Melting Behaviors And Forming Characteristics Of Filler Wire Acted By Laser Heat Source

Based on filler wire,laser welding and related technologies take laser energy as a heat source,which has high density of heat input and the smaller heat affected area so as to improve the stability of the welding process.Meanwhile,it is possible to improve the metallurgical properties of welds and the economy of welding because of the addition of filler wire.Therefore,it has broad application prospects in the automotive manufacturing,aerospace,ship-building,aerospace,defense military and other fields owing to its good properties such as high flexibility,integration,and high stability.However,due to the addition of filler wire,there exist many technical parameters in welding process,so it is difficult to control the stability of welding process and obtain the well-shaped weld.In recent years,an enormous amount of researches have been performed.Many researchers have reported effects of welding parameters on weld forming characteristics.However,the theoretical guidance to industrial application of laser welding with filler wire is very limited.In order to solve the above problems in application,combined with high-speed camera technology and theoretical analysis,the effects of welding parameters on the melting mechanisms of filler wire,the transfer behaviors of molten metal and the characteristics of weld were studied detailedly in this study.The results showed that the filler wire was melted sufficiently under the heating action of laser energy,metal vapor radiation heat and the conduction energy of molten metal in welding pool.It was concluded that three key welding parameters,which were laser energy,positions of filler wire feeded in and wire feeding speed,greatly affected the melting mechanisms of filler wire.By analyzing the welding dynamic process acquired by high-speed camera system,it was indicated that the transfer behaviors of filler wire can be divided into three categories,named as spreading transfer behavior,big-droplet transfer behavior and liquid-bridge transfer behavior.When molten metal was transferred into welding pool in spreading transfer behavior,the weld appearance was similar to self-fusible welding due to the smaller volume of metal transferred into welding pool.In the same time,the welding process was unstable and welding efficiency was low.It was difficult to guarantee the welding process stability and weld quality during welding while molten metal transferred into welding pool in big-droplet transfer behabior,the reason for this was that big droplet disturbed weld pool seriously.The surface of weld was composed of discontinuous weld scabs.Theoretically,the well-formed weld could be obtained by reducing the spacing of scabs.However,the process parameters range was and it was difficult to realize in the actual welding process.It was conclued that molten metal transferred into welding pool with liquid bridge in quite wide process parameters range while filler wire was covered partly by laser beam.Liquid-bridge transfer behavior was superior to droplettransfer behavior with much more stable welding process which led to better weld quality and lower porosity defect.On the basis of the previous research on the melting mechanisms of filler wire and the transfer behaviors of molten metal,the position of filler wire feeded in was optimized.Finally,by observing the dynamic melting process of filler wire in real time,the effects of welding parameters on weld forming characteristics were investigated detailedly,and the internal connection between weld quality and melting process was revealed systematically.