本文選題：局部負壓 + 激光焊接　； 參考：《上海交通大學》2015年博士論文

【摘要】：高功率激光焊接由于其高效及高品質(zhì)的焊接質(zhì)量,使其在中厚板構(gòu)件的制造上體現(xiàn)出顯著的優(yōu)勢。然而隨著板厚的進一步增加,對激光功率及光束質(zhì)量提出了更高的要求,且深熔焊接過程中的焊接缺陷也是制約高質(zhì)量制造的關(guān)鍵問題之一。真空激光焊接的出現(xiàn)不但大大增加了焊接熔深,且有效提升了焊接質(zhì)量,但真空室有限的空間尺寸限制了其在大型構(gòu)件厚板激光焊接中的應(yīng)用。為此,本文結(jié)合真空焊接的特點,提出了一種移動式負壓激光焊接新方法,該方法為厚板大型構(gòu)件的焊接制造提供了一條新途徑�！暗驼婵帐摇�(又稱“負壓腔”)的構(gòu)建是實現(xiàn)負壓激光焊接的關(guān)鍵,該腔內(nèi)的環(huán)境壓力低于大氣壓力,將焊接部位置于該腔體內(nèi)以實現(xiàn)焊接過程的局部負壓環(huán)境�；诖搜b置,論文開展了負壓環(huán)境下激光焊接過程中金屬蒸氣羽煙、熔池及小孔的動態(tài)行為的研究,進一步探討了蒸氣羽煙、熔池、小孔與激光能量之間的相互作用機制,從而揭示負壓環(huán)境下的激光焊縫成形過程及缺陷抑制機理,為推動高功率激光在大型構(gòu)件厚板焊接中的應(yīng)用提供了理論和實驗依據(jù)。首先,基于構(gòu)建的全封閉負壓腔光纖激光焊接實驗平臺,系統(tǒng)開展了不同負壓環(huán)境下的激光焊接試驗研究。其次,研究了不同負壓環(huán)境下金屬蒸氣羽煙的動態(tài)變化特征,并基于光譜診斷分析了負壓下激光焊接蒸氣羽煙的頻譜變化規(guī)律,進而分析了蒸氣羽煙溫度與環(huán)境壓力的內(nèi)在關(guān)聯(lián)。研究了不同負壓環(huán)境下蒸氣羽煙對光纖激光能量的衰減特性及規(guī)律。進一步開展了不同環(huán)境壓力下的焊接熔池及其小孔動態(tài)行為研究,分析了負壓對焊接過程飛濺和氣孔缺陷的抑制機理。最后,基于對全封閉負壓腔激光焊接過程的研究結(jié)果,探討了移動式局部負壓環(huán)境下激光焊接過程中焊縫成形與蒸氣羽煙及熔池動態(tài)行為的關(guān)系。全文的主要結(jié)論如下:1.環(huán)境壓力對焊接熔深及截面形貌的影響存在著臨界壓力值,約為20 k Pa:當環(huán)境壓力在101~20 k Pa內(nèi),熔深隨環(huán)境壓力降低而小幅增加,焊縫截面形貌主要特征為“Y”型;當環(huán)境壓力降低至20 k Pa以下時,熔深開始大幅增加,且壓力越低,熔深增加的幅度越大,在3 k Pa時的熔深約為常壓時的2倍,焊縫截面形貌主要特征為“I”型。2.建立了負壓環(huán)境下低合金高強鋼厚板高功率激光焊接熔深與環(huán)境壓力、激光功率、焊接速度的回歸模型:0,方差分析擬合度為98.9%。該結(jié)果表明,焊接熔深隨環(huán)境壓力和焊接速度的減小而增大,隨激光功率的增加而增加。當激光功率和焊接速度不變的情況下,焊接熔深與環(huán)境壓力呈指數(shù)關(guān)系。3.發(fā)現(xiàn)了負壓環(huán)境對金屬蒸氣羽煙的抑制規(guī)律,即最外側(cè)擴散型羽煙、中部壓縮羽煙及小孔附近駐留型羽煙被抑制的環(huán)境壓力分別為101~80 k Pa、80~20 k Pa和20~3 k Pa。常壓下光纖激光能量的衰減率約為11%,當環(huán)境壓力降至3 k Pa時,金屬蒸氣羽煙對光纖激光能量的衰減率約為1%,駐留型金屬蒸氣羽煙為金屬蒸氣羽煙影響激光能量傳遞的主要部分。得出了金屬蒸氣羽煙對激光能量衰減率計算公式,4.發(fā)現(xiàn)了負壓環(huán)境下蒸氣羽煙動態(tài)變化特征與熔池及小孔行為的內(nèi)在關(guān)聯(lián)。隨著環(huán)境壓力的降低,金屬蒸氣羽煙擺動幅度較常壓下減小,低于10 k Pa時趨于穩(wěn)定,此時熔池表面波動降低,小孔穩(wěn)定性增加,焊接質(zhì)量明顯提高。負壓下小孔后壁的波動被抑制,焊接過程飛濺減少。同時負壓加快了熔池內(nèi)氣泡逸出速度,縮短了其逸出路徑,改變了其逸出位置,使焊縫氣孔缺陷減少。5.基于氣體流體動力學原理對局部負壓腔的結(jié)構(gòu)進行了優(yōu)化,分析了負壓腔尺寸和抽氣孔位置對腔內(nèi)壓力分布和氣流狀態(tài)的影響。相比全封閉負壓裝置,采用局部負壓裝置獲得了具有更高熔深的連續(xù)無缺陷激光焊縫。局部負壓下的抽吸氣流對駐留型金屬蒸氣羽煙有抑制作用,增加了激光的能量密度,同時抽吸氣流對熔池的攪動作用有利于小孔對激光能量的吸收。
[Abstract]:Because of its high quality and high quality welding quality, high power laser welding shows remarkable advantages in the manufacturing of medium and thick plate components. However, with the further increase of the thickness of the plate, the laser power and the quality of the beam are higher, and the welding defects in the process of the deep welding are also the key problems to restrict the high quality manufacturing. One of them. The appearance of the vacuum laser welding not only greatly increases the welding depth, but also effectively improves the welding quality, but the limited space size of the vacuum chamber has limited its application in the laser welding of large plate thick plate. Therefore, a new method of moving negative pressure laser welding is proposed in this paper, which is thick with the characteristics of vacuum welding. This method is thick. A new way is provided for the welding of large plate members. The construction of "low vacuum chamber" (also called "negative pressure chamber") is the key to achieve negative pressure laser welding. The environment pressure in this cavity is lower than atmospheric pressure, and the welding position is placed in the cavity to realize the negative pressure environment of the welding process. In the process of laser welding, the dynamic behavior of metal vapour plume, molten pool and small hole is studied. The interaction mechanism between steam plume, molten pool, small hole and laser energy is further discussed, and the forming process of laser welds and the mechanism of defect suppression under the negative pressure are revealed, so as to promote the high power laser in the heavy plate of large components. The application in welding provides theoretical and experimental basis. First, based on the constructed fully enclosed negative pressure cavity optical fiber laser welding experimental platform, the system has carried out the laser welding experiment under different negative pressure environment. Secondly, the dynamic characteristics of the metal vapor plume under different negative pressure conditions are studied, and the negative pressure is analyzed based on the spectral diagnosis. The law of frequency spectrum change of vapor plume with laser welding is given, and the internal relationship between vapor plume temperature and environmental pressure is analyzed. The attenuation characteristics and laws of vapor feathers on optical fiber laser energy under different negative pressure conditions are studied. The dynamic behavior of weld pool and its small holes under different environmental pressure are further carried out, and the negative effect is analyzed. The mechanism of suppression of spatter and blowhole defects in welding process. Finally, based on the research results of the full closed negative pressure cavity laser welding process, the relationship between the weld formation and the dynamic behavior of the vapour plume and the molten pool during the laser welding process under the mobile local negative pressure environment is discussed. The main conclusions of the full text are as follows: 1. the welding depth of the ambient pressure on the welding The influence of the cross section morphology has a critical pressure value, which is about 20 K Pa: when the environmental pressure is in 101~20 K Pa, the weld depth is slightly increased with the decrease of ambient pressure, and the main feature of the weld section is "Y". When the environmental pressure is below 20 K Pa, the melting depth begins to increase substantially, and the lower the pressure, the greater the depth of the melting depth, at 3 K. The penetration depth of Pa is about 2 times that of normal pressure. The main feature of the weld cross section is "I" type.2., which establishes a regression model of high power laser welding depth and environmental pressure, laser power and welding speed in low alloy high strength steel thick plate under negative pressure environment: 0, the fitting degree of variance analysis is 98.9%. The result shows that welding depth is with environmental pressure and welding. With the increase of the speed, it increases with the increase of the laser power. When the laser power and the welding speed are constant, the welding depth is exponentially related to the ambient pressure..3. finds the inhibition law of the negative pressure environment to the metal vapor plume, that is, the most lateral diffused plume, the medium compressed plume and the resident plume near the hole. The ambient pressure is 101~80 K Pa, 80~20 K Pa and 20~3 K Pa. atmospheric pressure attenuation rate is about 11%. When the ambient pressure drops to 3 K Pa, the attenuation rate of metal vapor plume to fiber laser energy is about 1%. The main part of the laser energy transfer is the residing metal vapor plume as metal vapor plume. The calculation formula for the energy attenuation rate of the vapor plume is found. 4. the internal relationship between the dynamic characteristics of the vapour feathers and the behavior of the pores is found under the negative pressure. With the decrease of the ambient pressure, the amplitude of the metal vapor plume swings is less than that under the normal pressure, and it tends to be stable below 10 K Pa, and the fluctuation of the surface of the molten pool is reduced and the pore stability is stable. The welding quality is increased obviously. The fluctuation of the rear wall of the hole in the negative pressure is suppressed and the spatter in the welding process is reduced. At the same time, the negative pressure accelerates the escape velocity of the bubble in the molten pool, shortens the escape path and changes the escape position of the weld, and makes the weld hole defect reduction.5. based on the principle of gas flow dynamics to the structure of the local negative pressure cavity. The influence of the negative pressure cavity size and the suction hole position on the pressure distribution and the air flow state is analyzed. Compared with the full closed negative pressure device, the continuous defect free laser welds with higher melting depth are obtained by the partial negative pressure device. The suction flow under the local negative pressure has the inhibition effect on the residing type of the vapor plume, and the laser is added. The energy density and the stirring effect of the suction flow on the molten pool are beneficial to the absorption of laser energy by the small hole.
【學位授予單位】：上海交通大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG456.7

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