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

Abstract

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 et al. (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 et al. (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)

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

“…For this reason, a better understanding of the interaction between all these process parameters and their effect on product quality and on process performance and costs is a current core field of research. In a first group of works [ 8 , 9 , 10 , 11 , 12 , 13 ], one can find experimental studies that analyse the influence of a limited set of process variables on casting quality. Dargusch et al [ 8 ] implemented a series of pressure sensors in the cavity to measure the influence of the intensification pressure and casting velocity on the porosity level of the parts.…”

“…Moreover, Laws et al [ 9 ] developed a study where the process parameters of initial melt temperature, injection pressure, and injection velocity were analysed from the empirical data, finding an optimum operational window. In a similar way, several authors have also conducted quantitative measurements or used image analysis techniques to study the influence of injection pressure and melt temperature on casting porosity [ 10 , 11 , 12 , 13 ].…”

“…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.…”

Equipo de fusión al vacío para la determinación cuantitativa del gas atrapado en piezas fundidas

“…Entre los que utilizan ensayos no destructivos podemos destacar los métodos basados en la inspección visual [1] , el radiografiado [2] , la tomografía asistida por ordenador [3] , el uso de ultrasonidos [4] , el estudio de frecuencias de resonancia [5] o el método gravimétrico [6][7][8][9][10][11] . Entre los que utilizan métodos destructivos destacan el análisis de imagen de distintas secciones de la pieza [12 y 13] y el calentamiento Equipo de fusión al vacío para la determinación cuantitativa del gas atrapado en piezas fundidas (•) J.J. Hernández-Ortega * , R. Zamora * , F. Faura * y J. López *…”

Cold flow defects in zinc die casting: prevention criteria using simulation and experimental investigations

“…Elsewhere, researchers have focused on aluminum and magnesium alloys, which are more commonly used for automotive structural parts. The simulation results are primarily concerned with the fill pattern [22], air entrapment in the shot sleeve [23,24], shrinkage defects in the hot spots [25,26], and microstructural defects affecting the tensile properties [27,28]. With the exception of a single attempt to optimize the process parameters and avoid long fill times [29], few simulation studies have a direct relation to the cold flow defects.…”