Thermal Mapping of Metal Casting Mold Using High-Resolution Distributed Fiber-Optic Sensors

Abstract

This article reports a technique to embed optical fiber into a copper mold plate for generating high-density thermal maps of the mold during the process of metal casting. The temperature measurements were based on acquiring and interpreting Rayleigh backscattering (RBS) signals from embedded fiber, using the interrogation technique of optical frequency domain reflectometry (OFDR). The instrumented mold plate was used to perform a cast-iron dip test and a steel dip test in a 200 lb induction furnace. The maximum temperatures recorded by the embedded fiber-optic sensors were 469 °C and 388 °C in the cast-iron and steel dip tests, respectively. The closely spaced and rapidly fluctuating temperature features that were imparted to the mold wall during solidification were successfully mapped with a high spatial resolution (0.65 mm) and a fast measurement rate (25 Hz) using a commercial OFDR interrogator (LUNA ODiSI 6108). Moreover, the thickness of the solidified steel shell was measured, and a thickness map of the shell was generated. A good correlation was observed between the thickness of the solidified shell and the temperature of the mold, as regions with higher and lower temperatures in the thermal profile of the mold corresponded to thicker and thinner areas on the shell, respectively. The dip testing experiments demonstrate that RBS-based fiber-optic sensing is a feasible and effective method for generating information-rich thermal maps of caster molds. The information obtained from thermal maps can be useful for improving the quality of the metal and productivity of the metal casting process.