Study On Stainless Steel In CO₂Laser Welding Process And Plasma Behavior

As a21st century state-of-the-art manufacturing technology, the laser weldingwas widely used in shipbuilding, aerospace, automobiles, trains, manufacturing. Withthe progress of modern society, energy conservation and environmental protection arethe two main themes. So it is inevitable to put forward new requirements on productsafety and aesthetics of the subject. Laser welding is a new method developed inrecent years with the obvious advantage compared to the traditional joining method.But the adverse effects of plasma on the joints in CO₂laser welding process areinevitable. In this thesis, the electron temperature and conformation was plasma wasinvestigated in detail.During CO₂laser welding, a mass of blue light-colored plasma was observedabove the bath. The plasma will partially shield the incident laser energy, therebyreducing the energy coupling between laser and materials. In addition, the cyclicalfluctuations of the plasma will directly affect the stability of the laser welding process.Therefore, it is necessary to suppress the generation of laser induced plasma as far aspossible so as to achieve the favorable welding joint. This paper systematicallystudied the plasma electron temperature and morphology under the protection of inertgas. The tested material was selected as the2mm thick sheet of stainless steel with thelap welding. The protection gas was chosen the pure He of10L/min flow rate. Theresult indicates the good weld shape was obtained.In the experiment of inert gas controlling the plasma, synchronous high-speedcamera and spectrometer were used to observe the plasma temperature and shape.Using the Boltzmann diagram method, the plasma temperature is changed from thefocal volume to the "U" shape.High-speed camera is set to2000f/s. The extension line of the lens is parallel tothe weld plate surface. The result indicates that the size and height of the plasma ischanged with the defocus distance and the plasma temperature, showing the "U"shape.In view of the expensive price of inert gas, especially the pure He, this paperstudied in further the effect of external magnetic field on plasma shape. Along to thewelding direction, when the magnetic field is toward to the right, the plasma cross-sectional area and height are larger than that without magnetic field. And theupright "U" shape was observed. When the magnetic field is toward to left, the plasmacross-sectional area and height are smaller than that without the magnetic field.