Conclusion
A GTA welding process is schematically drawn in a right figure. Quite large differences of temperature among the cathode, arc plasma and the base metal region are the most important matter to understand GTAW process. And the space is normally less than 20mm cubic. A quality of the weld metal is the most important matter for construction and using of welded structures. So many person have focused the behavior of liquid metal and resolidification.
The actual physical and chemical processes acting in the cathode are sometimes ignored.I had taken many high-speed video of welding processes. However, almost all videos are not open for public, they are used only for my own pastime. It is a bad situation for many welding videos and person who wants to watch welding processes. That is the reason why I am going to open my videos into UTUBE. 2016TWR pushed my back.
Erosion process of tungsten electrodes is focused this time. I also have many SEM pictures of electrodes. But my server capacity reaches almost the upper limit to show many AEM pictures.
Concluding remarks of my presentation for 2016TWR are as follows.
Cleaning action occurs every kind of cathode material in arc ignition stage, especially debris remained electrode by former welding. When the cathode exposed in air, cleaning action occurs only on the top of cathode, because the temperature at the top increases quite short by oxidation reaction, and metal ion produces enough current path.
Plasma contains much metal elements in plasma at early ignition stage, and transient gas excitation is different from stable condition. Much reaction occurs on hot cathode surface metal atoms and ions.
Acknowledgments
The author thanks for high-speed video companies NAC and Photron for preparing excellent high-speed cameras.
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