Comparison of three different arc modes for laser-arc hybrid welding steel

Abstract

Traditionally, Laser Arc-Hybrid Welding (LAHW) is made using a gas metal arc heat source in pulsed mode. In this study, welds made with three different arc modes under various conditions are compared. The arc modes compared for LAHW are: Standard, Pulsed, and Cold Metal Transfer (CMT). The pulsed mode, using power modulation, is more controlled than the “natural” Standard mode and offers globular drop transfer with reduced heat input to the work piece, enabling thinner materials to be welded. The CMT arc mode also uses power modulation as well as controlled wire feeding. This enables surface tension drop transfer, involving even less heat input and is also considered to generate less undercuts and spatter than the other two arc modes. The welds compared were made in 7 mm thick S420 laser cut steel sheets with two different welding speeds and gap sizes. They were made using close-to-production setup within the limitations of the CMT capabilities, i.e., low and medium wire feed rates. The weld caps and roots were studied optically and the structures were analyzed by making cross-sectional macrographs longitudinally and transversally. These cross sections were analyzed geometrically, structurally, and also hardness tested. The welds were also studied and analyzed by means of pre- and postweld scanning as well as high speed imaging. The study shows that the laser keyhole reduces the effect of the arc modes, enabling higher welding speeds than without the laser. The gouge formed in front of the keyhole determines occurrence of undercuts and bead uniformity. The material mixing of filler and base material, and laser penetration spiking is also influenced by the depth of the arc gouge. The material structure is also affected to some degrees for expected performances. Even though the short-arc technique CMT show promising results, the pros and cons for each arc technique are discussed.