Laser Welding Plasma High-speed Photographic Image Processing And Its Characteristics

During high power laser beam welding, within a few milliseconds , the surface of the work-piece is melted and gasified , which is quickly ionized and form plasma with the shielding gas above the melted zone. The plasma has bad effects, such as : the absorption , the reflection , the scatter etc , on the laser beam ; while the laser beam goes through the plasma , which refractive index is lower than vacuum's, the laser beam is scattered and defocused . So the plasma has great effects on the laser beam welding process , the welding quality and the efficiency of the laser beam energy .which can not be ignored during the laser beam welding .In the paper , the digital image processing (DIP) technology are introduced to deal with the one-direction (two-dimensions) high speed photograph of laser beam welding plasma. From its out to core, the plasma image is divided into three zones : fringe zone , smoothing zone and core zone. the image gray scattergrams , the equal gray diagram and the gray histograms are presented .The characteristic of plasma gray 2D-distribution is like-Gausse . The plasma refraction index is statistically erdered distribution . Using the equal gray diagram and the laser welding melt-zone temperature , the plasma temperature can be indirectly determined . The laser plasma can be regarded as 3-D solid body which has different layers, different thickness and different refraction index . Using two perfect plasma models(concentric sphere and variable focus ellipsoid), which have different shape and different gray distribution, the different cross-section tomograph figure and the gray density diagram are presented . The offset distance formula , which describes the laser beam penetrates through the laser welding plasma, is presented.