ABSTRACT
The economic feasibility of the end-of-life (EOL) scenario of a mechanical component depends on the disassembly cost, the revenue from disassembled components, and the regulatory requirements on components and materials. Regulatory requirements are quite diverse among countries and even between different states in the United States. While designers have to obey the regulations of the country or state, mostly economic considerations outweigh everything else. If we look at the disassembly cost, which depends on the number of fasteners in the assembly, it is clear that the disassembly of a product will be disadvantaged by a large number of fasteners in the assembly. To disassemble such a component will involve locating the fasteners, gripping them in difficult-to-reach places, and handling them in a confined space. They need to be reached and removed in an optimal sequence; otherwise, disassembly will take more time and cost more money. Therefore, it is desirable for designers to look into the assembly process and EOL treatment of a product. In reality, this means that designers should design components with fewer fasteners in the assembly, such that disassembly, recycling, and reuse of components are easy. Sometimes this is called design for disassembly (DFD) or product-embedded disassembly. Since disassembly cost is a major driver of recycling and reuse, the time component of the disassembly should be carefully estimated. Sometimes, the design of fasteners or fastener configuration should be examined carefully. There are number of objectives we want to achieve at the EOL, most importantly,
1. Maximize profit, as no business will attempt to disassemble, recycle, or reuse a component if it is not profitable. So, we can understand that a recycling or reuse business will not pick up unless it is profitable. We can write the objective function for profit as total return minus total costs of disassembly. This can be presented as Equation 6.1:
(6.1)
where: i = 1,2,…n = number of components in the assembly pi = sales price of each component ci = the disassembly and associated costs
2. Minimize the environmental impact of the EOL scenario:
f z e zi i i i
( ) ( )= =
(6.2)
where ei(zi) is the environmental impact of the ith component at EOL. The environmental impact can be measured in different ways, such as minimization of greenhouse gases (GHG), minimization of the energy embodiment, minimization of eco-indicators, or all of them together. These values can be determined by life cycle analysis (LCA).
