Simple Solutions That Work! Issue 15

CASE STUDIES 19 DAVID C. SCHMIDT Vice President Finite Solutions, Inc. ARTICLE TAKEAWAYS: • Different molding processes require different setups for accurate simulation • Sand casting is the simplest setup, followed by investment casting and permanent mold • Setups can be reused to reduce operator time and increase consistency in simulation SIMULATION SETUPS FOR VARIOUS MOLDING PROCESSES Continued on next page W hen simulating various molding processes, it’s important to account for the specific features of each process to make sure the overall simulation result is as accurate as possible. Calculations should also be efficient to provide results quickly. Heat transfer calculations deal with heat flow through materials and the barriers to heat flow between materials. Figure 1 shows these relations. Consider an aluminum casting poured into a sand mold. Heat flows through the casting based on its thermal properties. The heat flows from the casting into the mold based on the properties of the internal interface (or gap) that forms between the casting and the mold. Heat continues to flow through the mold until it reaches the outside edge of the mold, where it finally goes out into the air on the foundry floor. If the mold material is insulating, like with sand or investment casting, you can usually ignore internal interfaces because their contribution to the overall result is negligible. Internal interfaces are very important in permanent mold casting where die coatings are frequently used to control heat transfer. Heat transfer coefficients (HTCs) are used to measure the resistance to heat flow across these interfaces. As mold temperatures go up, it’s important to deal with heat flow from the mold surfaces out into the foundry air. Radiation heat flow is significant as temperatures rise, like the hot shells used in investment casting. Figure 1: Heat flow is affected by material properties and interface properties.