Page 388 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

368 Chapter 15 Metal Extrusion and Drawing Processes and Equipment

EXAMPLE l5.2 Manufacture of Aluminum Heat Sinks
Aluminum is used Widely to transfer heat for both standpoint using computer simulations. The fins are
cooling and heating applications because of its very very difficult and expensive to machine, forge, or roll
high thermal conductivity. In fact, on a Weight-to-cost form. However, the tooling for hot extrusion can be
basis, no other material conducts heat as economically produced through electricahdischarge machining
as does aluminum. (Section 27.5 ), so the process is favorable economically.
Hot extrusion of aluminum is preferred for heat- Figure 15 .11b shows a die and a hot-extruded
sink applications, such as those in the electronics cross section suitable to serve as a heat sink. The
industry. Figure 15 .1 1a shows an extruded heat sink shapes shown could be produced through a casting
used to remove heat from a transformer on a printed operation, but extrusion is preferred, since there is
circuit board. Heat sinks usually are designed with a no internal porosity and the thermal conductivity is
large number of fins that are intended to maximize the slightly higher.
surface area and are evaluated from a thermodynamics

(bl
(H)
FIGURE |5.| I (a) Aluminum extrusion used as a heat sink for a printed circuit board, (b) Extrusion die and
extruded heat sinks. Source: Courtesy of Aluminum Extruders Council.

l5.4 Cold Extrusion

Developed in the 1940s, cold extrusion is a general term that often denotes
a combination of operations, such as direct and indirect extrusion and forging
(Fig. 15.12). Cold extrusion is used Widely for components in automobiles, mo-
torcycles, bicycles, and appliances and in transportation and farm equipment.
The cold-extrusion process uses slugs cut from cold-finished or hot-rolled
bars, Wire, or plates. Slugs that are less than about 40 mm in diameter are sheared
(cropped), and if necessary, their ends are squared off by processes such as upsetting,
machining, or grinding. Larger diameter slugs are machined from bars into specific
lengths. Cold-extruded parts weighing as much as 45 kg and having lengths of up to
2 In can be made, although most parts weigh much less. Powder-metal slugs (pre-
forms) also may be cold extruded.