Min-Jung Yoo
email: min-jung.yoo@epfl.ch

Jumyung Um
email: jumyung.um@epfl.ch

Ian Stroud
email: ian.stroud@epfl.ch

Soumaya El Kadiri
email: soumaya.elkadiri@epfl.ch

Dimitris Kiritsis
email: dimitris.kiritsis@epfl.ch

on Product Lifecycle Management -PLM14 Integration of Design Intent during the Product Lifecycle Management

Keywords: product lifecycle, semantic ontology, design intent, knowledge, know-how, OWL, Protégé, QLM

There has been significant achievement in integrating product data during the whole lifecycle phases with shared common ontologies while taking advantage of intelligent retrieval mechanisms. In order to support integrated decision making on product redesign or maintenance operations, we should solve a challenging issue: 'how the product lifecycle management (PLM) stores and retrieves the know-how and the knowledge of an organization concerning manufactured products'. This paper describes the extension of a previously developed PLM Semantic Ontology Model toward integration with design intent. The proposed approach uses OWL2 to represent product lifecycle data and design knowledge. The approach was applied to the redesign of a car door part for laser welding. Our work demonstrates how to retrieve design intent as a specific type of knowledge data in the context of design decisions. Such an approach can ultimately contribute to reducing design time, making knowledge transfer clear and thus improving the quality of designed products.

Introduction and motivation

The closed-loop product lifecycle management (PLM) system focuses on tracking and managing the information of the whole product lifecycle, with possible feedback on information to product lifecycle phases. It provides opportunities to reduce the inefficiency of lifecycle operations and improve competitiveness (Kiritsis 2013). Thanks to the advent of hardware and software related to product identification technologies, e.g., radio frequency identification (RFID) technology, closed-loop PLM has been recently highlighted as a tool for companies to enhance the performance of their business models. However, the information on PLM has primarily dealt with some predefined physical product data, i.e., material characteristics of designed products and their usage information. Knowledge data concerning the design of products has not been dealt with sufficiently in depth in currently available PLM approaches. Within the range of our knowledge, there are very few research results which handle the design knowledge coming from the product design phases or redesign phases. The impact of design changes on the other manufacturing information has not been sufficiently studied, so there is a lack of experience in this area.

The management of companies' intangible assets and intellectual capital has long been a key issue in the domain of business and management science. Some parts of product data should be shared with the other intangible assets of a company. Product design requires intensive communication between designers and production engineers. In a general case, only the geometry and numerical data remain in the company's database once a product shape has been determined. This entails the loss of information about why this design was determined and what designers intended during redesign. The design is defined as this-is-the-way-we-do-things in the company. Lost knowledge, however, is critical information when introducing new manufacturing technology or new composite materials.

For the reasons mentioned above, domain professionals have already acknowledged the importance of representing and sharing product data during the different phases of the product lifecycle. There has been significant achievement in integrating product data from beginning of life (BOL), to the middle of life (MOL), until its end of life (EOL), especially using shared common ontologies and intelligent retrieval mechanisms [START_REF] Matsokis | An ontology-based implementation on a robotic assembly line for supporting lifecycle data management[END_REF]. PLM has specific objectives in each phase of the lifecycle: During the BOL, the improvement of product design and production quality is the main concerns; During the MOL, improving reliability, availability, and maintainability of products is the most interesting issue; In the EOL, optimizing EOL products' recovery operations is one of the most challenging issues. Turning to the research on representing know-how and knowledge, we can find some literature about approaches using meta-data and history-based models in design activities of BOL. At the end of the 1970s and early 1980s Kjellberg proposed having a 'description of origin' associated with geometric elements (Kjellberg 1983). After the publication of standard for product data exchange, Pratt mentioned the necessity to capture the intention of the designer which can get lost during product changes (Pratt and Anderson 2001). Mun defined 'design intent' and proposed macro files for saving the modelling commands with the parametric approach, which was standardized by ISO 10303 [START_REF] Mun | A set of standard modeling commands for the history-based parametric approach[END_REF]. Han also realized a macro-parametric method in commercial CAD systems [START_REF] Han | Macro-parametric: an approach for the history-based parametrics[END_REF]. Through the efforts of these researchers, the fundamental of capturing design intents is possible. In the context of aircraft manufacture, Price tried to maintain intent by redesigning the parameters of frames related to joining processes in [START_REF] Price | Maintaining design intent for aircraft manufacture[END_REF].

This paper discusses new concepts for capturing general knowledge and shows how to share it during the real redesign process of an automotive door assembly line. Such integration will play an important role during decision making across different divisions including decisions about product redesign or maintenance operations.

From now on the paper is organized as follows. Section 2 presents a global concept of extended PLM Semantic Ontology Model (SOM) based on our previous work [START_REF] Matsokis | An ontology-based implementation on a robotic assembly line for supporting lifecycle data management[END_REF]. Section 3 is devoted to the introduction of our case study: a car part manufacturing example focusing on its design data and parameters in use. Then in Section 4, we will show how the model presented in Section 2 is adapted to the case study, in terms of data popularization and query proposition for knowledge retrieval. Finally, Section 5 gives a short summary of our work and its impact.

Product-lifecycle data management with knowledge management 2.1 Semantic model

Ontology-based approaches to semantic modelling of product lifecycle management were one of the main outcomes from the European project PROMISE (Promise 2009). The PROMISE approach manages information and knowledge generated during the product lifecycle which are then linked with decision support systems and data transformation software. Their implementation demonstrated that the use of ontology makes it possible to reuse the PLM model increasing interoperability between different PLM phases. Currently the results are being submitted to Open Group Open Platform 3 (OpenPlatform3) in order to get the status of approved standard, which is one of the main activities of the QLM workgroup (Quantum Lifecycle Management -see QLM)

Fig. 1 illustrates the different phases of product lifecycle in general. The products' beginning of life (BOL) phase can be further divided into two categories of activity: i) The design of products, ii) the manufacturing of products. In PROMISE, the management of BOL data was mainly considered based upon the fact that a product has already been designed (Fig. 2). As a result, the model describes well some details on the physical product, their composition and manufacturing information, however, still missing the capability of describing knowledge related with design activity of BOL.

Subsequently, our work focused on the extension and integration of Beginning of life (BOL) product data, putting special emphasis on the Design Phase BOL (corresponding to the upper-left part of Fig. 1). Given that "Personal_Resource (the role of Human Actor)", "Material Resource" and "Physical Product" are already defined in PLM SOM, the new concepts in the extend semantic model include (Fig. 3): 1. Integration of the concept (i.e., ontology class) of "Knowledge Data" and "Knowledge Resource" 2. Definition of the "Competence" concept 3. Integration of the concept of "Service" which is on the hub of four other concepts, i.e., "Competence", "Knowledge", "Material Resource", and "Actor" The service concept represents general business activities offered by a human actor, a team or an organization. In that context, "Competence" is an important intangible asset for achieving the required service by a distinctive actor. Competence can be reinterpreted as being capable of doing some activities; capable of managing some situations; capable of using a tool or an application. Knowledge Data has two sub-concept definitions: i) Knowledge Resource, and ii) Know-How.

The Know-how class represents the company's information on cumulative, lifelong experience and activities which are related with the tangible and intangible product creation and improvement. Different to the technical knowledge on physical products, Know-How data may contain even some negative experience and resulting outcomes. From the point of a company's competence development, such kind of know-now management is important for the purpose of studying past cases and use it for "learning from experience". Therefore the following two points have driven this research direction: i) how to integrate an industry's intangible assets which are related to the product PLM data; and, ii) how to reuse them.

For that purpose, the model extension has been achieved being based on the high-level semantic model presented in Fig. 3. The resulting model was then further specialized in order to be suitable for an industrial design case: the welding assembly line of the car door frame (Fig. 4). Here we use the words 'class' and 'concept' as mutually interchangeable (similar) terms, which are the object class definition in Protégé (Protégé).

1. The class of Design_Parameter is created for the purpose of modelling some important parameters which are considered through design decision making. 2. Design_Process_Activiy class is defined as a subclass of existing Activity concept. 3. Computer_Aided_Tool is further specialized containing several subclasses: CAD_tool, CAM_tool, Specific_Software. 4. In this extended model, another product information in design phase is added, i.e., Design_InProgress, for the purpose of associating data which can either be produced or referenced during the product design phase. Consequently, the classes which indicate product lifecycle phases are also distinguished while representing more specialized product lifecycle phases, i.e., Prod-uct_BOL_Design and Product_BOL_Supply. 5. The Design_Intent class is newly created as a subclass of Know_How. Another subclass of Know_How, Consumer_Intent plays a similar role from the customer sides and internal service designe teams, which will not be detailed in this paper. 6. The existing class Physical_Resource is specialized providing three subclasses: i) Environmental_Asset which represents information such as buildings, workshops; ii) Equipement; iii) Materials.

Model description

The above-presented semantic model was built and tested using the Protégé-OWL ontology tool. Since its creation, OWL-DL(Description Logic) was used for the purpose of describing classes and individuals included in PLM PDKM SOM. OWL-DL was initially developed to provide the maximum expressiveness in tandem with guaranteeing both computational completeness (all conclusions are guaranteed to be computable) and decidability (all computations will finish in finite time). OWL-DL includes all OWL language constructs (such as transitive properties, which allow more of the semantics of sequences to be represented explicitly than in RDF or OWL lite) and it allows modelling at multiple levels of abstraction (and thus, sequences of classes can be characterized by their general or more specific properties).

In PROMISE SOM, there are already more than 70 object property definitions which relate different concepts and individuals. Some of them are given below as an example:

-isDesigned: in order to relate a physical product to its design details; -hasDefined: as an inverse relation of isDesigned, that is to say, from a designed product to a physical product; -Life_Cycle_Phase2Activity: which links the life cycle phase of a product to its activity details; -Life_Cycle_Phase2Physical_Product: similarly to Life_Cycle_Phase2Activity, this property allows to retrieve the physical product of a given life cycle phase; -Equipment_Resource2Property: for the purpose of searching the property of a given equipment resource, and so on.

For the purpose of complementing the existing object properties, we have newly created some supplementary relationships. Some key elements are given below.

-Contains_DesignedPart: this object property helps, based on a given types of physical product, retrieve the information of a designed product part. -Defines: this object property is added in order to get the evaluation criteria of a given resource characteristic. The material characteristics are retrievable by giving a certain design intent category with the help of 'DesignRe-source_Concerns' (see below). -DesignResource_Concerns: thie property links a particular design intent type to all related resources. Such an information is important for the purpose of retrieving a part of physical product information which were designed according to a certain design intent type. -Design_Concerns: this property links a particular design intent type to a physical product for the purpose of retrieving information on past experience. With the help of this object property, we can answer to the questions as 'which products are designed as a result of design intent type xxx?' -Refers2_Parameters: in order to search the KPI parameters which are related with a give design intent and to find further information such as equipment and material resources.

Case study

An example of the importance of explicit design intent can be illustrated using the example of a car door and its use in the Remote Laser Welding project RLW Navigator. The RLW Navigator project studies laser welding, in particular in the car industry and uses the welding of a car door as an example.

Laser welding is an alternative to spot welding and offers several benefits over the traditional technology. However, it is not easy to realise all the benefits because current practice is built into the design at an early stage. In addition, the car door is a complex product for which commercial time pressures preclude rationalisation of the design process. However, without such rationalisation it is difficult to change process elements and hence take advantage of new technological advances. The car door example and its handling in the RLW project can be illustrated in Fig. 4. The input for the modification task is a CAD file which lacks design intent information. As for many other applications the design intent has to be supplied through human interaction or semi-automatic feature recognition. The relevant features are those which can be modified for laser welding, in this case the flanges. The flange redesign tool is illustrated in Fig. 5. The flanges are classified, resized and reintroduced into the design to make the final CAD model. In terms of design intent, this work is hindered both by the lack of special CAD tools and the integration of manufacturing information into the design at an early phase. Logically there should be a shaping phase to determine the part to be made and then a manufacturing phase to realise the shape, making appropriate modifications to the original shape to accommodate the manufacturing decisions. The realisation decision has various implications for manufacturing. For example, if the door is to be made as a solid frame with overlaid panels then this would be record-ed as a decision, the door frame shape extracted from the overall shape and the door panels designed. A different decision about the manufacturing method would start from this point.

Current practice involves making the door out of pressed sheet metal. This involves creating a sheet metal frame which is done by splitting the door shape into parts, pressing them and then welding them together. Another consequence of this decision is that the hinge part needs to be reinforced because the rest of the door has to be made from thin material for weight reasons which is too weak for normal use. Other elements, such as a strengthening bar, are also added for different reasons. All these decisions need to be recorded and structured in order to be able to cope with future developments and avoid becoming locked into an inefficient production cycle. The flanges are added to the design as a consequence of the decision to split the door shape. The flange shapes depend on the join line and it would be logical to have an automatic tool to create the flange shape. This would also mean that the shape can be classified automatically as a flange rather than identified manually later. The use of advanced application tools to provide highlevel information about complex shapes is an important step in recording design intent.

Instantiation of the semantic model for the purpose of data popularization

The following individuals (i.e., instances of classes) are created in order to associate required field data with the PLM Semantic Ontology Model. Fig. 6 shows a part of individuals created and visualized using Protégé: 1.

The five parts of flanges are modeled as five distinctive individuals of the Complex_Physical_Product, e.g., Flange1, Flange2, Flange3, Flange4, and Flange5.

2.

Individuals of Design_Parameter class is created and linked : Efficiency, En-ergy_Use, Welding_Reduction, Processing_Time, Quality, Environmen-tal_factor.

3.

The individual elements of Design_Process_Activity have been created according to the general concept described by Nigel Cross, (Engineering design methods, Cross 2008): Clarifying_objective, Establishing_function, Set-ting_Requirement, Determining_characteristics, Generating_alternative, and Evaluating_alternative, Improving_details. 4.

While using the existing class "Parameter" in PLM SOM, De-signe_Parameter is associated.

Afterward, we verified the model using "Pellet" reasoner (Protégé). As a proof of concept of the case study, we used the DL Query and SPARQL Query tabs supported by Protégé, while looking for answers to the following queries: -Which types of design intent were used in the past? -Which design intent variables (primitives) are primarily considered for each type of design decision? -Which design intent types are used for the purpose of "Flange design", for example? -Which physical products are related with a given type of design intent? And in what PLM cycle (BOL, MOL, EOL) is the product currently? -Considering a given material resource, which design intent is associated with it? This question is particularly important for the purpose of knowing the impact on the material resources and equipment in the case of choosing a certain design intent among several options.

Concluding remarks

The purpose of the work presented in this paper is to demonstrate how to extend and improve previously developed ontology for product lifecycle management with the design intent know-how data within a semantically understandable concepts and relationships. The benefits from such integration are clear:

1. The relationship between a) Design Decision data (i.e., design intent) and b) Designed Product data (manufacturing details determined through some design intent and design decision.) during the whole cycle of PLM is visible and traceable. 2. We can predict which parameters or manufacturing processes are important whenever new design is proposed, and which tools were used for evaluating previous design. It means how to use the know-how and how to collaborate with related persons. 3. Supposing that individuals of human resources shall be provided according to the defined ontology, we shall be able to find as well who are the persons related to the decision of each part design or manufacturing process, which means who has the know-how.

Our work demonstrates suitable ontology model as well as the way of retrieving a particular type of know-how (i.e., design intent) in the context of current design decisions. Such an approach can ultimately contribute to reducing design time, making knowledge transfer clear and thus improving the quality of designed products.

Fig. 1 .

 1 Fig. 1. Product lifecycle phase and data sharing

Fig. 2 .Fig. 3 .

 23 Fig. 2. PROMISE Product Data and Knowledge Management (PDKM) Semantic Object Model (SOM)

Fig. 4 .

 4 Fig. 4. Operation procedure of guideline

Fig. 5 .

 5 Fig. 5. Flange classification

Fig. 6 .

 6 Fig. 6. Extended PLM Semantic Object Model -Classes in Protégé (Protégé)

Acknowledgement. The work on the PLM Semantic Ontology Model and its extension was partly funded by the LinkedDesign (FP7-2011-NMP-ICT-FoF-284613). The work on the flange tool described in the case study was funded by the Resilient Automotive Factories (FP7-2011-NMP-ICT-FoF-285051).


Joel Sauza Bedolla

Javier Martinez Gomez

Paolo Chiabert
email: paolo.chiabert@polito.it

A short portable PLM course

This paper presents the modern education principles of a short PLM course designed to be deployed all over the world in universities that do not have a PDM software. The main objective of this course is to present the advantages of using a PLM strategy during the Product Development Process. A case study is used to present and explore different process areas of a product lifecycle within a collaborative environment. Students are required to perform tasks and develop a technical solution. Special attention is devoted to the information exchange using an open source PDM system.

Introduction

The new economy demands that today's engineers are able to work in a distributed, interdisciplinary, problem-based, and technology-enhanced environment [START_REF] Peng | Teaching collaborative engineering design in a distributed environment through experiential learning[END_REF]. The growing interest in PLM in the industries has demanded college education to impart engineering students the necessary skills for collaborative design in a distributed environment [START_REF] Peng | Integration of Collaborative Engineering Design Using Teamcenter Community in Mechanical Engineering Curricula[END_REF]. In other terms, industry is requiring a new profile of students able to understand the PLM principles and to be trained in the tools that industry uses.

The purpose of engineering education is to provide the learning required by students to become successful engineers-technical expertise, social awareness, and oriented towards innovation [START_REF] Crawley | Rethinking Engineering Education: The CDIO Approach[END_REF]. The big issue for universities is which topics to include and how to teach them.

In the last years, Politecnico di Torino has been asked to assist other universities and technical institutes in the deployment of PLM courses. Specially, it was explicitly required to use the PDM software during the lectures. This situation had lead us to search for a PLM course that could be deployed all over the world using a PDM instrument.

Nowadays, there is no standard for defining the necessary skills and capabilities for a PLM expert and therefore it is impossible to define the educational path for new engineers. In this chaos, every university has decided to apply its own strategy: IT oriented, CAD oriented, PLM Project Management, user (data creators, reviewers or consumers) or super user (administrator). The first challenge was to define an original PLM course that covers different areas of a product lifecycle without being partial to one area.

Usually, the PDM software requires a server and client installation that requires time and technical skills. This condition makes almost impossible to use the tool outside the network where the installation was made. In literature there are some examples of curriculum development of PLM courses or PLM projects with information exchange between different teams [START_REF] Chang | PLM curriculum development: Using an industry-sponsored project to teach manufacturing simulation in a multidisciplinary environment[END_REF][START_REF] Bedolla | A Tool to Support PLM Teaching in Universities[END_REF][START_REF] Sanin_Perez | A "PLM" implementation in a design project course of Product Design EAFIT[END_REF]. In these examples, the university which organizes the course is the owner of the PDM system and the course was executed with groups that work inside the network of the university. Instead, Segonds et al [START_REF] Segonds | Educational practices for collaborative distributed design of an innovative eco-designed product[END_REF] develop a project using Dropbox as PDM for a collaborative project between two universities. This solution solves the installation problem but Dropbox cannot manage the configuration and change management process necessary to work in a PLM environment. The second challenge was to find a PDM solution that could be easily installed, managed and reachable from the outside of the university network.

This article presents an original short PLM course focused in the development of a new product (section 2). The exercise covers different process areas (section 3) and its integration (section 4) using an open source PDM. The course deployment and results are discussed in section 4 and 5 respectively. Finally, conclusions are stated in section 6.

Case Study

The sliding door trolley (Fig. 1) is a key component of commercial and garage doors and gates since it links the gate framework to the surrounding structure. The trolley runs on a monorail which is fixed to the wall. It should be designed and constructed in such a way as to prevent it from falling down, collapsing or derailment during normal operation or in case of contact with stationary obstacles.

Process Areas

During the development of the exercise there are a series of processes with similar goals which are grouped in Process Areas (PA). A PA is a cluster of related practices in an area that, when implemented collectively, satisfies a set of goals considered important for making improvement in that area [START_REF] Chrissis | CMMI for Development: Guidelines for Process Integration and Product Improvement[END_REF].

Requirements Management (RM)

The purpose of this PA is to manage the requirements of the project's products and product components and to identify inconsistencies between those requirements and the project's plans and work products [9].

Project Management (PM)

Project Management is the application of knowledge, skills, tools and techniques to project activities in order to meet or exceed stakeholder needs and expectations from a project [10].

Quality Planning (QP)

Quality planning is part of quality management focused on setting quality objectives and specifying necessary operational processes and related resources to fulfil the quality objectives [11]. One of the most significant methods to assure quality is the Failure Mode and Effects Analysis (FMEA). FMEA is an analytical methodology used to ensure that potential problems have been considered and addressed throughout the product and process development phases [START_REF] Aiag | Potential Failure Mode and effects Analysis (FMEA)[END_REF].

Product Design (PD)

Product design is to conceive the idea for some artifact or system and to express that idea in an embodiable form [START_REF] Ontwerpen | DELFT Design guide[END_REF].

Process Design (PrD)

Process design is to conceive the looks, arrangement and workings of something before it is constructed [START_REF] Slack | Operations and process management[END_REF].

Configuration and Change Management (CCM)

Configuration is a management activity that applies technical and administrative direction over the life cycle of a product, its configuration items, and related product configuration information [15]. It is composed by four basic functions: identification, configuration control, status accounting and audit. The Institute of Configuration Management [START_REF] Cmii | CMII Standard for Integrated Process Excellence and Configuration Management[END_REF] has defined a closed-loop change process used to release new information and to change information already released. This loop is formed by a Problem Report (PR), Engineering Change Request (ECR) and Engineering Change Notice (ECN). A PR form is used to report a problem, where it occurred and the steps which led to its occurrence. An ECR form is used to request changes and initiate reviews that will result in a proper disposition. An ECN form is used to implement approved ECRs and provide the authority to upgrade and release associated documents.

Integration

Information technology, by the way of collecting, sharing and gathering data, exchanging information, optimising process through package software, is becoming one of the key developments and success for collaboration strategies [START_REF] Neubert | Collaboration and integration through information technologies in supply chains[END_REF]. The integration of the process areas was achieved by using the open source PDM software Aras Innovator [START_REF] Aras | Aras Innovator[END_REF]. Aras has been successfully used in different universities [START_REF] Pérez | A "PLM" implementation in a design project course of product design engineering program[END_REF]20] Innovator's solution suite constitutes of a full-featured engineering business solution supporting engineering and manufacturing processes throughout the plant and the extended supply chain [START_REF] Cimdata | How PLM is Being Applied to Support Today's Dynamic Enterprises[END_REF]. Aras takes advantage of HTTP/HTTPS, XML, and SOAP protocols to deliver its functionality through a standard web browser (Internet explorer).

The server installation resides at Politecnico di Torino and is reachable from the outside. Even though Aras does not need a client installation, a small client configuration is mandatory. It consists of setting up some browser security issues.

All modules used in the development of the exercise come along with the standard version of Aras Innovator 9.3. The only exception is the Requirements Management module that was developed by a third party and delivered as an addon to the software.

The only customizations made to the software were:

 Requirements classification  Requirements sequence number  Part sequence number  Document sequence number Fig. 2 presents an overview of the exercise. It covers the Imagination and Definition phases of a product lifecycle and includes the PAs described previously. PM and the CCM play in parallel to the other process areas. Further description of the graph will be given in the next sections.

Before starting, a training on the PDM software is essential. It is supposed that the attendees are new in the use of this instrument so in the first part of the course, the students receive the credentials to enter the system and a general overview of the most used applications.

The collaboration is achieved by using a project structure that permits information access to all team members. Projects inside Aras Innovator use a Work Breakdown Structures (WBS), which allows users to break down the project into manageable phases, activities and tasks. Each activity is identified uniquely and it can be associated to a deliverable, start and due date, assignee, and role. It is also possible to define predecessors or other constraints.

A project template (see Fig. 3) has been used to develop the new product. The template was previously prepared and filled with the information and dates of the course.

Phase 0

The kick off for the exercise is the list of requirements for the product. The requirement list was established by the role of Requirement Analyst (RA) which is an expert of the product. The RA has to understand customer needs and to translate this into product requirements. Finally, he has to validate them. Students are not involved in the requirements definition, instead they are asked to consider these requirements and to satisfy them. Requirements were classified according to FURPS+ [START_REF] Grady | Practical Software Metrics for Project Management and Process Improvement[END_REF].

For the sake of brevity, only one requirement is presented here that is going to continue for the rest of the phases as an example. Referring to the design constraint (Fig. 2) "the distance between the wheels", it can be deduce that it is a critical requirement since the distance assures the correct assembly between the trolley and the monorail. This requirement is identified and managed by the CCM.

Phase 1

The Quality Manager is asked to form a group and to perform a Design FMEA (DFMEA) using the integrated FMEA matrix. In Fig. 2, the failure mode "Trolley does not fit on the rail" is analysed. As a consequence, the trolley may impair the sliding operation. The cause of such failure could be an improper tolerancing of the parts. A Digital Mock-Up (DMU) is planned to prevent the failure. Then, the Risk Priority Number (RPN) is calculated according to the effect severity (9), the cause probability of occurrence (4) and the probability to detect the failure (1). The RPN helps to classify and rank the failure modes.

The most important thing is that once the FMEA is performed, an action is assigned to a role. The designer who has been commissioned will receive a notification and will be asked to give evidence of completing the task.

A product characteristic (distance between wheels) is created. This characteristic is managed by the CCM and must be considered during the product design. Aras links the FMEA characteristic to the product configuration by adding a tab in the BOM. Links can be made at assembly or part level.

The DFMEA lifecycle has a particular way of being conducted. It is created as draft and it remains in that state until the phase of product design is closed. The DFMEA can be released only after receiving the completion of all taken actions.

Phase 2

During the product Design, the Design leader creates the BOM of the product and assigns the design of the parts to other team members. Team members create the 3D models of the parts and deliver the technical drawings. The material selection is a task assigned to the quality team. Finally, the team leader performs the product assembly.

While performing this tasks, designers must take into account the product requirements and characteristics that have been established in previous phases. For example, the distance between the wheels requirement and characteristic are linked to the assembly level of the product. This distance can be obtained after all parts are assembled. Also, the designer must answer to the task assigned in the DFMEA.

By linking requirements, characteristics and DFMEA actions, the designer is lowering the risk level of committing a mistake. After completing the required actions, the DFMEA table will be updated adding two more rows, the action taken and a new RPN (which is expected to be lower).

During the product design, the single part is responsibility of the designer in charge and he performs a manual releasing. Instead, the assembly, due to its importance, is submitted to an ECN for its releasing.

Phase 3

The Process leader assigns the analysis of a part to different team members. Every team member develops the necessary operations to produce the part. During this development, the process designer has to link the part to the process and to consider all necessary resources (tools, machines, work areas, etc.).

Process leader is responsible of the operations definitions of the final assembly. He is also responsible for taking into account the product requirements and characteristics that are influenced by the process. For example, Op. 60 (see Fig. 2) is the final operation made to the assembly; by riveting a dowel, the trolley gets its final shape. This operations is the one that produces the desired distance between wheels. It is also possible to perform a Process FMEA and to establish a quality control plan of the operations.

All items of the process development must be managed according to CCM. Single part production are manual released while the final assembly is controlled by an ECN. Phase 3 ends up the project. The products is considered to be successfully produced and it reaches the market.

Phase 4

A client complaint is reported and managed with a PR automatic workflow. The change specialist evaluates the problem and asks for technical expert opinion. If the problem is accepted, it is then taken to an ECR.

The change board team evaluates the problem and looks for a technical solution. For example (Fig. 4), a change in the dimensions of the client's rail will cause a change to the requirement associated to the distance between the wheels. In the same way, the new requirement version will produce a change to the product, and the it will cause a process change. Finally, an ECN must be performed to inform all stakeholders that the change has been achieved.

Deployment

The course has been deployed several times in different universities (Ss. Cyril and Methodius University in Skopje, FYROM; University of Novi Sad, Serbia; Arts et Mètiers ParisTech, France) and technical institutes (ITIS OMAR Novara, Italy). The course can be limited to a demonstration of the tool or expanded to a practical exercise. The number of hours employed vary according to this constraint.

The most complete experience (in terms of project achievement, number of students involved and number of hours dedicated) has been reached in June 2013 at University Federico II of Naples. Results and conclusions refer to this last experience.18 professional master level students from different backgrounds (electrical, mechanical, industrial and system engineering) participated in the 27 hours course. Students were assigned to different teams according to their preferences: 2 Project Managers, 4 Quality Engineers, 4 Product Designers, 4 Process Designers and 2 Change Specialists. The course was given in 6 days in sessions of 3 and 6 hours.

The connection to the PDM worked correctly and students accessed without problems. The performed activities were fairly clear and team leaders gave evidence of the completion of the tasks on time.

Results

At the end of the course an anonymous questionnaire (Likert scale) was used for measuring student perception. The more relevant (positive and negative) aspects are listed below.

Positive Aspects

Overall, the course achieved its objectives satisfactorily (Fig. 5a) and the contents of the course were considered original by the majority of students (Fig. 5b). The teaching method and material given were highly appreciated.

Negative Aspects

Up to version 9.3, Aras worked exclusively on Internet Explorer (IE) using a .NET security framework. This situation limited the use of computers with Windows operating system. However, version 10 of Aras has been recently released and it does not require the .NET security framework and therefore it will be possible to connect also with Firefox on Windows and OSx.

During the days before the course, IE passed from version 9 to 10. This update caused a delay during client configuration. Though, from 17 computers, only one presented problems that were solved in the same day.

Moreover, Aras presents some usability errors (i.e. the insert row tab is missing while creating an FMEA) that made impossible some operations and influenced negatively student perception (see Fig. 6). In order to connect to the server, a nonrestricted WIFI or LAN is compulsory. Other software (i.e CAD software) needed during the development of the course must be installed and licensed in the students computers.

Conclusions

This paper presents an original PLM course that covers different phases of a product lifecycle integrated in an open source PDM. This course includes the development of a new product within a collaborative environment.

Students are exposed to the complexity of managing product information through different process areas (product requirements, quality management, product and process design, project management, and configuration and change management). The course encourages the integration of product information, processes and people, and it is not oriented to a single technological area. A project structure is used to consent information access to all team members while they develop a technical solution.

The use of a web based open source PDM eliminates the need of a client/server installation and facilitates its use outside the network where the tool was installed. Despite some technological and usability problems, the system performs well.

From experience gained by organizing the course in different institutions, it is found that this course can be deployed all over the world. It is our belief that other universities can take this paper as a model to develop PLM courses exploiting the advantages of open source PDM or similar solutions.

Fig. 1 -

 1 Fig. 1 -Sliding door trolley

Fig. 2 -

 2 Fig. 2 -Exercise overview

Fig. 4 -

 4 Fig. 4 -Change Management

Fig. 5 .

 5 Fig. 5. a)Course contents are original. b) The course achieved its objectives.

Fig. 6 -

 6 Fig.6-I used the system (Aras innovator) without difficulty.


Kazuo Hiekata
email: hiekata@k.u-tokyo.ac.jp2bry@mit.edu

Bryan Moser

A Requirements Evaluation Method for Ships to Maximize Operational Value under Uncertainty

Requirements defined by shipping firms play a role as the communication interface of product information between these firms and shipbuilders, and the product design is optimized based on the requirements. Ship service life is about 30 years, during which original requirements may lose some relevance. In this paper we explore the introduction of uncertainty and flexibility into requirements so that ships are designed optimally not only for a single given technical condition but for a range of possible operational scenarios, including shifts in the economic environment for shipping firms.

Introduction

Background

Shipping firms design their business plans and define the requirements for vessels to be newly acquired. The requirements include essential performance and constraints depending on planned routes and their forecasted demand. Therefore the characteristics of the vessels will be optimized for the specific requirements based on the shipping firm's strategy. Shipbuilders then proceed with basic design work to satisfy these requirements and constraints such as cost, delivery, performance and other dependencies. From a shipping firm's point of view, the basis to measure performance of vessels will be different from the shipbuilders'. At the delivery of vessels, shipbuilders and shipping firms must find some common criteria for evaluation. Today, key performance characteristics are evaluated under standard protocols. Classification societies check the structural performance and the propulsive performance as evaluated in sea trials. During these propulsive performance evaluations, the protocol for sea trial considers only calm sea conditions, even though actual operation might occur across a large variation of sea conditions. Nominally, a shipbuilder can optimize the design of a vessel for calm seas at a given service speed, and the ship might demonstrate good performance in severe weather. Recently shipping operations are in need of better fuel consumption rate and reduction of greenhouse gas (GHG) emissions. For example, the "10 Mode Performance Index for Ships [START_REF] Tsujimoto | A Calculation Method of 10 mode Index for Ships[END_REF]" was developed to evaluate the decreases in service speed at a given power rating for the predefined sea conditions. The development and deployment of this kind of index may expose the performance of vessels in various conditions which were not explored in the trials held at calm seas. As mentioned above, requirements defined by shipping firms play a role as the communication interface of product information between these firms and shipbuilders, and the product design is optimized based on the requirements. Ship service life is about 30 years, during which original requirements may lose some relevance. In this paper we explore the introduction of uncertainty and flexibility into requirements so that ships are designed optimally not only for a single given technical condition but for a range of possible operational scenarios, including shifts in the economic environment for shipping firms.

Objective

This research proposes the requirements evaluation method to maximize the benefit of ships in the operation. The key idea is to consider the changes in economic conditions in addition to the optimization for a given design requirement.

Proposed Method

Overview

The performance in fuel consumption rate is governed by the resistance of the ship hull in operation. Generally the resistance by the sea water increases for larger service speed as shown in Figure 1. Froude Number (Fn) is defined as the ratio of a characteristic velocity to a gravitational wave velocity and Reynolds number (Rn) is defined as the ratio of inertial forces to viscous forces. The design service speed is defined by ship owners to fit the planned route for the vessel and the design of the vessels is optimized for the service condition, therefore the main engine and propeller demonstrate optimal performance at the condition. Though the fuel consumption rate is optimized at the given speed, the shipping firms will operate their ships at faster or slower speed to maximize the profit or minimize the loss in uncertain future economic situations during the service life of the vessels.

The proposed method calculates the performance at designed service conditions and possible various conditions to support the evaluation of requirements definition.

Fuel consumption model

The fuel consumption is the outcome of the interactions of the main engine, the propeller and the hull. The characteristics of these factors are nonlinear and the design of the plant is usually optimized for reducing the fuel consumption rate at the service speed which is assumed to be most likely at the acquisition. The fuel consumption model is based on the systematized ship design theory such as [START_REF] Gillmer | Introduction to Naval Architecture[END_REF].

The ship hull is the major source of the resistance. Wave, viscous and viscous pressure resistances gives large effects on the performance. The total resistance of the ship hull will be calculated by the results of towing tank tests. The total resistance will be separated to friction and residual resistances . The friction has significant impact on slow vessels and the residual on the faster. Each type of resistance will be calculated as non-dimensional coefficients depending on Froude number and Reynolds number. The Froude number are about 0.15 for slow vessels such as tankers and about 0.27 for the faster such as container ships. The resistance is usually described as EHP (Effective Horse Power) at any ship speeds.

The output of the main engine is given by the rotation speed and the torque delivered from the shaft. BHP(Brake Horse Power) indicates the power generated by the main engine. Engines generally have their optimal load in the specific fuel consumption per output. A typical example is shown in Figure 2. Detailed behavior of the engine may be found in [START_REF] Sanguri | How to Use Main Engine Performance Curve for Economical Fuel Consumption on Ships?[END_REF]. The power generated by the main engine will be transferred to the propeller with a certain amount of losses. Finally, propellers will give the thrust to the ship hull through the use of the torque delivered from the shaft. The condition of the propeller in operation must be defined to calculate the performance of propellers. The performance of propellers is normally described like a graph shown in Figure 3. J is advanced coefficient and given by the following equation. V 𝐴 is advanced velocity into the propeller, K 𝑇 is thrust coefficient given by open water test and 𝐾 𝑄 is propeller torque coefficient. Ship designers usually try to maximize the propeller efficiency 𝜂 0 .

J = 𝑉 𝐴 𝑛𝐷

K T K Q η 0 0 0.04 0 K T K Q η 0
The service speed is defined in the requirement for a specific vessel, and then the propeller and the main engine will be configured. The design process will be iterated to improve the design of the vessel. The efficiency of ships is optimized at the specified service speed. The fuel consumption rate for other service speed can be calculated based on the characteristics of main engine, propeller and hull.

Marine transportation cost and revenue model

The forecast of the oil price is required to predict the ship service speed for maximizing the profit rate per oil consumption or the amount of the profit. The historical data of the oil price is shown in Figure 4. According to the fluctuation of the oil price, the vessels should be designed for varieties of the market situation. The shipping market for oil tankers are described by using Worldscale flat rate issued by Worldscale association (LONDON) limited and Worldscale association (NYC) inc. The flat rate is defined as a tariff based on standard tankers in USD/metric ton for each shipping route. For example, the route from Ras Tannurah, Saudi Arabia to Chiba, Japan has the flat rate. The negotiations in shipping market are based on this Worldscale flat rate, and the rate for a specific route will be defined as the rate in Worldscale. If the rate for the route from Ras Tannurah, Saudi Arabia to Chiba, Japan is 50 percent (WS50) and the flat rate (WS100) is 20 USD/metric

USD/Barrel

Year ton, the freight will be 10 USD/metric ton, 50 percent of flat rate. The flat rates for all the routes in the world are published on January 1 and July 1 every year. As Worldscale flat rate is calculated based on the oil price, it has strong correlation with the oil price, so the flat rate can be calculated by given oil price. The historical data is shown in Figure 5.

If a route is given, revenue the amount of and fuel consumption can be estimated by the fuel consumption model described in 2.2. The fuel cost can be calculated by the fuel consumption is if the oil price is given. The revenue can be calculated if the duration of a round trip is given by defining the service speed. Finally the cost and the revenue will tell the gross margin of a designed vessel.

Simulation

If a profile of a ship is given, the ship performance including the fuel oil consumption rate can be calculated. The round trip date for a voyage can be estimated by the ship speed, so the basic revenue of a ship can be calculated based on the Worldscale rate. The general flow diagram is shown in Figure 6.

Case Study

This case study focuses on the requirement definition of tankers. The case illustrate potential for the improvement in terms of economic value to explore design requirement though configurations of the main engine, propellers, ship hulls and other components are optimized for a certain condition.

Route and ship

In the case study, a route from Arabian Gulf to Japan is selected for detailed calculation. Basic information is shown in Table 1. In addition to the route, an average ship design model is also defined as shown in Table 2. This is a typical principal particulars referring to several ship design provided by shipyards and ship owners such as [START_REF] Ihi | [END_REF]. The specific oil consumption rate for the main engine is assumed based on the calculation provided by Man Diesel & Turbo SE web page. The performance of the ship hull and the propeller is assumed as shown in Figure 7. Load is the ratio of actual output to maximum continuous output of the main engine. The data is not actual data though the assumption is based on several design data.

Results

The calculation results of the gross margin which is subtraction of revenue and cost, and the fuel oil consumption rate given by the ship performance model. The revenue goes up by increasing the ship speed as the duration for a round trip of a voyage is getting smaller. The cost is getting higher because of the nonlinear increase of the resistance of ship hull shown as EHP. The results are shown as lines with markers in Figure 8. In this simulation, the Worldscale flat rate is projected by the oil price and the Worldscale rate for the route is fixed to WS45. In terms of the fuel consumption rate, the main engine and the propeller have an optimal condition for operations. Ship design is usually optimized for the condition. This performance from the technological point of view is shown as a solid line in Figure 8. The peak performance in terms of the technological perspective is found at around design service speed; however the optimal speed for the gross margin moves as the oil price changes. The oil price goes up and the optimal speed for maximizing the gross margin will getting smaller.

Discussion

The results are reasonable and explain the current marine transportation situation. The oil price is getting higher these years and slow steaming is widely deployed to decrease the cost of shipping firms. The design of ships still has to focus on the optimization in terms of the technological performance. It can be suggested that ship design should have a certain level of consideration for the economic performance to respond the uncertainties such as oil price and market in the future. This kind of idea is proposed by de Nufville [START_REF] De | Flexibility in Engineering Design[END_REF]. Specifically, this research focuses on the evaluation of service speed and the performance with limited collected data. The detailed ship and market model and more data are required to obtain accurate simulation results.

Conclusion

A requirements evaluation method to maximize the benefit of ships in the operation is proposed and applied to a tanker traveling between Arabian Gulf and Japan. The simulation results based on the proposed method show that the optimal conditions are different in terms of economic and technological perspective. This research suggests ship design should consider the maximization against the uncertainties in economic situation because of the length of the service life.

Fig. 1

 1 Fig. 1 Resistance of ship at various conditions

Fig. 2

 2 Fig. 2 Load and efficiency of a main engine

Fig. 3

 3 Fig.3 Characteristics of a propeller

Fig. 4

 4 Fig.[START_REF]Crude Oil Prices: West Texas Intermediate (WTI) -Cushing, Oklahoma (MCOILWTICO)[END_REF] Spot Oil Price West Texas Intermediate[START_REF]Crude Oil Prices: West Texas Intermediate (WTI) -Cushing, Oklahoma (MCOILWTICO)[END_REF]

  1985-06 1990-12 1996-06 2001-11 2007-05 2012-11

Fig. 5

 5 Fig.[START_REF]No 21 -2013 Worldscale Flat Rate Forecast[END_REF] Worldscale Flat Rate[START_REF]No 21 -2013 Worldscale Flat Rate Forecast[END_REF][START_REF]No 11 -2012 Flat Rate Forecast[END_REF] and Worldscale Rate from Arabian Gulf to Japan[START_REF] Mol | Market Data[END_REF]

Fig. 6

 6 Fig.6 General flow diagram of simulation

Fig. 8

 8 Fig.8 Ship performance in terms of economic and technological evaluation

Table 1 .

 1 Route overview

	Origin and destination	From Ras Tanura (Arabian Gulf:AG), Saudi Arabia to
		Chiba, Japan via Strait of Malacca
	Main Cargo	Crude oil
	Distance (one way)	6,590 (mile)

Table 2 .

 2 Principal particulars of the ship (based on[START_REF] Ihi | [END_REF])

	Ship performance model
	(Engine, Propeller and Hull Resistance)
	Change Service Speed	OUTPUT: Fuel Consumption Rate at
		Various Service Speed
	Marine transportation cost and revenue model
	(Oil Price, Route and Freight)
	Change Oil Price	OUTPUT: Gross Profit at Various Service
		Speed in given oil prices

Table 3 .

 3 Specific fuel consumption of main engine (calculated on Man Diesel & Turbo SE web page)

	Load(%	SFOC(g/kWh	Load(%	SFOC(g/kWh	Load(%	SFOC(g/kWh
	)	)	)	)	)	)
	100	173.3	75	170.6	50	175.6
	95	172.2	70	171.1	45	177.2
	90	171.3	65	171.9	40	179
	85	170.6	60	172.9	35	181.1


Alejandro Romero
email: romero-torres.alejandro@uqam.ca

Darli Rodrigues

Using the Product Lifecycle Management Systems to Improve Maintenance, Repair and Overhaul Practices: the Case of Aeronautical industry

Keywords: Maintenance, repair, overhaul, aeronautical, product lifecycle management

Airlines companies trust in MRO facilities for extending lifespan of their assets to ensure the availability of transportation services. Nevertheless, MRO services are complex because they involve several processes whose performance depends on the design and manufacturing of products while airlines require the best-cost efficiency, quality and safety. Product lifecycle management (PLM) could improve the productivity and quality of MRO since it enables the collaborative creation, management, dissemination, use, maintenance and repair of products and its operational process information across the entire life of products from market concept to product retirement. However, it seems that PLM and MRO relationship in the aeronautical industry has been studied very sparsely in the literature. This paper attempts to gain a better understanding of the influence of product life management system in MRO services. The objectives of this study are twofold: 1) to identify MRO provider's requirements concerning PLM systems, and 2) to assess how PLM system could be improved to better support MRO services.

Introduction

The aeronautical sector including aircraft construction, aircraft parts supply or maintenance, repair and overhaul (MRO) service is today one of the most dynamic industries in the world. This industry creates enormous amounts of economic activity and fiscal benefits for several countries. AeroStrategy assessed that the global aerospace industry will be worth 1,200 billion dollars by 2014 [1]. Specifically, the defense sector will represent 71.8% of the market while the commercial aviation will contribute the remaining 28.2% [START_REF]Aerospace Globalization 2.0: Implications for Canada's Aerospace Industry[END_REF]. The aerospace industry is closely linked to the continuous innovation and development of new technologies, new materials and new procedures, contributing in a significant manner to the economic and social development of countries.

The actual number of aircrafts in the air and the significant increase of new production, order backlog for Airbus and Boeing was approximately 9055 aircrafts in 2012 (Flight Global, 2013), have increased the importance of MRO services in this industry. For instance, U.S. airlines operate a mixed fleet of aircraft comprised of primarily older planes (60 % of their inventory). It was estimated that a large percentage of these old aircraft will be due for heavy checks or overhauls [START_REF]Team SAI and back Aviation, Maintenance, Repair and Overhaul (MRO) world market forecast[END_REF]. The increase in capacity of commercial and military sector, along with greater aircraft utilization, will lead to increased maintenance and safety demands, creating new challenges for the MRO industry [START_REF] Jackman | MRO market up modestly as efficiencies take hold[END_REF]. In fact, MRO providers create the capability to support the functioning of the aeronautical machines, extending their lifespan and ensuring transportation services.

MRO services are complex since they involve several processes whose performance depends on the design and manufacturing of products while airlines require the best-cost efficiency, quality and safety. MRO entities ensure the maintenance of a variety of aircraft systems, components and parts, which requires investments in infrastructure, compliance with government regulations and updating of technical staff. Product lifecycle management (PLM) could improve the productivity and quality of MRO. Indeed, it enables the collaborative creation, management, dissemination, use, maintenance and repair of products and its operational process information across the entire life of products from market concept to product retirement. However, it seems that PLM and MRO has not been studied sufficiently in the literature [START_REF] Lee | Product lifecycle management in aviation maintenance, repair and overhaul[END_REF]. Therefore, this paper attempts to gain a better understanding of the influence of maintenance repair and overhaul requirements on the product life management strategies in the aeronautical industry.

The objectives of this paper are twofold: 1) to identify MRO provider's requirements concerning PLM systems, and 2) to assess how PLM system could be improved to better support MRO services. The paper is structured as follows. The next section briefly presents a review of the literature. The third section outlines the methodological strategy. The fourth one examines the main PLM strategies to strengthen MRO services. The paper concludes with a discussion on the suitability of PLM in MRO.

Literature review

Aeronautical industry

The aerospace industry can be divided into two large sectors delimited by the operating range of products. The aeronautics sector is responsible for aircrafts operating within the earth's atmosphere and the astronautics is for products that may operate outside the atmosphere [START_REF] Alternatives | Competitive Alternatives -Highlights[END_REF]. MRO services are necessary in both sectors, but MRO providers for aeronautical product are not equipped to provide the same service for astronautics products. Aeronautical sector include both military and commercial aircrafts [START_REF] Alternatives | Competitive Alternatives -Highlights[END_REF]. All these sub-sectors share similar functional structure but focus on different markets and products (see figure 1). Some products use the same technological platform irrespective of whether they were developed for military purposes or for commercial transport of passengers and freight [START_REF] Anand | Domestic use of unmanned aircraft systems: an evaluation of policy constraints and the role of industry consensus standards[END_REF]. Nevertheless, most aircrafts require special procurement procedures, certifications and specific technological features [START_REF] Moir | Aircraft systems: mechanical, electrical and avionics subsystems integration (21)[END_REF]. For instance, the interiors of the executive and civil aircraft have a high degree of customization and advanced materials, which will be used later in commercial aviation. The structure of the commercial aviation industry is frequently compared to the automobile industry; however there are substantial differences in the level of demand certifications and standards, quality, safety, security, time to market, volume parts and life of the cycle product [START_REF] Rossetti | Supply management under high goal incongruence: An empirical examination of disintermediation in the aerospace supply chain[END_REF]. To better understand the differences between both industries, it's crucial to describe how aircraft products are structured. The largest unit is the aircraft, which is defined as a complete and operational unit. The aircraft is segmented into systems, covering key functions of the aircraft such as the turbine whose function is to provide the power for the lifting of the craft in the air [START_REF] Kozakiewicz | Unstable operation of the turbine aircraft engine[END_REF]. Further, systems can contain subsystems or components depending upon their complexity. In the above example, a subsystem of the turbine is the compressor which has the function of compressing the air prior to mixing it with the fuel in the combustion chamber [START_REF] Kozakiewicz | Unstable operation of the turbine aircraft engine[END_REF]. The turbine has several components such as the rotor and shaft. The rotor compresses the air to gradually reduce its size and the shaft spins the rotor [START_REF] Kozakiewicz | Unstable operation of the turbine aircraft engine[END_REF]. Finally, these components are composed of several parts such as rotor blades (see figure 2).

Maintenance, repair and overhaul (MRO)

MRO is the set of activities designed to allow aircrafts to operate safety, efficiently and respecting aviation regulations. MRO services involve the repair of any mechanical, electrical, electronic, hydraulic component (unscheduled maintenance, faults detection and repairs). They also include the execution of routine activities that keep the components in working condition (scheduled maintenance) or that simply prevent failures (preventive maintenance). For the aeronautical industry, MRO is the basis for adding value to the products' performance.

MRO services worldwide reach a value of $149.2 billion by 2013 and are equivalent to 35% of sales in the aeronautical sector [START_REF] Lombardo | Study: 2013 World MRO Market Worth $49.2B, AIN Online[END_REF]. Military sector represents 70% of the total market while the commercial aviation contributes the remaining 30% [START_REF] Michaels | Air transport MRO Outlook, implications of high fuel prices. Aerostrategy management consulting[END_REF]. For instance, commercial companies spent 35% of their MRO budget on turbine maintenance, 23% on subsystems and components maintenance, 20% on line maintenance, 15% on aero-structures repair and 7% on modifications [START_REF] Michaels | Air transport MRO Outlook, implications of high fuel prices. Aerostrategy management consulting[END_REF]. The global MRO market has 300-400 suppliers, located in all continents. It is estimated that the global market for MRO services will have long-term growth rate of 3.3%, representing by 2019 a total expenditure of $ 183 billion dollars [START_REF]The Commercial Aircraft Maintenance, Repair and Overhaul (MRO) Market[END_REF]. MRO service will be the fastest growing segment of the aerospace industry. MRO facilities principally offer three services: maintenance, repair and overhaul. Maintenance corresponds to the review, cleaning, lubrication and replacement of minor parts of the aircraft. It's often programmed to be undertaken after a certain amount flight hours (every day for line maintenance or every month for minor maintenance) [START_REF] Al-Kaabi | An outsourcing decision model for airlines' MRO activities[END_REF]. Repair refers to the mechanical reprocess for serious failures discovered during maintenance. Finally, overhaul corresponds to the complete review of the aircraft which is executed when aircraft has completed 4000 and 5000 flight hours. The objective is to check thoroughly every system, component and tool of the aircraft and meet the condition standards of quality required for all the components. Overhaul also includes the incorporation of new technologies or systems [START_REF] Dixon | The maintenance costs of aging aircraft: Insights from commercial aviation[END_REF].

MRO providers offer different type of check services, namely A, B, C and D [START_REF] Yu | New advances in aircraft MRO services: Data mining enhancement[END_REF][START_REF] Zhilkin | Aircraft maintenance repair and overhaul market in Russiachallenges and opportunities of the high-tech industry in Russia[END_REF]. An "A" check is performed approximately every 500-800 flight hours. It is usually done overnight at the airport. The recurrence of this service varies by aircraft type, the cycle count (one cycle consists of one takeoff and one landing), or the number of hours in air since last service. A "B" check is executed approximately every 3 or 6 months. It usually lasts for 1 to 3 days in a hangar. "B" check recurrence depends on the same factors as that of an "A" check. A "C" check happens approximately every 15 to 21 months or a certain number of flying hours. This service is more extensive than a "B" check. Almost the entire aircraft is inspected keeping it out of service until this check is completed at the maintenance site. The space required for the execution of the service is also higher. It requires the hangar and a maintenance base equipped with set of workshops. The average completion time is usually 1-2 weeks. Recurrence depends on flying hours, but specifically on the manufacturer's recommendations. A "D" check, also known as Heavy Maintenance Visit (HMV), is the most demanding of MRO services. This check is performed approximately every 5 or 6 years. Almost all the aircraft is disarmed for inspection and repair purposes. It can last for 3 weeks to 2 months depending on the service provider, its resources, and the general condition of the aircraft. A Boeing 747 for instance requires the participation of 100 technicians for executing a "D" check to the aircraft parts, executing tests and ensuring the necessary installations [START_REF] Dixon | The maintenance costs of aging aircraft: Insights from commercial aviation[END_REF].

Product lifecycle management (PLM) for MRO services

In the aeronautical industry, PLM aims principally to manage the aircraftproduct definition with respect to the functioning of its relative subsystems (see figure 2), from their conception to their final disposal. PLM systems by inclusion of functionalities such as requirement management, data management, digital visualization and configuration management, allow for sharing product information throughout the product value chain. Furthermore, PLM allows for synchronizing nomenclatures resulting from different lifecycle phases namely design, manufacture, assembly and service.

Technology advancements could bring important benefits to improve MRO services. For instance, MRO facilities are looking for ways to streamline their maintenance operations through automation by way of informational technology. Advances in computer technology especially in the area of information technology have made the MRO procedures highly technical [19]. They can benefit from pervasive advantages of technology such as electronic manuals and electronic information which eliminates the need to deal with high volumes of paper to obtain needed maintenance information Adopted years ago by different industries, PLM system could bring information about the aircraft components and pieces to the actors participating in the lifecycle of aircrafts. PLM systems are developed and adopted to gather all the relevant information that affects a product throughout its life, from concept through retirement (including its maintenance and repair) and managing the communication of that information to facilitate product and process improvement [START_REF] Dimitri | Integrated Design and PLM Applications in Aeronautics Product Development[END_REF]. PLM capture principally information of the activities conducted during design engineering such as computer-aided design applications, 3D modeling and simulation or Bill of Material [START_REF] Rashid | Smart factory: E-business perspective of enhanced ERP in aircraft manufacturing industry[END_REF]. Specification data regarding component parts, materials, tools and other attributes is defined in these systems. Information improving MRO services are also integrated into PLM platforms such as process flows, work instructions and inspection criteria [START_REF] Yu | New advances in aircraft MRO services: Data mining enhancement[END_REF]. The resulting documentation contains every detail about the product and process definition.

The benefits of extending PLM to production can be realized quickly with manufacturing operations software tightly integrated to a manufacturer's PLM system, such as enterprise resource planning (ERP) customer relationship management, management of supply chain (SCM) and design applications (CAD) [START_REF] Rashid | Smart factory: E-business perspective of enhanced ERP in aircraft manufacturing industry[END_REF]. Supported by PLM, Aircraft manufacturers could improve their ability to enforce as-planned execution results with fewer mistakes, integrate engineering data facilitating faster decision making and communicate manufacturing data to engineering and providers [START_REF] Dimitri | Integrated Design and PLM Applications in Aeronautics Product Development[END_REF][START_REF] Cantamessa | Understanding the organizational impact of PLM systems: evidence from an aerospace company[END_REF].

However, data contained in PLM applications often does not encompass the complete lifecycle of the product. Several authors in the literature stated that PLM improves the collaboration from design to manufacturing procedures but it must extend their benefits to the MRO services and final disposal [START_REF] Lee | Product lifecycle management in aviation maintenance, repair and overhaul[END_REF][START_REF] Yu | New advances in aircraft MRO services: Data mining enhancement[END_REF]. Further, PLM must capture and spread information into two directions: from supply chain upstream to downstream and vice versa. Lee et co-authors [START_REF] Lee | Product lifecycle management in aviation maintenance, repair and overhaul[END_REF] studied the adoption of PLM tools by an MRO provider. They identified that PLM could establish a more comprehensive relation between customers, suppliers and business partners since MRO providers could get manufacturing information easily to provide the right MRO services. In turn, MRO facilities could register maintenance and repair information into PLM tools to share it to manufacturers and airlines for product improvement purpose [START_REF] Lee | Product lifecycle management in aviation maintenance, repair and overhaul[END_REF]. Yu and Gulliver [START_REF] Yu | New advances in aircraft MRO services: Data mining enhancement[END_REF] conclude that PLM could provide accurate information to MRO providers to ensure quality and to reduce service cost.

Methodology

We executed an exploratory study based on a content analysis. Our goal is to answer to the following research questions: What are the main stakes for MRO providers? Which are the benefits of integrating PLM systems into MRO services? How do MRO providers use PLM systems? How could PLM systems be improved? The executed content analysis is based on public information about PLM uses and MRO requirements. We identified several documents such as research papers, academic documents, white papers, industrial documents and news. Data were coded and classified based on the current topics: such as needs of MRO providers for its functioning, benefits of PLM in aeronautical section, information required by MRO's and PLM implementation. Table 1 shows the distribution of information collected in function of the above classification. Based on these classifications, we analyzed MRO needs and PLM capacities for aeronautical industry to identify the main benefits of integrating PLM systems into MRO procedures. Some limitations were also identified by analyzing MRO information requirement and current PLM applications. No relevant information were found from available PLM implementations documents. Preliminary results were then validated by an expert on product lifecycle management in the aeronautical industry, by senior specialists from two aircraft manufacturing companies and by one senior specialist representing an MRO provider. Experts gave interesting insights that support research results.

Preliminary results

PLM opportunities for MRO

As shown in the literature and validated by the specialists, MRO services are complex for several reasons: First, they must deal with a big variety of systems and sub-systems that have different maintenance procedures. Aircraft are sophisticated products since they are made up of thousands of components that come from a long supply chain and whose cycle life is measured in decades. To illustrate this, Airbus A300 was launched in 1969, he entered in service in 1974 and the last aircraft was delivered in July 2007. Apart from their long periods of production, aircrafts have long periods of use and consequently long periods of maintenance. For instance, the A380 underwent fatigue testing for 25 years of use. A quarter of the Airbus aircraft currently in service has exceeded its usage life of 20 years. These very long periods of service and production involve inevitably changes to the supply chain and changes to the system design. As mentioned by a specialist from an aircraft constructor, "during the prolonged life cycle of aircrafts, the customer requirements could evolve resulting in several product versions that differ from original design". PLM systems could capture this dynamic data and provide accurate information to MRO providers. In case of any version update, MRO provider could receive the instructions to upgrade systems and ensure that aircrafts in used respect requirements and specification of original manufacturers.

Second, MRO procedures depend deeply upon the production structure of aircrafts. Production comprises 5 levels (see figure 1): the first level is occupied by the main contractors, also called original equipment manufacturers (i.e. Airbus, Boeing, Embraer or Bombardier), that are responsible for designing and assembling aircrafts [START_REF] Pritchard | Boeing's diffusion of commercial aircraft design and manufacturing technology to Japan: Surrendering the US aircraft industry for foreign financial support[END_REF]. The first-tier supplier is in charge of assembling primary system and manufacture main components [START_REF] Doran | Rethinking the supply chain: an automotive perspective[END_REF]. The second-tier supplier is responsible for sub-assembling primary systems and its components [START_REF] Doran | Rethinking the supply chain: an automotive perspective[END_REF]. The third-tier supplier is in charge of manufacturing components. Finally, forth-tier supplier is responsible for producing simple components and parts [START_REF] Doran | Rethinking the supply chain: an automotive perspective[END_REF]. For MRO services, providers must ensure the compatibility of their procedures with the recommendations provided by OEM manufactures, suppliers from all tiers, and airlines companies. They also require highly specialized aircraft expertise, a field that is constantly evolving and where specialties are changing over time. Following the above design-manufacturing structure, PLM systems could integrate the product information and the structure of their manufacturing. Indeed, OEM and systems providers integrate product information into a same platform for product assembly purposes. Using an effective PLM solution, MRO could get access to this integrated information and then communicate easily with the appropriate owner of products in case of any technical or specification problem.

Third, MRO demands are centered on safety and quality which are necessary to ensure airplanes are free from factors that may lead to injury or loss. Nevertheless, literature shows that MRO service could frequently fail. For instance, Aircraft maintenance and inspection errors have contributed to anywhere from 9 to 23 percent of airline accidents [START_REF]Network newsroom[END_REF]. As described by a specialist participating in this study, the most common aviation maintenance problems include engine shutdowns, structural design problems, defective plane parts and flight employee negligence. Apart from high quality requirement, MRO solutions providers are also under pressure from commercial airlines for reducing costs. An estimated 20 to 30 percent of engine shutdowns are caused by maintenance errors, resulting in flight delays that could cost as much as $10,000 per hour [START_REF] Tegtmeier | Training not immune from market, technology forces shaping industry[END_REF]. The increasing pressures to maintain a highly competitive advantage in the aviation industry have dramatically changed perceptions from tradition models of the past. Therefore, MRO provider could use a PLM system to share the information produced during maintenance and repair procedures. As in original production, material and process data will need to be collected to document MRO procedures. This electronic record ensures operations are approved in sequence; replacement materials meet specifications and tasks are performed by authorized MRO providers. In order to reduce time and cost of MRO services, several lean strategies are adopted such as 5S process or Kaizen. PLM system could support the integration of these strategies. Indeed, it enables the identification of pieces using nomenclatures or codes. This identification system enables a better control of important volume of pieces. Therefore, MRO providers could decrease time spent on searching parts and finding their related information.

Finally, technology innovations not only bring opportunities to improve MRO services, they could increase the complexity of specifications and conditions for maintenance and repair. For instance, technological advancements in avionics systems require MRO providers to continuously provide up-to-date training to keep up with newer avionic platforms. Due to this increasing use of technology, more time is spent to repair aircraft systems. As mentioned by several specialists, sharing the same PLM solution with aircraft constructors and their suppliers could decrease the time to repair and improve knowledge. Extending PLM to mainte-nance can incorporate work instructions that are delivered in 3D just like during the manufacturing process. MRO workers could interact with the model to quickly and thoroughly understand the exact issue and solution. Original designs and historical maintenance data recorded in the as--built his-tory can be viewed and compared.

PLM limits for MRO

Some of the participants of this study pointed to the actual limits of PLM solution that could explain why this system is not totally used by MRO providers. The first limit described is that actual PLM solutions meet the needs of engineers and only extend up to the point where a product is built. For MRO providers looking for knowledge of the life cycle beyond design through production of aircraft parts and subsystems, the information is limited and don't meet MRO needs. Specialists participating into this study stated that current systems don't encourage collaboration between engineering, manufacturing, the supply network and MRO service. Actually, they hinder continuous improvement efforts. Another specialist examining the MRO documents observed that the information available electronically is astronomical. He suggested a better aggregation of information to allow MRO providers to have all the information they need to complete a repair anywhere and anytime, from any location.

Apart from sharing information, MRO providers, airlines, OEM and systems providers must use PLM to improve their relative processes. Critical information is collected and could be used to better understand the procedures and need of aircraft lifecycle partners. OEM and aircraft system providers should focus on MRO stakes in order to improve the design of their products and, therefore, make easier their maintenance and repairing. For instance, they could identify that disassembly of systems is a complex process for MRO providers. Therefore, they could add as design requirement that aircraft systems could easily be disassembled. Some participants suggested that PLM system could enable this type of analyses to change design strategies to make it easier for MRO's to provide services.

Conclusion

PLM system allows MRO providers to decrease the complexity of their activities since it enables sharing and collecting information about aircraft systems. This information could be used to improve the control of all the aircraft components, to obtain a better knowledge of pieces requirements and updates but also it contribute to improve MRO quality and decrease time and cost. Beside these benefits, PLM systems are not completely used by MRO entities because they are not totally compatible with maintenance and repair processes and because the actual available information don't meet MRO requirement. It seems that even if PLM solutions become more sophisticated, aeronautical supply chain actors tend not to share their information. Improving PLM system to meet MRO needs could have several opportunities for MRO providers and commercial airlines. But, OEM and aircraft system providers could also get benefits. For instance, OEM could increase their revenues if they ensure that their products need less costly and timely MRO services [START_REF] Lee | Product lifecycle management in aviation maintenance, repair and overhaul[END_REF]. To accomplish this objective, aircraft lifecycle actors must invest in improving their collaboration across their business wall. They should coordinate their efforts from design and manufacturing to MRO procedures. Indeed, PLM could make easier this task. This paper presented an exploratory study that enables to have better understanding of the actual position of PLM in MRO services. This represents the first step for a grounded theory. Different data was collected from the content analysis and from specialist's validations and was coded into two main classifications: PLM benefits and limits. Further research will focus on analyzing how designers and manufacturers in aeronautical industry include into their activities the needs of their partners to improve the last phases of the product lifecycle, namely maintenance services provided by MRO's, recycling and final disposal.

Fig. 1

 1 Fig. 1 Aerospatiale industry structure (based on [2])

Fig. 2

 2 Fig. 2 Aircraft product and manufacturing structure (based on [10])

Table 1 . Classifications of collected data Type of documents Research papers Academic documents White papers Industrial documents

 1

	News	Total

Acknowledge

The authors would like to thank the two anonymous reviewers for their valuable and insightful comments and suggestions.