3D particle tracking velocimetry for the determination of temporally resolved particle trajectories within laser powder bed fusion of metals

Abstract

Within this work, we present a system for the measurement of the three-dimensional (3D) trajectories of spatters and entrained particles during laser powder bed fusion (L-PBF) of metals. It is comprised of two ultrahigh-speed cameras and a reconstruction task specific processing reconstruction algorithm. The system enables an automated determination of 3D measures from the trajectories of a large number of tracked particles. Ambiguity evolving from an underdetermined geometrical situation induced by a two-camera setup is resolved within the tracking using a priori knowledge of L-PBF of metals. All processing steps were optimized to run on a graphics processing unit to allow the processing of large amounts of data within an appropriate time frame. The overall approach was validated by a comparison of the measurement results to synthetic images with a known 3D ground truth.

In-situ measurement and monitoring methods for metal powder bed fusion: an updated review

“…Off-axis video-imaging in the visible range Yang et al, 2020a, b;Tan et al, 2020;Yin et al, 2020;Zhang et al, 2019a, b;Nassar et al, 2019;Bidare et al, 2018a,b;Zheng et al, 2018;Zhang et al, 2018;Ye et al, 2019Ye et al, , 2018aAndani et al, 2018;Ozel et al 2018;Repossini et al, 2017;Ly et al 2017;Andani et al, 2017;Liu et al, 2015;Bidare et al, 2017 Off-axis stereo vision in the visible range Eschner et al, 2020a;Eschner et al, 2019;Barrett et al, 2019;Barrett et al, 2018a Off-axis NIR/IR video imaging Yang et al, 2020b;Grasso and Colosimo, 2019;Grasso et al, 2018a;Ozel et al, 2018 Off-axis X-ray video imaging Young et al 2020;Leung et al, 2019;Guo et al, 2018;Zhao et al, 2017Off-axis Schlieren videoimaging Bidare et al, 2018aBidare et al, 2017 Air-borne acoustic emissions Air-borne acoustic emission detector Shevchik et al, 2019;Wasmer et al, 2019;Ye et al, 2018b;Kouprianoff et al (2018) Level 2 monitoring methods involve off-axis mounted sensors, mainly cameras in the visible range or thermal cameras. Unlike in level 1 methods, high temporal resolution is needed to capture fast and transient phenomena, whereas high spatial resolution is needed to characterise the spatial features of interest.…”

“…15 c)). Eschner et al (2019) used two ultrahigh-speed cameras combined with a particle detection matching and tracking algorithm, which allowed them to determine the 3D position and velocity of spatters. The same approach was used in a more recent study (Eschner et al 2020a) to correlate spatter signatures with the penetration depth measured ex-situ and with the transition from heat conduction to evaporation dominating the process regime.…”

A Review of Spatter in Laser Powder Bed Fusion Additive Manufacturing: In Situ Detection, Generation, Effects, and Countermeasures

“…Barret et al [43] established a stereo vision spatter detection system for spatter tracking analysis at a cost of less than USD 1000 using two slow-motion cameras (FPS1000 by The Slow Motion Camera Company), as illustrated in Figure 6. Later, Eschner et al [44] combined two ultra-high-speed cameras with algorithms to create a 3D tracking system for measuring spatter in L-PBF. Visible in situ detection systems for L-PBF in recent years are summarized in Table 2.…”

“…Barrett et al used a low-cost binocular sensor for spatter detection, laying a foundation for future analysis of the data [43]. Eschner et al [44] used algorithms in a binocular sensor system to carry out many processes on the images, including (1) identifying particle positions and calibrating the camera system, (2) matching particles between multi-camera images, (3) determining the 3D coordinates, (4) using a priori knowledge of processes and particles to distinguish ghost particles from real particles, (5) tracking particles, and (6) processing the 3D data. Those processes require more complex algorithms to complete.…”

Direct selective laser sintering of hexagonal barium titanate ceramics

“…SLS, as an additive manufacturing technique, offers freedom to design and produce complex geometric build‐parts without the use of molds 17,18 . SLS fabricates dense parts by using a continuous‐wave (CW) laser beam to sinter the material powders selectively and additively layer‐by‐layer to build 3D objects.…”