Metal additive manufacturing (AM) technologies are classified into two groups according to the consolidation mechanisms and densification degrees of the as-built parts. Densified parts are obtained via a single-step process such as powder bed fusion, directed energy deposition, and sheet lamination AM technologies. Conversely, green bodies are consolidated with the aid of binder phases in multi-step processes such as binder jetting and material extrusion AM. Green-body part shapes are sustained by binder phases, which are removed for the debinding process. Chemical and/or thermal debinding processes are usually devised to enhance debinding kinetics. The pathways to final densification of the green parts are sintering and/or molten metal infiltration. With respect to innovation types, the multistep metal AM process allows conventional powder metallurgy manufacturing to be innovated continuously. Eliminating cost/time-consuming molds, enlarged 3D design freedom, and wide material selectivity create opportunities for the industrial adoption of multi-step AM technologies. In addition, knowledge of powders and powder metallurgy fuel advances of multi-step AM technologies. In the present study, multi-step AM technologies are briefly introduced from the viewpoint of the entire manufacturing lifecycle.

Abstract
1. Introduction
2. Metals Additive Manufacturing
    2.1 Single-step AM processes
    2.2 Multi-step AM processes
3. Binder Jetting Additive Manufacturing
4. Material Extrusion Additive Manufacturing
5. Post-AM Densification Processes
    5.1 Debinding
    5.2 Sintering
    5.3 Molten-metal infiltration
    5.4 Hot isostatic pressing
References

• Ji-Won Oh(Advanced Materials and Process R&D Department, Korea Institute of Industrial Technology)
• Jinsu Park(Advanced Materials and Process R&D Department, Korea Institute of Industrial Technology)
• Hanshin Choi(Advanced Materials and Process R&D Department, Korea Institute of Industrial Technology) Corresponding Author