Research On The Quality Of CFRP Hole Making Based On Femtosecond Laser

Carbon fiber composite is a new type of multi-functional special engineering material,which is widely used in civil and military fields,especially in aerospace field.However,due to the high hardness and difficult processing of carbon fiber composites,the traditional tool processing can not meet the requirements of fine processing,resulting in large defects in the processed parts.Considering the advantages of femtosecond laser in fine processing,femtosecond laser is applied to the processing of carbon fiber composites drilling in this paper.By means of numerical analysis,mathematical modeling and experimental research,the interaction mechanism and processing technology between laser and carbon fiber composite were explored.The main contents of this paper are as follows:(1)The interaction mechanism between femtosecond laser and metal and non-metal was analyzed.Based on the simplified two-temperature equation,the interaction process between femtosecond laser and material was simulated by finite difference method.The ablation effects on the variation of surface electrons and lattice temperature during the process of single pulse energy,acoustic-electric coupling coefficient,incident laser pulse width and material surface reflectivity were analyzed.(2)Femtosecond laser ablation experiment was designed,and the ablation process of CFRP with laser power was observed.The ablation thresholds of epoxy resin matrix and carbon fiber reinforcement were calculated respectively.The influence of the cumulative effect of multi-pulse laser ablation on ablation threshold is analyzed,and the cause of the fluctuation of ablation threshold is explained.(3)The process of femtosecond laser cutting CFRP is analyzed.Firstly,the mathematical model of laser cutting is established based on energy conservation law,and the model is modified by experimental data.Then,the mathematical model of slit roughness is established from the angle of mathematical geometry.By increasing the laser repetition frequency,the difference of inner and outer circular arc tangential roughness can be eliminated.Finally,the influence of fiber arrangement direction,laser power,cutting speed and cutting cycle times on the cutting heat affected zone(HAZ)was analyzed by experiment.When the laser power is 200 mW,the cutting speed is 2 mm/s and the repetition times are 5 times,the width of HAZ is 5 micron and the cutting depth is about 220 micron.At this time,the width of the HAZ could be guaranteed and the deeper cutting depth could be obtained.(4)Completing femtosecond laser CFRP hole-making experiments,the effects of laser power,single-layer scanning times,focal defocusing amount and focal feed amount on hole diameter deviation,roundness and roughness are analyzed.When the laser power is low,the single-layer scanning times are three times,the defocusing amount is 0,and the feed rate is lower than the theoretical cutting depth,it can be used to ensure the dimensional accuracy and roundness of the hole and the lower roughness of the hole wall.Aperture tolerance level is IT4?IT5 and axial roughness is guaranteed to be less than 2 micron.