adaption of a heatsink to additive...
TRANSCRIPT
ADAPTION OF A HEATSINK TO
ADDITIVE MANUFACTURING
INCLUDING A GUIDE TO INDUSTRIAL STARTUP OF AM
Richard Ingman
Master of Science Thesis TRITA-ITM-EX2019:239
KTH Industrial Design and Management
Machine Design
SE-100 44 STOCKHOLM
Kungliga Tekniska Högskolan
MF213X Examensarbete inom maskinkonstruktion, avancerad nivå
Examinator: Ulf Sellgren
Master of Science Thesis
TRITA-ITM-EX2019:239
Adaption of a Heatsink to Additive
Manufacturing – Including a guide to
industrial startup of AM
Richard Ingman Approved Examiner Supervisor
2019-06-04 Ulf Sellgren Ulf Sellgren Commisioner Contact person
Saab AB Josefine Grimfeldt
ABSTRACT
This thesis is an investigation of the current status of additive manufacturing
(AM) regarding different technologies, the level of implementation in industry
and the future obstacles for further implementation. As a secondary objective, an
existing heatsink for electronic equipment was redesigned, adapted to and
improved using the design advantages of AM, and was later manufactured
through 3D-printing in aluminium (AlSi10Mg). The thesis resulted in a
summarized roadmap of recommended actions for Saab Surveillance in Järfälla in
the near future. And a redesigned heatsink, which was tested to hold a static
pressure of 30 bar, and simulated to achieve the same pressure drop in the channel
and withstand the same vibration load as the old heatsink. At the same time, the
new design reduced the total weight by 20% and increased the heat transferring
surface area of the channel by 100%, potentially doubling the heat transfer
capability.
Keywords: Additive Manufacturing, AM, 3D printing, Industrialization, Heatsink.
Examensarbete TRITA-ITM-EX2019:239
Anpassning av en elektronikkylare till
Additiv Tillverkning – Inklusive en
industriell uppstartsguide för AM
Richard Ingman
Approved Examinator Handledare
2019-06-04 Ulf Sellgren Ulf Sellgren Uppdragsgivare Kontaktperson
Saab AB Josefine Grimfeldt
SAMMANFATTNING
Detta examensarbete har undersökt den nuvarande statusen hos additiv
tillverkning (AM) vad gäller olika teknologier, hur långt implementeringen i
industrin kommit och framtida hinder som måste lösas för vidare implementering.
Som sekundärt mål för projektet har en existerande elektronikkylare designats om
och förbättrats med hjälp av designfördelarna hos AM, och tillverkades sedan
genom 3D-printning i aluminium (AlSi10Mg). Arbetet har resulterat i en
sammanfattad ’roadmap’ med rekommendationer för vad Saab Surveillance i
Järfälla bör göra inom AM den närmaste tiden, samt en ny kylare som
framgångsrikt trycktestades upp till 30 bar. Genom simuleringar visades den
uppnå samma tryckfall och klara samma vibrationer som den tidigare kylaren,
samtidigt som den väger 20% mindre och har en 100% ökning av kylkanalens
våta area vilket potentiellt innebär en dubblering av kylförmågan.
Nyckelord: Additiv Tillverkning, 3D-printning, Industrialisering, Kylare.
CONTENTS
Acknowledgements .................................................................................................. 1
Nomenclature ........................................................................................................... 3
Notations ............................................................................................................... 3
Abbreviations ....................................................................................................... 3
1 Introduction ....................................................................................................... 5
1.1 Background ............................................................................................... 5
1.2 Purpose and goals ...................................................................................... 7
1.3 Delimitations ............................................................................................. 7
1.4 Methodology ............................................................................................. 7
2 Frame of reference ............................................................................................ 9
2.1 Additive manufacturing ............................................................................ 9
2.2 Design for AM ........................................................................................ 18
2.3 Industrialization of AM ........................................................................... 20
2.4 Heatsink design ....................................................................................... 24
2.5 The original heatsink ............................................................................... 27
3 Method ............................................................................................................ 28
3.1 Building a roadmap ................................................................................. 28
3.2 Designing the AM heatsink ..................................................................... 29
3.3 CFD simulation setup .............................................................................. 33
3.4 Static pressure testing .............................................................................. 37
3.5 Stress analysis - Random vibration simulation ....................................... 37
4 Results ............................................................................................................. 39
4.1 The Roadmap .......................................................................................... 39
4.2 The manufactured AM heatsink .............................................................. 41
4.3 CFD Simulation results ........................................................................... 42
4.4 Static pressure results .............................................................................. 42
4.5 Random vibration simulation results ...................................................... 43
5 Discussions ...................................................................................................... 45
5.1 On the introduction of a new technology to a field of established ones. 45
5.2 On the implementation of AM on a national level. ................................. 46
5.3 On the AM process and materials ........................................................... 47
5.4 On the design rules for AM ..................................................................... 48
5.5 On the methodology and results of this thesis ........................................ 50
5.6 Future work ............................................................................................. 53
6 Conclusions ..................................................................................................... 55
7 References ....................................................................................................... 57
8 Appendix .......................................................................................................... A
8.1 Appendix A – AM process categories ..................................................... A
8.2 Appendix B – Pictures of the original heatsink ....................................... B
8.3 Appendix C – Pictures of the AM heatsink ............................................. C
1
ACKNOWLEDGEMENTS
This project is dependent on a great number of people, more than who can be
individually presented here. These are primarily all the helpful employees at Saab
Surveillance in Järfälla and other Saab-sites. In addition, external actors such as
suppliers of machines and products and branch organizations have been vital for
the success of this report. My first thanks is directed toward all of you.
I would also like to express my gratitude towards some who have been especially
generous with their time, knowledge, ideas and encouragement:
Torbjörn Holmstedt, Lasertech, for excellent support on design rules
during the design phase of the additively manufactured (AM) heatsink and
for manufacturing it.
Fredrik Finnberg, Digital Mechanics, for fruitful discussions on several
aspects of additive manufacturing (AM), including industrialization,
materials, methods and customization of industrial 3D-printers.
Johan Nyström, Protech, for providing a business chain perspective,
insight into the work of Stratasys and other machine developers, and
invitations to useful events broadening my AM contact network.
Jonas Severin, Saab AB, for the structural mechanics analysis and
dialogue on material stress and related design aspects.
Samuel Gottfarb, Saab AB, for invaluable assistance with the fluid
dynamics analysis and computational fluid dynamics (CFD) simulations
on the coolant channel.
Håkan Johansson, Saab AB, for the initiative to this thesis and continuous
inspiration with new ideas and ways around all problems encountered.
Most importantly: Josefine Grimfeldt, Saab AB, for her work as supervisor
with constant encouragement, following the process and always lending a
hand, should any obstacle appear.
2
3
NOMENCLATURE
Notations
𝜺 Relative error
𝒑 Simulated pressure drop
Abbreviations
AM Additive Manufacturing (n.), or Additively Manufactured (adj.)
CAD Computer-Aided Design
CAM Computer-Aided Manufacturing
CFD Computational Fluid Dynamics
DFAM Design For AM
DMLS Direct Metal Laser Sintering (AM-technology)
EBM Electron Beam Melting (AM-technology)
EW Electronic Warfare
PBF Powder-Bed Fusion (AM-technology)
SLM Selective Laser Melting (AM-technology)
4
5
1 INTRODUCTION
1.1 Background
Saab AB is a world-leading manufacturer of products, services and solutions for
military defence and civil security. Saab Business area Surveillance offers
effective solutions for monitoring, detection and protection against various threats
in land, sea and airborne applications. The product range includes systems for
radar surveillance and jamming, sea and air traffic control as well as self-
protection such as missile approach warners and countermeasure dispenser
systems.
Electronic warfare (EW) refers to the use of electronic equipment such as sensors
for the detection of other aircraft, incoming threats or detection of another
surveillance unit, the use of jammers which counteract and interfere with such
systems, and also the use of direct countermeasures against incoming threats.
Figure 1 illustrates the use of the EW systems. This electronic equipment requires
cooling to maintain its functionality and the search for more efficient and
lightweight solutions is ever ongoning in the aircraft industry.
6
Figure 1. Illustration of Electronic warfare applications (Saab, 2019)
A common challenge in the design of heatsinks for aircraft is to achieve a high
cooling-power-to-weight ratio while also maintaining its capability to withstand
the tough environmental conditions such as vibrations and fast temperature
changes. Using additive manufacturing (AM) may be a way to further increase
these properties beyond what is possible or economical with the manufacturing
methods of today.
1.1.1 Additive Manufacturing
AM, commonly referred to as “3D-printing” or sometimes “Rapid
Manufacturing” is a method of creating products by adding material together in
layers rather than removing material as in traditional subtractive manufacturing
methods such as milling and lathing. Building in layers opens a completely new
set of design possibilities not previously achievable. Internal cavities, lattice
structures and a greater usage of “biological shapes” which mimic the skeletal
structure of animals and are naturally optimized after millions of years of
evolution, to name a few. This new technology also comes with its own set of
limitations, which must be understood and mastered in order to make efficient use
of AM.
7
1.2 Purpose and goals
The purpose of this thesis is to find the necessary first steps for introducing AM as
a viable manufacturing alternative at Saab Surveillance, Järfälla. The result should
be a well-structured representation (i.e. “Roadmap”) of the requirements in
administration and design procedures that are necessary to get AM-products to
pass qualification at Saab Surveillance. As a way to learn this, but also formulated
as a project goal itself an existing product, a heatsink, should be redesigned,
improved and adapted to be manufactured using AM. The redesign of the heatsink
is aimed at improving its heat transferring capabilities, while reducing its weight
and keeping the pressure drop across the channel the same.
1.3 Delimitations
Additive manufacturing is a huge field of technology and a single thesis cannot
cover its entire width and depth in detail. The theory chapter includes an overview
of the AM process categories but does not explain all technologies in detail. The
materials section presents a select few materials of particular interest to Saab, the
one used to manufacture the redesigned heatsink being one of them. The design
rules that are presented are primarily suited for metal AM but may be applicable
to other processes and materials as well. The research for industrialization efforts
by other companies is limited to Sweden but due to many companies being
international, this could not always be kept strict.
The improvements to the performance of the heatsink will focus on its thermal
properties. Analytical methods are limited to simulations and does not include real
life testing of flow characteristics. Reduced mass and strength improvements may
be considered but are not analysed in detail. Surface treatments of the AM
heatsink is not considered, and the selection of manufacturers for the AM heatsink
is limited to suppliers in Sweden to avoid issues with export control.
1.4 Methodology
The first part of the project is a screening of additive manufacturing and its related
subjects, in an effort to find and determine the boundaries of the subject. Such an
overview provides the necessary knowledge of what to research in detail and what
to exclude from the work on the roadmap. Interviews with Saab employees are the
main source of knowledge on the workflow and product development processes at
Saab. Communication with suppliers and other organizations working on AM is
8
also an important source of background information for building the roadmap,
together with visiting fairs and seminars on AM.
In short: the methods used to create the roadmap are literature studies, interviews,
and discussions with knowledgeable people in the field of AM, combined with
studies of the design and qualification processes at Saab.
The original heatsink is studied to understand the design intent and to make
improvements without obstructing its possibility to be tested in the original
application. A new model is constructed using the CAD software ‘Siemens NX’.
Flow simulations are carried out using Ansys CFX and a physical prototype is
manufactured to prove the manufacturability and make a static pressure test to
compare the new design to the original.
9
2 FRAME OF REFERENCE
This chapter is aimed at giving the reader an overview and basic knowledge of
many different aspects of AM, which will be key to understanding the roadmap.
Section 2.1 describes AM in general, its current state and many commonly
discussed topics about the technology. Section 2.2 highlights design rules for AM
which have played an important role during the redesign of the heatsink in this
thesis. Section 2.3 presents ongoing research by different organisations on the
implementation of AM. Section 2.4 provides the literature study of traditional
heatsink design, and finally Section 2.5 presents the original heatsink and the
properties which have to be fulfilled by the redesigned AM-heatsink.
2.1 Additive manufacturing
What is the real novelty in additive manufacturing? Creating something by adding
materials together has been done for thousands of years, the layer-by-layer
strategy is already used in brick-buildings and known by all children playing with
LEGO®. Computer aided manufacturing (CAM) where the movements of a
manufacturing machine is controlled by digital software is not new either. The
combination of these two principles, the “Adding of layers” by a “computer-
controlled machine” directly from a 3D-model is a description which sets
Additive Manufacturing apart from all other manufacturing methods.
The standardized definition of the term can be found in ISO/ASTM 52900:2015
and reads as follows:
“Additive Manufacturing (AM): process of joining materials to make
parts from 3D model data, usually layer upon layer, as opposed to
subtractive manufacturing and formative manufacturing methodologies.”
(52900, 2015)
About this much is common for all different AM technologies, because the wide
diversity of materials and binding methods make most other aspects individual to
a specific technology and should be studied individually.
The standard definition was initially formulated by ASTM committee F42 in 2009
and in some regards marked the beginning of the large-scale industrial interest in
AM (3D Hubs, n.d.), but the history of AM stretches further back than this.
10
2.1.1 Early History
The 267 pages “Wohlers Report 2014” provides an in-depth report of both the
technical evolution of 3D-printing as well as the actions of many (if not all)
companies within this business field and is considered one of the most thorough
documentations of AM history within the community. Its shortened 34-page
version, which is free to download will be the main source of this section.
(Wohlers & Gornet, 2014)
In the 1960’s, researchers at the Battelle Memorial Institute attempted to create
solid objects by intersecting two laser beams in a fluid volume of photopolymer
resin, Wohlers describe this as the first attempt of a process resembling AM.
But it was not until 1987 that the first commercially available additive
manufacturing system appeared. It was the SLA-1 machine, made by 3D Systems
who are still one of the largest companies in the AM field. Until the 1990’s, SLA
(Stereolithography Apparatus) which solidifies layers of a resin material through
polymerization using a laser, was the only available technology.
In 1991, Stratasys commercialized the FDM (Fused Deposition Modelling)
technology, which builds layers by extruding a melted plastic filament very
similar to a hot glue gun. It is the most common of all 3D-printing technologies
today. The 90’s is considered the childhood of 3D-printing when most of the basic
technologies were developed and patented, most notably the arrival of metal AM
in 1998 with the LENS (Laser Engineering Net Shape), a method similar to metal
arc welding.
The first decade of the 21st century saw a wide range of new materials, Many new
and smaller AM companies emerged and disappeared or were purchased within a
few years of their foundation.
2009 marked an important milestone as ASTM Committee F42 on Additive
Manufacturing released its first standard – “Standard terminology for Additive
Manufacturing Technologies”. This was the first definition of the now
standardized term “Additive Manufacturing”, and it gave an important message of
relevance to the industrial world. In the same year, Stratasys’ patent on the FDM-
technology expired which resulted in a quick appearance of consumer grade 3D-
printers with the RepMan kit (Based on the RepRap open-source system) being
one of the first with a hobbyist-friendly price tag of $750. The conjunction of
these two separate events in the same year resulted in an exploding interest for
AM throughout the world. (3D Hubs, n.d.)
11
Beginning in 2011, industries started adopting AM as their primary manufacturing
method, in-ear hearing aids being the first, soon to be followed by the much larger
dental market. Polymer-based AM was a few years in front of the Metal-based, in
terms of large-scale adoption. Nevertheless, many were already convinced by that
time, that once the metal materials became close-to-equivalent to its machined
counterparts, the adoption of Metal-AM would come much quicker than that of
the polymers.
2011 also saw the introduction of electrostatic dissipative materials such as
Stratasys ABS-ESD7, EOS announced having passed 1 000 installed laser-
sintering machines, and Asiga released its Freeform Pico, a machine capable of
1µm (0.001mm) layer thickness, the technology was advancing rapidly.
2.1.2 Technologies
ISO/ASTM 52900:2015 defines seven process categories for AM, and within each
there exist several AM processes (or technologies) which describe different
methods of achieving the layer-by-layer manufacturing, also using different
materials (52900, 2015). An overview of this structure is provided in appendix
8.1.
3D-printer companies tend to market their machines using other, more individual
names for the processes than the ones provided by the ISO standard, possibly in
an attempt to distinguish their products from their competitors. The reader is
advised to learn and use the standardized terminology.
The seven standardized process categories of AM are:
Vat polymerization – a process where a liquid resin is polymerized and solidified
in selective areas by any type of light source, most commonly a laser or UV-light.
This technique is known for its thin layers and capability of transparent materials.
Material extrusion – a process where the build material is extruded through a
nozzle and deposited selectively to form an object. This process is most
commonly known as FDM (Fused deposition modelling) which is the patented
name by Stratasys, or FFF (Fused filament fabrication). This technique is the most
common and machines range from consumer-level at 1000 SEK to industrial
manufacturing machines above 1 000 000 SEK. Its applications range from at-
home toy production using simple plastic materials like PLA (Polylactic acid) to
airliner interior parts printed in the PEI-based plastic ‘Ultem 9085’ (Wheeler,
2015) and high-performance lightweight components in carbon fibre reinforced
nylon for tricycles (Protech, 2017).
12
Material Jetting – In this process, the machine selectively places tiny droplets of
photopolymer resin or wax and solidify them by a passing light-source for each
layer. A comparably quick and very popular process in industrial design
prototyping as it has capabilities for full-colour printing as well as making parts
with different hardness in different areas in one piece but is also used for actual
end-product manufacturing.
Binder Jetting – By selectively dropping a liquid bonding agent at a layer of
powder, binder-jetting can produce parts of many different materials depending
on the powder used. Sand-powders can be used to directly produce casting
moulds, metal powders can be joined by wax and later sintered as with metal
injection moulding (MIM). This process is at the time of writing able to produce
the most detailed metal parts of all AM processes, and building them without
support material, which is highly desirable within AM. The sintering process
however, may impose a need for supports. (Sakratidis, 2018).
Powder bed fusion – instead of binding it, processes in this category melts the
powder where solid material is wanted, using any form of thermal energy, most
commonly laser. As with all powder-based methods, particular care must be taken
not to build parts with cavities which traps the powder, unless saving the powder
itself is the intention, perhaps for later analysis. The powder bed fusion family is
the most developed when it comes to Metal 3D-printing, and the Direct Metal
Laser Sintering (DMLS) process is the one used to build the heatsink in this
thesis. (Warholm & Sönegård, 2017)
Direct energy deposition – a process category only using metals, with similarities
to MIG/MAG welding. These processes usually result in rougher surfaces than
with powder-based processes but is instead faster and can also be used to directly
repair parts or tools by re-adding material which has been lost or worn away.
(Anon., 2019)
Sheet Lamination – This process cuts cross-sections in thin sheets of paper, metal
or composite-weaves and adhere them together to produce an object. While
perhaps having received less attention compared to other processes Sheet
Lamination, or Laminated Object Manufacturing (LOM) as it is commonly
referred to, boasts extra-large build volumes and has been very popular amongst
architectural firms and civil engineers for landscape models and 3D-maps.
13
2.1.3 Materials
When discussing AM materials, it is important to keep in mind that the final
quality and mechanical property of AM materials and parts is affected by several
factors. The quality of the feedstock (the powder, filament or other base material),
the accuracy of the 3D-printer machine components as well as parameters such as
printing speed, temperature and material flow or laser power and focus to name a
few. Process parameters are presented further in section 2.1.4 Compared to
machining processes where the desired shape is cut from a block of material
which gets its properties from other processes such as casting, rolling, extrusion
etc, Metal AM builds both the shape of the part and the material with its
microstructure and properties at the same time. This section will continue to
present some general questions regarding AM-materials and only go into detail on
the most common AM-aluminium in use today: AlSi10Mg.
Each AM-process has its own set of materials, and due to their nature (powder,
filament or liquid) they are not interchangeable. A trend among manufacturers
since the start of commercial 3D-printing has been to develop new materials to
provide a wider selection for the customers of both metal and plastic machines.
Some processes and machines have a wider range of materials available, which
might be a selling point for one process or machine over another.
Only a handful of metal materials are available for AM at the time of writing, but
their diversity allows for a wide range of applications already. Titanium and
aluminium alloys, stainless- and tool steels, and the NiCr-based superalloy
Inconel are frequently mentioned, although not all of them are available for all
metal AM processes. (GE, 2019)
A commonly asked question is how well AM materials compare to their
counterparts in traditional manufacturing. A previous thesis study at Saab found
that no significant difference in fatigue performance could be noted between a set
of machined test rods made from the aerospace grade aluminium Al6082 T6 and
two sets (built in different orientations in the 3D-printer) of AM rods, (Mattson,
2018) which gives an indication of similarity. (Kempen, et al., 2012) investigate
the effect of the printing process by comparing 3D-printed AlSi10Mg from SLM
to cast AlSi10Mg and find that the mechanical properties of the additively
manufactured version is definitely comparable and sometimes even exceeds those
of the conventionally cast version. (Fulcher, et al., n.d.) compare microstructure
and mechanical properties of AlSi10Mg and Al 6061 manufactured using Direct
Metal Laser Sintering (DMLS) which is a part of the Direct Energy Deposition
14
AM process category. Not only do they bring to attention that AlSi10Mg is not
the only currently available 3D-printing aluminium, but they conclude that
AlSi10Mg show relatively isotropic properties, something which is not
universally agreed. Al 6061 test pieces made by DMLS in their work show the
problems with cracking, warping and other heat-induced dilemmas faced in metal
AM. This may be an explanation to the arrival of AlSi10Mg, the Silica component
is suspected to reduce the coefficient of thermal expansion (CTE) effectively
making the Al-alloy easier to 3D-print.
2.1.4 3D-printing parameters
Like most other machines, 3D-printers have settings which allow the user to
adjust and adapt the behavior of the machine to suit the component being
manufactured. For the digitally controlled 3D-printers this is done in the interface
software commonly referred to as a “slicer” program, from the idea of cutting the
model into thin sections. This program is used to import a CAD model, calculate
shape of each cross-sectional layer, adjust suitable settings for printing this model
and export the workload to the machine.
This section presents some of the most important general parameters for 3D-
printing. Even a simple consumer grade 3D-printer can have over 100 different
parameters, which is too many to present here, and each AM process has its own
set of control settings due to their different method of creating the layers.
Nevertheless, some common settings exist for all, such as:
Layer thickness – The thickness of each cross-sectional layer impacts the printing
time, the surface quality of sloped surfaces due to the staircase effect, and the
strength and microstructure of the final part. (Sufiarov, et al., 2016) found that
thicker layers result in lower strength but higher plasticity for Inconel samples
made using SLM.
Printing speed – This is technically not controlled as a single parameter, but
instead controlled individually for different areas and structures of a 3D-printed
part. For example: the visible surfaces may be printed slower than the internal
structure to increase the accuracy and reduce the probability of errors. When
discussing print-speed, powder bed fusion can be compared to welding, the sweep
speed of the laser has a similar impact on the melt pool as welding speed and
energy deposition in MIG-welding, and it is important to adjust this correctly to
reduce pores and gain the correct melting depth. (Kusuma, 2016)
15
Temperatures – In FDM-printing, temperatures of 200-300°C at the nozzle and
50-150°C at the heated bed and/or build volume are critical parameters for the
extrusion of plastics as well as the adhesion to the bed and between the layers. For
metal AM such as the EBM process the heated build chamber (typically 700-
900°C) is used to reduce the residual stresses and eliminate the need for post heat
treatment. SLM printers only reach 100-200°C within the build volume and may
require post heat treatment.
The above-mentioned parameters are only a small sample to demonstrate the type
of considerations a 3D-printer operator or manufacturer may need to deal with. In
some cases, the parameters may be pre-set by the machine manufacturer for
different types of materials and in other cases the user will need to work out the
optimal settings for a particular environment or product.
2.1.5 Testing methods
Making sure the end result meets the requirements and achieve the intended
functionality is not unique to AM, neither are the available testing methods. In
most regards, AM products may be tested with the same methods as traditionally
manufactured parts, but some are particularly well suited for AM. With traditional
manufacturing the need to see the inside of a part has been small, but the complex
design possibilities of AM calls for a tool which can verify internal structures
without cutting things open.
Computerized Tomography, or CT-scanning creates X-ray images of thin cross-
sections of the scanned part, ironically similar to the reverse of the AM building
process. Combine this with a powerful analytical software that can overlay the
original CAD-model with the scan of the manufactured part and show the
deviation between them (Albright, 2018). Figure 2 shows an example of how this
may look. The drawbacks of X-ray technique are its limitations to see through
highly dense materials or thick objects, and for CT-scanning in particular, the
cost. The versatility however is an advantage. With some X-ray techniques being
able to spot material defects as small as 5 µm (RX-Solutions, 2019), this could
also be used to assess the presence of pores after printing, as well as the shape of
the part.
16
Figure 2. Coloured deviations in a comparative analysis between a CAD and the 3D-
printed specimen. (Albright, 2018)
As mentioned in section 2.1.3 Materials, the quality of the feedstock material has
an impact on the properties of the outcome product. It may therefore be desirable
to save a portion of the exact powder (in Powder bed fusion processes) used in
each batch for later analysis if one or several parts in the same batch fail. This can
easily be done during printing by simply building a small enclosure in which the
powder will be completely sealed from the outside world. It could even be text-
marked in the printing process and sent directly to storage.
2.1.6 Tolerances and Accuracy of AM
Another commonly asked question is how accurate AM parts are, and how tight
tolerances it can work with. This is a difficult question to answer at the current
state of the technology, and many AM professionals would rather avoid answering
than create false pretence. One of the reasons behind this is the issue of
repeatability. Two separate AM machines of the same brand and type will
produce parts which are geometrically and mechanically different. This is a well-
known issue, but very little research is dedicated towards quantifying the
boundaries of this inconsistency in parts. (Shah, et al., 2016).
To give a hint on the current performance of the technology, the following points
are some of the properties presented in the EOS material datasheet for AlSi10Mg
(EOS, 2019). Note that EOS do not give any guarantees of achievability on any of
the numbers in the datasheet, even if the printer runs on factory settings under all
the right conditions.
Typical achievable part accuracy: ± 100µm. This is based on users’
experiences with an EOSINT M270, and EOS specifically note that it can
17
be achieved using the correct preparation and post-processing in
accordance with their instructions.
Surface roughness, as built: Ra 6-10µm, Rz 30-40µm. This is heavily
dependent on the build orientation and the numbers are only an indication
of what can be expected for horizontal (up-facing) and vertical surfaces.
Relative density: 99.85%
Density: 2.67 g/cm3
Tensile strength (as built): 460/460 ± 20 MPa (XY/Z direction)
Young’s modulus: 70/75 ± 10 GPa, (XY/Z direction)
2.1.7 International Standards
Standard methodologies are an important prerequisite for industrial
manufacturing. ASTM Committee F42 released the first standard on AM in 2011,
and shortly after they joined forces with ISO to avoid dual efforts, creating the
Technical Committee TC 261 on additive manufacturing. ISO/TC 261 have
currently released 9 standards on AM, and another 22 are under development.
These are the released ones:
ISO 27547-1:2010, Preparation of test specimens of thermoplastic
materials using mouldless technologies. Laser sintering of test specimens.
(This was released prior to the release of the standardized term “Additive
Manufacturing” in 2011, but it refers to an AM technology.)
ISO/ASTM 52921:2013 Standard terminology, coordinate systems and test
methodologies.
ISO 17296-3:2014 Main characteristics and corresponding test methods
ISO 17296-4:2014 Overview of data processing
ISO 17296-2:2015 Overview of process categories and feedstock
ISO/ASTM 52900:2015 General principles – Terminology
ISO/ASTM 52915:2016 Additive manufacturing file format (AMF)
ISO/ASTM 52901:2017 Requirements for purchased AM parts
ISO/ASTM 52910:2018 Design – requirements, guidelines and
recommendations.
The release of international standards on AM is an important part of the
legitimization process and will help both the technical adaptation as well as
improve the public opinion among mechanical engineers and business leaders.
18
2.2 Design for AM
As with any other manufacturing method, the abilities and limits of AM need to
be taken into consideration from the very first step in the design process. The
design rules of AM differ quite heavily from those of traditional manufacturing,
for example: a bone-like, semi-hollow internal structure may pose no challenge to
AM, while a simple T-shape might be impossible without support structures if it is
unfavourably oriented. Education in these design rules are already recognised as
an important part of the industrialisation of AM.
2.2.1 Sources for design rules and guidelines
A previous master thesis at Saab, written by (Warholm & Sönegård, 2017)
contains a Designers handbook for Metal AM and was used as the main source for
design guidelines during this thesis. In 2018-07, ISO released a standard on
design, requirements, guidelines and recommendations for AM (ISO/ASTM-
52910, 2018) which should be encouraged as a main source if possible. Design
guides and recommendations aimed at the hobbyist community are widespread
across the internet, but the information is mostly limited to the cheaper FDM and
SLA technologies. While learning to design for AM on simple systems may be a
good entry-point for education, it is important to keep in mind that all AM
technologies also have their individual set of design rules, especially when
designing for industrial use.
2.2.2 Critical design rules for metal AM
This section will briefly present the most important design rules for metal AM,
which were critical to the redesign of the AM heatsink, as stated by (Warholm &
Sönegård, 2017).
Build direction – (Also: build orientation) The direction in which layers are added
will have the biggest impact on the design of most AM made parts. It does not
necessarily have to be the first decision in the design process, but every added
feature must be able to be built in at least one direction. And once a build
direction is set and features start depending on it, it cannot be changed without
careful consideration.
Following the standardized coordinate system for AM (ISO/ASTM-52921, 2013),
a part is always built in the Z-direction of the build platform, as shown in Figure
3.
19
Figure 3. Standardized coordinate system for a 3D printer build platform
Overhang and horizontal holes – Two of the greatest challenges when designing
for AM is to make sure that all horizontal down-facing surfaces are properly
supported, preferably by their surrounding walls in order to avoid additional
support structures which may be hard and costly to remove. Figure 5 illustrates
the issues of an over-extended layer, which is collapsing due to the lack of support
below. Different AM-technologies have different limits to how far from the
previous layer the next can protrude without collapse. This is usually denoted by a
minimum overhang angle between the horizontal plane and the outwards
chamfered wall. See Figure 4 for an example of the effect of different overhang
angles.
Figure 4. Illustration of the effect of low overhang angles
The effect also affects horizontal holes, see Figure 5. With an increasing hole size,
the top surface will start to fall in and the hole can no longer be considered round.
For the SLM process used to manufacture the AM heatsink, holes above 10 mm in
diameter require additional support according to (Warholm & Sönegård, 2017). A
20
common recommendation is to let the printer make a smaller hole and bore it up
during after-treatment.
Figure 5. Illustration of max overhang and horizontal hole issues
Powder removal – For AM-processes which use powder or liquid as build
material, designing a part with closed cavities will trap the build material inside.
While this could be desirable for saving material samples of a batch, it is typically
unwanted in most constructions. Designers should make sure to include escape
holes before printing, or plan for drilling afterwards.
Rounded corners – Rounded outer edges are usually a cost-increasing operation
with machining methods and therefore often avoided unless necessary, but with
3D-printing they come basically free. Inner corner radii however share the same
problems of stress build-up and the risk for crack initiation as with other methods
but add to that the risk of thermal expansion during the building process. Inner
corners are very important and should have a radius of at least 0.1 mm with SLM.
(Warholm & Sönegård, 2017).
2.3 Industrialization of AM
The introduction of AM will concern a huge part of the production industry. It
will touch the entire chain from raw material providers to the recycling business.
Workshops and product development companies will have to adapt their methods
of working. Legislators, standards organisations, educational institutes and
occupational health bodies have to update and develop new rules, guidelines and
courses for additive manufacturing to become an established and accepted
industrial technology.
This chapter attempts to give the industrial context in which additive
manufacturing is supposed to be implemented. Many of the traditional
manufacturing technologies have evolved together with the industry and the
society over the course of tens or even hundreds of years and have left a landscape
21
of fine-tuned laws, regulations, praxis and expectations, which is not easily
challenged by a newcomer such as AM.
AMEXCI, in their Strategic Research Agenda (SRA) (AMEXCI AB, 2018), takes
on the extensive task of analysing the introduction of metal AM on a national
perspective, identifying three major sectors: Education, Industrial quality and
occupational health, where a lot of work needs to be done for the implementation
of AM. Most of this chapter will be limited to describe the industrial part from the
viewpoint of Saab.
2.3.1 Current technical challenges
One of the main concerns is the robustness and quality of the 3D-printing process.
For AM to be a useful manufacturing method, it needs to deliver an equivalent
product every time, within acceptable tolerances. The material properties and
selection of materials is also noted as an area of improvement. Right now there
exists a handful of metal AM materials and they are diverse enough to provide at
least one for each major type of industry (steel for tools and cars, aluminium and
titanium for aerospace etc.). However, there is a demand for a wider selection of
materials and they need to be tested and characterized well enough to be used.
The third issue stated in the SRA is the lack of verification methods. Not only
when it comes to physical testing, but the digital analytical tools for dynamic
loads and AM-possible shapes such as lattice structures are also lacking right
now. They say that “Today, it’s possible to design more advanced structures than
can be analysed”. Development in this area is however underway and expected to
arrive during the next few years.
2.3.2 Non-technical challenges
“Design culture, or rather lack thereof, is probably the single most important
factor hampering the Swedish industry from adopting AM. There are of course
examples where AM can make an existing component much lighter, or where AM
can reduce lead time for existing component designs, but one-to-one replacements
rarely add enough value to justify additive manufacturing.” (AMEXCI AB, 2018)
This quote indicates an importance of having AM-knowledgeable people in
several areas of a company, not only among the design engineers, but also in
management and systems architecture to be able to identify and improve the
overall product and not just individual parts.
22
2.3.3 Distribution of efforts
It would be impossible for one single actor in Sweden to solve all of the
difficulties with AM, this is why AMEXCI calls on all Swedish corporations with
an interest in AM to cooperate and share the efforts and results for a mutual
benefit. They also suggest strategic courses of action for everyone involved:
Individual corporations should focus on the internal AM-education of
employees and set up AM-teams who can work purposefully on finding
suitable business cases and prepare the company for when the technology
comes to a useful state. They should also make it clear to the research
institutes what they need in order to completely adopt AM.
Educational institutes should develop AM-courses on several levels and
work towards 100 examined AM-master students within the next five
years, and another 900 people with AM-competence. In the long term, AM
should become a natural part of all technical and design educations.
Research institutes should listen to the industrial needs and coordinate the
efforts to focus on the issues regarding quality and productivity, which the
industry cannot solve on their own.
It is important for all involved parties to stay up to date on the progress of others
in order to avoid dual efforts. Organizations such as RISE (Research Institutes of
Sweden), Vinnova (Swedish government agency for research funding), AMEXCI
and ISO are already aboard the industrial AM-train and are reaching out to
companies to climb aboard.
2.3.4 Visions for the future
It is estimated that within five years there will be an industrial demand for 1000
AM-knowledgeable people within engineering, procurement, management and
operators for the machines in Sweden. In ten years, there will be a need for 5000.
(AMEXCI AB, 2018)
(Warholm & Sönegård, 2017) found that from 2011 to 2025 the global
manufacturing industry is estimated to rise from 10.5 trillion dollars to 15.9
trillion, which is an increase of about 50%. Between the same years AM is
expected to rise from 1.7 billion to over 10 billion dollars, an increase of almost
600%, which is still only an estimation, but it gives some indication about the
potential in this field.
The ambition of everyone involved in the endeavour of introducing additive
manufacturing to the modern industry is that it will be used as easily as any other
23
technology of today. It is not believed to completely replace other manufacturing
methods but regarded as a new tool in a well-known toolbox, and it should not be
disregarded.
24
The introductory quote of the AM-SRA provides an excellent end to this chapter:
“Additive manufacturing is an industrial tsunami. Swim towards the
wave – prepare yourself to the best of your abilities – or run to the
mountains and find other things to do. But don’t stand still on the beach,
do nothing and pretend that it’s business as usual.” (AMEXCI AB, 2018)
2.4 Heatsink design
The ability of transferring thermal energy from one place or object to another
have been widely researched. Almost every possible shape and architecture of
heatsinks and fluid flow ducts, which are manufacturable with traditional
methods, have been explored in detail. But the shapes which are possible with
AM seems to not be investigated yet. This section presents research on classical
heatsink design and relevant parts of flow theory that was used as an inspirational
platform for designing the AM heatsink.
2.4.1 Air vs Liquid cooling
(Kandlikar & Hayner, 2009) describe a dramatic increase in demand of more
efficient cooling devices due to the development of high-power electronic
equipment in military and industrial applications in the last decade (before 2009).
The previously sufficient air cooling will have to be replaced by heavier but more
efficient liquid cooling systems, something which pose a particular challenge in
the military aircraft industry.
The transition to liquid cooling is not only a matter of increased weight. Leakage
of conductive cooling fluid (or coolant) in the system could cause a short-circuit
in the electronics, and there is also the matter of increased corrosion with water-
based coolants. While (Kandlikar & Hayner, 2009) do not include AM in their
work, as it was barely known in 2009, many of their suggested improvements for
cold plate designs could benefit significantly from being manufactured using AM.
Several of the concepts they present could also be carried over to AM-designed
heatsinks.
2.4.2 Heat transfer processes
There are three mechanisms of heat transfer: Conduction, Convection and
Radiation. (Cengel & Ghajar, 2011)
Conduction is the transfer of heat in a solid body or within a still fluid by the
propagating vibration of its molecules. The conductive capability of a material is
25
dependent on factors like its density and the shape of molecules and grains. As a
result, some materials have higher thermal conductivity than others. Aluminium
for example is more thermally conductive than titanium, making it a better
material for use in lightweight heatsinks. The thermal resistance in an interface
between two solids is dependent on factors such as surface roughness and actual
contacting area.
Convection is the mechanism for heat transfer from a solid material to an adjacent
fluid in motion and can be either natural; when the hot fluid rises due to buoyancy
and is replaced by cooler fluid, or forced; when the movement of the fluid is
agitated by something like a pump or a fan. Fluid mechanics and convection is
closely related and there is a large number of factors affecting the heat transfer,
the flow regime (laminar or turbulent flow), the ‘wet surface area’ between the
fluid and the solid, and the flow speed to name a few. Turbulence improves the
internal convection within the fluid and helps mixing the temperature gradient
which otherwise exists in laminar flow and is an obstacle to efficient heat disposal
through the laminar layers of the fluid. Unfortunately, creating turbulence may be
difficult and costly in terms of pressure drop and manufacturing costs.
Radiation is the emission of energy through electromagnetic waves (or photons)
from any matter with a temperature above absolute zero (0 K), it does not require
the presence of a medium. The amount of heat transferred through radiation is
affected by parameters such as the surface area and the material emissivity.
Not all of the three can be present at the same time. Within an opaque solid body
heat is only transferred through conduction. While between a solid body and a
flowing fluid it’s through convection and radiation, which is the most interesting
case for designing coolant ducts. Due to the fairly low temperatures and the use of
two very similar materials the effects of radiation are neglected in this work,
leaving only the convective effects to be considered during the design phase.
2.4.3 Pressure drop
The pressure drop in a duct is a measurement of the flow resistance, and thus is an
important parameter for knowing the power necessary to drive a fluid through that
duct. A liquid cooling system consists of several components including hoses,
connections and often series of different heatsinks, and a pump to drive the
coolant. To select a suitable pump, the total pressure drop must be determined,
and once a pump is selected any changes within the system must be carefully
evaluated as to not disturb the total pressure drop beyond the limits of the pump.
(Kandlikar & Hayner, 2009).
26
An instinctive engineering reaction may be to try keeping the pressure drop at a
minimum to save power and perhaps use a smaller pump, but the pressure drop is
also correlated to the overall cooling performance of a heatsink. (Soodphakdee, et
al., 2001) compared the heatsink performance of different fin geometries and
found that “In general, the geometries providing the highest heat transfer
coefficients do so at the expense of excessive pressure drop”. A high pressure
drop is not a goal in itself but by increasing the pressure drop through various
inserts (fins) may lead to an increased thermal performance of the heatsink.
2.4.4 Fin geometries
Fins increase the surface area between the heated solid and the passing fluid.
Depending on the application and configuration of the heatsink, different shapes
and positions of the fins may be more or less beneficial for convective heat
transfer. (Soodphakdee, et al., 2001) studied five different shapes of fins (round,
square, plate, elliptical and long parallel plates), organised in either in-line or
staggered positions as shown in Figure 6, and found that staggered elliptical fins,
and staggered plate fins give the best heat transfer coefficients and lowest pressure
drops for air cooling heatsinks.
Figure 6. Illustration of different fin geometries and configurations
The fin shapes studied by (Soodphakdee, et al., 2001) are all adapted to the
possible and economically viable alternatives which are manufacturable using
traditional methods.
2.4.5 Channel shapes
Most of today’s channels are often based on circular or rectangular shapes due to
easier fabrication, but since these shapes are often difficult for AM there is an
incentive to look for other, self-supporting, shapes. The first to come to mind is
probably a triangle. Triangular shapes have received less attention by researchers
27
but gained popularity in compact heat exchangers over the last decades due to
their lower pressure drop compared to other shapes, at the cost of lower heat
transfer (Yusoff, et al., 2015).
2.5 The original heatsink
The original heatsink, seen in Figure 7, is part of an aerial application with high
demands on a lightweight construction. Its current method of manufacturing is
milling the outer shape followed by drilling and plugging the channels. It is a
liquid cooler with electronic equipment mounted to both sides at different
distances from the plate, hence the protruding tower-like features on one side.
Figure 7. Front view of the original heatsink.
Additional pictures are provided in Appendix 8.2. Table 1 shows the relevant
properties of the original heatsink.
Table 1. Properties of the original heatsink
Property Value Source
Mass 553 g CAD model
Total pressure drop ~9000 Pa CFD Simulated
28
3 METHOD
The first section of this chapter will concern the work on gathering information
for drawing the “Roadmap to AM”. It then proceeds to describes the CFD
simulation setup and methods of verifying the simulation results, and the setup of
the static pressure test on the manufactured AM heatsink. The chapter also
presents all details in the design process of the AM heatsink; the order its features
were built in, critical design dilemmas imposed by the decision to use AM and it
concretizes some of the design rules for AM by examples of when they were used
in this application.
3.1 Building a roadmap
Introducing a new technology and manufacturing method to the industry is not
done overnight. It requires massive amounts of research, and actively staying
updated on the latest news in several fields of technology and business strategy.
Most of the work towards this roadmap has been directed towards understanding
the various aspects of the AM technology itself but also seeing the bigger picture
of AM’s position amongst the already established manufacturing methods.
3.1.1 Interviews
This work began with interviews of Saab employees at the Surveillance site in
Järfälla. Questions were focused on the current processes of design, construction
and verification of parts using traditional manufacturing methods and discussions
on how the introduction of AM would impact their work, and also how the
implementation of AM have to be adapted to fit in the processes at Saab. The
interviews were kept informal and not recorded. Documentation was made
through written notes and the exact questions varied heavily depending on the
position and field of the person being interviewed. The purpose of the interviews
were to assess the span of questions and uncertainties that exists around AM at
Saab today.
3.1.2 Communication with suppliers and other organizations
Learning about the business network and the capabilities of 3D-printing suppliers
is an equally important part to looking into improvements in-house. By knowing
about the services provided by suppliers and trade associations, it is possible to
streamline the industrialization process by avoiding dual efforts where
cooperation is possible. One important part of the work has therefore been to
29
communicate and meet with suppliers of 3D-printed products, suppliers of 3D-
printing machines and AM-associations to discuss different roles, services,
possibilities and responsibilities in the supply chain and education of AM.
3.1.3 Seminars and fairs
Another source of information for this roadmap has been AM seminars and 3D-
printing fairs during the thesis period. Both internal at Saab, and external events
arranged by other organisations. Attributing specific parts of the roadmap to one
or other source is difficult as information from many different areas have
contributed to a holistic view of the AM field, from which conclusions have been
drawn continuously. The main purpose of visiting the fairs have been to establish
contact with new actors in the industry, not using the fairs themselves as primary
sources of information.
3.2 Designing the AM heatsink
A CAD model was designed and developed in Siemens NX. Concepts were
continuously evaluated against the requirements and improved until all
requirements were met and the abilities of AM sufficiently exploited. The overall
design process was as much of an exploration of the functions in the Siemens NX
software as an exploration of the possibilities of AM.
3.2.1 Requirements
The AM heatsink is designed with the intention to be able to replace the current
heatsink with regards to hole positions, position of components, thermal
capabilities and withstanding of static and dynamic loads. Requirements were set
accordingly, see Table 2.
Table 2. Requirements for the AM Heatsink
Nr Requirement
type
Requirement Data
1 Function The AM heatsink should aim to
be able to transfer a higher heat
flux than the original.
Only a relative
change will be
shown.
2 Function The AM heatsink should have
the same pressure drop as the
original heatsink.
Original pressure
drop: 9000 Pa
30
3 Shape The position of all mounting
holes should be the same as the
original.
4 Shape Parallel or split channels are not
allowed.
5 Shape The channel should be
constructed in a way which
allows for the escape of air
bubbles.
6 Weight The AM heatsink should have a
lower mass than the original.
Original mass: 553 g
3.2.2 Design evolution
The path of the cooling channel was the primary focus, everything else apart from
set requirements would be adapted to it. See
Figure 8 to follow the design evolution steps described in this section. Starting out
with the original cooling channels, the first idea was to round off the corners and
give the channel a more serpentine path, still within the middle plane of the base
31
plate. Secondly, a goal was set to try to reach as close as possible to all of the
mating faces where the heat load from electronic devices was applied. Different
paths were discussed with flow mechanics experts at Saab, and some were
discarded due to a risk of bubble trapping. When the path was set, the cross-
sectional shape of the channel, which had been circular with the same 5 mm
diameter up until this point, was altered to increase the wet surface area. Due to
volume restrictions in the heatsink, different regions got different shapes, and in
some areas where there was no heat load applied, a triangular shape was selected
for reasons mentioned in section 2.4.5. At this point, the first CFD simulation was
made to investigate the pressure drop, which was found insufficient, and inserts
were added to the final version of the channel to increase the pressure drop to the
wanted level.
Figure 8. Design evolution steps of the AM heatsink channel path
3.2.3 Shape of the channel
The channel path is modelled as a 3D-spline with 71 nodes, perpendicularly
anchored at the inlet and outlet, and raised into the four corner towers to get closer
to the heated mating surface at the tower top. Its 25 cross section sketches are
32
used to create a swept surface forming a tube. With the “area law”-function
available in Siemens NX sweep command, it is possible to force the tube into a
constant cross-sectional area regardless of the shape or size of the sketches. A
constant cross-sectional area is helpful for avoiding sudden pressure changes
which may be harmful in a system with high flow velocity. Figure 9 shows the
shape of the 3D-spline, and how different cross-sections may be placed along the
spline as bases for a swept channel surface. Note the difference in size between
the triangular sketch and the actual size of the sweep, this is the result of the area
law.
Figure 9. 3D-spline, shape and position of cross-sections and a swept surface.
3.2.4 Insert fins
In three of the four raised corners of the channel, just below the protruding towers,
vertical pin fins were inserted to increase the total pressure drop of the channel.
By placing them below the towers the pressure drop was purposefully located in
an area where a boost in heat transfer could be useful. They were modelled as
vertical pins for easier printing. Fins of a different shape were also placed in other
parts of the cooling channel to increase the surface area in those regions, but they
were not a part of the attempt to increase the pressure drop.
33
3.2.5 Mass reductions
Once the path and shape of the channel was completed, the work on removing
material and weight in the CAD-model began. With the new channel not running
through the middle of the heatsink a large portion of weight could be saved by
inserting a large hole there. Dynamic load FE-simulations were made on an early
model of the heatsink in order to test the concept of such a large material removal
on this heatsink. The cutouts were carefully shaped according to the AM design
rules of overhang wall angles and hole top radii.
3.3 CFD simulation setup
CFD simulations were used both during the design evaluation stage, to estimate
the pressure drop of the new design and see if any changes would be necessary,
and as a final verification tool to see if the new design would meet the required
pressure drop. The simulations were made using ANSYS 18.2, with the help of a
fluid dynamics engineer at Saab. Two simulations were carried out on the final
design, with a ‘standard’ and a ‘finer’ mesh to get mesh-independent results. The
previous simulations which were made on earlier versions of the coolant channel
during the design evolution stages are omitted from the report, only the
simulations made to verify the final design are presented.
3.3.1 Meshing
The general mesh structure consists of larger elements in the bulk part of the fluid,
and successively finer elements toward the edges. Closest to the edge, elements
were generated using the ‘inflation layer’ function in Ansys. It creates rectangular
elements of decreasing thickness toward the stationary walls to give the
simulation a more detailed mesh for calculating the boundary layer in the fluid,
which has great impact on the pressure drop. The final mesh is illustrated in
Figure 10 and mesh parameters are given in Table 3, below.
34
Figure 10. Appearance of the mesh with increasingly smaller elements closer to the outer
surfaces (L) and inflation layer with primarily rectangular elements at the wall (R).
Table 3. Mesh Properties of CFD simulations
Parameter/Property Simulation 1 Simulation 2
General element size in bulk (mm) 1.0 0.4
General element size close to faces (mm) 0.2 0.14
Inflation layer, number of layers 8 8
Inflation layer, growth 1.2 1.2
Inflation layer, max element thickness (mm) 0.2 0.2
Resulting mesh Size (No. of Elements) 10 × 106 20 × 10
6
3.3.2 Inflation layer and y+
The y+-value is an important control number for the equations governing the
simulation of boundary layers used in ANSYS. The value is attached to each
surface element of the mesh and may be displayed with a contour map on the
surface of the mesh as shown in Figure 11. The error of the simulation increase
with an increasing y+-value, and a mesh with y
+-values of more than 5 is generally
considered unfit. y+-values are preferably kept below 1. The meshes used in this
project had y+-values of typically 0.7 - 0.9 and a maximum of 1.5.
35
Figure 11. Illustration of y+-value contour map, with local maximum areas of 1.5.
3.3.3 Boundary conditions
The boundary conditions used for the AM heatsink simulations were the same as
for the original heatsink. The output was modelled with a total pressure of zero Pa
to easily show the total pressure drop along the channel. Boundary conditions are
shown in Table 4.
Table 4. Boundary conditions for CFD simulation
Position Type Value Unit
Inlet Mass flow rate 20 g/s
Outlet Total pressure 0 Pa
3.3.4 Terminal conditions
Simulations were set to halt after reaching RMS-errors below a certain value, or
after a certain amount of time due to planning of resources for calculation.
Conditions are shown in Table 5.
Table 5. Terminal conditions of CFD simulations
Parameter Simulation 1 Simulation 2
36
Maximum run time 24h 14h
Convergence limit for RMS values 10-7
10-6
3.3.5 Relative error
The relative error between the two resulting pressure drops are calculated as:
𝜀 = |𝑝2 − 𝑝1
𝑝2|
(1)
Where 𝜀 is the relative error and 𝑝 is the simulated pressure drop indexed
accordingly to the simulation run.
37
3.4 Static pressure testing
A static pressure test was conducted to see if the new design could withstand the
pressure in the cooling system. The test setup consisted of a manual hand-
operated pump, a pressure gauge with a maximum allowed pressure of 30 bar and
the inlet of the heatsink connected to the pump via an adaptor and the outlet of the
heatsink plugged. Pressures were tested at three levels: 15 bar, 20 bar and 30 bar.
After pumping the pressure up to each level, the pressure was kept within ± 1 bar
for 15 minutes before proceeding up to the next level. The static pressure
requirement of the original heatsink may not be shown, and no comparison to
such a value will therefore be made.
3.5 Stress analysis - Random vibration simulation
A FEM simulation was conducted on the AM heatsink by a Saab solid mechanics
engineer (Severin, 2018) to give an indication of whether the new design was
strong enough to withstand the same dynamic load case as the original heatsink.
Since all of the mounting positions of the AM heatsink were kept the same as on
the original heatsink, the same analytical load setup could also be used. The
simulation was made on an earlier model, but the structural difference compared
to the final model is small and the result is good enough as an indication. This
analysis was not carried out as a part of the thesis, but made on specific request by
the commissioner to verify the structural shape of the AM heatsink. It is included
in the thesis as an interesting side note, hence it was not carried out by the author
but by an external analyst.
38
39
4 RESULTS
4.1 The Roadmap
The actions stated below are identified as useful or necessary steps for the
introduction of AM as a manufacturing method at Saab Surveillance in Järfälla,
and possibly other Saab sites. They are presented in a partially chronological
order. Some actions may be taken in parallel and some may benefit from being
started only once knowledge and experience from previous actions has been
gained. Their in-between connections are not considered here.
Establish expert teams, a group of people at each site or business area,
whose main task is to make AM available as a manufacturing method.
They will develop the processes and methods for testing and
documentation of AM articles which are necessary to qualify any product
at their site. Cooperation and regular communication between AM-teams
at different sites is critical to avoid double efforts and to spread the
knowledge within Saab. The team unifies the AM-efforts on each site and
should be updated on ongoing AM-work in all projects there. The AM-
team should also identify the need for tools and education and stay
updated on ongoing trends in AM outside Saab.
Start using AM in real projects, because R&D efforts alone may cause a
too slow progress and run the risk of leaving Saab far behind the rapidly
moving frontier of manufacturing development. The technology is already
in a useful state and an innovative company such as Saab should have no
problem coming up with creative ways around today’s obstacles with AM.
Projects could include a parallel AM-track for relevant products, where
smaller problems could be solved and communicated to the AM-team to
be used in other projects if necessary. Larger problems which cannot be
solved in individual projects should be raised through the AM-team to an
R&D-level.
Find a method for qualification of AM products. This is a task for the
AM-team, but it is critical for the implementation of AM at Saab. The
details of this qualification plan are left to the AM-team.
40
Education of employees will be the next step once qualification is
possible. This concerns not only designers, but also project leaders,
systems engineers, managers and recruiters. The performance increase in
individual parts may not be enough to justify the use of AM, but the
possibility to combine parts and redesign systems of several components
has proven to give both increases in performance and cost reductions in
lead times and production. To manage this requires AM-competence and
knowledge in several offices. The AM-team should identify the need and
find internal or external providers of the relevant education.
Find and organize the research needs for Saab. Scattered and
unplanned research efforts should be avoided. Identifying important
research goals and creating a plan of consecutive studies may take some
extra time at the start but will reduce the risk of questions falling between
stools and provide a fuller picture of the research and its results in the end.
A structured workload also allows for easier cooperation with external
parties and the exchange of work-packages with research institutes.
Become an active part in the national implementation effort of AM. Keep
a close cooperation with AMEXCI and other partners, for a mutually
beneficial exchange of knowledge and data with other companies. Sweden
is a small country, and we need to cooperate to meet the global
competition.
Prepare for multidisciplinary optimization. The recent advances in
software development towards topology optimization and generative
design is still unknown to many. Design tools which takes into
consideration both physical factors such as weight, heat transfer and fluid
flow, and the limitations of a selected manufacturing method as input
parameters for an iterative process which generate the most
mathematically optimal design which is still manufacturable will soon be
readily available. Combining this with the possible AM shapes will
become an extremely powerful and efficient way to develop products, to
those who choose to learn, implement and master it.
Guide the evolution. The AM industry is facing many challenges right
now. Saab should seize this unique opportunity at the dawn of a new
technology to voice their own needs to make AM useful for them first.
41
Direct the AM industry towards solving the problems which are most
important for Saab before focusing on solving other problems with AM.
4.2 The manufactured AM heatsink
Table 6 shows how well the requirements for the AM heatsink are met.
Table 6. Comparison of results against requirements from Table 2.
Nr Requirement Data Result
1 The AM heatsink should aim
to be able to transfer a higher
heat flux than the original.
Only a relative
change will be
shown.
Unable to prove any
increase, but the wet
surface was doubled.
2 The AM heatsink should have
the same pressure drop as the
original heatsink.
Original
pressure drop:
9000 Pa
Fulfilled
The difference is ~1%
3 The position of all mounting
holes should be the same as
the original.
Fulfilled
4 Parallel or split channels are
not allowed.
Fulfilled
5 The channel should be
constructed in a way which
allows for the escape of air
bubbles.
Partially fulfilled
6 The AM heatsink should have
a lower mass than the
original.
Original mass:
553 g
Fulfilled; new mass:
409 g
42
4.3 CFD Simulation results
Table 7 shows the resulting pressure drop from the CFD simulations.
Table 7. CFD Simulation results
Simulation Total pressure drop [Pa] Notation
1 9147 𝑝1
2 9031 𝑝2
The relative error 𝜀 between the two pressure drops is calculated from (1),
𝜀 = |𝑝2 − 𝑝1
𝑝2| = |
9031 − 9147
9031| = 0.012 ≈ 1%
The contour maps of the pressure drop simulations are very similar for simulation
1 and 2. The contour map from simulation 2 is shown in Figure 12.
Figure 12. Pressure distribution in AM heatsink channel, second run.
4.4 Static pressure results
The AM heatsink showed no sign of leakage or bulging during the static pressure
test. It survived a static pressure of 30 bar for 15 minutes.
43
4.5 Random vibration simulation results
The preliminary model of the AM heatsink have a positive margin in the random
vibration analysis. The highest stress was recorded to 40 MPa at an inner radii
close to (but not at) one of the mounting points. See Figure 13. (Severin, 2018)
Figure 13. Random vibration simulation results
44
45
5 DISCUSSIONS
At the current stage of the technology, discussions about AM often leave more
questions than answers and the topics tend to drift quite a bit. This chapter has
been allowed to sometimes exceed the limitations set for the rest of the thesis in
order to provide the reader a fuller picture of the current status of AM, which may
be helpful to the industrial implementation of the technology. The chapter is
divided into several topics arranged from the more general matters of AM to the
more technology specific. The discussion on how this thesis was conducted with
regards to the timeframe and the methodology is left to the end.
5.1 On the introduction of a new technology to a
field of established ones.
New technologies always face the challenge of adapting to an existing
environment of expectations and regulations. One of the major obstacles found
during this thesis of introducing additive manufacturing is to make it fit within a
framework made for other technologies. Eventually, it became increasingly
tempting to change the framework rather than squeezing AM into it, and the
search for similarities in other fields began. Autonomous cars is another popular
modern technology which has some difficulties establishing itself. Not because it
is technically lacking, but because the roads are made and regulated for human-
controlled vehicles. It is natural that our current systems in society and industry
are attuned to the technologies which already exist, but we cannot expect new
technologies to always fit in the old frames. So it may come down to the
uncomfortable question of changing our habits and rules if we want to use the
benefits of this development. With this said, let us keep in mind that all rules may
not have to change. The first step should be to analyze the existing rules and
decide which are necessary to keep and which might become obsolete. Not only to
pave the way for AM into use, but also to be able to use it effectively.
Many are skeptical towards AM, which is both understandable considering the
state of the technology just a few years ago, but also something to welcome (to
some extent) because they identify problems which may be overlooked by the
hyped parts of the AM community. AM is by no means perfect in its current state,
and there are reasons to be suspicious, especially after the recent years extreme
coverage by the exaggerating parts of technology media which unfortunately have
led many off track from the real status of AM. It is important to look for solid
46
evidence of both the success stories and the failures. And it is even more
important that AM-knowledgable people make an extra effort to speak true about
the technology, about both the good and the bad sides to restore the trust in the
technoloy. New ideas are always met with a mix of skepticism and excitement,
and in the end they are both equally important for a solid development.
5.2 On the implementation of AM on a national
level.
As stated by AMEXCI, Swedish companies cannot afford to compete among each
other over AM in the face of a globalized market, and their initiative for
cooperation and coordination of Swedish efforts to industrialize AM is welcomed.
Cooperation and coordination really is the key to a quick success for Swedish
based companies in the AM field, because there are too many tasks on the road to
full implementation for any company to adress on their own. The amount of
available data for materials and process parameters is one of the reason we trust
the existing technologies, and building an equal library for AM is both a necessity
for its widescale use, but it also improves the precieved legitimacy of the
technology. Exploration of design rules is another task, adaptation of rules,
development of new boundaries and regulations such as export control, education
of AM engineers etc. are all important steps towards the full implementation. The
next question is: who should take on which task? The most practical solution
would be to divide the tasks according to the proficiency of each company or
institution. Not only should this guarantee the best results, but it should also
minimize the economical burden on both a local and national scale, which seems
to be yet another prerequisite for the implementation of a new technology.
An extra notice should be made on the status of education for AM, because there
are currently almost no courses on additive manufacturing in Swedish
universities. In their SRA, AMEXCI forsee a need for 1000 “AM-savvy people”
in the swedish industry within five years, and 5000 in ten years. The educational
institutions really need to pick up the pace and start developing courses to meet
this need. Otherwise, we may just have to keep our fingers crossed for 200-1000
engineers (per year) to find an interest in hobby 3D-printing to provide the
industry with personell of basic AM competence to educate further through
internal training programs, which one may suspect is not be the best solution. I
strongly encourage the Swedish universities, colleges and even elementary
47
schools to include and use AM in their education to help Sweden stay innovative
and keep the image of a technological nation.
5.3 On the AM process and materials
The great variety of different processes and materials available within AM makes
it difficult to lead a meaningful discussion that covers all of them at the same
time. Let us start with metal AM, even though some of the points that will be
made here may be applicable to plastics and other materials as well.
5.3.1 AM – two processes in one
Metal AM is a coupled process where both the material microstructure and the
overall shape of the product is created at the same time. Consider a supply chain
for common subtractive manufacturing of a detail. The raw material is formed
into a basic shape through a primary process of casting or rolling or forging etc.,
and then machined in a secondary process such as milling, turning, or grinding.
Most of the material properties are created in the first process, and the outside
tolerances and shape is created by the second. Because of this, we are used to
analyse the material properties on the output of the first process before using it as
an input in the second process, and then measure the geometrical shape on the
final detail. With AM, there is no gap between these two, the whole process is
done in one action and all testing need to be conducted on the final part. The
thought of this may sound easy but implementing it in industry could prove to be
difficult. AM will require new routines to be developed for how this new
manufacturing method should be handled, because it does not only replace an
existing method, it combines several different methods into one.
5.3.2 Control of parameters – pre-sets or manual skill
This coupled process, which is AM, is controlled by a large number of parameters
and finding optimal settings for each raw material and CAD geometry is a great
challenge. The development of industrial 3D-printers is trending towards
manufacturer pre-sets of the parameters for different materials rather than operator
control. Such a development may be thankful for the product developing
companies who can buy an AM machine which someone else always guarantees a
certain result from, but it also puts an awesome amount of power and
responsibility in the hands of the 3D-printer companies who could make sure you
can only use materials which are supplied by them. At the current status of the
technology, the operator may have to adapt the settings by experience to suit the
48
particular CAD-model to produce a part, at least with FDM machines. Hopefully,
the need for manual tweaking will fade as AM machines become more robust and
able to build parts with the same settings no matter their size. Or perhaps it will
become an integrated operation in the slicer software to read the CAD-file and
automatically apply suitable settings.
5.3.3 Input material for milling vs AM
The input material for milling is often a wrought or cast solid block which is
selected based on material properties such as tensile strength, hardness and
thermal expansion. The input material for Metal AM is often a powder, and it
should rather be compared to the molten stream which is poured into a casting
form, rather than the solid block which we machine into shape. The properties of
the molten stream is usually not interesting for the product developing company
which is more interested in the resulting material properties of the solid cast
object. I think it is reasonable to have a similar view on the powder or other input
material for AM, focus more on the final result and leave the analysis of the
effects of different powders to the manufacturers of the AM machines.
5.3.4 Recognize issues, solve and use
In summary: we have a lot of input parameters, to a machine which creates a solid
precision object from a fundamentally different raw material, and we expect it to
be quick. Naturally, there is a lot of things that can go wrong here. The fact that it
is possible at all is astonishing. The AM process is a difficult one, because it
combines both the benefits but also the difficulties of several other processes into
one, and they must all be controlled at the same time. These issues are recognized
and being worked on. The technology has advanced this far, and the systematical
thinking, the mathematical tools and both the software and hardware available to
control these processes to perfection are available to us. AM is already in a useful
state, and it should be underway to be implemented now. The technology has
improved tremendously over the past few years and indications say it is still
growing. Large companies need to board the AM-train today if they want to stay
competitive in the product development industry in the next couple of years.
5.4 On the design rules for AM
Mechanical designers always have to take into consideration the limitations of the
manufacturing method they aim to use. The do’s and don’ts of each method are
described as design rules, and AM comes with a new set which mechanical
49
engineers have to learn and become experienced in, in order to use the technology
efficiently. The design rules for AM are very different from the design rules for
milling. There are some similarities to welding due to thermal expansion, but they
are probably best regarded as a complete new set of rules. An important question
for the management of companies is whether it will be better to train and educate
all design engineers to have knowledge in both Additive and subtractive
manufacturing, or if these two very different ways of thinking is better to keep
separated in the workforce to allow for deeper knowledge in each individual field.
5.4.1 After redesigning the heatsink
From the redesign of the AM heatsink in this thesis and working first-hand with
these design rules, I would like to share some experiences. At first impression
there is a staggering freedom while designing for AM, but it fades quickly once a
horizontal hole or downward facing unsupported surface (so called ‘downskin’) is
added. Some details may be possible to 3D-print in several directions, but a single
feature may lock you into just one single printing direction, severely limiting your
future design options. With milling you may have to constantly think about how
to reach everywhere with a rotating tool. With AM, you have to constantly think
in layers and downskin surfaces needing supports. Do not be afraid of excessive
use of rounded edges, they are basically free with AM, and internal radii in
corners are critical. Hole-positions may be pre-printed and bored up afterwards to
achieve better hole dimension tolerances. For powder and liquid based processes,
you have to be careful not to create closed cavities which traps the base material
inside, unless you plan on either storing it there or extracting it in a later stage.
The most important tip I have about design for AM is to not take a part which is
designed for another method and simply send it to the 3D-printer. You will
probably get a part which is decent (as opposed to putting a part designed for AM
in a mill which will probably not work at all), but it would be a painfully
inefficient use of the technology. And more often than not will it create a
disappointment which is misinterpreted as a lack in AM technology rather than
the AM technology being used the wrong way. Build with AM what is designed
for AM.
5.4.2 Topology optimization and generative design
The AM technology opens the door for direct manufacturing of topology
optimized structures. This is regarded as one of the main reasons for
implementing AM in a business, because topology optimization and generative
design is the way for us to economically mimic millions of years of nature’s
50
evolution-optimised biological lightweight structures. It opens a completely new
design space, and the advantages could make it possible to challenge aluminium
and titanium as the kings of aerospace metals. Other metals such as Inconel with
its superior corrosion, oxidation and chemical resistance could prove to be hugely
beneficial if its higher density can be counteracted by smart design.
5.5 On the methodology and results of this thesis
This has been a very interesting topic to research, and there is a noticeable interest
from many partners both within the company and outside. The project was a bit
diffuse at the beginning. AM is new to most people and since it is a technology
born during the internet-era, it may be easier to find information but it is harder to
discern facts from popular beliefs. To make a reasonable roadmap it is important
to investigate a large number of aspects of AM and gather information from many
different sources. I went into the project with a quite skeptical mind to not let
myself be pulled along by the recent hype over 3D-printing. My goal was to learn
the technology on a fundamental level to make my knowledge useful even after
the master thesis was finished.
5.5.1 On the roadmap
Building a roadmap for the implementation of a new manufacturing method in a
corporation I had just begun to know was by far the most difficult part of the
thesis. A ‘roadmap’ is a somewhat diffuse concept, there are no real boundaries
on what to include and leave out. Moreover, the situation at Saab changed
dramatically during the course of the thesis making it increasingly difficult to
identify ‘future actions’ which would not be outdated before the end of the
project. That is yet another demonstration of how fast AM is developing right
now. In the end, the roadmap ended up containing all recommendations which
were identified throughout the thesis, regardless if they were implemented or not
at the finishing of the thesis.
The level of detail of the roadmap was also a difficult dilemma. Learning the
workflow of a large corporation at the level necessary to make recommendations
of changes on specific methods may take too long for a master thesis. And
revealing the internal know-how of a company in a public report is not preferable
either. Thus, the final roadmap contains recommendations at a higher
organizational level and the detailed plans are left for future work within the
company.
51
5.5.2 On the heatsink design
The design of the AM heatsink was to many degrees limited by the demands to fit
the mounting points of the old heatsink. And the design evolution was also based
on the same principle as the old heatsink, a baseplate with protruding towers. If I
could start over, I would probably choose a more dramatic change in basic
concept design. Perhaps start with only the mounting faces and connect them with
a coolant tube and finish the piece by only adding material where it would be
needed for strength and as a heat buffer magazine. After all, such a design would
not be impossible to create with AM, and this thesis was supposed to challenge
the possibilities of the technology.
This current redesign did also challenge the possibilities of AM. The upper
horizontal diameter of the coolant tube was at the stretch of what could be
manufactured in the EOS M290, and the shape of the internal fins were also a bit
of a gamble. The path of the channel was more of a challenge of the imagination
and the CAD tool, Siemens NX. A 3D-spline is difficult to position correctly, and
it seemed impossible to constrain its nodes except for the first and last ones.
Constraints are usually very important when creating a CAD model, and I was
only lucky to not run into problems due to the unconstrained nodes. I’m sure this
is a feature which could be added by the software developer, there might just not
have been a demand for fully constrained nodes in 3D-splines so far.
I received a lot of help in the design process from the manufacturer, Lasertech
AB. Their knowledge of the limitations in the manufacturing process was
invaluable and solved some important dilemmas along the way. The handbook on
AM design rules written by (Warholm & Sönegård, 2017) was also used
frequently, and I received many ideas on the path and insert fins of the channel.
My work was mainly to connect all of the ideas into one coherent part which was
possible to build with AM and which satisfied all the demands on the heatsink,
but to do that required a lot of knowledge of the AM build process. I think hands-
on experience in building with the 3D-printing technology is equally important to
any other manufacturing technology out there. To try for oneself and see the
results by holding it in your hand is one of the best ways to learn. Perhaps even
more so with AM since it is a completely new technology which requires a
different way of thinking and designing. It is recommended for most companies to
invest in a cheaper 3D-printer just to accelerate the designers’ learning process.
The resulting AM heatsink was above expectations, both externally and the
internal channel geometries. The total lead-time from order to delivered product
52
of just over one week was also very impressive, and is in itself a good argument in
favour of AM.
5.5.3 AM heatsink testing
The resources for physical testing of the AM heatsink was unfortunately very
limited. It was designed with the intention to be able to replace the original
heatsink in most testing aspects, and this is still possible if wanted at a later stage.
It would be most interesting to test the channel pressure drop and heat transferring
capabilities, both to compare to the simulation and to see if the heat transfer was
actually improved compared to the original. A heat transfer simulation would also
be interesting, as well as a full vibration test to verify the structural integrity of the
design with this material. We did however conduct a static pressure test, to
provide some basic verification of the reliability of the material, and the fact that
it held for 30 bar (which was the maximum of the testing equipment) is not
insignificant, even if further testing is required to really prove its strength.
5.5.4 Meeting the goals and requirements
The two main goals of this thesis were to find the necessary first steps for Saab to
introduce AM as a viable manufacturing alternative, and to redesign a heatsink
and improve it using the design advantages of AM.
The first goal was achieved in some sense, because the thesis managed to present
actions which the general AM community regard as necessary for the industrial
implementation of AM and apply these to the specific conditions at Saab.
Whether these steps are the only steps required is unknown thus far and has to be
investigated further. The specific work is more suitable to be carried out by Saab
employees rather than students to protect the know-how and keep it within the
borders of company confidentiality.
The second goal was not completely achieved. Most of the requirements on the
redesigned heatsink were met, but the most important could not be tested and the
actual increase in heatsink performance is therefore unknown, further research on
the relations between heat transfer and pressure drop compared to heat transfer
and wet surface area must be conducted to give a theoretical answer. A real-life
test could provide an answer for this specific design. The pressure drop was
arguably the same with the new design, which is astounding due to the doubled
wet surface area. Requirement no.5, was considered to great extent in the
beginning of the design and was later believed to be solved by the high flow
velocity which would carry any created bubbles through the duct. The corners
53
were carefully smoothed to help this process. The final requirement was fulfilled
above expectations. A decrease in mass of almost 150 grams (27% of original
mass) show a great potential with the design advantages of AM. And this was
done without the help of advanced design tools such as topology optimisation and
use of lattice structures.
5.6 Future work
The roadmap already presents many suggestions for future work, but on a non-
specific level. This section will contain some hands-on examples of research
questions and projects which are related to AM and could help the overall AM-
effort at Saab. Many of the points suggested below fill out what this thesis was not
able to achieve.
An analysis of the product development process used at Saab. With the
purpose to identify the areas which will be affected by the introduction of
AM, how they will be affected and give suggestions for necessary
education of the staff working in these areas.
Possible master thesis: Investigate the effect of surface roughness
produced by DMLS on heat transfer. The downskin surfaces of AM are
notoriously coarse, but could this in fact be beneficial for horizontal
coolant tubes?
Possible master thesis: Investigate the possibility of smoothing the walls of
complex internal channels.
Possible master thesis: Explore new heatsink fin geometries which are
now manufacturable through AM, perhaps including lattice structures and
the support structures generated by different AM methods and softwares.
Possible master thesis: Evaluate surface treatment methods which are
available for common metal AM materials.
Possible master thesis: Investigate the porosity of AM materials and how
prone they are to erosion, especially for internal channel flow with
different fluids.
Possible master thesis: Investigate the usefulness of Compliant
Mechanisms (also known as flexures) which are manufacturable using
AM, for the product range at Saab.
Possible master thesis: A study on the relation between pressure drop and
heat transfer. Can the heat transfer rate be increased without an increase in
54
pressure drop? Could AM be the key to create such shapes which would
make this possible?
Possible master thesis: An investigation on the effects of vortex generators
on the heat transfer of internal fluid flow. Perhaps to find an optimal shape
of such vortex generators.
55
6 CONCLUSIONS
The main purpose of this thesis was to find the necessary first steps for
introducing AM as a viable manufacturing alternative at Saab. It was supposed to
be represented through a well-structured roadmap of the requirements in
administration and design procedures that would be necessary for AM-products to
pass qualification. A task like that, in such detail, proved immensely difficult to
finish in one single thesis. It would require in-depth knowledge of the company
procedures, which was not reasonably achievable within the timeframe. And
presenting the findings of company know-how in a public report would not be
suitable. This resulted in a more generalized roadmap, while the specific topics
regarding qualification of AM will continue to be researched internally at Saab
Surveillance Järfälla.
The second purpose of redesigning the heatsink however was fulfilled, it could
unfortunately not be satisfactory tested due to resource shortages. The testing and
simulations that were carried out showed promising results, and the design
properties with reduced weight and a doubled heat transferring area show a
potential for a significant improvement of this particular heatsink. Such results
encourages further research into AM for heatsinks, and is already underway
through other theses at the time of writing.
Regarding conclusions about the general field of AM, two things should be
particularly noted after reading this report:
1. Additive manufacturing is a very large new technology. Many different
methods and technologies fit within its description, but they cannot be
treated as one. There are too many different materials, and methods of
fusing them together, and the areas of application are too varied. To
effectively implement AM, it needs to be divided into smaller parts,
perhaps one method or machine or material at a time. Companies are
encouraged to start by selecting a few technologies to fully implement
based on their needs and products.
2. Additive Manufacturing is a coupled process. It alters the microstructure
of the input material and creates much of the final shape at the same time,
resulting in a situation where all material testing and geometrical
measurement needs to be carried out on final parts rather than after each
sub-process, i.e. casting and then milling. A coupled process may
introduce a need for more control and testing than the two sub-process
56
together. And finding out what is totally new to us is the real challenge of
introducing AM.
57
7 REFERENCES
3D Hubs, n.d. What is 3D-printing? The definitive guide. [Online]
Available at: https://www.3dhubs.com/guides/3d-printing/
[Accessed 14 01 2019].
52900, I. -., 2015. ISO/ASTM 52900:2015 Additive Manufacturing - General
Principles - Terminology. [Online]
Available at: https://www.iso.org/obp/ui/#iso:std:iso-astm:52900:ed-1:v1:en
[Accessed 16 01 2019].
Albright, B., 2018. Digital Engineering 247. [Online]
Available at: https://www.digitalengineering247.com/article/combine-ct-
scanning-additive-manufacturing/
[Accessed 10 02 2019].
AMEXCI AB, 2018. The Strategic Research Agenda for the Swedish Additive
Metal Manufacturing Industry, Karlskoga: BrandFactory.
Anon., 2019. LENS Metal 3D-printer systems. [Online]
Available at: https://www.optomec.com/3d-printed-metals/lens-printers/
[Accessed 22 01 2019].
Capobianchi, M., Irvine, J. & Thomas, F., 2011. Triangular Ducts, Flow and Heat
Transfer. [Online]
Available at: http://www.thermopedia.com/content/1205/
[Accessed 26 01 2019].
Cengel, Y. A. & Ghajar, A. J., 2011. Heat and Mass Transfer - Fundamentals and
Applications. 4th Edition in SI-units ed. New York: McGraw HIll Education.
EOS, 2019. Materials for metal additive manufacturing. [Online]
Available at: https://www.eos.info/m-
solutions/material_parameter/download/Aluminium_AlSi10Mg.pdf
[Accessed 10 02 2019].
Fulcher, B. A., Leigh, D. K. & Watt, T. J., n.d. Comparison of AlSi10Mg and
AL6061 Processed through DMLS, Austin: The University of Texas.
GE, 2019. A guide to metals used in additive manufacturing. [Online]
Available at: https://www.ge.com/additive/additive-
58
manufacturing/information/metal-additive-manufacturing-materials
[Accessed 09 02 2019].
ISO/ASTM-52910, 2018. ISO/ASTM 52910:2018. [Online]
Available at: https://www.iso.org/standard/67289.html?browse=tc
[Accessed 26 01 2019].
ISO/ASTM-52921, 2013. Swedish Standards Institute. [Online]
Available at: https://www.sis.se/api/document/preview/916219/
[Accessed 26 01 2019].
Kandlikar, S. G. & Hayner, C. N., 2009. Liquid cooled cold plates for industrial
high-power electrinic devices - Thermal design and manufacturing
considerations, Rochester, New York, USA: Taylor & Francis Group, LLC.
Kempen, K., Thijs, L., Van Humbeeck, J. & Kruth, J., 2012. Mechanical
properties of AlSi10Mg produced by Selective Laser Melting, Leuven, Belgium:
Elsevier.
Kusuma, C., 2016. The effect of Laser Power and Scan Speed on Melt Pool
Characteristics of Pure Titanuim and Ti-6Al-4V Alloy for Selective Laser Melting,
s.l.: Wright State University.
Mattson, S., 2018. Additive Manufactured Aluminium Components - Mechanical
Properties and Material Characterization, Uppsala: Teknisk- naturvetenskaplig
fakultet UTH-enheten.
Protech, 2017. Protech. [Online]
Available at: http://www.protech.se/nyheter/kundberattelser/utah-trike
[Accessed 03 02 2019].
Redwood, B., n.d. Additive Manufacturing Technologies Overview. [Online]
Available at: https://www.3dhubs.com/knowledge-base/additive-manufacturing-
technologies-overview
[Accessed 21 01 2019].
RX-Solutions, 2019. or3D. [Online]
Available at: https://www.or3d.co.uk/knowledge-base/x-ray-inspection-for-
additive-manufacturing/
[Accessed 10 02 2019].
Saab, 2019. Saab.com. [Online]
Available at: https://saab.com/globalassets/commercial/air/gripen-fighter-
59
system/electronic-warfare.jpg
[Accessed 01 02 2019].
Sakratidis, A., 2018. Digital metal, Binder jetting technology. Kista, Stockholm,
3dp.se.
Severin, J., 2018. Random vib. analysis AM kylare [Interview] (15 10 2018).
Shah, P., Racasan, R. & Bills, P., 2016. Comparison of different additive
manufacturing methods using computed tomography, United Kingdom:
ScienceDirect.
Soodphakdee, D., Behnia, M. & Watabe Copeland, D., 2001. A comparison of Fin
Geometries for Heatsinks in Laminar Forced Convection: Part I - Roundm
Elliptical and Plate Fins in Staggered and In-Line Configurations, Sydney,
Australia: International Microelectronics And Packaging Society.
Sufiarov, V. et al., 2016. The effect of layer thickness at selective laser melting,
St. Petersburg, Russia: ScienceDirect.
Söderström, M., 2018. Heat transfer in flow ducts [Interview] (?? ?? 2018).
Warholm, M. & Sönegård, J., 2017. Industrialization of Additive Manufacturing,
Gothenburg, Sweden: Chalmers University of technology.
Wheeler, A., 2015. Engineering.com. [Online]
Available at:
https://www.engineering.com/3DPrinting/3DPrintingArticles/ArticleID/10081/Str
atasys-Produces-3D-Printed-Parts-For-New-Airbus-Aircraft.aspx?e_src=relart
[Accessed 03 02 2019].
Wohlers, T. & Gornet, T., 2014. History of Additive Manufacturing. [Online]
Available at: http://www.wohlersassociates.com/history2014.pdf
[Accessed 15 01 2019].
Yusoff, M., Ahmed, M. & Ahmed, H. E., 2015. Heat transfer enhancement in a
triangular duct using compound nanofluids and turbulators, Gombak, Malaysia:
Elsevier Ltd..
60
A
8 APPENDIX
8.1 Appendix A – AM process categories
B
8.2 Appendix B – Pictures of the original heatsink
Front (left) and back (right) of the original heatsink.
Transparent illustration of the original heatsink
C
8.3 Appendix C – Pictures of the AM heatsink
Front (left) and back (right) view of AM heatsink
Transparent illustration of the AM heatsink