Production of A357 motor mount bracket by the metal compression forming process Page: 4 of 26
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mold cavity, limiting their ductility and fatigue strength and making them unsuitable as safety
critical structural components. The Metal Compression Forming (MCF) process, a variant of the
squeeze casting process, allows the manufacture of pore-free cast aluminum alloy components with
properties comparable to forged parts. This allows cast aluminum alloy parts to be used in safety
critical structural applications requiring high tensile strength and ductility, and importantly, high
fatigue strength, particularly for automotive applications.
The formation of gas porosity cannot usually be avoided in traditional gravity assisted casting
processes. In addition, in both gravity assisted filling or in rapid metal injection such as in high
pressure die casting, turbulence during filling of the mold cavity introduces trapped gas and oxide
films into the casting, creating defects that cause castings to fail prematurely under cyclic loading.
The MCF process can use low-pressure bottom-filling to allow the filling of the mold cavity in a
quiescent manner and avoid the formation of trapped gas pockets and oxide films. In addition, in
the MCF process, molten metal is allowed to solidify under pressure in order to close porosity and
form a sound part. The MCF process applies pressure on the entire mold face, thereby directing
pressure uniformly on all regions of the casting and producing a uniformly sound part.
Processes such as indirect squeeze casting that apply pressure on the gate area via a plunger also
use pressure during solidification to eliminate porosity. However, parts made by the indirect
squeeze casting process may be sound near the gate where pressure is applied, but may exhibit
higher levels of porosity away from the gate, making certain areas of the casting weaker than
others. In addition, the introduction of molten metal into a cavity by the use of a plunger promotes
turbulence during filling, trapping gas pockets and oxide films that weaken the casting. Figure 1
shows the calculated pressure distribution' for a given temperature distribution in Al-4.5% Cu
alloy, indicating that a rapid drop in pressure can occur in the mushy zone of aluminum alloys.
Figure 2 shows a schematic of the indirect squeeze casting process, and the expected non-uniform
pressure distribution during solidification. Figure 3 shows a schematic of the MCF process, and
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Viswanathan, S.; Brinkman, C.R.; Porter, W.D. & Purgert, R.M. Production of A357 motor mount bracket by the metal compression forming process, article, September 1, 1997; Tennessee. (digital.library.unt.edu/ark:/67531/metadc690952/m1/4/: accessed January 22, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.