Various in-situ monitoring techniques have been developed for the detection of process drifts in the Laser Powder Bed Fusion (LPBF) process. Currently, optical emission monitoring can retrieve information regarding molten pool characteristics, such as temperature, width, length and area which provide substantial process signatures. Nonetheless, a fundamental indicator for the retrieval of a complete set of spatially distributed information is missing: the molten pool depth. Within the present investigation, a system for the estimation of the penetration depth based on the detection of molten pool surface oscillations is reported. Initially, the fundamentals of the monitoring technique are presented. The principle relies upon the observation of molten pool surface ripples through the measurement of probe light reflections in the melt area. Proof of concept testing of the sensing principle was conducted through an experimental investigation on a prototypal platform. A monitoring system (consisting of a high-speed camera and a secondary illumination light) was employed to view the process while realising both bead-on-plate material remelting and single track powder bed fusion depositions of AISI316L at different levels of laser emission power. Oscillation frequencies were extracted from the high-speed imaging acquisitions after image processing and signal analysis. The surface wave oscillations were measured to be in the range of 3.5–5.5 kHz in keyhole conditions. Metallographic cross-sections allowed to observe the effective molten pool penetration depth and cross-sectional area and were correlated to oscillation frequencies. Higher values of oscillation indicated shallower penetration and consequently a smaller mass of molten material.

已经开发了各种原位监测技术来检测激光粉末床熔合（LPBF）过程中的过程漂移。当前，光发射监视可以检索有关熔池特性的信息，例如温度，宽度，长度和面积，这些信息可提供重要的过程特征。但是，缺少用于检索完整的空间分布信息集的基本指标：熔池深度。在本研究中，报告了一种基于对熔池表面振荡的检测来估算穿透深度的系统。最初，介绍了监视技术的基础。该原理依赖于通过测量熔体区域中的探测光反射来观察熔池表面波纹。通过在原型平台上进行的实验研究，对传感原理进行了概念验证。使用监视系统（由高速相机和辅助照明灯组成）来查看过程，同时在不同的激光发射功率下实现AISI316L的板上珠子材料重熔和单轨粉末床熔融沉积。经过图像处理和信号分析后，从高速成像采集中提取振荡频率。在匙孔条件下，测得的表面波振荡范围为3.5–5.5 kHz。金相横截面可以观察有效的熔池渗透深度和横截面积，并与振荡频率相关。