Hot cracking during laser welding of steel: influence of the welding parameters and prevention of cracks

Modulation of the laser power to prevent hot cracking during laser welding of tempered steel

“…As the susceptibility to hot cracking during welding without power modulation increases with rising feed rate, 2 and to evaluate the robustness of the modulated welding process, the influence of the welding speed on the reduction of hot cracks with modulated laser power is summarized in Fig. 3.…”

“…Provided that high modulation amplitudes P are applied, the normalized frequency K defines the process window where hot cracks vanish. The power modulation, characterized by K and P, provides further degrees of freedom to reduce hot cracking during welding of tempered steel, beyond the common adaptation of line energy, 2 beam quality, and focal position. Now, the remaining question is whether it is the assumed mutual interaction between the geometry of the weld pool, and the thus thermally induced tensile stresses and strains in the weld zone that are determining the formation of the hot cracks, or whether there are other reasons like a dynamically changing melt flow that influences the refilling of gaps between the growing dendrites that are torn apart.…”

“…There is evidence that the distribution of the incident laser power in the keyhole can influence the susceptibility to hot cracking: the formation of hot cracks was reported to depend on line energy, 2 beam quality, and focal position. 1 One may, therefore, suppose that this is due to the influence of the focal position on the geometry of the weld pool, 4 which leads to different distributions of temperature, stress, and strain in the solidification zone.…”

“…1,2 The occurrence of hot cracks is strongly connected to thermally induced stresses and strains that tear at the mushy zone at the trailing edge of the weld pool during the solidification. 3 For the tempered steel 42CrMoS4, the cracks are oriented transverse to the direction of penetration, 1 implying that the stress and strain in the vertical direction exceeds the level that can be sustained by the material.…”

Experimental and numerical study on the influence of the laser hybrid parameters in partial penetration welding on the solidification cracking in the weld root

“…The welding speed, which was variated in a range between 1.7 and 3.2 m min −1 , showed no significant influence on the crack number. Schaefer et al [17] demonstrated that crack formation can be eliminated for partial penetration HLAW using a higher optical magnification of 2.67. They also showed that the focal position of the laser beam affected the melt flow during laser welding of steel, the keyhole shape, and the weld pool geometry [18].…”