1. IE 337: Materials & Manufacturing Processes
IE 337 Lecture 8 Glass & Ceramics Processing
IE 337: Materials & Manufacturing Processes
Lecture 13:
Ceramics, Glass and Powder Processing
Chapters 7, 12, 16 & 17
S.V. Atre

2. This Time Ceramics Glass Processing
Powder Processing: Ceramics and Metals
Homework #5 on Thursday (2/25/10)

3. Ceramics General properties Hard High wear resistance Brittle
High compressive strength
High elastic modulus
High temperature resistance
Good creep resistance
Low conductivity
Low thermal expansion
Good chemical inertness

4. Ceramics: Classification
Al2O3-SiO2
SiC
Si3N4 BN
ZrO2
ZrO2 WC
Al2O3
Al2O3
Diamond
AlN

5. Common Ceramics Oxides: Al2O3, ZrO2 Nitrides: AlN, Si3N4, BN, TiN
Carbides: WC, SiC, TiC, TaC
Glasses: SiO2 + others
Carbon: Graphite, Diamond
sinter
Processed as powders

6. Whiteware Ceramics Clay Processing Products Quartz Feldspar
Water addition, mixing
Air removal
Shaping
Drying
Coating
Firing
Products
Brick
Structural Tile
Drain / sewer pipe
Decorative applications
Bath / kitchen structures

7. Refractory Material Retain properties at high temperature Products
Mechanical
Chemical
Products
Fire brick
Insulating fibers
Refractory linings
Coatings
Silica
Alumina
Magnesium Oxide

8. Abrasives High hardness Examples Roughing Applications Super-Finishing
Silicon carbide
Aluminum oxide
Cubic boron nitride
Roughing Applications
Grinding
Cutting
Water-jet
Sawing
Coatings
Super-Finishing
Honing
Lapping

9. Glasses Amorphous solid Silica Glass Products
Vitreous (noncrystalline) structure
Amorphous
Cooled to semi-solid condition without crystallization
Subject to creep
Silica Glass
Optical properties
Thermal stability
Products
Window glass
Fiber optics
Chemical containers
Lenses

10. Glass Ceramics Crystalline solid Glass Ceramic Products
0.1 to 1.0 micron grains
Use of nucleating agents
Glass Ceramic
Efficient processing in glassy state
Net shape process
Good mechanical properties versus glass
Low porosity
Low thermal expansion
Higher resistance to thermal shock
Products
Cookware
Heat exchangers
Missile radomes

11. Cermets Combination of metals & ceramics Properties Applications
“Cemented” carbides
Bound with high temperature metal
Properties
High hardness
High temperature resistance
Improved toughness
Improved strength
Improved shock resistance
Applications
Crucibles
Jet nozzles
High temperature brakes
Production
Press powder in metal mold
Sintering in controlled atmosphere
WC-Co

12. GLASS

13. Shaping Methods for Glass
Methods for shaping glass are different from those used for traditional and new ceramics
Glassworking: principal starting material is silica
Usually combined with other oxide ceramics that form glasses
Heated to transform it from a hard solid into a viscous liquid; it is then shaped into the desired geometry while in this fluid condition
When cooled and hard, the material remains in the amorphous state rather than crystallizing

14. The typical process sequence in glassworking:
preparation of raw materials and melting,
shaping, and
heat treatment

15. Glassworking Processes
Piece Ware
Flat and Tubular Glass
Glass Fibers

16. Piece Ware Shaping Processes
Spinning – similar to centrifugal casting
Pressing – for mass production of flat products such as dishes, bake ware, and TV faceplates
Blow forming – for production of smaller-mouth containers such as beverage bottles and incandescent light bulbs
Casting – for large items such as large astronomical lenses that must cool very slowly to avoid cracking

17. Spinning
Spinning of funnel‑shaped glass parts such as back sections of cathode ray tubes for TVs and computer monitors:
gob of glass dropped into mold; and
rotation of mold to spread molten glass on mold surface

18. Pressing
Pressing of flat glass pieces: (1) glass gob is fed into mold from furnace; (2) pressing into shape by plunger; and (3) plunger is retracted and finished product is removed (symbols v and F indicate motion (velocity) and applied force)

19. Blow Forming
Blow forming sequence: (1) gob is fed into inverted mold cavity; (2) mold is covered; (3) first blowing step; (4) partially formed piece is reoriented and transferred to second blow mold, and (5) blown to final shape

20. Casting A low viscosity glass can be poured into a mold
Uses: massive objects, such as astronomical lenses and mirrors
After cooling and solidifying, the piece must be finished by lapping and polishing
Casting of glass is not often used except for special jobs
Smaller lenses are usually made by pressing

21. Rolling
Starting glass from melting furnace is squeezed through opposing rolls whose gap determines sheet thickness, followed by grinding/ polishing

22. Float Process
Molten glass flows onto the surface of a molten tin bath, where it spreads evenly, into a uniform thickness and smoothness - no grinding or polishing is needed

23. Forming of Glass Fibers
Products can be divided into 2 categories:
Discontinuous fibrous glass for insulation and air filtration, in which the fibers are in a random, wool‑like condition
Produced by centrifugal spraying
Long continuous filaments suitable for fiber reinforced plastics, yarns, fabrics, and fiber optics
Produced by drawing

24. Drawing
Continuous glass fibers of small diameter are produced by pulling strands of molten glass through small orifices in a heated plate made of a platinum alloy

25. Heat Treatment
Annealing to eliminate stresses from temperature gradients
Annealing temperatures are around 500C followed by slow cooling
Tempering to make the glass more resistant to scratching and breaking due to compressive stresses on its surfaces
Heating to a temperature above annealing, followed by quenching of surfaces by air jets

26. Finishing Operations
Glass sheets often must be ground and polished to remove surface defects and scratch marks and to make opposite sides parallel
Decorative and surface processes performed on certain glassware products include:
Mechanical cutting and polishing operations; and sandblasting
Chemical etching (with hydrofluoric acid, often in combination with other chemicals)
Coating (e.g., coating of plate glass with aluminum or silver to produce mirrors)

27. Powder Processing Parts
Figure A collection of powder metallurgy parts (photo courtesy of Dorst America, Inc.).

28. Powder Processing The Characterization of Engineering Powders
Production of Metallic Powders
Conventional Pressing and Sintering

29. Powder Metallurgy (PM)
Metal processing technology in which parts are produced from metallic powders
Usual PM production sequence:
Pressing - powders are compressed into desired shape to produce green compact
Accomplished in press using punch-and-die tooling designed for the part
Sintering – green compacts are heated to bond the particles into a hard, rigid mass
Performed at temperatures below the melting point of the metal

30. Why Powder Metallurgy is Important
PM parts can be mass produced to net shape or near net shape, eliminating or reducing the need for subsequent machining
PM process wastes very little material - ~ 97% of starting powders are converted to product
PM parts can be made with a specified level of porosity, to produce porous metal parts
Examples: filters, oil‑impregnated bearings and gears

31. More Reasons Why PM is Important
Certain metals that are difficult to fabricate by other methods can be shaped by powder metallurgy
Tungsten filaments for incandescent lamp bulbs are made by PM
Certain alloy combinations and cermets made by PM cannot be produced in other ways
Non-equilibrium microstructures possible
PM compares favorably to most casting processes in dimensional control
PM production methods can be automated for economical production

32. Engineering Powders
A powder can be defined as a finely divided particulate solid
Engineering powders include metals and ceramics
Geometric features of engineering powders:
Particle size and distribution
Particle shape and internal structure
Surface area

33. Measuring Particle Size
Most common method uses screens of different mesh sizes
Mesh count - refers to the number of openings per linear inch of screen
A mesh count of 200 means there are 200 openings per linear inch
Since the mesh is square, the count is equal in both directions, and the total number of openings per square inch is 2002 = 40,000
Higher mesh count = smaller particle size

34. Screen Mesh
Figure Screen mesh for sorting particle sizes.

35. Particle Shapes in PM
Figure 16.3 Several of the possible (ideal) particle shapes in powder metallurgy.

36. Observations
Smaller particle sizes generally show greater friction and steeper angles
Spherical shapes have the lowest interpartical friction
As shape deviates from spherical, friction between particles tends to increase
Easier flow of particles correlates with lower interparticle friction
Lubricants are often added to powders to reduce interparticle friction and facilitate flow during pressing

37. Particle Density Measures
True density - density of the true volume of the material
The density of the material if the powders were melted into a solid mass
Bulk density - density of the powders in the loose state after pouring
Because of pores between particles, bulk density is less than true density

38. Packing Factor Bulk density divided by true density
Typical values for loose powders range between 0.5 and 0.7
If powders of various sizes are present, smaller powders will fit into spaces between larger ones, thus higher packing factor
Packing can be increased by vibrating the powders, causing them to settle more tightly
Pressure applied during compaction greatly increases packing of powders through rearrangement and deformation of particles

39. Porosity
Ratio of volume of the pores (empty spaces) in the powder to the bulk volume
In principle
Porosity + Packing factor = 1.0
The issue is complicated by possible existence of closed pores in some of the particles
If internal pore volumes are included in above porosity, then equation is exact

40. Chemistry and Surface Films
Metallic powders are classified as either
Elemental - consisting of a pure metal
Pre-alloyed - each particle is an alloy
Possible surface films include oxides, silica, adsorbed organic materials, and moisture
As a general rule, these films must be removed prior to shape processing

41. Production of Metallic Powders
In general, producers of metallic powders are not the same companies as those that make PM parts
Any metal can be made into powder form
Three principal methods by which metallic powders are commercially produced
Atomization
Chemical
Electrolytic
In addition, mechanical methods are occasionally used to reduce powder sizes

42. Coventional PM Sequence
Figure Conventional powder metallurgy production sequence: (1) blending, (2) compacting, and (3) sintering; (a) shows the condition of the particles while (b) shows the operation and/or workpart during the sequence.

43. Blending and Mixing of Powders
For successful results in compaction and sintering, the starting powders must be homogenized
Blending - powders of same chemistry but possibly different particle sizes are intermingled
Different particle sizes are often blended to reduce porosity
Mixing - powders of different elements/alloys are combined

44. Compaction
Application of high pressure to the powders to form them into the required shape
Conventional compaction method is pressing, in which opposing punches squeeze the powders contained in a die
The workpart after pressing is called a green compact, the word green meaning not yet fully processed
The green strength of the part when pressed is adequate for handling but far less than after sintering

45. Conventional Pressing in PM
Figure Pressing in PM: (1) filling die cavity with powder by automatic feeder; (2) initial and (3) final positions of upper and lower punches during pressing, (4) part ejection.

46. Press for Conventional Pressing in PM
Figure A 450 kN (50‑ton) hydraulic press for compaction of PM parts (photo courtesy of Dorst America, Inc.).

47. Sintering
Heat treatment to bond the metallic particles, thereby increasing strength and hardness
Usually carried out at between 70% and 90% of the metal's melting point (absolute scale)
Generally agreed among researchers that the primary driving force for sintering is reduction of surface energy
Part shrinkage occurs during sintering due to pore size reduction

48. Sintering Sequence
Figure Sintering on a microscopic scale: (1) particle bonding is initiated at contact points; (2) contact points grow into "necks"; (3) the pores between particles are reduced in size; and (4) grain boundaries develop between particles in place of the necked regions.

49. Sintering Cycle and Furnace
Figure (a) Typical heat treatment cycle in sintering; and (b) schematic cross section of a continuous sintering furnace.

50. Limitations and Disadvantages
High costs
High tooling and equipment costs
Metallic powders are expensive
Typically requires a unique material or geometry to justify
Problems in storing and handling metal powders
Degradation over time, fire hazards with certain metals
Limitations on part geometry because metal powders do not readily flow laterally in the die during pressing
This is true for traditional punch and die
Variations in density throughout part may lead to yield issues especially for complex geometries

51. Interparticle Friction and Powder Flow
Friction between particles affects ability of a powder to flow readily and pack tightly
A common test of interparticle friction is the angle of repose, which is the angle formed by a pile of powders as they are poured from a narrow funnel

52. Angle of Repose
Figure Interparticle friction as indicated by the angle of repose of a pile of powders poured from a narrow funnel. Larger angles indicate greater interparticle friction.

53. Powder Injection Molding
final
powder
dry/ debind
flow
shape
sinter (firing)

54. CERAMICS

55. Ceramics Processing
(a) shows the workpart during the sequence, while (b) shows the condition of the powders

56. Slip Casting
A suspension of ceramic powders in water, called a slip, is poured into a porous plaster of paris mold where the water from the mix is absorbed to form a firm layer of clay
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, mold not drained

57. 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

58. SLIP CASTING

59. Tape Casting Fabrication process for thin ceramic sheets Doctor Blade
Polyester Film
Carrier
Slip
Dried Tape
Doctor Blade
Polyester Film Roll

60. Miniaturization of Complex Circuits
High Temperature Co-Fired Ceramic (HTCC)
Low Temperature Co-Fired Ceramic (LTCC)
Thick film metal traces are printed on several tape layers of ceramic and are co-fired
Tape layers are electrically connected through vias
Significant miniaturization of circuit form factor with this technology

61. Extrusion
Compression of clay through a die orifice to produce long sections of uniform cross‑section
Products: hollow bricks, shaped tiles, drain pipes, tubes, drill bit blanks, and insulators

62. Extruder Sectional View
Components and features of a (single‑screw) extruder for plastics and elastomers

63. Ceramic Extrusion: Examples
cordierite
catalytic converter
50 cells/cm2

64. Powder Injection Molding (PIM)
Ceramic particles are mixed with a thermoplastic polymer, then heated and injected into a mold cavity. Polymer provides flow characteristics for molding

65. Mold-Filling Interactions
IE 337 Lecture 8 Glass & Ceramics Processing
Mold-Filling Interactions
Jetting
Weld-line
Air trap
Short shot
It is important to understand the complex nature of the mold-filling process to have an appreciation for the study.
During mold-filling, the molten feedstock flows into an empty mold cavity maintained at a specific temperature.
The material continuously loses heat and starts solidifying while fighting to completely fill the cavity.
After a certain time in the cycle, usually after the cavity is about 98% filled, the switchover from filling to packing occurs. During which extra material is pushed into the cavity to compensate for the material shrinkage due to solidification.
Due to improper specifications of the process parameters, several defects may occur. Like Weld-line, air trap, short shot, flashing, powder- binder separation, jetting.
With all these obstacles of simultaneous heat and mass transfer occurring and also possibilities of several defects, the process of trying to fill a cavity for thin-walled microfluidic geometry is a very complex task.
If the injection molding engineer knows how the material behaves and which knobs to turn on the molding machine when something doesn’t seem right, then the task becomes more easier.
This study aims at making the task easier for the molding engineer.
Filler-polymer separation
Flashing
S.V. Atre

66. Die Pressing

67. Semi-Dry Pressing
Semi‑dry pressing: (1) depositing moist powder into die cavity, (2) pressing, and (3) opening the die sections and ejection

68. Next Time Joining Chapter 30 & 31 IE 337 Lecture 12: Forming 2
S.V. Atre