High Power Fiber Laser Welding of Thick Section Materials – Process Performance and Weld Properties

Abstract

High power fiber laser systems have reached output powers far beyond 30 kW and a fiber laser source of 100 kW output power has recently become available for fundamental research. With the high laser power that is now attainable and the ability to deliver a highquality beam in a flexible fiber with high wall plug efficiency and low maintenance requirements, high power fiber laser systems are becoming of increasing interest for joining thick section materials in industrial applications.

In this work, fiber laser systems with output power of up to 30 kW are used to investigate the feasibility of autogenous laser welding and laser arc hybrid welding for joining thick section materials. The focus is placed on joining pipe steels and shipbuilding steels of up to 28 mm thickness with the aim of developing welding strategies and parameter sets that can meet the requirements of industrial standards and guidelines. The reliability of the parameter sets developed for the joining processes is tested against process boundaries or limits such as maximum penetration depth, ability to compensate for linear misalignment, air gaps and change in welding position. To verify the quality of the welded joints, characterisation of the material properties is carried out using destructive and nondestructive test methods.

The results of the experimental test series and materials characterisation support the use of high power fiber laser sources as suitable tools for laser arc hybrid welding and autogenous laser welding of thick section materials. Considering especially the autogenous laser welding process, it is shown that varying the power density or oscillating the laser beam can benefit the weld result to the same extent than laser arc hybrid welding.

The research presented in this work provides an improved understanding of the behavior of deep penetration welds in thick section material, referring to the properties of the welded joint and performance of the process. The achieved results are a solid foundation for meeting the requirements of industrial applications in the pipeline and shipbuilding industry.