In this study, the mold filling analyses of a thin-walled LED heat sink combined with the vacuum valve runner are simulated by FLOW-3D software. Two topics are analyzed and discussed. First, numerical simulations for variety of molding conditions, including effects of thermal conductivity, vacuum pumping pressure, mold temperature, filling velocity, respectively, are conducted for the computational model of the thin-walled LED heat sink connected with the vacuum shut-off valve. Second, effects of several geometrical parameters, including fin thicknesses of the LED heat sink and dimensions of the vacuum shut-off valve are explored. In these two topics, melts are set to liquid metal of Al 384.0 materials. The first topic of analysis mainly to investigate the effects of molding parameters based upon the same computational model of the thin-walled LED heat sink connected with a vacuum valve runner. The simulated results show if molding conditions are changed, different sizes of defects are appeared in castings; if vacuum pumping pressure is higher, the casting is also firmness, density prone to increase; if vacuum pumping pressure is too low, then pumping efficiency of mold cavity is low and it will be easy to form the casting porosity defects. For the second topic of analysis, molding conditions are hold constantly, and effects of different geometrical dimensions to castings qualifications are simulated. Characteristic dimension of trigger mechanism can effectively operate the vacuum shut-off function; but too thin or too thick of channel, it will affect the pumping time if different degrees of vacuum is imposed. Decreasing of gas residuals in castings for the vacuum pumping pressures of 760Torr, 200Torr, 100Torr compared with 10Torr, were 0.311%, 0.174%, 0.008%, respectively. It shows the appropriate and effective vacuum level for vacuum die-casting of the thin-walled LED heat sink is in the range of 100Torr.

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