Effects of groove parameters on space constraint of narrow gap laser-arc hybrid welding

Obvious space constraint effect (SCE) related to energy transfer was found in narrow gap laser-arc hybrid welding (NGHW). It was significantly affected by changing the width of rectangle groove (W-G) and the angle of Y-shape groove (alpha(G)), and the central crack and sidewall notch occurred on weld cross-section when W-G <= 4 mm or alpha(G) <= 60 degrees. The SCE was quantitatively characterized by the dimensionless parameter of melting energy increment (psi), which is the increment of melting efficiency of NGHW to the hybrid welding without narrow gap. The larger the psi, the stronger the SCE. The psi of rectangle groove was up to 30% when the W-G was at 6 mm, while the maximum of the psi of Y-shape groove was only 7% when the alpha(G) was at 60 degrees. According to the calculated psi and the defect occurring tendency, the optimized groove of NGHW was confirmed as the rectangle groove with 6 mm-width, and was verified by a 25 mm-thick joint. Besides, the effects of SCE on the energy transfer in narrow gap were discussed according to the behaviors of arc column and laser-induced plasma.