大熔深K-PAW熔池及电弧视觉行为特征分析研究

Visual Behavior Features of the Weld Pool and Plasma Arc in Deep Penetration K-PAW

穿孔等离子弧焊接(K-PAW)以其独特的优势,在中厚板的焊接制造中应用广泛,并逐渐向更大厚度的方向发展。然而,随工件厚度增加熔池穿孔出现不稳定等问题,制约了其在实际生产中的应用。分析了14 mm厚304不锈钢在“受控恒定穿孔”控制策略下的大熔深K-PAW熔池特征尺寸变化规律和焊接过程中的熔池行为。通过视觉检测与电信号同步采集系统,对大熔深K-PAW过程中熔池的形貌特征进行定量分析,探究在受控脉冲条件下的熔池特征参数变化情况,以及熔池特征与电信号的同步动态行为规律。以初始电流270 A进行焊接,在起弧的前14 s的盲孔阶段,随着电弧热量积累,熔池不稳定,尺寸出现震荡,最大震荡幅度超过10 mm,同时熔池长宽比也在1.0~1.6范围内变化;随着穿孔于第15 s发生,熔池达到平衡,且长宽比在19 s时达到峰值;维孔阶段,熔池保持稳定,形状未发生大变化。综上,可以通过熔池形状变化趋势来区分焊接阶段。比较了不同焊接电流(280 A、275 A、270 A)的盲孔阶段,发现采用较大的初始电流有利于缩短盲孔时间,由270 A时的22.9 s减小到了280 A时的19.8 s,并降低焊接气孔出现的可能性。最后,发现电弧中心与熔池前边缘的距离可以反映穿孔状态。结果验证了“受控恒定穿孔”控制策略的可行性,并验证了通过视觉特征判断焊接阶段及是否穿孔的可行性。

With the unique advantages,keyhole plasma arc welding(K-PAW)is widely used in the welding and manufacturing of medium-thick plates,and is gradually developing for larger thicknesses welding.However,the increase of thickness is also accompanied by the problem of keyhole instability,which restricts its application in practical production.In order to provide theoretical basis for the design of stable piercing process,the characteristic size variation of K-PAW weld pool of 14 mm thick 304 stainless steel under the control strategy of"controlled constant piercing"and the weld pool behavior were analyzed.Through visual detection and electrical signal synchronous acquisition system,the morphology characteristics of molten pool in the process of large-penetration K-PAW were quantitatively analyzed,and the changes of molten pool characteristic parameters under controlled pulse conditions were explored,as well as the synchronous dynamic behavior rules of molten pool characteristics and electrical signals.In the blind hole stage of the first 14 seconds of plasma arc initiation,the weld pool is unstable with the accumulation of arc heat,and the size oscillates,with the maximum oscillation amplitude exceeding 10 mm.At the same time,the aspect ratio of the weld pool also changes in the range of 1.0~1.6.With the perforation occurring at the 15th second,the molten pool reached equilibrium,and the aspect ratio reached its peak at 19 s.The molten pool remained stable and its shape did not change greatly in the sustaining stage.In summary,the welding stage can be distinguished by the changing trend of the shape of the molten pool.Then,the authors compared the blind hole stage of different welding currents(280 A,275 A,270 A),and found that the use of larger initial current is conducive to shortening the blind hole time,from 22.9 s at 270 A to 19.8 s at 280 A,and reduce the possibility of welding holes.Finally,the authors found that the distance between the arc center and the front edge of the molten pool can reflect the perforation state.This study verifies the feasibility of the"controlled constant piercing"control strategy,and verifies the feasibility of distinguishing the welding stage and piercing by visual features.