An Experimental and Numerical Study of Flow Patterns and Air Entrapment Phenomena During the Filling of a Vertical Die Cavity

Abstract

One of the most important problems encountered in die-casting processes is porosity due to air entrapment in the molten metal during the injection process. The aim of this work is to study experimentally and numerically the different air entrapment phenomena that may take place in the early stages of the filling of a vertical die cavity with a rectangular shape for operating conditions typically used in low and medium-pressure die-casting processes. Special attention is given to determining the influence of the gravitational forces on the flow pattern. Numerical simulation of the flow in the die cavity is carried out for the liquid phase using a commercial computational fluid dynamics (CFD) code (FLOW-3D) based on the solution algorithm-volume of fluid (SOLA-VOF) approach to solve the coupling between the momentum and mass conservation equations and to treat the free-surface, while the amount of air evacuated through vents is calculated by using an unsteady one-dimensional adiabatic model that retains friction effects. The main characteristics of the flow at the early instants of the die cavity filling are analyzed for different operating conditions, and the different flow patterns are summarized in a map as a function of the Reynolds and Froude numbers. Also, filling visualization experiments are carried out on a test bench using water as working fluid in a transparent die model and a high-speed camera. The numerical and experimental results obtained for the free-surface profile evolution are compared for different inlet velocities of the fluid and the viability of the numerical tools used to predict the final amount of trapped air in the die cavity is discussed.

Direct Observation of Filling Process and Porosity Prediction in High Pressure Die Casting

“…It is well known that porosity is the main defect in die-castings, and porosity can seriously damage mechanical properties of die-castings. Air entrapment in the liquid metal during the filling process is the major source of porosity [4]. Therefore, to obtain high-performance castings, it is extremely important to observe the die casting filling process and predict the air entrapment.…”

A Decision Support System (DSS) for the Prediction and Selection of Optimum Operational Parameters in Pressure Die-Casting Processes

“…Mention should be made of the works by Khayat [ 24 ] and Barone and Caulk [ 25 ], where numerical models were applied for the prediction of air trapped in the parts. Similarly, the VOF (Volumen of Fluid) method was successfully used for the same purpose in the studies carried out by Zhao et al [ 26 ] and Hernández-Ortega et al [ 27 ]. In the work of Hu et al [ 28 ], experimental and numerical data were employed to predict different designs of the runner and the gating system.…”

“…Previous experience of our research group in DSS development [ 47 ], and the work carried out on the definition of analytical, numerical, and experimental models in die-casting processes on the plunger movement in the slow shot phase [ 12 , 14 , 15 , 29 ], as well as the numerical and experimental study of die cavity filling [ 27 ], has led us to the development of a DSS capable of addressing this problem.…”

The Influence of Returnable Material on Internal Homogeneity of the High-Pressure Die-Cast AlSi9Cu3(Fe) Alloy

“…It is well known that porosity is a major disadvantage of high-pressure die-castings, as it can seriously affect the mechanical properties of the castings. The main source of porosity is considered to be the entrapment of air in the liquid metal during the mold filling process [9]. Therefore, it is extremely important to monitor the mold filling process and predict air trapping in order to obtain high-quality high-pressure die-castings.…”