A Experimental Investigation On Optical Plasma Temperature Measurement During Deep Penetration Laser Welding

The deep penetration Laser welding is the base of extensive utilization for the high-laser welding of metal materials. And the keyhole is characteristics of deep penetration laser welding. The plasma of the high density always exists above work piece and in the keyhole, so that the interaction relation between plasma and laser energy is one of important studies of the laser and material interaction mechanism.The plasma temperature is the most important one in plasma parameters while others can always be described by the function of plasma temperature under certain condition. Then the author launches the research about simulated experimentation result for the plasma temperature. The former workers mainly concentrated on the measurement of density and temperature of plasma outside the keyhole because of the limits of experimentation methods, but thought less about the parameter of the plasma inside the keyhole. A new experimental method and the instrument made by oneself is utilized to investigate the temperature inside the keyhole in this thesis for the first time. So this is decided the studies.Firstly, designing the experimentation scheme. It is determined to adopt simulation experimentation to study the plasma temperature inside the keyhole on the base of studying the achievement at home and abroad. The author draws the thought of sandwich", that is grasping the aluminum film of certain thickness between two pieces of transparent glasses. GG 17 Glass was used to grasp aluminum film that is only 0.2 mm. For the sake of not interfering with the plasma physics field, the relative spectral analysis was used to calculate the temperature. The spectral line of A1II was chosen.Secondly, Optical Multi-channel Analyzer system is designed and developed by oneself and the corresponding software is programmed on the basis of hardware. Then Opticak Multi-channel Analyzer is a kind of main tool for the temperature measurement. A lot of present products have already been presented, but most of them can only do measurement for the stable light sources. The responding time to the dynamic motion is relatively slow. In earlier stage of the thesis, the author concentrate on Optical Multi-channel Analyzer design for experimental request mainly. This optical instrument is so accurate that its resolution ration comes to nm level. So, it is satisfied with the experimentation request basically.At last, it is well studied that the relation between the technical parameters and temperature by the relative spectrum method .The plasma temperature over the stainless steel work piece is from 7000K to 8000K.At the same times, the relation of the plasma temperature and the technical parameter is also investigated .The plasma spectrum of aluminum work piece inside the keyhole is observed firstly and the temperature is computed. The results show that the plasma temperature is over 20000K under the specified conditions of the thesis. In addition that the relation in different process conditions and quality of weld such as weld breadth and weld depth is also analyzed.The author utilizes the digital camera of high speed to shot the dynamic course of the deep penetration weld, and analyzed the links between plasma density and the keyhole dynamics. Additionally malting use of the knowledge optics and the spectral device to measure the scale of the plasma .The experimental result shows that the plasma scale is 1-3mm.