Powder recycling in laser beam melting: strategies, consumption modeling and influence on resource efficiency
Laser beam melting (LBM) is a powder-bed and laser-based additive manufacturing technology that is increasingly used for the production of metal components. For a sustainability assessment of a production technology, the global warming potential (GWP) can be used, which is commonly referred to as CO2-footprint. Looking at the resource demand of LBM, material losses and powder recycling play a significant role. In the LBM build-up process, powder material is selectively solidified, generating the part layer-by-layer. The non-solidified powder material can be recycled, which is beneficial to the resource efficiency of the process. Due to considerations regarding powder quality degradation, the number of reuse powder cycles in industrial practice varies significantly, ranging from only one to more than several dozen cycles. Similarly, material losses during the process have shown to differ between LBM machines. However, previous approaches for LBM resource efficiency assessment lack a detailed representation of these two factors. In this study, two interacting models are introduced for the evaluation of the GWP of LBM parts. Firstly, a powder reuse cycle calculation model is described. Secondly, a LBM resource and energy consumption model based on the CO2PE!-methodology is put forward with a refined focus on powder recycling and material losses. The models are implemented and validated based on three LBM production use cases including the acquisition of resource and energy consumption data for three commercial LBM machines. GWP-impact values are used from the ProBas database, provided by the German Federal Environmental Agency. Based on the results regarding the three LBM use cases, the role of powder recycling and material losses on the GWP-impact of LBM during the production phase is discussed. The results show that the number of attainable powder reuse cycles lies around 35 cycles (ranging from 1 to 117 cycles) for the analyzed LBM production scenarios when applying the suggested powder recycling strategy. If powder is not recycled and only used once, more than 90% of the powder batch might be discarded. The volume-specific CO2-equivalent of 0.175 kgCO2eq/cm3 can be used as a rule of thumb for a quick estimation of the GWP for LBM parts made from Al-alloy or steel. Electric energy consumption constitutes for the largest share of GWP-impact, followed by the solidified metal powder and the occurring powder losses.