短路过渡CO2焊接熔滴形状数值模拟与控制

为了进一步提高短路过渡CO2气体保护电弧焊的工艺性能和焊接质量,根据高速CCD摄像获得的熔滴及其短路过渡图像,分析了熔滴与熔池短路前的形状对熔滴与熔池的短路、熔滴在熔池中的铺展及液桥缩颈形成的影响.采用熔滴静力平衡模型研究了电磁力(燃弧电流)、表面张力、重力与熔滴形状的关系,并通过对燃弧电流的精确控制实现了对熔滴形状的有效控制.当熔滴与熔池短路前为细长形状时,短路过渡过程稳定柔顺,而当熔滴为扁平形状时,则不利于熔滴的短路过渡,甚至产生瞬时短路.燃弧阶段的熔滴形状体现了各种力对熔滴的作用,而电磁力(燃弧电流)是决定熔滴形状的主要因素.根据燃弧电流对熔滴形状的影响规律,提出了采用前期大、后期小的燃弧电流控制原则,以在燃弧的不同阶段获得不同的熔滴形状.试验结果表明该控制方法获得了良好的适合于熔滴短路过渡的短路前熔滴形状,短路过渡过程柔顺稳定,消除了瞬时短路以及由此导致的飞溅,改善了熔滴的短路过渡行为,短路过渡结束后焊丝端部的残余液态金属具有良好的一致性.

NUMERICAL SIMULATION AND CONTROL OF MOLTEN DROPLET SHAPE IN SHORT-CIRCUIT CO2 ARC WELDING

To improve the welding process behavior and quality of short-circuit CO2 arc welding further, the effects of molten droplet shape just before short-circuit on the short-circuit of molten droplet with weld pool, the spread of molten droplet in weld pool and the formation of liquid bridge neck are analyzed through the images of molten droplet and its short-circuit transfer photographed by a high-speed CCD camera. By using a static force balance model of molten droplet, the relationships between molten droplet shape and electromagnetic force (arc current), surface tensile force, gravity is studied. And then the molten droplet shape is controlled effectively via precise adjusting of arc current. When the molten droplet shape just before short-circuit is columned, the short-circuit transfer process is stable and gentle. But the flat-shaped molten droplet makes the short-circuit transfer unfavorable, generates transient short-circuit even. The molten droplet shape during arc phase embodies the action of various forces on the molten droplet, in which the electromagnetic force (arc current) is the dominative factor to determine the molten droplet shape. To obtain appropriate molten droplet shape during different stages of arc phase, a control principle by adopting a large arc current in prophase and a small current in anaphase during the arc phase is proposed according to the influence regulation of arc current on the molten droplet shape. The experimental results show that a favorable molten droplet shape just before short-circuit is achieved with this control approach, which is adapt to short-circuit transfer. The short-circuit transfer is stable and gentle, the transient short-circuits and the metal spatter induced by them are eliminated, the short-circuit behavior of molten droplet is improved and the residual liquid metal quantity at the end of wire electrode after the completion of short-circuit transfer has a good equality.