本文選題：水下激光焊接　切入點：激光/水/金屬相互作用機理　出處：《哈爾濱工業(yè)大學》2017年碩士論文

【摘要】：隨著人類的活動范圍向更深、更廣的海洋領域擴展,以及新材料的大量使用,傳統(tǒng)水下焊接方法受到了越來越多的限制。另外,在核電修復領域,高壓、高輻射的水下環(huán)境也對水下焊接技術提出了更高的要求。與水下電弧焊接相比,水下激光焊接具有受水壓影響小,焊接材料廣泛,熱輸入量低,冷卻速度快,熱影響區(qū)小,殘余應力低等優(yōu)點。然而,由于技術封鎖等原因,我國的水下激光焊接技術仍然處于十分落后的地位,尤其是在高功率激光與水中金屬相互作用機理以及水下激光焊接排水裝置設計等方面尚未取得實質性突破。本文首先對高功率激光與水中金屬相互作用機理進行了研究,采用傳統(tǒng)可見光成像系統(tǒng),獲得了不同水深下水下濕法激光焊接過程視頻序列及焊接等離子體形態(tài)圖片,建立了水下濕法激光焊接過程中“光束通道”形成、長大、關閉的力平衡和能量平衡模型。研究發(fā)現(xiàn),隨著水深的增加,水下濕法激光焊接過程穩(wěn)定性和焊接質量逐漸變差,在激光功率6.0 k W,焊接速度0.1 m/min,離焦量0 mm時,水下濕法激光焊接的可焊接水深超過了20 mm。在此基礎上,從進氣方式設計以及內部流體動力學模擬計算入手,利用Solid Works和ANSYS Workbench 14.5,自主設計了兩套水下激光焊接排水裝置——單層氣體輔助排水裝置和雙層氣體輔助排水裝置。針對所設計的排水裝置分別進行了氣液兩相流的流場數(shù)值模擬計算,通過對流體流線圖、速度矢量圖、速度云圖和壓力云圖的分析,驗證了排水裝置設計的可靠性。其中,單層氣體輔助排水裝置采用帶等距離出氣孔的環(huán)向進氣方式,雙層氣體輔助排水裝置外層筒體采用側切向進氣方式,內層筒體采用斜切向進氣方式。最后搭建了局部干法水下激光焊接試驗系統(tǒng)。利用所設計的兩套水下激光焊接排水裝置分別進行了304不銹鋼水下激光焊接工藝研究。試驗結果表明,本文所設計的兩套水下激光焊接排水裝置均能夠得到外觀成形良好、內部無缺陷、性能優(yōu)異的水下焊接接頭。其中,利用單層氣體輔助排水裝置得到的水下焊縫抗拉強度和沖擊韌性分別為665 MPa和107 J/cm2;利用雙層氣體輔助排水裝置得到的水下焊縫抗拉強度和沖擊韌性分別為620 MPa和152 J/cm2。與陸上焊接相比,水下焊縫中鐵素體除了以樹枝狀形態(tài)存在外,還能夠以板條狀形態(tài)存在,焊縫強度滿足要求,韌性有所降低,微觀硬度相差不大。
[Abstract]:Traditional underwater welding methods are more and more limited with the extension of human activities to deeper and wider ocean fields and the extensive use of new materials.In addition, in the field of nuclear power restoration, high pressure, high radiation underwater environment also put forward higher requirements for underwater welding technology.Compared with underwater arc welding, underwater laser welding has the advantages of less influence by water pressure, wide range of welding materials, low heat input, fast cooling rate, small heat affected zone and low residual stress.However, due to the technical blockade and other reasons, the underwater laser welding technology in China is still in a very backward position.Especially the mechanism of interaction between high power laser and metal in water and the design of underwater laser welding drainage device have not made substantial breakthrough.In this paper, the mechanism of interaction between high power laser and metal in water is studied. The video sequence of underwater wet laser welding process and the shape picture of welding plasma are obtained by using traditional visible light imaging system.The model of force balance and energy balance for forming, growing and closing of "beam channel" in underwater wet laser welding is established.It is found that with the increase of water depth, the process stability and welding quality of underwater wet laser welding become worse. When the laser power is 6.0 kW, the welding speed is 0.1 m / min, and the defocus is 0 mm, the weldable water depth of underwater wet laser welding exceeds 20 mm.On this basis, starting with the design of intake mode and the internal hydrodynamic simulation calculation,Using Solid Works and ANSYS Workbench 14.5, two sets of underwater laser welding drainage devices, single-layer gas-assisted drainage device and double-layer gas-assisted drainage device, are designed.The flow field of gas-liquid two-phase flow was simulated and calculated respectively for the designed drainage device. The reliability of the design of the drainage device was verified by the analysis of the flow line diagram, velocity vector diagram, velocity cloud diagram and pressure cloud diagram.The single-layer gas-assisted drainage device adopts the annular air intake mode with equal distance air outlet, the bilayer gas-assisted drainage device adopts the lateral tangential air intake mode, and the inner layer adopts the oblique tangential air intake mode.Finally, a local dry underwater laser welding test system is built.The underwater laser welding process of 304 stainless steel was studied by using two sets of underwater laser welding drainage devices designed in this paper.The experimental results show that the two underwater laser welding drainage devices designed in this paper can obtain underwater welded joints with good appearance, no internal defects and excellent performance.The tensile strength and impact toughness of underwater weld are 665 MPa and 107J / cm ~ 2, respectively, and the tensile strength and impact toughness of underwater weld are 620 MPa and 152J / cm ~ 2, respectively.Compared with onshore welding, the ferrite in underwater weld exists not only in dendritic shape, but also in strip shape. The strength of weld meets the requirement, the toughness is reduced, and the microhardness is not different.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG456.7;TG439.4

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