Abstract
It is shown that a temporal modulation of the laser power can prevent the formation of hot cracks during deep-penetration laser welding of tempered steel. For this purpose, the influence of the modulated laser power on the cumulated length of the hot cracks in the weld seams was quantified. Varying amplitude and frequency of the modulation significantly changes the pattern and length of the hot cracks. Moreover, hot cracks can be prevented entirely in a specific range of the modulation frequency that depends on the welding speed. Our results indicate that the reduction of hot cracks might be related to a change of the fluctuating length of the weld pool, which was detected by means of thermographic imaging.
Highlights
Our results indicate that the reduction of hot cracks might be related to a change of the fluctuating length of the weld pool, which was detected by means of thermographic imaging
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
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
Summary
Deep-penetration laser welding of steel alloys with high strength, such, as 42CrMoS4, which are commonly used for powertrain components, is affected by the formation of hot cracks in the weld seam. 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. For the tempered steel 42CrMoS4, the cracks are oriented transverse to the direction of penetration, implying that the stress and strain in the vertical direction exceeds the level that can be sustained by the material.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, beam quality, and focal position. One may, suppose that this is due to the influence of the focal position on the geometry of the weld pool, which leads to different distributions of temperature, stress, and strain in the solidification zone.5The supposed influence of the geometry of the weld pool on stress and strain and on the susceptibility to hot cracking is suggested by the correlation that can be observed between the coinciding periodicity of the pattern of the hot cracks and the periodic change of the welding depth as reported in Ref. 2. 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, beam quality, and focal position.. Suppose that this is due to the influence of the focal position on the geometry of the weld pool, which leads to different distributions of temperature, stress, and strain in the solidification zone.. The supposed influence of the geometry of the weld pool on stress and strain and on the susceptibility to hot cracking is suggested by the correlation that can be observed between the coinciding periodicity of the pattern of the hot cracks and the periodic change of the welding depth as reported in Ref. 2.
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