with intricate cavities can be cast by inserting cores made of foundry sand. Of all the ag- gregates used to produce sand molds and cores, silica sand is the most popular in producing highly dimensionally accurate castings at a cost more favorable than other materials such as zircon, chromite, and mullite ceramic. In molding operations, resin binders and hardeners are generally added into silica sand. Sand with these mixtures is called resin-bonded sand, and it typically consists of 93-99% silica and 1-3% binders. Simulation technology has


actual temperature profiles and cracking locations. Te established material model for the sand mold, based on the actual mechanical test data, can be used to predict casting defects related to cracking, such as veining defects.


PRESENTATION Comparing the Mechanical


Properties inside the Same Cast Frame Produced in Alloy A356- T6 and in Alloy 206-T4, 17-015


This picture shows a surface hardness scratch on a three-point bending sample after test.


AUTHORS Franco Chiesa, David Levas-


seur, Gheorghe Marin and Ber-


made remarkable progress in casting design and process optimization prior to actual manufacturing, which reduces the time and cost of conventional trial-and- error methods. Although many experi- ments have been done to study sand molds and cores, simulation techniques for predicting and controlling them are still underdeveloped due to the com- plex mechanical behavior and failure mechanisms of sand materials. Tus, it is necessary to develop reliable and robust process simulation models of sand molds/cores for more efficient manufac- turing. In the present study, mechanical tests of resin-bonded silica sand with 98.7% silica and 1.3% phenolic resin binder were performed. Experimental data from mechanical tests, together with some key data from literature, were used to build a material model for sand molds/cores for casting process simula- tion. Ten, casting simulation for three different geometries of sand cups was performed, and corresponding experi- mental validation was carried out.


CONCLUSION


1.3% phenolic resin binder was studied to develop a material model for casting process simulation. Tirty-six three-point bending tests were completed with an average fracture stress of 3.233 MPa and a standard deviation of 0.585. Inelastic behavior of this sand was found and elastic modulus was measured as 2,300 MPa from the three-point bending tests. Density was also obtained from three-point bending samples as 1,628


A commercial resin-bonded silica sand mixture with 98.7% SiO2


and kg/m3 . Seven uniaxial tensile tests were


performed with an average UTS of 1.450 MPa and a standard deviation of 0.258. Te data from mechanical tests are used to establish a material model for sand molds/cores in casting process simulation. Tree types of sand cup molds were made and poured with A356. Stress was in- creasingly concentrated from intact mold to flat-notch mold to V-notch mold, which eventually resulted in cracking. Te casting simulation results confirmed the locations of stress concentration and demonstrated excellent accuracy with the


nard Duchesne, Centre de Métallurgie du Québec (Trois-Rivières, Quebec, Canada)


BACKGROUND Te mechanical properties of an


industrial casting weighing 31 lbs. (14kg) and measuring 23 x 17 x 10 in. (560 x 410 x 250 mm) was poured, first in aluminum A356 (AlSi7Mg03), then in aluminum 206 (AlCu4). ASTM E7 sub-size tensile specimens were excised from the castings and pulled in the T6 condition for alloy A356 and in T4 and T6 conditions for alloy 206. Te degas- sing procedure was identical for the two alloys and the pouring temperature was 1,328F (720C) for alloy A356 and 1,364F (740C) for alloy 206. Six regions of the casting were investigated (19 ten- sile samples per casting) with solidifica- tion times varying from 2.8-7 minutes. Te tensile properties in the castings


This is an aluminum 206-T4 housing substi- tuting for ferritic ductile iron.


42 | METAL CASTING DESIGN & PURCHASING | May/Jun 2017


also were compared to those of stan- dard ASTM B26 test bars, of which properties were always superior to those measured inside the castings. In the 206-T4 casting, the yield strength was 30% higher than in the A356-T6 casting. For the identical degassing condition, the percentage surface area of porosity was higher in alloy 206; however, the maximum length of porosities was greater in the A356 alloy due to their inter-dendritic nature. An important segregation of copper was observed in alloy 206 which was not found to be overly detrimental to the tensile properties. Since the increase of the use of aluminum castings from the 1970s, the


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