本文關鍵詞： 局部干法 電弧 微型排水罩 數(shù)值模擬　出處：《南昌航空大學》2015年碩士論文　論文類型：學位論文

【摘要】：水下焊接技術在水下工程建設和修復方面具有大量的應用需求。在眾多的水下焊接方法中,局部干法焊接利用微型排水罩將焊接區(qū)域的水排開后進行焊接,接頭質量容易保證,而且無需大型排水設備,易于實現(xiàn)水下焊接自動化,在海洋工程建設方面具有良好的應用前景。局部干法焊接時需要在微型排水罩內通入高壓空氣,然而高壓空氣在微型排水罩內的流動難免會形成橫向流動的風場,影響電弧形態(tài)和焊接過程的穩(wěn)定性。若能利用這一橫向流動的風場,用于橫向焊接中抑制重力作用下熔池下淌的問題,將會化弊為利,從力學和能量兩方面抑制熔池下淌,改善焊縫成形。首先利用數(shù)值模擬的方法,研究了不同結構的微型排水罩內高壓氣體的風場結構。綜合對比發(fā)現(xiàn),在出口上側設擋板可大大增加出口流速,而使用多孔介質隔板又可降低流速,減少環(huán)流,并在其底部形成了穩(wěn)定的層流風場。最終綜合其優(yōu)點,確定了微型排水罩的具體結構,并加工出了微型排水罩。其次建立了MIG焊接電弧的數(shù)學模型,借助于UDF/UDS功能對商業(yè)CFD軟件Fluent進行二次開發(fā)后,以磁流體動力學理論為依據(jù),模擬出了不同側向風速和環(huán)境壓力下電弧等離子體的溫度場、速度場、壓力場,并得到其變化規(guī)律:隨著環(huán)境壓力的升高,電弧有收縮跡象,電弧等離子體的溫度場、速度稍有減小,弧柱區(qū)壓力場強度增大;在側向風場的吹襲下電弧偏向一側,溫度場、壓力場、速度場變化較為一致,其偏角與風速大小均呈線性增長關系,且增長斜率相當。然后進行了焊接實驗,采用高速相機拍攝電弧在不同側向風速下的形態(tài),發(fā)現(xiàn)其實際變化與模擬結果基本一致。最后,做了不同參數(shù)下有側向風場與否的兩組對應焊接實驗,利用線性回歸的方法,得到了電弧的靜態(tài)傳感特性數(shù)學模型,并與實驗結果相比較,偏差在合理的范圍內,結果較為真實、可信。對比發(fā)現(xiàn)在側向風場的影響下,電流信號波動增大,焊接參數(shù)的設置要求更為嚴格,干伸長隨電流變化的斜率增大。
[Abstract]:Underwater welding technology has a lot of application requirements in underwater engineering construction and repair. In many underwater welding methods, the local dry welding uses micro-drain cover to weld the water in the welding area, and the quality of joint is easy to be guaranteed. Moreover, it is easy to realize the automation of underwater welding without large drainage equipment, so it has a good application prospect in marine engineering construction. However, the flow of high pressure air in the miniature drain hood will inevitably form a transverse flow wind field, which will affect the arc shape and the stability of the welding process. If the wind field of this transverse flow can be utilized, The problem of restraining the flow of molten pool under the action of gravity in transverse welding will turn the disadvantages into advantages, which can restrain the flow of molten pool in both mechanics and energy, and improve the forming of weld. First, the method of numerical simulation is used. The wind field structure of high pressure gas in the miniature drain cover with different structures is studied. It is found by comprehensive comparison that the outlet velocity can be greatly increased by installing a baffle on the top side of the outlet, while the velocity of velocity can be reduced and the circulation can be reduced by using the porous media partition. A stable layer flow wind field is formed at its bottom. Finally, the concrete structure of the micro drain cover is determined and the micro drainage cover is machined. Secondly, the mathematical model of MIG welding arc is established. Based on the theory of magnetohydrodynamics, the temperature field, velocity field and pressure field of arc plasma under different lateral wind speeds and ambient pressures are simulated after the secondary development of commercial CFD software Fluent with the help of UDF/UDS function. With the increase of ambient pressure, the arc shows signs of shrinkage, the temperature field of arc plasma decreases slightly, the pressure field of arc column region increases, and the arc deflects to one side and the temperature field increases under the impact of lateral wind field. The variation of pressure field and velocity field is consistent, and the deviation angle is linearly increased with the wind speed, and the increase slope is equal. Then welding experiment is carried out, and the shape of arc under different lateral wind speed is photographed by high speed camera. It is found that the actual variation is basically consistent with the simulation results. Finally, two corresponding welding experiments with or without lateral wind field under different parameters are done, and the mathematical model of the static sensing characteristics of the arc is obtained by using the linear regression method. Compared with the experimental results, the deviation is within a reasonable range, and the results are more real and reliable. It is found that under the influence of the lateral wind field, the fluctuation of the current signal increases and the welding parameters are set more strictly. The slope of dry elongation increases with current.
【學位授予單位】：南昌航空大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TG456.5

【參考文獻】

相關期刊論文 前1條

1 林忠厚;淺談輸油(氣)管道建設焊接技術[J];焊接技術;2002年S1期

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本文編號：1544733