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FUTURE DEVELOPMENTS IN DIE CASTING
Figure 12.2 Motor cycle sprocket die cast using an SiC particulate reinforced
aluminum matrix composite. Courtesy of Alcan, Inc.
ously reinforced metal matrix composites are under development for commercial use with high integrity die casting processes. Dis-
continuous reinforced casting alloys are a class of metal matrix composites in which a metal alloy matrix is reinforced with ce-
ramic particles or whiskers. Figure 12.2 is an illustration of a component produced using such a composite with the die casting
process. Discontinuously reinforced composite materials exhibit improved characteristics when compared to traditional casting al-
loys, including
reduced structural weight, increased tensile modulus,
improved yield strength, increased ultimate tensile strength,
improved fatigue limit, improved dynamic response, and
enhanced wear resistance.
12.6 REDUCING TOOLING LEAD TIMES
175
Several aluminum and magnesium metal matrix composites are commercially available utilizing several ceramic reinforcing ma-
terials. Reinforcing materials used with magnesium have been limited to SiC.
8
However, reinforcing materials commonly used with aluminum alloys include SiC, Al
2
O
3
, B
4
C, and flyash.
9–11
Of these reinforcing materials, flyash is the most economically fa-
vorable filler as it is a waste product from coal-burning power plants. Flyash has a raw material cost ranging from 15 to 30
per ton.
Of the high integrity die casting processes presented in this text, semi-solid metalworking is best suited for use with metal matrix
composites. Maintaining homogeneity of the composite is difficult when the composite material is molten due to differences in den-
sities. The thixotropic properties of the semi-solid metal slurry and the stirring inherent in semi-solid metal preparation create
ideal conditions for maintaining composite homogeneity.
12.6 REDUCING TOOLING LEAD TIMES
Speed to market is a necessity in today’s competitive economy. Months, and sometimes weeks, can drastically change a com-
pany’s competitive edge and profitability. A major quandary to any high integrity die casting process is the time required to build
tooling, specifically in the manufacture of the complex casting cavity.
Long tooling lead times frequently force designers to choose other manufacturing strategies. Most manufacturing methods with
short tooling lead times are limited in their ability to produce complex geometries. Typically, hastily tooled components are fab-
ricated assemblies composed of numerous subcomponent parts. Although a product may reach the marketplace before competi-
tors, the product may be very costly. In the drive to reduce product lead times, the economic benefits possible with high integrity die
castings are often sacrificed.
Over the last decade vast improvements in computer hardware, computer-aided design CAD, and computer-aided manufacturing
CAM have made rapid prototyping possible. Often individual components can be manufactured in days or hours, giving today’s
176
FUTURE DEVELOPMENTS IN DIE CASTING
product engineers and designers the ability to evaluate designs quickly. These same rapid prototyping techniques can be applied
to quickly manufacture die casting cavity inserts for use in high integrity die casting processes.
12–14
As the accuracy of CADCAM technology advances, carbon electrodes are being machined with greater precision for use with
plunge electrodischarge machining EDM. Many die-making companies are also using prehardened tool steel inserts manufac-
tured using EDM technology. As carbon electrode technology ad- vances, tool shops may be able to produce die cavities with a
single electrode, eliminating the iterative EDM process commonly used today.
Stereo prototyping methods are also being developed for direct production of die cavity tooling. Instead of using liquid resin, laser
sintering with metal powder has been used in the development of this technology. Experimentation is underway utilizing several dif-
ferent nontraditional metal powders, including polymer-coated zir- conium diboride, bronze–nickel mixtures, and 316 stainless steel.
Casting cavity inserts are also being produced using an indirect form of rapid prototyping. Wax patterns of a casting cavity can
be produced using polymer stereo lithography technology. These patterns can then be investment cast, producing die cast tooling
inserts in H13 tool steel. However, the investment casting method has several problems. Large metal masses such as a casting cavity
inserts are difficult to cast, resulting in porosity and distortion. To overcome these problems, experimentation is underway to test
hollow casting cavity inserts investment cast with a uniform thick- ness.
12.7 LOST-CORE TECHNOLOGIES
A major limitation of high integrity die casting processes is the ability to produce complex internal geometries. Simple coring is
regularly performed, but high integrity castings cannot be pro- duced with undercuts. However, most casting processes that do
not utilize reusable molds regularly produce complex internal ge- ometries, as illustrated in Figure 12.3. With such casting pro-
cesses, the core is lost. In the cases of resin-bonded sand, the heat
