Optical Spectral Radiometric/Laser Reflectance Method For Noninvasive Measurement Of Weld Pool Surface Temperatures

A unique experimental method has been developed for measuring weld pool surface temperatures. An equation for determining temperature was developed based on Planck's blackbody spectral distribution of emissive power, the definition of spectral directional emissivity, Lambert's cosine law for diffuse emitters, and Kirchhoff's law for spectral directional reflectivity. The necessary measurements are the spectral directional emissive power and the spectral directional emissivity of the weld pool surface. Detailed pool surface temperature measurements were made of gas tungsten arc (GTA) welding of 1.5mm thick stainless steel (SS) 304 plates using an argon cover gas. Because argon plasma arc spectroscopy measurements over molten SS 304 revealed insufficient emission gaps, the spectral emissive power was measured by high speed film radiometry as the arc was shut off so as to obtain information at the instant the obscuring arc emissions disappear. Similar measurements were made of the spectral directional reflectivity (and thus the spectral directional emissivity) by reflecting a focused laser beam off the weld pool. Detailed weld pool surface temperature maps were generated.