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for the sand are accurate and reliable.


Cracking Position Comparison Process simulation and laboratory


Fig. 4 A356 temperature profiles between FEA casting simulation and thermocouple measurement are compared.


the simulation and experiment are plotted in Figure 4. Both solidus tem- perature (TS = 1018F [548C]) and liquidus temperature (TL = 1135F [613C]) lines are indicated on the plot. From the cooling curve measured by thermocouple, the average cooling rate between TL and TS is 0.157C/s, and the cooling rate at the initial 25 seconds of the curve is about 4C/s. Te simulation result agrees well with the experimental data in the first 300 seconds. After 300 seconds, discrepancy between the experimental measurement and simulation calcu- lation is presented in the slope and temperature values. Temperature profiles of the sand


in the original intact cup mold are drawn in Figure 5. Te simulation curve shows a good agreement with the experimental measurement during the initial temperature rise region. Tere is little discrepancy at 100-350 seconds between the simulation and experiment, but the general trend is similar during this period. After 350 seconds, as in the case of Figure 4, more discrepancy is seen in the slope and temperature values. Te reason for such discrepancy after longer periods is still not clear, but it is less critical after the solidification. Nevertheless, simulation prediction at high temperatures and initial stages


of solidification and casting processes is of primary focus. For both graphs, the experimental measurements and simulation results of A356 and sand show good agreement at high temperatures in the beginning, which indicates that the improved input data and the selected material model


casting experiments were completed for three different geometries of sand cup molds. Figure 6a presents the simulation results of maximum first principal stress during the process. A scale bar is labeled with unit of MPa. Figure 6b and 6c show cup molds before and after pouring. From the first principal stress contour, tension is on the outer surface of cup molds and compression on the inner. Te maxi- mum first principal stress is increased from 1.332 MPa of original intact cup mold, to 2.372 MPa of flat-notch cup mold and to 4.205 MPa of V-notch cup mold. Te stress concentration of the V-notch mold is on the tip of the notch, as labeled. Terefore, cracking should initiate at this location if it would occur. Tis also confirms it is tensile stress tearing the mold apart to cause cracking. Experimental results in Figure 6c validated the simulation results. No cracking occurred on the intact cup mold and flat-notch one. From the color difference between the flat notch and intact cup, the mold was


Fig. 5 Sand mold temperature profiles between FEA casting simulation and thermocouple measurements are compared.


July 2017 MODERN CASTING | 33


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