【作者】 王恒；

【导师】 陈茂爱；

【作者基本信息】 山东大学 ， 工程硕士（材料工程）（专业学位）， 2017， 硕士

【摘要】 TIG焊接过程稳定,焊缝成形良好,但存在焊接效率低下的不足;传统单MIG焊接具有生产效率高,且易于实现自动化等优点,但焊接过程不够稳定。随着现代工业的发展,传统焊接工艺难以满足人们对于高效低成本焊接的需求。因此,众多高效焊接工艺出现并迅速发展。直流TIG-MIG复合焊接有效克服单独焊接工艺不足,综合焊接工艺的优点,在高效焊接领域得到广泛认同。但当设置TIG焊接为小参数焊接电流时,直流TIG-MIG复合焊接稳定性差,断弧现象严重,驼峰缺陷难以克服,并伴有严重的焊接飞溅。改变焊接工艺参数,对TIG-MIG复合焊接工艺进行优化具有十分重要的意义。方波交流具有正半波与负半波转换速度快,零点过渡区几乎为零,电弧稳定等优点。本文提出在TIG焊接参数选择上,利用方波交流代替直流进行方波交流TIG-MIG复合焊接工艺试验,为该工艺后续优化及工程应用提供理论基础。从焊接过程断弧数量、电参数波形等方面对比分析了直流TIG-MIG复合焊接工艺和方波交流复合焊接工艺焊接过程的稳定性,结合焊缝成形,客观分析两种工艺的优势与不足。小参数TIG直流TIG-MIG复合焊接整体稳定性差,断弧现象严重,焊缝成形较差,驼峰现象难以克服,并伴有大量飞溅。方波交流TIG-MIG复合焊接断弧较少,电参数波形更加稳定,焊缝成形良好,极性比为10焊接工艺最优。分析了方波交流TIG-MIG复合焊接电弧物理特性,并对极性比对该工艺电弧物理特性的影响展开研究。时间方面,极性比增大,复合电弧吸引时间增长,排斥时间缩短。电弧形态方面,极性比增大,复合电弧强度增强,两电弧电磁力作用强化,吸引和排斥形态更加明显。极性比小,复合电弧形态收缩,电弧集中,热量集中。分析了方波交流TIG-MIG复合焊接熔滴过渡特点,并探究极性比对熔滴过渡的影响机理。当TIG处于方波交流正半波时,MIG焊丝尖端熔化液态金属明.显后偏,向熔池后方过渡;负半波时,焊丝端部熔化液态金属前偏向熔池前方过渡。方波交流TIG-MIG复合焊接工艺MIG过渡熔滴主要维持后偏的过渡形态,过渡进入熔池的后方。随着极性比的增大,过渡熔滴向熔池后方过渡时间缩短,以前偏形态向熔池前方过渡时间增长。分析了方波交流TIG-MIG复合焊接熔池流动特点及驼峰缺陷机理,并对极性比对熔池流动的影响展开研究。极性比为0(直流),MIG焊丝尖端锥状液柱始终后偏过渡进入熔池尾部。尽管由于液态金属层较厚,其对后向液体流的驱动作用较小,熔池液态金属流向尾部形成壁面通道及熔池肿块,容易形成驼峰。极性比为10,波形处于负半波时,过渡熔滴进入熔池的位置在一范围内变化,不会对熔池形成持续的后推力,熔池金属的后向流速变小,不会在焊缝区域出现熔池肿块现象。极性比为40,波形处于负半波时,过渡熔滴前偏进入熔池前部,熔滴撞击弧坑前沿,后向液态金属流以较大的速度向熔池尾部流动,在后方形成液态金属凹陷,形成驼峰。更多还原

【Abstract】 TIG welding process is stable and can get good weld bead surface,however it is low efficient.MIG welding process is high efficient and easy to be used in automatic line,however it is not stable in weldig.With the development of morden industry,traditional welding process can not satisfy the need of high efficiency and low cost.As a result,many welding processes with that strength appear and develop very fast.TIG-MIG hybrid welding process can overcome the shortcomings of single TIG or MIG,and play their respective advantages.So,the process is widely acknowledged in high efficient welding field.But when low current is used in TIG process,DC TIG-MIG hybrid welding process is unstable with severe current interruptions and spatters.Moreover,there are also severe humpings.To change the process parameters and overcome defects like that is with high significance in optimizing TIG-MIG hybrid welding process.TIG AC square wave is good with nearly no zero point region.And the change speed is very fast between the positive and negative polarity,so it can output current with high stability.AC square wave is used to take the place of DC wave in TIG in this paper.AC square wave TIG-MIG hybrid welding process is studied to get more fundamental theory for further optimizing and industry usage.Combined with the weld bead appearance,the stability distinction between DC TIG-MIG hybrid welding process and AC square wave process is analysed from many respects,like the amount of current interruption,the wave of weld parameters and so on.DC TIG-MIG hybrid welding process is more unstable with severer current interruptions,worse weld bead appearance,more spatters and humpings than AC welding process.And when the polarity of AC square wave is set to be 10,the process behavior is the best.The characteristics of AC square wave TIG-MIG hybrid arc and the influence of different polarity are studied.In terms of time,as the polarity goes up,the mutual attractive time of coupled arc becomes longer and the repellent time becomes shorter.In terms of arc shape,as the polarity goes up,the strength of coupled arc is enhanced and the shape of attraction or repellence is more obvious.When polarity is small,the shape of coupled arc is contractive and the heat input is intensive.Droplet characteristic of AC square wave TIG-MIG hybrid welding process and the influence of different polarity are studied.When the wave goes positive,molten MIG wire transit to the rear of the molten pool;when the wave goes negative,the molten liquid metal of the end of MIG wire transit to the front of the molten pool.In AC square wave TIG-MIG hybrid welding process,the droplet of MIG maintains the deviation from tungsten and transits to the rear of molten pool for most of time.As polarity goes up,the time of transition to the rear of molten pool becomes shorter and to the front of molten pool becomes longer.The flow characteristic of molten metal of AC square wave TIG-MIG hybrid welding process and the influence of different polarity are studied to find out how humpings are overcome.When polarity is 0,tapered liquid column of MIG droplet passes into the tail of molten pool.Althoughthe driving effect on the backward liquid flow is smaller because of thick liquid metal layer,the liquid metal flows into the tail to form a wall channel and a molten metal mass,which can easily lead to hump formation.When polarity is 10 and the waveform is in the negative half,the position of the transition droplet into the bath varies within a range,and the continuous thrust of the weld pool will not be formed.The backward flow velocity of molten metal decreases,weld pool lumps will not occur in the weld area.When polarity is 40 and the waveform is in the negative half,MIG droplet passes into the front of molten pool.Thebackward flow velocity of molten metal increases,and it will lead to the formation of liquid metal depressions and finally a hump.更多还原