Research On Heat Source Coupling And Metal Transfer In Laser-MIG Hybrid Welding Of 316 Stainless Steel

Laser-MIG hybrid welding which combines the advantages of laser welding and arc welding possesses higher processing speed and efficiency.However,there are huge differences between laser source and arc source in physical properties and energy transfer mechanism.Coupling those two heat sources will change the characteristics of metal transfer,arc plasma and keyhole,resulting in unsteady processing.In recent years,researches mainly focus on optimizing welding parameters and mechanical properties of laser-MIG hybrid welds,few studies concern about characteristics of the weld processes.Therefore,the current research aims to discuss the characteristics of heat source coupling and metal transfer in laser-MIG hybrid welding using 8 mm-thick 316 stainless steels.Firstly,the characteristics of weld appearance and metal transfer was analyzed.The results indicated that heat source coupling improved the weld depth.The power of heat source,distance between heat source and leading mode of heat source changed weld appearances by affecting heat source coupling.The type and frequency of metal transfer mainly determined by the current.The transfer mode changed from shortcircuit transfer to spray transfer with increasing weld current.The coupling with laser source would differ the metal transfer frequency.The actual weld current increased by strong coupling between heat source according to electrical signal s.Secondly,the features of heat source coupling were researched.It was discovered that geometry and energy features of arc plasma were not identical under different coupling conditions.Higher source power improved heat source coupling,leading to increased area and energy of arc plasma.Increased distance between heat source weakened the coupling effects,thus decreasing the area and energy of arc plasma.Stronger coupling effects was observed in laser-leading mode.What's more,heat source coupling also affected the keyhole depth and its stability.The coupling with arc source improved the keyhole depth while decreased the stability.Shortcircuit transfer might collapse the keyhole.Weakened coupling effects were examined with increasing distance between heat sources.Consequently,the keyhole depth reduced.Deeper keyhole was demonstrated in arc-leading mode while better keyhole stability was obtained in laser-leading mode.Thirdly,the mechanism of changing metal transfer under heat source coupling effects was discussed.The transfer frequency was found to increased firstly and then decreased when laser power kept increasing.Force analysis for droplets indicated that Lorentz force and reaction force of metal vapor were influenced by heat source coupling.Theoretical calculation implied that the size relationship between the two force was significant.On the one hand,heat source coupling increased arc energy,resulting in improved Lorentz force and metal transfer.On the other hand,the reaction force of metal vapor suppressed metal transfer according to the varied distribution of droplets.It was concluded that metal transfer of hybrid welding depended on the two aspects above,which was proved by simulation results using the Fluent software.