Abstract
A new real-time implementation of the Boltzmann-plot technique for optical spectroscopic analysis of thermal plasmas is presented. Applications are found in the monitoring of industrial processes in which plasma emission naturally occurs, such as arc and laser welding. Experimental results show the feasibility of using the Boltzmann-plot technique for real-time calculation of the electronic temperature of the plasma, a parameter that has been correlated with common defects found in the weld seam. The foundations of the proposed technique, its implementation, and its capability for the on-line detection of defects in tungsten inert gas (TIG) welding of steel parts are discussed.
Highlights
Quality assurance of the welding process is of major importance in some critical applications, such as those within the aerospace sector, in which extensive nondestructive testingNDTprocedures are routinely performed to every welded part
It is worth noting that some welding methods, like arc welding or laser welding in the so-called “keyhole” regime, exhibit an inherent plasma emission in the ultravioletUVand visible bands
By substituting the traditional solutions used for the spectral lines characterization, like the Levenberg-Marquardt technique, this approach allows the real-time calculation of the electronic temperature of the plasma Te using a single pair of spectral lines
Summary
Quality assurance of the welding process is of major importance in some critical applications, such as those within the aerospace sector, in which extensive nondestructive testingNDTprocedures are routinely performed to every welded part. These optical approaches to quality monitoring exhibit some advantages over electrical or acoustic methods, one of the most important being their immunity to the strong electromagnetic interferencesEMItypically found in these processes, especially if the light is collected far from the welding torch This is usually not a problem due to the high intensity from the thermal plasma, and setups with remote photodiodes[5] and optical fiber capturing[6] have been. In a previous work,[12] a real-time monitoring principle for the analysis of thermal plasmas was proposed With this technique, the central peak wavelength estimation and, the spectral line identification, was performed by using the lineal phase operatorLPOsubpixel technique.[13] By substituting the traditional solutions used for the spectral lines characterization, like the Levenberg-Marquardt technique, this approach allows the real-time calculation of the electronic temperature of the plasma Te using a single pair of spectral lines. The experimental results of tungsten inert gasTIGwelds performed on steel plates show that the proposed technique is able to detect, in real-time, common defects such as oxidation due to insufficient flux of shielding gas, or lackor excessof penetration of the weld seam
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