Wet and dry turning of Ti6Al4V EBM parts: implications on the life cycle assessment and surface roughness

The low-quality surface finish of the parts is among the main drawbacks of the Electron Beam Melting (EBM) process, which is an Additive Manufacturing (AM) technique highly employed in the fabrication of high-performance titanium parts. Postprocessing of the parts is always required to meet high standards of quality, and machining is often a valuable solution. Due to its peculiarities, titanium is usually machined in wet conditions, but in the last years, machining in dry environments has gained interest in reducing the overall carbon footprint due to the non-negligible impact of lubricant use. In the existing literature, some researchers investigated the optimization of the turning process parameters to minimize the surface roughness of wrought titanium. Few studies investigated the optimization of process conditions in titanium alloys manufactured by EBM. From a sustainability perspective, few studies have conducted cradle-to-gate life cycle assessments (LCAs) for parts produced by EBM and subsequently post-processed through wet or dry turning. Additionally, existing LCA databases often lack primary data on AM processes and the machining of AM components. This work seeks to address these challenges and help bridge current gaps in literature. In this work, a cradle-to-gate LCA has been performed using the CML 2001 method to evaluate the environmental impact of producing a single part by EBM and post-processed by machining. Moreover, the effect of different combinations of turning processes in wet and dry environments on surface roughness and environmental impact has been jointly evaluated to provide guidelines to support decision-making in the industry. Moreover, a sensitivity analysis on the buy-to-fly ratio (BTF) was performed, thus enabling us to find a critical value for turning, that is 125:1, above which it would be better to choose to manufacture the parts by EBM selecting a BTF of 2:1 or 3:1 to minimize the Global Warming Potential (GWP).