AND THE MAIN FIELD OF STUDY MECHANICAL ENGINEERING, SECOND CYCLE, 30 CREDITS STOCKHOLM, SWEDEN 2021
Investigation and implementation of rapid prototyping in development of a
high-speed light craft
ULRIK SKÖLDKVIST
Utredning och implementering av iterativ prototyptillverkning för utveckling av lätta höghastighetsfartyg
Author
Ulrik Sköldkvist, ulriksk@kth.se SCI, School of Engineering Sciences KTH Royal Institute of Technology
Place for Project
Stainless Steel Yachts Sweden AB Stockholm, Sweden
Examiner
Karl Garme
KTH Royal Institute of Technology
Supervisor
Adrian Falk
Stainless Steel Yachts Sweden AB
Designing and constructing boats or ships is a slow, iterative process where the design goes through several steps in each iteration, and every loop in the process leads closer to the result. However, to verify if the boat’s design functions, it must be built if there is no possibility to design, build, and evaluate smaller prototypes during the development.
This report presents a method for rapid prototyping based on additive manufacturing and agile development methods. The method was applied in a development project were an engine hatch concept, based on a sandwich construction, is evaluated for a high-speed light craft. The concept was tested and evaluated with built prototypes during three iterations with increasing complexity.
The development project’s result confirmed the engine hatch concept with a
recommendation of using it in production. It also showed that the rapid prototyping
method was well suited for this project and other development projects for high-speed
light craft.
Sammanfattning
Att designa och konstruera båtar och fartyg är en långsam, iterativ process där designen går igenom flera steg i varje iteration och varje varv i processen leder närmare slutresultatet. Men för att verifiera om designen fungerar behöver båten byggas i sin helhet. Om det inte finns möjlighet att designa, bygga och utvärdera mindre delar med iterativ prototyptillverkning under utvecklingens gång.
Denna rapport presenterar en metod för iterativ prototyptillverkning baserad på additiv tillverkning och agila utvecklingsmetoder. Metoden har sedan applicerats på ett utvecklingsprojekt där ett koncept för en motorrumslucka, baserad på en sandwichkonstruktion, utvärderas för på ett lätt höghastighetsfartyg. Konceptet testades och utvärderades med byggda prototyper under tre iterationer med stigande komplexitet.
Resultatet av utvecklingsprojektet visade att konceptet för motorrumsluckan kunde
bekräftas med rekommendation att använda konceptet i produktion. Metoden för
iterativ prototyptillverkning visade sig också väl tillämpbar på projektet samt inom
annan utveckling för lätta höghastighetsfartyg.
I wish to express my gratitude towards the staff at Stainless Steel Yachts Sweden AB
(SSY) for all the support and for letting me write my thesis with them. Moreover, I
would like to thank Adrian Falk at SSY and Karl Garme at KTH, the Royal Institute of
Technology, for their help and advise as supervisors and examiner. Finally, I want to
thank my family and friends for their support while writing this thesis in the middle of
a pandemic.
Acronyms
RP Rapid Prototyping AM Additive Manufacturing CAD Computer Aided Design FEM Finite Element Method HSLC High Speed Light Craft SL Stereolithography
FDM Fused Deposition Modelling
SLS Selective Laser Sintering
SSY Stainless Steel Yachts
DED Direct Energy Deposition
1 Introduction 1
1.1 Problem description . . . . 2
1.1.1 Development project . . . . 3
1.2 Goal . . . . 3
2 Theory 4 2.1 Additive Manufacturing . . . . 4
2.1.1 Summary of Additive Manufacturing technologies . . . . 8
2.1.2 Applications of Additive Manufacturing . . . . 8
2.2 Rapid Prototyping . . . . 10
2.2.1 Applications of Rapid Prototyping . . . . 11
2.3 Agile development . . . . 13
2.3.1 Scrum . . . . 14
2.4 Ship design . . . . 17
3 Rapid Prototyping in ship development 19 3.1 Structure . . . . 19
3.1.1 Roles . . . . 20
3.1.2 Development phases . . . . 21
3.1.3 Iteration length . . . . 23
3.2 Rapid prototyping method . . . . 23
3.2.1 Initiating the project . . . . 24
3.2.2 Concept . . . . 25
3.2.3 Prototype . . . . 25
3.2.4 Review . . . . 26
3.2.5 Refine and iterate . . . . 27
CONTENTS
4 Development project 28
4.0.1 Background and initialisation . . . . 28
4.1 Hatch concept . . . . 29
4.1.1 Development with rapid prototyping . . . . 29
5 Results 32 5.1 Development project - Prototyping . . . . 32
5.1.1 First iteration . . . . 32
5.1.2 Second iteration . . . . 33
5.1.3 Third iteration . . . . 34
5.2 Rapid Prototyping method . . . . 37
5.2.1 Development project . . . . 37
5.2.2 Comparison to traditional development . . . . 38
6 Conclusions 39 6.1 Rapid prototyping method . . . . 39
6.1.1 Development project results . . . . 39
6.1.2 Utilising additive manufacturing . . . . 40
6.2 Further Work . . . . 40
6.2.1 Rapid prototyping method . . . . 40
6.2.2 Hatch concept . . . . 41
Bibliography 42
Introduction
Before the days of Computer Aided Design (CAD), shipbuilding required Naval Architects to utilise knowledge and experience, sometimes passed on from previous generations. Resulting in slow iterations, as a fault discovered in one ship could only be adjusted in the next ship built. The limitations in the number of performed calculations meant that most developments came from improving previous designs. However, as the ability to perform calculations improved and with the introduction of CAD in ship design in the 1960s, it became possible to do most of the design and perform many of the calculations in the software [1]. With that said, the ship design process is still highly iterative. Illustrated as a spiral in figure 1.0.1, with multiple performed iterations, and with each iteration come closer to a final design [2].
Ship construction has similarities with Rapid Prototyping (RP), with the main goal and purpose when using RP are to manufacture prototypes or similar quickly to reduce development time. It is not common within shipbuilding and construction to utilise the method, but the similarities with iteration and model testing could mean that RP could improve the shipbuilding process. Especially for High Speed Light Craft (HSLC) where weight and strength is crucial [4].
Today rapid prototyping is used in various fields such as automotive, aerospace, and
medical to develop parts and concepts. The industries have discovered multiple
benefits from using RP such as faster development cycles, cheaper development and
a possibility to manufacture physical prototypes at a low cost. With the advances in
additive manufacturing and rapid prototyping and the benefits that follow, a structured
development process is needed to utilise those benefits fully.
CHAPTER 1. INTRODUCTION
Figure 1.0.1: Ship design spiral [3].
1.1 Problem description
The project aims to investigate how to utilise rapid prototyping in the development
process of HSLC and create an adapted rapid prototyping process. The aim is to
investigate if it is possible to save time or resources in the development process or if
the process of producing prototypes results in a better solution. As rapid prototyping
covers multiple different techniques, one of the more important questions is how
to implement rapid prototyping? Which technique works best, and which methods
provide results that closely resemble the material used for actual production? Most
commonly, additive manufacturing is used to manufacture early prototypes as it allows
for fast manufacturing of prototypes, usually in plastic. However, in later stages of
development, or depending on the prototype’s characteristics, it might be necessary to
do metallic prints or build them with other techniques.
1.1.1 Development project
A development project will be performed at Stainless Steel Yachts (SSY) where a hatch concept will be constructed, prototyped and tested with the devised rapid prototyping process. SSY is unique to build boats using this particular super duplex stainless steel in boats that allows for building light and durable hulls with very little corrosion and fatigue. However, it has been challenging to manufacture lightweight and solid feeling hatches in super duplex steel in previous boats. To counter this and utilise the material thoroughly, a hatch concept will be developed with the devised rapid prototyping process.
1.2 Goal
The project’s goal is to investigate if it is possible and beneficial to introduce rapid
prototyping in the development process and in what way. By evaluating the result from
the pilot project and comparing it with previous work performed within SSY, the goal
is to investigate whether any benefits from utilising rapid prototyping is seen. The
final product will guide how to implement and use rapid prototyping in a company or
development team.
Chapter 2 Theory
This section presents the theory behind Additive Manufacturing (AM), the included technologies and some of the applications. Continuing to rapid prototyping, explaining the history, basic principles and how it is being used in several industries today. Rapid prototyping is not the only iterative design process. It has some similarities with agile development described after that, with a focus on Scrum. Lastly, describing how ship design processes look today. There are similarities between ship design and rapid prototyping as they both are based on an iterative process.
2.1 Additive Manufacturing
Compared with more conventional manufacturing, where the material is removed from a block to create the final shape or cast in a mould. AM is a collection of methods where the material is instead added layer-by-layer to create the final shape, also referred to as 3D printing. According to the ISO standard
1describing the AM process, seven different types of additive manufacturing can be used in a few different ways: vat photopolymerisation, material jetting, binder jetting, powder bed fusion, material extrusion, directed energy deposition and sheet lamination [5]. The various methods range from using powder bound by a resin or melted with a laser to a wire melted and extruded onto a build plate in the desired shape. However, there are many variations;
they all use some layered manufacturing variation and are differentiated by how these layers are formed and fused [6].
1
ISO/ASTM 52900:2015
Vat Photopolymerization
This technology uses a resin that is hardened layer by layer by an energy source, such as a laser or light projector. By directing the light or laser to specific points, the resin is cured in that spot. A common form of this technology is called Stereolithography (SL) [5], figure 2.1.1 illustrates the process.
Figure 2.1.1: Illustration of Stereolithography (SL) [5].
Material Extrusion
The material is extruded onto a platform in layers. Usually, a plastic heated up and deposited through a nozzle on a build platform in the desired shape. After the material has been extruded in melted form, it hardens once it cools [5]. The process can be seen in figure 2.1.2. This technology is unique thanks to the low-cost components, leading to it being the most common and easily accessible AM technology [7].
Binder Jetting
It uses a bonding agent deposited onto a bed with powder in a controlled pattern that
binds it together. Adding coloured powder with the bonding agent makes it possible
to create full-colour prints [5].
CHAPTER 2. THEORY
Figure 2.1.2: Illustration of an material extrusion application called Fused Deposition Modelling (FDM) [5].
Material Jetting
In this process, a liquid material, usually resin, is sprayed onto a printing platform and then hardened with UV-light [5].
Direct Energy Deposition
This technology is used to print metals by feeding material in powder- or wire form in front of an energy source, such as a laser or electron beam, to melt the material onto a printing platform layer by layer [5], see figure 2.1.3.
Powder Bed Fusion
A powder is deposited layer-by-layer onto a platform, then directing an energy source,
laser or electron beam, onto the powder bed to melt the particles together. When
one layer has been heated up and melted, another layer of powder is deposited. This
technology is commonly used to print metals and plastics, and a typical application is
Selective Laser Sintering (SLS) [5], see figure 2.1.4.
Sheet lamination
This technology uses sheets of material fused instead of the other technologies that use powder or wires. When finished, the final object must be removed from the bound sheets [5].
Figure 2.1.3: Illustration of Direct Energy Deposition (DED) [5].
Figure 2.1.4: Illustration of Selective Laser Sintering (SLS) [5].
CHAPTER 2. THEORY
2.1.1 Summary of Additive Manufacturing technologies
The different AM technologies all have their similarities and differences, used in multiple applications. Additive manufacturing started to be commercialised in the mid-1980s with several applications using Vat Photopolymerization. The other techniques were introduced in the following decades, but due to high costs, AM was not yet widely available [8]. Less expensive systems were introduced in the 1990s and 2000s. However, it was not until the early 2010s, when small, low-cost desktop printers became widely available, that the general public caught on to the possibilities of additive manufacturing [5].
The reduction in cost that came from the expanding interest in the technology became important for wider adoption. Development of additive manufacturing will continue with larger printers available to build larger objects in more materials even faster and cheaper than today [9]. Today these factors are still limitations in the AM process, but as more companies invest and use the technology, the development will continue to progress [5].
However, there are other drawbacks than cost. Most parts manufactured with AM requires, depending on the technique, post-processing where support structures are removed, and the surface finish is improved. The parts also risk warping or shrinkage when the part cools, as heat is applied in most processes. In some cases, due to inadequate adhesion in between layers, additive manufactured parts have poor durability, and strength [10].
2.1.2 Applications of Additive Manufacturing
The wide variety of possible materials and ways of printing with benefits such as faster manufacturing time, cheaper parts and solutions only available with AM provides several benefits in several applications. Even if additive manufacturing is a relatively new manufacturing technology compared to other methods, it has spread to multiple industries. Industries that utilise additive manufacturing in some capacity are aerospace, automotive, medical and many more.
The use of AM can be divided into a few different categories. First, creating prototypes
of parts as AM allows for fast and accurate manufacturing. This will be more closely
described in section 2.2. It can also be used to create moulds or patterns, a 3D printer
could accurately print a mould, and then a part or tool could be cast from it. Lastly, it can also be used to print end parts. The reasons to utilise additive manufacturing for certain end-use parts are usually the flexibility of having a product produced just in time, producing a lighter part, or the requirements for a part means it can only be produced with AM [5].
Producing a part just in time or on-demand can simplify and reduce an assembled product’s cost. Instead of storing parts, they can be printed when needed. This possibility also extends to the production of spare parts, which might benefit from the technology. It makes it possible to produce a spare part when and where it is needed.
Instead of keeping spare parts in stock, it is possible to have a 3D printer ready with material and files for the parts that can print a specific part when needed [11].
They can print spare parts at the International Space Station, using a 3D printer, from files sent from the earth instead of sending the whole part. This means that spare parts and tools can be printed instead of sent with a cargo shipment, saving valuable weight [12]. Additive manufacturing has also been used to print spare parts for the F-18 Super Hornet
2. With AM, it was possible to combine several parts, which reduced the weight and shortened the installation time [13]. However, the cost, speed and quality of AM are in some cases today less efficient than traditional manufacturing, but as additive manufacturing evolves, it might become more common [5].
With AM it is also possible to manufacture parts that are impossible to manufacture in other ways. The procedure of adding material layer by layer means that irregular shapes or cavities can be inserted inside the part, which would have been impossible with traditional manufacturing methods such as casting in a mould. One example of this is a coolant clamp manufactured by Sandvik AB for Seco tools. The part was made possible with additive manufacturing as the coolant channels inside the clamp needed to be curved, making them impossible to be drilled or cast [14].
Applications of AM is not limited to small objects as the worlds largest 3D printed object as of 2019 and largest 3D printed boat measure almost 8 meters in length and weighs 2,200 kg [15]. The possibilities of AM increase when the technology is fully utilised, which can be summarised in Design for Additive Manufacturing, DfAM.
The part is designed from the beginning to be manufactured with AM to fully take advantage of the possibilities and be aware of the drawbacks and limitations [16].
2
The F-18 Super Hornet is a fighter aircraft originating from the United States
CHAPTER 2. THEORY
2.2 Rapid Prototyping
Rapid prototyping utilise the technology of AM to create prototypes or models to test and verify the function [9]. It is a relatively new approach regarding product development, manufacturing and tooling. Starting in the 1980s, when additive manufacturing started making an appearance, it became a way to produce physical models during product development to validate new designs [17]. The possibility to create relatively inexpensive physical prototypes early in the development stages meant that design changes could be introduced earlier, and with that reducing the risk for expensive amendments later in the design process [18].
This can be important for the development cost, as the changes or problems discovered have a greater possibility to be changed and at less expense. See figure 2.2.1 for a graph illustrating this phenomenon where early in a project, the possibility of changing parameters is greater and the cost is lower [19]. This is one of the main ideas with RP, producing cheap prototypes to help discover issues [9]. The time it takes to develop a product also affects the total cost of development, and with rapid prototyping, it is possible to decrease the time it takes to bring a product to market, called ”time to market”. Meaning from decision to initiation of the development to the introduction to the market, and if that time is shorter, the development cost is lower [9].
Figure 2.2.1: Illustration of change vs. cost as a project progresses [19].
This is one way that rapid prototyping can help reduce development costs [17]. There are other benefits, as well. By focusing on creating scale models or parts on a smaller scale, the prototypes’ cost can be reduced. Building prototypes utilising additive manufacturing is another way to create relatively low-cost parts. Both the material used and the machines or printers have a low cost. A 3D printer can also be operated without much oversight apart from starting the print and some post-production steps leading to a finished prototype [9].
This is especially important when performing quick iterations during the development of a product. A model can be created in CAD during a workday, and then the prototype can be printed from the model overnight, leaving an almost finished model when coming into work the next day. Some post-processing later, the prototype can be reviewed and tested. With the improvements and experience from the previous prototype incorporated into the CAD model, a new prototype can be printed overnight, meaning the rapid prototyping process can be repeated almost once per day [18].
One example of the short iteration time from rapid prototyping is the tire company Hankook, where designers perform an iteration cycle per day. They work on a tire design during the day and then print the design during the night. The printed tire model can then be studied, iterated and improved on for the next prototype [20].
These are some of the benefits of using rapid prototyping to develop products.
However, the technology does have its drawbacks. As RP mostly utilise additive manufacturing, the drawbacks and limitations of AM also apply. This includes the limitations in size, material and cost of the prototypes. With these limitations, there are still many applications of the technology used today [5].
2.2.1 Applications of Rapid Prototyping
As additive manufacturing becomes more widely adopted, the use of rapid prototyping
follows. The gains from creating low-cost prototypes early in development to test
functionality and its looks are taken advantage of in several industries. In the
automotive industry, it is used for various projects, with one example being the
development of a convertible top for a car. The construction of a convertible top is very
complex as it must fold into a small amount of space, look good when folded up and
perform the folding operation successfully. A construction so complex requires that
the development and design begin early in designing the whole vehicle with prototypes
CHAPTER 2. THEORY
Figure 2.2.2: Scale model of a convertible top assembly [9].
and models to test. These prototypes go through multiple iterations in various stages, from concept and data control to a functional model. The concept and data model is built to coordinate the creative and construction aspects to validate the function.
Such a model can be found in figure 2.2.2, printed in one piece to show the complete assembly. The functional model is built to test the kinematics, how the different parts interact, and that the complex construction functions as designed. The parts were printed individually to be assembled into a functional full-scale prototype [9].
Producing functional prototypes with rapid prototyping and additive manufacturing
is also utilised in the aeronautical industry. Apart from printing end-use parts for
their aeroplanes, the aeroplane manufacturer Airbus utilises rapid prototyping when
developing and testing concepts [21]. By building small scale models from mainly
3D printed parts, they can design, build and test different solutions fast. The 3D
printed aeroplane used in one project, see figure 2.2.3, made it possible to test various
technologies in actual flying conditions by exchanging wings and other parts. The main
benefit of this is the possibility to create an entirely new model in a few weeks if it were
to fail [22].
Figure 2.2.3: 3D printed Airbus aircraft model [22].
2.3 Agile development
Agile is a development practice mainly used in software development centred around an iterative and flexible mindset where the focus of development is on four core values forming the Agile manifesto [23]:
• Individuals and interactions over processes and tools.
• Working software over comprehensive documentation.
• Customer collaboration over contract negotiation.
• Responding to change over following a plan.
These values where written and agreed upon by a group of developers in 2001, and together with 12 principles (see figure 2.3.1) based upon the values and manifested through different practices, they form the ”Agile mindset” [24].
The 12 principles further develop the guiding practices to support teams using agile.
Here the focus and link to the core values are evident with the principles connecting
the core values and how they interact. As an example, the first and second principle is
CHAPTER 2. THEORY
Figure 2.3.1: The 12 principles behind the Agile Manifesto [23].
closely related as customer collaboration is essential. They, in turn, relate to delivering working software frequently represented in point three and seven. The core values and principles are then enabled by different practices depending on application [24].
The agile mindset originated in software development. However, many other industries have also adopted the practices and adapted to the work there[24]. When viewing the core values and thinking past the software, the mindset is whats important part and can be applied in many other cases. Agile then becomes an adjective to describe how to perform an activity. The agile mindset allows for a way of working that helps handle change, focusing on customer collaboration and the individuals in the project [25].
2.3.1 Scrum
While agile describes a mindset and way of thinking about development, Scrum is a framework created to enable collaboration on complex problems [26]. It was developed before the Agile manifesto was published. However, they are closely linked and based on similar values. The agile mindset underpins several frameworks, and two co-creators of Scrum, Ken Schwaber and Jeff Sutherland, were part of the group that wrote the agile manifesto [23] [26]. Scrum and Agile are then closely related.
As described in section 2.3 the agile mindset does not cover how a project should be
events, and the rules that bind them together [26]. It is described and defined in The Scrum Guide by Schwaber and Sutherland [27]. A graphical representation of the Scrum framework is shown in figure 2.3.2. It is possible to see how the different parts of the framework are related and covers the Scrum team, the various events and artefacts.
Figure 2.3.2: Graphical representation of the Scrum framework [26].
Scrum team
The Scrum team consists of developers, a product owner and a Scrum manager who work as a team towards the set goals. Scrum teams are self-organising and cross- functional, meaning they decide how to perform the work and have all the necessary competencies needed for the project.
Developers are the members of the Scrum team, creating and adding value to the product. Meaning they perform tasks that add to each incremental development, and they need a broad set of skills.
The product owner is responsible and accountable for the product that comes as a result
of the development. They also support the developers by managing the product backlog
and product goal.
CHAPTER 2. THEORY
The Scrum master is responsible for the Scrum process itself and makes sure that the team understands the theory and practice. They enable the team to improve its practices [27].
Scrum events
The Scrum process revolves around sprints. They are fixed periods of between one week and up to one month, most commonly two weeks [28]. In figure 2.3.2 there are a few things included in a sprint to achieve the product goal, from the sprint planning to sprint review and sprint retrospective. The sprint planning initiates the sprint and is where the Scrum team sets the extent of the sprint, what and how it can be done, and why the sprint is valuable. This results in a sprint backlog, one of the Scrum artefacts. In the sprint review, the team analyses the sprint outcome and presents it to the stakeholders that, in turn, provide feedback. Before initiating a new sprint, the team have a retrospective to discuss what worked, what could be improved and what to commit to doing in the next sprint [27].
Scrum artefacts
The Scrum artefacts represent work or value in the process and are designed so
that everybody involved in the project understands critical information by proving
transparency. There are three various Scrum artefacts: product backlog, sprint backlog
and increment. The product backlog is a list of tasks that can improve the product,
and for each sprint, the developers select some backlog items to work on and include
them in the sprint backlog (what). It also includes the sprint goal (why) and a plan for
delivering the increment (how). An increment is the development building together
towards the product goal where each increment is added to all previous ones. It
represents the finished items in the product backlog that are useful and therefore
add value to the product, the result from the sprint shown in figure 2.3.2. The work
performed can only be considered of adding value and being a part of an increment if
it fulfils the definition of done defined by either the Scrum team or the organisation
[27].
2.4 Ship design
Designing and constructing a ship, yacht, or boat is a large and complex task. There are several functions, systems, and parameters that influence the design from essential functions such as; the ship must be able to float, be stable, and move under its own power [2]. Apart from that, the naval architect has to consider cost, structural performance, safety and more. All these different requirements and functions must be taken into account in the design process, and it is not possible to build a full-scale prototype first. The design must be right when the ship is built. The design process must then be methodical and thorough.
Traditionally the process has been evolutionary as possibilities to calculate and compute where limited, and the naval architects gained experience with each ship built. Learning from past experiences and being reactive rather than proactive meant that the designer or naval architect were considered conservative. However, with the introduction of CAD and computing power in the past six decades, the approach can be more forward-thinking [1]. The use of computers and software has helped; however, the same steps still have to be performed in the design process. Seen in figure 2.4.1 illustrates the ship design process with the different phases and steps [3].
The four phases here are; concept, preliminary, contract and detail design phase, where all the stages go through the steps from mission requirements to cost estimates. In some cases, the concept and preliminary design phase are combined into the same stage [2]. As illustrated in figure 2.4.1 the process is very iterative, where all steps of the development are performed for each iteration.
The process starts by going through mission requirements, proportions, preliminary power and basic hull form. To then move on to more detailed arrangement, structure, power and weight estimate. Lastly, they will handle trim, impact stability, damaged stability and cost estimates to move into the next iteration.
The repetition and iteration in the process are necessary as results from later steps can affect and change early results. One example is the intact stability which could be insufficient, leading to a necessary change in the hull form. Even if this procedure is time-consuming, it is vital to designing a ship, as when it comes to building the ship.
The design needs to be right [2].
CHAPTER 2. THEORY
With the design process’s iterative nature, there are some similarities with agile development and rapid prototyping. The iterations in the ship design spiral and in, for example, the Scrum framework leads to somewhat similar processes where one of the thoughts is not to solve all problems at the same time. Instead, start with smaller parts and then iterate until the ship, product, or solution fulfils the requirements.
Figure 2.4.1: Ship design spiral [3].
Rapid Prototyping in ship development
Rapid prototyping is at its core a relatively simple process based on an iterative model of development. The process starts with creating a prototype, reviewing it, and refining it, as seen in figure 3.0.1. The process then continues to iterate with these three steps until the prototype is deemed completed [18]. To aid this process, a structure is needed to guide the engineers, designers or others involved in the process. This is one of the goals of this work, to present a framework or a structure that can aid someone through a rapid prototyping development process to get the most out of it.
Rapid prototyping can then help a company or individual engineers to develop products or parts by reducing development time and cost. It is also possible that it will result in a better product. Managing these processes in detail might lead to more complex and time-consuming projects. Therefore, a structure is necessary to guide a project through its various stages, from initiation to finalisation [18].
The devised method provides a guide with a structure for initiating a project, working through the rapid prototyping process, suggested role division and description of the process in different phases of development.
3.1 Structure
The method is based on and inspired by a few different development frameworks
and strategies, mainly Scrum and Agile, apart from rapid prototyping itself. The
CHAPTER 3. RAPID PROTOTYPING IN SHIP DEVELOPMENT
Figure 3.0.1: Rapid prototyping process [29].
iterative nature of Agile and Scrum development practises is similar to that of a rapid prototyping process. They were developed for software development; however, they are not limited to that field. Parts of the Agile way of thinking and the structuring of teams with Scrum has been implemented into this method [25] [26].
3.1.1 Roles
The roles within a rapid prototyping project are essential to define as each member’s responsibilities greatly impact the outcome of the project. There are multiple ways such a team could be comprised; however, the roles set by Scrum are widely adopted and used. This method uses the Scrum framework’s roles with adaptations for the rapid prototyping process described here [27]. There are three prominent roles involved directly in the project: product owner, developer and development manager.
An external group of stakeholders are also involved, although not directly, in the project.
The product owner is responsible for the project but not involved directly with
the development work in the process. They also represent the stakeholders in the
project, such as the client or company management. Usually, the product owner
is responsible for the overarching project or product that the development project
belongs to. However, they should not focus on the project’s technical details but rather that it fulfils the customer’s demands and specifications or internally [27].
The developers are the members adding value to the project, meaning they perform the construction or design of the prototypes [30]. Depending on the extent of the project, there are 1-3 developers. If more is required, the project should be divided into several projects with the product owner coordinating the work between the teams [27].
The developer manager is also a part of the development team, however not included in the 1-3 developers. Their primary responsibility is to facilitate the group and make sure that the process is followed. The development manager is not responsible for the team’s people management, but instead, the team is meant to be self-organising. Some direction might be provided though [27].
One more external entity involved in the project are the stakeholders, they could be the clients, customers, production staff, consultants and other parties with interest in the project [19]. An illustration of the roles and the respective groups can be seen in figure 3.1.1.
Figure 3.1.1: Roles in the process.
3.1.2 Development phases
The development will move through phases that require focus on various factors, ways
of development and manufacturing of prototypes. There are four main stages in the
CHAPTER 3. RAPID PROTOTYPING IN SHIP DEVELOPMENT
development going from concept to life test where various factors are relevant, shown in table 3.1.1.
Table 3.1.1: Stages in the rapid prototyping process and corresponding factors [31]
Stages Factors
Concept model Speed and appearance Assembly/fit model Form and fit
Functional test Mechanical-, chemical-, electrical-, thermal properties
Life test Long term durability
In the first stage, where the concept model is developed, early prototypes are created trying different concepts. Here the focus is on fast iterations and appearance rather than function as the goal is to iterate through several concepts before deciding on one.
The speed factor means that short manufacturing time of the prototypes is essential, therefore additive manufacturing is recommended [31] [18].
The second stage focuses on evaluating the model’s assembly and fit in relation to either other developed parts or existing parts. This stage is not always applicable, as some parts do not need to fit in with other parts. Here, manufacturing speed is still important if the prototype’s form and fit are comparable to the finished product.
Additive manufacturing should be used if possible. However, other manufacturing technologies could be used [31].
For the third stage, functional tests, the focus is testing the prototype in similar ways to how the finished product used. Properties such as mechanical or thermal are important to test and validate here. If the prototype does not fulfil the required specifications, it is essential to spend development time on this step to ensure functionality. This then focuses on the prototype materials as they would have to be similar or the same as the finished product to represent it correctly. Additive manufacturing could still be applicable, but the prototypes can also be created with other methods [9]. It is possible to 3D print metal parts if a printer capable of printing parts to the right quality is available. Another alternative is to perform the same manufacturing process for the final product in a scale model [31].
In the fourth stage, certain life or durability tests are performed to focus on how the
product will last over time, both in mechanical or ageing properties. As in the third
stage, the prototype’s material is essential, and it should be similar in properties to the
finished product [31] [18].
The process of going through these stages are not linear. It might be necessary to go back and forth between the stages. If the functional tests are essential and critical to the project, the team can focus on the functional tests after deciding upon it. These might show critical flaws in the concept, meaning that the project must revert to the concept stage and focus on developing a new concept for the product [32].
3.1.3 Iteration length
The rapid prototyping process’s goal is to iterate on a project several times over a short period. This means that each iteration should be brief. However, depending on which phase the project is in, the time for one iteration could vary, especially when considering the various manufacturing techniques required for the different phases. Manufacturing a prototype with additive manufacturing, the manufacturing time could vary between hours up to a day or two depending on size, complexity, material and process [18]. Considering preparation time and post-processing of the prototype, the total manufacturing time is a few days. A prototype manufactured for the functional or life test stage might be necessary to create a model with other techniques such as welding metal parts, building wooden structures, glue sandwich structures, or assembling other parts. This could take longer than manufacturing with AM. The time for one iteration loop then differs depending on the development stage and the necessary manufacturing technique.
The recommended iteration time is from one week up to a month, where one week is applicable in the concept and assembly/fit stages and two weeks for functional and life test stages. If the manufacturing of prototypes allows for it, the iteration can be shorter than one week if it is possible to review and refine the prototype. Longer iterations than two weeks are not advisable but could be necessary for functional and life tests if the glue used needs to cure [28].
3.2 Rapid prototyping method
The rapid prototyping method has three main steps, as shown in figure 3.2.1. The prototype stage first, then the feedback stage and lastly, the refine and iteration stage.
These three steps form the basis of the rapid prototyping process.
The method is based on this simple principle. However, to develop it and adapt to ship
CHAPTER 3. RAPID PROTOTYPING IN SHIP DEVELOPMENT
and boat building, some further steps are taken. Before initialising any project planned to be performed with rapid prototyping, some preparatory work must be performed and get the most out of it.
Figure 3.2.1: Rapid prototyping method [29].
3.2.1 Initiating the project
A development project can be initiated for multiple reasons. It can be a client’s request, an internal need to develop a part, investigate a new idea or any number of other reasons. Various projects have different requirements and are initiated by a certain need. However, they all require some amount of organisation. In this method, the product owner is responsible for initiating a project and selecting the development team depending on the nature of the project and what skills and competencies are needed. The stakeholders must be identified at this stage and be informed of the project [19]. At this stage of the project, it is not necessarily a well-suited project for rapid prototyping. To figure out and decide this, the development group must consider a few things before beginning the project with support from the product owner.
• Is the part complex and requires a large amount of design and development?
• Will it perform any movement or belong in an assembly of parts that will move?
• Could multiple different concepts solve the problem?
• Is the part custom made for a specific customer? Who might have input on the
development?
If any of the criteria or questions above are fulfilled, it might be beneficial to utilise RP to develop the part [9]. The first three questions regarding design and construction as a part requiring a large amount of design and development could benefit from physical prototypes during development. If the part or the assembly moves, a prototype could be tested to verify the function. Having physical prototypes are important if the part is made for a specific customer. During development, it can help them understand how the part will look and come with accurate feedback [9].
It is also tied in with the following question regarding scale, proportions, and feel. If it is an internal or external customer, physical prototypes can be crucial to understand the part’s scale and proportions. A physical prototype also becomes essential for the part’s feel as it is a subjective matter and difficult to calculate. After asking these questions and concluding that RP is applicable, the development team can move on to the concept stage [18].
3.2.2 Concept
The concept stage is a preparatory stage where the project team brainstorm ideas and solutions for the initiated project. It might be necessary to simultaneously perform the concept stage with the project’s initiation and contemplate questions posed in the previous section. They differ in focus, though, while the initiation focuses on more overarching questions regarding the choice of method and needed competencies, the concept stage focuses on which solution should enter the first prototyping loop. The requirements and specifications of the part developed should be set here with input from the stakeholders.
When deciding on the requirements, the aim is to identify the most critical aspects and rank them to aid the development team during the rapid prototyping process evaluation and feedback stages. The prioritisation of the requirements helps the development team during the process on which aspect is the most important. Though, during the development, the developers can change the requirements’ priority if approved by the product owner [32].
3.2.3 Prototype
The prototyping step includes various steps, but the focus is on designing and
building a prototype, first designing the CAD prototype. Here the demands and
CHAPTER 3. RAPID PROTOTYPING IN SHIP DEVELOPMENT
requirements and the concept idea form a prototype designed to the desired level of detail. Depending on how far the development process has progressed, the level of detail will be different.
Early in the process, the prototype should not be complex and instead focus on the core functionality and requirements. The goal should be to create a simplified model for the first iteration. Then further develop the prototype for each iteration. This is to not spend too much time designing a prototype in CAD only to discover problems once the prototype is produced and tested.
Inspiration here comes from Agile development and parts of the Agile manifesto, mainly the continuous interaction with the customer, delivering working prototypes frequently and most importantly, breaking the development down into small increments [23]. After the prototype is designed, it should be prepared for manufacturing. Depending on which stage (concept, assembly/fit, functional or life), the manufacturing technique is different and requires different preparation [31].
Regardless of the manufacturing technique, the prototyping step aims to produce a physical prototype that can be evaluated and tested against the set requirements. At this stage, the development team must formulate the testing procedures necessary to evaluate the prototype. These procedures should be related to the functionality or requirements and especially the focus of that iteration.
3.2.4 Review
When the prototype has been produced and post-processed, it must be reviewed and evaluated against the set requirements, specifications and criteria. This is performed by the developer team, together with the product owner. The evaluation and review of the prototype have in themselves different requirements depending on the development stage. In the early concept stages, the review might be simple observations of the prototype to see if the shape or proportions align with expectations.
Further along in the development, the tests could include bend or load tests in the functional stage.
Apart from evaluating the prototype, it is beneficial to evaluate and review the
requirements and specifications themselves. The development team might discover
that some requirements are missing, superfluous or not applicable to the prototype
throughout the development process. The product owner must approve any changes to the requirements before they are removed or altered.
After the review, the prototype can be showcased to the stakeholders for feedback.
This should not be done for every iteration, not to slow down the process too much.
Instead, the product owner should be the primary contact with the stakeholders for most iterations. However, it can be beneficial to present the prototype to the stakeholders at important milestones, such as moving from one prototyping stage to another. Alternatively, at other stages where the developer team feel they need feedback from the stakeholders [27].
3.2.5 Refine and iterate
After the review stage, the development team gather the feedback and analyse it.
This part of the rapid prototyping process is the shortest and most important as it decides the next step in the iteration. Here the development team and product owner decide what to change and the focus of the next iteration. If the prototype fulfilled the requirements, the team can develop, prototype and test the next part with the changes from the feedback added. However, if it did not fulfil the requirements, another iteration is required to improve the prototype.
Changes from the refine and iterate stage are then brought into the prototype stage
again. The process continues until all requirements are fulfilled, then the development
team and the product owner decide if the project is finished. During the project, the
development team, product owner, or customer might choose to end the development
prematurely. This can be due because the customer or development team is satisfied
with the result, or any number of other reasons [17].
Chapter 4
Development project
To test and evaluate the devised rapid prototyping method in chapter 3, a development project has been initialised together with Stainless Steel Yachts Sweden AB, a company manufacturing high-speed light craft made of super duplex stainless steel [33]. The method will be applied in a development project, and the focus of this report is the method and not the development project. Therefore some technical details are excluded.
4.0.1 Background and initialisation
The stainless steel alloy used to manufacture SSY’s boats is very strong and allows for thin sheets to be used together with stiffeners throughout the construction. This allows for a relatively light and stiff hull, though it comes with some drawbacks. Some panels on the boat are sufficiently strong but with greater than acceptable deflections under load. To counter this, reinforcements are added, which results in higher weight.
While this solution solves large deflections, the increased weight led to a search for
an alternative solution. An internal project was initiated to investigate an alternative
solution where the steel is utilised and keep the weight down. An internal need initiates
the project, and understanding the part’s feel is one of the more important reasons for
utilising the rapid prototyping method.
4.1 Hatch concept
A proposed solution is a sandwich construction with super duplex stainless steel as the skin, and divinycell
1as the lightweight core material [35]. One of the sandwich material applications are the hatches used throughout the boat, such as engine and storage hatches, that should be lightweight enable easy operation. Therefore, they were chosen as the first application for the testing, where the goal was to build an engine room hatch measuring 1.5 times 1 meter. The existing design for such a hatch would require reinforcements in the form of beams mounted in a cross pattern and a thicker steel plate.
With the sandwich construction, the resulting hatch should be stiffer and lighter.
However, there are some unknowns in the construction. The stiffness has been calculated to be enough. The deflections are only a few millimetres; however, as the feeling of walking on the hatch is very subjective physical prototypes are needed.
Another point of uncertainty was the adhesion of the glue used to bind the steel and divinycell together. A series of prototypes and test pieces would be manufactured to achieve the right feeling and test how the glue behaves and holds up.
The most crucial requirement for the hatch is to create a robust and solid feeling hatch. However, it should also be lighter than a hatch reinforced with cross beams instead. These two requirements are the main focus of the development, with other requirements such as longevity and ease of manufacturing also considered but of a lower priority.
4.1.1 Development with rapid prototyping
Development of the project will be performed using the rapid prototyping process described in section 3 as there are several steps in the development where prototypes have to be produced and tested. All properties and requirements will not be evaluated in the same prototype, instead of breaking down the requirements and testing them on specific prototypes. The rapid prototyping process decides the development project’s structure with roles, division of development phases, and iteration length.
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