12.8 CONTROLLED POROSITY
177
Figure 12.3 Hollow a aluminum automotive suspension arm and b resin-
bonded sand core. Courtesy of Teksid.
of the metal causes the resin to combust and the core can be removed from the casting as loose sand.
Die casting component producers have experimented with lost- core processes for several years. Finding a material is difficult.
Several conflicting requirements must be met. The core material must withstand erosion during metal injection. The material must
remain dimensionally stable under high pressures. After solidifi- cation, the core material must be easily removed. Trials have been
conducted using salt core materials and low melting point alloys. Although these materials survive the metal injection, removal of
the cores is time consuming and costly.
Resin-bonded sand was abandoned years ago because sand cores could not stand up to the high metal injection velocities
encountered in die casting. However, this technology is being re- examined for use with squeeze casting. Since metal velocities are
significantly less for squeeze casting, sand cores may survive. Ex- perimentation is currently underway to prove this potential solu-
tion.
12.8 CONTROLLED POROSITY
Porosity is a defect commonly found in die cast components. However, if the porosity does not affect fit or function, one cannot
call it a defect.
178
FUTURE DEVELOPMENTS IN DIE CASTING
With this philosophy in mind, experimentation is being con- ducted to produce die cast components with a controlled amount
of porosity. This approach, although counterintuitive, is also being studied intensely by the injection molding industry. Benefits of
this technology are reduced weight and less material usage. Can- didates for this technology are limited to nonstructural applica-
tions.
12.9 INNOVATIONS CONTINUE
Numerous other projects are underway related to high integrity die casting processes. Some research is focusing on casting ma-
chine development. Other work is underway to extend tooling life. Although some future developments related to high integrity die
casting processes can be predicted, one can only speculate as to the state of this art in years to come.
REFERENCES
1. Adachi, M., and S. Sato, ‘‘Advanced Rheocasting Process Improved Quality and Competitiveness,’’ SAE Paper Number 2000-01-0677, Society of Au-
tomotive Engineers, Warrendale, PA, 2000. 2. Zehe, R. ‘‘First Production Machine for Rheocasting,’’ Light Metal Age,
October 1999, p. 62. 3. Wang, G., K. Stewart, R. Berkmortel, and J. Skar, ‘‘Corrosion Prevention
for External Magnesium Automotive Components,’’ SAE Paper Number 2001-01-0421, Society of Automotive Engineers, Warrendale, PA, 2001.
4. Powell, B., A. Luo, V. Rezhets, J. Bommarito, and B. Tiwari, ‘‘Development of Creep-Resistant Magnesium Alloys for Powertrain Applications: Part 1,’’
SAE Paper Number 2001-01-0422, Society of Automotive Engineers, War- rendale, PA, 2001.
5. Luo, A., M. Balogh, and B. Powell, ‘‘Development of Creep-Resistant Mag- nesium Alloys for Powertrain Applications: Part 2,’’ SAE Paper Number
2001-01-0423, Society of Automotive Engineers, Warrendale, PA, 2001. 6. Larsen, D., and G. Colvin, ‘‘Vacuum-Die Casting Titanium for Aerospace
and Commercial Components,’’ Journal of Metals, June 1999, p. 26. 7. Larsen, D., ‘‘Vacuum-Die Casting Yields Quality Parts,’’ Foundry Manage-
ment and Technology, February 1998, p. 32.
8. Wilks, T., ‘‘Cost-effective Magnesium MMCs,’’ Advanced Materials and Processes,
August 1992, p. 27.
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