Measurement of Tool Internal Temperatures in the Tool-Chip Contact Region by Embedded Thin Film Micro Thermocouples

Abstract

Monitoring and controlling thermomechanical parameters in tooling materials are imperative for improving the fundamental understanding, reliability and workpiece quality of material removal processes. Polycrystalline boron nitride (PCBN) tools are being used heavily in hard machining/turning. These processes are very sensitive to variation in local machining conditions at tool-workpiece interface and lack a thorough understanding of fundamental thermo-mechanical phenomena, both often leading to abrupt tool failures. Existing sensors to monitor the machining conditions are not suitable for robust process control as they are either destructively embedded and/or don’t possess the necessary spatial and temporal resolution to monitor temperature during machining at the cutting tip/edge effectively. This paper presents an emerging approach for assessing dynamic temperatures in the close vicinity of the tool cutting edge. An array of 10 micro thin film micro thermocouples, fabricated using adapted semiconductor microfabrication methods, has been embedded into PCBN using a modified diffusion bonding technique. Scanning electron microscopy was performed to examine material interactions at the bonding interface and determine optimal bonding parameters. The sensors’ performance is statically and dynamically characterized. They show good linearity, sensitivity and very fast response time.