CH 14 - Powder Metallurgy.ppt
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Transcript of CH 14 - Powder Metallurgy.ppt
XII 1
Practical MetallurgyMEC 172
Introduction
Powder Metallurgy is one of the four methods of forming metal: casting molten metal plastic deformation of hot or cold metal machining
PM was developed by the auto industry- still the greatest user
XII 2
Advantages of PM
Good surface finish can be obtained
Suited for high volume of production of small parts
Almost any combination of alloys can be used to produce high temperature components
Close dimensional tolerances
Eliminates/Minimizes machiningXII 3
Disadvantages of PM
Compared with solid material:
Lower resistance to corrosionPoorer plastic properties
Reduced impact strength Less ductility Reduced elongation
XII 4
Products made of PM
Cutting tools such as tungsten carbide inserts and cerments
Precision parts such as cams gears
Antifriction materials bearings that are self lubricating
High strength magnets
Jet engine turbine bladesXII 5
Steps to manufacture PM parts1. Blending – mixing metal powders with alloys
and lubricants until blended
2. Compacting – powders are fed into a precision die and pressed at 10 to 60 tons/in2 The parts ejected are call briquette or green
compact
3. Sintering – heating the green part in a controlled atmosphere just under the melting point to bond the compressed powders
XII 6
Powder Metallurgy Presses The most common is a simple die
compacting
Advanced process such as isostatic [pg. 245] pressing formed without die or
traditional press
XII 7
Simple Die Compacting
Usually very Small parts
Compacted to 20 to 30 tons/in2
XII 8
Cold and Hot Compaction Metal powder separated into two divisions:
Cold and Hot
Isopressing For hollow hemispheres or cones Chamber is pressurized to 50 to 60,000 psi with
liquid or gas Pressure is equal on all sides
Cold Isostatic pressing Powder is loaded into molds of rubber or plastics Placed under pressure at room temperature
XII 9
Metal Powders
Range ins size from .0001in to .002in diameter
Produced by several methods: Mechanical Milling Chemical Reduction Shotting Atomization
XII 10
Sintering
Solid phase sintering at 1.5 to 2 hours at 60 to 80 percent of melting point
Liquid phase is carried out at the melting point of one of the alloy metals Diffusion Densification Recrystallization & Grain Growth
XII 11
Advanced Processes
Powder Forging
Metal powder injection molding similar to plastic injection molding
Powder extrusion
XII 12
Powder Metallurgy Products & Uses Pre-lubricated bearings
Food and textile industries
Small motors lubricated for life – Oilite bearings
Aluminum based anti friction materials
Creep resistant alloys made from tungsten molybdeum and tantalum
Cutting tools: i.e. cobalt
Metallic brake shoes XII 13