Experimental and theoretical study on filling imbalance in geometrically balanced injection molds

Abstract

Experimental and theoretical studies were performed on filling imbalance in geometrically balanced injection molds. Balancing the melt flow between cavities was investigated using several different runner systems at various operating conditions. Experiments indicate that injection rate, mold, and melt temperatures substantially affect the filling imbalance. It is strongly dependent on runners layouts geometry, and it has never been eliminated completely. It is most difficult to remove for high injection rates and low melt temperatures. Standard element geometry and circled element geometry cause positive imbalance which means that inner cavities fills faster, and it is opposite for one/two overturn element geometries which induce negative imbalance. A special modeling procedure is required to simulate properly the imbalance. This includes inertia effects, geometrical modeling of the nozzle where the imbalance starts, 3D tetrahedron meshing with minimum 12 layers. Simulations were consistent with experiment, however, when the imbalance increased, the discrepancies between simulation and experiment also increased. It can be stated that filling imbalance problem is still unsolved. There are serious thermo‐rheological aspects to explain for better understanding this phenomenon. Trends in modeling of injection molding are presented and new concepts solving the problem are discussed including simulation/optimization approach and a novel concept of global modeling of injection molding process. POLYM. ENG. SCI., 59:233–245, 2019. © 2018 Society of Plastics Engineers

Simulation Studies on the Effect of Material Characteristics and Runners Layout Geometry on the Filling Imbalance in Geometrically Balanced Injection Molds

“…Additionally, it is generally established that the filling imbalance is caused by the shear gradients in the flow through the runners that lead to non-linear and non-symmetrical distributions of temperature and viscosity. This is strongly influenced and complicated by the geometry of the runners, the thermo-rheological material characteristics, and the process parameters of injection molding [1,2,3,4,5,6].…”

“…The filling imbalance has been examined extensively by scientists and engineers, e.g., [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]. Up to now, there have been no universal and commonly accepted solutions of this problem.…”

“…Up to now, there have been no universal and commonly accepted solutions of this problem. A detailed discussion of the literature review has been recently presented by the authors of this paper [1].…”

“…Recently, extensive experimental studies on the filling imbalance have been performed by the authors [1]. Balancing the polymer melt flow between cavities has been investigated at various operating conditions using different runner systems.…”

“…Thus, new concepts were necessary which included inertia effects and 3D, non-isothermal, and non-Newtonian flow [32,33]. Several simulation tests have confirmed the effectiveness of these methods [1,34,35,36,37].…”