飞秒激光加工过程的热积累模型及参数优化

发布时间：2018-09-01 07:39

【摘要】：飞秒激光具有高功率、高精确度、热影响区小等优点,可直接去除表面材料,实现微纳加工,在航空、航天、半导体、生物等材料表面加工领域具有不可替代的优势。然而,在多脉冲飞秒激光的作用下,材料内部可能产生热积累和温升,导致发生相变、氧化、甚至熔化。因此如何优化飞秒加工参数,控制热积累和温升是一个迫切需要解决的问题。本文对飞秒激光加工材料表面的热积累效应进行了论述,并且应用有限差分法,利用MATLAB软件对飞秒激光加工AZ31镁合金表面的热积累效应进行了数值模拟,模拟了不同的扫描速度、激光重复频率、光斑直径、激光能量对加工过程热积累效应的影响,优化激光工艺参数。并且通过对不锈钢加工过程的模拟,与其他的模型进行了对比。考虑与材料相关的热传导系数和热容,利用中心差分法分别模拟了AZ31镁合金在扫描速度为1 m/s、2 m/s、3 m/s、4 m/s下的表面热积累和温度变化。结果表明,扫描速度的提高会使热积累温度会有所降低,在扫描速度为1~3 m/s时,AZ31镁合金表面的热积累温度并没有稳定,当扫描速度为4 m/s时,AZ31镁合金表面的热积累温度在经过10个脉冲的作用后会趋于平衡。扫描速度主要是通过改变光斑重叠率影响加工过程的热积累;此外,分别模拟了AZ31镁合金在激光重复频率为100 kHz、500 kHz、1 MHz、2 MHz下的表面热积累和温度变化。结果表明,激光重复频率的提高使表面热积累温度升高,并且对热积累效应的影响非常大。激光重复频率可以影响光斑重叠率和热传递的时间这两个因素,从而影响加工过程的热积累;对减小光斑直径和提高激光能量这两种提高激光能量密度的方法进行了对比,结果表明,减小光斑直径所产生的热积累效应较弱;最后对不锈钢钢的飞秒加工过程进行模拟,并与其他模型的模拟结果进行了对比,结果表明本文所用模型可以有效的预计飞秒激光加工中的热积累和温度。
[Abstract]:Femtosecond laser has the advantages of high power, high accuracy and small heat affected zone, which can remove surface materials directly and realize micro-nano machining. It has irreplaceable advantages in the field of aerospace, semiconductor, biological and other materials surface processing. However, under the action of multi-pulse femtosecond laser, thermal accumulation and temperature rise may occur in the material, resulting in phase transition, oxidation, and even melting. Therefore, how to optimize femtosecond processing parameters and control heat accumulation and temperature rise is an urgent problem to be solved. In this paper, the thermal accumulation effect of femtosecond laser processing on the surface of AZ31 magnesium alloy is discussed, and the thermal accumulation effect of femtosecond laser processing on AZ31 magnesium alloy surface is numerically simulated by using finite difference method and MATLAB software. The effects of different scanning speed, laser repetition rate, spot diameter and laser energy on the thermal accumulation effect during processing were simulated, and the laser process parameters were optimized. And through the simulation of stainless steel processing process, compared with other models. Considering the heat conduction coefficient and heat capacity related to the material, the surface thermal accumulation and temperature change of AZ31 magnesium alloy at a scanning speed of 1 m / s ~ 2 m / s ~ (2) m / s ~ (3) m / s ~ (4) m / s were simulated by the central difference method, respectively. The results show that the thermal accumulation temperature of AZ31 magnesium alloy surface is not stable when the scanning speed is 1 ~ 3 m / s. When the scanning speed is 4 m / s, the thermal accumulation temperature of AZ31 magnesium alloy surface will be balanced after 10 pulses. The scanning speed mainly affects the thermal accumulation in the process of processing by changing the overlap rate of the spot, and the surface thermal accumulation and temperature change of AZ31 magnesium alloy at the laser repetition rate of 100 kHz,500 kHz,1 MHz,2 MHz are simulated respectively. The results show that the laser repetition rate increases the surface thermal accumulation temperature and has a great influence on the thermal accumulation effect. The laser repetition rate can affect the overlap rate and the time of heat transfer, thus the thermal accumulation in the process is affected, and the two methods of increasing laser energy density and reducing the spot diameter are compared. The results show that the heat accumulation effect caused by reducing the spot diameter is weak. Finally, the femtosecond machining process of stainless steel is simulated and compared with the simulation results of other models. The results show that the model can effectively predict the thermal accumulation and temperature in femtosecond laser processing.
【学位授予单位】：辽宁科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665

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