Measurement of molten pool temperature distribution by UV thermal radiation

Summary

Accurate measurement of temperature is an increasingly important aspect of modern production processes. The radiation thermometer, requiring no physical contact with the object being measured, is available for such temperature measurement. It is reported, however, that the IR radiation thermometer has led to significant errors in molten pool temperature measurements where the emissivity is variable.

It is evident from Planck's law of radiation that the luminance temperature (measured by radiation thermometry) approaches the true temperature of an object when the measurement wavelength is shorter than IR. This paper describes an investigation of molten pool temperature measurement by UV thermal radiation. In the experiments, stainless steel (SUS304) and mild steel are melted by GTA (gas tungsten arc or TIG) or a laser beam, and the temperature distribution of the molten pool is measured with a UV sensor (CCD camera, image intensifier, and interference filter).

The results show that the melting point of metals can be measured with high accuracy with a UV sensor without any correction of emissivity. The maximum temperature in the molten pool melted by GTA is some 90–130 K higher than the melting point, but the maximum temperature in the molten pool melted with the laser beam is much higher than the melting point when the focal distance is shorter.