## 4 Discussion
### Coherence of Temperature Distribution, Energy Deposition, Cut Kerf Properties, and Cutting Result  
This chapter analyzes the individual parameters and explains their potential influence on the cutting process. Geometrical as well as thermal and time-dependent parameters and influences have been considered. The aim is to evaluate the changed mechanisms of LBFC by applying beam oscillation. A first observation is geometrically based: the reduced cut kerf width for beam oscillation (see Figure 10), related to the changed focal plane. In combination with the oscillation amplitude, this defines the melt pool size (see Table 5) and therefore the necessary amount of energy to enable a cutting process. The melt pool size decreases for beam oscillation, which allows higher cutting speeds (see Table 5), as less melting energy is needed. Another geometric influence depends on the cut front topography. The cut front absorbs and converts the laser radiation to thermal energy. The amount of absorbed energy (that enables the melting and cutting process) is limited by the local absorptivity along the cut front. Beam oscillation increases the absorptivity over a wide range of the cut front (see Figure 12 and Table 5). This achieves a continuously flattened cut front. The angle of incidence approaches the theoretical maximum in case of beam oscillation. As a consequence, process efficiency enhances due to the increased energy conversion and reduced transmission losses of laser beam radiation. The cutting speed is additionally increased as a result. With regard to the cutting speed, the interaction time must also be taken into account. The previous section explained how beam oscillation achieves a sufficient interaction time (see Table 5) to ensure a cutting process despite a high cutting speed. Considering another consequence of the narrow cut kerf width leads to temperature based influences. While for the energy balance, a narrow cut kerf and a small melt pool is favorable, for the melt ejection, it is not [1; 3]. With static beam shaping, a focal plane between \(-\)3.2 and \(+\)3.2 mm is not practical for the evaluated sheet thickness. It would lead to aggravated melt ejection and increased burr formation due to the narrow cut kerf. In combination with a cutting speed higher than 0.7 m/min, this would result in a collapsed cutting process in the worst case. Beam oscillation extends these limitations. Regarding set #1 as reference point, several temperature-based observations have been made. Beam oscillation achieves higher maximum temperatures within the melt pool \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 & \\ amplitude [\(\upmu\)m] & 0 & 300 & 550 & 300 \\ frequency [Hz] & 0 & 500 & 500 & 2000 \\ focal plane [mm] & \(-\)10.5 & \(-\)3.2 & 3.2 & \(-\)2.8 \\ cutting speed \(\mathrm{v_{c}}\) [m/min] & 0.5 & 0.85 & 0.7 & 0.7 \\ melt pool size [mm\({}^{2}\)] in Figure 19 & 0.65 & 0.37 & 0.48 & 0.36 \\ averaged absorptivity [\(\cdot\)] in Figure 12 & 0.27 & 0.39 & 0.43 & 0.39 \\ interaction time [ms] in Figure 20 & 132 & 70 & 132 & 84 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Overview of cutting speed, melt pool size, absorptivity, and interaction time for static beam shaping and longitudinal, linear beam oscillation. (see Figures 15-20, Table 6). In addition, the average temperature is higher for set #2 and set #3. Overall, this results in low viscosity of the melt film, which improves the melt ejection and supports a reduced burr attachment compared to static beam shaping. Therefore, when applying beam oscillation, it is possible to achieve a good cut edge quality in terms of burr attachment, even in combination with a narrow cut kerf and high cutting speed (e.g., set #2 and set #3). However, an explanation is still missing as to why not all oscillation parameters, especially set #4, achieve a process improvement.