A comparative study of dry and cryogenic milling for Directed Energy Deposited IN718 components: effect on process and part quality

The integration of machining as a post-processing method for additive manufacturing (AM) can promote the industrialization of AM and enable it to meet the requirements of high-value industries. This integration introduces several challenges for the machining process, which are related to process design and planning. A major aspect that requires investigation is the cooling of the machining process. Effective cooling is a key part of the machining process, especially when hard materials with low machinability are involved, which is the case with parts built by AM. However, oil-based coolants cannot be utilized in the context of hybrid manufacturing because they contaminate the surface of the part that can lead to the introduction of defects in a successive AM process. Cryogenic cooling is a high-performance and sustainable cooling approach that can be employed to overcome this issue, since it provides a clean surface after the machining process. Although cryogenic cooling is a very promising and sustainable alternative for high-performance cooling, most studies only investigate limited benefits that it can provide in the machining process. Therefore, this paper aims to provide a full overview of the effect of cryogenic cooling with liquid nitrogen (LN2) during milling of Directed Energy Deposited IN718 samples, examining the cutting forces, tool wear, surface roughness and residual stresses on the machined components. The results prove that cryogenic cooling can reduce significantly the cutting forces and tool wear, while its impact on the surface roughness is limited.