The objective of this award is to embed micro- and nano-scale high temperature thermocouples and strain gauges in polycrystalline cubic boron nitride materials, and to provide thermomechanical sensing with unprecedented spatial and temporal resolution at and near the ceramic tool-work interface for manufacturing process studies. It will first focus on the design, fabrication, and embedding through diffusion bonding of thin film sensor arrays into polycrystalline cubic boron nitride. The performance of the embedded sensors will be characterized, and the interaction between the embedded sensors and ceramic inserts under simulated harsh conditions will be studied. Hard turning will be used as the vehicle for testing embedded thin film sensor arrays and for the measurement of temperature and stress distributions in ceramic cutting tools to advance the understanding of machining physics.
If successful, the embedded sensors will offer a capability of providing, for the first time, sets of simultaneous measurements over a finely spaced grid for mechanical and thermal distributions at the ceramic tool-chip interface. This will enable manufacturing engineers to better understand the processes, optimize ceramic tool design, and to effectively control the process. Advanced ceramic tooling with embedded thin film sensors will have significant implications on the national economy by markedly enhancing the competitiveness of US industries. Undergraduate and graduate students will be able to obtain hands-on experience in a range of advanced manufacturing concepts in addition to enhancements in related curricula. Interdisciplinary research will foster a new generation of engineers and scientists with broad and deep knowledge in the arena of thin film sensor and manufacturing technologies. Outreach science modules will be developed for high-school students. The program will also engage students from under-represented groups.
Collaborative Research: Embedding Thin Film Sensor Arrays in Advanced Ceramic Tools for Micro/Nano Scale Thermomechanical Measurements at and near the Tool-Workpiece Interface Prof. Xiaochun LI, University of Wisconsin – Madison Prof. Kornel EHMANN, Northwestern University Polycrystalline cubic boron nitride (PCBN) tool inserts are being used with increasing frequency in hard turning operations that are aimed at replacing finish grinding in many applications. Yet, the thermo-mechanical phenomena in the tool-workpiece contact zone that determine the life of the tool and the quality of the parts produced are not fully understood. The main hurdle is the unavailability of measurement methods that could, with high spatial and temporal resolution, ascertain the temperature and stress fields in the contact zone to verify the predictive models being formulated and to enable the development of novel process monitoring and control technologies. To address this problem, the scientific and technological foundation of a new sensing methodology that far exceeds current capabilities was developed. Temperature and stress sensing was realized by embedding micro-scale thin film thermo-mechanical sensors into the inserts only a few hundred micrometers away from the contact zone through diffusion bonding two polycrystalline cubic boron nitride plates, namely, the base plate with the sensors deposited through micro-fabrication techniques and the cover that is in contact with the workpiece. The processing methodology for both the sensor’s micro-fabrication and the diffusion bonding processes were developed. The necessary scientific and pragmatic advances for sensor embedding have included the study of the inter diffusion between the polycrystalline cubic boron nitride substrates and the deposited sensors, the influence of the sensor’s manufacturing conditions on their performance, and the static and dynamic sensor calibration methods. It was demonstrated that the sensors were capable of measuring the temperature distribution in the contact zone with unprecedented spatial resolution in a wide frequency range. It was possible, for the first time, to measure the three-dimensional temperature distribution with the aid of an array of ten sensors only about 75 microns from the rake and flank faces of the insert. The availability of such measuring capability was also instrumental in experimentally verifying a newly formulated thermo-mechanical model for the prediction of the temperature distribution in the contact zone. The outcomes of this research have lead to, as of yet, unavailable methods for the sensing of thermo-mechanical process variables. The availability of the unique embedded sensing technology will potentially result in a quantum leap in the fundamental understanding of the cutting mechanics and in innovative monitoring/control technologies. The ability of the sensors to provide real-time measurements of process variables from the vicinity of the tool insert-workpiece interface will allow the control and monitoring of optimal cutting conditions not only in hard turning but all material removal opertations. The developed methodology will also serve as a platform for the further migration/spillover of embedded micro-sensor technologies into various areas of advanced manufacturing.
