# Study of the Mechanism of a Stable Deposited Height During GMAW-Based Additive Manufacturing
## 2 Experimental Details
### Results of Experiments  
Table 1 lists the influence of the predefined layer height (PLH) on the total height and width of thin walls comprising 100 layers. If the total height of the thin wall comprising 100 layers is equal to the substrate moving distance (SMD), it can be assumed that the distance between the torch and the substrate or the top surface of the thin wall is constant. From Figure 2, we see that when the predefined layer height is 0.85 mm, it is similar to the mean height of the thin wall, and this value represents the ideal situation; the rate of accumulated error is less than 0.15%. As a result, the dry extension of the electrode and the effect of the shielding gas are nearly constant. If the predefined layer height is not equal to 0.85 mm, the mean height of the thin wall varies between the predefined layer height and the ideal layer height of 0.85 mm. Figure 1: Schematic of the GMAW-based additive manufacturing system. The values of the predefined layer height lead to different distances between the torch and the substrate or the top surface of the thin wall. Specifically, the distance consists of two parts: the dry extension of the electrode and the arc length. To study how the predefined layer height affects the total height of thin walls comprising 100 layers, it is necessary to determine the factors decided by the dry extension of the electrode and the length. If the dry extension of the electrode is constant, the arc length has the same change as the distance. It alters the arc pressure, the Lorentz force, the radiation and convective heat transfer between the torch and molten pool surface. The arc pressure and Lorentz force decrease as the arc length becomes longer, and the conditions of heat dissipation improve. As a result, the height of the bead increases and the width decreases. While the arc length decreases, arc pressure and Lorentz force increase, and the heat dissipation decreases, so the height of the bead decreases and the width increases. However, if the arc length remains constant, the dry extension of the electrode changes with distance, and the forces acting on the molten pool do not change. \begin{table}
\begin{tabular}{c c c c c} \hline
**PLH (mm)** & **SMD (mm)** & **Total Height (mm)** & **Deviation (mm)** & **Width (mm)** \\ \hline
0.80 & 80.00 & 82.58 & \(-\)2.58 & 6.14 \\
0.81 & 81.00 & 83.48 & \(-\)2.48 & 6.00 \\
0.82 & 82.00 & 84.12 & \(-\)2.12 & 6.0  
To find the relationship between the shape of the bead and the dry extension of the electrode, the experiments focused on using various dry extensions of the electrode to weld only one layer at a time. From Figure 3, the welding bead with an electrode dry extension of 12 mm is lower and wider than the welding bead with an electrode dry extension of 20 mm. From Figure 4, the mean arc power, mean welding current, and the voltage all decrease while the initial dry extension of the electrode increases. The heat input into the molten pool depends on the mean arc power; as the initial dry extension of the electrode increases, the heat input into the molten pool also decreases. Figure 5 shows the shape of the bead, which only welds a layer on the substrate with different initial dry extensions of the electrode. The dry extension of the electrode changes over time during the welding process. As the initial dry extension of the electrode increases, the shape of the bead will increase in height and decrease in width. When the welding of every bead was complete, the dry extension of the electrode reduced by a length that is equivalent to the height of the bead plus nearly 1 mm. From the experimental data, it can be inferred that the dry extension of the electrode has a greater variation than the arc length, while the distance between the torch and substrate or the top surface of the thin wall changes. The key factors that determine the shape of the welding bead are the heat input into the molten pool and the heat dissipation conditions.