Research For The Visual Sensing And Dynamic Behavior Of The Fusion Hole In TIG Thin Plate Welding

The fusion hole is a hole which ascribed to the sufficient melting of the welding groove by the arc in the one-side welding with back formation process.It locates at the front of the welding pool and is slightly larger than the gap.Existence of the fusion hole is beneficial for the liquid metal to transfer to the back of the weld to get beautiful and well-fused formation.The experienced welders attach great importance to the control of the fusion hole.By observing the fusion hole,adjusting the welding technique in real time and controlling the morphology of the fusion hole,good weld can be obtained.Lots of research works focused on the keyhole in the plasma arc welding and laser welding in the past few years.However,the understanding of the fusion hole existing in the one-side welding with back formation process is only on the experience level,and there is no systematic research on the key problems of its formation mechanism and dynamic behavior,etc.In this paper,a TIG welding experimental platform including the welding system and visual sensing system is established.The images of the butt welding process of Q235 low carbon steel plate with reserved gap are captured from the front of the welding pool.Through the analysis of the arc light spectrum of low carbon steel in TIG welding,a filter system composed of 610nm narrow band filter and neutral light reducer is designed,which effectively reduces the interference of the arc,and clear images of the fusion hole and gap are obtained.According to the image of the fusion hole and the gap,the gray features of different regions are analyzed.An image processing algorithm is developed on the Matlab platform based on the gray features of the edge area of the fusion hole and the gap.The edge is extracted by the combined detection operator algorithms,and then the edge lines are optimized by the gray morphology.Finally the continuous and complete edge of the fusion hole and the gap is obtained.The extraction algorithm of the width of the fusion hole and gap is also designed.A large number of TIG thin plate butt welding tests were carried out under different welding parameters.The mechanism and characteristics of the formation of the fusion hole and the behavior in the maintenance process are studied.The influence of different welding parameters on the fusion hole is researched,and the relationship between the morphology of the fusion hole and the penetration condition is analyzed.After the arc igniting,the metal of the butt plate is melted under the action of the arc heat,and the liquid metal is inclined downward to merge into a welding pool.The fusion hole is formed in the front of the welding pool.After forming,the fusion hole presents different growth rates at different stages and finally goes into the quasi steady state.Under the experimental conditions used in this paper,the welding parameter scoop to obtain the stable fusion hole is small.There will be different instability forms of the fusion hole in the welding process and it can be divided into longitudinal instability,lateral instability and gradual shrinking instability.The characteristics of each of them are studied.Welding current and welding speed are the main welding parameters affecting the fusion hole.The relationship between the welding current and the width of fusion hole presents nonlinear.Under relatively high welding speed,the width of the fusion hole is easier to keep stable.Study shows under different penetration conditions,the width of the fusion hole shows different regularity with time.The width difference between the fusion hole and the gap is more suitable for characterization of different penetration conditions including partial penetration,full penetration and burning through.The research on the behavior of the fusion hole lays the solid foundation for the intelligent control of the one-side welding with back formation technology.