JP3889587B2 - Method for predicting shrinkage of resin molded products - Google Patents

Description

【００１９】
を有することを特徴とする樹脂成形品の収縮率予測方法。
【００２０】
（２）前記（１）式の代わりに、下記（４）式を使用することを特徴とする。
【００２１】
Δ_ｉ＝ｍｃｏｓ^２（θ_ｉ−δ）＋ｔｓｉｎ^２（θ_ｉ−δ） …（４）
（３）前記（１）式の代わりに、下記（５）式を使用することを特徴とする。
【００２２】
Δ_ｉ＝ｍｃｏｓ^２θ_ｉ＋ｔｓｉｎ^２θ_ｉ …（５）
（４）前記板材の収縮率は、板材成形後、熱処理が加わる前に計測することを特徴とする。
【００２３】
（５）前記板材の収縮率は、板材成形後、予測したい製品に加えられる熱処理と同じ条件となる熱処理を加えた後に計測することを特徴とする。
【００２４】
【発明の効果】
上記のように構成された本発明は、請求項ごとに以下のような効果を奏する。
【００２６】
請求項１記載の本発明によれば、板材による収縮率の実測値に、流動解析の結果における流動ベクトルの方向を前記（１）式により加味して収縮率を予測することとしたので、樹脂成形品における射出成形時における樹脂の流れの方向による影響を加えた形での収縮率が予測できるようになるため、高精度で収縮率を予測することができる。また、金型のゲート位置の違いや数によって収縮率が異なるような場合でも、流動解析の結果を加味しているので、精度のよい予測を行うことができる。
【００２７】
請求項２記載の本発明によれば、前記（１）式に代えて、この（１）式よりも簡略化した（４）式を用いることとしたので、収縮率の予測にかかる計算時間を短縮することができる。
【００２８】
請求項３記載の本発明によれば、前記（１）式に代えて、前記（４）式よりもさらに簡略化した（５）式を用いることとしたので、収縮率の予測にかかる計算時間をさらに短縮することができる。
【００２９】
請求項４記載の本発明によれば、板材の収縮率を板材成形後、熱処理が加わる前に計測することとしたので、樹脂成形品の成形直後における収縮率を高精度で予測することができる。
【００３０】
請求項５記載の本発明によれば、板材の収縮率を、板材成形後、予測したい製品に加えられる熱処理と同じ条件となる熱処理を加えた後に計測することとしたので、樹脂成形品に熱処理が加えられた後における収縮率を高精度で予測することができる。
【００３１】
【発明の実施の形態】
以下添付した図面を参照して本発明の一実施の形態を説明する。
【００３２】
図１は、本発明を適用した樹脂成形品の収縮率予測方法の手順を示すフローチャートである。
【００３３】
図１を参照して、樹脂成形品の収縮率予測方法の手順に付いての概略を説明する。
【００３４】
まず、板材を実際に射出成形し、その流動方向に平行な方向の収縮率ｍ、および垂直な方向の収縮率ｔを求める（Ｓ１）。このとき、射出成形する板材は、具体的には均一な厚さの平板が好ましく、さらには実際に収縮率を予測したい樹脂成形品と同じ厚さの平板が好ましい。また、収縮率を予測したい樹脂成形品の厚さが均一ではない場合には、平板ではなく、実際に収縮率を予測したい樹脂成形品の厚さに合わせて部分的に厚さが異なるような板材を成形してもよい。
【００３５】
続いて、収縮率を予測したい樹脂成形品のシミュレーションによる流動解析を行い、流動方向のベクトル場を求める（Ｓ２）。
【００３６】
続いて、シミュレーションによって求めた摺動解析の結果であるベクトル場において、収縮率を予測したい部分および方向を定義する（Ｓ３）。
【００３７】
続いて、ベクトル場における個々の流動ベクトルの方向と定義した予測したい方向とが交わる角度が同じ流動ベクトル同士を一つに区分し、各区分をゾーンｉとする（Ｓ４）。
【００３８】
続いて各ゾーン内のベクトルの向きと定義した予測したい方向との角度（θ_i）をゾーンごとに求める（Ｓ５）。
【００３９】
続いて、各ゾーンごとの収縮率Δ_iを算出する（Ｓ６）。
【００４０】
そして、各ゾーンの収縮率Δ_i、および各ゾーンにおける部分への予測したい投影幅（Ｗ_i）を用いて、予測したい部分における収縮率Δを算出する（Ｓ７）。
【００４１】
以下、各段階ごとに詳細に説明する。
【００４２】
（Ａ）平板による収縮率の計測
平板は、たとえば全面フィルムゲートを有した平板の射出成形用金型を用いて、製品に使用する樹脂材料を射出成形し、流動方向と平行な方向の収縮率ｍ、およびそれと垂直な方向の収縮率ｔを計測する。
【００４３】
このとき、収縮率は、平板の成形直後（塗装前）と、塗装および乾燥などの熱工程後の収縮率を計測することが好ましい。これにより、製品の塗装前と、塗装後における収縮率を予測することができる。
【００４４】
なお、この収縮率の計測時において、平板金型の厚みは、収縮率を予測したい実際の製品の平均肉厚に対して±２０％程度であることが好ましい。これは、この範囲を逸脱した場合、平板成形品と実際の成形品との高次構造が異なるために、収縮率の予測誤差が大きくなるからである。
【００４５】
また、平板成形品の幅と長さの比率は（幅＝ｔ方向）：（長さ＝ｍ方向）＝１：２以上１：５以下が好適である。この比率が１：２よりも小さいと、流動が安定しないために予測誤差が大きくなるという問題が生じ、一方、１：５よりも大きければ、平板成形品と実際の成形品との高次構造が異なるために収縮率の予測誤差が大きくなるという問題が生じるためである。
【００４６】
さらに、平板を成形するときの温度、射出率は、収縮率を予測したい実際の製品を成形する時の条件を大きく逸脱しないようにする。大きく逸脱した条件で収縮率ｍ、ｔを求めた場合は、平板成形品と実際の成形品との高次構造が異なるために収縮率の予測誤差が大きくなるからである。
【００４７】
（Ｂ）シミュレーションによる流動解析
シミュレーションによる流動解析は、ＣＡＥ（ｃｏｍｐｕｔｅｒ ａｉｄｅｄｅｎｇｉｎｅｅｒｉｎｇ）流動解析を用いて、樹脂の流動場（ベクトル場）を求めるものである。これには、たとえば市販されているモールドフロー社のＭｏｌｄ Ｆｌｏｗ、プラメディア社のＰＬＡＮＥＴＳなどのシミュレーションソフトウエアを用いることができる。
【００４８】
これらのソフトウェアを用いる場合、製品モデルに割り当てるメッシュサイズは、用いるソフトウェアの仕様、あるいは用いるコンピュータの能力、計算時間によってある程度の制限はあるものの、予測したい部分のサイズに対して５％以下の大きさが好ましい。さらには２％以下であることがより好ましい。これは、５％を超えるほど大きなメッシュとした場合、精度の良い推定が困難になるからである。なお、下限については、前記のとおり、用いるソフトウェアの仕様、あるいは用いるコンピュータの能力、計算時間によって決めるとよい。
【００４９】
（Ｃ）収縮率を予測したい部分と方向の定義
収縮率を予測したい部分とその方向Ｘは、予測したい製品における任意の２点を選択することにより定義する。たとえば、製品における寸法精度が重要となる２点間、製品の取り付け穴位置の２点間など、管理を必要とする部分に対してＸを定義する。
【００５０】
（Ｄ）流動ベクトルのゾーン区分
流動ベクトルのゾーン区分は、先に定義した予測したい部分において、流動解析の結果である樹脂の流動場から規定されるベクトル（流動ベクトル）の向きが、それぞれ異なる部分を一つのゾーンとして区分するものである。
【００５１】
このゾーンの区分は、基本的には、ＣＡＥのモデルで使用したメッシュに対して、予測したい部分内に存在するすべての流動ベクトルの向きを抽出し、それぞれを比較して、同じ向きのベクトル同士が含まれた範囲を一つのゾーンとする。
【００５２】
なお、より簡便には、前記の予測したい向きを定義した２点間を結ぶ線上にある複数個のメッシュをあらかじめ決めた個数ごとに一つのゾーンとして定義してもよい。これにより、一つ一つのベクトル同士を比較する必要がなくなるので、処理時間を短縮することができる。ただし、この場合は、メッシュごとのベクトル方向のばらつきが、±５°以内であることが必要である。この範囲を逸脱して、一つのゾーンとしてとめる複数個のメッシュにおけるそれぞれのベクトルの向きが大きく異なる場合、予測誤差が大きくなり実用に供することが困難となる。
【００５３】
（Ｅ）収縮率を予測したい方向と各ゾーンにおけるベクトルの角度θ_iの算出収縮率を予測したい方向と各ゾーンにおけるベクトルの角度θ_iは、予測したい方向Ｘの両端を結ぶ線と、各ゾーンのベクトルとの角度である。
【００５４】
なお、ベクトルの方向は、２点間を結ぶ線の上側を＋の方向と定義する。なお、実際の予測においては、角度に関し偶関数となっているため、符号は関係なくなる。
【００５５】
（Ｆ）ゾーンごとの収縮率の算出
ゾーンごとの収縮率Δ_iは、平板から計測された収縮率と流動解析の結果における流動方向から、流動方向ベクトルのうち、予測したい収縮率方向成分の収縮率を求めるものである。
【００５６】
これには、各ゾーンごとに、下記（１）式により算出する。
【００５７】
Δ_i＝１−［（１−ｍ）²ｃｏｓ²（θ_i−δ）＋（１−ｔ）²ｓｉｎ²（θ_i−δ）］^1/2 …（１）
ただし、式中、δは（２）式で定義される。
【００５８】
δ＝ａｒｃｔａｎ［ｔ／（１−ｍ）］ …（２）
なお、このゾーンごとの収縮率Δ_iを求めるための算出式は、下記（４）式、または下記（５）式により求めてもよい。
【００５９】
Δ_i＝ｍｃｏｓ²（θ_i−δ）＋ｔｓｉｎ²（θ_i−δ） …（４）
Δ_i＝ｍｃｏｓ²θ_i＋ｔｓｉｎ²θ_i …（５）
この（４）式または（５）式を用いることで、（１）式を用いた場合より、計算時間を短縮することができる。
（Ｇ）収縮率を予測したい部分の収縮率の算出
収縮率を予測したい部分の最終的な収縮率Δの予測量は、下記（３）式に示すように、前記（１）式（または（４）式、あるいは（５）式）によって求めた各ゾーンの収縮率Δ_iに、収縮率を予測したい部分における投影幅Ｗ_iをかけたものの総和をとることによって求める。
【００６０】
【数３】

【００６１】
ここで、投影幅Ｗ_iは、各ゾーンごとにどの程度予測したい部分に対する影響があるかを重み付けするための値である。
【００６２】
この投影幅Ｗ_iは、小さいほど収縮率の予測量の精度を向上させることができるが、投影幅Ｗ_iを細かく設定すると算出時間がかかる。投影幅Ｗ_iと収縮率の予測量との関係は、予測するワークによって異なり、たとえば、あるバンパーの場合、投影幅Ｗ_iが、１０％変化すると予測量の精度が０．００２％変動するという関係が成り立つことがわかっている。また、この関係は、予測するワーク形状、あるいは成形型のゲート数によっても異なり、たとえばセンター１点のゲートでバンパーを成形した場合には、ゲート周囲を除いたほとんどの個所でベクトルがバンパーの長手方向と平行になるため、投影幅Ｗ_iを数１００ｍｍと大きく設定しても収縮率の予測量の精度はほとんど影響を受けない。
【００６３】
したがって、投影幅Ｗ_iは、収縮率を予測するワーク形状や、ゲート位置、ゲート数、および樹脂の流れの方向などにより適宜決定する。
【００６４】
以上のように、本実施の形態によれば、収縮率を実際に射出成形された平板から得られる収縮率の値に、シミュレーションによる流動解析の結果から得られた射出成形によって樹脂に加えられる方向性（配向）を加味することで、精度のよい収縮率の予測を行うことが可能となる。
【００６５】
【実施例】
以下、さらに実施例を用いて、本発明を説明する。
（実施例１）
平板による収縮率の計測
ポリプロピレン５８重量部、エチレン−プロピレン−ジエンゴム（ＥＰＤＭ）２６重量部、タルク１６重量部、抗酸化剤０．２重量部、および耐候剤０．３重量部から構成される樹脂材料を製造し、この樹脂材料を幅１４０ｍｍ、長さ３００ｍｍ、厚み３．５ｍｍの全面フィルムゲートを有した金型を用いて平板を成形した。
【００６６】
この時の樹脂温度は２１０℃、充填時間は２秒、金型温度は３０℃であった。平板成形後、温度２３℃、湿度５０％の恒温室内で４８時間放置した後、１４０℃で３０分間熱処理を施した。
【００６７】
この試験片をさらに温度２３℃、湿度５０％の恒温室内で４８時間放置した後、流動方向（すなわち長さ方向）の収縮率ｍ、およびそれと垂直方向（すなわち幅方向）の収縮率ｔを測定した。
【００６８】
なお、上記各熱処理は、実際の製品に行われる射出成形後の塗装および乾燥工程に相当するものである。
【００６９】
収縮率は、一般に、収縮率をａ、キャビティ寸法をＬ０、形成品の寸法をＬとすると、下記（６）式で定義される。
【００７０】
ａ＝（Ｌ０−Ｌ）／Ｌ０ …（６）
測定の結果、流動方向の収縮率ｍ＝７．４／１０００、流動方向に垂直な方向の収縮率ｔ＝８．７／１０００であった。
【００７１】
次に、自動車車体の樹脂成形部品を試料として予測を行った結果を示す。
【００７２】
図２に示す部品Ａ（バンパー）を、樹脂温度＝２１０℃、充填時間＝５秒、金型温度＝３０℃、保圧＝１０秒、射出圧＝１１０ｋｇ／ｍ²、クッション＝１０ｍｍの条件で射出成形するものとし、ＰＬＡＮＥＳを用いて流動解析を行った。
【００７３】
図３に、流動解析から得られた樹脂の流動場（ベクトル場）を示す。また、図３には収縮率を予測したい部分と方向Ｘの定義、ならびに予測値の結果もあわせて示す。
【００７４】
ベクトル場の結果から行ったゾーン区分は、ここでは、一つのゾーンはＸの線上の各メッシュを一つのゾーンに区分し、ゾーン１、ゾーン２、…ゾーンｉである。
【００７５】
ゾーンごとの収縮率Δ_iを前述した（１）式、（４）式、および（５）式によってそれぞれ求めた。なお、参考のために、（５）式による算出結果のみ示すと、Δ１＝８．６４／１０００、Δ２＝８．５９／１０００、…Δ_i＝７．５５／１０００となった。
【００７６】
そして、最終的な収縮率の予測値は、（１）式を用いた場合、収縮率の予測値＝８．５７／１０００、（４）式を用いた場合、収縮率の予測値＝８．５７／１０００、（５）式を用いた場合、収縮率の予測値＝８．５４／１０００となった。
【００７７】
一方、実際に部品Ａを射出成形し、現物による収縮率を測定したところ、８．８／１０００であった。
【００７８】
したがって、本発明の方法による収縮率の予測値は、実際の塗装された成形品の収縮率によく一致していることがわかる。
【００７９】
また、従来のように、単に平板の流動方向の収縮率ｍ＝７．４／１０００を用いて、これを実際の塗装された成形品の収縮率とした場合、実際との乖離が大きく、本発明の方法の方がより精度が高いことがわかる。
【００８０】
（実施例２）
以下、さらに他の形状の部品Ｂについて、縮小率の予測を行った。
【００８１】
図４は、前記実施例１と同様の射出成形条件により部品Ｂによる流動解析の結果を示す図面である。また平板の収縮率も実施例１と同じものを用いた。
【００８２】
この結果、最終的な収縮率の予測値は、各ゾーンの収縮率Δ_iを（１）式を用いた場合、収縮率の予測値＝７．９６／１０００、（４）式を用いた場合、収縮率の予測値＝７．９６／１０００、（５）式を用いた場合、収縮率の予測値＝７．９４／１０００となった。
【００８３】
一方、実際に部品Ｂを射出成形し、現物による収縮率を測定したところ、８．０／１０００であった。
【００８４】
したがって、他の形状においても本発明の方法による収縮率の予測値は、実際の塗装された成形品の収縮率によく一致していることがわかる。
【００８５】
また、前記実施例１と実施例２の結果から、ゾーンごとの収縮率を求める式間での差異は少なく、（１）式に代えて、（４）式または（５）式のような簡便な式を用いても、精度の高い予測が行えることがわかる。
（実施例３、４）
以下、さらに他の形状の部品ＣおよびＤについて、縮小率の予測を行った。
【００８６】
図５は、部品Ｃによる流動解析の結果を示す図面であり、図６は、部品Ｄによる流動解析の結果を示す図面である。流動解析の射出成形条件は、前記実施例１と同じである。
【００８７】
平板の収縮率は、前記実施例１と同じものを用い、各ゾーンの収縮率Δ_iは、（５）式を用いた。
【００８８】
表１に、各部品ごとの実施例１および２における（５）式を用いた場合の結果と、実施例３、４の予測の結果、各部品の現物による収縮率、および従来法による予測値を示す。
【００８９】
【表１】

【００９０】
表１に示すように、本発明を適用した実施例では、各部品における予測値と現物の実測値との誤差の平均値が２％であり、いずれの部品においても、予測値は、現物による収縮率とよく一致しており、一方、従来法では、誤差の平均が１２％であり、この結果から、本発明による予測方法による精度が高いことがわかる。
【００９１】
（実施例５）
平板の成形後、成形した平板試験片を１４０℃で熱処理する前の収縮率を測定した。収縮率はｍ＝５．５／１０００、ｔ＝６．１／１０００であった。
【００９２】
実施例１と同様に部品Ａの射出成形の流動解析を行い予測を行った。なお、各ゾーンの収縮率は（５）式を用いた。
【００９３】
その結果、予測値＝６．１／１０００に対し、塗装前の状態における現物の実測値＝６．１／１０００となり、良い一致を得た。
【００９４】
また、実測値は、先の平板における収縮率ｍ＝５．５／１０００の値に対して食い違いがみられるため、従来のように単に平板の収縮率を用いて予測した場合には予測精度が悪い。
【００９５】
したがって、本発明の方法によれば、塗装前の状態においても、従来より高い精度で収縮率を予測できることがわかる。
【００９６】
このように、本発明を適用することで、従来の方法に比ベて、収縮率の予測精度が格段に向上する。特に、長尺の樹脂形成品、たとえばバンパーフェイシャ、インパネ、サイドクラッディングなどの射出成形で得られる部品における金型設計に関し、製品精度を向上させるために使用すると効果的である。
【００９７】
また、同じ材料、同じ成形条件、同じ塗装条件であっても、金型のゲート位置の違いや数によって収縮率が異なるような場合でも、流動解析の結果を加味しているので、精度のよい予測を行うことができる。
【００９８】
以上、本発明の実施形態および実施例を説明したが、本発明はこれら実施の形態や実施例に限定されるものではなく、本発明の技術思想の範囲において当業者が様々な改変を加えることができる。
【図面の簡単な説明】
【図１】 本発明による樹脂成形品の収縮率予測方法の手順を示すフローチャートである。
【図２】 実施例１において収縮率予測を行った部品Ａを示す斜視図である。
【図３】 実施例１において部品Ａの流動解析結果を示す図面である。
【図４】 実施例２において収縮率予測を行った部品Ｂの流動解析結果を示す図面である。
【図５】 実施例３において収縮率予測を行った部品Ｃの流動解析結果を示す図面である。
【図６】 実施例４において収縮率予測を行った部品Ｄの流動解析結果を示す図面である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a shrinkage rate prediction method for resin molded products.
[0002]
[Prior art]
In the injection molding method using a resin material, since the resin material shrinks after molding, the mold for injection molding must be made in consideration of the shrinkage.
[0003]
Here, the shrinkage at the time of resin molding is generally a phenomenon in which the volume shrinks when the molten resin filled in the cavity of the mold is cooled and solidified. This degree of contraction is referred to herein as the contraction rate.
[0004]
Conventionally, the following method is used as a shrinkage rate prediction method for allowing shrinkage during injection molding using such a resin material.
[0005]
(1) A flat plate is actually injection-molded with a resin material to be injection-molded, and using this injection-molded flat plate, the shrinkage ratio m and t in the flow direction of the resin or the direction perpendicular thereto are obtained, and m or m A method of predicting the shrinkage rate when molding is actually performed with an average value of t.
[0006]
(2) A method for calculating a shrinkage rate by simulation by using a CAE method such as a mold flow.
[0007]
As specific examples of these conventional shrinkage rate prediction methods, for example, Japanese Patent Application Laid-Open No. 2000-313035 discloses a series of methods in which a molten thermoplastic resin is injected into a mold and cured, and the molded product is brought to room temperature. An injection molding process simulation method and apparatus for calculating a dimensional change and a shape change occurring in a molded product in the process are disclosed, and Japanese Patent Application Laid-Open No. 9-262887 discloses temperature, pressure, and crystallinity of the molding process. A method and apparatus for simulating the shrinkage process in a crystalline resin molded product by predicting the shrinkage rate using the data and the PVT characteristics of the resin at an arbitrary degree of crystallinity are disclosed in Japanese Patent Application Laid-Open No. 11-224275. Is a molding that can keep the dimension after deformation within the allowable range, even if deformation due to external factors occurs as well as internal factors of the molded product JP-A-8-230008 predicts the behavior of the plastic resin in the mold during filling, holding, and cooling processes based on the basic formula formulated by the finite element method. In addition, a method for predicting warpage deformation of an injection molded product for predicting warpage deformation of a plastic molded product is disclosed. Japanese Patent Application Laid-Open No. 1-146718 discloses a mold cavity using a pressure-volume-temperature relationship diagram. A control device that predicts molding shrinkage of injection compression molding by feedback control of internal pressure, cavity material temperature, and mold volume is disclosed.
[0008]
[Problems to be solved by the invention]
In such a conventional shrinkage rate prediction method, first, the method (1) is simple, but the shrinkage rate of the product to be actually molded is not always the same as m or the average value of m and t. In particular, in the case of a product obtained by using a long part or a mold having a large number of gates, there is a problem that prediction accuracy is poor and it cannot be put into practical use. Specifically, it often occurs an error of 1/100 0 2/100 0 extent.
[0009]
On the other hand, in the method (2), for example, in the case of simulation by the finite element method, a model shape of a resin molded product is created so that calculation can be performed, the model shape is divided into meshes, and each mesh is molded as a boundary condition. Given the conditions and physical property data of the resin, calculate the equation of motion, the energy conservation equation and the continuity equation for each mesh in the process of the resin filling the mold cavity using the formula formulated in the finite element method is doing.
[0010]
For this reason, although the flow of the resin at the time of injection molding can be expressed, the effect by the orientation of the resin that greatly affects the shrinkage rate cannot be incorporated. Therefore, when used to predict shrinkage, 1/100 0 extent, or more are at present occurs an error further improvement is desired.
[0011]
Furthermore, the molded product often becomes a product through heat treatment such as painting or drying, and these effects must be incorporated into the mold.
[0012]
In particular, in the method (2), it is difficult to incorporate such fluctuations in shrinkage rate due to subsequent processes because a large amount of data is required.
[0013]
The object of the present invention is to solve these problems, and provides a method for predicting the shrinkage ratio of a resin molded product with relatively high accuracy and accuracy.
[0014]
[Means for Solving the Problems]
The object of the present invention is achieved by the following configurations.
[0016]
( 1 ) Actually injection-molding the plate material, measuring the shrinkage rate m in the direction parallel to the flow direction, and the shrinkage rate t in the direction perpendicular to it, and performing flow analysis by simulation of the resin molded product to be predicted, A zone i is defined by dividing a step of obtaining a vector field in the flow direction, a step of defining a portion and direction in which the shrinkage rate is to be predicted in the vector field, and a portion in which the direction of each flow vector is different in the vector field. A step of forming, a step of obtaining an angle (θ _i ) between the direction of the vector in each zone i and the direction to be predicted for each zone, and calculating a contraction rate Δ _i for each zone according to the following equation (1): Stages,
Δ _i = 1 − [(1−m) ² cos ² (θ _i −δ) + (1−t) ² sin ² (θ _i −δ)] ^1/2 (1)
(In the formula, δ is defined by the formula (2).
[0017]
δ = arctan [t / (1-m)] (2))
Using the shrinkage rate Δ _{i of} each zone obtained by the equation (1) and the projection width (W _i ) of each zone onto the portion to be predicted, the shrinkage rate Δ at the portion to be predicted is expressed by the following (3) Calculating with a formula;
[0018]
[Expression 2]

[0019]
A shrinkage rate prediction method for a resin molded product, comprising:
[0020]
( 2 ) The following formula (4) is used instead of the formula (1).
[0021]
Δ _i = m cos ² (θ _i −δ) + tsin ² (θ _i −δ) (4)
( 3 ) The following equation (5) is used instead of the equation (1).
[0022]
Δ _i = m cos ² θ _i + tsin ² θ _i (5)
( 4 ) The contraction rate of the plate material is measured after the plate material is formed and before heat treatment is applied.
[0023]
( 5 ) The shrinkage ratio of the plate material is measured after the plate material is formed and subjected to a heat treatment under the same conditions as the heat treatment applied to the product to be predicted.
[0024]
【The invention's effect】
The present invention configured as described above has the following effects for each claim.
[0026]
According to the first aspect of the present invention, since the shrinkage rate is predicted by adding the direction of the flow vector in the flow analysis result to the measured value of the plate material according to the equation (1), the shrinkage rate is predicted. Since it becomes possible to predict the shrinkage rate in a form to which the influence of the direction of resin flow at the time of injection molding in a molded product is added, the shrinkage rate can be predicted with high accuracy. Further, even when the shrinkage rate varies depending on the difference in the gate position and the number of molds, the results of the flow analysis are taken into account, so that accurate prediction can be performed.
[0027]
According to the second aspect of the present invention, instead of the equation (1), the equation (4) simplified from the equation (1) is used. It can be shortened.
[0028]
According to the third aspect of the present invention, instead of the equation (1), the equation (5), which is further simplified than the equation (4), is used. Can be further shortened.
[0029]
According to the fourth aspect of the present invention, since the shrinkage rate of the plate material is measured before the heat treatment is applied after the plate material is molded, the shrinkage rate immediately after the molding of the resin molded product can be predicted with high accuracy. .
[0030]
According to the fifth aspect of the present invention, since the shrinkage rate of the plate material is measured after the plate material is molded and then subjected to the heat treatment which is the same condition as the heat treatment applied to the product to be predicted, the resin molded product is subjected to the heat treatment. Can be predicted with high accuracy.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0032]
FIG. 1 is a flowchart showing a procedure of a shrinkage rate prediction method for a resin molded product to which the present invention is applied.
[0033]
With reference to FIG. 1, the outline about the procedure of the shrinkage | contraction rate prediction method of a resin molded product is demonstrated.
[0034]
First, a plate material is actually injection molded, and a shrinkage rate m in a direction parallel to the flow direction and a shrinkage rate t in a direction perpendicular to the flow direction are obtained (S1). At this time, the plate material to be injection-molded is specifically preferably a flat plate having a uniform thickness, and more preferably a flat plate having the same thickness as that of a resin molded product for which a shrinkage rate is actually predicted. In addition, if the thickness of the resin molded product for which the shrinkage rate is to be predicted is not uniform, the thickness may be partially different from the flat plate, depending on the thickness of the resin molded product for which the shrinkage rate is actually predicted. A plate material may be formed.
[0035]
Subsequently, flow analysis is performed by simulation of a resin molded product whose shrinkage rate is to be predicted, and a vector field in the flow direction is obtained (S2).
[0036]
Subsequently, in the vector field that is the result of the sliding analysis obtained by the simulation, a portion and direction in which the shrinkage rate is to be predicted are defined (S3).
[0037]
Subsequently, the flow vectors having the same angle between the direction of the individual flow vectors in the vector field and the defined direction to be predicted are divided into one, and each division is set as zone i (S4).
[0038]
Subsequently, an angle (θ _i ) between the direction of the vector in each zone and the defined direction to be predicted is obtained for each zone (S5).
[0039]
Subsequently, the contraction rate Δ _i for each zone is calculated (S6).
[0040]
Then, using the shrinkage rate Δ _i of each zone and the projection width (W _i ) to be predicted to the portion in each zone, the shrinkage rate Δ in the portion to be predicted is calculated (S7).
[0041]
Hereinafter, each step will be described in detail.
[0042]
(A) Measurement of contraction rate by flat plate The flat plate is formed by injection molding a resin material used for a product using, for example, a flat plate injection mold having a film gate, and contraction rate in a direction parallel to the flow direction. m and the contraction rate t in the direction perpendicular thereto are measured.
[0043]
At this time, the shrinkage rate is preferably measured immediately after the flat plate is formed (before painting) and after the thermal process such as painting and drying. As a result, the shrinkage rate before and after the product can be predicted.
[0044]
When measuring the shrinkage rate, the thickness of the flat plate mold is preferably about ± 20% with respect to the average thickness of the actual product for which the shrinkage rate is to be predicted. This is because when the deviation is outside this range, the flat plate molded product and the actual molded product have different higher-order structures, and thus the shrinkage rate prediction error increases.
[0045]
The ratio of the width and the length of the flat molded product is preferably (width = t direction) :( length = m direction) = 1: 2 or more and 1: 5 or less. If this ratio is smaller than 1: 2, there is a problem that the prediction error increases because the flow is not stable. On the other hand, if it is larger than 1: 5, the higher order structure between the flat plate molded product and the actual molded product. This is because there is a problem that the prediction error of the shrinkage rate increases because of the difference.
[0046]
Further, the temperature and injection rate when molding the flat plate should not greatly deviate from the conditions when molding an actual product for which the shrinkage rate is to be predicted. This is because, when the shrinkage ratios m and t are obtained under conditions that deviate greatly, the prediction error of the shrinkage ratio increases because the higher-order structure differs between the flat plate molded product and the actual molded product.
[0047]
(B) Flow analysis by simulation The flow analysis by simulation is to obtain a resin flow field (vector field) using CAE (computer aided engineering) flow analysis. For example, commercially available simulation software such as Mold Flow (Mold Flow) or Plamedia (PLANETS) can be used.
[0048]
When using these software, the mesh size assigned to the product model is less than 5% of the size of the part to be predicted, although there are some restrictions depending on the specifications of the software used, the computer capacity used, and the calculation time. Is preferred. Further, it is more preferably 2% or less. This is because accurate estimation becomes difficult when the mesh is larger than 5%. As described above, the lower limit may be determined by the specifications of the software to be used, the ability of the computer to be used, and the calculation time.
[0049]
(C) Definition of the portion and direction in which the shrinkage rate is to be predicted The portion in which the shrinkage rate is to be predicted and the direction X are defined by selecting any two points in the product to be predicted. For example, X is defined for a portion that needs to be managed, such as between two points where dimensional accuracy in a product is important, or between two points in a product mounting hole position.
[0050]
(D) Flow vector zone classification The flow vector zone classification is a portion where the direction of the vector (flow vector) defined from the flow field of the resin, which is the result of the flow analysis, is different in the previously defined portion to be predicted. Are classified as one zone.
[0051]
Basically, the zones are divided by extracting the directions of all the flow vectors existing in the part to be predicted from the mesh used in the CAE model, and comparing the directions of the vectors. A range including is defined as one zone.
[0052]
More simply, a plurality of meshes on a line connecting two points defining the direction to be predicted may be defined as one zone for each predetermined number. Thereby, since it becomes unnecessary to compare each vector, processing time can be shortened. However, in this case, the variation in the vector direction for each mesh needs to be within ± 5 °. If the direction of each vector in a plurality of meshes that are regarded as one zone deviates greatly from this range, the prediction error increases and it is difficult to put it to practical use.
[0053]
(E) Calculation of vector angle θ _i in the direction in which the shrinkage rate is to be predicted and the vector in each zone The direction θ in which the shrinkage rate is to be predicted and the vector angle θ _i in each zone is the line connecting both ends of the direction X to be predicted and each zone The angle with the vector.
[0054]
The direction of the vector is defined as the + direction above the line connecting the two points. In the actual prediction, since the angle is an even function, the sign is irrelevant.
[0055]
(F) shrinkage delta _i for each calculation zone shrinkage for each zone, the flow direction in the result of flow analysis and the measured shrinkage from the plates, among the flow direction vector, shrinkage direction component to be predicted shrinkage The rate is to be calculated.
[0056]
This is calculated for each zone by the following equation (1).
[0057]
Δ _i = 1 − [(1−m) ² cos ² (θ _i −δ) + (1−t) ² sin ² (θ _i −δ)] ^1/2 (1)
However, in the formula, δ is defined by the formula (2).
[0058]
δ = arctan [t / (1-m)] (2)
The calculation formula for obtaining the shrinkage rate Δ _i for each zone may be obtained by the following formula (4) or the following formula (5).
[0059]
Δ _i = m cos ² (θ _i −δ) + tsin ² (θ _i −δ) (4)
Δ _i = m cos ² θ _i + tsin ² θ _i (5)
By using the formula (4) or the formula (5), the calculation time can be shortened compared to the case of using the formula (1).
(G) Calculation of the shrinkage rate of the portion for which the shrinkage rate is to be predicted The predicted amount of the final shrinkage rate Δ for the portion for which the shrinkage rate is to be predicted is expressed by the above equation (1) (or ( 4) or (5)) is obtained by multiplying the contraction rate Δ _i of each zone obtained by multiplying the projection width W _i at the portion where the contraction rate is to be predicted by the sum.
[0060]
[Equation 3]

[0061]
Here, the projection width W _i is a value for weighting how much influence is exerted on a portion to be predicted for each zone.
[0062]
As the projection width W _i is smaller, the accuracy of the predicted amount of shrinkage can be improved. However, if the projection width W _i is set finely, calculation time is required. The relationship between the projection width W _i and the predicted amount of shrinkage varies depending on the work to be predicted. For example, in the case of a certain bumper, the accuracy of the predicted amount varies by 0.002% when the projection width W _i changes by 10%. I know the relationship holds. This relationship also differs depending on the predicted workpiece shape or the number of gates in the mold. For example, when a bumper is formed with a single gate at the center, the vector is the length of the bumper at almost all points except the periphery of the gate. to become parallel to the direction, the prediction of accuracy even shrinkage is set larger as the number 100mm projection width W _i is hardly affected.
[0063]
Therefore, the projection width W _i is appropriately determined depending on the workpiece shape for predicting the shrinkage rate, the gate position, the number of gates, the direction of the resin flow, and the like.
[0064]
As described above, according to the present embodiment, the shrinkage rate is applied to the resin by the injection molding obtained from the flow analysis result by simulation to the shrinkage value obtained from the actually injection-molded flat plate. By adding the property (orientation), it is possible to predict the shrinkage rate with high accuracy.
[0065]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Example 1
Measurement of Shrinkage by Flat Plate Resin composed of 58 parts by weight of polypropylene, 26 parts by weight of ethylene-propylene-diene rubber (EPDM), 16 parts by weight of talc, 0.2 parts by weight of antioxidant, and 0.3 parts by weight of weathering agent A material was manufactured, and a flat plate was formed from the resin material using a mold having a full-face film gate having a width of 140 mm, a length of 300 mm, and a thickness of 3.5 mm.
[0066]
The resin temperature at this time was 210 ° C., the filling time was 2 seconds, and the mold temperature was 30 ° C. After forming the plate, the plate was left in a constant temperature room at a temperature of 23 ° C. and a humidity of 50% for 48 hours, followed by heat treatment at 140 ° C. for 30 minutes.
[0067]
The specimen was further left in a temperature-controlled room at a temperature of 23 ° C. and a humidity of 50% for 48 hours, and then the shrinkage rate m in the flow direction (ie, the length direction) and the shrinkage rate t in the direction perpendicular thereto (ie, the width direction) were measured. did.
[0068]
Each heat treatment corresponds to a coating and drying process after injection molding performed on an actual product.
[0069]
The shrinkage rate is generally defined by the following equation (6), where a is the shrinkage rate, L0 is the cavity size, and L is the size of the formed product.
[0070]
a = (L0−L) / L0 (6)
As a result of the measurement, the shrinkage rate m in the flow direction was m = 7.4 / 1000, and the shrinkage rate t in the direction perpendicular to the flow direction was t = 8.7 / 1000.
[0071]
Next, the results of prediction using a resin molded part of an automobile body as a sample are shown.
[0072]
The part A (bumper) shown in FIG. 2 is subjected to the following conditions: resin temperature = 210 ° C., filling time = 5 seconds, mold temperature = 30 ° C., holding pressure = 10 seconds, injection pressure = 110 kg / m ² , cushion = 10 mm. Assuming injection molding, flow analysis was performed using PLANES.
[0073]
FIG. 3 shows the flow field (vector field) of the resin obtained from the flow analysis. FIG. 3 also shows the definition of the portion where the shrinkage rate is to be predicted, the direction X, and the predicted value.
[0074]
Zone division performed from the result of the vector field is zone 1, zone 2,... Zone i, where each zone on the X line is divided into one zone.
[0075]
Shrinkage delta _i for each zone previously described (1), were respectively determined by equation (4), and (5). For reference, (5) shows only the calculation result by the equation, Δ1 = 8.64 / 1000, Δ2 = 8.59 / 1000, ... becomes Δ _i = 7.55 / 1000.
[0076]
When the equation (1) is used as the final predicted shrinkage rate, the shrinkage prediction value = 8.57 / 1000. When the equation (4) is used, the predicted shrinkage rate = 8. When using 57/1000 and the formula (5), the predicted value of the shrinkage rate was 8.54 / 1000.
[0077]
On the other hand, the part A was actually injection-molded, and the shrinkage due to the actual product was measured, and it was 8.8 / 1000.
[0078]
Therefore, it can be seen that the predicted shrinkage rate according to the method of the present invention is in good agreement with the actual shrinkage rate of the molded product.
[0079]
Further, as in the past, when simply using the shrinkage ratio m = 7.4 / 1000 in the flow direction of the flat plate as the shrinkage ratio of the actual coated molded product, there is a large difference from the actual, It can be seen that the method of the invention is more accurate.
[0080]
(Example 2)
Hereinafter, the reduction rate of the component B having another shape was predicted.
[0081]
FIG. 4 is a drawing showing the results of flow analysis using the component B under the same injection molding conditions as in the first embodiment. Further, the same contraction rate as that in Example 1 was used.
[0082]
As a result, the predicted value of the final shrinkage, when using a shrinkage delta _i of each zone (1), the predicted value of the shrinkage = 7.96 / 1000, the use of (4) The predicted value of the shrinkage rate was 7.96 / 1000, and when the formula (5) was used, the predicted value of the shrinkage rate was 7.94 / 1000.
[0083]
On the other hand, when the part B was actually injection-molded and the shrinkage rate due to the actual product was measured, it was 8.0 / 1000.
[0084]
Therefore, it can be seen that the shrinkage rate predicted by the method of the present invention also agrees with the actual shrinkage rate of the molded product even in other shapes.
[0085]
Further, from the results of Example 1 and Example 2, there is little difference between the equations for obtaining the contraction rate for each zone, and instead of Equation (1), it is simple as Equation (4) or Equation (5). It can be seen that accurate prediction can be performed even using simple equations.
(Examples 3 and 4)
Hereinafter, the reduction rate was predicted for the parts C and D having other shapes.
[0086]
FIG. 5 is a drawing showing the result of the flow analysis by the part C, and FIG. 6 is a drawing showing the result of the flow analysis by the part D. The injection molding conditions for the flow analysis are the same as in the first embodiment.
[0087]
Shrinkage of the flat plate is used the same as in Example 1, shrinkage delta _i of each zone were used (5).
[0088]
Table 1 shows the results of using the formula (5) in Examples 1 and 2 for each part, the results of predictions in Examples 3 and 4, the shrinkage rate of each part in-kind, and the predicted value according to the conventional method. Indicates.
[0089]
[Table 1]

[0090]
As shown in Table 1, in the example to which the present invention is applied, the average value of the error between the predicted value in each part and the actual measured value is 2%. In any part, the predicted value depends on the actual value. On the other hand, in the conventional method, the average error is 12%, and this result shows that the accuracy of the prediction method according to the present invention is high.
[0091]
(Example 5)
After the molding of the flat plate, the shrinkage before the heat treatment of the molded flat plate test piece at 140 ° C. was measured. The shrinkage ratios were m = 5.5 / 1000 and t = 6.1 / 1000.
[0092]
In the same manner as in Example 1, the flow analysis of the injection molding of the part A was performed for prediction. In addition, the shrinkage rate of each zone used the formula (5).
[0093]
As a result, the actually measured value of the actual product in the state before coating = 6.1000 was obtained against the predicted value = 6.1 / 1000, and good agreement was obtained.
[0094]
In addition, since the actual measurement value shows a discrepancy with respect to the value of the shrinkage ratio m = 5.5 / 1000 in the previous flat plate, the prediction accuracy is high when predicted using the flat plate shrinkage rate as in the conventional case. bad.
[0095]
Therefore, according to the method of the present invention, it is understood that the shrinkage rate can be predicted with higher accuracy than before even in the state before painting.
[0096]
Thus, by applying the present invention, the prediction accuracy of the shrinkage rate is remarkably improved as compared with the conventional method. In particular, it is effective to use for improving the product accuracy with respect to a mold design in a long resin-formed product, for example, a part obtained by injection molding such as a bumper fascia, an instrument panel, and a side cladding.
[0097]
In addition, even if the same material, the same molding conditions, and the same coating conditions, even if the shrinkage rate varies depending on the difference in the gate position and number of molds, the flow analysis results are taken into account, so the accuracy is high. Predictions can be made.
[0098]
Although the embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various modifications can be made by those skilled in the art within the scope of the technical idea of the present invention. Can do.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a procedure of a shrinkage rate prediction method for a resin molded product according to the present invention.
FIG. 2 is a perspective view showing a part A for which a shrinkage rate is predicted in Example 1. FIG.
3 is a drawing showing the flow analysis result of a part A in Example 1. FIG.
4 is a drawing showing the flow analysis result of a part B for which shrinkage rate prediction was performed in Example 2. FIG.
FIG. 5 is a drawing showing a flow analysis result of a part C for which a shrinkage rate is predicted in Example 3;
6 is a drawing showing the flow analysis result of a part D for which shrinkage rate prediction was performed in Example 4. FIG.

Claims (5)

A step of actually injection-molding a plate material and measuring a shrinkage rate m in a direction parallel to the flow direction and a shrinkage rate t in a direction perpendicular to the flow direction;
Perform a flow analysis by simulation of the resin molded product you want to predict, and obtain a vector field in the flow direction,
Defining a portion and direction in which the shrinkage rate is to be predicted in the vector field;
Partitioning portions having different directions of individual flow vectors in the vector field to form zone i,
Obtaining an angle (θ _i ) between the direction of the vector in each zone i and the direction to be predicted for each zone;
Calculating a shrinkage rate Δ _i for each zone according to the following equation (1):
Δi = 1 − [(1-m) ² cos ² (θ _i −δ) + (1-t) ² sin ² (θ _i −δ)] ^1/2 (1)
(In the formula, δ is defined by the formula (2).
δ = arctan [t / (1-m)] (2))
Using the shrinkage rate Δ _{i of} each zone obtained by the equation (1) and the projection width (W _i ) of each zone onto the portion to be predicted, the shrinkage rate Δ at the portion to be predicted is expressed by (3) Calculating with a formula;

A shrinkage rate prediction method for a resin molded product, comprising: Wherein (1) Instead, the following (4) according to claim 1 shrinkage prediction method of a resin molded article, wherein the use of expressions.
Δ _i = m cos ² (θ _i −δ) + tsin ² (θ _i −δ) (4) Wherein (1) Instead, the following (5) according to claim 1 shrinkage prediction method of a resin molded article, wherein the use of expressions.
Δ _i = m cos ² θ _i + tsin ² θ _i (5) The shrinkage rate of the plate material is measured before the heat treatment is applied after the plate material is molded, and the shrinkage rate prediction method for the resin molded product according to any one of claims 1 to 3 . The resin molding according to any one of claims 1 to 3 , wherein the shrinkage ratio of the plate material is measured after the plate material is molded and then subjected to a heat treatment that is the same condition as the heat treatment applied to the product to be predicted. Method for predicting shrinkage of products.

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