This paper describes a general methodology in Design for Environment (DFE), and a part of our research with a specific application using entropy minimisation. The entropy evaluation brings about the generation of a disassembly sequence in which the disassembly efficiency, the material value and the specific value are big and the liability is small, as a gold ship's chronometer. Fuzzy logic and feature modelling are used during the DFE evaluation for parts, assembly and operations analysis. Increasing and extensive environmental concerns lead to the establishment of general metrics and operational guideline. A case study shows the methodology; only the disassembly analysis is detailed.
Product design is a critical determinant of a manufacturer's competitiveness. It has been claimed that as much as 80% of the costs of product development, manufacture and use are determined during the initial design stages. The earlier in the product design life cycle, that a design team considers environmental factors, the greater the potential for environmental benefit and cost reduction. The needs in incorporating environmental consciousness into the design for a product or production process lead to the emerging of design for environment (DFE). DFE is the systematic consideration of design performance with respect to environmental, health, and safety objectives over the full product and process life cycle. The main environmental implication that a designer seeks to control in a product will dictate what strategy of DFE to pursue. These are Design For Recyclability (DFR), Design For Remanufacturability (DFRM), Design For Reusability (DFRU), Design For Disassembly (DFD), Design For Maintainability/Serviceability (DFMS), and Design For Energy Savings (DFES) in the use phase. Reuse implies that the component, part, or material can be utilised again as it, without modification or upgrade other than cleanup. Remanufacturing involves performing manufacturing operations onto the disposed item so that it can utilise again. Recently, recycling became an emphasis in most industrial countries due to the fact that the quantity of used products being discarded is increasing dramatically. It has been recognised that disassembly of used product is necessary in order to make recycling economically viable in the current state-of-the-art reprocessing technology. Three objectives that should be considered during design evaluation: maximisation of profit (benefit–costs) over a product's life span, maximisation of the number of parts reused, and minimisation of the amount (weight) of landfill waste. Due to their wide spread utilisation DFD and DFES have been reported to be the focus of greater research effort (Santochi et al., 2002; Mascle and Balasoiu, 2003; Subramani and Dewhurst, 1991). Some obstacles that made disassembly difficult or today's manufactured products: difficult to gain all the information necessary to plan the disassembly, many consumer products are not designed for ease of disassembly. Two engineering problems associated with DFR are dismantling techniques and recycling costs. The remanufacturing industry faces two issues: (1) components that fail, types of failure, and the distributions of times to failure are often unknown and/or present a large variance, and (2) lack of an incentive to customers to buy remanufactured products, as well as perception that they are “second” hand, hence have low quality. Both problems ultimately affect remanufacturing planning. In addition to that, another big issue is the technological barriers to remanufacturing that stem from product differentiation. As for recycling, perhaps the greatest problems that this industry faces are the lack of sufficient collection infrastructure, identification, sorting and compaction of materials, and economic ineffectiveness (Bhander et al., 2003).
In conclusion of this research, the disassembly for environment must be seen in the point of view of each sub-assembly or component can be disassembled as easy as possible for maintenance, reuse, remanufacturing, recyclability, etc. So, it is important to choose geometrical forms and surfaces for the disassembly that can assure an easy access to all other components. The algorithm is very fast: For n<35, it takes less than 30 s. Because of the interface type chosen, the dimension of the screen and especially the RAM memory are essential to treat cases where n>35. Most sub-assemblies can have several disassembly sequences. With the help of this algorithm, we will determine several disassembly sequences. After that, we choose the most suitable. A simulation of the all sequences found can do this and the algorithm will choose automatically the sequences with the minimal number of disassembly components.
The design engineer has to choose component, subassembly or operation that has a minimal impact on the environment (liability) and a maximal reusing for parts or materials (material value and specific value of a component). We propose a new approach, which determines the disassembly sequence depending on various criteria. In fact, various situations in some irreversible operations have to be done, could occur and some dismantling of some components should appear. Our algorithm takes into consideration the irreversible operations, and determines the disassembly sequence that avoids the realisation of these irreversible situations, therefore, the dismantling of components. The advantage in using our algorithm consists in fact that we try to avoid the dismantling of components for the disassembly. The best disassembly sequence is determined with a minimal information entropy factor, which also avoids irreversible operations. Finally, we propose a way to help the line designer with a set of assistance tools and a methodology. We need four object-oriented databases to help the user to design both product and assembly line. Geometric algorithms are implemented to even more automate the evaluation process and expand the software effectiveness. Furthermore, the addition of an assembly/disassembly CAD module to “FuzzyDFE” extensively improves the automation of the DFE.
To verify the proposed method, further research is required on simulation and experimental results. To extend the model and the methodology to Design for X (manufacturing, assembly, disassembly, maintenance, environment, etc.) some other researches should be undertaken.
