Fig. 3: Stochastic regime instabilities and subsequent transition from conduction to stable and unstable keyhole regimes.
a RM6 melt pool morphology variations under constant laser process parameters in a single scanning vector of 316 L stainless steel (c.f. Supplementary Movie 5). The normalized and filtered acoustic signal for each time frame is illustrated for each image set with event annotations represented by vertical lines. The boundaries of solid–liquid (melt pool) and gas–liquid (depression zone) are illustrated by yellow and white dashed lines, respectively. The time bar depicts the regime changes from conduction to stable keyhole (Ev1, t = 45.7 ms) and stable keyhole to unstable keyhole (Ev2, t = 49.7 ms). The resultant porosities in the unstable keyhole regime in the vicinity of each timeline are encircled by dashed green lines. The scale bar for all the images is shown in the top right corner. The laser intensity profile (−1.9, c.f. Supplementary Fig. 1) and the corresponding scanning direction are presented in the bottom right corner. b Melt pool length (lm), depth (dm), keyhole depth (dd), and width (wd) at the top of the depression throughout the scanning vector. c The normalized magnitude of melt pool length and depth over the scanning vector. d The first derivative of the melt pool length and depth magnitude over time. e Relations between mean keyhole wall angle the number of reflections, and total energy absorption. f Superimposition of total energy absorption evolution and the normalized and filtered acoustic signal (band pass: 35–105 kHz). g Melt pool rear wall velocity measured via summation of laser velocity and melt pool length variations in time.
