Precision Core Temperature Measurement of Metals for Use in Manufacturing Applications

Core temperature variation in metals during manufacturing processes affects both the dimensional accuracy and the surface integrity of manufactured workpieces. Different types of temperature measurement techniques have been applied for obtaining workpiece temperature. However, their main limitations have been an inability to give the core temperature of the workpiece and the reduction in accuracy due to the harsh environment of some manufacturing processes. The velocity of sound in any medium of propagation is dependent on the temperature of that medium. This relationship can be used to obtain a medium’s temperature, provided that the velocity of sound through the medium can be measured. This paper investigates the use of ultrasonic waves sent in the continuous mode to measure the temperature variation in a 100 mm steel sample (type EN24T) using the ultrasonic phase-shift method. Simulations and bench tests were performed to obtain a resolution and accuracy better than 0.5 °C and ±1 °C respectively. The results show that the method gives reliable results well within the target specification. Based on these results, ultrasonic thermometry experiments will be carried out during subtractive machining processes to determine the effects of the harsh environment on the accuracy of the proposed method.