【作者】 杨璐；

【导师】 康志新； 宋芳芳；

【作者基本信息】 华南理工大学 ， 机械工程（专业学位）， 2016， 硕士

【摘要】 行波管作为一种用于放大信号功率的电真空器件,广泛应用于交通运输、工程建设、野外检测、手机通讯等领域。行波管在制造过程中需要使用大量异种金属焊接工艺。由于行波管工作环境恶劣,焊接质量欠佳的敏感结构易导致行波管工作失效。现今在行波管的生产过程中缺乏对其焊接缺陷的检测与评价,故本文通过对行波管内敏感焊接结构进行理论分析,开展了焊接缺陷的无损检测及评价技术研究,深入探讨了焊接缺陷产生的原因及机理,并对其焊接工艺提出优化方案。首先对行波管内敏感焊接结构及其焊接工艺进行理论分析,发现收集极焊接结构内焊接界面结合不良严重影响收集极散热,最终导致收集极烧毁。根据收集极的焊接结构特点开展超声探伤、3D X-ray检测技术研究,对焊接缺陷进行定性、定量分析,从而制定缺陷评定判据,即从收集极底座底面或侧面进行超声检测时,焊接界面回波波高分别超过屏幕范围的35%或40%时便可判定此处存在缺陷。通过ANSYS Workbench仿真分析与试验相结合的方式研究了焊接缺陷对收集极焊接结构热学性能的影响。焊接面积不足会导致收集极及焊锡层的温度上升,焊接面积分布不均同样会造成收集极温度过高,而当收集极与底座侧面和底面均存在焊接接触时收集极温度最低。当焊接接触面积低于50%时,收集极和焊锡层的温度会急剧上升,可能会造成焊锡层熔化流动,且焊接结构的热导率会大幅下降,从而阻碍收集极散热。故提出收集极与底座至少要有50%以上的面积存在焊接接触,且收集极与底座的侧面和底面均应有焊接接触的焊接质量要求。最后探讨了收集极焊缝内主要焊接缺陷产生的原因及机理,模拟仿真了现有焊接工艺下焊锡层的温度变化及分布情况,并结合焊缝内缺陷产生的原因,模拟计算了不同焊接工艺下焊锡层的温度变化及分布情况,从而给出焊接温度为270℃,焊接时间不少于320s的焊接工艺优化建议。更多还原

【Abstract】 Travelling wave tube (TWT) is an electric vacuum devices used for amplifying signal power. It has been widely applied in the field of military and civilian markets. A number of dissimilar metal welding processes are needed in the manufacturing process of TWT. Due to the bad working conditions of TWT, the sensitive structure with poor welding quality can easily lead to the failure of TWT. There is no detection and evaluation of welding defects in the production process of TWT, so collector sensitive welding structure was theoretically analyzed, the detection and evaluation of welding defects were researched, the causes and mechanisms of welding defects were investigated, and the improvement suggestions on welding process were proposed in this research.First, the sensitive welding structure of TWT and its welding process were theoretically analyzed. They showed that poor binding welding interface in the collector had an adverse effect on collector’s heat dissipation, causing the collector to be burned. The ultrasonic testing and 3D X-ray testing technology for welding defects of collector were investigated, the welding defects were qualitatively and quantitatively analyzed, and then the criteria for assessing defects was made. It could be assessed that defects exist here when the echo amplitude of the bottom or sides of the brazing interface were respectively higher than 35% or 40%.Second, the effect of welding defects on thermal performance of welding structure was studied by means of ANSYS Workbench simulation analysis and experiment. Insufficient welding area could lead to the temperature rise of the collector and the solder layer. Uneven distribution of welding area could also cause the excessive temperature of collector. The temperature of collector was lowest when the side and bottom surface of the pedestal had a good welding contact with collector. When the welding contact area was less than 50%, the temperature of collector and solder layer would rise sharply, and the thermal conductivity of the welding structure would significantly decreased. They may cause the solder layer to melt flow, and hinder the heat dissipation of collector. So the welding quality requirements that the welding area size should be more than 50%, and the side and bottom surface of the pedestal should have a good contact with collector were put forward.Finally, the causes and mechanisms of main welding defects in the welding seam of collector were studied. The temperature variation and distribution of solder layer by existing welding process were simulated, and the temperature variation and distribution of solder layer with different welding temperature were simulated, which combined with the causes of welding defects. The improvement suggestions on welding process that welding temperature was 270℃, and welding time was not less than 320 s were proposed.更多还原