Temperature measurement of the tool-chip interface for cemented carbide tools using thin-film thermocouples in cutting of glass fiber-reinforced plastic

Abstract

Thin Film Thermocouples (TFTCs) show promising applications in the field of cutting temperature measurement due to their miniature size and ease of integration with the tools. However, the harsh environment at the tool-chip contact interface inevitably causes wear of the hot junction. Depositing a wear-resistant hard coating on the surface of the TFTCs is an effective way to improve their service lifespan. Nevertheless, the protective layer hinders heat transfer to the TFTCs. The influence of the hot junction wear on its temperature measurement performance cannot be overlooked. These factors collectively compromise the reliability of temperature measurement results obtained by TFTCs. The objective of this study is to directly fabricate the NiSi-NiCr TFTCs on commercial cemented carbide tools to measure the cutting temperature of glass fiber-reinforced plastic (GFRP). The hot junctions are fabricated at the tooltip using a customized mask, electrically isolated by the SiNx coating, and prepared with a top coating of TiAlN for protection. A steady-state heat conduction model is established to determine the temperature distribution along the coating thickness direction. The calculated results indicate that the TiAlN coatings with a thickness of 2 μm can produce a temperature reduction of up to 4 %. The cutting experiments indicate that the wear area of the TFTCs increases with both cutting speed and cutting length. The accelerated wear of the hot junction results in a significant attenuation of the temperature signal from the TFTCs.