Initial attempts to predict shrinkage in complex lost foam castings

Almost all commercial codes used for foundry applications have the ability to predict metal contraction. Experience shows that perform most of the commercially available code adequately when contraction in models predicting cavity empty, such as green sand, sand and die casting band. The molds are filled quickly which results in small temperature differences throughout the casting. Modeling shrinkage in castings from the casting process is simple and practical to fill instantaneous (at uniform temperatures) used only in complex solutions for thin wall sections. Lost Foam modeler challenged by relatively slow fill rate which non-uniform temperature throughout the casting. So the process must solidify the temperature variations for shrinkage during solidification predicting correctly. Initial attempts to predict that in complex castings contraction Lost Foam unsuccessful. Using the published values ​​for the simulation results enthalpy and metal density was compared with sectioned castings, had the predicted location and size of the contraction results agree with the solutions.

In addition, the temperatures were not measured with thermocouples in projections agree with temperatures4 predicted. The difference in temperature shows predicted and measured in solutions of four cylinder using published enthalpy. The temperatures were not predicted accurately predict metal shrinkage or other fault location and size. Track were reasons for the discrepancies to inaccurate values ​​of enthalpy published in the mushy zone (Liquidus to solidus temperature) where energy is released. Devoted significant efforts to correct enthalpy values ​​commonly used to develop aluminum – silicon casting alloys. Figure 1.3.2 shows the values ​​for enthalpy published for aluminum – silicon alloy compared with calculated values. The technique is used for calculations the equivalent Silicon Method described in the literature. This method includes the effect of silicon containing four times the enthalpy compared to aluminum. Using the calculated values ​​of enthalpy values ​​agreed satisfactorily predicted temperatures other key finding concerned the metal density values ​​used in predicting contraction.

When typical density values ​​used measure finished castings in prediction contraction predicted contraction simulations were accurate for large areas but did not predict smaller areas. When used theoretical density values ​​predicted the smaller areas of contraction and confirmed with sectioned castings.