1. Shaping

2. increasing liquid content
Shaping
Overview of shaping technologies
method
product geometry
Starting material
mold costs
product examples
axial die pressing
simple- complex
granulate
high
ferrite cores, piezo ceramics
isostatic pressing
simple
medium
tubes, spark plug, pistons
tape casting
simple (tape)
conc. suspension
very low
condensator substrates
extrusion
plastic mass
low
tubes
pressure slip casting
sanitary ceramics
slip casting
complex
injection molding
turbine blades
Liquid content of the starting material for the different shaping processes
Compaction of granulates ca. 5%
Extrusion, injection molding ca
Casting ca %
increasing liquid content

3. Pressing Pressure forming methods
Shaping
Pressing
Pressure forming methods
Compaction of powders is used for shaping simple forms.
pump
oil
rubber bag
Density (%) 20 40 60 80
100
Pressure(Mpa)
alumina granules
tile body
KBr powder
uniaxial pressing
isostatic pressing
Compaction process:
1. sliding and rearrangement of particles/granules
2. Deformation (elastic and plastic) of
particles/granules
(3. Densification of granules)
Problems:
- Unhomogeneous density distribution
- Residual large pores (hollow granules)
- Ejection problems
Yanagida et al.: p

4. Isostating pressing Green body Pressure vessel with liquid
Shaping
Isostating pressing
Green body
Pressure vessel with liquid
Elastic, shape stable form
The advantage of isostatic compaction is a more homogeneous density distribution. The complexity of the mold is, however, limited.

5. Die pressing: flow chart
Shaping
Die pressing: flow chart
Process flow diagram
for shaping by die pressing.

6. Compaction of granules
Shaping
Compaction of granules
End stage I
End stage II
End stage III
density
pressure
stage 1
stage 2
stage 3
Compaction behavior of granulated powders
stage I granule flow and rearrangement
stage II granule deformation
stage III granule densification
Evolution of the green-body microstructure during compaction of granules

7. Densification defects
Shaping
Densification defects
Pressure distribution in a die at the beginning and at the end of the second compaction stage. The spring back behavior after pressure is released is directly proportional to the pressure in a certain area. The differential pressure is mainly due to friction of the punch.
Densification defects occurring on
die pressed green bodies.

8. Die pressing additives
Shaping
Die pressing additives
Reed, 1995

9. Shaping
Die pressing powders
Reed, 1995

10. Products shaped by axial die pressing
Shaping
Products shaped by axial die pressing

11. Shaping
Slip casting I
a) The slurry is poored into the mold made of plaster of Paris (CaSO4  0.5H2O). b) The mold absorbs the liquid, while the powder particles are deposited on the walls of the mold. c) The surplus suspension is drained and d) the greenbody is removed from the mold.
Steps in slip casting of ceramics. (Source: From Modern Ceramic Engineering, by D.W. Richerson, p. 462, Fig Copyright © 1992 Marcel Dekker. Reprinted by permission.)

12. Shaping
Hollow molds
The holding time will dictate the wall thickness of the greenbody. Typical holding times are between 5 and 30 minutes.

13. Slip casting of sanitary ceramics
Shaping
Slip casting of sanitary ceramics

14. Rheology in slip casting
Shaping
Rheology in slip casting
Slip casting of porcellaine
250
500
750
1000
1250
1500
Viscosity (mPa sec) 20 40 60 80
100
spindle speed (rpm) V
The rheology of the cast is shear thinning. Before mixing, pumping and pouring the slurry has to be stirred
% sodium silicate
Influence of the viscosity on the shape of the slip casted white ware part

15. Kinetics of slip casting
Shaping
Kinetics of slip casting
The thickness of the cake deposited on the mold walls depend on mold and suspension characteristics. The wall thicknes growth is a parabolic.

16. Shaping
Slip casting examples
Slip casted silicon nitride turbine (Allied Signal)

17. Tape casting I Compositions of a alumina and titanate tape cast (vol%)
Shaping
Tape casting I
slurry
doctor blade
green body in form of a film
liquid absorbing, porous film
Compositions of a alumina and titanate tape cast (vol%)
Powder Al2O BaTiO
Solvent Trichlorethylene Methylethylketone
Ethylalcohol Ethylalcolhol 16.0
Deflocculant Menhaden oil Menhaden oil
Binder Polyvinylbutiral Acryllic emulsion
Plasticizer Polyethylene glycol Polyethylene glycol
Octyl phthalate Butylbenzlphtalate
Wetting agent Cyclohexanone
Such slurries exhibit also shear thinning. The quality and thickness of the tape is controlled by the size of the blade oppening, the speed of the tape, the rheology of the slurry and the shrinkage during drying. Industrial tape casting machines are up to 25m long, several meters wide and run with speeds. Up to 1.5m/min to produce tapes with thicknesses between 25 and 1250mm.

18. Shaping
Tape casting II
A doctor blade assembly. The ceramic slurry is held in the reservoir behind the blade [middle of the micrograph]. The twin micrometers [right] control the blade height above the carrier film. More sophisticated versions feature double blades and pumped metered slurry flow to keep the height of the slurry reservoir constant.
Example of a tape drying on the Mistler laboratory-scale batch tape caster. Industrially the process is often continuous with the tape being force dried prior to removal from the carrier, dicing and further processing.

19. Pressurized slip casting I
Shaping
Pressurized slip casting I
1. Closing of the mold
2. Injection of the slurry into the mold

20. Pressurized slip casting II
Shaping
Pressurized slip casting II
3. Pressurizing the slurry
4. Draining of surplus slurry

21. Pressurized slip casting III
Shaping
Pressurized slip casting III
5.Opening of the mold
6. Removal of the component

22. Pressurized slip casting examples
Shaping
Pressurized slip casting examples
Pressurized slip casting mold for sinks
Finished products

23. Injection molding Process flow diagram
Shaping
Injection molding
Process flow diagram
for shaping by injection molding

24. Injection molding products
Shaping
Injection molding products
Most products shown in the picture are guiding elements used in thread manufacturing

25. Extrusion casting cylindric greenbody slurry
Shaping
Extrusion casting
cylindric greenbody
slurry
Industrial pug mill ith deairing chamber and extrusion auger
Yanagida et al.: p. 160

26. Drying of greenbodies I
Shaping
Drying of greenbodies I
Drying geometry
moving drying air
Boundary layer
(air + vapour)
Particles
Suspension liquid
Drying kinetics will depend on the rate of heat transfer into the body and mass (liquid) transport out of the body. Four rate determining processes can be distinguished:
1. Boundary layer mass transfer 2. Pore mass transfer
3. Boundary layer heat transfer 4. Pore heat transfer
Each of the above steps are rate determining for some time during drying, the boundary layer process at the beginning, the pore processes towards the end. Mass and heat transfer rates are obviously coupled and equal to the evaporation rate E:

27. Drying of greenbodies II
Shaping
Drying of greenbodies II
as cast
Shrinkage and deformation
Moisture content at the surface const.
Rate determining step: heat and mass
transport through boundary layer
No further shrinkage, all particles
are in contact, leatherhard greenbody
Moisture cont.
constant rate
Partially filled pores. Rate determining
step: pore mass and heat transfer
completely dry
decreasingt rate
time
Typincal drying curve
The boundary processes are linear functions of the greenbody size (radius for spheres, cylinders, thickness for plates), whereas the pore processes go with the square of the greenbody dimension. The overall rate is ± a square function of the greenbody size. Example for a spherical ZrO2 greenbody:
Diameter: drying time
1cm h
10cm days

28. Shaping
Drying shrinkage
Linear and volume shrinkage of a greenbody can be defined by:
The shrinkage can be influenced by the moisture content (Dl) amd the particle dimensions (N)
shrinkage defects due to
1. Unhomogeneous drying of a homogeneous greenbody
2. Homogeneous drying of unhomogeneous green body
moisture content
drying rate
shrinkage
critical moist. cont.
warping
cracking
delamination
Unhomogeneities: - uneven moisture distribution
- preferred orientation of particles