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![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](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-4-320.jpg)
![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%](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-5-320.jpg)
![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](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-6-320.jpg)
![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](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-8-320.jpg)
![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)](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-12-320.jpg)
![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)](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-13-320.jpg)
![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?](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-16-320.jpg)
![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](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-18-320.jpg)
![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](https://image.slidesharecdn.com/b1d5b609-d09a-4e16-8490-097e0193b65a-150219094929-conversion-gate01/85/DNVGL-Additive-manufacturing-pospaper-v_02-19-320.jpg)
Uploaded byChristopher Taylor
DNVGL Additive manufacturing pospaper v_02
This document discusses additive manufacturing (AM) and its potential applications in the maritime and oil & gas industries. It provides an overview of important AM processes such as binder jetting, material jetting, powder bed fusion, sheet lamination, vat photopolymerization, and direct energy deposition. While AM currently only accounts for about 5% of these industries, its use is anticipated to rapidly expand. The document outlines both limiting and encouraging factors for AM adoption. It then presents a Bayesian network approach that can be used to assess risks to manufacturers and end users from AM part variability and lack of standards/regulations. Case studies demonstrate how this approach can evaluate risks from an original equipment manufacturer or end user perspective.
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DNVGL Additive manufacturing pospaper v_02
- 1. SAFER, SMARTER, GREENER ADDITIVE MANUFACTURING –A MATERIALS PERSPECTIVE DNV GL STRATEGIC RESEARCH & INNOVATION POSITION PAPER 7-2014
- 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
- 3. Additive Manufacturing –A Materials Perspective 3 INTRODUCTION 4 AM PROCESSES 6 Important AM Processes for Maritime and Oil & Gas Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Materials and Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 WILL AM FIND APPLICATION IN THE MARITIME INDUSTRY? 16 Limiting factors.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Encouraging factors.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Technology Qualification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 CONCEPTUAL APPROACH TO RISK ASSESSMENT OF AM 18 For OEM.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 For End Users. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 CASE STUDY 1: BAYESIAN NETWORK ANALYSIS OF RISKS FROM ADDITIVE MANUFACTURE ADOPTED BY OEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 CASE STUDY 2: BAYESIAN NETWORK ANALYSIS OF RISKS FROM ADDITIVE MANUFACTURED PARTS ADOPTED BY END USER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 LOOKING TO THE FUTURE 24 REFERENCES 25 IMAGES CREDIT 26 CONTENT
- 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.
- 15. Additive Manufacturing –A Materials Perspective 15
- 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
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- 26. 26 Additive Manufacturing– A Materials Perspective Figure 1. SLA250, Stereolithography (left): http:// www.3dsystems.ru/products/slaseries/sla250/index.asp. htm, and SLM 500 HL, SLS machine (right): http://www. rapidreadytech.com/2012/12/slm-solutions-releases-slm-500- hl/. Figure 3. An illustration of Fused Deposition Modeling (FDM) process and some plastic parts fabricated by FDM. (Image courtesy of CustomPartNet, Copyright © 2008 and Stratsys), for the plastic parts, image link: http://www.tritech3d.co.uk/ stratasys-printer-family/dimension.php, and http://www. tritech3d.co.uk/stratasys-printer-family/fortus.php Figure 4. An illustration of Selective Laser Sintering (SLS) process and some metal parts fabricated by SLS. (Image courtesy of CustomPartNet, Copyright © 2008 and EOS GmbH). Figure 5. An illustration of laser metal deposition process to build and repair metal parts. (Image courtesy of LPW Technologies, TRUMPF Laser, and Optomec). Figure 6. Typical porosity of AM metal part: (a) SEM image shows open pores on the surface of SLM-processed Inconel 718 (Image courtesy sees reference 4), and (b) optical microscope image shows pores in the bulk of DMLS-processed commercial Al-Si-Mg alloy (image courtesy sees reference 5). 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. (Image courtesy sees reference 5). Figure 8. Left, picture of bone structure. Right, Boeing new concept of for commercial airplanes, additive manufacturing process would allow to copy nature and make lighter and more efficient planes. Image courtesy left: http://www.brsoc.org. uk/gallery/images/19lg.jpg, and right www.industrytap.com/ airbus-planning-to-3d-print-planes-vital-components/8694. Figure 9. The irregular shape of the whales fins, provide reduced drag (current manufacturing processes for ships have difficulties imitating such structures). Image courtesy: http://4.bp.blogspot.com/-8DTmoSkSVpc/UMH9ieZq2LI/ AAAAAAAADKU/MAfrpsDB77M/s1600/animal+attacks +news++dangerous+animal+attacks+fromthe+deep+ sea+whale+ocean++blue+fin+whale+endangered+animals+ from+the+deep+sea+animal+migration+picture.jpg IMAGES CREDIT
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