【作者】 孙清洁；

【导师】 杨春利；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2010， 博士

【摘要】 本文以解决常规钨极氩弧(TIG)焊接过程中由于电弧能量不集中引起的焊接效率低为目的,提出了以电弧等离子体作为超声载体的超声-TIG复合焊接方法。常规钨极氩弧(TIG)焊适用于高品质焊接,具有电弧稳定、热源易于控制、成形优良和焊缝内部质量高等优点,但其焊接熔深浅和生产效率低等缺点制约了该方法的发展。而功率超声在焊接领域的应用范围越来越广泛,新发展起来的有超声振动辅助钎焊技术、超声辅助电弧焊方法、超声频脉冲焊接技术等。超声的引入改善了焊接过程,并对焊后晶粒大小有明显的细化作用。鉴于将超声和TIG焊接的相关优点结合起来,提出了超声-TIG复合焊接方法。将超声振动施加到TIG焊接电弧空间,其突出特点是引入的超声振动能对TIG焊电弧产生压缩作用并改善电弧特性,进而大幅度增加焊缝熔深和提高接头的机械性能。本文系统研究了U-TIG焊电弧特性、焊缝成形特点、超声对焊缝微观组织及机械性能的影响、阐明超声对电弧作用机制。首先在特定使用环境下提出了超声电源总体设计方案,完成了整流滤波电路、逆变电路、驱动电路和匹配电路的设计及计算,实现了超声频交流信号的输出。利用有限元软件对复合焊炬进行了设计及优化,确定了变幅杆辐射端、冷却机构及钨极装夹方式的最佳方案。其次以辐射声压相对强度为研究对象,考察了温度和介质对声场分布的影响,确定了声场谐振模式。实测超声振幅放大倍数与理论计算值接近,验证了变幅杆的优化过程,满足了超声振动系统谐振及焊接的要求。在此基础上搭建了超声-TIG复合焊接系统,焊接试验验证了该系统能满足试验及设计要求。发现了超声-TIG复合焊接电弧特性及工艺匹配条件。通过对焊接电弧形态的采集,利用电弧长径比分析了其变化规律,发现电弧收缩状态与超声辐射高度、电弧长度存在匹配关系。对复合焊接电弧压力进行测量结果显示,相同工艺参数下复合电弧压力峰值明显高于常规TIG焊电弧,并且不同电弧长度下复合电弧压力峰值受到辐射端高度的影响。随着焊接电流的增加,超声-TIG复合焊电弧压力增量降低。通过电弧静特性分析,超声-TIG复合焊电弧静特性曲线与常规TIG焊相比整体上移,计算得出弧柱区电压降是电弧静特性整体向上平移的主要原因。研究了超声-TIG复合焊接工艺参数对SUS304奥氏体不锈钢焊缝成形影响规律,为该方法实际应用奠定了基础。发现了只有当超声输入功率大于临界值时,焊接过程才得到明显改善;焊缝深宽比及熔化面积受辐射端高度与电弧长度匹配的共同影响。超声-TIG复合焊接过程焊缝热循环显示,复合焊接增大了焊接热输入,热量呈现出定向传递特点,高温停留时间变短。结合等离子流力对熔池表面作用受力分析,超声的引入改变了原有的受力状态。接头微观组织分析结果显示,超声-TIG焊缝中心区域出现了较多的等轴晶,焊缝微观照片也验证了硬度试验的结论。对成形优良的焊缝进行了机械性能测试结果显示,超声-TIG焊接头抗拉强度和延伸率均好于常规TIG焊;接头硬度显示超声-TIG焊热影响区范围更窄,并且焊缝组织均匀化程度明显好于常规TIG焊;疲劳试验中超声-TIG焊表现出更加明显的优势。最后通过试验验证及理论计算探讨了超声振动与焊接电弧作用机制。从理想介质状态方程出发,获得了超声场内粒子振动形式,电弧周围介质散热加强和电弧内部质点速度增加使得焊接电弧收缩,并计算了不同条件下的平面声场分布。在高强超声振动作用下,附加了整体向下超声辐射力,常规TIG焊电弧受力发生改变,粒子运动方向向轴线偏移。通过电弧局部光谱分析了电弧微观变化、电弧高速摄像研究了电弧能量分布,进一步证实了超声与焊接电弧之间的作用结果。更多还原

【Abstract】 In pursuit of increasing of low welding efficiency caused by not so concentrated arc energy during the conventional tungsten inert gas (TIG) welding process, in this paper the ultrasonic TIG hybrid welding method, in which arc plasma is used as the carrier of the ultrasonic, is proposed. Conventional tungsten inert gas arc (TIG) welding is fit for high-quality welding, with the strong points such as arc stability, easiness to control the heat source, forming an excellent pool and high internal quality of weld beam, but its shortcomings, shallow weld penetration and low welding productivity have hampered the development of the method. The power ultrasound are more and more widely used in welding, up with new developments of ultrasonic vibration-assisted brazing technology, ultrasound-assisted welding methods, ultrasonic frequency pulse welding technology etc. The introduction of ultrasonic has improved the welding process, and refined the after welding- grain size significantly. In view of the relevant merits of both the ultrasound and TIG welding, ultrasonic TIG hybrid welding method was proposed. This method, with the ultrasonic vibration applied to the TIG welding arc space, has an outstanding feature that the introduction of the ultrasonic vibration can produce compression effects of TIG welding arc and improve the arc characteristics, and thus increase substantially in weld penetration depth and improve the mechanical properties of joints. The U-TIG welding arc characteristics, weld forming characteristics, ultrasonic influence on weld microstructure and mechanical properties were systematically studied to clarify the mechanism of ultrasound on the arc.First, in a particular environment, the overall design plan of ultrasonic power supply was made, with completion of design and calculations the rectifier filter circuit, inverter circuit, driver circuit and matching circuit to achieve the ultrasonic frequency AC signal output. Composite welding torch has been designed and optimized using finite element software. The radiating ends of the amplitude transformer, the cooling bodies and the best option of the tungsten fixture were determined. Secondly, the relative intensity of radiation-sound pressure level was researched. The influence of temperature and medium on the distribution of the sound field was investigated to determine the sound field resonant mode. The measured magnification factor of ultrasonic amplitude is closed to the calculated values that the optimization process of the amplitude transformer was verified that met the need of resonance of ultrasonic vibration system and welding requirements. On this basis, the ultrasonic TIG hybrid welding systems has been set up and the welding test proved that the system can meet the testing and designing requirements.Finally the arc characteristic of ultrasonic and TIG arc hybrid welding and the matching process conditions were found. Through the collection of shape of the welding arc and an analysis of the length-diameter ratio of used welding arc, we found that there were relational matches between arc contraction and ultrasound irradiation height and the arc length. The results of the composite welding arc pressure measurements showed that the composite arc peak pressure was significantly higher than conventional TIG welding arc under the same process parameters, and the peak pressure value of the composite arc of different length was related to the height of radiation ends of welding arc. As the welding current increases, the increment of arc pressure of ultrasound-TIG arc hybrid welding reduces. Through the analysis of static characteristic of welding arc, ultrasound TIG hybrid welding arc static characteristic curve integrally shifted up compared with the conventional TIG welding. By calculation, we got the main reason for the overall upward shift of the static characteristic curve of the arc was the voltage drop in the arc pole area.The study of influence of process parameters of ultrasonic TIG hybrid welding on weld seam forming for SUS304 austenitic stainless steel was made, laying a foundation for the practical application of such a method. We found that the welding process was significantly improved only when the ultrasonic input power is greater than the critical value. Meanwhile, the depth-width ratio of weld and its melting area were the combined effect of the height of radiation-side and the matching of the arc length. The thermal cycle during ultrasonic TIG hybrid welding process shows that hybrid welding increases the welding heat input, heat transfer characteristics shows a directional transferring character and high-temperature residence time became shorter. With the mechanical analysis of plasma flow force on the weld pool surface, the introduction of ultrasound changes in the original stress state. The microstructure of weld joint were compared and analyzed, showing that more equiaxed grains appeared in the ultrasound TIG weld central region, and weld micro photo also verified the conclusions of the hardness test. The test results of the mechanical properties of well formed weld beam show that the tensile strength of ultrasonic TIG welded joints are better than conventional TIG welding and hardness test of joints showed that heat-affected zone of ultrasonic TIG welded joints was much narrower. For ultrasonic TIG welding, microstructure homogenization in weld seam is significantly better than conventional TIG welding and ultrasonic TIG welding fatigue tests showed a more obvious advantage.Finally experiment and theoretical calculation were done to verify the mechanism of action between welding arc and ultrasonic vibration. Starting from The Ideal-Gas Equation, we obtained the vibrating form of particles inside ultrasonic field. The enhancement of heat dissipation of arc surrounding medium and the fiercer movement of internal particle make the welding arc contract. And we calculated the plane sound field distribution under different conditions. Under the action of the high-strength ultrasonic vibration, the overall downward ultrasonic radiating force was attached. Force of conventional TIG welding arc changed and the direction of motion of the particles shift to the axis direction.The micro-changes of arc were analyzed by local spectra of the arc and the arc energy distribution was studied by high-speed camera, and the results further confirmed the action between ultrasound and welding arc.更多还原