Thick steel plates are typically joined using arc welding and partially laser-arc hybrid welding processes. Both methods have disadvantages besides their individual advantages. Arc welding processes usually feature comparatively low welding speeds, high heat inputs, high distortions, and high filler material consumption. Laser-arc hybrid welding processes have limitations in terms of penetration depth, particularly regarding crack formation, and gap bridgeability.

To overcome the limitations of defect-free weldable penetration depths, a multi-laser beam welding process is to be developed combining a root welding process and a filler layer welding process, performed parallel. By beam shaping, the characteristics of the molten pools, temperatures, solidification, and microstructure are precisely controlled to prevent hot cracks. The single-run process with welding depths beyond the state of the art significantly reduces number of weld passes, manufacturing time, consumption of filler material and shielding gas, and can conserve resources and reduce manufacturing costs.

The investigations presented are about laser beam root welding with filler wire of steel with plate thicknesses between 15 mm and 30 mm with different Y-shaped edge preparations using output powers of up to 6 kW. Influence of energy per unit length, focal diameter, focal position, wire feed rate, bevel angle, root face and plate thickness on the weld seam characteristics are analyzed. This includes visual and metallographic analyses.

Suitable edge preparations were determined regarding lowest possible bevel angle and highest possible root face with stable process window. The root beads showed no cracks or other imperfections by using suitable process parameters.