(i.e. 0.5 m/s for aluminum) are immediately detectable. The filling simulation shows the cooling behavior of the melt all the way to a potential premature solidification (Fig. 7). There- by, the deciding criteria to develop an effective gating system are available early in the gating design process (Fig. 8).
Current solidification simulation does not simply provide a description of the heat transfer process, however. Many of the criteria used to evaluate the solidification behavior are based on the information gained from the solidifica- tion simulation and thereby can provide the first clues of the casting quality. As soon as a 3-dimensional geometry of a casting is available, a basic solidification and cooling simulation can be performed in minutes (Fig. 9). The pre- diction of hot spots and areas of final solidification do not only help the metal caster in the engineering department,
but also support the designer in evaluating the designs. The heat loss prediction is an important factor for their layout, especially in permanent molds. The impact of boundary conditions such as preheating, coating, heating or cooling, can be determined quantitatively in a short period of time. The knowledge of temperatures and solidification behavior leads to a quantitative prediction of the local thermal mod- ulus in the casting, as well as solidification times, cooling rates, and temperature gradients (Fig. 10).
Figure 5. The prediction of the fluid flow in combination with the temperature loss of the melt is the key for the development of a robust gating system. Velocities and pressure distributions can be displayed quantitatively at any stage of the filling process. /1/
Figure 6. “Metal flows like water“– there is much truth to this. The viscosity of liquid melt is near the one of water. However, due to the multiple times higher density, liquid metal has a much higher energy content, which leads to big turbulence. The effects can be depicted in simulation tools by using virtual particles. /2/
Figure 7. Typical ingate velocities of more than 10 m/s lead to a break up of the melt surface, which lead to air entrapment. The filling simulation, therefore, not only considers the melt but also the air and gases in the die cavity. /3/
10 International Journal of Metalcasting/Spring 10
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