SUSTAINABILITY ANALYSIS AND CONNECTIVE COMPLEXITY METHOD FOR SELECTIVE DISASSEMBLY TIME PREDICTION RAGHUNATHAN SRINIVASAN

Transcription

1 SUSTAINABILITY ANALYSIS AND CONNECTIVE COMPLEXITY METHOD FOR SELECTIVE DISASSEMBLY TIME PREDICTION By RAGHUNATHAN SRINIVASAN A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN MECHANICAL ENGINEERING WASHINGTON STATE UNIVERSITY School of Mechanical and Materials Engineering DECEMBER 2011

2 To the Faculty of Washington State University: The members of the Committee appointed to examine the thesis of RAGHUNATHAN SRINIVASAN, find it satisfactory and recommend that it be accepted. Gaurav Ameta, Ph.D., Chair Jitesh H. Panchal, Ph.D. Uma Jayaram, Ph.D. ii

3 ACKNOWLEDGEMENTS This work would not have been possible without the constant support and guidance of my mentor, Prof. Gaurav Ameta. I thank him profusely for providing me with the best environment to work. I am grateful to him for giving me the freedom to explore and the excellent opportunities to learn and grow as a researcher. I would like to thank my committee members, Dr. Jitesh H. Panchal and Dr. Uma Jayaram for sparing their valuable time to interact with me and for sharing their inputs and feedback. I am grateful to them for accommodating my requests and deadlines. I would like to thank all the members of the Sustainable Product Lifecycle Design Lab and Collective Systems Lab at Washington State University. Thanks to He Huang, Martin Baker and Bryant Hawthrone it was an enriching and learning experience working with you. I would like to specially thank the faculty and staff of the School of Mechanical and Materials Engineering for funding my education through a Teaching Assistantship. I also thank them for all their support and effort to make my academic life a pleasant and memorable one. I would like to thank my brother Raghavendiran Srinivasan who is the constant source of encouragement for all the work I do. Thanks to all my friends for supporting me all through these years. Last but not the least; I would like to thank my parents Jayalakshmi and Srinivasan who are the key to success in every stage of my life. iii

4 SUSTAINABILITY ANALYSIS AND CONNECTIVE COMPLEXITY METHOD FOR SELECTIVE DISASSEMBLY TIME PREDICTION Abstract by Raghunathan Srinivasan, M.S. Washington State University December 2011 Chair: Gaurav Ameta The two main objective of this thesis are: 1) to develop a disassembly and selective disassembly time prediction methodology and, 2) to evaluate the use of environmental impacts of components in the selective disassembly time prediction method. Disassembly time is very critical as it impacts the planning and costs at the end of life of a product. Thus, disassembly time has direct effects on the decisions and activities related to recycle, reuse, remanufacture and disposal of a product. The disassembly time prediction method first utilizes the assumption that disassembly is the inverse of assembly and second uses the assembly time prediction method. The assembly time prediction method is based on the use of complexity metrics derived from assembly graph and bipartite graph of a product. The notion of selective disassembly implies disassembling a product in order to retrieve only a certain number of parts and not disassembling the other components. There could be many applications for selective disassembly iv

5 from disassembly for material recovery, parts reuse and remanufacturing to reduction in environmental impacts associated to disposing a hazardous component. The determination of selective disassembly time is based on recovering most material for recycling. The assembly graph for a product is re-organized to group together parts that are close and are of same material. The modified assembly graph is then used to compute the selective disassembly time. Although, the method developed targets material recovery for recycling, it can be used for parts recovery for reuse, remanufacturing or other such purposes. One of the widely used methodologies to assess the environmental impacts of a product is called Life Cycle Assessment (LCA). LCA is applied to selective components of the case studies (i.e. standard toaster and the eco-friendly toaster) using SIMAPRO 7 to calculate the environmental impacts. The environmental impacts of the selected components can be further utilized for decision making and planning regarding selective disassembly. v

6 TABLE OF CONTENTS ACKNOWLEDGEMENTS... iii Abstract... iv LIST OF TABLES... viii LIST OF FIGURES... ix Chapter 1 - Introduction Background Product Life Cycle Design phase Raw material phase Life Cycle Assessment Disassembly Problem Statement Outline... 9 Chapter 2 - Literature review Disassembly Modeling Assembly and Disassembly time estimation Life Cycle Assessment Chapter 3 Life Cycle Assessment of the toasters based on selective components for recycling Background Disassembly and Selective disassembly Components investigated Life Cycle of a Toaster Use Phase Energy Calculation Impact Assessment Methodology Using SIMAPRO Chapter 4 Assembly Time calculation using Connective Complexity Matrices method Complexity design Complexity Metrics Methodology vi

7 4.3.1 Assembly Graph Shortest Path Length Path Length density Disassembly time Selective Disassembly time prediction Chapter 5 Case studies Case Study 1: Standard Toaster Standard Toaster Components Bipartite Graph for a Standard toaster Assembly graph and disassembly time calculation before material-wise separation The total disassembly time for the standard toaster is estimated as 197 seconds Assembly graph and disassembly time calculation after material-wise separation Case study 2 Eco-Friendly toaster Eco-friendly Toaster - Components Bipartite Graph of an eco-friendly toaster Assembly graph before material-wise separation Assembly graph and disassembly time calculation of an eco-friendly toaster after material-wise separation Results Chapter 6 Conclusion and Future Work Contributions Limitations Future Work References vii

8 LIST OF TABLES Table 1 Weight of the Components Table 2. Use Phase energy in KWh Table 3 Disassembly time calculation before material separation Table 4 Disassembly time calculation after material separation Table 5 (a) Disassembly time calculation of a standard toaster before material separation Table 5 (b) Disassembly time calculation of a standard toaster before material separation Table 5 (c) Disassembly time calculation of a standard toaster before material separation Table 6 (a) Disassembly time calculation of a standard toaster after material separation Table 6 (b) Disassembly time calculation of a standard toaster after material separation Table 6 (c) Disassembly time calculation of a standard toaster after material separation Table 7 (a) Disassembly time calculation of an eco-toaster before material-wise separation Table 7 (b) Disassembly time calculation of an eco-toaster before material-wise separation Table 7 (c) Disassembly time calculation of an eco-toaster before material-wise separation Table 8 (a) Disassembly time calculation of an eco-toaster after material-wise separation Table 8 (b) Disassembly time calculation of an eco-toaster after material-wise separation Table 8 (c) Disassembly time calculation of an eco-toaster after material-wise separation Table 9 Disassembly time results viii

9 LIST OF FIGURES Figure 1 A typical product life cycle showing stages of assembly and disassembly..2 Figure 2 Components investigated - standard toaster 16 Figure 3 Components investigated eco-friendly toaster.16 Figure 4 Life Cycle of a Toaster 17 Figure 5 Experimental Setup.19 Figure 6 Network diagram of LCA of Standard toaster using Simapro 7.22 Figure 7 Network diagram of LCA of eco-friendly toaster using Simapro 7 23 Figure 8 Weighting for Standard toaster 24 Figure 9 Weighting for eco-friendly toaster..24 Figure 10 Environmental impacts of standard and eco-toasters 25 Figure 11 Assembly graph before material-wise separation.27 Figure 12 Bipartite graph...29 Figure 13 Assembly graph after material-wise separation 32 Figure 14 Outer Casing, Inner Casing, Heating Element, Wire Mesh..34 Figure 15(a) Bipartite graph of a standard toaster.37 Figure 15(b) Bipartite graph of a standard toaster...38 ix

10 Figure 15(c) Bipartite graph of a standard toaster.39 Figure 16 Assembly graph of a std. toaster before material-wise separation 40 Figure 17 Assembly graph of a std. toaster after material-wise separation..45 Figure 18 Outer Casing, Inner Casing, Heating Element, Wire Mesh of eco 49 Figure 19a) Bipartite graph of an eco-friendly toaster...53 Figure 19(b) Bipartite graph of an eco-friendly toaster.54 Figure 19(c) Bipartite graph of an eco-friendly toaster.55 Figure 19(d) Bipartite graph of an eco-friendly toaster.56 Figure 20 Assembly graph of an eco-toaster before material-wise separation.. 57 Figure 21 Assembly graph of an eco-toaster after material-wise separation.63 x

11 DEDICATION To my maternal grandparents, my mother Jayalakshmi, my father Srinivasan and my brother Raghavendiran Srinivasan. xi

12 Chapter 1 - Introduction 1.1 Background In a country with a population of about 300 million and counting, on an average, each person generates about five pounds of waste every day. In the year 2008 alone, the U.S. produced 254 million tons of solid waste of which more than a third was recycled or recovered [1]. Most of the solid waste ends up in landfills and the rest gets recycled through community recycling programs or through natural cycles. Also, the manufacturers should retake the product at its end-of-life (EOL). The manufacturers should try to figure out which EOL option can be more beneficial to the company and the environment. One way of doing the take back of products is by implementing strict legislative measures by the government. 1.2 Product Life Cycle Every product has its own life cycle. May it be a screw or an airplane, each product passes through five major phases known as the product life cycle. They are the design phase, raw material phase, the manufacturing phase, the use phase and the end-of-life phase. Figure 1 represents a typical product life cycle showing stages of assembly and disassembly. 1

13 Design Phase Raw Material Phase Recycle Manufacturing and Assembly Phase Remanufacture Use Phase Reuse End-of-life Phase Disassembly Disposal Figure 1 A typical product life cycle showing stages of assembly and disassembly. 2

14 1.3 Design phase The design and planning phase is where each and every component of a product is designed based on the data provided by the manufacturer and based on the customers requirements. There are many constraints like cost, tolerance, etc. involved while designing a product. The design team also collects feedback and suggestions from the manufacturing team regarding the possibility of manufacturing a product based on the design plan developed by the design team. Based on these feedbacks the design team modifies the design or creates a new design that can be manufactured more efficiently according to the requirements. So, this design phase play a key role in the product life cycle. 1.4 Raw material phase The raw material phase includes the gathering of the required raw materials from various suppliers and these raw materials are stored in storage houses in the manufacturing plant before processing. Some of these raw materials include hazardous materials or chemicals. These materials are safely transported to the storage houses. Once all the raw materials are in place, the manufacturing phase can begin Manufacturing and assembly phase These raw materials are transported to the shop floor of the manufacturing plant where these raw materials undergo various manufacturing processes to obtain each component of the product. Also these components are assembled 3

15 to form sub-assemblies and these sub-assemblies are combined to form the final assembly. Each manufacturing plant has its own predefined way of manufacturing and assembling a product which are based on constraints like time to assemble, ease of manufacturing and assembling, etc. When the final product is assembled it is then shipped to the quality control department where the products are inspected for any defects, after which these products are sent to the packaging department where these products are packaged and shipped to the consumer market Use phase The use phase includes the duration in which the consumer utilizes a product either for a household or business. These might also include the use of electrical or mechanical energy to use the product. The manufacturer also specifies a warranty for each product. The product is supposed to reach its end-of-life at the end of warranty provided by the manufacturer. Most products tend to last long than the warranty provided by the manufacturer. But products do tend to die before its warranty. Once the product stops functioning the way it is supposed the function then it is said to have reached its end-of-life End-of-life phase Once the products end-of-life is reached, the end-of-life (EOL) decisions have to be made. The possible EOL options include recycle, reuse, remanufacture and disposal. The product can be disassembled to recover 4

16 components or materials and this product or its components can be recycled or reused or remanufactured and the rest of the components can be disposed as landfill. These EOL decisions have to be wisely chosen in such a way that it s beneficial to the environment, manufacturer and the society. 1.5 Life Cycle Assessment One of the widely used methodologies to assess the environmental impacts of a product is called Life Cycle Assessment (LCA). LCA is a cradle to grave approach for assessing the environmental impacts of a product. The cradle to grave approach includes raw material phase, manufacturing and assembly phase, use phase and end-of-life phase. The United States Environmental Protection Agency defines a Life Cycle Assessment (LCA) as an objective process used to evaluate the environmental burdens associated with a product, process or activity by identifying and quantifying energy and materials used and wastes released to the environment, and to evaluate and implement opportunities to affect environmental improvements [1]. Life Cycle Assessment (LCA) can also be defined as a collection and estimation of the inputs, outputs and the possible environmental impacts of a product system throughout its life cycle [2]. Life Cycle Assessment (LCA) attempts to quantify the environmental impacts over the entire life-cycle of a product from its raw material extraction, manufacturing and assembly, and use phase to ultimate disposal [3]. 5

17 1.6 Disassembly In a product recovery environment, there are several situations where a product may be disassembled for economic and regulatory reasons. The main aim of a manufacturing system is to develop methods for manufacturing new products from the conceptual design to final deliverance, and ultimately to the end-of-life and disposal such that the environmental standards and requirements are satisfied. On the other hand, the amount of waste sent to landfills can be minimized by recovering parts or materials from old or outdated products by means of disassembly, remanufacturing and recycling, termed as product recovery. The objective of recycling is to recover as much material as possible from the retired products by performing the necessary disassembly, sorting, and physical and/or chemical separation. However, in the case of remanufacturing, the product s identity is preserved and also performs the required disassembly, sorting, refurbishing and assembly operations to bring the product to a desired level of quality. While the material and product recovery is feasible by allowing selective separation of desired parts and materials by disassembling the product [4]. Typical objectives of disassembly may include; recovery of valuable parts or subassemblies, parts or components that can be reused in the production of a new product, 6

18 retrieval of parts or subassemblies of discontinued products to suit a sudden demand for these parts, removal of hazardous subassemblies or parts, increasing the purity of the remainder of the product for the purpose of chemical reclamation, decreasing the amount of waste being sent to landfills, and achieving environmentally friendly manufacturing standards like successfully implementing the required ratio of using recycled parts to using new parts. Although, disassembly highly facilitates to the success of product recovery, it is an expensive process. Therefore, the disassembly has to be performed in a cost-effective manner. Already many researchers have focused on minimizing the resources invested in the disassembly process. To keep the profitability and environmental features of the product recovery process at a desired level some researchers have focused on the disassembly leveling problem which targets the disassembly level to which the product of interest is disassembled [5-7]. While other researchers focus on the generation of efficient disassembly sequencing plans (DSP). A disassembly sequencing plan is a sequence of disassembly operations that aide in feasibly disassembly of a product and terminates in a state where all of the parts/components are disconnected from one another. This can either be a partial disassembly or a complete disassembly. An efficient DSP can minimize the cost of disassembly process. Various researches have been done 7

19 in the area of disassembly sequence planning using graph theory, heuristics and Petri nets [9-17]. 1.7 Problem Statement Disassembling the whole product at EOL is influenced by time constraints, cost constraints and also based on the condition of the product after usage. So, in order to achieve an effective disassembly the manufacturer must figure out whether the complete disassembly of the product is needed for a product or not. If the cost and time to disassemble the whole product and recovering the material tends to end up in not making a profit then the complete disassembly principle is of no use to the manufacturer. However, the manufacturer can still apply the selective disassembly principle by which they can selectively disassemble few components or sub-assemblies thereby minimizing the manpower and time incurred for total disassembly, and also more material might be recovered from these selected components that can be reused or remanufactured while the rest of the product can be disposed. In this method of applying this selective disassembly principle based on size and weight the manufacturer can profit in material recovery and at the same time the junk being disposed as landfill can be reduced in huge amounts every day. This research proposes a method to calculate the assembly time based on complexity matrices to two toasters and a possible generalized methodology for applying to other possible products based on connectivity between the parts or components of a product. Also, LCA was performed on selective 8

20 components of the two toasters where the selection of components was based on weight and size. 1.8 Outline Chapter 2 includes the literature review. Chapter 3 provides the LCA of the Toasters based on selective components for recycling. Chapter 4 explains the methodology for selective disassembly of a product. Chapter 5 presents the application of this methodology to a case study of comparing two toasters (standard and an eco-friendly toaster). Chapter 6 gives the conclusion and future work of this research. 9

21 Chapter 2 - Literature review Some of the better alternatives for reducing the environmental problems resulting from the huge amounts of waste currently arriving at landfills are to recycle the products and components of these products. Further, the success of these alternatives varies based on the product esp. due to the difficulty in obtaining efficiency and also repairing or refurbishing [18]. When reuse, remanufacturing or repair are not competitive, in most cases the product is shredded in order to recover some value from material recycling or disassembling the product in order to carry out re-use or recycling of individual components. Although shredding is less time-consuming, disassembly seems to be much more interesting from the environmental perspective. Disassembly allows the separation of high recovery value or hazardous components and also the reuse or remanufacturing of individual components, thus avoiding waste generation [19]. Disassembly plays a key role when trying to select a product at the end of life (EOL). On one hand, it is essential to ensure the required purity of recycled materials by separating components made up of different materials so that they can be accepted by secondary manufacturers [20]. On the other, it is needed to release components and subassemblies susceptible to repair, re-use or remanufacturing [21]. Major research efforts in EOL practices focus on the field of disassembly because the approaches within this field of work basically differ with respect 10

22 to the kind of problem they address [22]. Also, it depends on the way of modeling the problem, and the techniques used for solving the problem. 2.1 Disassembly Modeling Regarding the modeling methods, three main approaches can be found in the literature for describing the disassembly process: 1. And/or graphs [23], 2. State diagrams [25] and 3. Disassembly precedence graphs [26]. The AND/OR graph lessens the number of nodes in the depiction of all possible plans and provides the basis for planning by tree search. The AND/OR graph representation is useful in assembly planning where it covers all possible partial arrangements of assembly operations with a reduced number of nodes. The ongoing researches focus on the construction of the AND/OR graph that will have the ability to find all connected stable subassemblies and all physically feasible disassembly operations of a given assembly. In the case of state diagrams, the assembly sequences are represented as paths through a network of assembly states which acts as nodes and the assembly moves are shown by arcs. A more vital improvement was the use of precedence diagrams for the representation assembly and disassembly plans, where the search space of a 11

23 disassembly precedence graph is large, but that technique has limitations such as it allows only a small amount of flexibility which is typically related to its number of components. 2.2 Assembly and Disassembly time estimation The main objective of design for assembly (DFA) is to create a design solution that will make the assembly process of a product more simple and feasible. In the 1960 s, many companies succeeded in developing handbooks for designers which helped in creating parts for manufacturing ease [27]. The advantage of using these design manuals was to facilitate and assemble many simple parts, focusing on making the method of manufacturing cheaper. However, this was before performing analyses both theoretically and experimentally on the assembly time of the parts based on the effects that part features had on these parts [28]. From such studies, a DFA Methodology was developed by Boothroyd and Dewhurst [29-31], which helps in comparing and rates the productability of various designs [32]. Minimizing the assembly times and costs based on minimizing the number of individual parts was addressed by the Boothroyd and Dewhurst DFA method [30], also individual part design was optimized for the ease of handling and joining [33]. But the Boothroyd method is tedious. Many high end manufacturing companies have their own customized DFA methods like Texas Instruments, Ford Motor Company, General Motors and Motorola [28]. 12

24 All these DFA processes discussed here are used towards the end of the design process and they don t account for the effective disassembly planning during the design stage which can beneficial towards the end-of-life of a product. However a methodology using the assembly graphs and bipartite graphs in computing the selective disassembly time has not yet been developed. 2.3 Life Cycle Assessment ISO describes LCA as a tool that helps in comprehending effectively and addressing the environmental impacts associated with products and services. LCA can also be applied to evaluate the impact of the energy and materials used and released into the environment. LCA can also be used to identify and evaluate the possibilities for environmental improvement [34]. Identifying the environmental burdens during each phase of the whole product life cycle can help in reducing the environmental impact, such as global warming, and ozone problems which can be achieved using LCA [35]. The main advantage of using LCA in disassembly is because it emphasizes that products must be produced, distributed, used and disposed of or recycled without harming the environment in any phase [36]. 13

25 Chapter 3 Life Cycle Assessment of the toasters based on selective components for recycling 3.1 Background In a country with a population of about 300 million and counting, on an average, each person generates about five pounds of waste every day. In the year 2008 alone, the U.S. produced 254 million tons of solid waste of which more than a third was recycled or recovered [37]. Most of the solid waste ends up in landfills and the rest gets recycled through community recycling programs or through natural cycles. Strict legislative measures should be implemented by the government so that the manufacturers should retake the product at its end-of-life and try to figure out which EOL option can be more beneficial to the company and the environment and thereby implementing it. 3.2 Disassembly and Selective disassembly Disassembling the whole product at EOL is influenced by time constraints, cost constraints and also based on the condition of the product after usage. So, in order to achieve an effective disassembly the manufacturer must figure out whether the complete disassembly of the product is needed for a product or not. If the cost and time to disassemble the whole product and recovering the material tends to end up in not making a profit then the complete disassembly principle is of no use to the company. However, the company can still apply the selective disassembly principle by which they can selectively disassemble few components or assemblies thereby they don t spend their manpower in 14

26 total disassembly, and also they might recover more material from these selected components that can be reused or remanufactured while the rest of the product can be disposed. In this method of applying this selective disassembly principle based on size and weight the manufacturer can profit in material recovery and at the same time the junk being disposed as landfill can be reduced in huge amounts every day. So, in this chapter, the possibility of applying the selective disassembly principle to the two toasters is investigated. Here this selective disassembly is implemented to components that are large and heavy and those which provide the possibility for more material recovery at EOL. 3.3 Components investigated The major components of the standard and eco-friendly toasters that are investigated include the outer casing, inner casing, heating elements and wire mesh. These components are shown in the figure below and their corresponding weights are tabulated. 15

27 Figure 2 a) Outer Casing, b) Inner Casing, c) Heating Element, d) Wire mesh Figure 3 a) Outer Casing, b) Inner Casing, c) Heating Element, d) Wire mesh Table 1 Weight of the Components Components Number of Components Standard Toaster (grams) Eco-Toaster (grams) Outer Casing Inner Casing Wire mesh Heating plate Total

28 3.4 Life Cycle of a Toaster Figure 4 Life Cycle of a Toaster Figure 4 presents a simplified schematic of the life cycle of a toaster. It includes the design phase, raw material phase, manufacturing and assembly phase, use phase and End-of-life. In the design phase the complete design specifications of each component is specified by the design team which also includes the tolerance specifications. In the next stage, i.e., the raw material phase, where these raw materials are brought in from a storage plant and they undergo various manufacturing processes like forging, casting, etc. to form each component which is assembled based on the design specifications in the manufacturing and assembly phase. Hazardous wastes and industrial wastes maybe generated during this manufacturing and assembly phase. Most of these hazardous and industrial wastes are usually drained in the neighboring 17

29 lakes or rivers which might cause severe damage to the marine habitat in that area. Next phase is the use phase, where the consumer s utilization of this product in his/her day to day routine which also causes air emissions. The final phase is the End-of-life phase, where the end-of-life (EOL) decisions such as recycle, reuse, remanufacture or disposal are made according to the cost and environmental constraints. 3.5 Use Phase Energy Calculation Three different situations were analyzed in this study. First, the standard toaster was experimented with two sets of bread (two slices in each set). Then, the eco-friendly toaster was experimented with its lid in open condition with similar sets of bread. Finally, the eco-friendly toaster was tested with its lid in closed condition with similar sets of breads. The time taken to toast was noted in all these three cases at the maximum and minimum positions of the knob and the time taken to toast was tabulated. Using this data from time taken to toast and the wattage readings the energy consumption of each toaster is found by using the formula,..(1) Where, E is the Energy Consumed, T is the time to toast, and W is the wattage value specified by the manufacturer. 18

30 Stop Watch Figure 5 Experimental Setup The wattage values specified by the manufacturer are 950 W and 900 W respectively for the standard and the eco-friendly toaster. All experiments were conducted using the electricity mix available in Washington State. The experimental setup is shown in Figure 5. The electricity mix is supplied to the toaster for the experiment from an electricity outlet available in the lab. To compare and calculate the energy efficient toaster, the recorded values were tabulated as shown in Table 2. Based on the preliminary study of use phase impacts, 6 trial readings were recorded and the average of the six values is tabulated as in Table 1. From Table 1, it can be concluded that the Eco- Closed lid is more eco-friendly with less energy usage compared to Eco-Open lid and Standard toaster. The standard toaster is more eco-friendly with less 19

31 energy used than Eco-Open lid. Also, In the case of a standard toaster, there is comparatively more heat loss than the eco-friendly toaster. This is due to the absence of lids in the standard toaster. These lids in the eco-friendly toaster help to minimize heat dissipation. It is important to note that the maximum and minimum level of toasting, in both the toasters, is assumed to be same. Table 2. Use Phase energy in KWh Type/Model Position Time to toast (s) Energy in KWh Oster Minimum 71 67,450 Oster Maximum ,400 Eco-Open lid Minimum 91 81,900 Eco-Open lid Maximum ,000 Eco-closed lid Minimum 72 64,800 Eco-closed lid Maximum , Impact Assessment Methodology Environmental impacts have gained high importance in manufacturing sectors due to legislative pressures to protect the environment and to upgrade their products in an environmentally conscious way [38]. Therefore, identifying factors that have a major influence on the environmental impact of the product is very important. Eco-indicators should be used as problem 20

32 pointers to indicate the order of magnitude of impact effects and to enlighten critical issues Using SIMAPRO This study is focused on the eco-indicator 99 method to compare various features of eco-friendly and standard toasters. Figure 8, 9 and 10, shows the environmental impacts of the standard and the eco-friendly toaster. This is calculated by applying eco-indicator method using SimaPro 7. These single core graphs clearly show that the standard toaster has higher environmental impacts than the eco-friendly toaster. One of the main environmental impact factors is the use of fossil fuels. 21

33 Figure 6 Network diagram of LCA of Standard toaster using Simapro 7 22

34 Figure 7 Network diagram of LCA of eco-friendly toaster using Simapro 7 23

35 Figure 8 Weighting for Standard toaster Figure 9 Weighting for eco-friendly toaster 24

36 Std Eco Carcinogens 2.Resp. inorganics 3.Climate change 4.Radiation 5.Ecotoxicity 6.Minerals 7.Fossil fuels Figure 10 Environmental impacts of standard and eco-toasters Figures 8 and 9 show how the two toasters affect the environment based on the carcinogenic effects produced, the fossil fuels generated, and the acidification rate. It also describes how it affects the ozone layer. Further, from Figure 10, we refer that the overall impacts reach 900 pt in the case of a standard toaster, while the overall impact is 500 pt in the case of an ecofriendly toaster. This result is of greater significance, since it describes how effective is the impact of standard and eco-friendly toasters on the environment and also why eco-friendly toasters are better than standard toasters. 25

37 Chapter 4 Assembly Time calculation using Connective Complexity Matrices method 4.1 Complexity design A design could be very complicated to create, but if it was quick to develop, economical to make, and flawless in performance then there would be no need to worry about its complexity. However, this also depends on the processes involved in making the product [43]. The complexity of a design increases the costs involved in manufacturing and makes it more prone to failure [44]. However, at the same time exceedingly simple designs can be completely spiked by a minor failure. As each component of a product might have multiple connections between the other components or subassemblies, the methodology described below is helpful in addressing the product which has components with multiple connections between them. 4.2 Complexity Metrics Most previous approaches to engineering design complexity have focused on addressing a single representation within a constrained set of conventional linking properties. One approach, proposed by [43], is capable of addressing multiple representations by translation through bi-partite graphs. However, this approach does not address the effects of directionality on the system. Therefore, there exists a need for complexity metrics which can address multiple aspects of complexity within a mixed graph environment. 26

38 4.3 Methodology In this methodology, the product under study has 15 components/parts namely part B, part C, part D, part E, part F, part G, part H, part I, part J and part K, part L, part M, part N, part O, part P which are assembled to form the whole product A as shown in the assembly graph below Assembly Graph Figure 11 Assembly graph before material-wise separation 27

39 This assembly graph is used in calculating the number of relationships between each component with the other components which helps in calculating the disassembly time. The bipartite graph here is used for individual representation of the instances that connect the products with one another and they are separately shown based on each manufacturing and assembly instance by the graph which has the products/components on one side and their connecting instances on the other side. 28

40 Figure 12 Bipartite graph Shortest Path Length Path length measurements are based on the number of relationships which must be passed through to travel from one element to another [40,41]. For example, to travel through the system A>B>C from A to C is a path length of 29

41 2. Here, we focus on the measurement of the shortest available path between any two elements in the system. Total Path length denoted by TPL, is the sum of all the shortest path lengths in the system. Average Path length (APL) is determined by dividing the total path length by the product of total number of components in the system and the total number of components in the system minus the empty identity (2) Where n is the total number of components in the system Path Length density Path length density, also known as PLD is derived from average path length by dividing the APL by the number of relationships in the system....(3) Where N is the total number of relationships in the system Disassembly time The disassembly time is calculated using the formula, t d PLD = APL n...(4) Where t d, is the disassembly time. 30

42 This equation has been developed by [44] for predicting the assembly time. The equation has been found to estimate assembly time within 16% of the assembly time as computed through the Boothroyd and Dewhurst method. Disassembly is usually considered as the inverse of assembly. By utilizing the assumption that disassembly is the inverse of assembly, in this research we have used the equation (4) for disassembly time prediction. Table 3 Disassembly time calculation before material separation PA PB PC PD PE PF PG PH PI PJ PK PL PM PN PO PP PA PB PC PD PE PF PG PH PI PJ PK PL PM PN PO PP Selective Disassembly time prediction After identification of materials, a new assembly graph is drawn to calculate the Path Length, Path Length Density and the Disassembly time based on material-wise separation. 31

43 Figure 13 Assembly graph after material-wise separation Here the focus is on material T5 which needs to be recovered. The disassembly is performed based on recovering more amount of material T5 which is the needed material that can be recycled, reused or remanufactured. This helps in reducing the manufacturing time and cost of this material T5 which is required for manufacturing a new product which uses the same material/component. Materials T2 and T3 are unwanted or materials that have to be disposed in a landfill and the components that contain these materials need not be disassembled which will minimize the disassembly time further and help in recovery of more material T5. 32

44 Table 4 Disassembly time calculation after material separation PA PB PC PD PE PF PG PH PI PJ PK PL PM PN PO PP PA PB PC PD PE PF PG PH PI PJ PK PL PM PN PO PP Based on the above described methodology the material T5 is recovered to a more extent in this case compared to the previous disassembly methodology and at the same time the disassembly time is also minimized because of not wasting time with disassembling the unwanted components. This same methodology is applied to the case study of two toasters in the next chapter. 33

45 Chapter 5 Case studies This chapter will present case studies demonstrating the selective disassembly methodology. The case studies selected are two toasters. The first one is a standard oster toaster model number #6325. The second one is EcoToaster model number #TE Case Study 1: Standard Toaster This section will describe the main components of the standard toaster, creation of bi-partite graph, assembly graph, total disassembly time estimation and selective disassembly time computation for the standard toaster Standard Toaster Components There are 32 components in the standard toaster as listed below and some of the components are shown in the figure 14. Figure 14 Outer Casing, Inner Casing, Heating Element, Wire Mesh 1) Casing A 2) Handle 1 3) Screw 1 4) Screw 2 34

46 5) Heating Element 1 6) Heating Element 2 7) Heating Element 3 8) Slide 9) Inner Casing base plate 10) Back Plate 11) Front Plate 12) Side Plate 1 13) Side plate 2 14) Bread Support Plate 15) Rod 1 16) Rod 2 17) Part-E 18) Slides & Hotches 19) Small spring 1 20) Small spring 2 21) Large spring 35

47 22) K plate 23) L plate 24) J plate 25) Handle 2 26) Bottom B 27) Slider C 28) Slider base D 29) Light 30) Switch 31) Knob 32) Electronic component Bipartite Graph for a Standard toaster The 32 components and their assembly are then used to create assembly and bipartite graphs. The bipartite graph is used in calculating the number of relationships (i.e, connection instances) between each component with the other components. The bipartite graph is shown in Figure 15 and represents the components of a standard toaster on one side and their connecting instances on the other side. Different types of assembly instances in the 36

48 standard toaster are bolting, press fit, sliding, welding, snap fit and series connection. Figure 15(a) Bipartite graph of a standard toaster 37

49 Figure 15(b) Bipartite graph of a standard toaster 38

50 Figure 15(c) Bipartite graph of a standard toaster 39

51 5.1.3 Assembly graph and disassembly time calculation before material-wise separation Now the assembly graph is drawn (Figure 16) which helps in calculating the shortest path between one component with the rest of the components. The shortest path is used in the calculation of the Total Path Length, Average Path Length, Path Length Density and Disassembly time as described in Chapter 4. Figure 16 Assembly graph of a standard toaster before material-wise separation 40

52 Then, the total disassembly time is estimated by creating a matrix (Table 5) and computing TPL, APL and PLD, as described in Chapter 4. Table 5 (a) Disassembly time calculation of a standard toaster before material separation CA H1 S1 S2 H.1 H.2 H.3 Se IC BP FP SP1 CA H S S H H H Se IC BP FP SP SP BSP R R P-E S&H S.Sp S.Sp L.Sp KP LP JP H BoB SC SBD Light Switch Knob E.C

53 Table 5 (b) Disassembly time calculation of a standard toaster before material separation SP2 BSP R1 R2 PE S&H SS 1 SS 2 LS KP LP JP CA H S S H H H Se IC BP FP SP SP BSP R R P-E S&H S.Sp S.Sp L.Sp KP LP JP H BoB SC SBD Light Switch Knob E.C

54 Table 5 (c) Disassembly time calculation of a standard toaster before material separation H2 BoB SC SBD Light Switch Knob E.C CA H S S H H H Se IC BP FP SP SP BSP R R P-E S&H S.Sp S.Sp L.Sp KP LP JP H BoB SC SBD Light Switch Knob E.C Total Path Length (TPL) = Mij 2712 Average Path Length APL = TPL/ n(n-1) Path Length Density = APL/ No. of Relationships (51) Disassembly Time (ta) = APL * n^( [PLD])

55 The total disassembly time for the standard toaster is estimated as 197 seconds Assembly graph and disassembly time calculation after material-wise separation For estimating the selective disassembly time, material recovery for recycling is considered in this case study. In order to compute the selective disassembly time for material recovery, material is assigned to each of the parts of the standard toaster. This material assignment is then labeled in the assembly graph as shown in Figure 25. The labels T1 through T5 are used as material labels in Figure 25 and represent the following materials. T1 Steel/Stainless steel, T2 Plastic, T3 Black Plastic, T4 Nichrome, T5 Aluminium wire and copper connections. The material in focus, for this case study, is T1-steel/stainless steel, which needs to be recovered. The selective disassembly is performed based on recovering more amount of steel (T1) that can be recycled, reused or remanufactured for the new toaster. This helps in reducing the remanufacturing time and cost associated with T1 Material T2-Black Plastic is an unwanted material in this case which has to be disposed in a landfill and 44

56 the components that contain these materials need not be disassembled which will minimize the disassembly time further and help in recovery of more T1- material. Figure 17 Assembly graph of a standard toaster after material-wise separation 45

57 After identification of materials, a new assembly graph is drawn to calculate the Path Length, Path Length Density and the Disassembly time based on material-wise separation, as discussed in Chapter 4. The computations are also demonstrated in Table 6. Table 6 (a) Disassembly time calculation of a standard toaster after material separation CA H1 S1 S2 H.1 H.2 H.3 Se IC BP FP SP 1 CA H S S H H H Se IC BP FP SP SP BSP R R P-E S&H S.Sp S.Sp L.Sp KP LP JP H BoB SC SBD Light

58 Switch Knob E.C Table 6 (b) Disassembly time calculation of a standard toaster after material separation BP FP SP 1 SP 2 BSP R 1 R 2 P-E S&H SS1 SS2 LS KP CA H S S H H H Se IC BP FP SP SP BSP R R P-E S&H S.Sp S.Sp L.Sp KP LP JP H BoB SC SBD Light Switch