Researches On Detection And Evaluation Of Typical Welding Defects Of Travelling Wave Tube

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.