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ScienceDirect Procedia CIRP 17 (2014) 260 – 265
Variety Management in Manufacturing. Proceedings of the 47th CIRP Conference on Manufacturing Systems
Integrated Product and Assembly Configuration Using Systematic Modularization and Flexible Integration Martin Landherr a, b *, Engelbert Westkämper a, b, c a Graduate School of Excellence advanced Manufacturing Engineering – GSaME, Nobelstr. 12, 70569 Stuttgart, Germany Fraunhofer Institute for Manufacturing Engineering and Automation – Fraunhofer IPA, Nobelstr. 12, 70569 Stuttgart, Germany c Institute of Industrial Manufacturing and Management – IFF, University of Stuttgart, Nobelstraße 12, 70569 Stuttgart, Germany * Corresponding author. Tel.: +49 (0)711 970-1851; fax: +49 (0)711 970-1009. E-mail address:
[email protected] b
Abstract Dealing with the varying demands deriving from the market, the technical innovations and the public authorities in a dynamic way, offers great potential to improve the competitive situation in the global market. The introduced approach supports the ability of manufacturing companies in the field of mass customization to respond to these changes in an effective and efficient way. The focus is on the understanding of the product and its assembly as a complex, socio-technical and integrated system to realize a target-oriented modularization. Configuration concepts are used to integrate the created functional self-contained and well-defined modules in a flexible way. Authors. byopen Elsevier B.V.article under the CC BY-NC-ND license © 2014 2014 The Elsevier B.V.Published This is an access Selection and peer-review under responsibility of the International Scientific Committee of “The 47th CIRP Conference on Manufacturing (http://creativecommons.org/licenses/by-nc-nd/3.0/). Systems” in thepeer-review person of theunder Conference Chair Professor Hoda ElMaraghy. Selection and responsibility of the International Scientific Committee of “The 47th CIRP Conference on
Manufacturing Systems” in the person of the Conference Chair Professor Hoda ElMaraghy” Keywords: System Theory; Product System; Assembly System; Modularization; Integration; Configuration.
1. Introduction Manufacturing companies are subject to a permanently changing environment. Megatrends like individualization, globalization and sustainability induce shorter product life cycles and increasing numbers of product variants that force the factories into a continuous adaptation to stay competitive in the global competition [1]. Fig. 1 illustrates the factory that is subject to manifold internal and external demands that are continuously changing and partially competing with each other. Mass Customization [2] represents a concept to use volume production to produce customized products. For that matter the advantages in the sense of economies of scale and economies of scope or possible optimization activities that are offered for instance by the concept of lean production [3] are tried to be applied. This demands enormous flexibility and changeability in the production. In this paper, flexibility subsumes the ability of production systems to answer to variations in the type or the volume of the products to be
produced in a predefined corridor. Changeability stands for the characteristic of a production system that enables an adaptation of the production system [4]. Therefore not only technical conditions like the consequent modularization, standardization and mobilization of production equipment but also the organizational conditions have to be created [5]. The approach introduced here aims at the support of the flexibility and changeability of production systems with a special consideration of the products to be produced. Therefore, a method for integrated product and assembly configuration is proposed. The following two sections outline the state of the art in the field of flexible and changeable manufacturing and product systems and create a common understanding of the used terms. Afterwards the method for integrated product and assembly configuration is described. The focus of the method is the systematic understanding of the product system and the accordant assembly system. The creation and use of this understanding is supported by an ontology-based information system that is also presented.
2212-8271 © 2014 Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the International Scientific Committee of “The 47th CIRP Conference on Manufacturing Systems” in the person of the Conference Chair Professor Hoda ElMaraghy” doi:10.1016/j.procir.2014.01.036
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Change Driver: Product
• Model Policy • Innovation and Product Life Cycles • Dynamics of Change • Technical and Technological Innovations
Change Driver: System
• Market and Customer • Finance • Competitors • Management and Strategy • Public Authorities
Corporate Strategy
Factory
Quality
Change Driver: Production
• Employees • Technical and Technological Innovations • Organization • Automation • Efficiency and Effectiveness
System (State A) (Re-)Configuration
Costs System (State n) Component
Product
Production
Property
Port for connection
Connection
Constraints for connection
Time
Fig. 2. Configuration Changeability
Sustainability
• Organisational Simplification • Reactability • Flexibility • Robust Decision Support • Knowledge Transfer
• Customer Integration • Planning Reliability • Quality Improvement • Dynamics • Effort Evaluation • Ecological Footprint
Complexity Management • Systematization • Module Description • Relations • Information Mgmt. • Reduction and Mastering of Complexity
Fig. 1. Factories in dynamic environment
For validation purposes, the method has already been applied in scientific and industrial environment. The results of this validation are outlined before the paper closes with a discussion, a summary and an outlook. 2. Basics This section is to create a common understanding of the terms used to describe the integrated product and assembly configuration. 2.1. Configuration A configuration task creates configured solutions out of a “fixed, pre-defined set of components, where a component is described by a set of properties, ports for connecting it to other components, constraints at each port that describe the components that can be connected at that port, and other structural constraints.” [6] This definition stipulates that a configuration task needs components that are well-defined and the possible connections under consideration of the respective contribution to the function of the configured solution have to be described (Fig. 2). Following the definition, individual products are not under consideration of this research task, because with individual products at least some components are not yet defined. But individualized products in the sense of products with many variants and a high degree of customer integration are in the focus of the approach introduced here. For the demarcation of individual and individualized products see [7]. Individual products are also identified as personalized products and individualized can be used similarly to customized products [8]. The configuration can be separated into the following two aspects: modularization and integration.
2.2. Modularization The above mentioned components can be considered as modules. Modules are independent and self-contained elements that can be combined to achieve an overall outcome of the superior system (so called supersystem) [9], where the functional interactions take place within rather than between the modules [10]. Thus, modularization is a way to reduce the complexity of systems by separating it in partial functions [11]. 2.3. Integration The target-oriented combination and connection of the modules to realize a valid functional unit is considered as integration. So the integration with its impact in the direction of reducing elements, that have to be considered separately by constructing supersystems, competes with the modularization. It is challenging to find the right balance between modularization and integration or to find the ideal granularity of the modules within the system boundaries [12]. 2.4. Theory of Technical Systems It is mandatory to understand the elements of a system and their interdependent behavior as a whole before identifying the ideal balance between modularization and integration to realize a target-oriented separation of a system into subsystems (modules). System Theory provides a reliable fundament for this task [13]. Fig. 3 illustrates the categorization based on the general system theory following [14] and [15]. Theoretical basic understanding of technical systems Function of the system Input
Structure of the system
Output
Factual structure Element
Logical / temporal structure
Part 1
Part n
Part 2 System
Super-system
Element
State System
Hierarchy of the system
Part 1
Part n
Part 2 Relation
System
System
Sub-system Relation
Fig. 3. Categorization of technical systems
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The main issue to be used for the integrated product and assembly configuration is the identification of the function of the whole system and its subsystems. This induces the interrelated task to create a hierarchy of sub- and supersystems with the above mentioned challenge of finding the balance between modularization in sense of building subsystems and integration in sense of building super-systems. Afterwards the structure of the system can be analyzed and modeled. With respect to the theory of technical systems, the relations in the integrated product and assembly system can be: x Physical: The physical relations between modules stand for the connection of product components using joining technologies or for the linking of production components like work stations or machines using handling and transportation technologies. x Organizational: The organizational relations represent the structure inside and between business units. x Informational: The informational relations are the key relations for the execution of technical and business processes. They represent the communication between the units where humans or machines can be considered as units. 3. State of the Art There are many relevant research fields concerning the introduced method of integrated product and assembly configuration. This section provides a short outline of the most significant approaches. Firstly, relevant concepts for modular and integrated product and production structuring are presented. Secondly, configuration in the product as well as in the manufacturing domain is highlighted with a special focus on the intersection between the product and the assembly system. 3.1. Flexibility and Changeability-oriented Production Concepts Approaches that support an economic production while complexity, dynamic and quality requirements are increasing have a long tradition with concepts like the Fraktale Fabrik [16], the modular factory [17], the agile manufacturing [18], the bionic [19] and the holonic manufacturing systems [20]. All these concepts have a holistic understanding and a module-oriented segmentation of the production in common. Additionally to this modularity should scalability, integrability, convertibility, customization and diagnosibility be embedded in the manufacturing system design to enable reconfigurability [21]. Koren and Shpitalni show a concept of designing reconfigurable manufacturing systems with respect to these essential characteristics [22]. Hu et al. propose a comprehensive concept for the design of assembly systems for products with high variety [8]. The Stuttgart Enterprise Model (Stuttgarter Unternehmensmodell, SUM) describes the factory as an integration of independent units across multiple scales from the manufacturing network, sites, segments, systems, cells, stations, and the manufacturing processes (Fig. 4) [23].
System level 1. Production network 2. Production site
Communication system
Business units - Objectives - Self-organization - Self-optimization - Cooperation
3. Production segmente 4. Production systeme
5. Production cell
Technical units - Adaptive - Flexible - Intelligent
6. Work station machine 7. Process
Fig. 4: Stuttgart Enterprise Model [23]
The approach introduced here uses the SUM for a systematic categorization of relevant elements of the considered assembly system and integrates the product system. 3.2. Systems for Customized Products The product system is defined as the combination of the structure of the product and its functions. Especially in the field of products with numerous variants, the analysis, modeling, documentation and the representation of the product system is still challenging. Besides the widely used structured bills of materials (BOM) for modular or platformbased product structure or as a manufacturing or assembly BOM, the Variantenbaum can be considered as a wellestablished concept [24]. This approach structures the product on the basis of the applied assembly sequence and represents all variants in a product tree. It supports the analysis and representation of a complex product structure but it lacks in the support of activities to optimize the product structure concerning a target-oriented balance between modularization and integration of functional units. The Design Structure Matrix (DSM) provides a possible answer by the mapping of technical-functional interactions between components [25]. This can be used for the development of a modular product structure [26]. But the ideal granularity level is still an object of research [27]. The Module Indication Matrix (MIM) is comparable to the DSM and represents the core of the Modular Function Deployment (MFD) that uses module drivers to structure the product [12]. 3.3. Product System Configuration The most common application of product configuration concepts and systems is still in the field of sales and marketing [2]. But the product specific configuration approaches are also used to support the product design process [28]. They have great potential to reduce the complexity in product variety management [29]. Therefore the configuration systems can be categorized according to the configuration knowledge as rule-based, model-based or casebased systems with an ontology-based approach as a special
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Problem definition
Real system
Target definition
Applying insight Problem solving
Experiment
Model
Model application
Analysis
Gaining insight
Model adjustment
Application and implementation
Model evaluation
Information demand 6. Selection of configured solution
Fig. 5. Model-based problem solving process [31]
3.4. Integrated Production System Configuration The configuration of production systems results in a highly complex system to be understood and modeled with respect to a highly-variant product to be produced and under consideration of increasing rates of changes [32]. ElMaraghy et al. provides a comprehensive analysis and discussion of managing variations in products, processes and manufacturing systems [33]. Schuh et al. proposed an integrative configuration approach with the four steps: a) integrative assessment of the production system, b) analysis of complexity-related interdependencies, c) implementation of integrative principal solutions, and d) definition of constitutive features of the production system [34]. These exemplary approaches of integrated production system configuration show that configuration concepts have great potential for the support of the management of complex systems. In the following section, the method for integrated product and assembly configuration is presented. For the development of this method, the state-of-the-art serves as a scientific fundament. The focus is on the understanding and the integration of the product and the assembly system based on the theory of technical systems using the SUM as a framework. 4. Method for Integrated Product and Assembly Configuration Fig. 6 shows the method for integrated product and assembly configuration. The method acts on the assumption of an existing system like initially depicted. The system boundaries include the product system with the product components and its functional structure as well as the assembly system under consideration of the technical processes that are necessary for assembling the product (Fig. 7). In the first step, the need for changes is identified using an adaptation of the technology calendar [35]. This is a powerful tool to identify and to align technological and organizational changes. The technology calendar is commonly used for longterm-oriented changes through technological innovations. But for the proposed method, the technology calendar is used for short-term adaptations of the product or assembly system. The result of this step is a formalized information demand to apply the identified adaptations.
Modeling
1. Identification of changes needed
Insight articulation
type of model-based configuration concepts [30]. The presented method uses the model-based approach as a configuration-specific adaptation of the model-based problem solving process (Fig. 5).
Product and assembly system
Provision of information
2. Virtual system configuration
Adaptation of the model
5. Insight formulation
3. Analysis
4. Evaluation
Fig. 6: Method for Integrated Product and Assembly Configuration
The second step provides the possibility to create virtual system configurations. Therefore an integrated product and assembly model has to be modeled. Due to the fact that it is a highly complex model with numerous elements and various relations, technologies coming from the Semantic Web are used [36]. The knowledge base that represents the model of the integrated product and assembly system is built as an ontology using OWL-DL [37] as language and Protégé [38] as the ontology-editor [39]. This model is of a hierarchical structure to support the understanding of the system by human beings. On the one side, the product is structured with help of the categories: portfolio, family, assembly, single part and feature. These are the system levels of the product. With respect to the functional structure of the product system, modules can be built on both, the assembly and the single part level. These modules are connected with function. The special characteristic to be considered for these functions is that a module can have different functions depending on the configuration of the system. That means that a product function can be achieved by different combinations of modules with their respective functions. To solve these combinative problems, ontologies can be used, facilitating the ability of inferring syllogisms by a so-called reasoner. In this case FaCT++ is used as the reasoner. On the other side, the assembly system is structured with help of the categories: segment, system, cell, work station, equipment and assembly process. Product
Assembly
Fabrication
Variant
Final assembly
= Driver for variants Customer
Creation of variant
Sourcing
Production
From customer to customer
Fig. 7: Integrated Product and Assembly System
Delivery
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These are the levels of the assembly system. Due to the fact that an assembly system is a socio-technical system that is mainly influenced and controlled by humans, the workers are also considered. They are integrated into the system with the abilities they provide to the assembly system domain and with the abilities that are needed for assembling the product. With the third step, the configured solutions are analyzed and the consequences of adaptations on parts and on the whole system are identified. This step concentrates on the convergence of the as-is-situation and the to-be-situation as it is formulated in step one. The fourth step is to evaluate the configured solutions using the following criteria: x Integration/modularization: This criterion offers a possibility to compare the number of modules with respect to the number of elements and functions of the systems. x Flexibility: This criterion is strongly connected to the level of integration: The higher the level of integration, the lower the level of flexibility in terms of configurability. x Robustness: This criterion provides a statement concerning the robustness of the assembly process and of the product variant. It is calculated with the use of historical information of quality indicators and the level of experiences with product modules and processes. x Efficiency: This criterion offers a statement about the degree of utilization of the available resources used in the configured solution. On the basis of these evaluation criteria, the insights are formulated and target-oriented visualized in the fifth step. This step is also supported by a digital tool that is feasible of presenting the relevant information in an appropriate manner. The information system has a modularized architecture following the Model-View-Control-Pattern. The technical information used for the configuration task is stored as the above mentioned ontology and represents the model. The control layer uses this model to generate the desired information. The system is realized as a web-based singlepage application to foster the flexibility. So the browser is used as the user interface to formulate queries and display the desired information. The user interface is divided into three parts: 1. Input area: Formulation of queries using text search, filter mechanisms, or facets. 2. Output area: Presentation of the results. 3. Options area: Selection of the visualization apps and definition of properties. Due to the fact that many different domains should be able to use the system the information provision should be situation based. This requirement is faced by app-based visualization modules. Therefor three different visualization apps are realized facilitating: x graph-based visualization to present relational information, x matrix-based visualization to present resource allocation and assembly requirements and x table-based visualization to present BOMs. In the sixth step, the best solution is selected. Based on this selection, the proposed adaption is applied in the real product and assembly system and the respective model is updated.
With this procedure a living model of the real system can be realized. 5. Validation of the Integrated Product and Assembly Configuration The method for integrated product and assembly configuration has been validated in industry. Therefore, a factory that assembles car seats for the automotive industry was selected. The highly variant product system and the applied assembly system were analyzed, modularized and modeled. Afterwards the two domains were interconnected. Most of the relations were applied between the functional modules of the product system and the equipment of the assembly work stations. The assembly system has a high degree of manual workforce and can be separated into 16 work stations. Through this strategy, it has the ability to respond to changes very fast. But it also makes optimization strategies to reach the optimal operation point hardly applicable. Through the proposed method, it gets possible to understand and to integrated the systems and to know, what product module needs which equipment to be produced und which work stations are able to assemble it. This information serves as an enabler of a highly flexible and changeable assembly system where optimization activities that are well-known in the field of volume production, can be applied. Two scenarios were performed for the validation of the method. In the first scenario, the demand decreases for a certain product variant. In this scenario, the method was used to evaluate the functional benefit of deleting the product variant from the portfolio. During the analysis, supported by the introduced information system, it turned out that there is no assembly resource that is only used for this product variant. Thus, no benefit could be identified from the functional point of view and it was suggested to hold this product variant. In the second scenario, a bottleneck analysis was supported by the introduced method. Using the information system that is based on the integrated product and assembly model, highly frequented assembly stations were identified. In the following step, alternative stations with comparable functionalities and abilities could directly be listed and alternative assembly system configurations could be suggested. With this information, the bottleneck analysis could be performed in less than half of the time and first solutions for avoiding the identified bottlenecks could already be suggested. 6. Discussion The validation showed that it is very helpful to understand the product and its production as an integrated system. The method supported not only the understanding but also the retrieval of information for adaptations and the respective consequences and effort. But it also showed that it is required to have a consequent function-oriented modularization of the product and the assembly system. The level of modularization depends on the focused goals of the manufacturing system like depicted above. The method is scalable in the sense of
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supporting all levels of modularization. However, the implementation of identified system reconfigurations is only possible, if the enablers of reconfigurability (section 3.1) are embedded in the physical, informational and organizational structure of the product and the assembly system. 7. Summary and Outlook The authors presented in this contribution the method for integrated product and assembly configuration. Initially, relevant terms like modularization, integration and the theory of technical systems were discussed to reach a common understanding. Afterwards the state-of-the-art in the field of flexibility and changeability-oriented production concepts, systems for highly-variant products and configuration approaches was outlined. The method for integrated product and assembly configuration was introduced and described in section 4. The application and validation of the method in an industrial environment was summarized in section 5. The contribution closes with a short discussion of the lessons learned from the validation scenario. The method is supported by a prototypical information system. This tool has to be further improved to enable that the domain experts can adapt and maintain the underlying model (ontologies) by themselves. Only they have the knowledge for understanding the system in a way that is needed for targetoriented adaptation and optimization activities. The method itself could be improved by further support of the identification of the right modularization strategy and level for specific objectives. The introduced approach provides a further step into the direction of highly flexible and changeable manufacturing systems by the application of integration and configuration concepts based on the theory of technical systems. References [1]
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