## 4 Discussion
### Coherence of Temperature Distribution, Energy Deposition, Cut Kerf Properties, and Cutting Result
The temperature characteristic within the melt pool has further consequences. Beam oscillation changes the energy deposition compared to static beam shaping. In concrete terms, volatile temperature characteristics with high peak values (see Figures 18b-d and 21b-d) were metrologically verified. Assuming optimal beam oscillation, which is set #2 in this investigation, obtains the following effects: The high peak temperature decreases the viscosity and enhances the temperature difference in the melt film. As stated before, the decreased viscosity improves the melt ejection, which in turn leads to a reduced melt film thickness. As already mentioned, periodic cooling is detectable with the measured temperature volatility. During these cooling periods, the existing melt volume continues to interact with the gas jet. As long as it remains in the molten phase, the cutting gas jet ejects this material. This further reduces the melt film thickness [24]. A high temperature difference within a small melt film thickness attains a high temperature gradient. In turn, the heat conduction rate toward the cutting direction increases. This is an important prerequisite to enhance the cutting speed [1; 3; 23]. A high temperature gradient is also advantageous for a high-quality cut edge [1; 3; 23]. These observations are not only valid for set #2, but also set #3. This set has larger amplitude compared to the optimal beam oscillation, which achieves the highest absorptivity (see Table 5). Overall, set #3 results in a good, but slightly lower cut quality compared to set #2 (see Table 4). In contrast, set #4 does not meet optimal beam oscillation. Although the geometric properties in terms of melt pool size and absorptivity are comparable to set #2, the resulting temperature characteristic, cutting speed, and quality differ significantly. The highest temperatures are only achieved for a small portion of the melt pool (see Figure 19). In concrete terms, only for 800 \(\mu\)m\({}^{2}\) were the measured temperatures higher than those for set #2. This is equivalent to 0.22% of the melt pool size. Therefore, the largest part of the melt pool remains colder compared to set #2. This mirrors the reduced average temperature in Table 6. Such a low average temperature indicates a high viscosity and results in aggravated melt ejection. Part of the melt remains on the cut edge and leads to an increase in surface roughness. Another part adheres to the bottom side of the sheet and produces the distinct burr attachment. In addition to this explanation, there are additional reasons for the reduced cut edge quality of set #4. A temporally based influence, as the oscillation frequency, is the main difference between set #2 and set #4. It was the highest at set #4 within the investigation. As a consequence, a very high beam velocity is achieved. This results in a low amount of deposited energy per time. The temperature sequence for set #4 is characterized by significant temperature drops (see Figure 18d). It is distinguished by the highest volatility and the lowest average temperature at the cut front for all evalu \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Set \#1** & **Set \#2** & **Set \# 3** & **Set \#4** \\ \hline beam shaping & static & & & longitudinal, linear \\ burr height \(\mathcal{O}\)\({}_{\text{burn}}\) [m/min] & 1.1 & 0.65 & 0.78 & 1.37 \\ surface roughness \(\mathcal{O}\)\({}_{\text{Rz}}\) [\(\mu\)m] & 79 & 75 & 116 & 125 \\ highest temperature of \(T_{\text{LJ}}^{\text{max}}\) [\({}^{\circ}\)C] in Figure 16 & 2250 & 2665 & 2600 & 2910 \\ average temperature of \(\overline{\text{T}_{\text{PJ}}}\)(t) [\({}^{\circ}\)C] in Figure 18 & 1890 & 1970 & 1930 & 1670 \\ volatility \(\Delta\Gamma\) of \(\overline{\text{T}_{\text{PJ}}}\)(t) \({}^{\circ}\)C] in Figure 18 & 575 & 1230 & 1420 & 1700 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Overview of burr height, maximum, and average temperatures and temperature volatility for static beam shaping and longitudinal, linear beam oscillation (calculated with e = 1).