【摘要】：隨著我國工業(yè)化進程的不斷加快,焊接作為一種獨特的材料連接工藝而被越來越重視。TIG焊接以其具有的焊接過程穩(wěn)定、焊縫成形性好、焊縫組織質(zhì)量高而被廣泛應(yīng)用,但是其單道焊熔深淺、焊接效率低的缺點限制了自身的應(yīng)用范圍。以往的研究表明,超聲電弧復(fù)合焊接以及活性劑焊接,在增大熔深,提高焊接效率方面表現(xiàn)出很大的優(yōu)勢,主要原因是焊接過程中提高了電弧等離子體能量密度。但是目前對于超聲及活性劑對電弧等離子體能量密度提高的作用機理方面研究尚少。本文圍繞TIG焊接過程中的電弧等離子體,以二次曝光全息干涉法為研究方法,研究了超聲及活性劑對電弧等離子體內(nèi)能量密度的影響機理。首先研究了常規(guī)TIG電弧等離子體,選取焊接電流、電弧長度、保護氣流量三個焊接參數(shù)為單一變量,分析參數(shù)改變后對電弧的影響規(guī)律。隨著焊接電流增大,干涉條紋條數(shù)增多,條紋間距減小,表明電弧的溫度升高,電弧內(nèi)部能量密度更加集中;隨著電弧長度的增大,干涉條紋的輪廓半徑增大,表明弧長的增大使電弧溫度場的分布更加擴展;氣流量過大時,干涉條紋紊亂,說明保護氣流量太大時引起電弧的不穩(wěn)定。其次研究了活性劑對電弧等離子體的影響機理。選取氧化物(SiO_2、TiO_2、Cr_2O_3)、氯化物(NaCl、KCl)、氟化物(AlF3)以及混合活性劑作為試驗對象,發(fā)現(xiàn)涂覆SiO_2、Cr_2O_3、Na Cl、KCl、AlF_3以及混合活性劑后,全息干涉條紋的分布更加密集,條紋數(shù)目增多,這意味著涂覆活性劑后電弧發(fā)生收縮,能量密度更加集中。測出涂覆活性劑后的電弧電壓升高,驗證了電弧發(fā)生收縮的結(jié)論。而涂覆TiO_2的電弧干涉條紋并沒有發(fā)生太大的變化,同時電弧電壓基本保持不變,這說明涂覆TiO_2后對電弧等離子體形態(tài)基本沒有影響。同時探究了超聲對電弧等離子體影響機理。選取了聲場能量集中、分布均勻且?guī)缀醪话l(fā)生衰減的凹球面狀發(fā)射端,在加載超聲時采集得到的電弧干涉條紋由兩側(cè)向中央靠攏,表現(xiàn)出與未加載超聲時得到的全息圖條紋分布方向完全相反的形態(tài)。從超聲對保護氣運動狀態(tài)的影響方面分析,由兩側(cè)進入的保護氣受到超聲場的“聲拘束”作用,從而向電弧中央聚集,使電弧中央能量密度更加集中,表現(xiàn)在電弧形態(tài)上就是電弧發(fā)生收縮。最后進行了電弧等離子體溫度場計算。分析運用全息干涉法度量電弧等離子體溫度場的過程,推導(dǎo)相關(guān)公式,采集了焊接參數(shù)為電流60A、弧長12mm、保護氣流量4L/min時電弧的有限全息干涉條紋,計算出常規(guī)TIG和涂覆SiO_2活性劑時電弧內(nèi)部距陰極7.92mm的橫截面上的溫度,最高溫度出現(xiàn)在該弧柱截面中心位置,分別為12776K和13043K。涂覆SiO_2活性劑后該截面的溫度整體有了提高,并且在靠近弧柱中心局部范圍內(nèi)隨電弧半徑增大時溫度降低幅度更小,由此說明涂覆活性劑具有壓縮電弧,提高能量利用率的作用。另外,假如在理想情況下能夠?qū)㈦娀⊙剌S向分為無限多橫截面進行溫度求解,就可以用全息干涉法得到電弧內(nèi)部各點的溫度。
[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.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG444
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本文編號：2215713