Research On Pulse-shaping YAG Laser Technology And Applications

This dissertation is focused on the pulse-shaping YAG laser technology and its applications in laser cladding and laser welding. Pulse-shaping is a technique that the pulse waveform of laser can be shaped in accordance with the software pre-set, which meets requirements on the laser energy for different materials, different processing and therefore get the best processing results by changing power density distribution of the laser pulse duration.The main contents of the dissertation include theoretical investigation, modeling analysis, shaping method, control system design and application experiments. Based on theory analysis of laser principal, relaxation oscillation as well as the interaction between light and matter, the feasibility of technical solutions that the laser waveform can be controlled by the method of software pre-set has been approved. According to optimal control theory, double-loop feedback control technology was applied for pulse-shaping system. AC small-signal dynamic modeling using state space averaging method was set up for the technology and a compensation network for voltage controller through transfer function of the equivalent power stage was also designed. The study also finished the design of control system for pulse-shaping based on ARM and completed the editing, driven design and download for waveform on the computer, and in the meanwhile realized the method of pulse-shaping. The research work also includes experiments of laser cladding repair for aircraft engine damaged blades and laser welding for lithium-ion battery tab using pulse-shaping technology. Metallographic analysis and microhardness evaluation for cladding layer were also conducted which demonstrated inspiring results.The major innovations in the work are summarized as follows:1. The realization of the output of the programmable waveform for pulse YAG laser, based on the request of the laser energy for different materials and different processing methods, a variety of laser waveform can be set.2. The application of double-loop feedback control technology based on peak current-mode in the field of the power electronics to the control of the laser beam power, and realized programmable pump pulse generation.3. The fulfillment of the experiments of laser cladding repair for damaged aircraft turbine engine blades using pulse-shaping laser, and got high quality cladding layer, and realized recovery of shape and functional. The results have important significance of economy and low-carbon value of environment.4. Specific software for setting of the laser waveform on the computer, waveform should be downloaded to pusle-shape control system via USB, and the latter drove chopper electrical for achieving of pulse-shaping.