Manufacturing, Forming and Shaping Flashcards
What are the three (?) or humidity powder mixtures?
- dry: uniaxial, isostatic
- plastic: extrusion, inj, molding
- wet/colloidal: slip casting, gelcasting, freeze casting, tape casting, EPD
Shaping capability
NNS: isostatic, inj, molding, s. casting, gelcasting, freeze casting
non NNS: uniaxial, extrusion, tape casting, EPD
What are consolidation methods?
methods that allow you to go from liquid-like (slurry/suspension) to solid like (green body)
What is the consolidation method from slip casting,
slip casting = filtration
gelcasting = gelation (polymerization)
freeze casting = freezing
tape casting = evaporation
EPD = particle migration & deposition
What are characteristics of gelcasting?
- produces complex 3D shapes
- closed cavity mold (low pressure injection or pouring)
- molding time can be shortened
What happens in a polymerization reaction?
a low MW monomer turns into a polymer w/ high MW
what are the four components needed when forming the green body through gelation
- monomer
- crosslinking agent
- initiator
- catalyst or activator
What are two properties of gelcasted materials?
- complex shapes
- machinable
What is the mechanism for forming the green body in gelcasting?
gelation
What is the method for forming the green body in freeze casting?
freezing
What are three components needed for freeze casting?
- refrigerant
- cryoprotector
- freezing device
why do you need a sublimation process in freeze casting
to remove the frozen solvent (turn it into gas)
What is a cool property about freeze casting?
it keeps the homogeneity very well
chemical/physical and composition/shape
What process do you need in freeze casting? what are the steps?
sublimation
What is tape casting used for?
to make ceramic tapes
What are the parts of a tape casting machine?
What is the mechanism for forming the green body for electrophoretic deposition?
deposition (where particles settle out of a fluid and accumulate on a surface)
What are the three components needed for electrophoretic deposition?
- electrodes
- electrical field
- substrate
What process happens in electrophoretic deposition?
particle migration due to electrical field
suspension —–> substrate
What are the three steps in electrophoretic deposition?
- (suspension) particles electrically charged in suspensions
- (migration) electrical field applied through electrodes
- (migration) to the opposite charge electrode
- (deposition) overcome sep. forces and contact/adhere to each other
- sintering (extraction/drying)
What does the drying/extraction step of the green body formation process for electrophoretic deposition do?
creates tensions that lead to the breaking of the deposited layer
How does shaping capability behave with dry, plastic, and wet processes? price? simplicity of process? reliability?
low –> high
dry, plastic, wet
*price same
dry- most simple, wet- least simple
wet process most reliable
What are some possible outcomes of electrophoretic deposition?
- thin/thick layers on substrates
- multilayer structures
- monolithic layer
- complex shapes
- functionally graded materials
What are shaping routes a function of?
the humidity content of the powder mixture
what are the dry shaping ceramic processing techniques?
- uniaxial pressing
- isostatic pressing
what are the plastic shaping processing techniques?
- extrusion
- injection molding
- ram pressing
- viscous plastic processing (VPP)
what are the wet shaping processing techniques?
- tape casting
- slip casting
- pressure casting
- gelcasting
- freeze casting
- direct coagulation casting (DCC)
- electrophoretic deposition (EPD)
What are the characteristics of near-net -shaping techniques
- complicated geometry and 3D shapes
- green body has the final desired shape
- minimization of machining stage in green, after drying or sintering
What are the three components to uniaxial pressing?
- lubricant
- powder
- compact
What are the two types of isostatic pressing?
wet bag and dry bag, also cold isostatic pressing
what are the stages in wet bag isopressing?
- filling
- loading
- pressing
- decompression
what are the stages in dry bag isopressing?
- loading powder into die
- pressing in x-y plane
- ejection of pressed part through top or bottom
What are the steps to cold isostatic pressing (CIP)?
- CIP blank
- firing at temp <1000C– densifies/strengthens the material
- final firing
- glaze
How do particles behave in the dry processing routes?
- fine powders are cohesive and don’t flow
- large particles will flow (need to be 100 micron for flow)
What are some defects from the dry processing routes like?
- incomplete deformation of agglomerates
- trapped air
- irregular pores
- deformed granules
- intergranular pores
What are three characteristics of plastic processing routes?
- mixture of ceramic powders w/polymers (up to 30%)
- viscous dough or paste
- dough gets extruded, injected, shaped into components.
How does extrusion work?
- viscous plastic mixture of ceramic powder, water, and binder is forced through a nozzle
- particles are held by surface tension bc of the binder mixture
- polycrylamides and PVA
How does injection molding work?
- large polymer/ceramic ratio
- viscous feed is heated till the material can flow into the cavity under the applied pressure
- mixture is cooled by the cool cavity
What is the result of wet/colloidal routes? why?
more reliable ceramics
dispersing the powder in a liquid (usually water) allows for improved reliability and more complex shapes to be formed
Control of the attraction/repulsion forces in wet routes allows for what 4 things?
- soft aggregates can be broken apart
- flaws can be removed by filtration
- high green densities can be achieved from efficient packing
- less shrinkage
How do you prepare suspensions for wet/colloidal routes?
ceramic powders and additives are put in a solvent (usually water)
What does suspension stability depend on?
interaction forces between particels
how can you identify unstable suspension between particles?
V repulsion < V attraction
(intermolecular potential energy)
What do additives serve as in wet/colloidal processing?
stabilization mechanism
What are three different ways additives can serve as a stabilization mechanism?
- electric double layer mechanism
- steric mechanism
- electrosteric mechanism
What would stable suspension look like?
stable suspension is where V repulsion is bigger than attraction
V is potential energy between particles
What is the process of slip casting?
porous mold – filled with the suspension – filtrate/plaster — excess of slurry is drained and trimmed
What are the pros and cons of slip casting?
pro: complex shapes
cons: limited to constant cross section, lengthy time in plaster of the mold
