A cradle-to-cradle life cycle assessment framework linking machining parameters, tool life and part durability

Machining operations influence sustainability not only through immediate energy and resource use but also through their effects on tool longevity and part durability. Conventional life cycle assessments (LCAs) of machining typically adopt gate-to-gate boundaries, overlooking how machining parameters affect surface integrity, fatigue life, and the frequency of cutting-tool and machined component replacement. This study develops a novel cradle-to-cradle LCA framework that incorporates machining-induced tool wear and part durability into system-level environmental impacts. The approach is demonstrated through a real case study of drilling the CFRP/Ti6Al4V stacks used for the Boeing 787 fuselage, comparing dry drilling with liquid carbon dioxide combined with minimum quantity lubrication (LCO₂+MQL). Experimental tests quantified energy demand, resource consumption, tool life, and hole quality, while part durability was evaluated via fatigue testing and finite element simulations. Results show that the cutting tool production was the dominant contributor to the overall environmental impact. Despite requiring additional auxiliary inputs, LCO₂+MQL drilling reduced overall environmental impacts by 60–70 % relative to dry drilling, due to extended tool life and improved component service life. These findings demonstrate that coolant-assisted machining, when durability and tool-life effects are considered, yields a net environmental benefit. The proposed framework provides a transferable method to expand LCAs beyond gate-to-gate boundaries by integrating the influence of machined part quality on durability and in-service repairs, enabling cradle-to-cradle assessments that better capture the system-level implications of machining decisions.