Εvaluating Carbon Emissions of Hybrid Manufacturing Process: A Case Study on Additive and Subtractive Manufacturing

Abstract

All environmental issues, and particularly climate change, have irreversible environmental, social, and financial impacts. Significantly reducing carbon emissions by 2030, as the highest contributor to climate change, is a vital for EU as expressed in the European Green Deal. In this direction, sustainable manufacturing intends to reduce negative impacts by minimizing energy consumption, lowering carbon emissions, and optimizing resource efficiency. Hybrid Manufacturing (HM), combining additive (AM) and subtractive manufacturing (SM) processes, is a very promising process in sustainable manufacturing, in addition of being a novel approach. The aim of this paper is to identify the carbon intensive parts of a HM cell, perform carbon footprint calculations through mathematical modelling and Life Cycle Assessment (LCA) and classify them as either energy or material related carbon emissions. This methodology is implemented in an HM including Direct Energy Deposition (DED) and CNC milling, successively alternating between the two to complete the part. Results indicate that at machine tool level, the material related emissions (4.64 kg CO₂-eq), slightly dominate over the energy related emissions (4.51 kg CO₂-eq). Powder consumption is almost solely responsible for material related emissions. Among energy related emissions, the AM cell’s chiller was the largest contributor (accounting for 28.3% of the total emissions), followed by the AM head motion system (10.9%), and laser machine (9.6%), while the subtractive process emitting considerably less in this case. Future work will aim to optimize process parameters to reduce HM emissions while ensuring high product quality.