Research On Plasma Arc Welding With Additional Focusing By Metal Powder

Improving welding efficiency and quality is the perpetual pursuit of researchers in welding field.Plasma arc welding is a kind of arc welding process,which is also a high energy density welding process.The cost in plasma arc welding is less than other high energy density welding process(such as LBW,EBW),while the assembly accuracy in PAW is lower than that in LBW and EBW.Plasma arc welding can penetrate steel plate by one single pass without groove when its thickness is within 5-8mm.However,in traditional plasma arc welding,arc penetrability is limited and keyhole stability is poor,which restrict the application of plasma arc welding in middle size or large size.Improving arc penetrability is one of the effective ways to improve the efficiency and quality of plasma arc welding.Plasma arc welding with additional focusing by metal powder is one kind of modified plasma arc welding.The metal powder around the arc will melt and evaporate,and the two physical process will absorb energy from the arc,which will cool the arc.And even,the metal vapor will change electric channel of the arc plasma.Thus,the plasma arc may be focused and arc penetrability is improved.To sum up,it is of great importance to conduct research on plasma arc welding with additional focusing by metal powder.First of all,the welding experiment platform of plasma arc welding with additional focusing by metal powder is designed and established.The electrical signals(such as arc voltage,welding current),visual signals(such as arc shape,molten metal transfer),and arc spectrum signals are detected and monitored in real time by the welding experiment platform,which lays the foundation for the research of plasma arc welding with additional focusing by metal powder.Secondly,the contrastive study has been carried out between traditional plasma arc welding and plasma arc welding with additional focusing by metal powder.The comparative research has been done from four aspects,which are weld formation,arc voltage,molten metal transfer and arc spectrum.Under the same welding current condition,weld penetration in plasma arc welding with additional focusing by metal powder is deeper than that in traditional plasma arc welding,while weld width in plasma arc welding with additional focusing by metal powder is narrower than that in traditional plasma arc welding,which indicates that arc penetrability in plasma arc welding with additional focusing by metal powder is increased in some way.Arc voltage in plasma arc welding with additional focusing by metal powder is larger than that in traditional plasma arc welding,and the fluctuation of arc voltage in plasma arc welding with additional focusing by metal powder is smaller than that in traditional plasma arc welding.The molten metal is dispersed in the arc which exert an impact force on the weld pool.The arc spectrum shows that,compared with traditional plasma arc welding,the characteristic spectral lines of Fe and Cr elements within the range of 230nm-270 nm are obviously increased during the plasma arc welding with additional focusing by metal powder.Finally,it is studied that the influence of welding process parameters on weld formation,arc voltage,molten metal transfer,and arc spectrum in the plasma arc welding with additional focusing by metal powder.When the welding current is within the range of 190A-200 A,the following conclusions are obtained.Weld penetration,weld width and weld reinforcement increase with the increase of welding current.Arc voltage get lager with the increase of welding current.Welding currents almost have no effects on distribution and size of molten metal.The speed of molten metal increases with the increase of welding current,and the impact force pressure of molten metal on the molten pool increases with the increase of welding current.Welding currents almost have no effects on distribution and quantity of the characteristic spectral lines of Fe,Cr,Ni and Ar.When the plasma gas flow rate is within the range of 3.0L/min-3.1L/min,the following conclusions are obtained.Weld penetration and weld width increase with the increase of plasma gas flow rate.The plasma gas flow rate almost has no effect on the weld reinforcement.Arc voltage get lager with the increase of plasma gas flow rate.Plasma gas flow rate almost have no effects on distribution and size of molten metal.The speed of molten metal increases with the increase of plasma gas flow rate,and the impact force pressure of molten metal on the molten pool increases with the increase of plasma gas flow rate.plasma gas flow rate almost has no effects on distribution and quantity of the characteristic spectral lines of Fe,Cr,Ni and Ar.When the metal powder feeding rate is within the range of 1.15g/min-2.19g/min,the following conclusions are obtained.Weld penetration and weld width decrease with the increase of metal powder feeding rate.Weld reinforcement increase with the increase of metal powder feeding rate.Arc voltage get smaller with the increase of metal powder feeding rate.Metal powder feeding rate almost have no effects on distribution and size of molten metal.Metal powder feeding rate almost have no effects on the speed of molten metal,and the impact force pressure of molten metal on the molten pool increases with the increase of metal powder feeding rate.Metal powder feeding rate almost have no effects on distribution and quantity of the characteristic spectral lines of Fe,Cr,Ni and Ar.