About powder metallurgy process

1. Powder Metallurgy
Unit IV Processing of Powder Metals, Ceramics and Glass
Production of metal powders:
Compaction – Sintering and Finishing – Design considerations for powder
metallurgy and Process capability
– Shaping of ceramics – Forming and shaping of glass – Design
considerations for ceramics and glass – Processing of superconductors.

2. I want a metal cube..not from conventional
methods………like…casting or Forming or by
machining…
Eg; I want to make a metal cube. How to do it?....there are many ways:
-
• Casting
• Forging
• Cut from a rolled bar and then machine it out…..
• Note that in all above cases, the solid form of any part is from a
liquid metal….and then over to different processes …and finally to a
CUBE

3. How about manufacturing like this?
•

4. The technology

5. • A bearing sleeve….. Or……

6. Look at some part shown…

7. Look at some parts…..
Upper trip-lever for a commercial sprinkler system, made of
un-leaded brass alloys by Powder Metallurgy. Replace an item made
by Die casting before. Change to this manufacturing technique has
lead to 60% cost savings……….

8. Look at some parts…..
Main Bearing caps – for GM automotive engines. Done with PM

9. The concept
• Metallic powders are compressed in to desired
‘shape’ and then heated to cause bonding of
those metal particles into a hard rigid mass.
• Heating is done below the melting point of those
parent metal powers.
• Therefore, no liquid phase is involved.
• Desired shape means, shapes of gear, plain-bearing etc.

10. The main stages of Powder
Metallurgy
Metal
powders
Blending
and
Mixing
Compacting Sintering
Further
Finishing
operations…
only if
needed.
1. Metal powders
2. Blending and Mixing
Compacting
3. Sintering
4. Further Finishing
operations…only if needed
The main STAGES in Powder
Metallurgy

11. Metal powder preparation
• A powder can be defined as a
finely divided particulate of
solid.

12. Different attributes to describe a
particle geometry….
• Shape
• Size
• Surface area
• Inter-particle friction
HOT

13. FI
HOT

14. Particle size
• Mentioned in terms of Mesh count
• Mesh count refers to the no.of openings
per linear inch of a screening sieve.
• Eg: If the MC is 50, then 50 square
openings are available per inch.
• width of each opening = 1/50 =0.02 in
• = 0.02 x 25.4 =0.50 mm
• That means max length of particle is
0.5mm
FI
HOT

15. Particle size
• Another popular measure of size of
particle is ‘Aspect ratio’
• = Maximum length of particle .
. Minimum length of same particle
Lmax
Lmin
FI
HOT

16. Metal Powder Production
technicques
. Metal powders are
manufactured in separate
factories. It is a separate
industry. Powder metallurgy
industry is another separate
industry.

17. Three Metal powder production
methods.
1. Atomization
method
2. Chemical method
3. Electrolytic method

19. Melt atomization method with
water spray
Atomization with rotating
‘consumable’ electrode method
FI

20. Atomization
method-1

21. Atomization method 2-melt atomization method
Inert gas /
water jet

22. Atomization
method 3

23. Scanning electron-microscope photo of particles
made by a) Atomization method b) by rotating
electrode method HOT

25. CARBONYL PROCESS
FI

26. SHAPE OF CARBONYL POWDERS
Purity ~ 99.5% ….these powders are very expensive
FI

27. Mechanical communition, pulverization method

28. Blending & Mixing……2nd step in Powder metallurgy process
Binding agents: Al,
Cu..
Defloculants: added to
prevent self cohesion of
parent metal particles, to
allow a free flow during
compacting
Popular lubricants
being mixed up:
Graphite, Mb
disulphide

29. Blending methods

31. • .
In conventional ‘pressing’ operation, we will not get
component with uniform density. This Uniaxial pressing
leads to density variations. The solution is “Isostatic”
pressing, where, attempt is made to apply pressure from
all possible directions, as shown in fig.
CIP (Cold
Isostatic
Pressing): Green
compact is
placed in a
flexible mold
(rubber)
Hydrostatic
pressure is
applied against
the mold to do
compacting of
powders.
Pressure is
reduced, and the
part is removed.
The difference in HIP (Hot Isostatic Pressing is that,
it is done at high temp & pressures. The pressing
medium is Argon or Helium. The mold is not rubber,
but made of sheet steel
Pressing & sintering is done in one step
High density, nearly zero porosity
But, …..expensive. Restricted to aerospace industry
applications
HOT

32. The sintering is usually
carried out at
temperatures between
0.7 – 0.9 times the MP.
Note that the metal
remains un-melted during
sintering. Therefore, no
liquid phase.
Sintering is a HT operation performed on the ‘green
compact’ to bond the metallic particles; done to
increase the strength and hardness.

33. Compacting pressures needed for
various metal powders..
Compacting
force
needed,
F = p Ap
F in N
P in MPa
Ap in mm2

34. Further secondary operations on
the sintered part. (5th stage in Powder Metallurgy)
• Machining is done to give exact shape.
• Machining is done to give dimensional
accuracy. (called ‘sizing’)
• Repressing is done to increase the density
and improve physical properties. (put
again in another die and squeeze the part)
• Coining is a press working operation on
the sintered part to press details into its
surface.

35. FI
End of PPT

36. Ceramics

37. PROCESSING OF CERAMICS
AND CERMETS
• Processing of Traditional Ceramics
• Processing of New Ceramics
• Processing of Cermets
• Product Design Considerations

38. Types of Ceramics and Their
Processing
• Ceramic materials divide into three categories:
1. Traditional ceramics – particulate processing
2. New ceramics – particulate processing
3. Glasses – solidification processing
• The solidification processes for glass are covered in a different
slide set
• The particulate processes for traditional and new ceramics as well
as certain composite materials are covered in this slide set

39. Overview of Ceramics
Particulate Processing
• Traditional ceramics are made from
minerals occurring in nature
– Products include pottery, porcelain, bricks, and
cement
• New ceramics are made from synthetically
produced raw materials
– Products include cutting tools, artificial bones,
nuclear fuels, and substrates for electronic
circuits
• The starting material for all of these items is
powder
Preparation
of starting
materials
Pressing
(shape
forming)
Drying Firing
(sintering)
Main stages in the Shaping of ceramics

40. Overview of Ceramics Particulate
Processing – cont….d
• For traditional ceramics, the powders are usually mixed with water to
temporarily bind the particles together and achieve the proper
consistency for shaping
• For new ceramics, substances other than water are used as binders
during shaping
• After shaping, the green parts are fired (sintered), whose function is
the same as in powder metallurgy:
– To effect a solid state reaction which bonds the material into a
hard solid mass

41. Fig -Usual steps in traditional ceramics processing: (1) preparation of
raw materials, (2) shaping, (3) drying, and (4) firing
Part (a) shows the workpart during the sequence, while (b) shows the
condition of the powders

42. Preparation of the Raw Material
for Traditional Ceramics
• Shaping processes for traditional ceramics require the starting
material to be a plastic paste
– This paste is comprised of fine ceramic powders mixed with
water
• The raw ceramic material usually occurs in nature as rocky lumps,
and reduction to powder is the purpose of the preparation step in
ceramics processing

43. Communition
Reducing particle size in ceramics processing by use of
mechanical energy in various forms such as impact,
compression, and attrition is called comminution.
• Comminution techniques are most effective on brittle materials
such as cement, metallic ores, and brittle metals
• Two general types of comminution operations:
1. Crushing
2. Grinding

44. Crushing
Reduction of large lumps from the mine to smaller
sizes for subsequent further reduction
• Several stages may be required (e.g., primary
crushing, secondary crushing), the reduction
ratio in each stage being in the range 3 to 6
• Crushing of minerals is accomplished by
compression against rigid surfaces or by impact
against surfaces in a rigid constrained motion

45. Jaw Crusher
Large jaw toggles back and forth to crush lumps against a hard,
rigid surface
Figure
Crushing operations:
(a) jaw crusher

46. Roll Crusher
Ceramic lumps are squeezed between rotating rolls
Figure - Crushing operations: (c) roll crusher

47. Grinding
In the context of comminution, grinding refers to the
operation of reducing the small pieces after crushing
to a fine powder
• Accomplished by abrasion, impact, and compaction
by hard media such as balls or rolls
• Examples of grinding include:
– Ball mill
– Roller mill
– Impact grinding

48. Ceremic processing…

50. Ball Mill
Hard spheres mixed with stock are rotated inside a large cylindrical
container; the mixture is carried up the container wall as it
rotates, and then pulled back down by gravity for grinding action
Figure - Mechanical
methods of producing
ceramic powders: (a) ball mill

51. Roller Mill
Stock is compressed against a flat horizontal grinding table by
rollers riding over the table surface
Figure -
Mechanical methods
of producing ceramic
powders: (b) roller mill

52. Ingredients of Ceramic Paste for
Shaping
1. Clay (hydrous aluminum silicates) - usually the main ingredient
because of ideal forming characteristics when mixed with water
2. Water – creates clay-water mixture with suitable plasticity for
shaping
3. Non-plastic raw materials, such as alumina and silica - reduce
shrinkage in drying and firing but also reduce plasticity of the
mixture during forming
4. Other ingredients, such as fluxes that melt (vitrify) during firing
and promote sintering, and wetting agents to improve mixing of
ingredients

53. Shaping Processes
• Slip casting
– The clay-water mixture is a slurry
• Plastic forming methods
– The clay is plastic
• Semi-dry pressing
– The clay is moist but has low plasticity
• Dry pressing
– The clay is basically dry (less than 5% water)
and has no plasticity

54. Slip Casting
A suspension of ceramic powders in water, called a slip, is poured into a
porous plaster of paris mold so that water from the mix is absorbed into
the plaster to form a firm layer of clay at the mold surface
• The slip composition is 25% to 40% water
• Two principal variations:
– Drain casting - the mold is inverted to drain excess slip after a
semi-solid layer has been formed, thus producing a hollow product
– Solid casting - to produce solid products, adequate time is allowed
for entire body to become firm
Fig- Sequence of steps in drain casting, a form of
slip casting: (1) slip is poured into mold cavity,
(2) water is absorbed into plaster mold to form a
firm layer, (3) excess slip is poured out, and (4)
part is removed from mold and trimmed

55. Plastic Forming Methods
1. Hand modeling (manual method)
2. Jiggering (mechanized method)
3. Plastic pressing (mechanized method)
4. Extrusion (mechanized method)

56. Plastic Forming method: Hand Modeling
Creation of the ceramic product by manipulating the mass of plastic clay into
the desired geometry
• Hand molding - similar only a mold or form is used to define portions of the
part geometry
• Hand throwing on a potter's wheel is another refinement of handcraft
methods
– Potter's wheel = a round table that rotates on a vertical spindle,
powered either by motor or foot-operated treadle
– Products of circular cross-section can be formed by throwing and
shaping the clay, sometimes using a mold to provide the internal shape

57. Plastic Forming method: Jiggering
Similar to potter's wheel methods, but hand throwing is
replaced by mechanized techniques
Figure; Sequence in jiggering:
(1) wet clay slug is placed on a convex mold;
(2) batting; and
(3) a jigger tool imparts the final product shape

58. Plastic Forming method: Plastic PressingForming process in which a plastic clay slug is pressed between
upper and lower molds
a vacuum is drawn on the backs of the mold halves, moisture is
removed from the clay
• The mold sections are then opened, using positive air pressure
to prevent sticking of the part in the mold
• Advantages: higher production rate than jiggering and not
limited to radially symmetric parts
Plastic Forming method: Extrusion
Compression of clay through a die orifice to produce long sections of
uniform cross-section, which are then cut to required piece length
• Equipment utilizes a screw-type action to assist in mixing the clay and
pushing it through die opening
• Products: hollow bricks, shaped tiles, drain pipes, tubes, and insulators
• Also used to make the starting clay slugs for other ceramics processing
methods such as jiggering and plastic pressing

59. Semi-dry Pressing
Uses high pressure to overcome the clay’s low plasticity and force
it into a die cavity
Figure - Semi-dry pressing: (1) depositing moist powder into die
cavity, (2) pressing, and (3) opening the die sections and ejection

60. Dry Pressing
Process sequence is similar to semi-dry pressing -
the main distinction is that the water content of
the starting mix is typically below 5%
• Dies must be made of hardened tool steel or
cemented carbide to reduce wear since dry clay
is very abrasive
• No drying shrinkage occurs, so drying time is
eliminated and good dimensional accuracy is
achieved in the final product
• Typical products: bathroom tile, electrical
insulators, refractory brick, and other simple
geometries

61. Clay Volume vs. Water Content
• Water plays an important role in most of the traditional ceramics
shaping processes
• Thereafter, it has no purpose and must be removed later from the
clay piece before firing
• Shrinkage is a problem during drying because water contributes
volume to the piece, and the volume is reduced when it is removed

62. Drying
The drying process occurs in two stages:
• Stage 1 - drying rate is rapid and constant as water evaporates
from the surface into the surrounding air and water from the
interior migrates by capillary action to the surface to replace it
– This is when shrinkage occurs, with the risk of warping
and cracking
• Stage 2 - the moisture content has been reduced to where the
ceramic grains are in contact
– Little or no further shrinkage occurs

63. Firing of Traditional CeramicsHeat treatment process that sinters the ceramic material
• Performed in a furnace called a kiln
• Bonds are developed between the ceramic grains, and this is
accompanied by densification and reduction of porosity
• Therefore, additional shrinkage occurs in the polycrystalline
material in addition to that which has already occurred in drying
• In the firing of traditional ceramics, a glassy phase forms among
the crystals which acts as a binder

64. Glazing
Application of a ceramic surface coating to make
the piece more impervious to water and
enhance its appearance
• The usual processing sequence with glazed
ware is:
1. Fire the piece once before glazing to
harden the body of the piece
2. Apply the glaze
3. Fire the piece a second time to harden the
glaze

65. Secondary Operations
• Subsequent processing is usually required after sintering
to achieve adequate dimensional control of the
cemented carbide parts
• Grinding with a diamond or other very hard abrasive
wheel is the most common secondary operation
performed for this purpose
• Other secondary operations include
– Electric discharge machining
– Ultrasonic machining

66. Shaping of Glass products

67. Natural Resources
• Silica sand 72%
• Soda Ash 17%
• Lime 5%
Percentage of Ingredients in Glass
silica sand
soda ash
lime
other ingredients
72%
17%
5%
6%

68. Then, we will now go to the
Utilization of Glass
•History of glass
•How is the utilization of glass importance for
communities?
•Global marketing and consumption status of glass
•The impacts of glass products

69. History of Human Using Glass:
• People have used glass dating back to 5000 B.C
• Ancient Egypt: earliest use of glass, for royalty
and priest as luxuries
• Usually use as containers or for decoration
purposes in human history

70. Utilization of Glass is important
for Human Development:
• Important for historical and modern
human development:
– Prism and lenses: to study light, important to further induce science
theories. E.g. Issac Newton used glass prism and lenses to explain the
color spectrum of light in 1672
– Magnifying glass: for astronomy study, without glass, we are not able to
observe stars and planets in space clearly
– Glasses: make lenses in spectacles that helped people to overcome
sight defect
– Main components in many new and advance technology devices: major
components of most modern communications systems, fiber optics
systems, is also depend on the transmission of light through glass
filaments

71. Different type of glass:
• practical glass
• industrial glass
• inspiration glass
• glass of science and
medicine

72. Examples of today’s glass
products:
 Containers (jars and
bottles)
 Flat glass (windows,
vehicle glazing, mirrors,
etc.)
 Lighting glass
(fluorescent tubes, light
bulbs, etc.)
 Tableware (drinking
glasses, bowls, lead
crystal, etc.)
 Laboratory equipments
(test tubes, cylinders,
measuring flasks, etc.)
 TV tubes and screens
 Decorative glass
 Fiberglass
 Optical glass
 Vacuum flasks

73. • GLASS:
• Glass is a ceramic material. But unlike its counterparts, it has
vitreous glassy structure (non crystalline).
• Glass is processed, first by preparing the melt from raw materials
(like the white sand, flint, limestone, spare etc.)
• The principal raw material is SiO2.
• We get SiO2 from natural quartz in the sand.
• The starting material is heated to transform it from a hard solid into
a viscous liquid (1500-1600oC).
• Then it is shaped to desired geometrical shape while still in this fluid
state.
• After the melt is prepared, in semi molten form, it is fed either in to
molds, or sent in between rollers or by blowers.
• When cooled and hard, the material remains in the glassy state
rather than crystallizing.

74. • Different shapes of Glass products:
•
• continuous products like
– Flat sheet, Plate,
– Rods, Tubing,
– Glass fibers and
• discrete products like
• Bottles,
• Headlights etc.

75. Shaping of GLASS Sheet, by
‘Drawing’ process:
Drawn glass
sheet
Support rolls
Molten glass, in
plastic form
Rollers

76. Shaping of GLASS Sheet, by ‘Float’
process (to make FLOAT glass)
Molten glass in
furnace
Glass spreads on liquid
tin, ‘floats’ as the top
layer.
Molten tin
Lehr chamber, for
solidification
Annealing
Glass stored as
‘cut’ sheets.
Molten glass Glass layer,
floating
Glass sheet on
rollers
Molten tin

77. Manufacture of Glass tubes:
(Drawing of Glass tubes)
Molten glass
Die for outer Ø Drawn out
glass tube
High pressure air
inlet
Hallow mandrel, also
rotates
Hi-pressure air
Rollers

78. Manufacture of glass fibers /
Glass wool:
Molten
glass
Rotating
bowl
Shaft
Glass
fibers,
solidifi
Molten
glass
flow
Manufacture of
Glass wool
Industrial applications: Fibrous
glass (glass-wool) for thermal
insulation, acoustical
insulation, air filtration etc.;
here, the fibers are in random,
wool-like condition

79. Manufacture of glass filaments
(continuous glass fibers)
Molten
glass in a
tank Platinum alloy plate
with tiny holes
Spray jet nozzle
Fiber strands,
hundreds in number
Fiber gathering shoe
Collection spool Manufacture of Glass fibers /
filaments
Strand of hundreds of fiber
bunched together, but not sticking
to each other.
Note that this glass fibers are used for making polymer composites, which
possesses high strength to weight ration characteristic.

80. Techniques for strengthening
glass:
• Thermal tempering/ chill tempering /
physical tempering:

81. Blow molding of glass is the popular glass
bottle manufacturing method
1. Traditional method
2. High volume production
method
Preform glass
melt
When you simply blow
the air, it becomes a
bubble;
No use to anybody
When you blow the air,
keeping the glass melt
within a split-die, then it
takes the shape of the
DIE
The shape could be a
bottle.
The blown air acts as
the core.
But we will have to
continue to maintain the
pressure, until
solidification
Gripped
here,
Blow molding for
glass-bottle
production
Hi-pressure air
Clamp the
die
Tube
Die1 Die2
All different operations are done in an automatic manner.

82. Design considerations for glass &
ceramic products
1. Careful selection of raw material composition, processing method, finishing
operations and methods of assembly.
2. Never forget the limitations of these materials like, lack of tensile strength,
sensitivity to internal cracks, low impact toughness etc.
3. Note that the dimensional changes and cracking possibilities during
processing are significant. Therefore selection of appropriate shaping
methods are important.
4. When our ceramic/glass workpiece is going to be part of an assembly, then
compatibility problems should be thoroughly analyzed.
5. Thermal expansion and type of loading our part is going to face during
service should be given important considerations.

83. Superconductors
• Superconductors are those materials which
transmit electricity almost without any losses.
Transmission efficiency is practically 100%
• Two basic types of superconductors are,
– Metals. …..this is LTSC..eg: Niobium, tin, titanium.
– Ceramics. …this is HTSC..eg: various copper
oxides. ..here high temp means..closer to ambient
temperature.

84. Processing of Superconductors..
• Raw material is available in powder form.
• Fundamental difficulty in manufacturing them is their
inherent property like the brittleness and anisotropy.
• Therefore the problem of aligning their grains to the part-
shape is a challenge.
• General steps in manufacturing:
– Preparing powder; mixing; grinding in a ball mill to a grain size of
0.5 - 10 micron.
– Forming it to required shape.
– Heat treating to get the final alignment of grains.

85. Most common forming process for super conductor….
the OPIT process
1. Pack the raw material powders in to silver tubes.
2. Seal the tube at both ends.
3. The tube is mechanically worked by metal forming processes like
– Forging
– swaging,
– Drawing
– extrusion,
– rolling etc
4. Get the required shape (could be to wire or tape or coil or bulk).
• Other superconducting shaping processes are,
– Give a coating of superconducting material on a silver wire.
– Doctor blade process
– Explosive cladding
– Chemical spraying etc. Oxide Powder in Tube
or
OPIST?