Heat Accumulation Model And Experimental Study Of TC4 Titanium Alloy By Femtosecond Laser Machining

The femtosecond laser is capable of non-thermal processing of materials due to its very narrow pulse width and high peak power.Femtosecond laser has a small processing area and high machining accuracy.It can be processed with micronano and has the advantages that other processing methods are difficult to replace.The mechanism of femtosecond laser and the double temperature model are discussed in this paper.In the multi-pulse femtosecond laser,the heat accumulation in the material will lead to the increase of temperature,which may lead to phase transformation or even melt.In order to maintain the temperature in a reasonable range to achieve good processing effect,proper machining parameters need to be selected,so that the heat accumulation temperature reaches a balance and below the melting point of the material.This paper has established the heat accumulation model of TC4 titanium alloy,with COMSOL Multiphysics software researching different scanning speed,repetition frequency and laser energy's influence of heat accumulation.The surface temperature is calculated according to the model.The model is applicable to different materials,providing the prediction of machining parameters for femtosecond laser processing.Compared with other heat accumulation models,the accuracy of the model is verified.The simulation result shows that the laser scanning speed influences the trend,selecingt the appropriate scanning speed can achieve the balance of heat accumulation temperature;The repetition frequency of the laser influences the thermal equilibrium temperature.As the laser repetition frequency increases,the equilibrium temperature reaches the thermal equilibrium state.The laser energy directly influences the temperature of heat accumulation,and the laser energy can cause a serious thermal effect.Therefore,the laser energy should be controlled in a reasonable range.The experiment of TC4 titanium alloy was selected according to the simulation results.Femtosecond laser ablation experiments mainly choose France Amplitude Systemes of Satsuma HP2 laser.Laser pulse width 320 fs,the laser light aperture spot is 2.3mm(before focusing),spot diameter 30-35 um,laser wavelength 1030 nm.The experiment was carried out in two parts,with four groups of materials carried out the ablation experiment of femtosecond laser and two groups of materials carried out the removal experiment of femtosecond laser.The processing parameters of the scanning experiment:(a)energy 10 ?J,velocity 4 m/s,repeating frequency 2 MHz;(b)energy 20 ?J,velocity 4m/s,repeat frequency 1 MHz;(c)energy 40 ?J,velocity 4 m/s,repeat frequency 0.5 MHz;(d)energy 40 ?J,velocity 2 m/s,repeat frequency 0.5 MHz.The roughness of the four groups of ablation experiments is 25.1?34.6?51.6?62.2 nm respectively.The surface remove depth of the two groups was 36 ? m and 27 ? m.