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Metal Casting Technologies : June 2006
METAL Casting Technologies June 2006 BacktoBASICS spreadsheet of component dimensions that can be used to create geometry in a CAD system, or in the software model builder itself. Many gating and feeder components are used on many different castings in a given foundry. For example, a foundry may have a series of standard sizes of downsprues, or use specific sizes of riser sleeves. These types of components can be created once in CAD, then saved and reused in any model in the future, without having to re-create the geometry each time. If a library of gating components is developed and used, the entire gating and riser design process, from loading the unrigged model to having a fully rigged geometry ready for verification simulation, can be as short as 30 minutes or so. Addition of a chill and riser to the valve body casting, using components, is shown on previous pages: Design Verification Using CFD and Solidification Analysis Once the rigging system is in place, a full Computational Fluid Dynamics (CFD) analysis is performed to accurately predict and visualise mould filling. This also provides the most accurate temperature distribution in the casting and mould, which, in turn, provides a better solidification analysis. In addition to temperature analysis, CFD can provide velocity information. It is important to keep metal stream velocities low during filling, to minimize chances for splashing, mould erosion and re-oxidation defects. The plots on the following page show how this information can be used. The first two figures show low stream velocities at the early filling stages. The third figure shows a plot at 40% full, with a minimum value of 1.0 m/s. Since the casting is 'clean', this means that all metal movement in the casting is below 1.0 m/s. Temperature distribution during mould filling. CFD analysis shows positive temperature gradients that promote directional solidification. Plots of metal stream velocities during filling. 38