Ch17 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.

Chapter 17Processing of Metal Powders


Parts Made by Powder-Metallurgy

Figure 17.1 (a) Examples of typical parts made by powder-metallurgy processes. (b) Uppertrip lever for a commercial sprinkler made by P/M. This part is made of an unleaded brassalloy; it replaces a die-cast part with a 60% savings. (c) Main-bearing metal-powder caps for3.8 and 3.1 liter General Motors automotive engines. Source: (a) and (b) Reproduced withpermission 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.

(a)

(b)

(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 whichthey are produced. Iron powders are produced by many of these processes.


Powder Particles

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

(a) (b)


Methods ofMetal-PowderProduction byAtomization

Figure 17.5 Methods ofmetal-powder productionby atomization: (a) gasatomization; (b) wateratomization; (c)atomization with a rotatingconsumable electrode; and(d) centrifugal atomizationwith 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 nickelparticles are flattened between the two balls, the second smaller phase is impresses into thenickel surface and eventually is dispersed throughout the particle due to successive flattening,fracture, and welding events.


Bowl Geometries in BlendingMetal Powders

(e)

Figure 17.8 (a) through (d) Some common bowl geometries for mixing or blendingpowders. (e) A mixer suitable for blending metal powders. Since metal powders areabrasive, mixers rely on the rotation or tumbling of enclosed geometries as opposed tousing aggressive agitators. Source: Courtesy of Gardner Mixers, Inc.


Compaction

Figure 17.9 (a) Compaction of metal powder to form a bushing. The pressed-powderpart 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 ofPressure and the Effects ofDensity on Other Properties

Figure 17.10 (a) Density of copper- and iron-powder compacts as a function of compactingpressure. Density greatly influences themechanical and physical properties of P/Mparts. (b) Effect of density on tensile strength,elongation, and electrical conductivity ofcopper powder. Source: (a) After F. V. Lenel,(b) IACS: International Annealed CopperStandard (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 greateruniformity of density from pressing with two punches with separate movements whencompared 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 forCompacting Metal

Powder

Figure 17.12 A 7.3-mn (825-ton)mechanical press for compactingmetal powder. Source: Courtesyof Cincinnati Incorporated.


Cold Isostatic Pressing

Figure 17.13 Schematic diagram of cold isostatic pressing, as applied to forming atube. 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 formvarious P/M operations. P/F means powder forging. Source: Courtesy of Metal PowderIndustries Federation.


Hot Isostatic Pressing

Figure 17.15 Schematic illustration of hot isostatic pressing. The pressureand 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 PowderIndustries Federation.


Powder Rolling

Figure 17.17 Schematic illustration of powder rolling.


Spray Deposition

Figure 17.18 Spray deposition (Osprey Process) in which molten metal issprayed 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 metalpowders: (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 GoodDesigns of P/M

Parts

Figure 17.21 Examples of P/Mparts showing poor and gooddesigns. Note that sharp radiiand reentry corners should beavoided and that threads andtransverse holes have to beproduced separately byadditional machining operations.Source: Courtesy of MetalPowder Industries Federation.


Design Features for Use with UnsupportedFlanges or Grooves

Figure 17.22 (a) Design features for use with unsupported flanges. (b) Designfeatures 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-injectionmolding to ensure uniform metal-powder distribution throughout a part.