1

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)