the extrusion die and the core with a developmental flow equation of a nonlinear viscoelastic fluid;
A step of calculating the elastic behavior of the molten resin after passing through the gap by applying the strain of the molten resin when passing through the gap,
including
Extrusion die and core design method characterized by the above. Extruding the molten resin through the gap between the extrusion die and the core A first means for simulating the shape change of the molten resin when forming
A second means for simulating the mold change of the extruded parison and the shape change of the molten resin due to the injection of compressed air into the parison;
A third means for simulating thermal deformation caused by cooling of the molded article after the molded article obtained by solidifying the molten resin in the mold is taken out of the mold in a high temperature state;
A fourth means for determining the shapes of the mold, the extrusion die and the core so as to obtain a molded product having a desired shape from the simulation results of the first to third means;
With
The first means includes means for determining the parison shape and the parison thickness distribution by giving parameters of the shape of the gap between the extrusion die and the core and the resin physical properties;
The second means includes means for predicting deformation by mold clamping and blowing with respect to the parison to obtain a thickness distribution in a state along the cavity of the mold,
The third means includes means for performing shrinkage prediction on the obtained thickness distribution,
The fourth means includes means for obtaining a mold shape so as to obtain a molded product having a desired shape from the result of the shrinkage prediction.
In the mold design method,
Means for obtaining the parison shape and the parison thickness distribution are:
Means for calculating the flow of the molten resin passing through the gap between the extrusion die and the core with a developmental flow equation of a nonlinear viscoelastic fluid;
Means for applying a strain of the molten resin when passing through the gap and calculating the behavior of the molten resin after passing through the gap using an elastic extension equation.
including
A mold design apparatus characterized by that. A first means for simulating the shape change of the molten resin when the molten resin is extruded through the gap between the extrusion die and the core to form a parison;
A second means for simulating the mold change of the extruded parison and the shape change of the molten resin due to the injection of compressed air into the parison;
A third means for simulating thermal deformation caused by cooling of the molded article after the molded article obtained by solidifying the molten resin in the mold is taken out of the mold in a high temperature state;
A fourth means for determining the shape of the extrusion die and the core so as to obtain a molded article having a desired shape from the simulation result of the first to third means ,
The first means includes means for determining the parison shape and the parison thickness distribution by giving parameters of the shape of the gap between the extrusion die and the core and the resin physical properties;
The second means includes means for predicting deformation by mold clamping and blowing with respect to the parison to obtain a thickness distribution in a state along the cavity of the mold,
The fourth means evaluates the thickness distribution in a shape along the cavity of the mold, and obtains the shape of the extrusion die and the core so as to obtain the optimum thickness distribution based on the evaluation. Including means
In extrusion die and core design equipment,
Means for obtaining the parison shape and the parison thickness distribution are:
Means for calculating the flow of the molten resin passing through the gap between the extrusion die and the core with a developmental flow equation of a nonlinear viscoelastic fluid;
Means for applying a strain of the molten resin when passing through the gap and calculating the behavior of the molten resin after passing through the gap using an elastic extension equation.
including
Extrusion die and core design apparatus characterized by the above.

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