Ch17 metal powders Erdi Karaçal Mechanical Engineer University of Gaziantep

Chapter 17
Processing of Metal Powders
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.
ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Parts Made by Powder-Metallurgy
(a)
(b)
Figure 17.1 (a) Examples of typical parts made by powder-metallurgy processes. (b) Upper
trip lever for a commercial sprinkler made by P/M. This part is made of an unleaded brass
alloy; it replaces a die-cast part with a 60% 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 P/M Parts, 1998. Metal Powder Industries Federation,
Princeton, New Jersey, 1998. (c) Courtesy of Zenith Sintered Products, Inc., Milwaukee,
Wisconsin.
(c)

Steps in Making Powder-Metallurgy Parts
Figure 17.2 Outline of processes and operations involved in making powder-metallurgy parts.

Particle Shapes in Metal Powders
Figure 17.3 Particle shapes in metal powders, and the processes by which
they are produced. Iron powders are produced by many of these processes.

Powder Particles
(a) (b)
Figure 17.4 (a) Scanning-electron-microscopy photograph of iron-powder particles made
by atomization. (b) Nickel-based superalloy (Udimet 700) powder particles made by the
rotating electrode process; see Fig 17.5c. Source: Courtesy of P.G. Nash, Illinois
Institute of Technology, Chicago.

Methods of
Metal-Powder
Production by
Atomization
Figure 17.5 Methods of
metal-powder production
by atomization: (a) gas
atomization; (b) water
atomization; (c)
atomization with a rotating
consumable electrode; and
(d) centrifugal atomization
with a spinning disk or cup.

Mechanical Comminution to Obtain Fine Particles
Figure 17.6 Methods of mechanical comminution to obtain fine particles:
(a) roll crushing, (b) ball mill, and (c) hammer milling.

Mechanical Alloying
Figure 17.7 Mechanical alloying of nickel particles with dispersed smaller particles. As nickel
particles are flattened between the two balls, the second smaller phase is impresses into the
nickel surface and eventually is dispersed throughout the particle due to successive flattening,
fracture, and welding events.

Bowl Geometries in Blending
Metal Powders
(e)
Figure 17.8 (a) through (d) Some common bowl geometries for mixing or blending
powders. (e) A mixer suitable for blending metal powders. Since metal powders are
abrasive, mixers rely on the rotation or tumbling of enclosed geometries as opposed to
using aggressive agitators. Source: Courtesy of Gardner Mixers, Inc.

Compaction
Figure 17.9 (a) Compaction of metal powder to form a bushing. The pressed-powder
part is called green compact. (b) Typical tool and die set for compacting a spur gear.
Source: Courtesy of Metal Powder Industries Federation.

Density as a Function of
Pressure and the Effects of
Density on Other Properties
Figure 17.10 (a) Density of copper- and iron-powder
compacts as a function of compacting
pressure. Density greatly influences the
mechanical and physical properties of P/M
parts. (b) Effect of density on tensile strength,
elongation, and electrical conductivity of
copper powder. Source: (a) After F. V. Lenel,
(b) IACS: International Annealed Copper
Standard (for electrical conductivity).

Density Variation in Compacting Metal Powders
Figure 17.11 Density variation in compacting metal powders in various dies: (a) and
(c) single-action press; (b) and (d) double-action press. Note in (d) the greater
uniformity of density from pressing with two punches with separate movements when
compared with (c). (e) Pressure contours in compacted copper powder in a single-action
press. Source: After P. Duwez and L. Zwell.

Compacting Pressures for Various Powders

Press for
Compacting Metal
Powder
Figure 17.12 A 7.3-mn (825-ton)
mechanical press for compacting
metal powder. Source: Courtesy
of Cincinnati Incorporated.

Cold Isostatic Pressing
Figure 17.13 Schematic diagram of cold isostatic pressing, as applied to forming a
tube. The powder is enclosed in a flexible container around a solid-core rod.
Pressure is applied isostatically to the assembly inside a high-pressure chamber.
Source: Reprinted with permission from R. M. German, Powder Metallurgy Science,
Metal Powder Industries Federation, Princeton, NJ; 1984.

Capabilities Available from P/M Operations
Figure 17.14 Capabilities, with respect to part size and shape complexity, available form
various P/M operations. P/F means powder forging. Source: Courtesy of Metal Powder
Industries Federation.

Hot Isostatic Pressing
Figure 17.15 Schematic illustration of hot isostatic pressing. The pressure
and temperature variation versus time are shown in the diagram.

Valve Lifter for Diesel Engines
Figure 17.16 A valve lifter for heavy-duty diesel engines produced form a hot-isostatic-
pressed carbide cap on a steel shaft. Source: Courtesy of Metal Powder
Industries Federation.

Powder Rolling
Figure 17.17 Schematic illustration of powder rolling.

Spray Deposition
Figure 17.18 Spray deposition (Osprey Process) in which molten metal is
sprayed over a rotating mandrel to produce seamless tubing and pipe.

Sintering Time and Temperature for Metals

Mechanisms for Sintering Metal Powders
Figure 17.19 Schematic illustration of two mechanisms for sintering metal
powders: (a) solid-state material transport; and (b) vapor-phase material transport.
R = particle radius, r = neck radius, and p = neck-profile radius.

Mechanical Properties of P/M Materials

Comparison of Properties of Wrought and Equivalent P/M Metals

Mechanical Property Comparisons for Titanium Alloy

Design Considerations for P/M
• The shape of the compact must be kept as simple and uniform as possible.
• Provision must be made for ejection of the green compact without damaging the
compact.
• P/M parts should be made with the widest acceptable tolerances to maximize tool life.
• Part walls should not be less than 1.5 mm thick; thinner walls can be achieved on
small parts; walls with length-to-thickness ratios above 8:1 are difficult to press.
• Steps in parts can be produced if they are simple and their size doesn’t exceed 15%
of the overall part length.
• Letters can be pressed if oriented perpendicular to the pressing direction. Raised
letters are more susceptible to damage in the green stage and prevent stacking.
• Flanges or overhangs can be produced by a step in the die.
• A true radius cannot be pressed; instead use a chamfer.
• Dimensional tolerances are on the order of ±0.05 to 0.1 mm. Tolerances improve
significantly with additional operations such as sizing, machining and grinding.

Die Design for Powder-Metal Compaction
Figure 17.20 Die geometry and design features for powder-metal compaction.
Source: Courtesy of Metal-Powder Industries Federation

Poor and Good
Designs of P/M
Parts
Figure 17.21 Examples of P/M
parts showing poor and good
designs. Note that sharp radii
and reentry corners should be
avoided and that threads and
transverse holes have to be
produced separately by
additional machining operations.
Source: Courtesy of Metal
Powder Industries Federation.

Design Features for Use with Unsupported
Flanges or Grooves
Figure 17.22 (a) Design features for use with unsupported flanges. (b) Design
features for use with grooves. Source: Courtesy of Metal Powder Industries Federation.

Use of Smooth Transitions in Molds
Figure 17.23 The use of smooth transitions in molds for powder-injection
molding to ensure uniform metal-powder distribution throughout a part.

Ch17 metal powders Erdi Karaçal Mechanical Engineer University of Gaziantep

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