CIRP Annals - Manufacturing Technology 57 (2008) 133–136

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CIRP Annals - Manufacturing Technology

journal homepage: http://ees.elsevier.com/cirp/default.asp

Modularization as an enabler for cycle economy

G. Seliger (1)*, M. Zettl

Chair of Assembly Technology and Factory Management, Department of Machine Tools and Factory Management, Technische Universitat Berlin,

Pascalstr. 8-9, PTZ 2, 10587 Berlin, Germany

A R T I C L E I N F O

Keywords:

Manufacturing

Module

Product

A B S T R A C T

Modularization proves to be a chance for increasing the use productivity of resources by enabling

multiple usage phases sometimes even in different applications. A module configuration software tool

has been developed for finding an appropriate modular product structure considering life cycle criteria. A

mathematical model has been implemented to solve this multi-criterion optimization task. The

application of the software tool is presented in a case study. The vision of developing and producing

modular products in sustainable value creation networks is introduced.

� 2008 CIRP.

1. Introduction

A challenge of sustainability in engineering is to perform aparadigm change from piece cost decrease by ever increasingmanufacturing products to providing functionality when, whereand as needed without dissipating resources thus meeting theglobally growing human needs. This goal of increasing the useproductivity of resources can be achieved by designing for thesame functionality with fewer resources, intensifying the use ofresources and recovering resources [1]. Using fewer resourcesincludes the use of regenerative resources without exceeding thelimits of natural regeneration and the recycling of non-regen-erative resources since they are limited.

In the framework of globalization partners with different corecompetencies organize themselves in value creating networks.Communication among them with respect to sustainability in thesense of economical, ecological and social criteria can be enabledand enforced by a common understanding of sustainable valuecreating modules [2].

Products are realized in processes performed by facilitiesaccording to organizational aspects of where and when underhuman activity and supervision. The useful functionality ispermanently evaluated and improved according to investment,costs and profitability, to resource effectiveness and efficiency, tohealth and education, qualification and creativity as criteria ofsustainability.

2. Potentials of product modularity

Modularization in product development can considerably helpin fostering sustainable value creating modules by structuringcomplex system functionality in several independent sub-systems,so-called modules [3]. Modules are uncoupled and perform at leastone designated function, which is analogous to Suh’s indepen-dence axiom [4]. A function can be described as transformation of

* Corresponding author.

0007-8506/$ – see front matter � 2008 CIRP.

doi:10.1016/j.cirp.2008.03.031

energy, signal and material input flow into an output flow [3]. Theinner physical and functional relations are stronger than theexterior relations with other modules and systems.

Companies implementing modularity are aiming on thedevelopment and handling of product variants to meet diversifiedcustomer needs. Lower product costs are resulting from lowercosts for the development of product variants and manufacturingdue to bigger lot sizes and economies of scale in purchase [5].

According to life cycle engineering, modularization is anintegrated part of Design for X with the goal of increasing productsuitability for cycle economy [6]. In fact, modularity can enable foreconomical modification and maintenance, remanufacturing andadaptation by changing defective and obsolescent modules as wellas the product configuration. Modification and maintenance allowthe extension of the use phase thus avoiding the end-of-use [7].The efficiency of maintenance can be improved by maintenancestrategies supported by, e.g. the life cycle unit concept [8].Remanufacturing and adaptation are options to allow multiple usephases of products and modules in different applications atdifferent markets. An example is the upgrade of a personalcomputer with a graphic card and a processor with advancedperformance to comply with new software standards. This caneither be carried out during the use by the owner or at the end-of-use by a specialised company [5]. Remanufacturing and adaptationallow in addition the compliance with regional standards andcustomer demands. With respect to recycling, modular productscan improve material recovery by module configurations separat-ing recyclable and non-recyclable [9].

Beside an improved suitability for cycle economy, modularproducts can additionally support the implementation of so-called usage strategies, which aim on increasing the use ratio ofproducts and modules. The use ratio can be increased byimplementing product-, usage- and system-oriented servicemodels [8] as well as by multiple-use of products and modules.Service models allow the reduction of product downtime bydistributed use. Hereby modularity enhances the maintainabilityand flexibility thus increasing reliability and customer-orientedadaptability, e.g. renting reliable and adaptable manufacturing

Fig. 1. Module drivers and specifications along the product life cycle.

G. Seliger, M. Zettl / CIRP Annals - Manufacturing Technology 57 (2008) 133–136134

equipment to customers with different needs. The multiple-use ofproducts and modules aims on the substitution of productfunctionality by increasing flexibility. For example a mobilephone today can be used for phone calls, photos and videos, musicand television and radio. In integrated use, the mobile phone cansubstitute a photo camera and music player.

Nevertheless, the effects of modularity contain also economicaland ecological risks. Ecological risks are related to increasedresource consumption due to frequent module changes fortechnology fresh-up and maintenance. This risk can be addressedby grouping a limited number of functional carriers to modules,which have similar properties regarding to technology andmaintenance cycles. Economical risks are mainly related to costand time intensive efforts for the initial development of themodular product structure. Once the product structure is defined,the development of new product generations and variants can becarried out with less effort by changing the product configurationand the modules. However, subsequent changes of the productstructure can cause additional costs. Further risks are low productdifferentiation and ease of competition by imitation.

3. Life cycle oriented modularization

Modularization is the structuring of a product into modules andthe specification of module interfaces. Two general approaches canbe identified. Firstly the development of the modular productstructure is carried out based on the defined functions and sub-functions supported by heuristic methods. The specification of thefunctions is limited to information, material and energy flows aswell as to geometric relations. The second approach is based on aconceptual product model supported by modularization criteriaand module drivers, respectively. Module drivers are strategicgoals for grouping functional carriers to modules [10].

3.1. Approach

The development of a life cycle oriented modularizationmethodology supported by the module configuration softwaretool has been carried out according to the second modularizationapproach. The reason is that based on the conceptual productmodel the properties of the functional carriers according tostrategic goals are known or can at least be estimated. This isprerequisite for the life cycle oriented modularization methodol-ogy. Possible strategic goals for product modularization have beenselected and formulated as module drivers. The module drivers areextended by specifications, which give more details about theircharacteristics (Fig. 1).

The selection and application of module drivers and specifica-tions during the product modularization has a direct influence onthe resulting modular product structure. For example, in order todevelop a product suitable for multiple use phases, the moduledriver specifications maintenance and innovation cycle as well asremanufacturing are relevant. However, in order to increase thesuitability for recycling the focus is on the specificationsmaintenance cycle and recycling. With respect to these productscenarios the resulting product structures can be different [11].

The development of modular product structures is a complexand challenging strategic task. Multi-criteria according to moduledrivers and specifications have to be considered at the same time.

3.2. Methodology

The modularization methodology addresses seven tasks, whichhave to be solved during the product development. The productdevelopment process from Pahl and Beitz form the framework forthe methodology [3]. In Fig. 2 the tasks and expected results areillustrated.

The pre-structuring of a product in sub-systems and the pre-grouping of functional carriers in obligatory, optional and specialfunctions in task 5 is vital for reducing the complexity of the

modularization process. In addition calculation time for theidentification of the optimal module configurations can be saved.In task 6, the module configuration software tool is applied togenerate modules based on the conceptual product model and thepreviously collected data about the properties of the functionalcarriers according to the module driver specifications.

3.3. Module configuration software tool

Basic idea of the software tool is the generation of moduleconfigurations by assigning at least one functional carrier to amodule considering relevant module driver specifications. Therelevance of the specifications is identified with respect to thecorporate strategy and to product scenarios. Hereby a strategictarget system is defined by weighting the module driverspecifications. The module configuration software tool supportsthe modularization of new products from the sketch as well as ofexisting products.

According to the module driver specifications illustrated inFig. 1 the benefit of combining functional carriers to modules isevaluated. These evaluations are carried out for each moduleconfiguration. Module configurations are systematically generateddepending on the overall number of modules in the productstructure. The number of modules can differs from at least twomodules to the most possibly number. The retrieved benefit valueis multiplied with the respective weighting factor according to thestrategic target system. All benefit values of a selected moduleconfiguration are added up to the overall benefit value.

Since all possible module configurations are generated andevaluated, the complexity of the benefit value calculation increasesexponentially with the number of considered functional carriers.Even for a small number the calculation of the overall benefit valueis complex and time consuming. Therefore mathematics andinformation technology have been utilized to develop the moduleconfiguration software tool supporting the calculation of moduleconfigurations with the highest benefit.

A systematic classification of mathematic optimization meth-ods in design is introduced by Franzke [12]. Regarding to thisclassification an integer linear program (ILP) is suitable to solvethe benefit value calculation of the module configurations. The

Fig. 2. Methodology for product modularization supported by the module

configuration tool.

Fig. 3. Data structure of the module configuration tool.

G. Seliger, M. Zettl / CIRP Annals - Manufacturing Technology 57 (2008) 133–136 135

handling of integer variables is necessary, because only entiremodules and functional carriers have to be considered. Theobjective function for the calculation of the overall benefit value(1) becomes maximal for the optimal module configurations.

maxX

S

X

K

WSNskXk (1)

The benefit of the module configuration Nsk and the module driverspecifications weight Ws are parameters. Xk is the decision variable,which determines the chosen module combination.

The benefit of Nsk is calculated by comparing the parameters ofall functional carriers K for each module driver specification S. Withrespect to the calculation of Nsk every module driver specification S

can be assigned to one of five classes (2). Within these classes thecalculation of Nsk is carried out by assessing the differences ininteger and binary input parameters, e.g. innovation cycle andrecycling, relations, e.g. material flow intensity, characteristics, e.g.

variations of functional carriers, and defined constraints, e.g.compatibility.

S ¼ S1 [ S2 [ S3 [ S4 [ S5 (2)

The factor Ws is set with respect to the strategic target system.The constraints of the ILP are: each functional carrier has to be inone module configuration (3) and the sum of all Ws is 1 (4) [5].X

K

ðaikXkÞ ¼ 1 8 i (3)

X

S

Ws ¼ 1 (4)

The module configuration software tool has been implementedas web-based application. Hereby a C++ program systematicallygenerates all module configurations and formulates the ILP. The ILPis solved by a CPLEX algorithm, which is implemented in a solverfrom the ILOG Company. The solver is fast, reliable and can beintegrated in the software tool. The product-related data and theweighting factors of the module driver specifications are stored in aMySQL database (Fig. 3).

4. Case study—modular mobile phone

The goal of the case study is the development of a modularmobile phone suitable for efficient mass customization allowingthe configuration of a flip, slide and candy-bar phone as well as formaintenance and modification, remanufacturing and adaptation.Thus the module driver specifications innovation and maintenancecycle, remanufacturing, and product variants, gain the highestweight. The specification production location gains a mediumweight.

The development process has been carried out according to thedesign methodology from Pahl and Beitz [3]. In the productplanning, scenario technique was utilized to analyze the market,the legislative and the technology development. Based on thesescenarios future customer requirements on new and used mobilephones in terms of functionality, quality and design, the feasibilityof remanufacturing and remarketing with respect to economicaspects, and the expected innovation cycles are determined. Theanalysis of the current situation revealed data according to themodule driver specifications maintenance cycle, remanufacturingpossibility after the first use, production location and productvariants.

On the basis of future and current customer needs, the list ofrequirements, the function structure and the conceptual productmodel have been developed. In this context customers are net

Fig. 4. Virtual prototype of the modular mobile phone.

G. Seliger, M. Zettl / CIRP Annals - Manufacturing Technology 57 (2008) 133–136136

providers and mobile phone users. With respect to the moduledriver assembly/configuration, the function structure is used todefine the intensity of the energy, material and information flowsbetween functional carriers.

Based on the conceptual product model a pre-grouping of thefunctional carriers in obligatory, optional and special functions hasbeen carried out to reduce the complexity for the calculation of theoptimal module configurations. As a result the functional carrierantenna, printed circuit board (PCB) with memory, chipset, GSM(global system for mobile communication) unit and processor(CPU), microphone, speaker, display (LCD), functional and numer-ical keypads, and energy and data interfaces are obligatoryfunctions. Optional functions are camera, fingerprint scanner,and global positioning system (GPS) PCB and antenna. Theadditional display and the flip mechanism for the flip phoneconfiguration as well as the slide mechanism are special functions.

After all, the modularization of the mobile phone has beencarried out by applying the module configuration tool for theobligatory functional carriers. The optional functional carriers aremodularized manually. Hereby the GPS PCB and antenna arecombined to one module. The functional carriers with specialfunctions are included in separate modules. The generated moduleconfigurations of the mobile phone are merged to the final productstructure.

The product architecture is characterized by slot-modularity.That means the modules are assembled on the product platform,the main PCB, which is only possible in their designated positionand orientation. With respect to the requirement of realizing flip,slide and candy-bar configurations the modular product structurehas been altered. To allow the configuration of the slide phone the

functional and numerical keypads are located in different modulesand the LCD with speaker are placed in an additional module. Thefinal design of the modular mobile phone is illustrated in Fig. 4.

5. Summary and outlook

A life cycle oriented modularization methodology based onmodule drivers and specifications, supported by a moduleconfiguration software tool have been described. For an industrialclient the methodology was applied to develop a modular mobilephone. Hereby it could be learnt that the module configuration toolhas the potential to reduce development time and costs by multi-criteria modularization. The calculation of module configurationsaccording to different product scenarios by changing the entre-preneurial strategic target system offers the possibility ofgenerating and comparing solutions in a short time to check therobustness of a developed modular product for changing condi-tions in different markets.

The software tool is useful to support the designer in finding asuitable modular product structure by considering the providedset of module drivers and specifications. However, the moduleconfigurations with the highest benefit must not be the bestsolution, because of subjective effects by defining the targetsystem and not considered geometric relations.

Product modularization is a first step for designing sustainablevalue creating modules. Process, facilities, organization and humanlabour as further elements can be specified in similar schemes ofmodule driving parameters. Improvement for global sustainablenetworks can be supported in a framework of both cooperation andcompetition in entrepreneurial activity.

Acknowledgements

We express our sincere thanks to the Deutsche Forschungsge-meinschaft (DFG) for financing this research within the Colla-borative Research Centre 281 on Disassembly Factories for theRecovery of Resources in Product and Material Cycles.

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