Simple Solutions That Work! Issue 18

Figure 1. "Naked" simulation of casting plotting solidification time. the subsequent cooling and solidification of the casting along with the gates and risers so that correct feeding of the casting can be obtained. Flow simulation is accomplished using Computational Fluid Dynamics (CFD), a technique that solves the equations of fluid flow for mold filling. The equations governing the flow of a liquid are the Navier-Stokes equations; these relate the flow of liquid to the principle of conservation of momentum as well as movement in reaction to body forces on the liquid (such as gravity, pressure and friction). Filling simulation lets the foundry engineer visualise the flow of the liquid metal from the pouring point, through the gating system and into the mold cavity during the entire filling process. This verifies the gating system design. If the gating is not functioning as intended (for example, there is unequal metal flow through various gates), the design can be modified and the new design re-tested. In addition, the fluid flow calculations are coupled with thermal calculations so that the heat transfer from the liquid during filling and the resulting temperature distribution within the liquid metal can be viewed. This allows the prediction of areas in the casting where premature solidification may be occurring during filling, leading to defects such as misruns and folds. Accurate calculation of the temperature distribution of Figure 2. Model of casting with initial rigging design 45 HOW TO ISSUE Continued on next page