Development of Innovative Temperature Measurement Instrumentation for CNC Machining

Accurate temperature measurement in machining is essential for understanding tool wear, workpiece integrity, and process efficiency. However, traditional thermocouples suffer from thermal lag, sensitivity to positioning, and limited ability to capture rapid temperature fluctuations. These limitations hinder both experimental validation and numerical modelling. Fibre-optic infrared radiation thermometers FO IRTs offer a high-speed, non-contact alternative, improving measurement accuracy in machining environments.

This thesis presents the development and characterisation of two novel FO IRTs: a long-wave infrared (LWIR) sensor for near-ambient temperature measurements; and a mid-wave infrared (MWIR) sensor for high-speed, high-temperature tool-embedded sensing. The LWIR FO IRT outperformed thermocouples in drilling trials, revealing peak temperatures occurring earlier than predicted by numerical models. A comparison of the FO IRT measurements with an AMRC-developed model showed discrepancies of up to 58 % which possibly resulted from the peak temperatures resulting before the tool reached the sensor depth, emphasising the need for high-fidelity experimental data.

The MWIR FO IRT, with a 15 μs response time and a temperature range of 150 °C to 1200 °C, successfully captured rapid thermal cycling during intermittent machining, outperforming high-speed thermocouples rated with a rise time of 5 ms. Additionally, a novel methodology for determining cemented carbide emissivity was developed, improving infrared-based calibration accuracy by providing more temperature and wavelength dependant surface emissivity values. The experimental framework established in this work provides a robust methodology for integrating FO IRTs into machining environments.

Beyond machining, these techniques have broader applications in additive manufacturing, aerospace, and extreme thermal environments. By demonstrating FO IRTs as a viable alternative to conventional thermocouples, this research advances thermal sensing technologies, promoting more accurate and accessible temperature measurement solutions.