| Hard and brittle dielectric materials represented by quartz are widely used in aerospace,consumer electronics and weaponry and many other fields.In view of the defects such as re-condensation and micro-cracks in the actual processing of femtosecond laser,an ultrasonic gas jet-assisted femtosecond laser processing technology is proposed.The steady jet is converted into a pulsating jet by the coupling of ultrasonic and gas jet,and the purging effect of the jet is used.And the highfrequency scouring action of the pulsating jet takes away the heavy condensate generated during the processing,reduces the adhesion of the heavy condensate on the processed wall surface,improves the processing efficiency and improves the processing quality.The main research contents of this paper are as follows:(1)An ultrasonic gas jet system is proposed,which is composed of a sandwich ultrasonic transducer and a jet nozzle through mechanical solid connection.Ultrasonic transducers at three frequencies of 20 k Hz,25 k Hz,and 28 k Hz are set up.The design errors of the three transducers are designed and calculated by the COMSOL Mutiphysics simulation software.The design errors of the three transducers are 0.62%,7.62%,0.54%,respectively.The vibration speed ratios of the three transducers can reach 23.33,64.31,and 97.10,respectively.In order to reduce the wall loss of the ultrasonic in the nozzle propagation,the inner cavity of the nozzle is designed as a straight cone.(2)The coupling simulation of ultrasonic and gas jet is realized by using ANSYS simulation software combined with dynamic mesh technology.Firstly,the nozzle size was carefully optimized without ultrasound,and secondly,the influence of ultrasound frequency and ultrasound amplitude on the flow field structure was explored.The results show that: under the action of ultrasound,the maximum flow rate at the outlet can be increased by about 5 times under the condition of low-speed jet inlet.With the increase of the inlet velocity,the increase of the maximum velocity of the outlet gradually decreases,and the maximum velocity of the outlet can also increase by about2 times under the condition of high-speed inlet.The ultrasonic amplitude mainly affects the pulsatility of the flow field and has little effect on the maximum velocity of the flow field.The maximum velocity of the flow field increases and the pulsation of the flow field increases.However,the concentration of the jet field is weakened under the action of ultrasound.(3)The technology of femtosecond laser etching of quartz micro-grooves with or without ultrasonic assistance was studied,and the post-processing of quartz microgrooves after laser processing was carried out in combination with wet etching technology.Firstly,the influence of single pulse energy,scanning times,scanning speed and defocus amount on the etching of quartz microgrooves was studied,and femtosecond laser stealth cutting technology was explored,and the surface roughness of the cracked area could reach below 50nm;Secondly,the effect of ultrasonic power,ultrasonic frequency and jet inlet pressure on the etching of quartz microgrooves was studied.The laser repetition frequency was 20 k Hz,the scanning speed was 4mm/s,the single pulse energy was 50μJ,the defocus amount was 0μm,and the depth of the quartz microgroove under a single scan was The width ratio increased from 0.81 without ultrasonic assistance to 1.23 with ultrasonic jet assistance(gas inlet pressure 0.6MPa,ultrasonic frequency 20 k Hz,ultrasonic full power 300W);Finally,the femtosecond laser etching combined with wet etching to treat the quartz micro-grooves is studied.The research shows that the "V" groove can be transformed into a straight-walled "U" groove under the action of 2% HF etching solution. |
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