Lecture 18 - Powder Metallurgy techi.ppt

important

1. Powder MetallurgyPowder Metallurgy
Bill PedersenBill Pedersen
ME 355ME 355

2. Example PartsExample Parts

3. Basic Steps In Powder Metallurgy Basic Steps In Powder Metallurgy
(P/M)(P/M)

Powder ProductionPowder Production

Blending or MixingBlending or Mixing

CompactionCompaction

SinteringSintering

FinishingFinishing

4. Powder Powder
ProductionProduction

Atomization the most Atomization the most
commoncommon

OthersOthers

Chemical reduction of Chemical reduction of
oxidesoxides

Electrolytic depositionElectrolytic deposition

Different shapes Different shapes
producedproduced

Will affect compaction Will affect compaction
process significantlyprocess significantly

5. Blending or MixingBlending 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 alloyspowders that are used to build up the alloys

Master alloys are with the normal alloy ingredientsMaster 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 manufacturerpowder producer or the P/M parts manufacturer

When the particles are blended:When the particles are blended:

Desire to produce a homogenous blendDesire 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 processvariability in the sintering process

6. CompactionCompaction

Usually gravity filled Usually gravity filled
cavity at room cavity at room
temperaturetemperature

Pressed at 60-100 ksiPressed at 60-100 ksi

Produces a “Green” Produces a “Green”
compactcompact

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 concernpart – handling concern

Friction between Friction between
particles is a major particles is a major
factorfactor

7. Isostatic Isostatic
PressingPressing
• 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. SinteringSintering

Parts are heated to Parts are heated to
~80% of melting ~80% of melting
temperaturetemperature

Transforms compacted Transforms compacted
mechanical bonds to mechanical bonds to
much stronger metal much stronger metal
bondsbonds

Many parts are done at Many parts are done at
this stage. Some will this stage. Some will
require additional require additional
processingprocessing

9. Sintering ctdSintering ctd

Final part properties Final part properties
drastically affecteddrastically affected

Fully sintered is not Fully sintered is not
always the goalalways the goal

Ie. Self lubricated bushingsIe. Self lubricated bushings

Dimensions of part are Dimensions of part are
affectedaffected

10. Die Design for P/MDie 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/MAdvantages 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 processby 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 utilizationVery good material utilization

12. Disadvantages of P/MDisadvantages of P/M

Limited in size capability due to large forces Limited in size capability due to large forces

Specialty machinesSpecialty machines

Need to control the environment – corrosion Need to control the environment – corrosion
concernconcern

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 – specialtythat design can be more – specialty

Less well known processLess well known process

13. Financial ConsiderationsFinancial Considerations

Die design – must withstand Die design – must withstand
100 ksi, requiring specialty 100 ksi, requiring specialty
designsdesigns

Can be very automatedCan be very automated

1500 parts per hour not 1500 parts per hour not
uncommon for average size partuncommon 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 pressa rolling press

Typical size part for Typical size part for
automation is 1” cubeautomation 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)