A Research On Circumferential Seam Positioning And Arc Length Control Technology In Fully Automatic Tube-to-tubesheet Welding

In the field of heat exchanger manufacturing,tube-to-tubesheet welding is a very important process.Usually tube-to-tubesheet welding adopts a welding method(orbital welding)with a fixed rotation center and a rotating torch.If the center positioning accuracy of the heat exchange tube is low,the welding seam will be inaccurate,and there will be deviation between the welding seam and the joint gap,which affects the welding quality and even the welding is damaged.Due to the deformation of the tube sheet,the tilt of the tube sheet or the loss of the tungsten electrode,the welding arc length is unstable,resulting in unstable welding quality and the tungsten is easily damaged.Therefore,this paper proposes a method for positioning the center of the heat exchange tube based on machine vision technology to accurately obtain the center position of the heat exchange tube,and solve the problem of inaccurate positioning of the center of the heat exchange tube.At the same time,an automatic arc length control method based on arc voltage is proposed to solve the problem.The problem of arc length instability.The specific work has the following aspects:Analyze the composition,function and operation process of the automatic tube-tube-sheet welding target and the automatic tube-tube-sheet welding system as a whole.According to the structural characteristics of the heat exchanger tube sheet and the characteristics of the tube-to-tubesheet welding joint,the welding method using orbital welding is determined.The five functional modules of the automatic tube-to-tubesheet welding system and the composition of the system are analyzed,and the fully automatic work flow of tube-to-tube sheet welding is determined.In order to realize the autonomous positioning of the tube-to-tubesheet welding system,a method for positioning the center of the heat exchange tube based on machine vision is proposed.By analyzing the relationship between the coordinate systems of the tube-to-tubesheet welding system,the reason for the error in the primary positioning is obtained,and a method of extracting the center of the heat exchange tube with machine vision technology to compensate for the primary positioning error is proposed.In order to accurately locate the center of the heat exchange tube,a heat exchange tube identification and center extraction algorithm based on template matching is proposed,and an autonomous positioning program is designed.In order to facilitate the selection of heat exchange tubes and automatically generate positioning programs,the host computer program is written to achieve visual operation.Taking the deviation between the actual rotation center of the welding gun and the theoretical rotation center as the basis for judging the center positioning error of the heat exchange tube,an experiment on the center positioning accuracy of the heat exchange tube was designed.The results show that the method can effectively compensate for the error of one positioning,and the positioning accuracy can reach 0.29 mm.Considering the influence of arc length stability on welding quality,this paper proposes an arc length control system based on arc voltage.The principle of pulse argon arc welding is analyzed,and the arc length negative feedback adjustment scheme with pulse peak arc voltage as feedback information is determined according to the characteristics of the proportional relationship between arc voltage and arc length.Considering that the arc voltage is relatively high and the arc voltage signal is noisy,the high voltage isolation circuit,filter circuit,photoelectric isolation circuit,voltage offset scaling circuit,etc.are designed,and then the average filtering algorithm with de-extreme value is used to obtain a smooth arc voltage signal.Finally,a fuzzy control-based multi-stage adjustment method of arc length for tube-tube sheet circumferential seam welding is proposed to achieve autonomous arc voltage adjustment.The welding experiments are carried out under the two conditions of non-adjustable arc length and adjustable arc length.The experimental results show that the arc length control scheme effectively controls the arc voltage within the range of ±0.2V.A large number of continuous welding experiments were carried out under the two conditions of non-adjustable arc length and adjustable arc length.The test results show that using machine vision technology to locate the circumferential seam before welding,and adjusting the arc length through the arc length control function during welding can significantly improve the welding quality qualification rate,while protecting the tungsten electrode and reducing damage to the tungsten electrode.