【作者】 卢振洋；

【导师】 殷树言；

【作者基本信息】 北京工业大学 ， 机械电子工程， 2006， 博士

【摘要】 焊接速度是薄板高效焊接的重要工艺参数,制约焊接速度提高的主要障碍之一是咬边缺陷的产生。文中通过计算机仿真、TIG定点焊接、TIG自由电弧焊接、TIG电磁压缩电弧移动焊接、以及双弧移动焊接等实验,研究了熔池液体金属表面张力温度系数、温度梯度、熔池液体流向以及熔池动态深宽比等因素对焊缝咬边形成的影响规律及其预防措施等。研究表明,熔池表面液体自熔合线向熔池中心流动是导致焊缝产生咬边的最重要因素。当表面活性物质的存在(例如钢中硫含量在0.02-0.04%左右)使得熔池表面张力温度系数由负值变为正值时,TIG定点不填丝焊点均发生咬边现象,而用含硫量极低的铁基金属(如硫含量小于0.01%)进行焊接时就不出现咬边。温度梯度是影响焊缝咬边程度的最重要因素。在其他条件不变的前提下,焊缝咬边程度随着温度梯度的增大而增大。大电流短时间TIG定点焊接时的咬边倾向和程度大于小电流长时间定点焊接时的咬边倾向和程度,大电流高速焊接时的咬边倾向远大于小电流低速焊接时的咬边倾向。增加熔化角可有效减小近熔合线区的液体流动阻力,降低近熔合线区凝固速度,对抑制焊接咬边有明显作用。当有填充金属加入熔池时,在重力作用下抑制了熔池金属向中心流动,降低了咬边程度。随着填充金属量的增加,咬边将最终消除。数值模拟和焊接实验表明,高速焊接条件下的熔池最大熔深截面滞后于最大熔宽截面,使得焊缝的深宽比不能反映熔池冷却时的实际情况,故而依据最大熔宽和最大熔深截面把熔池分为金属熔化的前段、熔池两侧金属开始凝固而熔池底部仍在继续熔化加深的中段和液体金属凝固的后段。显而易见,咬边正是出现在熔宽减小而熔深增加的中段。文中提出熔池动态深宽比概念:焊接过程中熔宽最大处的熔池深宽比称为熔池动态深宽比,其对准确描述高速焊接条件下的熔池行为具有重要意义。焊接热源形态对焊接熔池温度梯度和动态深宽比有重要影响,对提高焊接速更多还原

【Abstract】 Welding speed is a key parameter of high speed welding when joining thin sheets. Undercut is one of the most important problems which restrict welding speed.Both computer simulation and experimental studies were conducted to find the relations between undercut and surface tension temperature coefficient, temperature gradient, the direction of surface flow of welding pool, and dynamic ratio of depth/width. The preventive measures were given through the experiments of moveless welding, welding with single arc and pressing arc with electric magnetic field and double arc welding.The research indicated that surface flow direction of welding pool near the periphery is the most relevant reason of undercut occurred. When the existence of surface active elements (e.g. the content of S is about 0.02-0.04% in steel) change the sign of surface tension temperature coefficient from negative to positive, undercut always occurs in TIG moveless welding, and not occurs when the content of S in iron is very low( For example, S% is less than 0.01%).The temperature gradient is the most important factor which influences the depth of undercut. The depth of undercut is bigger with the increasing of temperature gradient when the other parameters are the same. The tendency and depth of undercut are bigger in the welding conditions of big current with short time than in the small current with long time in TIG moveless welding, and it is bigger under high speed welding with large current than under low speed welding with small current. By increasing molten angle, the movement resistance of liquid metal of the pool and the cooling speed near the periphery could be decreased, which restrains undercut obviously. Filling metal into welding pool restrains the molten metal moveing from periphery to the pool center, which reduces the tendency of undercut, and eliminates undercut ultimately.It was indicated by simulation and experiments that the biggest depth cross更多还原