Lecture 18 - Powder Metallurgy techi.ppt
- 1. Powder Metallurgy Powder Metallurgy Bill Pedersen Bill Pedersen ME 355 ME 355
- 3. Basic Steps In Powder Metallurgy Basic Steps In Powder Metallurgy (P/M) (P/M) Powder Production Powder Production Blending or Mixing Blending or Mixing Compaction Compaction Sintering Sintering Finishing Finishing
- 4. Powder Powder Production Production Atomization the most Atomization the most common common Others Others Chemical reduction of Chemical reduction of oxides oxides Electrolytic deposition Electrolytic deposition Different shapes Different shapes produced produced Will affect compaction Will affect compaction process significantly process significantly
- 5. Blending or Mixing Blending or Mixing Can use master alloys, (most commonly) or elemental Can use master alloys, (most commonly) or elemental powders that are used to build up the alloys powders that are used to build up the alloys Master alloys are with the normal alloy ingredients Master alloys are with the normal alloy ingredients Elemental or pre-alloyed metal powders are first Elemental or pre-alloyed metal powders are first mixed with lubricants or other alloy additions to mixed with lubricants or other alloy additions to produce a homogeneous mixture of ingredients produce a homogeneous mixture of ingredients The initial mixing may be done by either the metal The initial mixing may be done by either the metal powder producer or the P/M parts manufacturer powder producer or the P/M parts manufacturer When the particles are blended: When the particles are blended: Desire to produce a homogenous blend Desire to produce a homogenous blend Over-mixing will work-harden the particles and produce Over-mixing will work-harden the particles and produce variability in the sintering process variability in the sintering process
- 6. Compaction Compaction Usually gravity filled Usually gravity filled cavity at room cavity at room temperature temperature Pressed at 60-100 ksi Pressed at 60-100 ksi Produces a “Green” Produces a “Green” compact compact Size and shape of Size and shape of finished part (almost) finished part (almost) Not as strong as finished Not as strong as finished part – handling concern part – handling concern Friction between Friction between particles is a major particles is a major factor factor
- 7. Isostatic Isostatic Pressing Pressing • Because of friction between Because of friction between particles particles • Apply pressure uniformly from Apply pressure uniformly from all directions (in theory) all directions (in theory) • Wet bag (left) Wet bag (left) • Dry bag (right) Dry bag (right)
- 8. Sintering Sintering Parts are heated to Parts are heated to ~80% of melting ~80% of melting temperature temperature Transforms compacted Transforms compacted mechanical bonds to mechanical bonds to much stronger metal much stronger metal bonds bonds Many parts are done at Many parts are done at this stage. Some will this stage. Some will require additional require additional processing processing
- 9. Sintering ctd Sintering ctd Final part properties Final part properties drastically affected drastically affected Fully sintered is not Fully sintered is not always the goal always the goal Ie. Self lubricated bushings Ie. Self lubricated bushings Dimensions of part are Dimensions of part are affected affected
- 10. Die Design for P/M Die Design for P/M Thin walls and projections create fragile tooling. Thin walls and projections create fragile tooling. Holes in pressing direction can be round, square, D- Holes in pressing direction can be round, square, D- shaped, keyed, splined or any straight-through shaped, keyed, splined or any straight-through shape. shape. Draft is generally not required. Draft is generally not required. Generous radii and fillets are desirable to extend tool Generous radii and fillets are desirable to extend tool life. life. Chamfers, rather the radii, are necessary on part Chamfers, rather the radii, are necessary on part edges to prevent burring. edges to prevent burring. Flats are necessary on chamfers to eliminate feather- Flats are necessary on chamfers to eliminate feather- edges on tools, which break easily. edges on tools, which break easily.
- 11. Advantages of P/M Advantages of P/M Virtually unlimited choice of Virtually unlimited choice of alloys, composites, and alloys, composites, and associated properties associated properties Refractory materials are popular Refractory materials are popular by this process by this process Controlled porosity for self Controlled porosity for self lubrication or filtration uses lubrication or filtration uses Can be very economical at Can be very economical at large run sizes (100,000 parts) large run sizes (100,000 parts) Long term reliability through Long term reliability through close control of dimensions close control of dimensions and physical properties and physical properties Wide latitude of shape and Wide latitude of shape and design design Very good material utilization Very good material utilization
- 12. Disadvantages of P/M Disadvantages of P/M Limited in size capability due to large forces Limited in size capability due to large forces Specialty machines Specialty machines Need to control the environment – corrosion Need to control the environment – corrosion concern concern Will not typically produce part as strong as Will not typically produce part as strong as wrought product. (Can repress items to wrought product. (Can repress items to overcome that) overcome that) Cost of die – typical to that of forging, except Cost of die – typical to that of forging, except that design can be more – specialty that design can be more – specialty Less well known process Less well known process
- 13. Financial Considerations Financial Considerations Die design – must withstand Die design – must withstand 100 ksi, requiring specialty 100 ksi, requiring specialty designs designs Can be very automated Can be very automated 1500 parts per hour not 1500 parts per hour not uncommon for average size part uncommon for average size part 60,000 parts per hour achievable 60,000 parts per hour achievable for small, low complexity parts in for small, low complexity parts in a rolling press a rolling press Typical size part for Typical size part for automation is 1” cube automation is 1” cube Larger parts may require special Larger parts may require special machines (larger surface area, machines (larger surface area, same pressure equals larger same pressure equals larger forces involved) forces involved)