Numerical simulation of VPPA-GMAW hybrid welding of thick aluminum alloy plates considering variable heat input and droplet kinetic energy

In order to realize the high-efficiency and high-quality welding of thick aluminum alloy plates, a paraxial variable-polarity plasma arc-gas metal arc welding (VPPA-GMAW) hybrid welding method was developed in the present study. The target material was a thick plate of 7A52 aluminum alloy, which is widely used in the aerospace field because it offers high specific strength and high corrosion resistance. The thermal action characteristics of paraxial VPPA-GMAW hybrid welding during direct-current electrode-negative and direct-current electrode-positive phases were considered. A variable combined heat source model was developed to investigate the hybrid welding thermal process. In the model, the variable-polarity plasma arc (VPPA) was treated as two curve-rotated body heat sources with different distribution parameters for electrode-negative and electrode-positive durations; the two heat sources were loaded periodically to express the heat input form. The GMAW arc was described as a double-ellipsoidal heat source, the overheated droplet was described as a uniform-body heat source, and the impact effect of the overheated droplet on the weld pool was considered by accounting for its kinetic energy. This heat source model was employed to conduct a finite-element analysis of hybrid welding temperature profiles. The numerical simulation results indicated that the VPPA provided deep penetration in the hybrid welding. The subsequent GMAW increased the penetration achieved by the VPPA and filled the weld pool to achieve deep-penetration welding. Experiments were performed to measure weld geometries and thermal cycles, and the weld pool shape was captured by high-speed camera. The calculated weld bead geometry, weld pool shape and thermal cycles showed excellent agreement with the experimental results.