Abstract
The currently available high-power laser shows promising opportunities for the welding of thick plates in a single pass. However, weld-root defect frequently occurs when a high-power laser is used to join thick plates in a full-penetration mode, which has a significantly adverse effect on the serviceability of the weld joint. The purpose of this work is to understand the defect formation mechanism and reduce these defects through controlling welding parameters. In this study, the characteristics of weld root defects were investigated using a 10 kW fiber laser using a program of experiment and theoretical analysis. The corresponding defect formation mechanisms were discussed based on the bottom molten pool behaviors observed by the high-speed camera. The results showed that there were four types of weld-root appearances as follows with an increase of linear heat input from 300 J/mm to 1000 J/mm: weld-root humping (30 mm/s), sound weld (25 mm/s), weld sagging (20 mm/s) and excessive weld sagging. The remedies for reducing weld-root defects were also presented to obtain sound weld bead by optimizing welding parameters. Weld-root humping was formed due to the quasi-full-penetration keyhole. Weld sagging resulted from the imbalance of the hydrostatic pressure and surface tension in the condition of a through keyhole. It was also found that the sound weld was formed when a through keyhole and a proper molten pool size were obtained. Thus, the state of the keyhole and molten pool geometry were the major factors that affect weld-root defects.
Highlights
The solid-state laser, fiber laser or disk laser, with the advantages of high brightness, high Rayleigh length and high power output, can produce an ultra-high peak power density of MW/mm2 corresponding to a focused electron beam [1,2]
In order to clarify the effect of welding parameters on weld-root defects, a series of full-penetration bead-on-plate welding were conducted
In order to clarify the effect of welding parameters on weld-root defects, a series o of 13 full-penetration bead-on-plate welding were conducted
Summary
The solid-state laser, fiber laser or disk laser, with the advantages of high brightness, high Rayleigh length and high power output, can produce an ultra-high peak power density of MW/mm corresponding to a focused electron beam [1,2]. Laser welding has become a mature process of fabricating thin components in some manufacturing sectors, such as the automotive sector. High-power lasers (10–100 kW) are available for welding, which is of considerable interest for the joining of thick components, such as shipbuilding, power plants, pressure vessels, high-speed trains, lifting equipment, wind power towers, and oil/gas pipelines [3,4]. Defects frequently occur in the welding of thick components using a high-power laser. Several attempts have been made to use high-power lasers to join thick section components with a single pass [5,6]. Kawahito et al carried out the research of high-power (10 kW) laser welding in order to clarify the physical phenomena during the process [7]
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