为了研究飞秒激光螺旋加工工艺参数对小孔成形过程的影响, 以304不锈钢为靶材, 选取飞秒激光螺旋钻孔工艺的主要参数, 基于L25(56)正交表设计了5因素5水平正交实验, 分析单脉冲能量、重复频率、旋转速率、焦点下移速率、吹气压力对烧蚀深度影响的显著水平；基于反向传播(BP)神经网络建立这5个因素与材料烧蚀深度之间的关系模型, 并利用正交实验数据对网络进行训练, 通过附加钻孔实验数据对所建立网络的泛化能力进行测试, 结果表明所建立的模型预测误差在3%以内；针对螺旋钻孔的特征参数--焦点下移速率设计单因素实验, 得到了飞秒激光螺旋钻孔过程中焦点下移速率对小孔成形影响的规律。

To investigate the effect of femtosecond laser helical processing parameters on the evolution of hole formation process, we use 304 stainless steel as the target material, select main parameters of the helical drilling by femtosecond pulsed laser, and design orthogonal experiments with 5 factors and 5 levels based on L25(56) orthogonal table. The significance levels of the ablation depth affected by 5 main parameters, such as the single pulse energy, repetition frequency, rotation rate, rate of focus down, and the air-blowing pressure, are analyzed. Based on the back propagation (BP) neural network, we establish the relationship model between the 5 main parameters and the ablation depth of the laser drilling. The data obtained from the orthogonal experiment are used to train the neural network. The generalization ability is tested by additional experiments. The results show that the prediction error of the relationship model is less than 3%. Moreover, the single factor experiment is designed to analyze the influence of the rate of focus down during the helical drilling. The effect of the different rates of focus down on the hole formation during the femtosecond laser helical drilling process is obtained.