Study On Micro-polishing Theory And Technique Of Metal Materials Using UV Nanosecond Pulsed Laser

The laser micro-polishing of metallic materials is a newly developed surface processing technology in recent decade, which have been widely used in electronic equipment, precision machinery, instruments, medical equipment and other fields.Adapting the increase of requirement in laser micro-polishing of metallic materials, the theoretical and numerical analysis of the laser micro-polishing process was researched in this dissertation, and a laser micro-polishing system with real-time control of laser energy density was designed. The micro-polishing experiments for stainless steel, titanium and nickel metallic materials were made, and the results were evaluated.The completed works in this dissertation are as follows:Based on the basic equations of transient one-dimensional heat conduction, the thermodynamic process of the laser micro-polishing for the metal surfaces was analysed, the quasi-static and dynamic models on the metal laser micro-polishing process were respectively discussed. Used one-dimension finite difference method, the laser micro-polishing processes on the three sorts of metallic materials, stainless steel 316L, nickel and titanium, were numerically simulated. In this dissertation the parameters of laser micro-polishing process were optimized and the variational trend of the metallic surface morphology by laser polished was predicted.In this dissertation the relationship of micro-polishing effect and optimum laser energy density was studied. And it was proposed that a method for the real-time control of laser energy density using two beams of lasers (high power pulsed laser used for polishing, the low-power continuous laser used for detecting). It will be very important to the reseach of laser micro-polishing.A laser micro-polishing system using two lasers was made, the real-time feedback control of laser energy density by using a coaxial optical system was realised. And using the system, the micro-polishing experiments on stainless steel, nickel and titanium were made. The several factors, such as laser energy density threshold, the optimum laser energy density, scanning speed, defocus distance and overlap rate, and those can influence to polishing effects were considered and analyzed. The optimum parameters of laser micro-polishing were obtained and some better polishing effects were achieved: the surface roughness of 316L stainless steel sample reduced from 592.88nm to 329.47nm after polishing, titanium's reduced from 123.3nm to 80.96nm, nickel's reduced from 121.4nm to 94.41nm, respectively. Some of laser polishing experiments on the tilt and bending metallic surface were made and better results were also gotten.