Issue 50

L. Romanin et al., Frattura ed Integrità Strutturale, 50 (2019) 251-263; DOI: 10.3221/IGF-ESIS.50.21 259 Various authors have studied the keyhole formation and evolution in EBW or laser welding by using CFD analysis with the aim to predict gas porosity. In this case, a phenomenological approach has been adopted that uses thermocouples data and micrographs of the FZ to calibrate a power density distribution function. In particular, the characteristic nail-shape of the FZ has been simulated by superimposing a spherical and a conical heat source. The spherical heat source is defined by a constant power density distribution (q 0 ) in the range between r = 0 and r = R 1 (inner radius) and a linear power density decreasing from R 1 to R 2 (outer radius) (Eq. 1). 0 1 2 0 1 2 2 1 0 q if r R q R r q if R r R R R            (1) The conical heat source, on the other hand, is characterized by a Gaussian power density distribution centered in its axis (Eq. 2) 2 2 0 0 r r q q e   (2) In Eq. (2) r 2 =(z-vt) 2 +x 2 and r 0 =R e -(R e -R i )(y e -y)/(y e -y i ) for y i <y<y e . The heat source moves along the z axis with a speed v (t is the time). Fig. 10 illustrates the shape of the above defined power density distribution functions and their superposition. Figure 10: Spherical (a) and conical (b) power density distribution functions and their superposition (c). The heat source parameters have been chosen comparing experimental and numerical results. The parameters obtained for the ‘Test 4’ are given in Tabs. 3 and 4 for the spherical and conical heat source, respectively. q 0 [W/mm 3 ] R 1 [mm] R 2 [mm] 260 0.5 1.6 Table 3: Spherical heat source parameters. q 0 [W/mm 3 ] R i [mm] R e [mm] y i [mm] y e [mm] 90 0.9 0.9 -1.5 -2.5 Table 4: Conical heat source parameters. r q 0 R 1 R 2 q y x, z q 0 R e R i y i y e r z y Surface Welding direction a b c