PowderMet - POWDER METALLURGY The Characterization of...

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POWDER METALLURGY z The Characterization of Engineering Powders z Production of Metallic Powders z Conventional Pressing and Sintering z Alternative Pressing and Sintering Techniques z Materials and Products for PM z Design Considerations in Powder Metallurgy
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Powder Metallurgy (PM) Metal processing technology in which parts are produced from metallic powders z In the usual PM production sequence, the powders are compressed ( pressed ) into the desired shape and then heated ( sintered ) to bond the particles into a hard, rigid mass z Pressing is accomplished in a press-type machine using punch-and-die tooling designed specifically for the part to be manufactured z Sintering is performed at a temperature below the melting point of the metal
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Why Powder Metallurgy is Important z PM parts can be mass produced to net shape or near net shape , eliminating or reducing the need for subsequent machining z PM process wastes very little material - about 97% of the starting powders are converted to product z PM parts can be made with a specified level of porosity, to produce porous metal parts z Examples: filters, oil-impregnated bearings and gears
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More Reasons Why PM is Important z Certain metals that are difficult to fabricate by other methods can be shaped by powder metallurgy z Example: Tungsten filaments for incandescent lamp bulbs are made by PM z Certain alloy combinations and cermets made by PM cannot be produced in other ways z PM compares favorably to most casting processes in dimensional control z PM production methods can be automated for economical production
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Limitations and Disadvantages with PM Processing z High tooling and equipment costs z Metallic powders are expensive z Problems in storing and handling metal powders z Examples: degradation over time, fire hazards with certain metals z Limitations on part geometry because metal powders do not readily flow laterally in the die during pressing z Variations in density throughout part may be a problem, especially for complex geometries
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PM Work Materials z Largest tonnage of metals are alloys of iron, steel, and aluminum z Other PM metals include copper, nickel, and refractory metals such as molybdenum and tungsten z Metallic carbides such as tungsten carbide are often included within the scope of powder metallurgy
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Figure 16.1 - A collection of powder metallurgy parts (courtesy of Dorst America, Inc.)
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Engineering Powders A powder can be defined as a finely divided particulate solid z Engineering powders include metals and ceramics z Geometric features of engineering powders: z Particle size and distribution z Particle shape and internal structure z Surface area
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Measuring Particle Size z Most common method uses screens of different mesh sizes z Mesh count - refers to the number of openings per linear inch of screen z A mesh count of 200 means there are 200 openings per linear inch z Since the mesh is square, the count is the same in both directions, and the total number of openings per square inch is 200 2 = 40,000 z Higher mesh count means smaller particle size
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Figure 16.2 - Screen mesh for sorting particle sizes
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shapes in powder metallurgy
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This note was uploaded on 04/08/2012 for the course INDUSTRIAL IE 502 taught by Professor Meric during the Spring '12 term at Fatih Üniversitesi.

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PowderMet - POWDER METALLURGY The Characterization of...

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