Research On Processing Technology And Surface Quality Of Metal Micro-holes Machined By Femtosecond Laser

The pulse width of femtosecond laser is extremely short and the peak power is extremely high. So there are several advantages for processing of metals by femtosecond laser such as small heat-affected zone and high precision machining that traditional laser does not have in the field of metal drilling and cutting etc. Especially when processing film cooling holes in the aero-engine turbine blade, the requirements are very high on the quality and accuracy. Femtosecond laser is used to process high quality holes that recast layer and micro-crack is precious few under proper parameters. In this paper, effect of different processing parameters on size and quality of drilling holes with multi-pulse impact method and rotary cutting method by femtosecond laser is studied. The main research contents are as follows:1. The physical process and mechanism of femtosecond laser processing of metal were analyzed. The two-temperature model of femtosecond laser processing metal was simplified and solved, and the result showed that the thermal effect of femtosecond laser processing was smaller than picosecond or nanosecond laser processing.2. The different methods of femtosecond laser drilling metal holes and its application conditions were analyzed. Experiments were carried out to drill holes with multi-pulse impact method in copper foils. The ablation threthold of copper foil was determined according to the experiment results and the threthod theory. Obtained the pattern of different pulse energy, number of pulses, and defocusing amount influenced on the pore size,roundness, taper and the ablation rate.3. Multi-wedge rotary cutting processing system was used to conduct experiments of rotary cutting holes on metals by femtosecond laser. The experiments analysis of different process parameters influence on machining holes and get high precision deep holes with diameter controlled in range of0.1-1.2mm.4. The experiment of femtosecond laser cutting copper foil was conducted. The reasons for the reduction of surface quality processed by femtosecond laser were analyzed. The copper foil cutting section roughness was measured to get the effects of different single pulse energy and cutting speed on surface quality. A processing method with weak femtosecond laser scanning to repair the surface was proposed. The optimal process parameters were found to improve the machined surface quality and reduce the roughness value. The processing method was verified in the rotary cutting holes experiment. Pictures49, tables1, papers60...