powder metallurgy
Post on 14-Dec-2015
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Powder MetallurgyTRANSCRIPT
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POWDER METALLURGY
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Introduction• Highly developed method of manufacturing
precision metal parts.
• Concerned with the production of metal powders and converted them to useful shape.
• It is a material processing technique in which particulate materials are consolidated to semi-finished products.
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History• Early Egyptians iron implants which date
from at least 3000 BC.
• In Greece the manufacture of iron components were widespread in 800-600 BC.
• Manufacture of large objects were known to Indians as early as 300 AD.
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• Wollaston (England) and Sobolevskiy (Russia)-early nineteenth century for processing platinum.
• The first modern PM product was the tungsten filament for electric light bulbs developed in the early 1900s.
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Advantages
• Complex shapes can be produced
• Scrap is eliminated or reduced
• Wide composition variations are possible
• Eliminates or minimizes machining
• High production rates
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Disadvantages
• Inferior strength properties
• High material cost
• the size will always change on sintering.
• potential workforce health problems from atmospheric contamination of the workplace.
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•Atomization
Produces a liquid-metal stream by injecting molten metal through small orifice. The stream is broken up by jets of inert gas, air, or water.
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Reduction- Uses gases (hydrogen and CO) to remove oxygen from metal oxides.
Electrolytic deposition- Utilizes aqueous solutions. Produces purest form of metal powder.
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Mechanical alloying
-Powders of two or more pure metals are mixed in a ball mill. This process forms alloy powders
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Basic Steps In Powder Metallurgy (P/M)
1. Powder Production2. Blending or Mixing3. Compaction4. Sintering5. Finishing
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Powder Production
• Atomization the most common• Others
– Chemical reduction of oxides– Electrolytic deposition
• Different shapes produced– Will affect compaction process
significantly
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Blending or Mixing• Can use master alloys, (most commonly) or
elemental powders that are used to build up the alloys– Master alloys are with the normal alloy
ingredients
• Elemental or pre-alloyed metal powders are first mixed with lubricants or other alloy additions to produce a homogeneous mixture of ingredients
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Blending or Mixing
• The initial mixing may be done by either the metal powder producer or the P/M parts manufacturer.
• When the particles are blended:– Desire to produce a homogenous blend– Over-mixing will work-harden the
particles and produce variability in the sintering process
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EQUIPMENT USED IN MIXING:
DOUBLE CONE MIXER
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Compaction
• Usually gravity filled cavity at room temperature
• Pressed at 60-100 ksi• Produces a “Green”
compact– Size and shape of
finished part (almost)– Not as strong as
finished part – handling concern
• Friction between particles is a major factor
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Isostatic Pressing
• Because of friction between particles Because of friction between particles
• Apply pressure uniformly from all directions (in Apply pressure uniformly from all directions (in theory)theory)
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Sintering• Parts are heated to
~80% of melting temperature
• Transforms compacted mechanical bonds to much stronger metal bonds
• Many parts are done at this stage. Some will require additional processing
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• Final part properties drastically affected
• Fully sintered is not always the goal– ex. Self lubricated bushings
• Dimensions of part are affected
Sintering
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Die Design for P/M• Thin walls and projections create fragile tooling.
• Holes in pressing direction can be round, square, D-shaped, keyed, splined or any straight-through shape.
• Draft is generally not required.
• Generous radii and fillets are desirable to extend tool life.
• Chamfers, rather the radii, are necessary on part edges to prevent burring.
• Flats are necessary on chamfers to eliminate feather-edges on tools, which break easily.
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COMMON USESAutomotive ComponentsMedical Implants Tubing and PipingModelsRestoration projectsKitchenwareSculptures Artistic materialsMachinery
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IMPORTANCE TO SOCIETY
Powder Metallurgy is an effective and profitable material processing route to produce a variety of products for engineering industries.
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CONCLUSIONPowder metallurgy…
• utilizes 95% of the raw material used
• uses less energy compare to any other metal manufacturing