Munenobu Sato

Research On Laser-Arc Hybrid Welding Of Ht780 Steel

The use of thick steel components that can be joined by one-layer-one-pass laser welding or laser-arc hybrid welding has been increasing with the trend of reducing the plate thickness by using higher strength steels. This has enhanced the demand for laser-arc hybrid welding of HT780 steels in the bridge and industrial machinery applications. Taking this trend into account, the authors have researched the suitable welding parameters and consumables for the hybrid welding process that couples laser beam and MAG arc for joining HT780 steel plates. As a result the following welding parameters have been proven to be most appropriate for better root-gap tolerance and lower spatter: MAG arc for leading (kept at the right angle)/laser for trailing (kept at a push angle); laser-arc distance of 3–5 mm; laser beam focus position of ± 0 mm; and shielding gas of Ar-20%CO2. As to the welding wire for laser-arc hybrid welding of HT780 steel, the HT590-class MAG arc welding wire of Cr-Mo-Ti type with a small amount of titanium has been revealed to be suitable to obtain sufficient weld metal tensile strength(890 MPa with 6-mm thickness; 925 MPa with 9-mm thickness; 919 MPa with 12-mm thickness) and toughness(VE−20=38 J with 5-mm subsize; VE−20=59 J with 7.5-mm subsize; VE−20=103 J with 10-mm full size).

Study of spatter reduction in pulsed CO2 shielded arc welding

Summary Spatter reduction in pulsed CO2 shielded arc welding is studied with special reference to rectangular pulsed waveform control and the chemical composition of the welding wire. The spatter affecting pulsed CO2 shielded arc welding is mainly due to the molten droplet on the welding wire being blown off by the arc repulsive force at peak current. Droplet blowoff depends on the up-slope of the peak current, and a rapid up-slope causes heavy spatter to increase. Droplet blowoff is also affected by the deoxidising elements. An increased content of deoxidising elements (Al, Ti, Si) in the chemical composition of the welding wire greatly reduces weldpool spatter and droplet necking. Any excess content of deoxidising elements, however, upsets the stability of one pulse one drop transfer, and the molten droplet is blown off at the peak current. When waveform control and the content of deoxidising elements in the welding wire are optimised, the amount of spatter can be reduced to 1/6th of that found in conve...