Page 458 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

38 Chapter 17 Powd er-Metal Processing and Equipment

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(H) (D) (C)
FIGURE l7.| (a) Examples of typical parts made by powder-metallurgy processes. (b) Upper
trip lever for a commercial irrigation sprinkler made by PM. This part is made of an unleaded
brass alloy; it replaces a die-cast part with a 60% cost savings. (c) Main-bearing metal-powder
caps for 3.8- and 3.1-liter General Motors automotive engines. Source: (a) and (b) Reproduced
with permission from Success Stories on PM Parts, 1998. Metal Powder Industries Federation,
Princeton, New Jersey, 1998. (c) Courtesy of Zenith Sintered Products, Inc., Milwaukee,
Wisconsin.

now constitute about 70% of the PM market) such as piston rings, connecting
rods, brake pads, gears, cams, and bushings; (c) tool steels, tungsten carbides, and
cermets as tool and die materials; (d) graphite brushes impregnated with copper for
electric motors; (e) magnetic materials; (f) metal filters and oil-impregnated bear-
ings with controlled porosity; lg) metal foams; (h) surgical implants, and (i) several
others for aerospace, nuclear, and industrial applications. Advances in this technol-
ogy now permit structural parts of aircraft, such as landing gear components,
engine-mount supports, engine disks, impellers, and engine nacelle frames, to be
made by PM.
Powder metallurgy has become competitive with processes such as casting,
forging, and machining, particularly for relatively complex parts made of high-
strength and hard alloys. Although most parts weigh less than 2.5 kg, they can
weigh as much as 50 kg. It has been shown that PM parts can be mass-produced
economically in quantities as small as 5000 per year and as much as 100 million per
year for vibrator weights for cell phones.
The most commonly used metals in PM are iron, copper, aluminum, tin, nickel,
titanium, and the refractory metals. For parts made of brass, bronze, steels, and
stainless steels, prealloyed powders are used, where each powder particle itself is an
alloy. Metal sources are generally bulk metals and alloys, ores, salts, and other
compounds.

l7.2 Production of Metal Powders

The powder-metallurgy process typically consists of the following operations, in
sequence (Fig. 17.2):

Powder production;
I
2. Blending;
3. Compaction;
4. Sintering;
5. Finishing operations.