2. 2 Additive Manufacturing – A Materials Perspective
Additive Manufacturing (AM), of which 3-D
printing is but one technique, is becoming
increasingly applied to many different systems.
Although oil & gas and maritime industries
currently constitute only about 5 % of the
total AM market, it is anticipated that AM will
rapidly expand its reach in these industries.
AM proffers many possibilities in innovative
manufacturing, but in this position paper
we present our perspective on the risks
associated with AM as the technologies are
currently being developed. Qualification and
certification may provide significant challenges
in AM because of the potential for variability
in specified properties. Because building up a
product using AM incorporates many steps, the
traditional qualification methods of repeated
testing of an end product from a centralised
facility will not be sufficient. The distributed
nature of AM means that the product variability
determined for one location may be entirely
different from another; this may be due to
software and hardware differences, as well
as a myriad other factors. The methodology
needed will relate the variability of the many
steps leading to the end product. Here we
present a Bayesian network methodology that
can be used to assess the risks, both to the
manufacturer and the users, arising from AM.
Such a framework may also assist in developing
the information needed to reduce the risks
from implementation of AM parts. The overall
risk with AM involves many components. In
this position paper, we focus on the materials-
related risks, although some aspects of
software-related risks are also mentioned.
ACKNOWLEDGEMENTS
This Position paper has been co-authored
by Shan Guan, Liu Cao, Francois Ayello, and
Christopher Taylor, all in the Materials Program,
Strategic Research & Innovation, DNVGL. The
authors acknowledge the reviews and helpful
comments from Thomas Mestl and Joost
Vanden Berghe, DNVGL. The assessment of
AM technologies was originally motivated
by internal communication from Timo
Kouwenhoven, DNVGL.
Contact Details:
Shan Guan, Ph.D. Senior Researcher, Materials Program, Strategic Research & Innovation DNVGL: Shan.Guan@dnvgl.com
Narasi Sridhar, Ph.D. Director, Materials Program, Strategic Research & Innovation DNVGL: Narasi.Sridhar@dnvgl.com
PREFACE
4. 4 Additive Manufacturing – A Materials Perspective
Additive manufacturing (AM) enables the building
of three-dimensional solid objects from digital
models, and thus the realisation of complex parts.
This contrasts with many traditional manufacturing
methods, sometimes referred to as subtractive
manufacturing, in which pre-forms are made first
and from these the final parts are fabricated. Near
net shape manufacturing has existed for several
decades through various advanced casting and
powder metallurgy techniques. However, even
near net shape manufacturing techniques make
the whole component first and then finish it to its
final dimensions. A further distinguishing feature
of AM is its distributed nature. While traditional
manufacturing mostly takes place at a centralised
facility, with the resulting parts distributed to end
users, AM has the potential for implementation
at the point-of-use. This enables innovations in
manufacturing value chains, many of which are still
being realised.
The emergence of modern AM can be traced back
to the mid 1980s when Charles W. Hull was granted a
patent entitled “Apparatus for Production of Three-
Dimensional Objects by Stereolithography” (U.S.
Patent 4,575,330). Stereolithography was described
as a process of making solid objects by successively
“printing” layer-by-layer of ultraviolet-curable
material. Later, in 1988, 3D Systems commercialized
the most popular stereolithography machine at that
time: SLA 250. Following the creation of laminated
object manufacturing in 1991, the invention of
selective laser sintering (SLS) machines opened
the door to mass customisation of both plastic and
metallic parts. For example, powder fusion bed, an
AM process in which SLS technology is commonly
implemented, is currently the exclusive platform for
making metallic function-parts. As these machines
became viable at the beginning of the 21st century,
AM technologies finally indicated the possibility of a
new type of industrial revolution.
A survey of 105 manufacturers of 3-D printers
showed that Industrial/Business Machines, Consumer
Products, and Motor Vehicles were the three leading
industrial sectors (Fig 1). Shipping and Oil & Gas,
categorized as “others”, accounted for just 5 % of
overall application areas. [1]
The worldwide market for
AM, consisting of all products and services, was $2.2
billion in 2012, and is expected to reach $12 billion
by 2025, representing an impressive average annual
growth rate of 34% (Lux Research). Although AM
cannot yet manufacture large structures, it is capable
of making small components that can be critical to
the functioning of larger structures.
INTRODUCTION
5. Additive Manufacturing – A Materials Perspective 5
In examining the future role of AM in large-scale
industrial applications, two important questions
arise:
1. What is the risk associated with incorporating
AM components into systems?
2. Which tools can be used to assess the risk
added by using these parts?
Many factors could increase the risk in AM
utilization, for example large variation in processing
technologies and 3-D printers, lack of industrial
standards and regulations, and greater variability in
material properties compared with those made by
traditional manufacturing processes. In this position
paper, we introduce several important AM processes
of interest to maritime and oil & gas applications,
including their applications, technological readiness
levels, and limitations. Furthermore, we examine a
Bayesian network approach for assessing the risks
associated with utilizing AM.
Figure 1. SLA250, Stereo lithography (left), and SLM 500 HL, SLS machine (right). (See image credit 1)
Motor Vehicles (17%)
Other (5%)
Architectural (4%)
Government/Military (5%)
Academic Institutions (6%)
Medical (14%)
Consumer Products (18%)
Industrial/Business Machines (19%)
Aerospace (12%)
Figure 2. AM industrial applications and revenues in 2014 [1]
17%
4%
5%
6%
14%
18%
19%
12%
5%
6. 6 Additive Manufacturing – A Materials Perspective
A generic AM value chain typically contains eight
steps. [2]
1. Conceptualisation and Computer Aided Design
(CAD) to generate a 3-D model.
2. Conversion of 3-D model to STL or newer AMF
file format, which is supported by both CAD
software and AM machines.
3. 3-D file manipulation1
and transfer to AM
machine.
4. AM machine setup, tuning, and maintenance.
5. Building parts by joining materials deposited in
successive layers.
6. Removing parts and support structures, perhaps
additional cleaning.
7. Post-processing2
for application purposes.
8. Inspection.
AM system manufacturers have created unique
process names and material designations in order
to differentiate themselves from their competitors.
[2]
This has led to confusing terminologies as
1 File manipulation includes verification of part geometry,
selection of orientation and location, addition of support
structure, scale and duplication, etc.
2 Post-processing may involve infiltration, hot isostatic pressing,
heat treatment, surface finish, coating and assembly.
many processes sound different but basically
employ similar methods and materials. In January
2012, ASTM International Committee F42 on AM
Technologies recommended names and definitions
for seven AM processes in the specification of ASTM
F2792. [3]
1. Binder Jetting: a liquid bonding agent is
selectively deposited to join powder materials.
2. Directed Energy Deposition: focused thermal
energy is used to fuse materials by melting them
as they are being deposited.
3. Materials Extrusion: material is selectively
dispensed through a nozzle or orifice.
4. Materials Jetting: droplets of build material are
selectively deposited.
5. Powder Bed Fusion: thermal energy selectively
fuses regions of a powder bed.
6. Sheet Lamination: sheets of material are bonded
to form an object.
Vat Photopolymerization: liquid polymer in a vat is
selectively cured by light-activated polymerization.
However, some newly invented processes may
not fit into this system, e.g. Electrochemical Liquid
Deposition (ECLD), Laser Transfer Direct Write
(LTDW), Dip-pen Nanolithography, etc. A brief
summary of each category and related terminologies
from manufacturers is provided in Table 1.
AM PROCESSES
7. Additive Manufacturing – A Materials Perspective 7
Table 1. Comparison of Different AM Processes.
3 Cost of AM machines, materials feedstock, and regular
maintenance.
AM
PROCESSES
Directed
Energy
Deposition
Powder
Bed Fusion
Materials
Extrusion
Materials
Jetting
Binder
Jetting
Sheet
Lamination
Vat
Photopoly-
merization
Materials
Plastic √ √ √ √ √ √
Metal √ √ √ √
Ceramic √ √
Composite √ √ √
Others
Wax,
photo-
polymer
Sand Paper
Resin, liquid
photo-
polymer
Energy Source
Laser,
electron
beam
Laser,
electron or
ion beam
Heating
coil
Heating coil,
UV light
N/A
Laser,
ultrasonic
UV light,
X-ray or
y-rays
Relevant Terms
LENS, DMD,
LBMD, EBF3
,
DLF, LFF,
LC, CMB,
IFF
SLS, SLM,
DMLS, DMP,
EBM, SPS,
Laser Cusing
FDM,
FFF,
FLM
Inkjet,
PolyJet, MJM,
Aerosol Jet,
ThermoJet
3DP,
LPS,
DSPC
LOM,
UC,
UAM
SL, SLA,
MPSL,
DLP, FTI
Leading
Manufacturer
Optomec,
DM3D,
TRUMPF,
Fraunhofer
3D Systems,
EOS, Concept
Laser, SLM
Solutions,
Stratasys,
3D Systems
3D Systems,
Stratasys,
Solidscape,
3D
Systems,
Voxeljet,
ExOne
Mcor,
Cubic,
Fabrisonic
3D Systems,
EnvisionTEC,
RapidShare
Part Durability High LowDurability
Detail Precision High LowDetails or Precision
Surface
Roughness
High LowSurface Roughness
Build Speed Slow Slow Medium Medium Fast Fast Medium
Cost3
High High Low Low Medium Medium Medium
Support No Yes Yes Yes No No Yes
Post-process Yes Yes Minimum Minimum Yes Yes No
3DP, 3-Dimensional Printing
CMB, Controlled Metal Build-up
DLF, Directed Light Fabrication
DLP, Digital Light Processing
DMD, Direct Metal Deposition
DMLS, Direct Metal Laser Sintering
DMP, Direct Metal Printing
DSPC, Direct Shell Production Casting
EBF3, Electron Beam Freeform Fabrication
EBM, Electron Beam Melting
FDM, Fused Deposition Modelling
FFF, Fused Filament Fabrication
FLM, Fused Layer Modelling/Manufacturing
FTI, Film Transfer Imaging
IFF, Ion Fusion Formation
LBMD, Laser-based Metal Deposition
LC, Laser Consolidation
LENS, Laser Engineered Net Shaping
LFF, Laser Freeform Fabrication
LOM, Laminated Object Manufacturing
LPS, Liquid Phase Sintering
MJM, Multi-Jet Modelling
MPSL, Mask Projection Stereolithography
SL, Stereolithography
SLA, Stereolithography Apparatus
SLM, Selective Laser Melting
SLS, Selective Laser Sintering
SPS, Spark Plasma Sintering
UAM, Ultrasonic AM
UC, Ultrasonic Consolidation
8. 8 Additive Manufacturing – A Materials Perspective
IMPORTANT AM PROCESSES FOR MARITIME
AND OIL & GAS APPLICATIONS
Most AM processes have been pioneered for
a couple of decades by manufacturers listed in
Table 1, and who still possess the key technologies
and their improvements in the industry-level AM
machines. These machines are capable of managing
minimum feature size at micron scale and finishing
single part sizes as large as 4m x 2m x 1m (Voxeljet
VX4000). In general, AM machines have to address
the compromise between build speed and accuracy,
which has been improved by successfully employing
technologies such as different scan strategies,
multiple nozzles, and print heads, hybrid process,
etc.
Recent releases of earlier AM patents enable
production of low budget, consumer-level, desktop
3-D printers for prototyping. However, industries are
more interested in AM processes that enable direct
part production, with advantages in complexity
for free and quick 3 F’s – Form, Fit and Function.[2]
Applications of metal or plastic functional parts
made by AM processes have to tackle the potential
impact on performance and integrity compared with
counterparts made by traditional methods; adverse
consequences are unacceptable for many industries,
such as Aerospace, Automotive, Maritime, Energy,
Oil & Gas, and Medical. Three categories of AM
processes with high potential for implementation
in part production for Maritime and Oil & Gas
applications have been selected and are described
in greater detail in the following sections.
Materials Extrusion
Material contained in a reservoir is forced through a
nozzle and bonded with adjacent material when it is in
a semi-solid or liquid state, while the extrusion head or
the build platform moves in the x-y plane. The material
solidifies fully afterwards. After a layer is completed,
the build platform moves down, or the extrusion head
moves up, for the next layer to be extruded. The raw
material is typically a filament of thermoplastic coiled
onto a spool, but plastic pellets or granules are also
used. Support structures are required for bottom
surfaces and overhanging features.
The first material extrusion system, Fused Deposition
Modelling (FDM), was introduced in 1991 by
Stratasys. For the ease of support structure removal,
FDM machines use two spools of material in printing,
build material and support material. The latter either
has a lower melting point, or weaker mechanical
properties, or can be dissolved in a specific solvent.
In comparison with other AM processes, FDM
systems and materials are relatively inexpensive and
therefore dominate the budget 3-D printer market
($500~$5000).
A particular scan strategy is employed to balance
the build speed and precision in an FDM system:
an outline of the 3-D model is first plotted at low
speed using a small size nozzle and material is filled
inside later at high speed using a larger nozzle size.
Material flow rate must be accurately controlled to
match the changes in speed and direction of the
extrusion head. Alternate scan pattern of adjacent
layers, sufficient residual heat of extruded filament,
and minimum overlap with previously laid material
are also required to ensure minimal gaps between
extruded route and effective bonding to form a
coherent solid structure. However, the properties of
the final parts are not as uniform as for their injection-
moulded counterparts.
The properties along the z-direction and at places
where the extrusion nozzle changes direction are
usually the weaker points.
Powder Bed Fusion
Thermal energy is used to fuse selected regions
of a thin layer of powder that has been spread
across a build platform by a scraping blade or
counter-rotating levelling roller. The source of the
thermal energy could be a laser, electron beam, or
focused ion beam. On completion of a layer, the
build platform is lowered by one layer thickness
and the powder compartment is raised by one layer
thickness to feed the next layer. The entire process
takes place in a closed chamber filled with inert gas
to minimize oxidation of the powder materials.
Both polymer and metallic materials are available in
powder bed fusion processes, and are described by
“sintering” and “melting” respectively. For polymers,
the unfused loose powder around selected regions
serves as support structure, so no additional
supports are usually needed. For metals, anchors
are typically required to attach a part to the build
platform and support overhanging features, since
high thermal gradients in the build chamber can lead
to thermal stresses and warping. In order to prevent
non-uniform thermal expansion and contraction, the
build platform is usually maintained at an elevated
temperature to preheat the powder material.
Powder bed fusion systems usually cost more than
other AM processes to own and operate. The thermal
process has the potential to cause warping, residual
stresses and heat-induced distortion for all materials
9. Additive Manufacturing – A Materials Perspective 9
ULTEM®
Air duct
Functional
prototype
Tool and fixtures
Figure 3. An illustration of a Fused Deposition Modelling (FDM) process and some plastic parts fabricated by FDM.
(See image credit 2)
Support material filament
Build material filament
Extrusion head
Drive wheels
Liquifiers
Extrusion nozzles
Part
Part supports
Build material spool
Support material spool
Build platform
Foam base
Injection
mould
10. 10 Additive Manufacturing – A Materials Perspective
fabricated by powder bed fusion. Loose powders
are easily affected by heat surrounding the building
part, and grow a “skin” of porous attachment on
the desired part. The fine powder materials used
for this process degrade slightly each time they are
exposed to the elevated temperature; therefore
proper powder handling and recycling procedures
are required. The final part made from powder bed
fusion process also suffers from porosity, which
adversely impacts part performance and needs to be
minimized.
Directed Energy Deposition
Focused thermal energy is used to melt materials in
a narrow region as the material is being deposited
from powder or wire feedstock. Each pass of the
deposition head creates a track of solidified material,
and adjacent overlapping tracks of material make up
layers. Manufacturing of complex 3-D geometry may
require a support structure or multi-axis deposition
head. In most cases, the metal powders are injected
into a pool of molten metal created by a focused
laser beam, similar to laser cladding.
Figure 4. An illustration of Selective Laser Sintering (SLS) process and some metal parts fabricated by SLS.
(See image credit 3)
Lenses
X-Y scanning mirror
Laser beam
Sintered paint
Powder bed
Laser
Leveling roller
Powder feed supply
Powder feed piston
Build chamber
Build piston
Powder feed piston
Powder feed supply
Aluminium automotive
heat exchanger
Co-Cr dental
building platform
Co-Cr Fuel injector
and swirler
Micro-metal
gear
Titanium hinge
bracket
11. Additive Manufacturing – A Materials Perspective 11
Figure 5. An illustration of the laser metal deposition process to build and repair metal parts.
(See image credit 4)
Directed energy deposition systems are not as
popular as other AM systems on the market, but
they enable deposition of multi-component or
functionally graded materials. Many directed energy
deposition systems use a 4-axis or 5-axis motion
system to position the deposition head, which
provides extra flexibility to the building process
instead of being limited to successive horizontal
layers. This capability makes directed energy
deposition suitable for adding material onto an
existing part, such as a component repair.
Since all three types of processes involve deposition,
melting, and solidification of material powder on
a substrate surface, they result in a high density
of parts. The typical small size molten pool and
relatively rapid travel speed combine to produce
very high cooling rates and large thermal gradients,
which produce non-equilibrium solidification
microstructure and a finer grain structure than
traditional castings. On the other hand, residual
stresses as a result of fast solidification can lead to
cracking during or after part construction. The scan
Lens Repairing
Titanium Vane Edge
12. 12 Additive Manufacturing – A Materials Perspective
pattern is important for part quality and has to be
changed from layer to layer to minimize residual
stress built-up.
AM generally does not have any advantage for large
volume production of parts with regular geometries.
Nevertheless, AM technologies for production offer
several beneficial features for the maritime and oil &
gas industries:
a. “Complexity for free” enables complex
geometries to be manufactured. Examples
include cellular/lattice internal structures for a
better strength to weight ratio, high efficiency fuel
injector with fine flow channels, and conformal
internal cooling channels in heat exchangers
or drill heads that can lower operational
temperature and prolong lifetime.
b. Flexible manufacturing operation allows highly
customizable components in low volume and fast
production cycles to save lead time and cost.
c. Additive process and minimum need of tooling
are appealing for making components involving
expensive and hard materials.
d. Decentralised production using AM technologies
simplifies the supply chain and reduces inventory
required.
MATERIALS AND PERFORMANCE
The materials available for AM processes are
summarised in Table 2. A variety of plastic materials
with a diverse range of properties are commercially
available for AM machines. Nevertheless, plastics
are mainly used for prototyping and considered as
consumable components with a short lifetime. Even
as end-use parts, long-term performance is not a
critical concern for the application of plastics. Plastic
parts are cheaper and faster to fabricate using AM
technologies, and any damaged parts are routinely
replaced without severe consequences.
Powder bed fusion and directed energy deposition
processes are typically capable of producing metal
parts. Metallic components used in maritime or oil
& gas industries often operate under demanding
loads and environments, and are expected to
last a long period in service without compromise
in performance. Because of the critical nature of
such applications, several factors inherent in the
production of AM parts must be addressed:
Porosity
In most AM systems, metal parts are built by
solidification from metal powder-melt to obtain
nearly 100 % density. However, less than fully
dense parts often result in inferior properties and
performance than the cast or wrought counterparts.
Porosity could act as crack initiation sites and lead
to premature failure, especially under cyclic stress
conditions. [1]
Powder compaction methods, such
as hot isostatic pressing (HIP) used in powder
metallurgy, are transferred to AM as a post-
processing method to reduce parts’ porosity.
Figure 6. Typical porosity of AM metal part: (a) Scanning Electron Microscopy image shows open pores on the surface of
SLM-processed Inconel 718 and (b) optical microscope image shows pores in the bulk of DMLS-processed commercial
Al-Si-Mg alloy. (See image credit 5)
(a)
(b)
13. Additive Manufacturing – A Materials Perspective 13
Layered Structure
Building a 3-D object, layer-by-layer, may
unavoidably break the uniformity along the
z-direction perpendicular to the layers, leading to as
much as a 50 % loss of properties in the z-direction.
[2]
Improvement of properties in the z-direction relies
on the materials bonding between the adjacent
layers, which requires accurate control of sufficient
energy injection and residual heat energy to form
coherent solid structure across layer interfaces, and
alternate scan patterns of adjacent layers to minimize
gaps between them.
Quality and Reliability
AM parts are being increasingly used as final
products. The requirement for rigorous and
repeatable production quality is a considerable
challenge to the application of AM in several
industries that have minimum risk tolerance.
AM is capable of creating high quality parts, but
the consistency of their quality and long-term
performance have not been sufficiently investigated.
To be accepted, AM parts must comply with the
same international or company standards used for
conventional parts. ASTM International Committee
F42 formed in 2009 to address the lack of AM
standards in an attempt to control part-to-part
consistency.
Safety and Sustainability
Industries are also seeking safe and sustainable
development, while materials and technologies
advance. AM may be inherently more sustainable
than conventional manufacturing as it produces
less waste and transportation supply chains are
reduced significantly because of point-of-use
production capabilities. However, several safety
and sustainability issues need to be evaluated.
Manufacturing of metal powders can be an energy-
intensive and wasteful process compared with
conventional ingot and cast metallurgy. Powders of
raw material may also result in various health and
safety concerns if proper handling and recycling
of fine powders is not followed. A number of
photopolymers have been invented for lithographic
techniques, but they degrade slowly on exposure to
UV, resulting in the need for replacement. Specific
disposal procedures are required for those new
plastics and many other one-time used prototyping
parts. In evaluating AM, all these issues need to be
considered for a sustainable process.
Figure 7. Optical microscope images of Al-Si-Mg alloy sample fabricated by DMLS after etching with Weck’s reagent: (a) a
section along the build direction (z-axis) shows layer-wise structure consisting of individual scan paths; (b) a section parallel
to the powder deposition plane (xy-plane) displays overlaid multiple scan paths. (See image credit 6)
14. 14 Additive Manufacturing – A Materials Perspective
AM Materials AM Processes Major Manufacturer and Supplier Applications
PLA, ABS, PC, PC/
ABS blend, PP, TPE,
PMMA, wax
FDM, SLS,
Materials
Jetting, Binder
Jetting
Stratasys, 3D Systems, Solidscape,
Voxeljet
Automotive, aerospace, medical devices,
electronics housing, packaging, seals,
precision casting patterns, kitchen tools,
HVAC, art & fashion.
Nylon, ULTEM,
PPSF/PPSU, PS,
PET, PVA
FDM Stratasys
PA, PAEK, PS, TPU SLS EOS, 3D Systems,
CRP Technology, Materialise
Acrylics, acrylates,
epoxy, resin, rubber-
like, ABS-like
SLA, DLP,
PolyJet, MJM
3D Systems, Stratasys, Solidscape,
DSM Somos, EnvisionTEC
Medical & dental, packaging,
seals, investment casting patterns,
demonstration.
tool steel, SS 316L
& SS, Ti-6Al-4V & Ti
alloy, Co-Cr, Ni-Cr,
Ni alloy, Al-Mg-Sc,
AA 4047, Cu alloy
SLS, SLM,
DMLS, EBM,
LENS, DMD,
Aerosol Jet
EOS, Optomec, Arcam, ATI
Powder Metals, Carpenter,
LPW, GE Aviation, Airbus
Automotive, aerospace, maritime,
energy, oil & gas, mining, tooling,
cladding, metal component repair,
functionally graded laminates,
electronics, injection/die casting mould,
medical/biomedical implant, art &
jewellery.SS, tool steel,
bronze, Fe, W,
w/bronze infiltrant
Binder Jetting ExOne
Al, Cu, Ti, SS UC, UAM Fabrisonic
Silica sand, alumina/
silica
Binder Jetting,
SLS
Voxeljet, ExOne, EOS, Viridis3D Sand cores/moulds for casting,
art design
PA filled w/ glass,
carbon fibre,
aluminium, WC
SLS 3D Systems, EOS Automotive, aerospace, defence.
Al, Cu, SS foils
w/ TiNi fiber
UC, UAM Fabrisonic Superstructure, reinforced
low-cost matrix.
AA, Aluminium Alloy
ABS, Acrylonitrile Butadiene Styrene
HVAC, Heating, Ventilation
& Air Conditioning
PA, polyamide
PAEK, Polyaryletherketone
PC, Polycarbonate
PET, Polyethylene Terephthalate
PLA, Polylactic Acid
PMMA, Polymethyl Methacrylate
PP, Polypropylene
PPSF/PPSU, Polyphenylsulfone
PS, Polystyrene
PVA, Polyvinyl Alcohol
SS, Stainless Steel
TPE, Thermoplastic Elastomer
TPU, Thermoplastic Polyurethane
ULTEM®, amorphous thermoplastic
polyetherimide
Table 2. Types of materials used in AM and according AM processes.
16. 16 Additive Manufacturing – A Materials Perspective
AM technologies generate enthusiasm and bold
manufacturing ideas, from 3-D printing of an entire
house to an entire aeroplane. [6, 7]
What about an
entire ship? Will AM processes be used to build large
ships, for example? To answer this question we must
take into account both the requirements of future
ships and the prospective improvements in AM
technologies; and then we must attempt to predict
where the two technologies meet.
LIMITING FACTORS
Building time: Current AM processes are quite slow.
Only 4 litres of steel per hour can be deposited,
an equivalent of 0.75 tons of steel per day. The
speed is limited by the laser melting steel powder
and cooling time before the next pass of the laser
in order to deposit the next layer. We can expect
deposition speed to increase slightly, but because of
the physical constraints of the process this will not be
by orders of magnitude.
Building costs: The present high price of starting
material is the main factor in determining the high
price of 3-D printed parts. Human labour and
CAPEX are dwarfed in comparison with the high
price of starting materials (e.g. $180/kg for stainless
steel powder vs. $6/kg for stainless steel bar). In
order to be competitive, the price of raw material
will have to decrease by two orders of magnitude.
Depending on the AM process to be used and any
customization of AM equipment, capital costs can
also be high.
Uniformity of properties: Directionality and variability
of properties can be significant for AM parts and may
limit the type of parts made by AM. The metallurgical
quality of large parts made using powder
metallurgical techniques as implemented in AM has
not been clearly established nor have the techniques
been optimized. The fatigue and fracture strengths
of large-scale objects made by such methods need
further assessment.
ENCOURAGING FACTORS
On the other hand, AM is capable of providing new
manufacturing solutions. For example:
¾¾ Lighter and stronger structures (see Figure 8;
aeroplane structure mimicking bone structure)
¾¾ More efficient designs (see Figure 9; ship
construction mimicking ‘organic’ shape could
save significantly on fuel consumption). If
large-scale AM proves to be economically and
technical viable in the future, we can predict that
the freedom from conventional manufacturing
processes will allow ‘strange’ ships to roam the
sea.
WILL AM FIND APPLICATION
IN THE MARITIME INDUSTRY?
17. Additive Manufacturing – A Materials Perspective 17
TECHNOLOGY QUALIFICATION
Many approaches have been considered by
the engineering community in evaluating new
technologies and the pathways for inserting them
effectively into a system. In the 1980s, NASA
developed Technology Readiness Level (TRL) as a
way to define the position of a specific technology
with respect to its maturity and plan for its further
development. More recently, ISO has developed
a revised TRL definition, essentially mirroring the
original NASA definitions. These definitions can be
tailored to AM processes. An initial assessment of
AM technologies for small and large components
shows that AM is at a TRL 3 level for large
components (see inset for definitions). DNVGL
Technology qualification standard RP-A203 classifies
technology maturity levels in terms of a matrix. It
further identifies methods to assess the reliability
and risk of new technology through a variety of
methods, depending on the history of the system
examined. The end result, in addition to detailed risk
assessment, could be a qualitative risk ranking.
Figure 8. Left, picture of bone structure. Right, Boeing new concept for commercial aeroplanes; AM processes would allow
nature to be copied, thereby making lighter and more efficient planes. (See image credit 7)
Figure 9. The irregular shape of the whale fins provide
reduced drag (current manufacturing processes for ships
have difficulties imitating such structures).
(See image credit 8)
TECHNOLOGY READINESS LEVELS IDENTIFIED
FOR AM PROCESSES BASED ON NASA AND ISO
DEFINITIONS
TRL 1 Basic principles observed and reported
TRL 2 Technology concept and application
formulated
TRL 3 Analytical or experimental proof-of-concept
TRL 4 Technology validation in laboratory
environment
TRL 5 Technology validation in relevant
environment
TRL 6 Prototype demonstration in a laboratory
environment
TRL 7 Prototype demonstration in a relevant
environment
TRL 8 Technology integrated in relevant
environment.
TRL 9 Proven technology through years of
successful testing in relevant environment
(i.e. Marine environment)
18. 18 Additive Manufacturing – A Materials Perspective
Although it may be said that AM provides
“complexity for free”, there is no such thing as a
“free lunch.” With this caveat in mind, the decision to
adopt AM technology – either as an end user or as an
original equipment manufacturer (OEM) - should be
made with a keen awareness of the risks that would
be introduced throughout the lifetime of a given
part produced by this method. A generic lifecycle is
presented in Figure 10.
Risks that emerge during Phase I include the lack
of design principles for efficient design of the
AM process, reliability of models such as finite
element simulation to optimize part geometry,
and research and development costs associated
with optimizing the process and post-process
parameters (such as print orientation, materials
selection and heat-treatment) as well as developing
testing and characterization protocols for parts
produced according to this manufacturing
method. [8-12]
Regulation and qualification may also
prove challenging, given rapid advances in the
manufacturing process compared with the relatively
slower pace of standard development. [1, 3]
Risks that emerge in Phase II may arise from
variations in material quality and availability, changes
in production units/upgrades, and “user-dependent”
factors. Post-processing steps may also introduce
additional risks of non-conformance. Finally, parts
must pass quality control standards.
During Phase III, the end-user will encounter risks
that predominantly arise due to the relative novelty
of the technology and lack of extended lifetime data
for parts produced by AM. The exact magnitude of
risk will depend upon the expected longevity of the
part and the consequences of materials failure.
A layer-by-layer manufacturing technique introduces
isotropic and anisotropic heterogeneities (such
as voids and internal interfaces) in the material,
potentially creating new failure modes that may
be reduced through post-processing treatments.
[13, 14]
Accordingly, new materials inspection
procedures and decision-making criteria may need
to be developed, tested, and employed. Under-
appreciated risks could emerge if failure criteria
developed for conventionally machined parts are
applied to their AM counterparts. The end user will
also encounter risks due to increase in part cost
due to the AM procedure (as materials costs, for
example, are higher for metallic powders). [15, 16]
Risks
can also emerge when parts need to be replaced,
and these will be a function of the supply chain and
the availability of in-house AM units that could be
used for replacement and repair options. Finally,
the decision made by an end user to employ a part
produced by AM process will be largely motivated
by the degree to which a technology is enabled
by (that is, contingently dependent upon) the AM
component (for example, the production of highly
efficient heat exchangers where AM provides unique
design and manufacturing options [17]
).
CONCEPTUAL APPROACH TO
RISK ASSESSMENT OF AM
19. Additive Manufacturing – A Materials Perspective 19
FOR OEM
Risks from Phases I, II and II have been combined to
provide a generic and comprehensive model for risk
assessment using the method of Bayesian inference
and Bayesian networks. Bayesian networks provide
the opportunity to investigate the cause-effect
relationships between sources of risk and so can
be used to isolate the key contributors to any risk-
sensitive decision making; in this case, the decision
to employ AM or not. [18, 19]
Generic risk networks
have been created for two classes of user: the OEM
and the End User of the part. A risk analysis for OEMs
can be divided into three key categories: Design
risk, Production risk, and Qualification requirements.
Design risk can be reduced by the presence of
design principles, including FEM optimisation of
part geometries and rules for adjusting designs to
accommodate part-shrinkage and minimize the use
of supports. Design risk will also be a function of
the overall part complexity, including the materials
composition and number of components such
as overhangs and struts. The production risk has
similar contributors, such as the composition of the
material used (which will influence availability and
variability), the material quantity (small components
are more cost-effective to produce using AM than
large components), and the level of post-processing
required. Finally, qualification requirements will
be related to the application: more demanding
applications require stricter tolerances. Ultimately
the decision to apply AM to a component will require
a comparison between the risks associated with
using AM technology and the risks from producing
the material via a conventional route. In some cases
AM may be the only option, such as when it is an
enabling technology, yet this does not obviate the
fact that risks may still be incurred during service or
sourcing the part from an OEM.
Figure 10. The three phases of the lifecycle of a part produced by AM. Phase I: Design and qualification; Phase II: Additive
manufacture; Phase III: Deployment and use until failure.
Design specification
CAD Design
In silco Manufacture/
FEM Optimization
Additive
Manufacture
Installation and
Deployment
Inspection
Maintenance
Corrosion Mitigation
Exceeds
Lifetime
Failure
Dispose and
Recycle
Post-Processing
Validation
Prototype Print, Post Process,
Determination, Testing
Regulation and Qualification
PHASE I PHASE II PHASE III
20. 20 Additive Manufacturing – A Materials Perspective
FOR END USERS
The risk analysis for the end user follows a
similar decomposition. Risks are sub-divided
into Acquisition risk, Service risk, and Supply
risk. Acquisition risk will be based upon the cost
of the component compared with conventional
manufacture, system qualification requirements,
and whether or not AM is required as an enabling
technology. The Service risk will entail the risk
of failure, which must be considered based on
technology maturity, intended lifetime and the
service environmental conditions, as well as the
option that AM provides for facile component repair.
Supply risks may be reduced due to the ability of
AM to produce highly reproducible parts, given the
design algorithms, process and powder (i.e. raw
material) stability and control over supply sensitivity.
Furthermore, networking provides the ability for
distribution and control over designs from the
central design office to remote locations. The option
of a user having an on-site AM machine can also
decrease supply risk, but at the cost of increasing
the acquisition risk due to the necessity of owning
or leasing the machine, as well as obtaining the
in-house expertise. A cost-benefit analysis would be
required to evaluate the relative advantages, and
could particularly favour a distributed approach for
off-shore and remote applications.
Additive Manufacture Impact
Minimal Costly Catastrophic
LIKELIHOOD
Low Design challenges Supply chain
Medium
Production process
acquisition costs
Unforeseen failures
High Qualification and testing
Conventional
Manufacture
Impact
Minimal Costly Catastrophic
LIKELIHOOD
Low Qualification and testing Unforeseen failures
Medium
Supply C
chain
acquisition costs
High
Design challenges
production process
Table 3. General comparison of risks encountered in AM as compared with conventional manufacture
21. Additive Manufacturing – A Materials Perspective 21
CASE STUDY 1:
BAYESIAN NETWORK ANALYSIS OF RISKS FROM
ADDITIVE MANUFACTURE ADOPTED BY OEM
The power of Bayesian networks for assisting in
making a risk analysis can best be demonstrated
by concocting some simple examples. For an
original equipment manufacturer we consider the
primary sources of risk as emerging from design,
production and qualification. In the case of a metallic
component, with pre-existing design principles,
stringent qualification requirements and a high-level
of post-processing, a generic Bayesian network
analysis can be performed.
Under the assumptions made in our approximate
model, the combined probabilities for this feature set
led to a 16:84 ratio of go: no-go, i.e. leaning towards
a risk that weighs against the selection of additive
manufacturing for this technology. (See Network A)
Note: this analysis uses only a crude approximation,
and so a more sophisticated analysis would need to
be constructed for practical implementation of this
model, since, for instance, within the composition
category of “metal” many sub-selections exist,
and similarly for all other variables in the Bayesian
network.
Network A
A second case could be made for a polymer
component with high production, low post-
processing, with design-principles in place
and a relaxed qualification requirement.
In this case, the opposite analysis results:
80:30 go: no-go ratio, indicating that the
technology is mature enough to lead to the
selection of additive manufacturing with a
high confidence of success.
Manufacturer
15,22 Go
84,78 NoGo
Design
27,50 High
25,00 Medium
47,50 Low
Production
10,00 Low
90,00 High
Post
Processing
74,26 High
25,74 Low
Material Quantity
0,00 Low
100,00 High
Composition
100,00 Metal
0,00 Ceramic
0,00 Polymer
Qualification
Requirements
100,00 Stringent
0,00 Relaxed
Design
Principles
100,00 Yes
0,00 No
Part
Complexity
50,00 High
50,00 Low
22. 22 Additive Manufacturing – A Materials Perspective
CASE STUDY 2:
BAYESIAN NETWORK ANALYSIS OF
RISKS FROM ADDITIVE MANUFACTURED
PARTS ADOPTED BY END USER
Additive manufacturing may pose unique risks not
only to original equipment manufacturers, but also the
users of parts produced by additive manufacturing
technologies. As in the case of OEMs, some generic
probability matrices can be populated to gauge
the sensitivity of successful adoption of additive
manufactured parts to these control variables.
For instance, in Network B a part with low technological
maturity but relatively high intended lifetime, in which
additive manufacturing has a key role as an enabling
technology, with low costs and distributed manufacture
results in a 50:50 don’t adopt:adopt probability ratio.
The key reason for the risk assessment of this
nature comes down to the fact that the new level of
technological maturity does not provide much historical
evidence to build confidence against the risk of service
failure.
Network B
In contrast, when the technological
maturity is at a later stage the weighting
in favor of adoption of the technology is
increased to 60:40 for adopt:don’t adopt.
The network analysis provides the ability
to “slide the scales” of risk or selection
factors throughout the connected
diagram, as well as the opportunity to
add further factors as the particular
technology is framed in greater detail.
User
46,59 Don't Adopt
53,41 Adopt
Powder Stability
100,00 Stable
0,00 Unstable
Acquisition
55,00 Yes
45,00 No
Supply
18,13 Unreliable
81,87 Reliable
Repair
67,57 Yes
32,43 No
Failure
Environmental
Conditions Reproducibility
Process Stability
50,00 Stable
50,00 UnstableIntended
Lifetime
17,80 Short
29,84 Medium
52,36 Indefinite
Technology
Maturity
100,00 New
0,00 Early
0,00 Later
Service
51,13 Performs
48,87 Fails
23. Additive Manufacturing – A Materials Perspective 23
The risk analysis framework provided in these two
cases can be adapted to any particular industrial
component. Based on the information available
today, comparative risk matrices can be assembled
for complex parts manufactured using AM compared
with conventional manufacture (Table 3). The first
risk matrix shows that AM provides a lower risk for
design of parts with high complexity, a reduced
probability of costly supply chain risks compared
with conventional manufacturing, a medium
probability for high costs associated with production
and acquisition, and a high probability for costs
associated with qualification and testing, mainly due
to the relative novelty of the technology.
There is a medium probability assigned to
unforeseen failures, with potentially catastrophic
consequences, due to the lack of long-term historical
service data and testing, especially if the parts are to
be used as functional parts in maritime or oil & gas
industries. This should be compared with the risk
matrix for conventional manufacture. In this case, for
complex parts, the design challenges and production
process have a high probability of incurring a high
cost, and supply chain risks also become more likely.
We expect acquisition costs to be quite similar at
present, as additive manufacture tooling is still quite
high. On the other hand, qualification and testing
become less likely barriers to incurring a financial
risk, due to the maturity of these methods. For
similar reasons, unforeseen failures also become less
probable.
Enabling
Technology
100,00 Yes
0,00 No
Centralized
vs Distributed
0,00 Centralized
100,00 Distributed
Materials Cost
0,00 High
100,00 Low
Process Costs
0,00 High
100,00 Low
System
Qualification
33,33 Unprepared
33,33 Stringent
33,33 Relaxed
Supply Sensitivity
50,00 High
50,00 Low
Cost vs
Conventional
24. 24 Additive Manufacturing – A Materials Perspective
AM technologies have the potential to revolutionise
the manufacture of equipment in the maritime and
oil & gas industries. Efforts are already underway to
manufacture small parts using AM techniques and
the scope of these will broaden. Examples for the
oil & gas industry could include pumps, valves, drill
bits, and sensors. Examples for maritime applications
could include pumps, valves, sensors, and special
segments of ship structures, although building an
entire ship is perhaps for the future.
The promise of AM is that it will free designers from
traditional manufacturing constraints and free users
from traditional supply chain constraints.
Nevertheless, the risks of AM to both manufacturers
and users need to be carefully evaluated. Traditional
reliability assessment techniques, using repeated
testing of finished parts, are insufficient to address
AM. Reliability and risk assessment using a Bayesian
network is a promising approach to managing
the risks associated with introducing such exciting
technologies.
LOOKING TO THE FUTURE
25. Additive Manufacturing – A Materials Perspective 25
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