**2. Materials and Methods**

#### *2.1. Materials for WAAM process*

Experiments have been carried out on a substrate of a S235JR steel sheet of 3 mm thickness, 150 mm long and 100 mm wide. This substrate has two main functions: as a support for the deposited metal and as a heat dissipation system for the heat generated during the process by conduction transfer through the aluminum work table.

The wire material (AWS ER70S-6) is a 0.8 mm diameter mild steel wire with a copper coating supplied on a 15 kg coil. This steel is commonly used in a lot of applications related to construction work, pipes, shafts, car bodies, tanks, steel castings or forgings, and general shop fabrications.

The properties of the base material (substrate) and the deposited material are shown in Table 1. The density of both materials is approximately the same, while the mechanical properties are better for the case of the deposited material.


**Table 1.** Properties of the substrate and the welding wire.

Chemical composition of welding wire is shown in Table 2.

**Table 2.** Chemical composition of welding wire.


The results of the process depend on the protecting gas. It has been used a mixture composed of CO2 (15%) and Argon (85%) that led to the stability of the process, improvement in the surface finishing quality, and a reduction of the splatters. It has been observed that the welding drops are smaller with the reduction of the amount of CO2.

#### *2.2. WAAM Equipment*

The WAAM equipment is composed of two different systems (Figure 1), as described in detail in a previous work [38]:

• Welding system: cold metal transfer technology, patented by Fronius®, was used as welding process with a Fronius TPS 4000 CMT R machine (Fronius International GmbH, Wels, Austria). In this technology the intensity and voltage control is made during the deposition. By virtue of this principle, the temperature of welding temperature is reduced and the wire movement is optimized. As a result of this, the quality of weld beads is better than using conventional GMAW welding [39].

• Positioning system. The control of the movement in an easy way was made by a BF 30 Vario Optimum CNC milling machine (Optimum Maschinen Germany GmbH, Hallstadt, Germany). It has been adapted by fixing the welding torch to the milling head in the Z axis, while the X-Y table of the CNC system enables the deposition of a layer in the fixed Z level. To deposit the next layer, the Z axis elevates the torch and makes the deposition in the next Z level.

As shown in Figure 1, an auxiliary working table has been developed in order to isolate electrically both systems as well as to cool the working area.

**Figure 1.** Setup of the integrated WAAM system in the positioning table.
