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hollowed-out space inside the part. Only the complexity of the final cast part determines
if a single pattern will be used, or if it is necessary to use up to thousands of patterns in
conjunction with multiple sand cores.
To ensure correct flow of molten aluminum, a gating system of channels and
wells are also imprinted into the sand. These are specifically designed in an attempt to
equally distribute the aluminum across mold cavity, and when the molten aluminum
cools, the additional aluminum left on the part by the channels and wells can be later
machined off [10].
2.1 - Pouring Molten Aluminum
Pouring the aluminum into the cast is perhaps the most crucial point in creating a
quality part. If great care is not taken during this stage the mold must be scrapped with a
loss of material and time. The reason great care must be taken is due to the material
properties of molten aluminum, as discussed below.
2.1.1 - Properties of Aluminum
Pure aluminum can be alloyed with other metals to create a material that is easily
formed, cast, or machined. It also has a high thermal conductivity, maintains excellent
corrosion resistance and is also extremely lightweight when compared to the leading
engine block material, steel. On average, while still maintaining equal strength, a typical
aluminum part is 50 percent lighter than its steel duplicate; although it has 50 percent
more volume. However, even at the same weight, an aluminum part outperforms a steel
part with the ability to absorb twice the amount of energy [3d].
Aluminum will only retain its strength if it is free from any unwanted defects such
as inclusions of different materials, voids, or air pockets created in the casting process.
During the melting process nitrogen and argon are pumped through the melt to bring all
impurities to the surface of the crucible for removal. Once the impurities have been
removed from the crucible the remaining molten aluminum is still susceptible to the
formation of aluminum oxide (Al2O3) platelets. Aluminum oxide will form whenever air
touches the molten aluminum acting as a protective skin for the melt against any other
impurities.
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