The evolution and origin of Additive Manufacturing (AM), in particular metallic additive manufacturing, can be traced back to several decades. In its early incarnation, the technology was known as hard surfacing, where a small amount of metallic alloy is melted and added to worn out metallic components using the metal inert gas welding (MIG) process. The process used regular or specialized weld wires. Availability of flux cored and flux coated wires expanded the process further to include variations of MIG welding like SMAC (Shielded Metal Arc), FCMW (Flux Cored Metal Welding), etc. 

Typical examples of resurfacing are rolling mill rolls, turbine blades and marine structures, which are quite expensive to be scrapped after a limited lifetime. In this case, metal wires are used as feedstock. The advent of metal powder atomization to produce spherical powders gave rise to other competing process such as High Velocity Oxyfuel (HVOF) deposition to be used in place or along with MIG processing to perform hard surfacing.

Until a decade ago, AM, especially metallic AM, remained at the periphery of product manufacturing to support repair and rebuild of components. The true potential of AM of three-dimensional components must wait until further advancements in associated technologies like robotics, industrial automation, etc. Currently a large variety of processes are available as illustrated below. The processes are classified according to the feedstock used to melt or sinter the components. 

Current Processes for
Metallic Additive Manufacturing