Research On Pulsed Laser Ablation Surface Micro-texture Technology And Laser System

Laser surface texture technology(LST), a kind of laser surface treatment technology, mainly used for surface micromachining with the purpose of optimizing the surface tribology performance, reduce friction and wear on the surface of the parts,improve life of parts and reduce the energy consumption of mechanical system. Laser surface texturing technology is highly concerned with its high flexibility, high efficiency,low cost, non-contact processing and suitable for a wide range of materials and other outstanding features. To achieve the active design and fabrication of micro textured surface, in-depth to reveal the mechanism of laser micromachining, and to obtain optimum combination parameters of laser technology, this paper carried out the following main research work.Firstly, the mechanism of nanosecond pulsed laser ablation of metal is studied.Theoretical model is proposed to describe the nanosecond pulse laser and material interaction, including the target temperature field, melting and vaporization process,vapor density, velocity and temperature field, the degree of ionization of the plasma and density distribution of the particle, and plasma absorption of incident laser.Secondly, according to the requirement of laser parameters of micro texturing process, the all solid state Nd:YAG laser of laser micro machining system is successfully developed by using the acoustic optic Q mode and the flat convex resonant cavity. According to the stability condition of the resonator, we calculate the L1-L2 stability zone distribution, and analysis the effect of the convex mirror radius R to resonator stability, and by the self-consistent calculating cavity spot diameter. Measured on the static and dynamic laser output power, pulse width and output spot, the measured maximum Q switch off current is 20.6A, Q efficiency reached 72.5%, pulse width range of 100 ns to 250 ns. the spot is Gauss distribution and roundness is 92%.Thirdly, the effect of single pulse intervals(SPI) on processing of the laser micro texture was discussed. An investigation on target surface was performed by using Nd:YAG laser. The influencing laws of parameters(the laser fluence, number of pulses,different material) and the geometrical parameters of micro-crater as well as laser absorption rate of surface plasma were investigated. The results show that with the increase of the laser fluence, the micro-crater diameter increase with a logarithmic function, while the micro-crater depth increases, then leveled off, finally fell slightly.Effect of pulse number of micro-crater diameter was not significant, but the micro-crater depth increases linearly. Comparison of the effects of different materials on micro cavity morphology, it found that the hard chromium has a larger ablation threshold and trace elements in gray cast iron can increase the micro cavity size.According to the relationship between the diameter of the cavity and the laser energy density, It is concluded that the ablation threshold of 45 steel is 6.86J/cm2. In this paper,a method for measuring the absorption rate of plasma is presented.Finally, from the point of view of experiment and temperature field simulation, the characteristics and technical advantages of the SPI process and the same point continuous process were analyzed and compared. Compared continuous pulses processing, SPI can minimize the negative of heat effect, and the effect of multiple pulse on micro texture internal morphology has a "smooth" role; under the condition of guarantee a single pulse of material removal rate, the efficiency of the laser processing high quality micro texture was improved.