激光焊接等离子体高速摄影图象处理及其特性研究

【作者】 王义敏；

【导师】 刘金合；

【作者基本信息】 西北工业大学 ， 材料加工工程， 2002， 硕士

【摘要】 在大功率激光焊接中，被焊材料受到高能激光束的作用，在几毫秒的时间内就会发生熔化、气化，并与保护气体一起发生电离，在熔池上方迅速形成等离子体云。等离子体云对入射激光有吸收、反射、散射等负面效应；由于等离子体云是折射率比真空还小的光疏物质，当激光穿过等离子体云后，激光束将变得发散，降低激光束的聚焦性。可见，激光焊接过程中产生的等离子体对激光焊接过程、焊接质量以及对激光能量的利用率有非常大的影响，是一个不可忽视的现象。 本研究运用数字图像处理技术，对单方向拍摄的激光焊接等离子体的高速摄影照片进行了处理。等离子体图象由外向里依次为三个区：外缘区、平滑区和核心区；对图象中的灰度分布进行了讨论，建立了图象的等灰度线图、灰度分布立体图、灰度直方图；图象平面的灰度呈现出类高斯分布的特征；等离子体对激光束的折射率呈统计有序性；可以利用激光焊接熔池的温度间接确定等离子体的温度；激光焊接等离子体可以模化为n层、不同厚度、不同折射率层的夹心空间几何体。对两种理想的等离子体模型(三同心球体和变焦距椭球体)进行了分析，建立了不同剖面的密度分布层析图，给出了激光束穿越球形等离子体时由于折射引起的对光轴的偏移距离的公式。更多还原

【Abstract】 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.更多还原