Powder Metallurgy - PROCESS


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MET E 167 (Adaptive Metallurgy / Mechanical Metallurgy) Report.

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Powder Metallurgy - PROCESS

  2. 2. 1. • Blending and mixing (of powders) 2. • Compaction 3. • Sintering Three Major Steps * Optional and finishing secondary operations Powder Metallurgy
  3. 3. Blending – mixing powder of the same chemical composition but different sizes. Mixing – combining powders of different chemistries. Blending and Mixing Powder Metallurgy
  4. 4. Blending and mixing are accomplished by mechanical means: Powder Metallurgy
  5. 5. Except for powders, some other ingredients are usually added: Lubricants: to reduce the particles-die friction Binders: to achieve enough strength before sintering Deflocculants: to improve the flow characteristics during feeding Powder Metallurgy
  6. 6. Compaction Pressure: Cold Isostatic Pressing Hot Isostatic Pressing High Energy RateTechniques Vibratory Compaction Continuous Compaction Forging or Extrusion Pressureless: Slip Casting Gravity Compaction Continuous Pressureless Technique Powder Metallurgy Pressing process Blended powders are pressed in dies under high pressure to form them into the required shape. The work part after compaction is called a green compactor simply a green, the word green meaning not yet fully processed.
  7. 7. COLD ISOSTATIC PRESSING - Placement of powder in flexible rubber mold - Hydrostatic pressurization in chamber by water - Most common pressure of 400 MPa Typical Application: Automotive cylinder liner Compaction - Pressure Powder Metallurgy
  8. 8. Cold Isostatic Pressing Powder Metallurgy
  9. 9. HOT ISOSTATIC PRESSING - powder container is usually made up of high melting point sheet metal Pressurizing media: inert gas Common condition: 100 MPa, 1100°C Advantages: Compacts of 100% density, good metallurgical bonding, good mechanical properties Limitations: wider dimensional tolerances, greater cost & time Powder Metallurgy
  10. 10. Hot Isostatic Pressing Powder Metallurgy
  11. 11. HIGH ENERGY RATETECHNIQUES - Explosive or spark discharge methods are applied in closed die - Short time & high pressures -High punch & die wear, limited tolerances, high cost VIBRATORY COMPACTION - Simultaneous application of pressure & vibration - Use of much lower pressures - Complicated equipment design Powder Metallurgy
  12. 12. CONTINUOUS COMPACTION - Applied to simple shapes (rod, sheet, tube, plate etc) - Flowing loose powder between a set of vertically oriented rolls at much lower speed Powder Metallurgy
  13. 13. Continuous Compaction Powder Metallurgy
  14. 14. FORGING or EXTRUSION • Canning of powder • Heating or evacuation of sealed container followed by forging or evacuation • Mechanical or chemical removal of container material Powder Metallurgy
  15. 15. Typical Compaction Pressure for Various Applications Powder Metallurgy
  16. 16. SLIP CASTING - Preparation of slip (powder suspended in liquid and additives) - Keeping slip in mold made up of fluid absorbing material - Formation of slip casting - Removal of slip followed by drying operation Compaction - Pressureless Powder Metallurgy
  17. 17. CONTINUOUS PRESSURELESS TECHNIQUE - Application of powder in the form of slurry - Consolidation and drying - Used to produce porous sheets for electrodes of nickel- cadmium batteries Powder Metallurgy
  18. 18. Compressed metal powder is heated in a controlled- atmosphere furnace to a temperature below its melting point, but high enough to allow bounding of the particles. Purpose - to increase strength & hardness of a green compact Principal variables – temperature ( generally within 70 – 90% of the melting point of metal or alloy), time (10 min. – 8 hours) & furnace atmosphere Sintering process is concerned with – diffusion (surface of particles as temperature rises) – densification (decreases porosity, increases particle contact area) – recrystallization & grain growth (between particles at the contact area) Sintering Powder Metallurgy
  19. 19. The primary driving force for sintering is not the fusion of material, but formation and growth of bonds between the particles, as illustrated in a series of sketches showing on a microscopic scale the changes that occur during sintering of metallic powders. Powder Metallurgy
  20. 20. Powder Metallurgy
  21. 21. Powder Metallurgy
  22. 22. FINISHING / SECONDARY OPERATIONS 1. Sizing – cold pressing to improve dimensional accuracy 2. Coining or pressing - cold working process, to press details into surface - condensation of sintered product 3. Impregnation - impregnation with heated oil (self lubricated bearings) - oil fills the pores of the part 4. Infiltration - placement of slug of a lower melting point metal against the sintered part - infiltration of molten metal by capillary action - pores are filled with a molten metal 5. Heat treatment , Plating, Painting Powder Metallurgy
  23. 23. Elemental or Alloy metal powders Additives (lubricants or binders) Blending and Mixing Compacting Sintering Optional Secondary Finishing Optional Secondary Manufacturing Finished Powder Metallurgy Product Powder Metallurgy
  24. 24. Finished Powder Metallurgy Products Powder Metallurgy
  25. 25. Powder Metallurgy
  26. 26. Powder Metallurgy
  27. 27. THE END...