## 4 Discussion
### Explanatory Model  
The present paper aims to explain the changed mechanisms and process improvements due to beam oscillation. The thermographic analysis visualizes the temperature distribution and enables the interpretation of energy deposition and heat conduction. Thus, several aspects characterizing the process zone and the melting process during LBFC have been evaluated. As the main process improvements relate to an increased cutting speed and reduced burr height, this explanation focuses on these properties. According to the state of the art, an increasing cutting speed requires increased laser beam energy. Static beam shaping realizes this by setting the focal plane near the workpiece surface, enforcing the minimum operative spot size with maximum laser beam intensity. This narrows the cut kerf, causes a small melt volume, and enhances the cutting speed. Simultaneously, the interaction time inevitably decreases, which in turn has a negative effect on the melt ejection. This leads to insufficient melt ejection, degraded cut edge quality, and may provoke a process collapse in the worst case. By applying beam oscillation, the cumulative energy deposition does not change as long as focal position and cutting speed remain equal to static beam shaping. However, beam oscillation (with sufficient amplitude) extends the interaction time, which influences the melt ejection and cut edge quality. Optimized oscillation and cutting parameters increase the cumulative energy deposition, which enhances the cutting speed. Therefore, by applying beam oscillation, it is feasible to obtain the desired effects in combination: an increasing energy deposition with a simultaneous extended interaction time, which is impossible in the case of static beam shaping. Beam oscillation produces a steady and flat cut front compared to static beam shaping. The changed cut front angle due to beam oscillation enhances the absorptivity over a wide range of the cut front and increases the amount of dissipated energy. Additionally, this increases the peak temperature locally. The named effects are visualized in Figure 22.  
The gradual energy deposition causes a volatile temperature distribution, which is characteristic for beam oscillation. The high temperature reduces the viscosity of the melt film, which improves the melt ejection and in turn reduces the burr attachment and surface roughness. The sequential cooling periods of the process zone keep the melt film thin, avoid heat accumulation, and enable efficient melt ejection. A slight melt film thickness in combination with high peak temperatures implies high temperature gradients within the melt film, which accelerates the heat transfer and thus the ongoing melting process. This is another reason for obtaining higher cutting speeds compared to static beam shaping. Thus, the above-described improved melting process in combination with improved melt ejection enables a clearly higher productivity together with high quality. So, all the namedaspects--the energy balance, the volatility, the absorptivity and the interaction time--are essential to obtain the named process improvements due to beam oscillation. **Author Contributions:** Conceptualization, T.P. and C.G. ; methodology, T.P. and C.G. ; validation, T.P. and C.G. ; formal analysis, T.P. ; investigation, T.P. ; resources, T.P. ; data curation, T.P. ; writing--original draft preparation, T.P. and C.G. ; visualization, T.P. ; project administration, T.P. and C.G. ; funding acquisition, T.P. and C.G. All authors have read and agreed to the published version of the manuscript. **Funding:** This research received no external funding. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data presented in this study are available on request from the corresponding author. **Acknowledgments:** We thank our colleagues from the Heat Treatment and Plating department of the Fraunhofer IWS for their support in calibrating the measurement setup.