Synchrotron validation of inline coherent imaging for tracking laser keyhole depth
Synchrotron validation of inline coherent imaging for tracking laser keyhole depth
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用于跟踪激光小孔深度的内联相干成像的同步加速器验证
DOI：
10.1016/j.addma.2023.103798
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发表时间：
2023
影响因子：
11
通讯作者：
Fleming T
中科院分区：
文献类型：
--
作者：
Fleming T
对于工业上越来越多地采用激光粉末床熔合（LPBF）和激光焊接来制造复杂的金属部件来说，现场监测是至关重要的。光学相干层析成像（OCT）是一种应用于医学领域的干涉成像技术，广泛用于高功率激光材料加工过程中的形貌监测。然而，即使在稳定的加工制度，一些OCT深度测量从小孔（蒸汽腔形成的激光束点）显得太浅或太深时，相比ex-situ测量焊缝深度。目前还不清楚这些异常值是否是由于成像伪影、小孔内成像光束的多次散射或小孔深度的真实的变化造成的，这使得难以准确提取焊接深度并确定误差范围。为了提供一个明确的解释，我们结合联合收割机内联相干成像（ICI），OCT的一种，同步X射线成像的同时，operandomonitoring的全2维锁孔轮廓在高速（280 kHz和140 kHz，分别）。即使在高度湍流的孔隙生成模式下，ICI测量的深度也与射线照相提取的小孔深度密切相关（± 14 µm内>80%）。光线跟踪模拟用于确认ICI深度测量中的异常值（与射线照相术显著不一致）主要来自成像光的多次反射（57%）。同步加速器X射线成像还能够跟踪气泡和孔隙形成事件。在激光焊接过程中，当小孔的侧壁快速（>10 m/s）向内塌陷，从小孔根部夹断气泡并导致小孔深度快速下降时，会产生孔隙。气泡形成的证据可以单独在ICI深度剖面中找到，因为快速深度变化与气泡形成事件（0.26）表现出中等相关性。这项工作更接近于使用ICI在激光焊接和LPBF期间进行精确的局部缺陷检测。
In situmonitoring is critical to the increasing adoption of laser powder bed fusion (LPBF) and laser welding by industry for manufacture of complex metallic components. Optical coherence tomography (OCT), an interferometric imaging technique adapted from medical applications, is now widely used foroperandomonitoring of morphology during high-power laser material processing. However, even in stable processing regimes, some OCT depth measurements from the keyhole (vapor cavity formed at laser beam spot) appear too shallow or too deep when compared toex situmeasurements of weld depth. It has remained unclear whether these outliers are due to imaging artifacts, multiple scattering of the imaging beam within the keyhole, or real changes in keyhole depth, making it difficult to accurately extract weld depth and determine error bounds. To provide a definitive explanation, we combine inline coherent imaging (ICI), a type of OCT, with synchrotron X-ray imaging for simultaneous,operandomonitoring of the full 2-dimensional keyhole profile at high-speed (280 kHz and 140 kHz, respectively). Even in a highly turbulent pore-generation mode, the depth measured with ICI closely follows the keyhole depth extracted from radiography (>80% within ± 14 µm). Ray-tracing simulations are used to confirm that the outliers in ICI depth measurements (that significantly disagree with radiography) primarily result from multiple reflections of the imaging light (57%). Synchrotron X-ray imaging also enables tracking of bubble and pore formation events. Pores are generated during laser welding when the sidewalls of the keyhole rapidly (>10 m/s) collapse inwards, pinching off a bubble from the keyhole root and resulting in a rapid decrease in keyhole depth. Evidence of bubble formation can be found in ICI depth profiles alone, as rapid depth changes exhibit moderate correlation with bubble formation events (0.26). This work moves closer to accurate, localized defect detection during laser welding and LPBF using ICI.
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