超声及活性剂对电弧等离子体影响机理的研究
发布时间：2018-08-31 17:46
【摘要】：随着我国工业化进程的不断加快,焊接作为一种独特的材料连接工艺而被越来越重视。TIG焊接以其具有的焊接过程稳定、焊缝成形性好、焊缝组织质量高而被广泛应用,但是其单道焊熔深浅、焊接效率低的缺点限制了自身的应用范围。以往的研究表明,超声电弧复合焊接以及活性剂焊接,在增大熔深,提高焊接效率方面表现出很大的优势,主要原因是焊接过程中提高了电弧等离子体能量密度。但是目前对于超声及活性剂对电弧等离子体能量密度提高的作用机理方面研究尚少。本文围绕TIG焊接过程中的电弧等离子体,以二次曝光全息干涉法为研究方法,研究了超声及活性剂对电弧等离子体内能量密度的影响机理。首先研究了常规TIG电弧等离子体,选取焊接电流、电弧长度、保护气流量三个焊接参数为单一变量,分析参数改变后对电弧的影响规律。随着焊接电流增大,干涉条纹条数增多,条纹间距减小,表明电弧的温度升高,电弧内部能量密度更加集中;随着电弧长度的增大,干涉条纹的轮廓半径增大,表明弧长的增大使电弧温度场的分布更加扩展;气流量过大时,干涉条纹紊乱,说明保护气流量太大时引起电弧的不稳定。其次研究了活性剂对电弧等离子体的影响机理。选取氧化物(SiO_2、TiO_2、Cr_2O_3)、氯化物(NaCl、KCl)、氟化物(AlF3)以及混合活性剂作为试验对象,发现涂覆SiO_2、Cr_2O_3、Na Cl、KCl、AlF_3以及混合活性剂后,全息干涉条纹的分布更加密集,条纹数目增多,这意味着涂覆活性剂后电弧发生收缩,能量密度更加集中。测出涂覆活性剂后的电弧电压升高,验证了电弧发生收缩的结论。而涂覆TiO_2的电弧干涉条纹并没有发生太大的变化,同时电弧电压基本保持不变,这说明涂覆TiO_2后对电弧等离子体形态基本没有影响。同时探究了超声对电弧等离子体影响机理。选取了声场能量集中、分布均匀且几乎不发生衰减的凹球面状发射端,在加载超声时采集得到的电弧干涉条纹由两侧向中央靠拢,表现出与未加载超声时得到的全息图条纹分布方向完全相反的形态。从超声对保护气运动状态的影响方面分析,由两侧进入的保护气受到超声场的“声拘束”作用,从而向电弧中央聚集,使电弧中央能量密度更加集中,表现在电弧形态上就是电弧发生收缩。最后进行了电弧等离子体温度场计算。分析运用全息干涉法度量电弧等离子体温度场的过程,推导相关公式,采集了焊接参数为电流60A、弧长12mm、保护气流量4L/min时电弧的有限全息干涉条纹,计算出常规TIG和涂覆SiO_2活性剂时电弧内部距阴极7.92mm的横截面上的温度,最高温度出现在该弧柱截面中心位置,分别为12776K和13043K。涂覆SiO_2活性剂后该截面的温度整体有了提高,并且在靠近弧柱中心局部范围内随电弧半径增大时温度降低幅度更小,由此说明涂覆活性剂具有压缩电弧,提高能量利用率的作用。另外,假如在理想情况下能够将电弧沿轴向分为无限多横截面进行温度求解,就可以用全息干涉法得到电弧内部各点的温度。
[Abstract]:With the rapid development of industrialization in China, welding has attracted more and more attention as a unique material joining process. TIG welding has been widely used for its stable welding process, good weld formability and high quality of weld microstructure. However, its single pass weld penetration is shallow and welding efficiency is low. Previous studies have shown that ultrasonic arc hybrid welding and active flux welding have great advantages in increasing penetration depth and welding efficiency. The main reason is that the energy density of arc plasma is increased during welding. Focusing on the arc plasma in TIG welding process, the influence mechanism of ultrasonic and activator on the energy density in arc plasma is studied by double exposure holographic interferometry. With the increase of welding current, the number of interference fringes increases and the spacing of fringes decreases, indicating that the arc temperature increases and the energy density inside the arc becomes more concentrated; with the increase of arc length, the profile radius of interference fringes increases, indicating that the arc temperature field increases with the increase of arc length. Secondly, the influence mechanism of active agents on arc plasma is studied. Oxides (SiO_2, TiO_2, Cr_2O_3), chlorides (NaCl, KCl), fluorides (AlF_3) and mixed active agents are selected as the experimental objects. The holographic interference fringes of O_2, Cr_2O_3, Na Cl, KCl, AlF_3 and the mixed activator are more dense and the number of fringes increases, which means that the arc shrinks and the energy density becomes more concentrated after coating the activator. The fringes did not change much, and the arc voltage remained unchanged, which indicated that the coating of titanium dioxide had little effect on the arc plasma morphology. The mechanism of ultrasonic effect on arc plasma was also explored. The interference fringes of the arc acquired in acoustic time are close to the center from both sides, showing a completely opposite pattern to the fringes of the hologram acquired in unloaded ultrasound. From the analysis of the influence of ultrasound on the movement of the shielding gas, the shielding gas entering from both sides is restrained by the sound of the ultrasonic field, and then converges to the center of the arc. Finally, the temperature field of arc plasma is calculated. The process of measuring the temperature field of arc plasma by holographic interferometry is analyzed, and the relevant formulas are deduced. The welding parameters are 60A, 12 mm arc length and 4 L/min shielding gas flow. The temperature of the arc on the cross section of 7.92 mm from the cathode in the conventional TIG and coating with SiO_2 activator is calculated. The highest temperature appears at the center of the arc column section, which is 12776K and 13043K, respectively. The temperature of the cross section increases as a whole after coating with SiO_2 activator, and is near the center of the arc column. In addition, if the arc can be divided into infinite cross sections along the axial direction to solve the temperature problem, the temperature of each point in the arc can be obtained by holographic interferometry.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG444
，
本文编号：2215713
[Abstract]:With the rapid development of industrialization in China, welding has attracted more and more attention as a unique material joining process. TIG welding has been widely used for its stable welding process, good weld formability and high quality of weld microstructure. However, its single pass weld penetration is shallow and welding efficiency is low. Previous studies have shown that ultrasonic arc hybrid welding and active flux welding have great advantages in increasing penetration depth and welding efficiency. The main reason is that the energy density of arc plasma is increased during welding. Focusing on the arc plasma in TIG welding process, the influence mechanism of ultrasonic and activator on the energy density in arc plasma is studied by double exposure holographic interferometry. With the increase of welding current, the number of interference fringes increases and the spacing of fringes decreases, indicating that the arc temperature increases and the energy density inside the arc becomes more concentrated; with the increase of arc length, the profile radius of interference fringes increases, indicating that the arc temperature field increases with the increase of arc length. Secondly, the influence mechanism of active agents on arc plasma is studied. Oxides (SiO_2, TiO_2, Cr_2O_3), chlorides (NaCl, KCl), fluorides (AlF_3) and mixed active agents are selected as the experimental objects. The holographic interference fringes of O_2, Cr_2O_3, Na Cl, KCl, AlF_3 and the mixed activator are more dense and the number of fringes increases, which means that the arc shrinks and the energy density becomes more concentrated after coating the activator. The fringes did not change much, and the arc voltage remained unchanged, which indicated that the coating of titanium dioxide had little effect on the arc plasma morphology. The mechanism of ultrasonic effect on arc plasma was also explored. The interference fringes of the arc acquired in acoustic time are close to the center from both sides, showing a completely opposite pattern to the fringes of the hologram acquired in unloaded ultrasound. From the analysis of the influence of ultrasound on the movement of the shielding gas, the shielding gas entering from both sides is restrained by the sound of the ultrasonic field, and then converges to the center of the arc. Finally, the temperature field of arc plasma is calculated. The process of measuring the temperature field of arc plasma by holographic interferometry is analyzed, and the relevant formulas are deduced. The welding parameters are 60A, 12 mm arc length and 4 L/min shielding gas flow. The temperature of the arc on the cross section of 7.92 mm from the cathode in the conventional TIG and coating with SiO_2 activator is calculated. The highest temperature appears at the center of the arc column section, which is 12776K and 13043K, respectively. The temperature of the cross section increases as a whole after coating with SiO_2 activator, and is near the center of the arc column. In addition, if the arc can be divided into infinite cross sections along the axial direction to solve the temperature problem, the temperature of each point in the arc can be obtained by holographic interferometry.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG444
，
本文编号：2215713
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