Numerical And Experimental Research On Effect Of Pulse Laser Processing On Metal Surface

Pulsed laser is widely used in industry to obtain a specific surface morphology on metal.The formation of the specific surface morphology is the result of the complex physical process of the interaction between the light and the target,which is closely related to the laser pulse width.When the pulse width is greater than the thermal relaxation time,the thermal effect plays a key role in the formation of the surface topography.While the pulse width is less than the thermal relaxation time of the material,the thermal effect of the target is small.The formation mechanism of surface topography is quite different from that of long pulse laser.Femtosecond laser and microsecond laser are chosen to investigate formation and mechanism of surface morphology which is irradiated with the long pulse and the ultrashort pulse laser on metals,from the two aspects of experimental and numerical.The main contents are as follows:(1)With the COMSOL Multiphysics,the energy distribution irradiated by ultrashort pulse laser on metal and the distribution of the temperature field of metal after long pulse laser are numerically studied.It shows that the denser the surface microstructure is,the more laser energy the peak of the microstructure will be as well as because of the thermal effect of long pulse laser,the heat affected zone is larger than that of the spot.(2)Ultrashort laser irradiating metal surface forming microstructures are operated to investigate the impact of material,surface roughness of the target and laser energy on the evolution of surface morphology.It is concluded that due to the interference of the laser and the surface wave,resonant surface periodical structure is formed.Further-more it is easier to be formed with more laser energy the material absorbed.The contour of the surface periodic structure formed by ultrashort laser irradiating is more obvious while single pulse energy is greater.However,because of the uneven distribution of Gauss beam,the thermal effect of the beam of greater single pulse energy is more obvious.(3)Experimental study to demonstrate the effect of the repairing of crack surface of metal with long pulse laser irradiating is operated,as well as the influence of output power and defocusing distance to the surface of different metal was studied.It is revealed that the metal with low hardness can be easy to repair the crack of surface.When the output power is suitable,the quality of the metal surface can be improved by adjusting the defocusing amount.