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Research Papers

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

[+] Author and Article Information
J. J. Hernández-Ortega, R. Zamora, F. Faura

Department de Ingeniería de Materiales y Fabricación, ETSII, Universidad Politécnica de Cartagena, E-30202 Cartagena, Spain

J. Palacios

Department de Mecánica, ETSII, UNED, E-28040 Madrid, Spain

J. López1

Department de Ingeniería de Materiales y Fabricación, ETSII, Universidad Politécnica de Cartagena, E-30202 Cartagena, Spainjoaquin.lopez@upct.es

1

Corresponding author.

J. Manuf. Sci. Eng 132(5), 051011 (Oct 04, 2010) (9 pages) doi:10.1115/1.4002535 History: Received August 26, 2009; Revised September 02, 2010; Published October 04, 2010; Online October 04, 2010

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.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Visualization setup. (a) Schematic representation of the test bench and (b) photograph of the die cavity and injection chamber.

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Figure 2

Geometry of the problem

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Figure 3

Schematic representation of the (a) geometry and (b) mesh used to simulate the problem

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Figure 4

Grid sensitivity results at different instants (the instants have been made nondimensional using the filling time of the cavity tf). Case with Re=50. (a) Free-surface profiles at different instants. (b) Mass conservation errors.

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Figure 5

Flow pattern types: (a) shell, (b) mound, (c) palm, and (d) transition

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Figure 6

Free-surface profiles at different instants using (a) Re=0.2, (b) Re=50, and (c) Re=500

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Figure 9

Free-surface profiles at different instants using Fr=5.0. Comparison between the results obtained with Re=50,000 and Re=200,000.

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Figure 10

Flow pattern map as a function of the Reynolds and Froude numbers

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Figure 11

Comparison between the values of Fr∗ obtained from Eq. 2 and those deduced numerically for different aspect ratios L/Wi

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Figure 12

(a) Schematic representation of the mesh used and (b) grid sensitivity of free-surface profiles at different instants for the filling of the cavity of Fig. 2

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Figure 13

Comparison between the visualization and CFD results (at the right of each picture) of the free-surface profiles for different instants with u/(gL)1/2=1.73 and vents located in position B

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Figure 15

Experimental and numerical results of the residual air mass ratio in the die cavity at the instant at which the liquid reaches the vent as a function of u(gL)−1/2

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Figure 14

Comparison between the visualization results for the free-surface profiles at different instants with u/(gL)1/2=0.92 and vents located in positions (a) A and (b) B. The CFD results have been included on the right half of each frame.

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Figure 8

Free-surface profiles at different instants using Fr=2 and Re=0.2

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Figure 7

Free-surface profiles at different instants using Fr=2.0. Comparison between the results obtained with Re=50,000 and Re=200,000.

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