The Experimental And Numerical Simulation Study On Mass Migration During The Combined Pulsed Laser Drilling

In this paper,aiming at the condition of fused mass can’t move out of the hole and block the hole due to lack of power,a new combined double pulse laser drilling method is used to increase the migration ratio of melting mass and reduce the recast layer thickness.On the basis of studying the influence factors of millisecond pulsed laser drilling,the effect of the second nanosecond pulsed laser shock wave was also studied.The combined pulse laser drilling experiments were carried out,and the drilling process was simulated by finite element analysis in order to investigate the migration movements of melting material in the hole.Millisecond pulse laser drilling is the basement of the double pulse laser drilling.First,millisecond pulse drilling experiments were carried out to obtain the relationship between the laser energy and the ejection ratio of the melting material.The larger the laser energy was,the higher the ejection ratio was.The higher the laser energy was,the higher steam recoil pressure induced by vaporization was.At the millisecond laser energy of 46.2J,the ejection ratio was up to 24.3m/s,the recoil pressure was 1.007 × 10^-3N.In double pulse laser drilling process,the nanosecond laser was used to generate shock wave,which was used to promote the exiting of the melting mass.The role of shock wave was explored from two aspects of experiment and simulation.The results showed that the deeper the hole depth was,the effect of shock wave would get lower.When the depth of the hole increasing from 0.5mm to 3mm,the material ejection rate decreased from 95.57%to 29.97%,and the migration rate of melting mass decreased significantly.In the combined double pulse laser target impulse experiment,the sum of the recoil pressure induced by vaporization and the shock wave pressure can reach the order of MPa.The results of double-pulse experiments showed that the depth of the hole increases by 9.9%～25.4%compared to the single pulse millisecond laser drilling.The addition of nanosecond laser made the migration of the melting mass stronger.The time of second nanosecond laser addition also determined the amount of melting mass migration.Adding nanosecond pulsed laser at 125μs,the depth of the hole can be increased by 17.2%,the mass migration rate increased obviously.