Machinability Data to Sustainability Metrics: Cradle-to-Gate Life Cycle Assessment of Lubrication-Assisted Drilling of Cold Metal Transfer-Wire Arc Additive Manufacturing Ti-6Al-4V

Abstract

Abstract. With the rapid advancement of wire arc additive manufacturing (WAAM), assessing the sustainability of postprocessing operations such as machining has become increasingly important. This study investigates sustainability-oriented lubrication strategies using mono-nanofluids (MNFs) and hybrid nanofluids (HNFs) formulated from graphene nanoplatelets and hexagonal boron nitride dispersed in jojoba oil. Drilling experiments were performed on WAAM and wrought Ti-6Al-4V alloys to evaluate machinability and environmental performance. The results demonstrated that HNFs considerably improved machining responses, achieving reductions of nearly 30% in power consumption, over 40% in cutting forces, and around 50% in flank wear compared with dry conditions. A cradle-to-gate life cycle assessment (LCA) was further conducted to quantify the environmental impacts associated with each condition. The analysis revealed that machining WAAM components generated higher CO2 emissions and toxicity indicators than wrought machining, primarily due to increased energy demand. Nevertheless, the application of HNFs effectively mitigated these burdens, leading to approximately 35% lower CO2 emissions and notable decreases in human toxicity and resource depletion. Overall, the study highlights how tailored nanofluid lubrication can deliver measurable environmental benefits, bridging machinability improvements with sustainability goals in advanced alloy manufacturing.