# Simulation Analysis of Nanosecond Laser Processing of Titanium Alloy Based on Helical Trepanning
## 4 Conclusions  
In this study, the application of a nanosecond laser in practical engineering processing was numerically simulated. The long-time simulation results for the phase transition after nanosecond laser processing were discussed. Four states of material passing through two phases and temperature gradients were defined, and fluid dynamics were applied to the model. After a long-time simulation, the complex molten pool fluid behavior of a nanosecond laser was explained based on the interaction between the metal fluid and the steam. The simulation results were consistent with the actual data, and the effectiveness of the simulation model was verified. Based on the fact that solids are regarded as fluids with great viscosity coefficients, the complex nanosecond laser long-term processing model could be transformed into a time-domain thermodynamic fluid motion model to simulate materials. The characteristics of the micro hole's shape predicted by the simulation model were compared with the experimental results, and the following conclusions were derived:  
* A two-phase flow heat transfer model for nanosecond laser processing of titanium thin plate was established. The simulation model of microporous perforation was provided, which made up for the deficiency of deformation geometry simulation for perforation simulation.
* The model described the change in micropore shape under a spiral path and simulated the temperature distribution in the plate. By analyzing the isotherm and the shape of micropores, the movement behavior of molten pool was explained, and the thickness of the recast layer was displayed intuitively.
* The shape of the morphology depended on the distribution of laser energy. The shape obtained in the actual machining was consistent with the shape predicted by the simulation model. The flow change in the molten pool in the model explained the formation principle for a small number of fillets at the entrance of the material and the micro hole taper in the micro hole machining.
* With the increase in laser energy, the material removal rate, the depth and diameter of the morphology increased. The effect of laser energy on the morphology was more significant than other process variables. The relationship between laser power and scanning speed and the depth and width of micropores was established.
* The simulation model can be used as a prediction tool to select the best optical parameters to ensure the product quality and lowest cost of laser processing. In order to ensure the high efficiency and quality of laser processing, we should first select the appropriate laser energy parameters (such as the type and power of the laser), and then control the scanning speed, scanning path and other parameters to optimize the processing process.  
Conceptualization, K.Z. and F.L.; methodology, X.L., H.S. and W.X.; writing--original draft, Y.L.; writing--review and editing, Y.L. and G.F. All authors have read and agreed to the published version of the manuscript.  
This work is financially supported by Key Research and Development Program of Zhejiang Province (2022C01058); Key Projects of Natural Science Foundation of Zhejiang Province (LD22E050001).  
The authors declare no conflict of interest.