Dr. Surendra M. Gupta
According to a forecast, by 2005, almost 50 million computers will become obsolete and enter the waste stream annually in the US alone. And that is not all; there are countless types of products from automobiles to washers/dryers to electronic gadgets that enter the waste stream every year. The growing amount of waste caused by the disposition of end-of-life (EOL) products has become a severe problem in many communities. For electronic products in particular, rapid technological improvements have considerably shortened their useful lives and speeded up the disposition posing a significant threat to the environment. This fact, coupled with the customers' desire to acquire the latest technology has fueled the premature disposition of otherwise perfectly functioning electronics products.
It is no longer acceptable to discard items like cars and outdated military weapons and ammunition by blowing them up, burning them, dumping them into the ocean or sending them to landfills. As millions of products are dumped, landfills, often laced with toxic substances, are overwhelmed. In response, consumer and environmental organizations have begun to lobby for environmentally friendly products, and in many places governments are placing sharp restrictions on the dumping of hazardous materials. These trends have prompted corporations to reconsider their manufacturing practices and emphasize product recovery. The more forward-looking companies are sensing opportunities arising from this changing environment.
Environmentally Conscious Manufacturing (ECM) is a niche sector of industrial manufacturing that develops cradle-to-grave manufacturing methods. In the past five to ten years, these factors have come together to create a new trend in product design, one in which the product's EOL is considered from the beginning. For many companies, disassembly has become one of the key factors considered during the product design stage. Recent studies on ECM have added scientific models to a field where virtually none existed before. How to put together a product involves totally different principles than how to take it apart!
The process involves solving complex problems. Consider automobiles, for example. Traditionally, cars were taken to the junkyard, shredded, and separated into various metals, yielding up to a 97 percent efficiency rate. In today's marketplace, with the demand for fuel efficiency calling for lighter cars, an array of plastics has replaced metals in the manufacturing process. As the amount of polymers used in production increases the metal yield and the incentive to shred decreases. The sheer variety of plastic also cuts down on the incentive and ease of disassembly, since not all are equally recyclable.
Firms interested in recycling must answer a range of questions: which components to reuse, how to retrieve and store them, how to track inventory, manage the supply of EOL products, and control quality. Recent research efforts revolve around developing mathematical algorithms that address these concerns and host of other disassembly and production planning issues.
For example, recently an algorithm for scheduling the disassembly of a discrete, well-defined product structure was proposed. The principle surrounding the disassembly scheduling of a product is somewhat similar to Material Requirements Planning. The algorithm determines the disassembly schedule for the components such that the demands for those components are satisfied. Subsequent algorithms included components/materials commonality together with the disassembly of multiple product structures. Yet another method provided solutions for component recovery planning to determine the number and type of products to disassemble in order to satisfy the demand for a set of components while minimizing the disassembly and disposal costs. The methodology was further extended to analyze the design efficiency of electronic products for studying the effect of EOL disassembly and disposal on the environment.
In the area of disassembly process planning, some researchers have applied planning and sequencing techniques to create efficient disassembly plans by taking advantage of the product modularity, which minimize the total processing times and thus the cost of disassembly. Others have addressed the problems of disassembly processes and disassembly sequence planning. Neural networks methodology has also been applied to disassembly processing problem. Recently, Petri Nets have been used for modeling products with complex AND/OR precedence relationships for disassembly process planning. One researcher has used recursive search algorithms to define the subassemblies in the product structure to find the optimum way to disassemble.
Several researchers have applied mathematical programming and heuristic techniques in the area of disassembly and recycling modeling. Samples of techniques that have been used include linear programming, goal programming, physical programming, integer programming, fuzzy programming, genetic algorithm and tabu search.(Surendra M. Gupta is a Professor of Mechanical, Industrial and Manufacturing Engineering and Director of the Laboratory for Responsible Manufacturing at Northeastern University. He received his BE in Electronics Engineering from Birla Institute of Technology and Science, Pilani, MBA from Bryant College, and MSIE and Ph.D. in Industrial Engineering from Purdue University. His recent activities can be viewed at http://www.coe.neu.edu/~smgupta/ and he can be reached by email at email@example.com )
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