Leveraging Manufacturing Precision to Reduce Product Life Cycle Environmental Impacts.

摘要

Growing sustainability concerns have made manufacturers increasingly responsible for larger portions of the product life cycle. But, manufacturers have not been able to synthesize sustainability fully into their decision making because they do not completely understand the relationship between manufacturing and other life cycle stages. Specifically, manufacturing processes create part features that dictate the function of the finished product during its use. Understanding this relationship highlights opportunities to leverage improved manufacturing processes for environmental impact reduction for many consumer products. This dissertation evaluated these opportunities by using a data-driven approach that assessed the environmental, technical, and financial impacts of manufacturing precision on the manufacturing phase. It then analyzed the effect of improved manufacturing precision on product performance during the use phase to determine the subsequent change in environmental impacts over the product life cycle. Machining was chosen as an exemplary manufacturing process to explore these requirements, and three case studies were conducted to study different machining alternatives within the proposed framework.;The first case study investigated trade-offs between energy, maintenance activities, and cost for a steel milling process. Energy was measured using a power meter, maintenance activities were considered by measuring the cumulative damage on the axis bearings using a Weibull statistical reliability analysis, and costs included electricity and component charges. The machining alternatives assessed in this study decreased energy by up to 40% but also increased the cumulative damage on the axis bearings by as much as 110%, which increased the overall machining cost.;The second case study expanded on the first by including tool wear (maximum flank wear land width), part surface quality (surface roughness and local strain hardening), and service costs for a titanium turning process. Tool wear was measured using a microscope, surface roughness was measured using profilometry, local strain hardening was determined by analyzing x-ray interference patterns, and service costs were estimated by performing a Monte Carlo simulation with a Weibull statistical reliability analysis. The machining alternatives assessed in the study decreased energy by up to 500 kJ, electricity costs by up to Euro 0.03/part, and CO2 emissions by up to 60 g-CO2/part, which each represented a 40% improvement. But, these improvements increased tool wear by up to 800%, surface roughness by up to 660%, local strain hardening by up to 21%, and created more breakdowns and equipment variability that increased service costs by up to Euro 0.21/part-year; many of these negative impacts were primarily driven by changes in feed. These results emphasized the need for a comprehensive systems perspective when optimizing machining processes to ensure the sustainability of such decisions as well as the role of part functionality in dictating the extent to which green-machining strategies may be implemented.;The third case study evaluated the feasibility of leveraging surface roughness improvements to reduce the life cycle environmental impacts of spur gears in automotive drivetrain components. Improving the surface finish of one spur gear decreased life cycle primary energy consumption on the order of 1 MMBtu, which represents approximately 17% of the energy typically required to manufacture an automobile. Given the variety of gears in the drivetrain and the other automotive components where surface quality plays an important role in operational efficiency, the potential impact of a leveraging strategy could be significantly larger. Ultimately, manufacturing plays an important role in promoting sustainability across the product life cycle. Recommendations for appropriate decision-making tools and the requirements for their development are described so that manufacturers may exploit their processes to create sustainable products.