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Research Papers

Experimental Investigation of Porosity Formation During the Slow Injection Phase in High-Pressure Die-Casting Processes

[+] Author and Article Information
R. Zamora

Departamento de Ingenieria de Materiales y Fabricación, ETSII, Universidad Politécnica de Cartagena, E-30202 Cartagena, Spainrosendo.zamora@upct.es

J. J. Hernandez-Ortega

Departamento de Ingenieria de Materiales y Fabricación, ETSII, Universidad Politécnica de Cartagena, E-30202 Cartagena, Spainjuanjo.hernandez@upct.es

F. Faura

Departamento de Ingenieria de Materiales y Fabricación, ETSII, Universidad Politécnica de Cartagena, E-30202 Cartagena, Spainfelix.faura@upct.es

J. Lopez1

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

J. Hernandez

Departmento de Mecánica, ETSII, UNED, E-28040 Madrid, Spainjhernandez@ind.uned.es

1

Corresponding author.

J. Manuf. Sci. Eng 130(5), 051009 (Aug 15, 2008) (10 pages) doi:10.1115/1.2815344 History: Received April 02, 2007; Revised September 18, 2007; Published August 15, 2008

The air entrapment mechanisms in die-casting injection chambers that may produce porosity in manufactured parts are analyzed in this work using visualization techniques of the flow in a transparent injection chamber model, using water as working fluid. In particular, results for the free-surface profile evolution and for the volume of air remaining in the chamber at the instant at which the water begins to flow through the runner are analyzed for different maximum plunger speeds and initial filling fractions. A comparison between these visualizations and the numerical results of Zamora (2007, “Experimental Verification of Numerical Predictions for the Optimum Plunger Speed in the Slow-Phase of a High-Pressure Die Casting Machine  ,” Int. J. Adv. Manuf. Technol., 33, pp. 266–276) which were obtained using a three-dimensional numerical model, shows a good degree of agreement. After discussing the air entrapment mechanisms that may produce porosity in manufactured parts, different experiments, which were carried out under real operating conditions using an aluminum alloy in a high-pressure die-casting machine with horizontal cold chamber, will be presented. The die-cavity geometry used in the experiments was appropriately modified to isolate the slow shot phase from the rest of the injection process, and the porosity levels in the manufactured parts were measured using a gravimetric technique. The optimum values of the maximum plunger speed that minimizes porosity in the manufactured parts have been determined. These values are very close to the previous numerical predictions of López (2003, “On the Critical Plunger Speed and Three-Dimensional Effects in High-Pressure Die Casting Injection Chambers  ,” ASME J. Manuf. Sci. Eng., 125, pp. 529–537)

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Air entrapment mechanisms occurring during the slow phase. Maximum plunger speed (a) higher and (b) lower than the optimal one.

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Figure 2

Air entrapment effects due to high plunger speeds: (a) a standard photograph of a part made stopping the plunger when the molten metal just reaches the runner; (b) X-ray photograph of a completely filled part

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Figure 3

Experimental setup used in the water-analog experiments

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Figure 4

Schematic representation of the problem configuration

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Figure 5

Experimental setup used in the aluminum experiments: (a) Photograph of the die used in the experiments and of a manufactured casting; (b) schematic representation of the injection chamber; (c) sequence of the injection shot

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Figure 6

Comparison between the experimental and numerical results for the wave surface profiles for f=0.252. (a) Umax∕(gH)1∕2=0.42. (b) Umax∕(gH)1∕2=1.0. (c) Detailed view of the wall jet formation along the chamber ceiling for the case corresponding to the higher speed.

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Figure 7

Comparison between the experimental and numerical results for the wave surface profiles for f=0.374. (a) Umax∕(gH)1∕2=0.43. (b) Umax∕(gH)1∕2=0.74. (c) Detailed view of the wall jet formation along the chamber ceiling for the case corresponding to the higher speed.

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Figure 8

Comparison between the experimental and numerical results for the wave surface profiles for f=0.252 and the optimum value of Umax∕(gH)1∕2=0.88, predicted numerically by (15)

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Figure 10

Mean porosity and 95% confidence intervals for different maximum plunger speeds with (a) f=0.252, (b) 0.374, and (c) 0.5

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Figure 11

Porosity measured in Pieces A, B, and C, for initial filling fractions of f=0.252, f=0.374, and f=0.5

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Figure 12

Longitudinal section of a part, previously sectioned, injected with f=0.374 and maximum dimensionless plunger speeds of (a) 0.44 and (b) 1.04

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Figure 13

Comparison between porosity P and visualization results of the dimensionless volume of trapped air V∕(AL) for different maximum plunger speeds and initial filling fraction (a) f=0.252 and (b) 0.374

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Figure 9

Experimental and numerical results for the dimensionless volume of trapped air, V∕(AL), as a function of Umax∕(gH)1∕2, for the initial filling fractions (a) f=0.252 and (b) f=0.374

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