SOLIDCast UNIT 43: Low Pressure Permanent Mold Casting
SOLIDCast has the ability to better simulate the low pressure permanent mold process. This feature is really quite simple. What happens is that the gravity vector is inverted at the end of filling. This means that, if you build a model in the normal way (+Z = up), the filling will be shown as normal with gravity pulling down, but at the instant the fill is complete the direction of gravity switches 180 degrees, effectively inverting the mold and feeding from the bottom rather than from the top.
To activate this feature, click on Tools… Simulation Parameters. To activate Low Pressure Simulations, check the box labeled Low Pressure Simulation, then click the Apply button, then click Exit.
The sprue in this case will act exactly like a riser would if you inverted the model. Therefore, you want the sprue to have enough mass, and extend far enough below the casting model, so that it does not get emptied out by the casting contraction otherwise it will show shrinkage from the sprue into the casting, which would not be too realistic. What you are trying to do with this is to show potential for internal shrinkage in isolated hot spots that might be forming in the casting. Niyama and the FCC Criterion can also be used for prediction, but they are independent of orientation and are not affected by this feature.
Note that if you set a Simulation Parameter using this utility, it stays set until you come back in and change it. So, if you only do low pressure simulations occasionally, remember to come back in and reset the parameter when you are done, or you may mistakenly apply low pressure to normal gravity processes.