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Narrow gap (or groove) laser welding involves multiple layer additive manufacture for the joining of thick-section metallic components. Typical defects include porosity, cracking, lack of fusion to sidewalls, and between layers, and component distortion including the closure of the groove. This study aimed to understand the defect formation mechanisms and factors affecting them, and to develop appropriate welding procedures and parameters for joining ferritic steel sheets of 30 mm in thickness. High-quality welded joints in 30-mm-thick Grade 43 ferritic steel sheets have been achieved by multi-pass defocused laser beam welding with filler wire addition. The microstructure and the microhardness of the multi-pass welded joint were found to be affected by the tempering of the subsequent multi-pass welding layers. Post-weld heat treatment on the welded joints were required since, although the strength of the welded joints were higher than that of base metal, the ductility was much lower than that of base metal. [ABSTRACT FROM AUTHOR]

This paper presents a statistical analysis of the performance of an Ytterbium fibre laser utilising single and dual gas jets in a single pass to blind cut dry pine wood. Cutting wood with lasers is a multi-factor process and a proper combination of the parameters involved is needed to achieve high quality and optimum process efficiency. This study employs design of experiments and statistical modelling approach to investigate the significant process parameters along with their interactions. A high brightness, 1 kW IPG single mode Ytterbium-doped fibre laser was employed to produce blind cuts on samples of dry pine wood. The experiments were performed parallel to the direction of the wood fibre. The parameters investigated include laser power, focal plane position, traverse speed, gas pressure and single and dual gas jets. Results were compared using a number of process responses which define the efficiency of the cut in terms of kerf depth, mass removal and energy consumption as well as quality of the cut section considering the heat-affected zone, kerf width and roughness of the edge of the surface. It has been found that application of an additional gas jet produced a surface finish superior to the single jet. [ABSTRACT FROM AUTHOR]