GTBL042-14 GTBL042-Callister-v3 October 2, 2007 13:45
2nd Revised Pages14.3 Casting • 571Metal
blankDie DieDie holderDieTensile
force(a) (b)(c) (d)Dummy
blockForceContainerContainerRollRollRam Billet ExtrusionForceForceDieDieDie
Forged
piece
DieFigure 14.2 Metal deformation during (a) forging, (b) rolling, (c) extrusion, and
(d) drawing.Extrusion
extrusion Forextrusion,a bar of metal is forced through a die orifice by a compressive force
that is applied to a ram; the extruded piece that emerges has the desired shape and a
reduced cross-sectional area. Extrusion products include rods and tubing that have
rather complicated cross-sectional geometries; seamless tubing may also be extruded.Drawing
drawing Drawingis the pulling of a metal piece through a die having a tapered bore by means
of a tensile force that is applied on the exit side. A reduction in cross section results,
with a corresponding increase in length. The total drawing operation may consist of
a number of dies in a series sequence. Rod, wire, and tubing products are commonly
fabricated in this way.14.3 CASTING
Casting is a fabrication process whereby a totally molten metal is poured into a mold
cavity having the desired shape; upon solidification, the metal assumes the shape of
the mold but experiences some shrinkage. Casting techniques are employed when
(1) the finished shape is so large or complicated that any other method would be
impractical, (2) a particular alloy is so low in ductility that forming by either hot or
cold working would be difficult, and (3) in comparison to other fabrication processes,
casting is the most economical. Furthermore, the final step in the refining of even
ductile metals may involve a casting process. A number of different casting techniques
are commonly employed, including sand, die, investment, lost foam, and continuous
casting. Only a cursory treatment of each of these is offered.