# Arc Shape Characteristics with Ultra-High-Frequency Pulsed Arc Welding
## 3 Results and Discussion
### Arc Core Region, Total Area and the Ratio of the Core Region to the Total Area  
Under the circumstance of different currents and pulsed frequencies, images that contain stable welding arc physical information are chosen when the welding tungsten electrode is fully burning and the welding arc is burning persistently. Based on MATLAB, we get the area relative value by counting the amount of pixel points. The core region area, the total area, and the ratio of the core region to the total area are calculated, and the average values of the data obtained are presented in Table 1.  
Figure 5 illustrates the core and total areas against the pulsed frequencies. It is a double-coordinate line chart, with the horizontal axis representing the pulsed frequency and 0 kHz representing the conventional direct current, while the vertical axis on the left shows the region area relative value with 60 A and, on the right, it indicates the region area relative value with 80 A. The total arc region expanded with the large current, which coincided with the classical theory. That means the arc with the large energy input possessed a larger portion of the region. A possible reason for this is that more ionization results in a greater particle collision region. The welding current can be maintained in an expanded region as the charged particles are enough to guarantee the stable current transformation. Thus, the welding current level from 60 to 80 A made a large total area of the arc plasma. The current increased by 33% and, in contrast, the total arc region increased by 14.75%. Furthermore, the core region expanded with the large total area, and the increasing rate was about 22%. The ratio of the core region to the total increased from 47.7% to 50.5%. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Frequency**} & \multirow{2}{*}{**Current**} & \multicolumn{2}{c}{**60 A**} & \multicolumn{2}{c}{**80 A**} \\ \cline{2-7}  & **Core Area** & **Total Area** & **Core/Total** & **Core Area** & **Total Area** & **Core/Total** \\ \hline
40 kHz & 236,662 & 462,110.5 & 0.51213 & 270,029.5 & 501,016 & 0.53896 \\
20 kHz & 233,596.5 & 462,005.5 & 0.50562 & 257,142.5 & 497,471.5 & 0.51691 \\ C-DC & 202,868 & 426,122 & 0.47609 & 246,720.5 & 488,955 & 0.50458 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Average data of the core region area relative value, the total area relative value, and the ratio of the core region to the total area. C-DC means conventional direct current. Figure 5: Core region and the total area. When the current is constant at 60 or 80 A, from conventional DC to a pulsed frequency of 20 or 40 kHz, a larger core region, total area, and ratio of the core region to the total area can be found. At the 60 A current level, the absolute values were larger in the core/total regions with the increasing pulse frequency. The effect of the pulsed current was significant with the expanded core region, which increased by 15%, at least compared with C-GTAW (Conventional-GTAW). Furthermore, the ratio of the core region to the total area was even more than C-GTAW at the 80 A level. It needs to be noted that the differences of the absolute areas between 20 and 40 kHz were not significant. However, the ratio was 51.2% at 40 kHz, which meant a large core region. The variation of the arc total area shows the shrinkage-expansion of the arc shape. The variation of the core region reflects not only the ionization thermal motion, temperature, and current density, but also the shape, force, and others; it is a sign of the transmission of energy. As for the ratio of the core region to the total area, it is the efficiency of the energy transfer from the cathode to the arc to the welding material [25]. Obviously large currents can create more energy input with larger arc plasma. The ratio of the core region was recognized as the result of the energy concentration or arc constriction. The classical theory indicated the radial electromagnetic force compressed the arc plasma with a large or pulsed current.