Study On Image Acquisition System And The Temperature Field Of Plasma Arc

Flexible forming using plasma arc as a new processing technique without mould has very wide application prospect on large plates in multiple varieties and small-batch production. The quality of plasma arc affects forming quality and efficiency during the flexible forming process. So it appears to be particularly important to diagnose on thermodynamic parameters of the plasma arc.The technology of spectroscopic diagnosis is used in this paper. Experimental setup of plasma arc image acquisition is designed and established. The device is composed of generating system of plasma arc, the optical system, and the control and display system three components. Comparative analysis on the acquisition image of plasma arc in the different work parameters is made.The digital images of plasma arc are made pretreatment such as removal of background noise, filter processing and morphological features enhanced by using MATLAB. A new linear intersection point method is proposed to determine plasma arc column edge, and use the line corresponding the center of two edges of plasma arc as symmetry axis. Transform observed radiances into radial distribution of emission coefficients for plasma arc by using the least square fitting method to solve the Abel's inversion.Measurements of plasma arc by spectroscopic technique using assumptions of local thermodynamic equilibrium (LTE), cylindrical symmetry and optically thin. The relationship between spatial emission coefficient of arc column and temperature is obtained by calculating the particle density and partition function within plasma arc based on Saha's equation. The radial temperature field distribution of plasma arc is obtained by using Off-axis Peak Intensity Method. Furthermore, axial cross-section temperature field distribution of arc column is obtained.Results show that plasma arc can be captured by the acquisition system successfully, the design of the system is reasonable, performance is credible, and the system has good application prospect. With the application of the digital processing technique, the improvement of image quality is achieved successfully. Image with clear edge and good contrast is achieved, and gray-scale value extraction is made for next step. According to the method of Off-axis Peak Intensity Method, the 150th radial temperature distribution of the image of the plasma arc is calculated, then 17 groups of data covering the arc column selected by non-equidistant is calculated, and axial cross-section temperature distribution is finally obtained.This paper has a certain guiding significance to experimentally obtain 2D and 3D temperature distribution of plasma arc, a theoretical basis is provided to parameters controlling of flexible forming using plasma arc, as well as lays a good foundation on further solving the actual heat source model.