本文選題：等離子體 + 特征信號�。� 參考：《重慶理工大學(xué)》2017年碩士論文

【摘要】：在脈沖激光焊接過程中,激光焊接等離子體是一個(gè)不可避免的重要物理現(xiàn)象。激光焊接等離子體因其對入射激光的吸收、折射和散射等效應(yīng),極大地影響激光能量對材料的作用,從而影響激光焊接質(zhì)量及其穩(wěn)定性。激光焊接等離子體的動(dòng)態(tài)行為包含著與焊接過程和焊接質(zhì)量相關(guān)的許多瞬態(tài)信息。因此,研究激光焊接過程中等離子體的動(dòng)態(tài)行為特征變化,對提高激光焊接過程的穩(wěn)定性和質(zhì)量可靠性具有重要意義。論文構(gòu)建脈沖激光焊接等離子體多信息源融合傳感分析系統(tǒng),實(shí)時(shí)采集激光焊接過程中等離子體聲波信號、聲發(fā)射信號、電荷信號和圖像信號,分別研究了不銹鋼激光焊接等離子體的傳熱作用特征、保護(hù)氣體介質(zhì)對激光焊接等離子體的影響,以及激光焊接等離子體的能量耦合特征。基于單脈沖激光能量作用下的等離子體電荷信號,研究結(jié)果表明,等離子體的演變過程可分為激發(fā)、維持和衰減三個(gè)階段。基于激光焊接等離子體電流模型,計(jì)算了激光焊接等離子體電子溫度,研究了激光焊接等離子體熱效應(yīng)。研究結(jié)果表明,激光焊接等離子體電子溫度與等離子體電荷電壓呈正相關(guān)性,等離子體電子溫度維持在2000K~5500K之間,且激光焊接參數(shù)對等離子體電子溫度都有較大影響。同時(shí),研究分析了激光焊接等離子體的傳熱特征。結(jié)果表明,噴嘴與工件之間的激光焊接等離子體電子數(shù)密度增大,等離子體對激光的屏蔽作用加強(qiáng),焊縫熔深減小,反之,焊縫熔深增大�；诩す夂附拥入x子體電荷電壓信號和電子溫度,研究了保護(hù)氣體對激光焊接等離子體動(dòng)態(tài)行為和熱效應(yīng)的影響。研究結(jié)果表明,采用He保護(hù)氣體相對于Ar氣能夠?qū)す夂附拥入x子體產(chǎn)生更強(qiáng)的抑制作用和冷卻降溫效果;而采用旁軸送氣相對于同軸送氣同樣能夠產(chǎn)生對等離子體的抑制作用并降低等離子體溫度。隨著保護(hù)氣體流量的逐步增大,保護(hù)氣體對激光焊接等離子體抑制效果和冷卻降溫作用更加顯著。基于激光焊接等離子體聲波、聲發(fā)射信號和電子溫度所反映的能量耦合特征研究結(jié)果表明,激光焊接等離子體可聽聲波、聲發(fā)射和電荷電壓信號能夠較好的反映工件、噴嘴之間的等離子體,以及熔池內(nèi)部等離子體的動(dòng)態(tài)行為和能量傳輸特征。激光等離子體在產(chǎn)生的初期,其熱效應(yīng)變化以及對熔池或匙孔的力學(xué)沖擊變化最為顯著,并于激光等離子體維持階段進(jìn)入峰值,在激光脈沖能量作用的末期漸趨衰減。
[Abstract]:Laser welding plasma is an inevitable physical phenomenon in pulsed laser welding. The effect of laser energy on materials is greatly affected by laser welding plasma because of its absorption, refraction and scattering effects of incident laser, thus affecting the quality and stability of laser welding. The dynamic behavior of laser welding plasma contains a lot of transient information related to welding process and welding quality. Therefore, it is of great significance to study the variation of plasma dynamic behavior in laser welding process to improve the stability and quality reliability of laser welding process. In this paper, a multi-source fusion sensing and analysis system for pulsed laser welding plasma is constructed. The plasma acoustic signal, acoustic emission signal, charge signal and image signal are collected in real time during laser welding. The heat transfer characteristics of laser welding plasma of stainless steel, the effect of protective gas medium on laser welding plasma and the energy coupling characteristics of laser welding plasma were studied. Based on the plasma charge signal under the action of monopulse laser energy, the results show that the evolution of plasma can be divided into three stages: excitation, maintenance and attenuation. Based on the plasma current model of laser welding, the electron temperature of laser welding plasma is calculated and the thermal effect of laser welding plasma is studied. The results show that the plasma electron temperature is positively correlated with the plasma charge voltage and the plasma electron temperature is maintained between 2000K~5500K and the laser welding parameters have great influence on the plasma electron temperature. At the same time, the heat transfer characteristics of laser welding plasma are analyzed. The results show that the plasma electron density between the nozzle and the workpiece increases, the shielding effect of the plasma on the laser is strengthened, and the weld penetration decreases, whereas the weld penetration increases. Based on the plasma charge-voltage signal and electron temperature of laser welding, the effect of protective gas on the dynamic behavior and thermal effect of laser welding plasma was studied. The results show that the He-shielded gas can inhibit the laser welding plasma more strongly than ar gas, and the cooling and cooling effect can be improved. In contrast to coaxial gas, the side-axis gas can also inhibit the plasma and reduce the plasma temperature. With the increase of the flow rate of shielded gas, the effect of plasma suppression and cooling on laser welding is more obvious. Based on the energy coupling characteristics of laser welding plasma acoustic wave, acoustic emission signal and electron temperature, the results show that laser welding plasma can sound wave, acoustic emission and charge voltage signal can better reflect the workpiece. The plasma between the nozzles, and the dynamic behavior and energy transfer characteristics of the plasma in the molten pool. In the early stage of laser plasma generation, the changes of thermal effect and mechanical impact on molten pool or keyhole are most significant, and the peak value is reached at the stage of laser plasma maintenance, and gradually attenuates at the end of laser pulse energy action.
【學(xué)位授予單位】：重慶理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG456.7

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