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An Environmental and Economic Trade-off Analysis of Manufacturing Process Chains to Inform Decision Making for Sustainability


Increasing costs, consumer awareness, and environmental legislation have driven industry to reduce its resource consumption and the impact from that consumption. So, both traditional economic objectives (e.g., cost, time, and quality) and environmental objectives (e.g., CO2 emissions) have become strategically relevant for the manufacturing sector. For many manufacturing companies, production systems have a major influence on the environmental footprint of a product and therefore represent a major opportunity to minimize the company's overall environmental impact. Currently within industry, there is not an accurate, effective, or widely accepted method to assess the resource consumption of process chains used to manufacture a product. As a result, this information is often not considered when making decisions about what processes to use. A considerable part of the energy and resource demand in manufacturing is determined during production planning. An important component of this planning is determining the process chains to be used. Process chains are a combined sequence of specifically arranged, single processes used to manufacture a product. As manufacturing processes are very resource intensive, it is now necessary to assess the resource consumption as well as the economics of these process chains. Because of this, additional information must be considered when selecting the process chains used to manufacture a product.

Many life cycle assessment (LCA) tools focus on the materials and final disposition of a product, but do not include detailed information or data on the manufacturing required to fabricate the product. Sustainability impacts of discrete manufacturing processes and product value streams are needed to develop more complete LCAs. The development of a methodology and user tool to quantify sustainability impacts, leading to the identification of gaps and opportunities, is essential to facilitate decision making to support sustainability in manufacturing facilities.

To address these issues, this dissertation proposes an approach to evaluate and quantify the resource use in addition to the environmental and economic impacts associated with discrete manufacturing processes as part of a complex process chain. A methodology to evaluate multiple process chain configurations will be presented.

First, a database of industrial assessment metrics was compiled. This database allows users to sort and select from a list of key metrics in order to choose the metrics that are relevant for the performance that they want to measure. Next, an industrial assessment methodology was developed. This methodology gives users an overview of the key areas to address when conducting an industrial assessment. This methodology, which was applied to three case studies, can be used in combination with the key metrics.

In the second part of the dissertation, a resource consumption assessment and mapping methodology for complex manufacturing process chains was developed. This systematic methodology was developed to identify and quantify the resource consumption (energy, water, materials) for discrete manufacturing processes. The processes mapped include: welding (manual and robotic), cutting (plasma arc and laser), rework (air carbon arc cutting and hand grinding), and machining (milling).

Next, a model consisting of database modules for each process was developed. This model quantifies the sustainability impacts (energy, water, and material consumption, waste generation, emissions, and resource consumption cost) of manufacturing process chains. The model was validated using a case study with Caterpillar Inc. for a process chain including welding, plasma arc cutting, laser cutting, and milling.

Next, a process chain assessment tool was created. This tool enables manufacturers to assess the resource consumption and associated impacts of multiple fabrication process chain configurations. This enables a more comprehensive assessment compared to other software tools. Finally, a methodology modeled after the Six Sigma DMAIC (Define, Measure, Analyze, Improve, Control) process was presented to show how to translate the results from the model and tool to an Environmental Value Stream Map and to translate those results into improvements in manufacturing systems. This methodology was validated on a machining operation in a Caterpillar facility.

This research has developed and evaluated an effective approach for the analysis of energy, water, and other resource use in multiple processes in a manufacturing process chain. This allows manufacturers to better understand the resource consumption and environmental and economic impacts of fabrication process chains used to make a product. This dissertation helps to provide the technical understanding and tools to enable designers and manufacturing engineers to create manufacturing systems that are truly more sustainable. The implementation of this work can be directly applied to assessing and optimizing manufacturing process chains and the work presented in this dissertation directly contributes to the realization of a sustainable and prosperous manufacturing sector.

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