不锈钢脉冲激光焊接等离子体特征信息研究

发布时间：2018-05-13 08:15

本文选题：等离子体 + 特征信号　；参考：《重庆理工大学》2017年硕士论文

【摘要】：在脉冲激光焊接过程中,激光焊接等离子体是一个不可避免的重要物理现象。激光焊接等离子体因其对入射激光的吸收、折射和散射等效应,极大地影响激光能量对材料的作用,从而影响激光焊接质量及其稳定性。激光焊接等离子体的动态行为包含着与焊接过程和焊接质量相关的许多瞬态信息。因此,研究激光焊接过程中等离子体的动态行为特征变化,对提高激光焊接过程的稳定性和质量可靠性具有重要意义。论文构建脉冲激光焊接等离子体多信息源融合传感分析系统,实时采集激光焊接过程中等离子体声波信号、声发射信号、电荷信号和图像信号,分别研究了不锈钢激光焊接等离子体的传热作用特征、保护气体介质对激光焊接等离子体的影响,以及激光焊接等离子体的能量耦合特征。基于单脉冲激光能量作用下的等离子体电荷信号,研究结果表明,等离子体的演变过程可分为激发、维持和衰减三个阶段。基于激光焊接等离子体电流模型,计算了激光焊接等离子体电子温度,研究了激光焊接等离子体热效应。研究结果表明,激光焊接等离子体电子温度与等离子体电荷电压呈正相关性,等离子体电子温度维持在2000K~5500K之间,且激光焊接参数对等离子体电子温度都有较大影响。同时,研究分析了激光焊接等离子体的传热特征。结果表明,喷嘴与工件之间的激光焊接等离子体电子数密度增大,等离子体对激光的屏蔽作用加强,焊缝熔深减小,反之,焊缝熔深增大。基于激光焊接等离子体电荷电压信号和电子温度,研究了保护气体对激光焊接等离子体动态行为和热效应的影响。研究结果表明,采用He保护气体相对于Ar气能够对激光焊接等离子体产生更强的抑制作用和冷却降温效果;而采用旁轴送气相对于同轴送气同样能够产生对等离子体的抑制作用并降低等离子体温度。随着保护气体流量的逐步增大,保护气体对激光焊接等离子体抑制效果和冷却降温作用更加显著。基于激光焊接等离子体声波、声发射信号和电子温度所反映的能量耦合特征研究结果表明,激光焊接等离子体可听声波、声发射和电荷电压信号能够较好的反映工件、喷嘴之间的等离子体,以及熔池内部等离子体的动态行为和能量传输特征。激光等离子体在产生的初期,其热效应变化以及对熔池或匙孔的力学冲击变化最为显著,并于激光等离子体维持阶段进入峰值,在激光脉冲能量作用的末期渐趋衰减。
[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.
【学位授予单位】：重庆理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG456.7

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