Page 293 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

272 Chapter 11 Metal-Casting Processes and Equipment

CASE STUDY I.l Lost-foam Casting of Engine Blocks
I
One of the most important components in an Mercury Marine also was in the midst of
internal combustion engine is the engine block; it developing a new V6 engine utilizing a new corrosion-
provides the basic structure that encloses the pistons resistant aluminum alloy with increased wear
and cylinders and thus encounters significant resistance. This engine design also required a cylinder
pressure during operation. Recent industry trends block and head integration, featuring hollow sections
have focused upon high-quality, low-cost lightweight for water jacket cooling that could not be cored out in
designs; additional economic benefits can be attained die casting or semipermanent mold processes (used
through casting more complex geometries and by for its other V6 blocks). Based on the success the
incorporating multiple components into one part. foundry had with the three-cylinder lost-foam block,
Recognizing that evaporative-pattern (lost-foam) engineers applied this process for casting the V6 die
casting can simultaneously satisfy all of these block (Fig. 11.12b). The new engine block involves
requirements, Mercury Castings built a lost-foam only one casting that is lighter and cheaper than the
casting line to produce aluminum engine blocks and previous designs. Produced with an integrated cylinder
cylinder heads. head and exhaust and cooling system, this component
One example of a part produced through is cast hollow to create more efficient water jacket
lost-foam casting is a 45 kW, three-cylinder engine cooling of the engine during its operation.
block used for marine applications and illustrated The company also has developed a pressurized
in Fig. 11.12a. Previously manufactured as eight lost-foam process. First a foam pattern is made,
separate die castings, the block was converted to a placed in a flask, and surrounded by sand. Then
single 10 kg casting, with a weight and cost savings the flask is inserted into a pressure vessel where a
of 1 kg and $25 on each block, respectively. Lost- robot pours molten aluminum onto the polystyrene
foam casting also allowed consolidation of the pattern. A lid on the pressure vessel is closed, and
engine’s cylinder head and exhaust and cooling a pressure of 1 MPa is applied to the casting until
systems into the block, thus eliminating the it solidifies (in about 15 minutes). The result is a
associated machining operations and fasteners casting with better dimensional accuracy, lower
required in sand-cast or die-cast designs. In addition, porosity, and improved strength as compared to
since the pattern contained holes, and these could be conventional lost-foam casting.
cast without the use of cores, numerous drilling
operations were eliminated. Source: Courtesy of Mercury Marine.

(H) (D)
FIGURE ll.|2 (a) Metal is poured into a mold for lost-foam casting of a
60-hp, three-cylinder marine engine; (b) finished engine block. Source: Mercury
Marine.