a web-based system for reverse manufacturing and ...

A WEB-BASED SYSTEM FOR REVERSE MANUFACTURING AND PRODUCT ENVIRONMENTAL IMPACT ASSESSMENT CONSIDERING END-OF-LIFE DISPOSITIONS 1

H. C. Zhang’(2), J. Li’ , P. Shrivastava’ and A. Whitley’ Department of Industrial Engineering, Texas Tech University, USA 2 Dell Inc., Austin, Texas, USA Submitted by M. Eugene Merchant ( I ) , Techsolve, USA

Abstract Widespread usage of electronic equipment and shortened product life cycles have challenged original equipment manufacturers (OEMs) to handle End-Of-Life (EOL) product through environmentally benign reverse manufacturing and reusable resources recovery. This paper presents a web-based decision support and evaluation system for operations in remanufacturing and recycling including electronic product disassembly, materials recovery, and recycling management. An overall evaluation of the product’s lifecycle environmental impact considering EOL dispositions is also provided. The system has been tested by a major computer manufacturer with computer systems including desktop, laptop, and server. Comprehensive product analysis and environmental impact assessment are discussed in the paper. Keywords: Life cycle, Reverse Manufacturing, Decision-making

1 INTRODUCTION Widespread usage of electronic equipment and shortened product life cycles have resulted in a large amount of electronics destined for disposal. This end-of-life electronic product, electronic waste, is difficult to manage because of its complex construction and complicated material composition [I]. The decisions regarding the disposition of this EOL stream are very challenging to today’s industry. The operations related to the handling of E-Waste generally involve reverse manufacturing, which transforms the end of life product/assembly into its components. Other operations include various recycling processes that recover reusable materials from the separated components based on the material composition of the components. One concern with decision-making regarding reverse manufacturing is that knowledge of the environmental impact of the materials contained in electronic products is generally not available. From another point of view, product design and product evaluation also need information obtained from the reverse manufacturing and recycling processes, such as the disassembly and recycling techniques used in handling EOL products. This paper presents a web-based decision support and evaluation system for remanufacturing and recycling operations. Six functions are developed in order to support the decisions in electronic product disassembly, materials recovery, and recycling management. As a feedback to designers, product evaluation provides an overall score of the product’s lifecycle environmental impact considering end-of-life dispositions. This information may be used to improve product design, material selection and other considerations. The organization of the paper is as follows: Section 2, the methodologies used and developed in this research are discussed; Section 3, a web-based decision support system is introduced; Section 4, a case study of the computer is provided; and finally, conclusions are presented.

2

METHODOLOGIES

2.1 Automated disassembly analysis and reverse manufacturing scheduling The reverse manufacturing process generally starts with product disassembly, which is important to residual value recovery and reduction of environmental impacts as a result of recycling processes. Disassembly analysis [2, 31 in this regard, addresses three issues: (1) optimal disassembly strategy, (2) disassembly sequence planning, and (3) evaluation of disassembly time, cost, and disassembly difficulty rate, with component information provided. The disassembly relationships among the components of an EOL electronic product include component-fastener relationships and precedence relationships. These two graphs are required to fully represent the relationships among the components of an EOL product [4]. Fasteners are used to attach one component to another for the purpose of assembly. Examples of fasteners include screws, rivets, inserts, etc. In a componentfastener graph G,=(V,E), the components are represented as the vertices V={vl,v2, ....,v,}, where n is the number of components. Their relationships are represented as the edges E+el,e2,....,em},where m is the number of edges. If two components 4 and vj ( i # j) are joined by fasteners, then (vi,vj) E E; otherwise (vi,vj) E E. The graph Gc is an undirected graph. Vertices and edges in graph Gc are modeled using object-oriented techniques. While the object vertex consists of component information including its name, weight, material type, etc., the object edge consists of fastener information including the number of fasteners, fastener type, etc. For example, Figure 1 (a) shows componentfastener graph of a personal computer. The nodes representing computer components are labeled as: 1case, 2-driver case, 3-mother board, 4, 5, 6- extension card, 7-hard drive, 8-floppy drive, 9-1 0 socket, 1 1-power supply and 12- driver bay. A precedence graph represents the precedence relationship among the components of a product, namely, a component cannot be disassembled before certain other components. Figure 1 (b) shows the precedence relationship graph. As shown in (b), mother

board (node 3) has precedence relationships with node 2,4,5,6.

recycling. The cost model for determining the termination of disassembly is illustrated in Figure 3.

costl

f=f f+ffif3+f4

I

f Total cost f f : Disassembly cost fz : Material reprocessing cost f3:

Disposal cost

f4:

Salvage profit

00%

(a)

Figure 1 (a): Component-fastener graph for the assembly (b): Precedence relationship graph The disassembly tree can then be constructed based on the component-fastener graph and precedence graph. It consists of vertices representing an assembly or a component and information such as its name, material type and weightholume. A Vertex is decomposed into child vertices representing its child sub-assemblies or components. An edge, linking a child vertex with its parent vertex, represents the disassembly relationship between components and information about assembly method. The disassembly tree is generated through a search of cut-vertices in a component-fastener graph. A cut-vertex is a vertex whose removal disconnects the graph and splits it into two or more sub-graphs. The procedure is repeated until no cut-vertices can be found. In this way, a pseudo-disassembly tree is generated which is showed in Figure 2 a. The pseudo-disassembly tree is then modified by the precedence of the disassembly according to the precedence graph, and a disassembly tree obtained is as illustrated in Figure 2 b.

(a)

I\

(b) Profit

I

% of Disassembly

L

b

Figure 3: Optimal disassembly termination analysis The total cost is calculated as the sum of disassembly cost, material reprocessing cost, disposal cost, and salvage profit. The lowest point of the curve representing the total cost (f) determines the termination of disassembly where the cost is minimized, in other words, the benefit of disassembly is optimized. 2.2 Recycler selection and consideration of environmental performance All components that are not reusable must go into the recycling process or should be sent to downstream recyclers. The selection of recyclers (or recycling techniques) will not only affect the profit (or cost) of recycling but also the environmental impact of the EOL product. It is not realistic to generate a recycling plan for every single dismantled component, so the dismantled components are grouped into various component bins including printed circuit boards (PCBs), plastics, ferrous metal frames, nonferrous metals, glass/CRT, batteries, and others. These component groups are then treated by different recycling techniques. The resulting materials are sold to manufacturers or disposed of in a landfill or incinerated. Selection of an optimal recyclers or recycling processes for each component bin can be modeled as multiobjective decision-making. This involves ranking multiple alternatives according to the relative weights of their objectives. The least-squares fit (LSF) method is used to find the weight for each factor. The weight vector {W} can be obtained from the pairwise comparison data in the comparison matrix (CM). Assuming that for n criteria, the pairwise comparison of element i ( i=I,2,..., n) to element j ( j=1,2,..., n) has a numeric value called uij , the pairwise comparison matrix of criteria can be obtained as follows:

(b)

Figure 2 (a): Pseudo-disassembly tree (b): Disassem bly tree Optimal disassembly planning is determined based on the cost and profit. Three types of costs and one type of profit are addressed:(l) disassembly cost which includes labor and tooling cost, (2) material reprocessing cost, i.e. cost of recycling (3) disposal cost, which includes transportation and landfill costs, and (4) salvage profit, which is the profit gained by component reuse, resale or

(note that = uij = l / u j i ) The reasonable weight vector {W} can be obtained through LSF:

2

T x [ a i j i=l j > i

In these objectives, profit is one consideration that includes recycling cost and material quote price. The formula set for recycling profit is as following: Profit = Q P x Wt- [DC + IC + RPC

+ TC]

system to be seamlessly integrated with other systems such as CAD and PDM. Material information is stored in the Database. Based on the methodology discussed in previous sections, six functions are used for decision support in product disassembly, product recycling, material assessment, environmental impact assessment, product evaluation, and product and material information management.

(3)

where QP: the quote price in the market Wt: the weight of material recovered DC: disassembly cost IC: inspection cost RPC: recycling cost TC: transportation cost Other objectives of the selection problem include the recycling rates and environmental impacts of the recycling process itself. These decision-making factors have different units. It can be solved by minimizing the weighted Chebychev-Norm distance function [6] as follows: r

1

where wiis the weight of each factor calculated through the LSF method.

zmax is the ideal value, z,"'" is the nadir

value, and fi(x)is the objective function, i=1,2, ..., p, where p is the total number of objectives. A higher weight wi corresponds to a higher reluctance to deviate from the ideal value. Using the CM, the preferred recycler can be selected based on calculations performed by the method discussed. The results of these analyses can be synthesized and used to conduct design evaluations and suggest improvements. 3 THE WEB-BASED SYSTEM The web-based system is developed with Java Servlet and XML (extensible Markup Language). It has three-tier architecture and is illustrated in Figure 4. The "Product and Material Information Management" module provides information fusion of the data required by the system. It utilizes XML as its tree model in the description of the product structure. XML also enables the

Figure 4: System architecture The interface for the product recycling function is illustrated in Figure 5. Seven sub-functions are provided in this module. "Sorted component" function sorts the component of product to different component bins according to its material composition. It also selects the best recycler for each component bin. "Recoverable material" function estimates the materials that could be recovered from these sorted component bins. "Cost and profit" provides the economic analysis for the whole product. A score on product recycling is also given based on the recycle rate, cost and profit, recovered materials. "Report" function generates a comprehensive report that covers all the salient information related to product recycling. Details about other function modules are omitted here, but will be discussed in the case study.

Figure 5: Interface for the function of product recycling

4 CASESTUDY As a case study, a desktop computer was analyzed in this research using the system developed. Only a portion of the results are presented in this paper. The disassembly analysis is listed in Table 1. Table 1 : Disassembly analysis & disassembly sequence

Based on the performance in product disassembly, recycling and material the overall performance of the product can be estimated. Disassembly score, which ranges from 1 to1 00, is based on number of components disassembled, disassembly time and difficulty. Recycling score (1 to 100) is based on the recycling recovery rate. Material score (1 to 100) is computed according to material compatibility and hazardous materials in the product. Product Eco-indicator score is calculated from individual material eco-indicators. An overall product score is determined by aggregating all the scores. The results of this case study are listed in Table 5. Table 5: Product overall evaluation

Based on available recyclers and their recycling processes and environmental performance, an optimal recycler can be selected as listed in Table 2 and Table 3.

11.19

A portion of the material analysis is listed in Table 3. Table 3:Material report

5 CONCLUSION The web-based system developed in this research is a useful tool that could support information sharing over Internet by manufacturers, recyclers and government agencies. The system has been implemented and tested by several companies including reverse manufacturers and OEMs. It is proven to reduce environmental impacts by focusing attention on better product design, more effective recycling processes, and improved recycler selection. It can also help reverse manufacturers obtain increased profit by optimizing reverse production planning. 6 ACKNOWLEDGMENT This research was supported by the Texas Higher Education Coordination Board's Advanced Technology Program (ATP) award under grant contract #0036440241-2003.The authors would like to thank Dell for supporting the research in data collection. 7 REFERENCES [l] "Electronic Product Recovery and Recycling Baseline Report", National Safety Council, Washington DC, 1999. [2]Beasly D. and Martin R. R., 1993,Disassembly sequence for objects built from unit cubes. Computer-Aided Design,

25:751-761. [3]Zussman E., Kriwet

A. and Seliger G., 1994, Disassembly-oriented assessment methodology to support design for recycling. Annals of the CIRP, 43: 9-

14. [4]Zhang H. C., Kuo T. C., Lu H. and Huang S. H., 2000,

Eco-Indicator 99 [7] is used in evaluation of the environmental performance of the product design. The result is partially listed in Table 4. Table 4:Environmental performance (Estimated Values)

Disassembly analysis for electronic products: a graphbased heuristic approach. International Journal of Production Research, 38:993-1007. [5]Kroll E., Beardsley B. and Parulian A,, 1996, A methodology to evaluate ease of disassembly for product recycling. IIE Transactions, 28:837-845. [6]Lootsma, F. A,, 1997, Fuzzy Logic for Planning and Decision Making, Kluwer Academic Publishers. [7]"Eco-indicator 99 Manual for Designers", www.pre.nl. [8]Boothroyd G. and Alting L., 1992,Design for assembly and disassembly. Annals of the CIRP: 41,625-636. [9]Jovane F., Alting L., Armillotta A,, Eversheim F., Feldmann K., Seliger G. and Roth N., 1993,A key issue in product life cycle: disassembly. Annals of the CIRP, 42:

1-13.

[lo] Santochi, M.,

Dini, G., Failli, F., 2002, Computer Aided Disassembly Planning: State of the Art and Perspectives, Annals of the CIRP, ed. Hallwag, Berna, 51, 2 : 507-

530.