金属在强Laser辐照下的时间分辨吸收率和熔池动力学
Time-resolved Absorptance and Melt Pool Dynamics during Intense Laser Irradiation of Metal
摘要：
高辐照度激光入射到金属表面会产生一个复杂的动态过程，通过这个过程，金属可以迅速从高反射转变为强吸收。对这一过程的绝对了解是激光焊接、切割和金属增材制造等重要工业激光工艺的基础。确定材料对激光的时间依赖性吸收率非常重要，不仅可以从根本上了解光与物质的相互作用，还可以改进制造过程中的工艺设计。动态光学吸收率的测量是众所周知的困难，由于吸收介质的快速变化的性质。这些数据对于过程建模人员也至关重要，他们的复杂模拟需要可靠、准确的输入数据;然而，可用的数据很少。在这项工作中，我们测量的时间依赖性，反射光在10毫秒的激光点焊使用积分球装置。由此，我们计算了入射到316L不锈钢上的1070 nm波长光的动态吸收率。我们实验的时间分辨率（< 1 us）允许确定几个重要物理现象发生的精确条件，如熔化和小孔形成。光学确定的平均吸收率进行了比较，量热法确定的值，它被发现，量热计严重低估了吸收的能量，由于在点焊过程中的质量损失。为了验证我们的解释的光学结果，以及焊接模型验证提供实验数据的焊缝熔核横截面。
英文摘要：
High irradiance lasers incident on metal surfaces create a complex, dynamic process through which the metal can rapidly change from highly reflective to strongly absorbing. Absolute knowledge of this process underpins important industrial laser processes like laser welding, cutting, and metal additive manufacturing. Determining the time-dependent absorptance of the laser light by a material is important, not only for gaining a fundamental understanding of the light-matter interaction, but also for improving process design in manufacturing. Measurements of the dynamic optical absorptance are notoriously difficult due to the rapidly changing nature of the absorbing medium. This data is also of vital importance to process modelers whose complex simulations need reliable, accurate input data; yet, there is very little available. In this work, we measure the time-dependent, reflected light during a 10 ms laser spot weld using an integrating sphere apparatus. From this, we calculate the dynamic absorptance for 1070 nm wavelength light incident on 316L stainless steel. The time resolution of our experiment (< 1 us) allows for the determination of the precise conditions under which several important physical phenomena occur, such as melt and keyhole formation. The average absorptances determined optically were compared to calorimetrically-determined values, and it was found that the calorimeter severely underestimated the absorbed energy due to mass lost during the spot weld. Weld nugget cross-sections are also presented in order to verify our interpretation of the optical results, as well as provide experimental data for weld model validation.
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