Slides accompanying 2.008x* video module on Additive Manufacturing, Prof. John Hart, MIT, 2016.
*Fundamentals of Manufacturing Processes on edX: https://www.edx.org/course/fundamentals-manufacturing-processes-mitx-2-008x
5. 2.008x
Earlier AM parts (arguably not the earliest)
Photopolymerization
Kodama, Rev Sci Instr. 1981
Sintering of metal/ceramic powder
Housholder, 1979 (Patent)
Image: http://nsfam.mae.ufl.edu/Slides/Beaman.pdf
6. 2.008x
Additive Manufacturing (AM) refers to a process by
which digital 3D design data is used to build up a
component in layers by depositing material.
The term ‘3D printing’ is increasingly used as a
synonym for AM. However, the latter is more accurate in
that it describes a professional production technique
which is clearly distinguished from conventional
methods of material removal.
From the International Committee F42 for Additive Manufacturing Technologies, ASTM.
and http://www.eos.info/additive_manufacturing/for_technology_interested
8. 2.008x
Why is AM such a big
deal now?
§ Wide availability of CAD/CAM
software.
§ Improved automation and
component technologies.
§ A growing library of ‘printable’
materials.
§ Major industry and government
investment.
§ Freedom to operate enabled by
patent expirations.
§ Momentum, confidence, and
creative vision.
9. 2.008x
Agenda: Additive
Manufacturing
§ What and why?
§ Overview of AM processes
§ Extrusion AM (FFF/FDM)
§ Photopolymerization (SLA)
§ Powder bed fusion
(SLS/SLM)
§ Emerging AM technologies
§ Conclusion
11. 2.008x
The AM industry today
Wohlers report 2016
Machines
Services
2015: $5.2B AM machines and services
2015 growth = 26%
27-year CAGR = 26%
Worldwide mfg is ~$15 trillion (16% of
the world economy)
àà AM = 0.03%.
12. 2.008x
The AM industry today
“How do you use the parts made on your
industrial AM machines?”
Ti64 hip implant cups
(Arcam)
Orthodontic aligners
(Align Tech)
Wohlers report 2016
13. 2.008x
Aston
Martin DB7:
Skyfall
Custom airway stent: U. Michigan
Shoe cleats: NIKE
Tooling: Linear Mold,
Triform
Airbus
GE leap fuel nozzle
The diverse industrial uses of AM
Modular products:
Google Ara
17. 2.008x
How good (or bad) is additive manufacturing?
(it depends on the process, machine, settings, and post-processing)
Rate LOW 0.01-1 kg/hr
(getting better!)
Quality LOW ~0.1 mm resolution
(rate-quality tradeoff)
Cost HIGH $0.1-10 per gram!
(highly dependent on
material and process)
Flexibility AMAZING (if you know what to do)
24. 2.008x
Material and Binder Jetting
Laminated Object
Manufacturing (LOM)
Directed Energy Deposition
Stratasys/Objet
mCorFabrisonic
Sciaky
Optomec
Objet
Voxeljet
https://en.wikipedia.org/wiki/Laminat
ed_object_manufacturing
25. 2.008x
The 7 AM methods (from ASTM F42)
§ Vat photopolymerization (àà SLA): material is
cured by light-activated polymerization.
§ Material jetting (à Objet): droplets of build material
are jetted to form an object.
§ Binder jetting (à 3DP): liquid bonding agent is jetted
to join powder materials.
§ Material extrusion (àà FFF/FDM): material is
selectively dispensed through a nozzle and solidifies.
§ Sheet lamination (à LOM): sheets are bonded to
form an object.
§ Powder bed fusion (àà SLS/SLM): energy (typically
a laser or electron beam) is used to selectively fuse
regions of a powder bed.
§ Directed energy deposition (à LENS): focused
thermal energy is used to fuse materials by melting
as deposition occurs.
LowenergyHighenergy
26. 2.008x
We must master all the steps
Gibson, Rosen and Stucker, Additive Manufacturing Technologies
35. 2.008x
Discretization and toolpath effects
Diagrams from Gibson, Rosen and Stucker, Additive Manufacturing Technologies
Accuracy Strength
36. 2.008x
Polymer extrusion in FDM
Thermoplastic
à amorphous polymer network,
linear chain architecture
Comparison to injection into a mold
Tf = forming temp.
The chains align then slip during flow
Heated bed
ABS ~80C
Extruder
ABS ~260C
Groover, Fundamentals of Modern Manufacturing
Osswald et al., International Plastics Handbook
Malloy, Plastic Part Design Injection Molding
38. 2.008x
Extrusion force vs temperature
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
0 2 4 6 8 10 12 14 16
Extruder(Force((N)
Feed(Rate((mm/s)
200+C
230+C
260+C
59+N
à Force increases with feed rate
à Force is greater at lower temperature
à Force saturates at ~60 N
Extruder
Load+cell
Heater
assembly
Jamison Go
39. 2.008x
Shear failure of the filament
Drive knurls
(normal operation)
Material shear
(extrusion failure)
1 mm
Drive&wheel
Filament&
shear&area
Material&
under&drive&
wheel&teeth
Feed Direction
40. 2.008x
Geometry of the FDM nozzle
𝑰𝑰
𝑰𝑰𝑰𝑰
𝑰𝑰𝑰𝑰𝑰𝑰
𝑙𝑙#
𝑙𝑙$
𝑑𝑑#
𝑑𝑑$
𝛽𝛽
Heater block
Extrusion nozzle
I
II, III
Zone I: heating
Zone II: transition
Zone III: area reduction (dominates pressure drop)
41. 2.008x
Extrusion rate is limited by heat transfer
à Feed rates found to cause extrusion failure correspond with inadequate
filament core temperatures
3 mm/s 9 mm/s1 mm/s
Temperature(C)
1 mm/s
3 mm/s
9 mm/s
42. 2.008x
ABS blended with chopped carbon fiber
~5 mm bead size
Big area additive manufacturing (BAAM!)
50. 2.008x
Materialise NV (Belgium): excerpt from https://www.youtube.com/watch?v=98xG86GKj7A
à Material is cured by light-activated polymerization.
Stereolithography (SLA)
58. 2.008x
1. The laser beam scans the surface of the resin
2. Each laser pass cures a parabolic
cross-section of the resin
3. Resin properties determine the relationship
between light exposure and cure depth
(1mil=0.001”
=25.4microns)
From an example SLA resin
Gibson, Rosen and Stucker, Additive Manufacturing Technologies
y
x
v
(xstart, ystart)
Point i (xi yi)
(xend, yend)
yi
position x
Intensity [W/m2]Amplitude of electric
field [V/m]
Figure 1 (b) from "Epoxy and Acrylate Stereolithography
Resins: In-Situ Measurements of Cure Shrinkage and
Stress Relaxation" by Guess, et al.
59. 2.008x
Layers
The complete scan pattern
A ‘Star-weave’ pattern is
used to raster the surface
Top view
Side view
à This allows the resin to shrink
locally while curing (it happens)
while minimizing overall part
shrinkage and residual stress.
hs
0.01 inch
Hatch
Border
Side view
Gibson, Rosen and Stucker, Additive Manufacturing Technologies
70. 2.008x
Figure 1 from “Binding Mechanisms in Selective Laser Sintering and
Selective Laser Melting” by Kruth, et al. 2004
Critical process parameters
§ Laser power
§ Laser scan speed
§ Laser scan pattern
§ Particle size and packing density
§ Layer uniformity and thickness
§ Bed temperature
§ And more..
72. 2.008x
What’s different for SLM? (vs. FDM, SLA)
§ Powder = can be ~anything (flexibility, bulk properties!)
à Typically ~10-100um diameter (wide size distribution)
§ Complexity of powder handling (why?)
§ Flammable
§ Inhalation risk
§ Oxidation/contamination à often need inert atmosphere for metals
§ Energy required = high
§ SLA: 0.1 W for photopolymerization (at ~1 m/s scan)
§ FDM: 1-10 W for melting the filament
§ SLM: 100-1000 W for melting the powder (at ~1-10 m/s scan)
§ Post-processing: powder removal, machining away metal
support
74. 2.008x
Before and after
Figure 5 f) from "Analysis of defect generation in Ti-6Al-4V parts made using
powder bed fusion additive manufacturing processes" by Gong, et al., Additive
Manufacturing (2014)
Advanced Powders and Coatings Inc.
15-45 um 45-106 um0-25 um
Advanced Powders and Coatings Inc.
75. 2.008x
Zone%II
(subsurface%voids)
Zone%I%(fully%
dense)
Process map: SLM of Ti64
Gong, et al, “Analysis of defect generation in Ti–6Al–4V parts
made using powder bed fusion additive manufacturing
processes,” Additive Manufacturing, 2014.
Zone I: Fully dense (few defects)
Zone II: Sub-surface porosity due to excess
heating (gas bubble generation, trapped, do not
appear on surface)
Zone III: Insufficient melting
OH: Serious surface deformation (jams recoater)
Increasing energy
density
76. 2.008x
Process map: SLM of Ti64
Gong, et al, “Analysis of defect generation in Ti–6Al–4V parts
made using powder bed fusion additive manufacturing
processes,” Additive Manufacturing, 2014.
Zone I: Fully dense (few defects)
Zone II: Sub-surface porosity due to excess
heating (gas bubble generation, trapped, do not
appear on surface)
Zone III: Insufficient melting
OH: Serious surface deformation (jams recoater)
Overheated)
Zone)III
(underheat)
77. 2.008x
Prof. JP Kruth says…
During SLM, the short interaction of powder bed and
heat source caused by the high scanning speed of
the laser beam leads to rapid heating, melting
followed by drastic shrinkage (from 50% powder
apparent density to ~100% density in one step), and
circulation of the molten metal driven by surface
tension gradients coupled with temperature
gradients.
The resulting heat transfer and fluid flow affect the size
and shape of the melt pool, the cooling rate, and the
transformation reactions in the melt pool and heat-
affected zone.
The melt pool geometry, in turn, influences the grain
growth and the resulting microstructure of the part.
78. 2.008x
Chaos in the melt pool!
à Evaporation and recoil
à Ejection of ‘sparks’ (hot droplets)
Presented by Dr. Wayne King (LLNL) at ASME AM3D 2015
80. 2.008x
Ti frame = 1400g
Renishaw Plc; http://www.core77.com/blog/digital_fabrication/from_the_uk_the_worlds_first_3d-
printed_bike_frame_26463.asp
Success! Lots of parts in
close proximity.
Renishaw plc
82. 2.008x
Vrancken, et al. (2012) doi:10.1016/j.jallcom.2012.07.022
Mechanical properties of SLM Ti64
à Fine microstructure = high strength
à Small defects = lower ductility than standard (wrought) material
à Highly dependent on process parameters including post-print annealing!
84. 2.008x
Ti6Al4V hip implant cups
§ >40,000 acetabular (hip cup) implants in patients (Wohlers 2014);
approved in Europe and US.
§ Surface texture promotes osseointegration (bone attachment).
§ Arcam (EBM):
§ “now allows the ability to specify pore geometry, pore size, and density and
roughness of structures for trabecular structures and surfaces.”
§ 16 cups built simultaneously in 8 hours à then post-processing (intensive).
EOS/Arcam/Within; orthoinfo.aaos.org/topic.cfm?topic=a00377
86. 2.008x
High speed SLA: Carbon3D ‘Continuous liquid
interphase production’ (CLIP)
Carbon3D, Inc. / Tumbleston et al. Science, 2015.
TED talk by Prof. Joe DeSimone:
https://www.ted.com/talks/joe_desimone_what_if_3d_printing_was_25x_faster?language=en
Legacy effects / carbon3D
Ford / carbon3D
Dead zone thickness ~20-30 μm
87. 2.008x
Industrial automation of AM
Additive Industries: http://additiveindustries.com/Industrial-am-systems/Metalfab1
screenshot from https://www.youtube.com/watch?v=TssX2JsL0uk
94. 2.008x
Challenges to
accelerate AM
§ Design tools and data
management to fully realize the
potential of AM.
§ Process control; higher quality
at faster rate and process/part
qualification.
§ Standards.
§ Education!