Additive Manufacturing 09July2013 - ALPlastics school presentations... · SLA STL DLP Stereo...
Transcript of Additive Manufacturing 09July2013 - ALPlastics school presentations... · SLA STL DLP Stereo...
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ADDITIVE MANUFACTURING PROCESSES
FOR MATERIALS FORMING
Part 1 : Basic principles and examples
Claire Barrès, Jean-Yves Charmeau,Stéphane Dupin, Amir Msakni
INSA-Lyon
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Additive manufacturing technologies
❶ Basic principles
❷ 3D Printing
❸ @manufacturing
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Different types of material forming processes
By ablation
SculptureSculpture
MachiningMachining
By deformation
PotteryPottery
StampingStamping
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By addition
Rapid Manufacturing /
Additive processes
Building
❶ Basic principles
❷ 3D printing
❸ @manufacturing
Additive manufacturing technologies
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Creating a 3D physical model directly fromdigital data
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3D model from a computer
(CAD file)
S.T.L. file
Machine software
fabrication
• STL file :– Description of the surfaces of the part by
triangular facets
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SLICING
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The model is placedin the virtual spaceof the machine
Slicing into thin layers(thickness depends on the process)
Layer by layer building
LAYER ADDITION
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LAYER ADDITION AND SURFACE FINISHING
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Physical object out of the machine (final surface quality depends on the layer thickness ).
Object afterfinishing
Additive manufacturing technologies
❶ Basic principles
❷ 3D printing
❸ @manufacturing
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3D PrintingThere are a number of 3D printing technologies. They differ in the way
layers are deposited to create parts, in the materials that can be used,
and they all work differently.
Inkjet 3D-printing systems create the model one layer at a time by
spreading a layer of powder (plaster, or resins) and printing a binder in
the cross-section of the part using an inkjet-like process. This
technology allows the printing of full color prototypes. The strength of
bonded powder prints can be enhanced with wax or thermoset polymer
impregnation.
Some methods melt or soften material to produce the layers, e.g.
selective laser melting (SLM), selective laser sintering (SLS), fused
deposition modeling (FDM), while others cure liquid materials using
different technologies, e.g. stereolithography (SLA).11
PRINTER RESOLUTION
• It describes layer thickness and X-Y resolution in dpi(dots per inch) or micrometers.
• Typical layer thickness is around 100 micrometers (µm),although some machines such as the Objet Connexseries and 3D Systems' ProJet series can print layers asthin as 16 µm.
• X-Y resolution is comparable to that of laser printers.
• The particles (3D dots) are around 50 to 100 µm indiameter.
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Source Ex-one
3D PrintingPrinciple : using a printhead .
Advantage :- Can be used in engineering and design depts,
in drawing offices, at homeDrawback :- Fragile parts
Applications :- Prototyping, design office
Materials :- Light sensitive resins, epoxy- Polymer melt- Polymer binder on polymer, metal, sand,
ceramic powders.
Some machine manufacturers :- Molten polymer thread: Stratasys- Light sensitive systems : Objet- Powder + binder system : Prometal.Dimensions : up to 4 x 2 x 1 metres (Voxeljet, binder jetting)
FUSED DEPOSITION MODELING (FDM)
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Examples Fused Deposition Modelling (FDM)
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Stratasys
• Materials :
– ABS
– Polycarbonate
– PC-ABS
– Elastomer
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Fused deposition modeling (FDM)
Machine manufacturer :Stratasys, USA
Advantages :– Functional and flexible
models.– Soluble supports– Simple system, possibility
of desktop use.– Non-toxic materials
Drawbacks : − Extrudable materials only− Layer thickness (0.2 mm mini) and
wall thickness (0.3 mm mini)− Precision : +/- 0.15 mm
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BINDER JETTING ON A POWDER
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STEREOLITHOGRAPHY (SLA)
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STEREOLITHOGRAPHY (SLA)
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Laser scanning ���� point-by-point solidification of resin.
Alternative light source : Digital Light Processing or
DLP® projectorsto project voxel data (volumetric pixels).
Each voxel dataset is made up of tiny voxels with dimensions
as small as 16µm x 16 µm x 15 µm in X, Y and Z direction
Stereolithography
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Envisiontec
3D Systems
Examples of models for investment (« waste
wax ») casting
Objet
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STEREOLITHOGRAHY
• Advantages :+ Surface aspect, precision (esp.
DLP systems)+ Well-known, mature technology+ Large volume machines+ …
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• Drawbacks : – Only light-sensitive resins– Supports necessary– Quite fragile parts, UV-sensitive– Uncontrolled shrinkage
• Materials :– light-sensitive epoxy resins .– UV-curable flexible or high-T°resins…
LASER SINTERING
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Selective Laser Melting : equivalent of SLS for metal p owders
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Classification of additive processes
Materials
to betransformed
Principles of transformation
Technologies Acronyms Pictures Main groups
Photo-
sensitive resin
Photo polymerization
Laser or UV flashing
SLA STL DLP Stereolithography
Printhead Polyjet 3D printing
Powder : polymeric, metal, ceramic, sand
Binding Printhead 3DP
Sintering / fusion
Laser, IR flashing, or electronbeam
SLS SLM DMLS EBM SMS
Laser Sintering/Melting
Projection DMD Deposition
Polymerfilament
Liquid state « welding »
Deposition FDM
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La fabrication Rapide peut être la 1 ère étape pour la fabrication par réplication : moule s able, ou pièce modèle.
Additive manufacturing technologies
❶ Basic principles
❷ 3D Printing
❸ @manufacturing
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Industrial targets• Reduction of marketing times• Decrease of costs• Quality control (and standards)
Trends : • Evolution towards small / medium size series,
mass customization, increased complexity• Product lifetime �
• Delocalization of large series manufacturing, of mouldmaking industry …
• Need for flexibility and reactivity of production
Important economical stakes
PRODUCT DEVELOPMENT : CONTEXT AND STAKES
COMPARISON OF COSTS
Cost/part as a function of production volume
⊕ of AM development :� Independant on part complexity� Fast� No specific tooling
BUT :� Limited choice of materials� Materials cost� Production time� …
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SLS : on the way to
industrial production
Laser sintering
principle:• Powder preheating below melting T°• Spreading of powder layer• Scanning with CO2 laser (infra-red),• Particles fusion and « sintering »• Build tank going down by a layer
thichness• Next layer…
Advantages :• Self-supporting powder• Great freedom of shapes,• Possible assembling and functional
systems
Drawbacks :• Few commercial materials available• Anisotropy of parts.• Limited part size
Application field :• Prototyping, direct part manufacturing,
rapid manufacturing.
Main current materials available : Polyamide 11 or 12 : plain, filled : glass beads, aluminium, carbon, and/or flame retardantPolystyrenePEEK (specific machine, 1 in Germany)
Main machine manufacturers :EOS GmbH, 3D Systems.
Dimensions : 700 X 380 X 60027
Frittage Laser Polymère
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EOS – Systèmes d’aide à
l’assemblage
EOS – chambre à air pour
hélicoptère
EOS – Maquettage
EOS – centrifugeuseEOS – prothèse
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DEVELOPMENT OF ADDITIVE MANUFACTURING
FDM machines at the production facility of RedEyeOn Demand, a business unit of Stratasys in Eden Prairie, Minnesota
ADDITIVE MANUFACTURING PROCESSES FOR
POLYMERIC MATERIALS FORMING
Part 2 : Selective sintering processes for polymer powders
- Analysis of SLS physical mechanisms- Introducing SMS
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Prior to sintering, 2 conditions are very important for the process:
Powder flowabilityPowder bed density
Main influent parameters
Particle size►►
►►
►►
Size distribution
Sphericity
IDENTIFICATION OF THE KEY MATERIALS PARAMETERS
DIFFERENT POWDER MORPHOLOGIES
InnovPA : Exceltec
Duraform PA : 3D Systems
PA2200 : EOS
All of them need SiO2 as flowability agent
(< 1 wt%)
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Innov PA
50µm
Duraform PA
50µm
PA 2200
50µm
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Warpage due to shinkage throughout the crystallization is a key issue
Sintering of semi-crystalline polymers
IDENTIFICATION OF THE KEY MATERIALS PARAMETERS
►►
Re-crystallization must be controlled
Tf = 181°C
Tc = 151°C
Powder bed T° maintained in the processing window w : Tm - Tc
Part warpage (« curling ») avoided
Polyamide 12 mostly used thanks to very wide w range
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The energy provided to the polymer material by the laser
Process conditions of first order influence are :
The heat provided to the powder during the whole
fabrication cycle
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MOST INFLUENT PROCESS PARAMETERS
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135°C 135°C
150°C
173°C
Right feed heater Left feed heaterPart heater
Piston heater
Cylinderheater
Process parametersThermal cycle
■ Different temperatures of preheating35
Process parameters
The energy supply depends on the:
■ Scan spacing (S) via laser beam superimposition
■ Laser beam celerity (v)
■ Laser radius (r)
■ Laser power (P)
Energy Density ED : a single parameter
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Power supply by
surface unit
Time of exposure
Number of exposures
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By application of Archimedes’ principle on samples infiltrated with CH2I2
Calculation of open and closed porosities
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CHARACTERIZATION OF MICROSTRUCTURE1- POROSITY
Closedporosity
Open porosityfilled by CH 2I2
Evolution of the global porosity (vs. ED) :
■ Porosity decreases when ED increases
■ Porosity reaches a minimum value about 2%37
By 3D X-Ray tomography
Computation of closed porosity fraction, information
on size and spatial distribution of pores
Analogy with
medical
scanner
After image analysis, 3D
reconstruction of porosity
distribution
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ENHANCED CHARACTERIZATION OF POROUS MICROSTRUCTURE
Succession of 2D
sections of the
sample
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Characterization of porosity
by Xray tomography
Example for Innov PA powder
Position of the part in the
build tankPosition of the part
during analysis
Tomographic sections
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LOW ED : bad weldingbetween layers
Observation of the 2 types of porosity : open and closed
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INFLUENCE OF ENERGY DENSITY ED ON POROSITY
Open porosity
reaches core of
parts
Example for Innov PA powder
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INTERPRETATION OF PART ANISOTROPY
Porosity is concentrated at the interface between successive layers
This is mostly noticeable at low ED, but still present at high ED
Mechanical properties are anisotropic
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InnovPA parts, ED = 0.024J/mm²
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Final microstructure is governed by:
DENSIFICATION PARAMETERS
During sintering 2 stages occur : Coalescence and melt densification
■ Evolution of the particles during coalescence : Frenkel’s model
With η : viscosityΓ : surface tension
■ Melt densification is due to diffusion/dissolution of gases from pores
� Granular characteristics which impact powder bed density
� Melt viscosity
� Crystallization temperature (and build tank T°during proce ss)
a0
x
a
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XCR: recrystallized phase crystal weightfraction (30%)
Source: D. Jauffres et al, Polymer 48, 6375-6383, 2007
With ∆HR: recrystallized phase enthalpy of fusion
∆HN: nascent phase enthalpy
XCN: nascent crystal weight fraction (50%)
Recrystallised fraction (fr) can becalculated by a deconvolution
method:DSC shows the presence of both
recrystallized and nascent fractions
CHARACTERIZATION OF MICROSTRUCTURE –2) CRYSTAL WEIGHT FRACTION AND RECRYSTALLIZED
PHASE
∆HR
∆HN
Objective:measure the evolution of fr and Xc with ED
Recrystallizedphase
Nascentphase
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Evolution of fr with ED
Occurrence of nascent particles between successive layers
From ED ≈ 2J/cm², no more nascent particles in the core of parts, but still present at the surface
INFLUENCE OF THE ENERGY PROVIDED BY THE LASER ON PARTICLE MELTING AND CONSOLIDATION
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Strong increase of fr up to ≈ 2.5J/cm² then stabilizes
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Eρ�
INFLUENCE OF THE PROCESSING WINDOW
Crystalline fraction measured by DSC:
Xc when ED
because more nascent
polymer is melted
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Comparison between InnovPA and DuraformPABuild tank T° = 150°C
Crystallization T° measured by DSC at 10°C/min :
Innov PA Tc = 151°C / Duraform PA Tc = 147°C
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►► Xc lower for Innov PA samples
lower Tc for Duraform PA
slower crystallization,larger crystalline ratio
Comparison between InnovPA and DuraformPABuild tank T°= 150°CCrystallization T°measured by DSC at 10°C/min :Innov PA Tc = 151°C / Duraform PA Tc = 147°C
Nascent powders
Injection molded parts
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CONCLUSION ON FORMATION OF
POROUS AND CRYSTALLINE MICROSTRUCTURE
Powder bed density (granulometry and morphology of powders) strong impact on porosity formation
Time spent in molten state (also depends on T° of build tank) strong influence on porosity and on final crystallinemicrostructure
Eρ < 2 J/cm² Eρ > 2 J/cm²
Duraform PA/PA2200 : Innov PA :
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►►
Porosity can be also influenced by viscosity (coalescence )
low ED high ED low ED high ED
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RELATIONS BETWEEN MECHANICALPROPERTIES (TENSILE) AND MICROSTRUCTURE
Elongation at break is oneof the most critical featuresof sintered polymer parts
P2
P1
General trend : when ED � ,ductility � because Xc �
But relations are more complex
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Material parameters
■ Melt viscosity
■ Powder size/morphology
■ Tm
■ Tc
Process parameters
■ Laser features (ED)
■ T° of build tank
■ T° of powder bed surface
Microstructure
■ Porosity
Pore size
■ Fr
■ Xc
Mechanical properties
■ Eab
■ Stiffness
CONCLUSION
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SMS – Selective Mask Sintering by IR flashing
Principales différences avec SLS :
• Each section (slice) is sintered as a whole by IR flashing through a mask which is regenerated for each layer
• Potentially faster than SLS
• Size part less limited
• Present technological issue : mask generation
• Process still in development
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powder spreading printing flashing repeat cyclePrinciples of sintering by IR flashing through a mask
Patent owned by Sintermask GmbH, Parsberg, Germany
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SMS-IR flashing :Lab-built prototype machine at INSA
� Manually operated, but automatization in project� Can be equipped with thermocouples for T°monitoring
during sintering
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Temperature monitoring in lab-IR machine(here 3 thermocouples inserted)
Comparison with numerical simulation
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A few orders of magnitude :
Maximum build velocities : SLS : ~ 25 mm/h (small area )IR-SMS : 35 mm/h , 10 à 20 s / layer, 5s target
Cooling time ~ fabrication timeNb of powder re-uses : ~ 7 times, mixed with « fresher » powder (e.g. 50% from feed tanks, 50% from build tank, or 75% used + 25% fresh)
Layer thickness : ~ 100 µmMinimum wall thickness : ~ 300 – 500 µm
Diameter of laser beam : 250 µm
Material cost : 50 - 150 Euros/kg
Some features of polymer sintering processes
SOME CONDITIONS FOR THE INDUSTRIALDEVELOPMENT OF ADDITIVE MANUFACTURING
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- Reliability of the production :- Availability of adequate materials- Good control over the process- Good understanding of the physical
phenomena, and of the relations betweenprocess parameters, material featuresand final part properties
- Development of quality control- Development of standardization and
qualification of AM systems and materials- Increase production speed- Improve powder re-usability
… still much work to be done !