Novel discretization methods for improved simulation precision in injection molding

Abstract

Mold filling is an important stage of injection molding, which is one of the most commonly used manufacturing processes for the production of thermoplastic components in high volumes. As a consequence, the numerical simulation of this process based on computational fluid dynamics (CFD) is of great significance for production engineering [1,2]. However, modeling of the mold filling is a tremendously demanding process, when considering interfacial physical phenomena, such as two-phase flows, building a sharp interface between the molten plastics and the present air in the cavity or the dynamic wetting contact line at the cavity surface. A method for dealing with these phenomena is a local mesh refinement both in space and time. In this paper, the numerical solution of a mold filling problem using simplex-type space-time finite elements is presented and compared with experiments. These elements can be suited to increase efficiency, when used for the aforementioned refinement. In addition, a Navier's slip boundary condition is applied to the solid boundaries of the mold allowing the contact line to evolve along the boundary, while enabling a better prediction of the pressure distribution. The presented work was performed in collaboration of the subprojects B3 and B5 of the collaborative research center 1120 "Precision Melt Engineering".Keywords: Injection molding / Navier's slip boundary condition / simplex elements / space-time elements / two-phase flow Die Formfü llung ist ein wichtiger Vorgang des Spritzgießens, das eines der hä ufigsten verwendeten Verfahren zur Herstellung thermoplastischer Bauteile in hohen Stü ckzahlen ist. Infolgedessen ist die numerische Simulation dieses Prozesses auf der Grundlage der numerischen Strö mungsmechanik von großer Bedeutung fü r die Produktionstechnik [1,2]. Allerdings ist die Modellierung des Fü llvorgangs ein anspruchsvoller Prozess, wenn die komplexen physikalischen Phä nomene, wie die Zweiphasenströ mung, mit einem Interface zwischen der flü ssigen Kunststoffformmasse und der vorliegenden Luft oder die Kontaktlinie zwischen Formmasse und Kavitä tsoberflä che berü cksichtigt werden mü ssen. Eine Mö glichkeit, dies zu erreichen, ist eine lokale Netzverfeinerung in Raum und Zeit. In dieser Arbeit wird die numerische Lö sung des Fü llvorgangs eines plattenfö rmigen Formteils mittels Simplex Raum-Zeit-Gittern prä sentiert und mit experimentellen Ergebnissen vergli-Corresponding author:

High‐resolution numerical simulations of polymer injection molding: Analysis of mesh size and refinement

“…To avoid this phenomenon and allow the interface to move, we impose a slip condition around the interface, maintaining a no-slip like condition for the rest of the polymer domain. This is a generally accepted approach in the literature [9,12,13].…”

Simplex space-time meshes in thermally coupled two-phase flow simulations of mold filling

“…The last term (Pn) h w h • h h dP in ( 27) is of primary importance for applying the Navier-slip boundary condition to the cavity walls (as stated in [9]), as it is a formulation to apply traction h h to a boundary of the domain. The term h corresponds to the imposed traction, whereas the superscript h stands for discretized quantities.…”

Technical and Economic Study on Cleaning the Cooling Channels of a Plastic Injection Mold

“…Karyofylli [3] based on the premise that mold filling is an important stage of injection molding, which is one of the most used manufacturing processes for the production of thermoplastic components in large volumes, in his paper presents a numerical solution to a problem of filling the mold, using finite elements and then comparing the results with the experiments.…”