Computation of Die Swell behind a Complex Profile Extrusion Die Using a Stabilized Finite Element Method for Various Thermoplastic Polymers

塑料挤压模具的设计继续依赖于实验研究和模具设计师的经验。直接设计模具通常是不可能的；原因是塑料熔体的高度非线性行为，这是与其粘弹性特性密切相关的一个因素。后者导致熔体在离开模具定形区时发生严重且不均匀的膨胀。该产品的最终几何形状可能既不类似于尺寸，也不类似于流出模具几何形状的关键特征。考虑到目前模具设计中需要进行昂贵和耗时的实验，在计算建模的基础上能够预测工业相关挤压模具后的模具膨胀是有利的。在这个项目中，一种合适的有限元方法正在开发中。关于材料属性的建模，重点在于可以用oldyd - b模型表示的材料（例如，LDPE或HDPE）。新开发的方法侧重于两个主要组成部分：稳定的离散化方法和符合边界的高分辨率自由表面处理，能够在第一个项目阶段后呈现高达170%的模具膨胀率。

The design of plastics-extrusion dies continues to rely on both experimental studies and the experience of the die designer. Direct die design is in general not possible; reason being the highly non-linear behavior of the plastics melt - a factor strongly tied to its viscoelastic properties. The latter cause the melt to swell severely and non-uniformly when exiting the shape-defining zone of the die. This final geometry of the product may resemble neither the size, nor the key features of the outflow die geometry. Considering the costly and time-consuming experiments that are presently needed in die design, it is advantageous to be able to predict the die swell behind industrially relevant extrusion dies on the basis of computational modelling. In this project, a suitable finite-element method is being developed. Regarding the modeling of the material properties, the focus rests on materials that can be represented by the Oldroyd-B model (e.g., LDPE or HDPE). The newly developed method focuses on two main ingredients: a stabilized discretization method and a boundary-conforming, highly resolved free-surface treatment capable of presenting die swell ratios of - after the first project phase - up to 170%.