Visual Sensing Of Fusion Hole And Penetration Closed-loop Control In Thin Plate High Frequency Pulsed TIG Welding

Fusion hole is a semi-open hole existing in butt welding with reserved gaps,which is formed by the fully melted base metal on the both sides of the gap.Due to the problems of thermal deformation in the welding process and the inability to maintain an uniform butt gap,it is difficult to ensure the complete penetration of the weld.An experienced welder can judge the penetration status of the weld by observing the behavior of the fusion hole.High-frequency pulsed TIG welding has the advantages of high arc stiffness,heat concentration and small welding thermal deformation.It is of great significance to study the dynamic behavior of fusion holes during high-frequency pulsed TIG welding.This paper build a high-frequency pulsed welding experimental platform,which includes four parts:welding system,visual sensing system,electrical parameter acquisition system and control system.The power of the welding system is provided by TIG DC welding machine and high frequency power;the visual sensing system is mainly composed of two CMOS cameras,which can monitor the welding process on the front and back in real time;the electrical parameter acquisition system is used to collect welding current signal and voltage signal of the welding process,and the control system can adjust the parameters in the welding process in real time.According to the collected pictures of fusion holes,using MATLAB software write image processing programs to extract the edges of fusion holes.The characteristic parameters representing the fusion hole behavior and dynamic changes were defined,and the characteristic parameters of the fusion hole were extracted and calculated by image processing software.Obtaining characteristic information such as the shape and size of fusion hole.The fusion hole image is calibrated with calibration target,which convert the pixel information of the fusion hole image to the actual size.A comparative experiment between high-frequency pulsed welding and DC welding was carried out.The experimental results show that high-frequency pulsed welding can widen the range of process parameters for the stable existence of fusion holes.When other conditions remain the same,the high-frequency pulsed welding can use a smaller equivalent welding current obtaining penetration state than DC welding.When the fusion hole is unstable,the instability process of the fusion hole in the high-frequency pulsed welding experiment is slower and the instability time is longer,which provides sufficient time for the Penetration closed-loop control experiments.High-frequency pulsed welding experiments with different frequencies,amplitudes and duty ratios were carried out.Which are used to analyze the effects of the frequency,amplitude and duty cycle of the high-frequency pulsed current on the fusion hole status and weld appearance,and obtain the optimal pulse parameter window.High-frequency pulsed welding process experiments were carried out to analyze the effects of welding current,wire feed speed,welding speed and gap on the dynamic behavior of the fusion hole.The experimental results show that the change of fusion hole size is positively correlated with welding current,and negatively correlated with wire feeding speed and welding speed.The high-frequency pulsed welding process experiment under dynamic parameters was carried out,and it was found that compared with the welding current and welding speed,when the wire feeding speed took a step change,the fusion hole had a faster response speed,and the front and back weld were formed more uniformly before and after the step change.It is suitable to be a control variable for control experiments.According to the fusion hole image and weld appearance in the high-frequency pulsed welding experiment,combined with the image of weld cross section,it is found that there is a certain corresponding relationship between the penetration state of the weld and the fusion hole size.By adjusting the welding process parameters to control the size of the fusion hole,the penetration state of the weld can be controlled.In this paper,a fuzzy control system is established with the wire feeding speed as the control variable,and the size of the topside fusion hole size as the controlled variable.The fuzzy control experiment under the condition of variable gap is carried out.The control experimental results show that the weld is completely penetrated,the size of the fusion hole is controlled within a certain range,and a good weld appearance was obtained.