毫秒激光金属打孔的解析和实验

Analysis and experiment on millisecond pulsed laser drilling of metals

研究了用毫秒脉宽的长脉冲激光单个脉冲打深孔的成形过程和打孔速率。首先,由切割法得到了1 ms脉宽的Nd∶YAG高斯激光对厚铝板打孔时孔的形貌,激光能量为7.9和28.9 J时,对应的孔深分别为1.849和2.975 mm。根据实验建立了轴对称模型,通过热传导方程得到了固相温度的解析解。然后,假设物质一旦熔融就离开孔,由能量平衡原理得到了孔形状的表达式。实验发现随激光能量增加,孔深增加,计算与实验结果差异也增大;进一步的计算显示,在其他条件不变时,光束半径的变化对孔深的影响较大。因此,引入离焦效应对算法进行了改进,改进后的计算结果与实验总体相符。最后,研究了长脉冲激光对铝、铜、银和钛4种金属的打孔速率,结果表明,钛对激光吸收最强、热传导率能力最弱,打孔速率最大。

With the purpose of investigating the millimeter order hole＇s formation and the drilling speed drilled by a single millisecond pulse laser,the shapes of holes in an aluminium slab drilled by a Nd： YAG Gaussian laser with 1 ms pulse width were obtained with the cutting method in an experiment.The hole depth is 1.849 mm and 2.975 mm when the laser energy is 7.9 J and 28.9 J,respectively.A semi-infinite axisymmetric model was established according to the experiment and the analytical solution of temperature in a solid phase was derived based on the thermal conduction equation.Meanwhile,by assuming that material was removed from the hole once it was melted,the function describing the hole＇s shape was obtained with the energy balance theory.It was found that the difference between the calculation and the experimental results becomes larger as well as the hole＇s depth increases with the increase of laser energy.Further investigation indicates that the variation of beam radius affects the hole＇s depth greatly under other unaltered conditions.Thus,the defocusing effect was induced to modify the analytical solution and obtained results are in agreemeat well with those of the experiments.Finally,the drilling speed of millisecond pulsed laser for aluminum,copper,silver and titanium were studied.The results show that drilling speed for titanium is the fastest one due to its high absorptivity for laser and poor heat conduction ability.