| 42CrMoA belongs to medium carbon quenched and tempered steelof Cr-Mo series,which has been widely used in thermal power?petrochemical industry?aerospace?maritime traffic and other industries due to its excellent mechanical properties and tissue chemical stability in high temperature. But the alloy system of this material is complex,which results in its high sensitivity tocold and hot crack.So it is mainly used in casting and forging.Conventional arc welding due to its large heat input and low welding efficiency can't completely meet the demand of high quality and high efficiency welding manufacture.Laser-arc hybride welding with deep welding penetration, small welding deformation, low thermal damage of material, etc, is the ideal heat source for welding. "Process-type" porosity is a common problem in the process of conventional laser-arc hybride welding.At the same timeoverlap can't be avoided at the back of weld seam. In this paper, the technology of laser-MAG hybrid welding with beam oscillation is investigated to inhibit the above defects and improve the welding quality. The main results are as follows:The effects of welding parameters such asoscillating trace, oscillating amplitude and oscillating frequency on the weld appearance and porosity inhibition are studied.Threedifferent patterns of beam movement(line to the weld?circular and eightoscillation)are included.Results showthat three patterns have inhibitory effect on the welding porosity and the eight patten is the least effective.Under the condition of 6k W in laser power,0.7m/min in welding speed,4m/min in wire feed speed,164 A in electric current,17 V involtage,different oscillating amplitude and frequency restrain the porosity differently.In the line to the weld pattern,it isvery difficult to suppress the generation of porosity when the oscillation amplitude is less than 1.0 mm;whenoscillationamplitude ranges from 1.0mm to 2.0 mm, the generation of porosity can be effectively suppressed with corresponding frequency 20Hz-60Hz;when the oscillationamplitude is larger than 3.0mm,the porosity can be suppressed effectively in the whole range,but the mode of laser welding is heat conduction.In the circle pattern the rule is similar to line pattern,it isvery difficult to suppress the generation of porosity when the oscillation amplitude is less than0.5mm;whenoscillationamplitude ranges from 0.5mm to 1.0mm, the generation of porosity can be effectively suppressed with corresponding frequency 20Hz-60Hz;whenthe oscillationamplitudebeyond 2.0mm, the laser keyhole feature disappeares, there is no "process-type" porosity occure.When taking the welding ability and weld formation into consideration,the circle pattern is better than line to weld pattern.On the basis of studying the laws of the effect of oscillation parameters on porosity inhibition and weld appearance, using high speed camera and methods of mathematical statistics, the fluctuation characteristics of laser keyhole is studied. Statistical analysis showsthat the open area of the keyhole in laser-MAG hybrid welding with beam oscillationis about 1.7 times as much as that of conventional laser-MAG hybride welding.The stability of keyhole in laser-MAG hybrid welding with beam oscillation increases firstly and then decreases with the increases of oscillation frequency,which is corresponding to rate of porosity.The crack occured in the butt weld is cold crack,which can be inhibited when the weldworkpiece is pre-heated to 100 ?.The crack appearedin the actul workpiece is hot crack,which is caused by the segregation of S?P and structural stress,via the method of improving welding groove and changing wire this problem is solved. |
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