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and 2 are 710C and 730C. No heat treatment of any kind was applied in this work. Figure 1 illustrates the major geo- metrical features (dimensions shown in mm) of each of the four gating configurations.


As it is observed, configurations A1 and A2 (Figure 1) both have tapered bottom ingates, while configuration B has tapered side ingates. The B and B0 configurations have the same basic geometry, only differing in the num- ber of side ingates, where flow is permitted from only one side in B0. These are the major geometrical differ- ences among the molds. All of the designs have in com- mon a runner connected to side ducts (effectively “surge tanks”), which redirect first metal from the plate cavity and serve as filling channels for the B configuration, and risers at the top of the plates in order to assist the feeding of the cavity during solidification.


A series of simulation and experimental works were ac- complished in order to research the links existing among process conditions, casting structure, and mechanical properties. The latter two include microstructural and surface analysis as well as mechanical testing of selected samples.


Casting Simulations


Casting simulations were a valuable tool used to gain insight of the melt behavior throughout the filling process, specifically at the entrance to the mold cavity. The main objective of the mod- els is to observe the velocity at the ingates, as it is important to re- main below the critical values established for each configuration to reduce turbulence in the melt.6-8


For the B


configurations, the tar- get velocity at the in- gates is approximately 25cm/second, and for the A configurations the value is 50cm/ second. These val- ues were determined based on the cross- sectional areas of the ingates. Fill time also was monitored during the simulations. This


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result indicates the melt location at specific times during the process and can be an indication of regions of air entrapment if the metal inside a small area fills at a later time than the surroundings. In this work, only the results for fill time, ve- locity, temperature, and material trace will be discussed, al- though several other filling and solidification results, such as flow length, air pressure, and flux through ingates, were used in the analysis of possible areas prone to defect formation. After preliminary parameters were established, models were altered using volumetric flow rate as a function of time versus fill time only, so the filling correlated with actual values at the foundry.


Fill Time


As was mentioned previously, air entrapment during filling, which leads to void formation, is of particular interest and can be monitored by the fill time simulation results. From preliminary B configuration results (Figure 2) areas of pos- sible oxide entrapment appear to be in the lower center re- gion of the plate cavity where the streams from opposing ingates meet. This produces a small jet (Figure 2[a]) which later evolves into a “swaying” flow (see Figure 2[b]). It is


A1


A2


B


B0


Figure 1. Four multiple-gated designs developed for this research: Configuration A1; Configuration A2; Configuration B; Configuration B0.


(a)


(b)


Figure 2. Filling results for the B configuration: (a) Fill time results upon joining of opposing streams (fill time values refer to the instant that the melt starts its horizontal flow upon the lower part of the casting). (b) Schematic representation of the swaying type of flow found for this configuration.


International Journal of Metalcasting/Spring 2012


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