Simple Solutions That Work! Issue 15

CASE STUDIES 21 Contact: DAVID C. SCHMIDT [email protected] casting contracts and tries to pull away from the mold. HTCs and radiation view factor calculations can also be used to predict cooling on the outside of the die in the foundry environment. Other Considerations Another major setup consideration is how to handle die cycling. Most dies are preheated before casting starts, but it still takes a number of cycles for the die temperatures to heat up to the operating conditions. In simulation, the number of warm-up cycles can be reduced by starting the die at a hotter temperature than normal and let the die cool slightly to the operating temperature. For example, you may heat a die to 300°F in the foundry, but the overall operating temperature may be in the 600-700°F range. If you start the die at 800°F in a simulation, it may take five cycles to cool to the operating temperature instead of 15 cycles if the die had to warm up from 300°F. You can also speed up the warm- up section of the simulation by creating two meshes: one coarse and one fine. The coarse mesh is used for the warm-up phase, where the detailed progression of solidification is not important. With fewer nodes making up the mesh, the simulation can progress Figure 5. Simulation Setup Using Coarse and Fine Meshes. quite rapidly. If you use an 8:1 fine/ coarse ratio, the warm-up phase of the simulation can run up to ten times faster. You can even use simplified filling analysis to speed this up even more. Once the die is at an operating condition, the temperature distribution from the coarse mesh is mapped into a fine mesh, and detailed and accurate CFD filling analysis and solidification can be calculated for maximum accuracy with minimum time spent. An example of the setup can be seen in Figure 5 .