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Metal Casting Technologies : June 2006
METAL Casting Technologies June 2006 BacktoBASICS The Design Process The general design process consists of the following steps: ● Simulation of the 'Naked' Casting ● Feeder Design ● Gating System Design ● Rigging Geometry Creation ● Verification via CFD/Solidification Simulation The balance of this paper will demonstrate these steps, using a valve body casting, typical of many commercial castings produced today. "Naked" Simulation The first step in the rigging process is to run a simulation of the part 'naked'; that is, without any rigging system. Simulation results show the effects of the part geometry on the overall solidification. In this initial simulation, filling analysis is typically not done, which provides extremely rapid results, and can point out preferred gate and feeder locations which would promote directional solidification. All that is required for the initial simulation is a casting model, normally provided by the customer in STL file format, and basic process details such as casting alloy, mould material and pouring temperature. Riser Design Once the initial simulation is complete, the data from the simulation can be used to design the rigging components. The feeders, or risers, are typically designed first, followed by the gating system. The software uses the progression of solidification, along with a pattern recognition algorithm, to determine the separate feeding paths on the casting, as shown below. Further, the software can find the last points to freeze on each feeding path, which will be the preferred feeder contact points. Feeder sizes for each feeding zone are calculated by the software using variations on the well-known Modulus Technique. Solidification time information from the initial simulation is converted into a 'thermal modulus'. This takes into account not only casting alloy and mould material, but also the solidification dynamics of the specific mould situation. Feeding aids, such as insulating or exothermic sleeves, can be accommodated in the calculation. Gating System Design After all feeders have been calculated, the next stage is to design the gating system, to bring the metal into the Gating system component design. Riser and chill added to the casting model using component parts. 36