**4. Metal additive manufacturing materials (alloys)**

*Concepts, Applications and Emerging Opportunities in Industrial Engineering*

heat accumulation between the layers and improves quality [24].

processes; the next sub-section outlines the main processes of DMD.

over the other current methods of manufacturing [28].

*3.2.2 Gas tungsten-wire arc additive manufacturing*

*3.2.1 Wire arc additive manufacturing*

ing method) and they are as follows:

3.Plasma Transferred Arc (PTA)

5.Electron Beam Freeform (EBF)

1.Plasma Arc (PA)

4.Laser Beam (LB)

2.Gas Metal Arc (GMA)

**3.2 Direct metal deposition additive manufacturing**

The Electronic Beam Melting (EBM) is also a powder-bed additive manufacturing process. The difference between EBM and other powder bed AM (SLS, DMLS, and SLM) processes is the source of energy; EBM utilizes electron beam instead of laser. This process was invented by Arcam in 1997. The electronic beam provides higher energy density than laser. This makes the EBM process more flexible with metallic alloys. Nevertheless, this has a drawback of increasing the chances of shrinkage. The EBM has a high scanning speed (several kilometers per second) which helps to reduce

Direct Metal Deposition (DMD) additive manufacturing method was invented by Precision Optical Manufacturing (POM). The metallic powder or wire used in the DMD is sprayed directly onto the laser beam or the electric arc beam. The beam melts the metallic powder or wire by the laser or electric arc heat source, then the molten metal drops on bed to build the part layer by layer. Because of that, it is called direct deposition process and not powder bed in DMD. There is a possibility to build multilateral parts from various metallic alloys. To produce complex geometry parts, the nozzle is placed onto a 5-axis CNC machine to offer more flexibility in the movement of the nozzle. Several factors control this method of MAM: layer thickness, deposition rate, nozzle feed rate, laser power, gas flow, and the gap between the nozzle and printing surface [3]. The DMD can be divided into several

The Wire Arc Additive Manufacturing (WAAM) is used to build large components of titanium, aluminum, steel, and other metals. In this method, arc welding tool and wire (feedstock) are required to perform the process. This process is distinguished by high deposition rate, low material and equipment cost, variety of used materials, and good structure. These features make WAAM process dominant

Gas Tungsten-Wire Arc Additive Manufacturing (GT-WAAM) is the same as WAAM process with one difference; a localized gas tungsten shielding is used in GT-WAAM. The tungsten reduces the oxidation on the surface and increases the quality of the layer [15]. There are methods of Direct Energy Deposition (DED) available, and they function on the same concept of WAAM and GT-WAAM (weld-

*3.1.4 Electron beam melting*

**244**

Several metals (alloys) can be utilized in the MAM method. In this section, the most important metals (alloys) are listed as follows:

