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

塑料挤出模具的设计仍然依赖于实验研究和模具设计者的经验。直接模具设计通常是不可能的；原因是塑料熔体的高度非线性行为--这一因素与其粘弹性特性密切相关。后者导致熔体在离开模具的形状定义区时严重且不均匀地膨胀。该产品的最终几何形状可能既不类似于流出模具几何形状的大小，也不类似于其主要特征。考虑到目前在模具设计中需要昂贵和耗时的实验，能够在计算模型的基础上预测工业上相关的挤出模具后面的挤出胀大是有利的。在这个项目中，正在开发一种合适的有限元方法。关于材料属性的建模，重点在于可以由Oldroyd-B模型表示的材料(例如，LDPE或HDPE)。新开发的方法专注于两个主要组成部分：稳定的离散化方法和边界一致、高分辨率的自由表面处理，该处理能够在第一个项目阶段之后提供高达170%的挤出膨胀率。

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%.