Modeling methods for complex manufacturing systems : studying the effects of materials substitution on the automobile recycling infrastructure

Abstract

Classically, technical cost models have been constructed using commercial spreadsheet problems. Spreadsheets, however, are not well suited to construct models of industrial systems, especially those where variable configurations of operation steps arc of interest. In light of this, a methodological framework and complementary computer tool were developed to address the existing impediments to system modelinb. This tool parametrizes the components of a system model and of spreadsheet based TCMs. Here, parametrization means creating both data structures which describe each system part and procedures which emulate the behavior and interrelationship of those parts. Using this strategy, a tool was created which successfully permits definition and manipulation of any real configuration, ensures consistent application of model formulae, provides a mechanism for appropriate and conveniently audited linking of variable values, and affords extensive auditing. This modeling tool was applied against a real-world case study of the automobile recycling infrastructure. For this system, concerns exist regarding how it will sustain as vehicles continue to decline in mass and change in composition. To reveal this, a process-based cost model of the automobile recycling system was created and used to I) expose retiring fleet compositions which pose a problem for recyclers and 2) evaluate strategies for using the system's waste, automobile shredder residue (ASR). The system model was run against retired fleets made up of three vehicles: predominantly steel, aluminum intensive, and polymer composite intensive (CIV). Results indicated that the current recycling system maintains profitability except when presented with a 100% CIV fleet. Also, the material value within a vehicle containing an aluminum structure, closures, chassis, and engine block would be sufficient to prompt extensive dismantling, consuming the bulk of the shredder's feedstock. For a similar vehicle without the aluminum chassis, shredders would have to offer 18¢/kg. for hulks, to preserve their profitability. Of the ASR processing technologies investigated, pyrolysis seems the most promising. Pyrolysis achieves profitability at a landfill price of $50/ton. In contrast, mechanical separation and selective precipitation require landfill prices of $70/ton.