Process planning for IT-equipment remanufacturing

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    CIRP Journal of Manufacturing Science and Technology 2 (2009) 1320

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    Contents lists available at ScienceDirect

    CIRP Journal of Manufacturin

    .eing product quantities, types and conditions that are long associatedwithremanufacturingprocesses limit theentranceofnewactors intothe sector. Although planning decisions highly inuence theefciency of a production system carrying out remanufacturingoperations, decision support and planning tools, which are standardin assembly industries, are seldom available and applied. The needfor such tools is evident. Based on a market analysis and theidentication of actors that are aiming to extend their operations byestablishing remanufacturing processes as value adding processes,an integrated planning system is presented in this paper.

    2. Actors involved and task denition

    Actors involved in closed-loop-economy and their relation isgiven in Fig. 1, not considering legal aspects. The actors vary inaccess to product and material condition, amount and informa-tions about these. The following are identied as capable to extendtheir operations with remanufacturing oriented value addingprocesses: OEMs, suppliers, maintenance shops, existing rema-nufacturing companies, and partly recycling companies.

    These actors have in common the access to functional or non-functional products and components that are valuable enough to

    To what extent do I incorporate remanufacturing activities in myexisting facility/facilities?

    Which specic remanufacturing processes am I able to carry out? How much investment is needed in order to offer high qualityremanufacturing?

    What are my specic costs and revenues once the remanufactur-ing processes are operational?

    To answer these questions in a suitable manner, a three stepplanning approach has been developed, implemented in a softwaretool and applied to the example of at screen monitors remanu-facturing.

    3. Planning method

    The proposed approach involves three steps: the data analysis,the process design phase and the remanufacturing processoptimization of the remanufacturing tasks phase.

    3.1. Data acquisition

    The product and facility relevant data that are required for theproposed planning approach are determined and acquired.

    Data regarding the product need include the product structure,i.e. components and component groups, joining elements andtechniques, disassembly sequences, material ratios etc. and end-

    * Corresponding author.

    E-mail address: (S. Heyer).

    1755-5817/$ see front matter 2009 CIRP.doi:10.1016/j.cirpj.2009.07.003Process planning for IT-equipment rem

    Sebastian Kernbaum, Steffen Heyer *, Stylianos Ch

    Institute for Machine Tools and Factory Management, Technical University Berlin, Berl

    1. Introduction

    Reuse and Remanufacturing of Waste Electrical and ElectronicEquipment (WEEE) are a matter of current concern, driven byeconomic, ecologic, social and legislative factors. The potential thatlies in the reuse and remanufacturing of IT-equipment is not fullyexploited yet. Only a few specic products have been considered e.g. mobile telephones [14] and not all treatment opportunitiesavailable are applied. Moreover the nancial uncertainties concern-

    A R T I C L E I N F O

    Article history:

    Available online 21 August 2009



    Process planning

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    justify their upgrade, through some remanufacturing treatment, toa marketable state or condition.

    The same actors differ in their specic knowledge on theproduct itself, the products status and condition as well as theiroperational capability to bring it to a valuable condition. They alsodiffer in available equipment, processes and capacities, i.e. inremanufacturing capabilities. This raises the following questionsfor each specic actor:

    e design, evaluation and implementation of remanufacturing processes in

    escription of the market situation and involved actors, a planning method

    rocedures for product, process and facility are described. A mixed integer

    timization of a remanufacturing process and evaluation of its economic

    per describes the technical implementation, the software workow and

    roduct category Flat Screen Monitors.

    2009 CIRP.

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  • S. Kernbaum et al. / CIRP Journal of Manufacturing Science and Technology 2 (2009) 132014of-life data (disassembly times and costs and recycling quota). Forease of system integration, product models are developed usingthe commercially available software system ProdTect [7]. ProdTectis a software tool which supports the development of ecologicallysound products by providing information related to a productstreatment and recycling at an early product development stage [8].In the ProdTect product model input module, the productstructural information is composed of:

    Parts information, such as material composition, disassemblymovement, dimension, shape, accessibility.

    Connection information composed of the different joiningelements in the product.

    Priorities information, which gives an order of the parts insidethe product. A part is prior to another if it needs to be dismantledto get access to the other.

    ProdTect calculates technical, economic and ecological para-meters. The resulting data, such as disassembly times andsequence, can then be utilised for the planning of the end-of-lifeprocesses for a product [9]. An overview of the software toolProdTect is given in Fig. 2.

    Product accompanying information were analyzed and pre-pared for being used for the proposed planning approach.

    The next step involves acquiring data regarding the resourceand capacity planning of the given facility. Such data include theavailable installed capacity, the actual job schedule and theinventory levels and can be acquired from the ERP (EnterpriseResource Planning) system of the facility. Facility accompanyingdata were analyzed and prepared for application in the proposed

    Fig. 1. Complexity in replanning approach in accordance to the VDI 3633 guideline ([10],Fig. 3).

    3.2. Process design

    The second planning step is the development of the processmodel. The process model design determines all possiblesequences and types of remanufacturing steps that are requiredin order to process a batch of incoming products, e.g. testing,cleaning, disassembly, reassembly froma specic product type, screen monitors. The sequence is derived by conducting trialruns on a number of sample products. A graphical user interface(GUI) has been developed in order to assist the planner to visualizethe developed remanufacturing process in the form of a network.This network acts as the interface of the database that contains theproduct, process and facility information.

    Fig. 4 gives an overview of the structure in the example of atypical remanufacturing process. Products entering are rstexamined according to product relevant testing criteria. Basedon these tests, a list of failures can be documented for each specicproduct. These lists of failures need to be treated to bring theproduct back to a valuable conditionthey therefore createspecic remanufacturing paths for each single product in theoverall designed process network.

    Based on results of preliminary tests, treatment decisions aremade: if the amount of failures exceeds a threshold of acceptablefailures in the designed process, the product is sent to materialrecovery processes. In the case where a product is in a condition tobe sold to customers, only cleaning and packaging operations needto be carried out. If failures are worth to be treated, the product is

    manufacturing [6].

  • S. Kernbaum et al. / CIRP Journal of Manufacturing Science and Technology 2 (2009) 1320 15send to a rst disassembly operation. Information available fromProdTect (e.g. disassembly times and costs) is connected to thisoperation and further information needed for the planningapproach can be added by means of the GUI, e.g. stationassignments.

    3.3. Remanufacturing process optimization

    The objective of the third planning step is to determinewhethera batch of incoming products is to be commissioned forremanufacturing, i.e. whether the remanufacturing of a certainnumber of products of a certain type is of economical interest for agiven facility and to what extent the remanufacturing processeswill be carried out. This implies that there are a variety of optionsto be examined; fully refurbish, partly refurbish, recycle etc. Amixed integer optimization program (MIP) has been developed to

    Fig. 2. ProdTect overview.assess the economic feasibility of processing the batch of theincoming products under given capacity situation of the facility.The objective of the optimization is to maximize the prot ofremanufacturing the incoming batch under constraints of capacity

    Fig. 3. ERP system data structure.availability (workers and machines), operational costs, productow, product condition, inventory levels, transportation costs andadditional capacity investments that may be required. All relevantdata for the optimization model are provided from the productmodel, the process model, the ERP system of the facility and theinput of the planner regarding cost related parameters. Especiallyfor the condition of the incoming products, the planner can selectbetween using available historical data or an estimate based on hisown experience. A strategic decision of the available budget to beallocated for additional capacity investments needs to be takenbeforehand. Based on the solution of the model, the planner candecide whether the available batch of products is to be acquired ornot and determine the optimal number of steps of the remanu-facturing process.

    The remanufacturing process has been modelled in remanu-facturing stepswhich are arranged in seven categories Type (1, . . ., 7)respectively: test steps, reassembling, disassembling, steps thatrequire additional parts to be purchased and access to thewarehouse, sale steps after which products can be sold to generateincome, the entrance steps (product entrance) and nally generalremanufacturing steps. This categorization is executed by theplanner (the planner denes which steps belong to each category)at the beginning of the optimization and is required due to specialproduct ow constraints that accompany the different types ofsteps. In addition, it should be mentioned that our model does notdifferentiate between a product to be remanufactured, a part or acomponent.

    The following set notation is used in the remainder of the paper:

    I f1; . . . ; ig; i2N : remanufacturing step; (1)

    This set includes all remanufacturing steps. The various steptypes (and thus corresponding subsets) are dened with the use ofthe binary parameter:

    Type 1; . . . ;7i 1 if step ibelongs to category1; . . . ;70otherwise


    i2 i;(2)

    W f1; . . . ;wg;w2N workstations (3)

    The decision variables that are used are shortly explained:NPLij, NPTIi, NPTOi, i 2 I respectively denote the number of

    products that are between two remanufacturing steps i and j, thenumber of products at step i before performing the remanufactur-ing task and the number of products at step i after theremanufacturing task is performed. NPTSi stand for the numberof parts required from storage for step iwhere i 2 {i 2 I: Type4i = 1},NPGSi for the number of parts returned to the storage after step iand variables NPSFi denote the nal storage level after step i,where i 2 {i 2 I: Type4i = 1}. NPPi denote the number of additionalparts/components that need to be purchased for step i 2 {i 2 I:Type4i = 1}. Variables NNWSw illustrate the number of additionalworkers to be assigned to workstation w while NNSw the numberof newworkstations to be installed. Finally,NTi denote the numberof batches of parts/components to be purchased andNMCi are usedfor modelling convenience and stand for the number of maincomponents to be reassembled in a reassembly step. All decisionvariables are restricted to take values from the set of non-negativeintegers.

    The following parameters have been used in the model:

    PFBi; j 1 if the transition fromstep i to step j is allowed0otherwise


    i; j2 I;(4)

  • is the sale price of each product after completing step iwhere, CPNi


    S. Kernbaum et al. / CIRP Journal of Manufacturing Science and Technology 2 (2009) 132016BOMi 1=Xk1

    PFBk;i; 8 i2fi2 I : Type2i 1g; k2 IXj


    Parameter (4) indicates the allowed step sequences, i.e.whether the transition from remanufacturing step i to remanu-facturing step j is meaningful, while parameter (5) is used tomodelthe different ow conservation behaviors of the various remanu-facturing steps types. Some steps result in a change in the numberof product, i.e. a disassembly stepwould result in an increase in thenumber of products while a disassembly would result in itsdecrease thus different step types need to be addressed explicitlyin the model.



    NPTOi SalePiXw

    HRw Xi

    OPTi WCBi;w NPTIi 1 Type2i NPTOi Typ


    NNWSw NWSw 1 Lw CWw CapaW DD


    CSw NNSiXi

    NPPi CPNiXi

    CTN NTi

    8>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>:The objective function (6) maximizes prot, i.e. maximizes thesum of income from the process minus the sum of relevant costs. Pi

    ss design (simplied).the cost of purchasing a new part, CW the labour cost per workerper hour, HRw the machine hour rate for every workstationw, CTNithe transportation cost per batch of purchased parts for each step ithat requires parts to be purchased, NTi number of batches ofpurchased parts for each step i and CSw the cost of a newworkstation. The MIP model follows (6)(23):

    Subject to:

    NPTIi Xk1

    NPLk;i PFBk;i 8 i2fi2 I : Type6i 0g; k2 INPSIi; otherwise

    8>: (7)

    NPTOi NPTIi BOMi; 8 i2 I; (8)



    I;w2W (6)

  • S. Kernbaum et al. / CIRP Journal of Manufacturing Science and Technology 2 (2009) 1320 17Xi

    NPLi; j PFBi; j NPTOi NPTSi NPPi;i2fi2 I : Type4i 1andType5i 0g;

    NPTOi; i2fi2 I : Type5i 0g

    8>>>: 8 i; j2 I; (9)

    NPGSi NPTOi Xj

    NPLi; j NPTSi NPPi;

    8 i2fi2 I : Type4i 1g; j2 I; (10)

    NPPi MaxPPi; 8 i2 I; (11)

    NPLi; j NPLi; j PFBi; j 8 i; j 2 I I;NPLi; j NPTOi PTi; j; (12)

    8 i; j 2 fi2 I : Type1i 1g I;NMCi NPLk;i; (13)

    8 i; k 2 fi2 I : Type2i 1g fk2 I : Maink 1g;NPLk;i NMCi PEBk;i; (14)

    8 i; k 2 fi2 I : Type2i 1g I;NPLi; j

    NPTOi PFBi; jBOMi


    8 i; j 2 fi2 I : Type3i 1g I; (16)Xi

    OPTi WCBi;w NPTOi Type2i NPTIi 1 Type2i

    CapW DD NWSw NNWSw NWSw Lw; 8w2W ; i2 I; (17)

    NWSw NNWSw NESw NNSw MaxWSw; 8w2W ; (18)

    NPSFi NPSIi NPGSi NPTSi; 8 i2fi2 I : Type4i 1 andType6i 0g; (19)

    NPTSi NPSi; 8 i2fi2 I : Type4i 1g; (20)

    NTi MaxPTiNPPi; 8 i2fi2 I : Type4i 1g; (21)


    NPLi; j;NPTIi;NPTOi 2R: (23)The rst group of constraints (7)(16) addresses the ow of



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