本文選題：等離子弧焊接 + 等效熱源模型　； 參考：《北京科技大學(xué)》2014年博士論文

【摘要】：焊接是現(xiàn)代制造業(yè)中非常重要的基礎(chǔ)工藝技術(shù),高效、優(yōu)質(zhì)和低成本的焊接工藝是生產(chǎn)過程永恒的需求。等離子弧焊接因?yàn)槠錆撛诘膬?yōu)勢(shì),成為21世紀(jì)最具發(fā)展前景的高效焊接技術(shù)之一。與常規(guī)電弧焊相比,等離子弧焊接具有能量集中、電弧挺度大、一次焊透深度大、熱影響區(qū)窄、焊接變形小、效率高等優(yōu)點(diǎn)；而與激光焊和電子束焊相比,等離子弧焊接在設(shè)備造價(jià)、維護(hù)、操作復(fù)雜程度及焊槍運(yùn)動(dòng)靈活性等方面又具有較大優(yōu)勢(shì)。然而,等離子弧焊接在實(shí)際應(yīng)用中存在一些尚未解決的關(guān)鍵問題,主要是小孔對(duì)工藝條件的變化比較敏感；焊縫成形的穩(wěn)定性較差；獲得優(yōu)質(zhì)焊接接頭的適用參數(shù)區(qū)間窄、裕度小。這些問題制約著這種高效焊接技術(shù)的應(yīng)用。本文針對(duì)該問題開展了焊接熔池與小孔動(dòng)態(tài)耦合傳熱特性的研究,以期為優(yōu)質(zhì)焊縫成形的可控性提供理論指導(dǎo)。 基于文獻(xiàn)調(diào)研工作,確立了理論與實(shí)驗(yàn)相結(jié)合、機(jī)理分析循序漸進(jìn)的研究方案。首先搭建了焊接實(shí)驗(yàn)系統(tǒng),根據(jù)焊接過程中的關(guān)鍵參數(shù)和相應(yīng)的熱物理現(xiàn)象提煉出數(shù)學(xué)模型,并且開展了不銹鋼板的焊接實(shí)驗(yàn),為模擬結(jié)果提供驗(yàn)證。 理論研究從宏觀的傳熱過程出發(fā),通過建立合適的體積熱源分布模式來反映小孔效應(yīng)的影響,暫時(shí)不涉及真實(shí)小孔的形成,而是將小孔的熱-力作用體現(xiàn)在恰當(dāng)?shù)捏w積熱源分布模式上。本文稱之為等效熱源模型,著重考察在這種體積熱源模式作用下的焊接溫度場(chǎng)。然后開始探討焊接熱場(chǎng)和溫度場(chǎng)隨小孔增長(zhǎng)的演變機(jī)制,建立了小孔-熔池動(dòng)態(tài)耦合的傳熱模型,利用流體體積函數(shù)(VOF)追蹤小孔界面,研究了定點(diǎn)焊接條件下熔池穿孔的動(dòng)態(tài)演變過程,同時(shí)分析了小孔和熔池之間的耦合熱-力作用機(jī)制及其所引起的熔池流體流動(dòng)。在定點(diǎn)焊接的動(dòng)態(tài)熱源模型的基礎(chǔ)上,又開展了連續(xù)焊接條件下熔池穿孔的動(dòng)態(tài)演變過程及熔池內(nèi)傳熱和流動(dòng)特性的研究,該模型不僅考慮了小孔動(dòng)態(tài)變化的影響,同時(shí)也增加了焊接速度的影響。 目前國(guó)內(nèi)外針對(duì)穿孔等離子弧焊接的理論研究普遍不考慮電弧部分,僅關(guān)注熔池部分的傳熱。然而電弧的熱力特性是小孔型等離子弧焊接穩(wěn)定進(jìn)行的基礎(chǔ),只有開展等離子電弧和熔池耦合的全模型才能準(zhǔn)確認(rèn)識(shí)其中的真實(shí)熱物理機(jī)理。因此本文建立了一個(gè)包含電弧、小孔和熔池的二維焊接全模型,模型中不再包含內(nèi)熱源,而是通過等離子電弧向工件傳熱。該模型更為真實(shí)的描述了等離子電弧熱場(chǎng)、電場(chǎng)、磁場(chǎng)和流場(chǎng)的耦合輸運(yùn)作用,更加接近實(shí)際的焊接熱物理過程。最后應(yīng)用該模型開展了7因素3水平的正交試驗(yàn),有效地預(yù)測(cè)了各工藝參數(shù)對(duì)焊縫成形的影響水平。
[Abstract]:Welding is a very important basic process technology in modern manufacturing industry. High efficiency, high quality and low cost welding process is the eternal demand of production process. Plasma arc welding has become one of the most promising welding technologies in the 21st century because of its potential advantages. Compared with conventional arc welding, plasma arc welding has the advantages of concentrated energy, large arc stiffness, large penetration depth, narrow heat affected zone, low welding deformation and high efficiency, while compared with laser welding and electron beam welding, plasma arc welding has many advantages. Plasma arc welding has great advantages in equipment cost, maintenance, operation complexity and welding torch movement flexibility. However, there are some unsolved key problems in the practical application of plasma arc welding. The main problems are that the keyhole is sensitive to the change of process conditions, the stability of weld formation is poor, and the suitable parameters for obtaining high quality welding joints are narrow. The margin is small. These problems restrict the application of this high-efficiency welding technology. In this paper, the dynamic coupling heat transfer characteristics of weld pool and hole are studied in order to provide theoretical guidance for the controllability of high quality weld forming. Based on the literature research, the research scheme of combining theory with experiment and mechanism analysis is established. Firstly, the welding experiment system was built, and the mathematical model was extracted according to the key parameters and the corresponding thermo-physical phenomena in the welding process, and the welding experiment of stainless steel plate was carried out, which provided the verification for the simulation results. Based on the macroscopic heat transfer process, the theoretical study reflects the effect of the pore effect by establishing a suitable volumetric heat source distribution model, and does not involve the formation of the real pore for the time being. The thermal-force action of the pore is reflected in the proper volumetric heat source distribution model. In this paper, the equivalent heat source model is called, and the welding temperature field under the action of this volumetric heat source mode is investigated. Then the evolution mechanism of welding heat field and temperature field with the growth of small hole is discussed. A dynamic coupling heat transfer model between small hole and molten pool is established, and the pore interface is traced by fluid volume function (VOF). The dynamic evolution of weld pool perforation under fixed-point welding was studied. The coupled thermal-force mechanism between the holes and the weld pool and the fluid flow in the molten pool were analyzed. On the basis of the dynamic heat source model of fixed-point welding, the dynamic evolution process of weld pool perforation and the heat transfer and flow characteristics in the molten pool under continuous welding conditions are studied. The model not only takes into account the influence of the dynamic change of the pore, but also the heat transfer and flow characteristics in the molten pool. At the same time, it also increases the influence of welding speed. At present, the theory of perforated plasma arc welding is generally concerned with the heat transfer in the molten pool. However, the thermal characteristics of the arc are the basis for the stability of the keyhole type plasma arc welding. Only by developing the whole model of plasma arc and pool coupling can the true thermo-physical mechanism be accurately understood. In this paper, a two-dimensional welding model with arc, orifice and molten pool is established. The model no longer contains internal heat source, but transfers heat to the workpiece by plasma arc. The model describes the coupling transport of plasma arc heat field, electric field, magnetic field and flow field more realistically, and is closer to the actual thermal physical process of welding. Finally, the orthogonal experiments of 7 factors and 3 levels were carried out by using the model, which effectively predicted the level of influence of each process parameter on weld formation.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TG456.2

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本文編號(hào)：1973010