# Simulation Analysis of Nanosecond Laser Processing of Titanium Alloy Based on Helical Trepanning
## 1 Introduction  
Titanium alloy has been a commonly used material in the aerospace field, but it often requires high-precision processing in the modern manufacturing industry [1, 2]. Laser processing is a new special processing technology with high processing accuracy that has been developed in recent decades [3, 4, 5]. However, different laser processing methods achieve different processing accuracy and effect. Laser scanning methods mainly include doughnut beam mode [6], helical drilling methods [7], and laser prerunning drilling [8]. Laser prepanning drilling has the advantage of high machining efficiency but a drawback of insufficient machining quality. The doughnut beam mode can easily lead to the formation of a recast layer and cause repeated thermal effects. The helical drilling methods have the advantages of controllable energy distribution and good machining quality but relatively poor processing efficiency. Owing to the advantage of helical drilling, laser helical drilling has been widely applied to welding [9] and drilling [10, 11, 12]. In Hongyu, [PERSON] et al. [13], the quality of a series of micropores, such as recast layer, microcracks, roundness and taper, produced on 304 stainless steel by a helical laser drilling system was discussed. The formation of a recast layer with thickness of about 25 \(\upmu\)m was detected on the side wall, and the taper phenomenon was also observed. A laser spiral drilling technology was proposed, which can be used to effectively manufacture high-quality micropores. As for helical drilling methods, [PERSON] et al. [7] reported an experimental investigation of shallow angle laser drilling of Inconel 718. Trials to improve drilling performance were conducted. Theyfound that a higher laser power, lower speed, and closer focal position to the workpiece surface contributed to the further removal of material by the absorption of more laser energy and larger beam intensity. However, in the simulation model of nanosecond laser drilling, deformation geometry is often used to track the interface change in micropores, and the change in recast layer is tracked by dividing the heat affected zone [14; 15; 16]. The deformation geometry model can not simulate the flow behavior of the molten pool. The simulation of molten pool behavior is mostly used for welding rather than drilling. For the simulation of phase explosion and other behaviors, the mathematical model has only recently been established and has not been applied to the actual processing [17; 18; 19; 20]. There have been fewer simulation studies on nanosecond laser helical drilling. In the interaction between the laser and the material, the material first absorbs the laser energy and converts it into heat energy. In this process, the material melts and forms a molten pool to further absorb the laser energy. With the increase in material temperature, the material vaporizes, and the degree of vaporization increases. Under the action of the thermal stress field, the material is removed in the form of vaporization fly-out and a small amount of liquid splash. This process is the main process of nanosecond laser material removal. The influence range of a nanosecond laser is concentrated near the laser spot area. However, changes in the laser scanning path affect the accumulation of laser energy in a material, resulting in different removal effects. Spiral scanning has often been used in actual processing, but it is time consuming. In the nanosecond laser processing process, the main processing mechanism is the evaporation of the processed material and the re-condensation of the material after melting. Therefore, analyzing the interaction between laser spiral scanning and materials is crucial to explore and master further improvements in laser processing technology. Owing to the fact that a solid heat transfer simulation model can not accurately reflect the interface separation generated, there have been fewer simulation studies on laser spiral scanning.