Problems and issues in laser-arc hybrid welding

Abstract

Hybrid welding, using the combination of a laser and an electrical arc, is designed to overcome problems commonly encountered during either laser or arc welding such as cracking, brittle phase formation and porosity. When placed in close contact with each other, the two heat sources interact in such a way as to produce a single high intensity energy source. This synergistic interaction of the two heat sources has been shown to alleviate problems commonly encountered in each individual welding process. Hybrid welding allows increased gap tolerances, as compared to laser welding, while retaining the high weld speed and penetration necessary for the efficient welding of thicker workpieces. A number of simultaneously occurring physical processes have been identified as contributing to these unique properties obtained during hybrid welding. However, the physical understanding of these interactions is still evolving. This review critically analyses the recent advances in the fundamental understanding of hybrid welding processes with emphases on the physical interaction between the arc and laser and the effect of the combined arc/laser heat source on the welding process. Important areas for further research are also identified. List of symbols and acronymsa coefficient in the surface tension pressure term A area of the transverse weld cross-section (mm 2 ) B magnetic flux (kg s 22 A 21 ) c molar concentration of vapour inside keyhole (mol cm 23 ) C concentration of surface active elements (wt-%) C p heat capacity or specific heat (J kg 21 K 21 ) DCEN direct current electrode negative DCEP direct current electrode positive D LA horizontal distance between laser focal point and arc electrode tip dT/dy spatial temperature gradient on the weld pool surface (K mm 21 ) E A attenuated incident radiation (W) f distribution factor F b buoyancy force (N m 23 ) F emf Lorentz or electromagnetic force (N m 23 ) g acceleration due to gravity (m s 22 ) GMA gas metal arc GMAW gas metal arc welding GTA gas tungsten arc GTAW gas tungsten arc welding h depth of keyhole (mm) H heat input per unit length (J mm 21 ) HAZ heat affected zone HCP hexagonal close packed H f latent heat of fusion (J kg 21 ) I arc current (A) I a attenuated laser beam intensity (W) I m imaginary portion of the complex refractive index I o initial laser beam intensity (W) J flux of evaporating particles in keyhole (mol cm 22 s 21 ) J c current density (A m 22 ) k e extinction coefficient k thermal conductivity (W m 21 K 21 ) L characteristic length (half of the weld pool width) (mm) L P length of the plasma (mm) L R characteristic length of the weld pool (mm) m complex refractive index n refractive index N number density of scattering particles (no./mm) Nd:YAG neodymium:yttrium aluminium garnet P incident heat source power (W) P d power density (W mm 22 ) Pe Peclet number P r recoil pressure (Pa) P v vapour pressure (Pa) P n power or nominal power (W) P t total power of the heat source (W) International Materials Reviews 2009 VOL 54 NO 4223 P c pressure due to surfa...

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