powder technology from landslides and avalanches to ...€¦ · standard forming methods –dry...
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LTPÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE
Powder Technology
From Landslides and Avalanches to Concrete
and Chocolate
Prof. P. Bowen (EPFL), Dr. P. Derlet (PSI)
WEEK 13
Sintering Mechanisms & New Technologies- (3)
Processing – Forming - Shaping
P. Bowen, EPFL. 2
Teaching plan 2018
•Files of lectures and notes to be found on PTG website : http://lmc.epfl.ch/PTG/Teaching
Week-
DATE
File.
no.
Powder Technology – Wednesday 10.15-13.00 – MXG 110
1- sept 19 1&2 PB Introduction – example rheology – Yodel - Powder packing and compaction – 1 (i) – (3hrs)
2 – sept 26 2&3 PB MS Powder packing and compaction – 1(ii), 2- Examples and DEM guest lecturer – (3hrs)
3 – oct 3 4 PD Powder packing and compaction -3 & 4(i) – (3hrs)
4 – oct 10 4&5 PD PB Powder packing and compaction - 4 (ii) – (1hr)
Particle – Particle Interactions 1 - 2hrs
5 – oct 17 6&7 PB Particle – Particle Interactions 2 & 3(i) – (3hrs) – Download Hamaker
6 – oct 24 7 PB Particle – Particle Interactions – 3(ii) YODEL-PB (1hr)
Exercises – Intro to Hamaker & YODEL software & groups project (2hrs)
7 – Oct 30 AKM Exercises - Hamaker and Yodel Modelling – group projects
8 – nov 7 8 PB PD Exercises –presentation of interparticle project results (1 hr)
Introduction to atomistic scale simulations – (2hrs)
9 – nov -14 9& 11 PD Compaction, Sintering & Defects in metals at atomistic scale (2hrs)
Sintering Mechanisms – 1(i) (1 hr)
10 – nov 21 11 PD Sintering Mechanisms - 1 (ii) & 2 (3hrs)
11 -nov-28 PD Excercises -Introduction to Molecular Dynamics Modelling using LAMMPS (3hrs) .
12 - dec 5 PD Excercises - MD- DEM modelling exercise using LAMMPS –particle packing - Effect of parameters (3 hrs)
13 – dec 12 10 PB New Technologies -1 Processing – Forming – Shaping (2hrs) & visit – to laboratory of applied photonics
devices *https://lapd.epfl.ch – volumetric 3D printing - BM 4108.
14 – dec 19 12 PB New Technologies-2 – Sintering Methods & Exercises or invited lecture or visit & Exam method
PB – Prof. Paul Bowen (EPFL), PD – Dr. Peter Derlet (PSI)
MS- Dr. Mark Sawley (EPFL), AKM - Aslam Kuhni Mohamed(EPFL)
Today’s Objectives
This Week
• Standard forming methods…..ceramics and metals
– Dry Pressing…(Generalities from 3rd year & summary PT compaction
courses – weeks 4&5 file PowderTech 4)
– Wet methods – overview - slip casting, tape casting, injection moulding
– Limitations …why additive manufacturing approach is interesting
– Look at historical development via direct casting techniques
– General intro to additive manufacturing…video…importance of dispersion!!!
– Green bodies…Sintering…standard procedures (next week)…
• Additive manufacturing and sintering combined – SLS
– Introduction…..Video…..
– Detailed study thesis Cedric André importance of particle packing …..
Next week …
• Summary of standard sintering methods and procedures
• New sintering processes, SPS, flash sintering, cold sintering…
• Typical questions, Powder Technology – Learning outcomes, Exam..method
4
Standard forming methods – Dry pressing ceramics
• Dry pressing – Compaction – Ceramics (3rd year* p.209 & TP2)
• Ceramics – powders granulated (PT week 3 – Neural network –
particle packing) with
• Binder (e.g. polyvinyl alcohol PVA) and
• Plasticizer (e.g. polyethylene glycol PEG [-CH2-CH2-O-]n)
• 3- stages of compaction
– i) rearrangement →RCP of granules
– ii) deformation → plastic…PEG/PVA
– iii) granule fracture/densification
– Ceramic particle density ~ 60% →RCP
• Limitations L/D – density gradients - friction
4
*Les Traité des Matér, Vol. 16 « Les Céramiques » J. Barton, P. Bowen, C. Carry & J.M. Haussonne, PPUR, 2005
Grey – C, Red – O, White- H
PVA
Standard forming methods – Compaction metals
• Dry pressing – Compaction – Metals (PT weeks 4&5) – higher plasticity cf
ceramics…also 3 stages …
– Stage 0 – packing…. rearrangement → RCP ….
– Stage 1 – deformation – increase in contact area -connected pores (60%-80%)
– Stage 2 – sealing off of pores between particles (80%-90%) - porous solid
• Density variations as L/D increases…lubrication walls vs powder
• 4 major mechanisms controlling densification (pressure and temperature) are
– rearrangement, plastic deformation, (power-law creep and thermal diffusion)
5
DEM modellingDrucker-Prager-Cap
(DPC) model
Limitations – compaction
• Generally shapes have to be symetrical and simple in 2D i.e.
small orthogonal features not possible
• Ceramics limited in size…few cm..
• Length to diamter ratio…> 2 start getting density gradients
• Ceramics max force 150-200 MPa – otherwise elastic rebound
leading to defects..
• For cylinders and tubes – isostatic pressing (10’s cm)
• Metals …work hardening can limit compact density
• Sizes higher – cars 9-25 kg compacted & sintered steel parts..
• 10’s cm ..but again… too big get density gradients
• E.g. http://www.perrytool.com/ precision gears, pulleys, bearings,
• cams, sprockets, fasteners, soft magnetic components and
• complex multi-level, close tolerance mechanical parts
6
3cm
2cm
7
Wet Ceramic Slip Casting technique
Suspension forming method
Prepare suspension – called slip
Slip = concentrated suspension
Need adequate viscosity to pour into
the mould
Want a minimum of liquid
Give us a minimum shrinkage during
drying
Porous mould – cappilary suction Pc
Deposit thickness α t 0.5
Can also use to make films – tape
casting - 10-250 mm thickness
Suspension
Filter 0.2 mm
Mould - Silicone
Porous Support
rP lv
c
cos2
8
Slip casting – cups or solid forms
empty mouldfilled with suspension
drained of excess suspension
taken from mould for drying
empty mould filled with suspension
pressure or slurry suppliment
final green solid form - for drying
drain casting
– par vidange
solid casting
- forme remplit
9
Application Traditional Ceramics
Porcelaine – hand basin, toilets
Complex shape and big!!!
Slip casting 45% vol solids - 80 minutes per
mould
Pressure casting – add gas pressure
2 minutes!! 40 times quicker
Modern plants semi-automatic
1week to mix and mill powders before using
the « slip »
High green densities (before firing) of 69%
can be reached with optimum dispersion and
particle size distribution
LAUFEN - Switzerland
P. Bowen, EPFL. 11/12/2018 10
Wet methods – injection moulding – metals & ceramics
Small precision pieces –very complex forms - precise… 1-2 microns without machining
Mixture of ceramic or metal powder – polymers (20% wt, 50% vol)
Heat to 150 - 200°C – plastic injection
Limitations – expensive tooling (80,000 €) - size limited – cm…
Very good for large series, thousands of pieces
Binder burnout… slow 1-3 days…new technology BASF – 2-4 hrs
HNO3 at 120°C (limited to BASF powder quality…no control)
http://www.pim-international.com/metal-injection-molding/binders-and-binder-removal-techniques/
SPT Roth SA- Ceramic injection moulding (CIM) of small complex & precise
components in micron tolerances. Materials include Alumina, Zirconia, Zirconia-toughened
Alumina and polycrystalline Ruby. Limitation size max cm….
•Medical tools & implants - Dental applications - Industrial and Electronic components
•Nozzles with hole diameter less than 15µm - http://www.smallprecisiontools.com/
Nozzles
https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_1.html
Wet methods - general limitations
• Slip casting slow…can speed up with – addition of pressure but complexity
of form still limited
• Drying – slow – days…
• Limited thickness…cm’s
• Injection moulding – high cost of tooling...need to test proof of concept
before making expensive tools…
• Additive manufacturing – initially called rapid prototyping – proof of
concept…for complex pieces...then perhaps use injection moulding…
• Much work over past 20 years …become interesting for pieces…
• improved resolution, improved green body homogeneity
• Giving comparable sintered densities to standard techniques
• New Horizons are promising – even more complex pieces…..
• A little bit of a historic development of advanced forming methods or direct
casting methods…
11
P. Bowen, EPFL. 11/12/2018 12
Direct Casting Techniques
Giuliano Tarì -American Ceramic Society Bulletin, Vol. 82, No. 4 - 2003
• Traditional slip casting in plaster molds has serious limitations in terms of maximum
achievable thickness.
• To overcome these limitations, several near-net-shape forming techniques developed in
which fluid slurries can be transformed into rigid bodies without liquid removal.
• Overview of direct consolidation forming techniques, their comparison with traditional
wet- or paste-processing forming techniques and selection criteria.
• He lists 13 different variations…..and gives an idea of what they are good at and what
they are not so good at…
Jinlong Yang, Juanli Yu, Yong Huang, JECERS 31 (2011) 2569–2591
• At present, the studies on gelcasting are mainly focused on the following aspects:
• (1) the development of low-toxic/nontoxic gelcasting system;
• (2) the development of control methods for reducing defects in the green body;
• (3) gelcasting applications for porous ceramics and complex-shaped ceramics (e.g.,
microbeads, rutile capacitor, thin-wall rutile tube, refractory nozzle and so on);
• (4) colloidal injection molding of ceramics (CIMC).
Classic – Novel colloidal methods paper.....
Sigmund, Bell, Bergstrom -J. Am. Ceram. Soc., 83 [7] 1557–74 (2000)
P. Bowen, EPFL. 11/12/2018 13
Gel-casting…direct casting
• All disperse a slurry then destabilise
Using
• pH
• Ionic concentration
• Chemically –
• Monomer reaction – form polymeric gels
• Temperature
• Simply freeze
• Lower temperature – natural gel
• e.g. agarose* – gels at 35°C
• All interesting….none used widespread in
industry…to my knowledge…
• Sometimes tested…coatings of complexparts..
• *Isabel Santacruz, Ma Isabel Nieto, Rodrigo
MorenoCeramics International 31 (2005) 439–445
P. Bowen, EPFL. 11/12/2018 14
Direct Coagulation Casting – Ludwig Gauckler - ETHZ
Ceramic Processing by Colloidal Chemistry
• The key to improved ceramic components is the control of hierarchical structures
within the material from the millimeter down to the Ångström range - interfaces.
• They applied these results directly to the engineering of improved materials, processes,
and product innovations.
• Controlling the structural and mechanical behavior of concentrated colloidal
suspensions and gels is important in producing high-tech ceramic components.
• Also in the fabrication of papers, paints, pharmaceuticals and composites the
processing technology is often based on colloids.
• Often ceramics are not reliable and fracture at low loads.
• These problems have been circumvented by using a novel in-situ destabilization
method developed at ETHZ .
• This method allows the formation of gels of highly concentrated particles without
significantly disturbing the microstructures that develop during gelation processes.
• These gels can be produced by two different destabilization mechanisms:
• Either the pH of the suspension is shifted towards their isoelectric point or the ionic
strength of the stable suspension is increased at a constant pH.
• Both reactions are enabled by enzymatic hydrolysis.
http://www.cerion.ch/ceramic-processing
P. Bowen, EPFL. 11/12/2018 15
Direct Coagulation Casting
Direct Coagulation Casting (DCC) by destabilizing ceramic suspensions by enzymatic reactions.
By increasing ionic strength (DM) or by shifting pH from 4 to the isoelectric point (IEP) of the
oxide (here Al2O3).
P. Bowen, EPFL. 11/12/2018 16
Direct Coagulation Casting
• The suspension is cast in a mold - Coagulation proceeds and
• the slurry solidifies to a rigid body without any shrinkage.
• The kinetics of this reaction is followed by the auto-correlation functions obtained from
Diffusing-wave-spectroscopy (DWS) on gels coagulated either by pH or ionic strength shift.
http://www.cerion.ch/var/m_e/e0/e0e/29376/6608671-dcc%20cogulation%20email.mp4?download
P. Bowen, EPFL. 11/12/2018 17
Direct Coagulation Casting
Higher strenghts…lower defect densities….
Commericla vehicule launched ….but method was too expensive…withpout enough
benefits…as far as I could gather
Additive manufacturing
• Ceramics –
• The most difficult thing for ceramic processing is to make a
complex shape with high reliability!
• The most critical part for ceramic processing is particles, not
sintering…
• Once forming done to best possible packing and best
homogeneity and uniformity (densities, pore sizes) then
advanced sintering techniques can be useful
• If not always limited by heterogeneities…weak points for
mechanical properties or optical properties…
• Slides 46-79 week 1……
• Metals
• …complex shapes …and sintering at same time
• Selective Laser Sintering…
18
Additive manufacturing – 3D printing techniques for
ceramics* - direct technologies
19
DIWDIPFDC
3DP SLSDLP/SLA
Lewsi et al J. Am. Ceram. Soc., 89 [12] 3599 (2006)
Ceramic particles in appropriate
thermoplastic binders
Ink is continuously
extruded through a fine
cylindrical nozzle
Direct ink-jet printing
Ink-jet printing of material
in the form of droplets
in a desired pattern via a
layer-by-layer build
sequence
Lous et al J. Am. Ceram. Soc., 83 [1] 124 (2000)
*Franks et al. J Am Ceram Soc 2017; 1–33
*Zocca et al. J. Am. Ceram. Soc., 98 [7] 1983–2001 (2015)
Suspension/ink
Additive manufacturing – 3D printing techniques for
ceramics – powder beds – indirect technologies
20
3DP SLSDLP/SLA
Stereolithography
https://www.youtube.com/watch?v=NM55ct5KwiI
Stereolithography (SLA) and
Digital light processing (DLP)
-similar principles – different possible
outputs.
Both use UV or light curable resins
SLA - laser that travels over the cross
sectional area of each layer of the part
DLP uses digital light projector screen to
flash a single image of each layer all at once
Powder bed Powder bed
binder
Powder-Based 3D Printing –
an inkjet printing head spits
a binding liquid onto a
powder bed, thus defining
the cross section of the
object in that layer.
Selective Laser Sintering local densification of the powders by directly sintering. Direct laser sintering of ceramics
is complicated by the poor resistance of this class of materials to thermal shock. But good with metals
European leaders
21
Lift-up DLP
Common Strategy: flocculated ceramic resin with very high viscosity!
Top-Down SLA
What can it do?
- - Shanghai (China) (Prof. Zhao Zhe)
26
Low shrinkage during printing, the thin sheet of 300mm can be sintered
without noticeable deformation
Low viscosity which lead to potential applications with desk-top machines
Easy to be burned resin design which is critical for fast processing and also
low post-processing cost
Top-Down DLP and SLA;
Low Viscosity dispersion-type ceramic resins
3D Printing Ceramic Materials
• Practical Properties:
– Shelf life-time:6 months with re-dispersability
– Continuous Work Time:2 weeks
– Smallest channel size:200mm
– Thinnest wall thickness:300mm
– Smallest support size:200mm
– Viscosity at 30s-1: 800-3000cps
– Exposure time:3-30sec (DLP), >1500mm/sec (SLA)
– Penetration thickness:>100-300mm
27
• Density after sintering: 3.93g/cm3 for 99.99% pure
alumina and 6.03g/cm3 for zirconia 3Y-TZP
• Printing time: 50mm layer thickness, each layer
20sec, almost 1cm/hour
• The principles for printing materials development:
surface modification of powder is the key!
Still defects observed….cf standard processing
28
Reality: inter-layer defects, incomplete edges and fringes of layer thickness….
Reduced Defects By Better Power Dispersion
29
Inter-layer can be reduced but still some small pores need to be removed! Further development of slurry is necessary。
3Y-TZP,1600°C
3Y-TZP,1600°C
Topological Design For Structure And Functions
• Light-weight design;truss-like cellar/lattice structure design; Biomimitic
structure and functions.
• It is very promising that 3D printing ceramics can break the bottle-neck limits
for ceramic material applications…open new avenues….
30
The Intrinsic Benefits from 3D Printing
31
• Built through layer-by-layer mode, limited thickness and volume of elastic
ceramic materials will decrease the residual stress during the forming and
sintering stages.
• It is expected that 3D printed Ceramics can be better than traditional processing
products if material design can be good enough.
• Material design golden rule: low shrinkage during the layer
stacking/solidification.
• This will improve the binding strength between layers and also reduce all
structural defects which severely affect the reliability of ceramics.
• Key for Success:good powder dispersion and good material
design
• Commercialization:focus on Sterolithography but with solid
consideration with precision and size.
P. Bowen, EPFL,CdP 11/12/2018 32
Steric -polymer adsorption – layer thickness
Dispersion – Colloidal Stability - IMPORTANT
Repulsive
Electrostatic, ion adsorption, dissociation, polyelectrolyte
h
(a)
(b)
++
+
+
++
+
+
+
++
++
+
+
++
+
+
+
++
(distance h between particles)
hak
al
r = ( h + 2a )
*U. Aschauer, et al J. Dispersion Science Technology, 32(4), 470 – 479 (2011).
( ), , 212k lha a h
aF A
h 2 k l
k l
a aa
a a
Harmonic average radius
2
2
0 22
1
h L
ES h L
eF a
e
Electrostatic potential
From zeta potential)
1/ Electrical
double layer thickness
5
3
2
3 2, 2 1
5
B adsster k l
k T LF a a a
s h
Lads - Adsorbed layer thickness, s - Spacing of adsorbed molecules
In mushroom configuration – geometry important
Attractive - dispersion or Van der Waals forces – A(h) – Hamaker constant
(dielectric properties)
32
L – charge/zeta plane
Dispersion – Colloidal Stability - IMPORTANT
♦ Net potential/force is algebraic sum of
repulsive and attractive forces
#Robert J. Flatt, Paul Bowen, J. Am. Ceram. Soc., 89 [4] 1244–1256 (2006)
0
Inte
rac
tio
n E
nerg
y
charge
polymer
Attraction - VdW
h
(-)
(+)
1-4 nm
Repulsion total
,htotal VdW ES Sterha
F F F F
Total Interaction
VT = VA + VR
Maximum Energy Barrier, VT = VVdW + VE (+ VS )
33
2 k l
k l
a aa
a a
Harmonic average radius
hak
al
r = ( h + 2a )
Selective Laser Sintering - ExampleTHESE N◦ 3716 (2006)
PRESENTEE A L’ INSTITUT DE PRODUCTION ET ROBOTIQUE (IPR)
ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE
POUR L’OBTENTION DU GRADE DE DOCTEUR `ES SCIENCES
PAR
CEDRIC ANDRE
EPFL
Laboratoire de Gestion et Procédés de Production (LGPP)
Institut de Production et Robotique (IPR)
CH-1015 Lausanne
Switzerland
acceptée sur proposition du jury :
Prof. R. Glardon, directeur de thèse
Dr. E. Boillat, directeur de thèse
Prof. N. Boudeau, rapporteur
Dr. P. Bowen, rapporteur
Dr. C. Martin, rapporteur
Lausanne, EPFL, 2006
Selective Laser Sintering (SLS)
Applications....2017...
-Stainless steel - automotive industry
-Heat exchangers (SS)
-T- Blade Aerospace (thermal barrier support)(Ti)
-Laminar flow reversers (Al) (plant engineering)
-Dental crowns and bridges, Sensor element - CoCr (Medical)
https://www.youtube.com/watch?v=te9OaSZ0kf8
VIDEO _ https://www.youtube.com/watch?v=rEfdO4p4SFc
METHOD
1. First layer
2. Laser sweeps surface
-partial melting of particles
- consolidation on cooling
3. Reservoir descends
– second layer sintered
4. Repeat steps 1-3…
UT Austin, 1995Advantages
1. Metals, polymers,
ceramics(mixed with polymers)
2. Rapid fabrication – CAD file
3. Recycle non-used powder
4. Complex geometries…possible
5. Graded layers or gradients
Powder technology related questions
• Powder bed density (particle arrangement)
• Heat transport in a powder bed
• Mass transport in a powder bed
• Sintering, surface quality....
P0 - power (w)
f - pulse frequency kHz)
h – distance de ratser (mm)
v – speed of sweep (mm/s9
ecouche - layer thickness (mm)
(200-700 mm)
rbed - layer density before
sintering (g/cm3)
tp- pulse duration (nsecs)
Parameters Microstructure
Density
Roughness
Mechanical
Hardnes
Precision
…
Properties
Key Parameters for SLS
37
• How energy is supplied to the powder ?
• How much energy is supplied to the powder ?
• To what is this energy brought?
Microscopic properties of the powder and bed
• Stainless steeel – model powder
• Follows log-normal distribution
• Low agglomeration factor 1.4
• Apparent density (RLP) – 4.4 g/cm3 (56%)
• Tapped density (RCP) – 5.2 g/cm3 (67%)
• Bed density varied from 4.3 to 4.6 g/cm3
38
DEM – modelling (C. Martin – Grenoble)
• Gas – compressed – particle coordination number (Z) and density (rbed)
39
o DEM results between RLP and
RCP found experimentally
o Apparent density - 56%
o Tapped density - 67%
m - coefficient of friction
w energy of adhesion (J/m2)
DEM
conditions
Properties
m w r bed Z
0 0 65.2 5.4
0.2 0 58.3 4.7
0.2 1 57.4 5.6?
Effective thermal conductivity
DEM : calculation of the thermal resistance for all contacts interparticle
of the stack .
the temperature of each particle of
the stack is determined.
Cédric André
Heat Transfer in Powder bed
The heat transfer phenomena taking place in SLS process are complex including incident laser radiation penetration into the powder bed, thermal radiation transfer, and thermal conduction through the gas filling the pores and through the contacts between the particles.
Thermal conductivity of gases at the normal pressure is 3–4 orders lower than that of metals, therefore in a wide range of neck size to particle size ratio, contact conductivity predominates in the powder bed effective thermal conductivity. It becomes more important if sintering is performed in vacuum.
Gusarov et al. International Journal of Heat and Mass Transfer 46 (2003) 1103–1109
Experimental ObservationIn the practical range of scan rate in DMLS process, i.e. 50–2000 mm/s,
exposure period of the laser irradiation (d/v) (d beam diameter (mm)) ranges
between 0.2 and 8ms whilst the radial thermal diffusion time (d2/4α) for a
powder bed with thermal diffusivity of (0.5–1)×10−6 m2 /s is about 40–80 ms.
In a such time scale, the heat flow distance during the interaction time is
considerably less than the particle diameter, leading to very fast heating up
the skin of the particles. The absorbed energy is then transferred to the
surroundings by thermal diffusion. Therefore, the DMLS process can be
considered as “high power density short interaction time”. The temperature
of the exposed powder particles can easily exceed the melting temperature,
leading to full melting of the particles
Experimental Observation II
• It was found that as the laser energy input increases (higher laser power; lower scan rate; lower scan line spacing; lower layer thickness) better densification is achieved. Nevertheless, there is a saturation level, in which, even at very intensive laser energy full density cannot be obtained.
• When melting/solidification approach is the mechanism of densification, the rate changes in void fraction of powder bed in DMLS process obeys the first order kinetic law:
∂ε/∂t =−kε. The sintering rate (k) was found to be a function of the laser energy input. Therefore, the sintered density of metal powders in DMLS process should be an exponential function of the laser energy input.
• Besides the fabrication parameters, the powder properties strongly influence the densification kinetics. Finer particles provide lager surface area to absorb more laser energy, leading to a higher sintering rate.
Simchi 2006
SLS – control of microstructures
Statistical analysis and simulation (DEM)
• 39 points – statistical experimental hybrid design – looking for
• Relationship – microstrcrural parameter - h = h(tP, Er, rbed).
44
rb
ed
g.c
m-3
[]
Er [J.mm-2]tP [ns]
tP [ns]
Er
[J.m
m-2
]
h
X1 ≡ tP
X2 ≡ Er
X3 ≡ rlit
Microstructural Parameter* - h
• From solid area ( = total area-pore area) – Fs
• Perimeter of pore-solid interface – p
• And equivalent perimeter of powder bed before sintering – pFs
• pFs = dv50 nFs , where nFs the number of particles to cover analysis area)
• From image analysis….get binary image ….
• Can describe the fineness and denisty of the sintered layer
45
Original grey scale Binary image
*Thesis Cedric Andre , EPFL, N◦ 3716 (2006)
Microstructural Parameter* - h
46*Thesis Cedric Andre , EPFL, N◦ 3716 (2006)
h = 0.35 0.5 0.7
Classe 1 :
fine
heterogeneous
Classe 2 :
fine
homogeneous
Classe 3 :
large
oriented
Classe 4 :
Large melted
Affinement de la structure
• 4 – classes of microstructure…according to h
0.9
Energy Density
47
sample a03, h = 0.87sample m074, h = 0.80
P0 = 11W, v = 40mm.s-1, h = 45mm, P = 2 kW^
Er = 6.1 J.mm-2
tP = 550 ns
rlit = 4.3 g.cm-3
P0 = 6W, v = 22.2mm.s-1, h = 45mm, P = 0.5 kW^
• Same energy density but different power and velocities….
• Similar if slightly different features…according to h
Influence of powder bed
thickness
Concrete!!!!
• https://www.youtube.com/watch?v=WzmCnzA7hnE
49
• ETHZ – NCCR
• Digital
Fabrication
VOLUMETRIC 3D PRINTING OF ELASTOMERS BY TOMOGRAPHIC
BACK-PROJECTION – Loterie et al - EPFL
• Most additive methods create objects sequentially one layer at a time.
• Limitations on the shapes and the materials that can be printed. e.g overhanging
structures need additional supports during printing, and soft or elastic materials
are difficult to print since they deform as new layers are added.
• While casting can be used instead to create certain elastic parts, design freedom
is limited because cavities or tubes are difficult to unmold.
• They use a volumetric 3D printing method based on tomography,
• the entire volume of a photopolymerizable resin is solidified at the same time.
We demonstrate very rapid (<30s) printing of a variety of complex
• structures with acrylates and silicones – resolution 30-50 mm.
50*https://lapd.epfl.ch/page-40467-en-html/volumetric-3d-printing/
(a) Mouse pulmonary artery model (b) Cross-section view of the Micro-CT
Today’s Objectives
This Week
• Standard forming methods…..ceramics and metals
– Dry Pressing…(Generalities from 3rd year & summary PT compaction
courses – weeks 4&5 file PowderTech 4)
– Wet methods – overview - slip casting, tape casting, injection moulding
– Limitations …why additive manufacturing approach is interesting
– Look at historical development via direct casting techniques
– General intro to additive manufacturing…video…importance of dispersion!!!
– Green bodies…Sintering…standard procedures (next week)…
• Additive manufacturing and sintering combined – SLS
– Introduction…..Video…..
– Detailed study thesis Cedric André importance of particle packing …..
Next week …
• Summary of standard sintering methods and procedures
• New sintering processes, SPS, flash sintering, cold sintering…
• Typical questions, Powder Technology – Learning outcomes, Exam..method
4
Teaching plan 2018
Files of lectures and notes to be found on PTG website : http://lmc.epfl.ch/PTG/Teaching
Week-
DATE
File.
no.
Powder Technology – Wednesday 10.15-13.00 – MXG 110
1- sept 19 1&2 PB Introduction – example rheology – Yodel - Powder packing and compaction – 1 (i) – (3hrs)
2 – sept 26 2&3 PB
MS
Powder packing and compaction – 1(ii), 2- Examples and DEM guest lecturer – (3hrs)
3 – oct 3 4 PD Powder packing and compaction -3 & 4(i) – (3hrs)
4 – oct 10 4&5 PD PB Powder packing and compaction - 4 (ii) – (1hr)
Particle – Particle Interactions 1 - 2hrs
5 – oct 17 6&7 PB Particle – Particle Interactions 2 & 3(i) – (3hrs) – Download Hamaker
6 – oct 24 7 PB Particle – Particle Interactions – 3(ii) YODEL-PB (1hr)
Exercises – Intro to Hamaker & YODEL software & groups project (2hrs)
7 – Oct 30 AKM Exercises - Hamaker and Yodel Modelling – group projects
8 – nov 7 8 PB PD Exercises –presentation of interparticle project results (1 hr)
Introduction to atomistic scale simulations – (2hrs)
9 – nov -14 9& 11 PD Compaction, Sintering & Defects in metals at atomistic scale (2hrs)
Sintering Mechanisms – 1(i) (1 hr)
10 – nov 21 11 PD Sintering Mechanisms - 1 (ii) & 2 (3hrs)
11 -nov-28 PD Excercises -Introduction to Molecular Dynamics Modelling using LAMMPS (3hrs) .
12 - dec 5 PD Excercises - MD- DEM modelling exercise using LAMMPS –particle packing - Effect of parameters
(3 hrs)
13 – dec 12 10 PB New Technologies -1 Processing – Forming – Shaping (2hrs) & Exercises or invited lecture or
visit
14 – dec 19 10 PB New Technologies-2 – Sintering Methods & Exercises or invited lecture or visit & Exam method
PB – Prof. Paul Bowen (EPFL), PD – Dr. Peter Derlet (PSI)
MS- Dr. Mark Sawley (EPFL), AKM - Aslam Kuhni Mohamed(EPFL)
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