Comparative Life-Cycle Analysis of Additively Manufactured vs. Conventional Metals

Thesis Abstract

The rapid adoption of additive manufacturing (AM) in metal engineering promises significant environmental and economic benefits, yet a comprehensive, harmonized life-cycle perspective comparing AM metals with conventional metallurgy remains underdeveloped. This study addresses the gap by evaluating the cradle-to-grave environmental and economic performance of metal components produced via laser powder bed fusion (LPBF) against traditionally processed counterparts (casting and subtractive finishing) for a structurally demanding aerospace alloy system (Inconel 718 and Ti-6Al-4V) under realistic usage scenarios. The aim is to quantify trade-offs in material efficiency, energy intensity, emissions, and total cost of ownership, enabling decision-makers to align manufacturing choices with sustainability targets. Specific objectives are (1) to compile a unified life-cycle inventory (LCI) for LPBF-produced and conventionally manufactured components of the selected alloys; (2) to assess environmental impacts using ISO 14040/44-compliant life-cycle assessment (LCA) across midpoints (global warming potential, ozone depletion, cumulative energy demand) and endpoints (human health, ecosystem quality); (3) to compare economic performance through a full life-cycle cost (LCC) analysis, incorporating production, material, energy, post-processing, and end-of-life costs; (4) to evaluate mechanical performance and durability through accelerated fatigue and creep tests, linking results to LCA/LCC results; and (5) to synthesize findings within a theoretical framework of the Resource-Efficient Manufacturing paradigm and the Theory of Planned Behavior as it relates to supplier and consumer adoption decisions. The methodology employs a mixed-methods design combining quantitative LCA/LCC modeling with experimental testing and qualitative stakeholder insights. The population comprises metal components designed for structural aerospace applications fabricated from IN718 and Ti-6Al-4V. A factorial sample of 20 LPBF-built parts and 20 conventionally manufactured parts per alloy, matched for geometry, weight, and nominal load path, is selected. Data collection instruments include (i) an LCI database augmented with primary energy measurements from a micro-utility energy meter and LPBF machine logs; (ii) standardized mechanical test rigs for quasi-static, fatigue, and creep testing; (iii) post-processing energy and material usage records; (iv) a survey and semi-structured interviews with design engineers, manufacturers, and procurement specialists to capture decision drivers and perceived risks. Validity and reliability are addressed through calibration of energy meters, cross-validation of LCI data with ecoinvent 3.8, repeatability tests for mechanical experiments, and triangulation of qualitative responses. Data analysis integrates multiple techniques. LCA employs SimaPro 9 to compute midpoints using ReCiPe2016 and normalize against a common functional unit (1 kg of finished alloy component) with a consequential approach for end-of-life scenarios. LCC uses a discounted cash flow model over an assumed 20-year service life, incorporating material prices, energy tariffs, capital depreciation, maintenance, and end-of-life recovery. Statistical analysis includes regression and ANOVA to identify effects of processing route and alloy on mechanical performance and environmental/economic indicators, with post hoc tests to determine significance between groups. A thematic analysis of interview data identifies barriers and enablers to adoption, framed by the Resource-Efficient Manufacturing theory and the Theory of Planned Behavior to interpret intention-behavior gaps. Expected findings indicate that AM metals exhibit lower material waste and higher design freedom, yielding reductions in non-renewable energy consumption for complex geometries, but exhibit higher energy use during production due to LPBF process intensity. The LCA is anticipated to reveal a trade-off where midpoints such as global warming potential are favorable for AM in certain alloys, while ozone depletion and mineral resource depletion may favor conventional processes depending on energy mixes. The LCC is expected to show higher upfront costs for AM parts but lower post-processing and potential end-of-life credits, with break-even horizons differing by alloy and component complexity. Mechanical tests are anticipated to show comparable or superior fatigue performance for AM parts with optimized heat treatments, contingent on porosity control and microstructural management. The study contributes to knowledge by delivering a harmonized, cross-validated framework for evaluating AM vs. conventional metals across environmental and economic dimensions, informs policy on sustainable manufacturing pathways, and advances theory by integrating Resource-Efficient Manufacturing and behavioral decision-making in the context of technology adoption. Recommendations include targeted process optimization to reduce energy intensity in AM, standards development for comparative LCA/LCC reporting, and stakeholder-informed strategies to accelerate the uptake of sustainable AM practices in aerospace supply chains.