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AFS/FEF Student Technology Contest


Editor’s note: The American Foundry Society and Foundry Education Foundation (FEF) instituted the Student Technology Contest to recognize excellence in metalcasting related research and activities of undergraduate and graduate students in the FEF school network. FEF scholarships were awarded to the first and second place winning projects, Measuring Energy and Material Flows and Costs of Innovative Technology Adoption in Ductile Iron Foundry Production, submitted by Rose Torielli, Pennsylvania State University, and ASTM B-108 Aluminum Tensile Bar Mold Redesign, submitted by Mark Twilley, Michigan Technological University. One of these projects, along with an honorable mention project, High Strength Low Alloy (HSLA) Aluminum, submitted by Nicholas Johnson, Michigan Technological University, have been adapted for publication in the IJMC.


ASTM B-108 AluMinuM TenSile BAr Mold redeSign M. Twilley


Michigan Technological University, Houghton, MI, USA Copyright © 2012 American Foundry Society


mold, a pouring temperature of 1472F(800C) and mold preheat of 842F(450C) were required. The porosity in the tensile bars is visible with x-ray computed tomography (Fig. 2). A Magmasoft simulation shows similar porosity (Fig. 3) using a comparable aluminum alloy. The project’s goals were to remove the porosity from the bars and to minimize mold preheat.


The ASTM B108 aluminum tensile bar mold (Fig. 1) ex- hibits problems with freeze-off and porosity in castings of Al-0.06Sc-0.06Zr at% (Tm


Simulations showed premature freezing of the thin ingates leading to poor feeding of the tensile bars. This porosity was eliminated by increasing the gate thickness from 16% to 67% of the riser diameter, enabling increased feeding (Fig. 4) and elimination of porosity (Fig. 5).


The melt freeze-off temperatures predicted by MAGMA (Fig. 6) agree with foundry and literature observations (Fig. 7). The thin (0.2”) thick sprue (Fig. 8) led to issues with fill- ing and resulted in high required mold preheats. Increasing the sprue thickness to 0.6” enabled filling of the mold (Fig. 9). Although some porosity reappeared (Fig. 10) it was miti- gated by enlarging the lower riser diameter by 150% along the length of the ingate (Fig. 11).


The final mold geometry (Fig. 12) produces melt front tem- peratures (Fig. 13) and porosity profiles (Fig. 14) that indi-


International Journal of Metalcasting/Winter 2012


Figure 1. The mold used was a filter modified ASTM B108 Mold.


57


cate quality castings with a 212F (100C) preheat. The cast- ing yield decreased from 8.6% to 7.5%.


= 1220F or 660C). To fill the


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