An activity based method for sustainable manufacturing modeling and assessments in SysML
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Traditionally, environmental impacts of man made products have been determined by performing a life cycle assessment (LCA) on the product. As the name implies, LCA is usually covers the entire life of the product in a so-called "cradle-to-grave" assessment. In determining environmental impacts over the whole product life, LCA's are reasonably adequate. However, in providing detailed impacts on a particular phase of life, LCA's are lacking. Detailed assessments are important because very few stakeholders have influence over a product during all phases of life. Stakeholders need detailed impact assessments in their particular phase of life. More detailed assessments give stakeholders more information that can be used for better environmental management (EM) and more environmentally benign operations. In many LCA's, the manufacturing phase of life has been over-generalized and over-simplified because of its relatively small environmental impact, as compared to other phases of life. Nevertheless, certain stakeholders, such as manufacturing companies, need detailed impact information for the manufacturing phase of life so that they can create a more sustainable manufacturing process. Most traditional LCA's use a case-based approach, which was deemed to be inadequate. For these LCA's, the information provided for each case is often quite detailed and specific. However, this makes the assessment less flexible, limiting the quality of the assessment to the degree that the current scenario matches the existing cases. In order to make a more user-specific assessment, a model-based approach was used. To give the model flexibility, a parametric model was created based on mathematical equations that represent various parts of the manufacturing process. To give the model structure, an activity-based costing (ABC) approach was used. Using the ABC structure, the manufacturing process was broken down into activities, each of which was characterized by mathematical models. Large models would be difficult to construct and simulate by hand, so a model was built with the aid of a computer. The modeling language SysML (Systems Modeling Language) was used to create an object-oriented model of the manufacturing process, using the ABC structure. SysML defines overall properties and behaviors of the various elements in the model, while the plug-in tool ParaMagic was used to execute the model via a Mathematica Solver. The model computes carbon dioxide emissions, energy consumption, and waste mass generation for a particular manufacturing scenario. The goal of the model was to quantify environmental impact factors in order to aid manufacturing stakeholders in EM. The overall goal of the research was to determine whether an activity-based, object-oriented model was a valid approach, and whether the computer-aided tools adequately implemented this approach. Findings show that SysML is capable of modeling large and complex systems. However, due to some limitations of Paramagic, only some of SysML's capabilities were utilized. Nevertheless, Paramagic is capable of extracting information out of a manufacturing model built in SysML, and solving parametric relations in Mathematica in a timely manner. Timely solutions of complex models are critical for stakeholders keeping a competitive edge.