# Investigations of the Absorption Front in High-Speed Laser Processing Up to 600 m/min
## 5 Conclusions  
In this study, the processing zone in high-speed laser processing of stainless steel AISI 304 with speeds from 1 m/s up to 10 m/s was examined. The effects on the process zone due to the processing speed while using a half-section setup were described with the aid of external process observations. It was shown that a keyhole only formed at a processing speed of 1 m/s. Already at 2 m/s, the processing zone could instead be described as a leading absorption front with a trailing melt-free zone. Increases of the processing speed beyond 6 m/s led to an enhanced spatter formation. Finally, four empirical process model conditions were illustrated based on the measured and observed aspects. Considering these results, for the process and material parameters applied in this work, the following conclusions were drawn:  
1. The resultant loss of mass clarified the different process regimes that dominated in the range of processing speeds from 1 to 10 m/s. There was an increase by a factor of more than 10 for the resultant loss of mass at 10 m/s compared to that found at 1 m/s. It could be observed that the loss of mass started to increase significantly at processing speeds of 7 m/s. Examinations on metallographic cross-sections showed differences in the amount of remaining melt at the walls and bottom of the resulting kerfs for high processing speeds.
2. The resulting inclination angle increased nearly linear with the increased processing speed. Under the applied process parameters, an angle of about 14\({}^{\circ}\) was produced at 1 m/s, while the absorption front was inclined at about 70\({}^{\circ}\) for processing speeds of 10 m/s. The correlation with the resulting loss of mass showed significant increases at inclination angles of about 60\({}^{\circ}\).
3. At processing speeds between 4 and 6 m/s, the preferred orientation of single spatter detachments was observed to be lateral and frontward relative to the scanning direction, with velocities comparable to the processing speed. The orientation of the spatter detachment occurring at processing speeds beyond 7 m/s was characterized as being primarily against the scanning direction. At the same time, a much higher amount of finer spatter was observed to occur at a processing speed of 7 m/s, when the absorption front was inclined at about 60\({}^{\circ}\). As such, the formation of long trajectories for a single spatter demonstrated its immense acceleration out of the processing zone.  
Conceptualization: [PERSON], [PERSON] and J.P.B.; methodology: P.H. and K.S.; investigation: P.H.; formal analysis: P.H. and K.S.; data curation: P.H.; visualization: P.H.; writing--original draft: P.H.; supervision and discussion: [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
This research was funded by EUROPEAN UNION FUNDS UNDER THE EUROPEAN REGIONAL DEVELOMPENT FUND (ERDF), grant number 2017 FE 9091.  
Not applicable.  
The precision balance was provided by the Machine Elements Group of the Technische Universitat Ilmenau. The support is gratefully acknowledged.  
The authors declare no conflict of interest.