Physical mechanisms in hybrid additive manufacturing: A process design framework

This study defined hybrid additive manufacturing (AM) as “in-situ or series combination of an additive manufacturing process and secondary energy sources in which physical mechanisms are fundamentally altered/controlled to affect the resulting properties of material and/or part.” This definition includes in-situ secondary processes as well as process chains, and it is anchored in multi-physical mechanisms such that new hybrid-AM processes can be freely and systematically sought or invented through a systems approach epitomized by the “property – mechanism – energy source – hybrid-AM process (PMEH)” thought process. The sequence of driving forces in this framework are as such: desired material properties determine which mechanism is utilized and, in turn, the energy source to be applied, which ultimately defines the hybrid-AM process. The five unifying physical mechanisms that were identified in this study are: melt pool dynamics, microstructure development, stress state, surface evolution, and thermal gradients. Analysis of properties, mechanisms, energy sources, and processes was conducted on more than 100 papers, and the results ultimately show the effect of mechanisms on material properties. Mechanisms are further classified by energy source, which are in turn broken down by hybrid-AM process. Additionally, each mechanism was defined and reviewed in detail, highlighting the PMEH relationship for metal hybrid-AM materials. Further analysis compares reported mechanical property values for hybrid-AM processes to both AM only and wrought properties for 316 L, Alloy 718, and Titanium Gr 5. Finally, future directions of research as well as clear gaps in knowledge are identified, which includes lack of variety in utilized energy sources, lack of material diversity, process chain integration and improvement, and promising hybrid-AM processes. With the presented analysis and PMEH framework, it is determined that metal AM hybrid processes are well suited to address current problems and show promise in creating superior and versatile materials. Further growth in this field is expected to be exponential, and the developed PMEH framework will aid in framing these innovative processes.