Boron Doped Diamond for Real-Time Wireless Cutting Temperature Monitoring of Diamond Coated Carbide Tools
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-11-30 |
| Journal | Materials |
| Authors | SĂ©rgio Pratas, Eduardo L. Silva, M.A. Neto, C.M. Fernandes, A.J.S. Fernandes |
| Institutions | University of Aveiro |
| Citations | 12 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study successfully demonstrated the feasibility of using Boron-Doped Diamond (BDD) thin films as integrated Negative Temperature Coefficient (NTC) thermistors for real-time, wireless monitoring of cutting temperatures in carbide tools.
- Integrated Sensing Solution: A one-step approach was developed where the BDD coating simultaneously provides enhanced wear resistance, heat dissipation, and integrated thermal sensing, aligning with Industry 4.0 concepts.
- High Thermal Sensitivity: The BDD thermistors exhibited high sensitivity, quantified by a beta (ÎČ) parameter reaching 3500 K in the critical machining temperature range of 250-400 °C.
- Wireless Data Transmission: Temperature-dependent resistance variation was wirelessly transmitted using a âLi-Fiâ (LED-to-LED) communication system from the rotating tool holder to a fixed receiver.
- Fast Response Time: The BDD sensor response closely matched that of an IR thermographic camera, showing a rapid response with an average delay of only ~1 second.
- High Output Resolution: Calibration during face milling of Inconel 718 demonstrated a high sensitivity of 0.84 mV/°C variation registered at the photodiode receiver.
- Material Robustness: The use of CVD diamond ensures high chemical inertness, thermal conductivity, and mechanical robustness, making the sensor ideal for harsh machining environments.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Tool Substrate Material | WC-7Co | N/A | Cemented tungsten carbide (0.5 ”m grain size, 7 wt.% Co). |
| Undoped Coating Architecture | Multilayer (9 layers) | N/A | Intercalated Nanocrystalline (NCD) and Submicrocrystalline (SMCD) diamond. |
| BDD Thermistor Substrate | Si3N4 | N/A | Insulating substrate for BDD film. |
| BDD Doping Concentration | ~1014 | cm-3 | Estimated boron concentration in the BDD film. |
| BDD Room Temperature Resistance | ~600 | kΩ | Measured at 25 °C. |
| BDD High Temperature Resistance | ~10 | kΩ | Measured at 400 °C. |
| Highest Sensitivity (Beta, ÎČ) | 3500 | K | Temperature range 250-400 °C (highest sensitivity regime). |
| Lowest Sensitivity (Beta, ÎČ) | 1220 | K | Temperature range 50-150 °C. |
| Wireless Communication Sensitivity | 0.84 | mV/°C | Voltage variation measured at the photodiode receiver. |
| Sensor Response Delay | ~1 | s | Compared to IR thermographic camera response time. |
| Maximum Spindle Speed (Li-Fi Limit) | 4000 | rpm | Limit before signal transmission disruption due to LED fading. |
| Workpiece Material Tested | Inconel 718 | N/A | Tested during face milling operation. |
| Cutting Speed (Vc) | 5.48 | m/min | Machining condition used for testing. |
| Spindle Speed (n) | 30,000 | rpm | Machining condition used for testing. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on Hot Filament Chemical Vapor Deposition (HFCVD) for diamond growth and a custom Li-Fi system for wireless data transmission.
- Carbide Tool Pretreatment:
- Roughening: 15 min treatment with Murakami reagent (10 g KOH + 10 g K3Fe(CN)6 + 100 mL water).
- Cobalt Etching: 3 s immersion in H2SO4:H2O2 (1:14 ratio).
- Seeding: Tools were seeded with diamond powder prior to coating.
- Undoped Multilayer Diamond Coating (HFCVD):
- A 9-layer structure of Nanocrystalline Diamond (NCD) and Submicrocrystalline Diamond (SMCD) was deposited on the WC-Co tool for enhanced adhesion and stress relaxation.
- Growth Parameters: H2 (200 mL/min), CH4 (4-8 mL/min), Tfilament (2250-2300 °C), Tsubstrate (800-850 °C), Pressure (10-15 kPa).
- BDD Thermistor Fabrication (HFCVD):
- A Microcrystalline Diamond (MCD) morphology BDD film was grown on a Si3N4 substrate for the thermistor.
- Doping: Argon carrier gas (5 mL/min) bubbled through a B2O3/ethanol solution (B/C ratio 10,000 ppm).
- Growth Parameters: H2 (100 mL/min), CH4 (4 mL/min), Tfilament (2300 °C), Tsubstrate (700 °C), Pressure (75 kPa).
- Ohmic Contact Formation:
- Tungsten carbide (WC) ohmic contacts were formed by vaporizing tungsten oxide (WO2) from the hot filaments at 1800 °C, followed by reduction using H2 and CH4.
- Wireless Monitoring Setup (Li-Fi):
- The BDD thermistor and a high-brightness LED emitter circuit (powered by 3V) were housed in a 3D-printed adapter coupled to the rotating tool holder.
- The LED brightness varied according to the BDD resistance (temperature).
- A fixed photodiode receiver, coupled to the CNC body, received the optical signal, converting the resistance variation into a voltage reading.
- Simultaneous Temperature Measurement:
- Testing involved face milling Inconel 718.
- Temperature was monitored simultaneously by the BDD thermistor and an IR thermographic camera (FLIR Systems, 30 cm distance) for calibration and validation.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides a robust, integrated sensing solution critical for optimizing high-value manufacturing processes.
- Aerospace and Energy Machining: Real-time thermal monitoring during the milling of superalloys (like Inconel 718) and other difficult-to-machine materials where precise temperature control is essential to prevent thermal damage and rapid tool wear.
- Smart Tooling and Industry 4.0 Integration: Enables the development of âsmart toolsâ that self-monitor their condition, allowing for predictive maintenance, automated process adjustment, and minimization of manufacturing downtime.
- High-Speed and Dry Machining: The BDD coating improves heat dissipation and wear resistance while providing thermal feedback, supporting higher cutting speeds and reduced reliance on costly and environmentally harmful cutting fluids.
- Harsh Environment Sensing: BDDâs inherent properties (chemical inertness, high thermal conductivity, mechanical hardness) make these thermistors suitable for temperature measurement in aggressive chemical or high-pressure industrial processes beyond machining.
- Integrated Sensor Fabrication: The methodology allows for the direct inclusion of sensing elements within the protective coating layer, simplifying tool design and improving sensor proximity to the heat source (the cutting interface).
View Original Abstract
Among the unique opportunities and developments that are currently being triggered by the fourth industrial revolution, developments in cutting tools have been following the trend of an ever more holistic control of manufacturing processes. Sustainable manufacturing is at the forefront of tools development, encompassing environmental, economic, and technological goals. The integrated use of sensors, data processing, and smart algorithms for fast optimization or real time adjustment of cutting processes can lead to a significant impact on productivity and energy uptake, as well as less usage of cutting fluids. Diamond is the material of choice for machining of non-ferrous alloys, composites, and ultrahard materials. While the extreme hardness, thermal conductivity, and wear resistance of CVD diamond coatings are well-known, these also exhibit highly auspicious sensing properties through doping with boron and other elements. The present study focuses on the thermal response of boron-doped diamond (BDD) coatings. BDD coatings have been shown to have a negative temperature coefficient (NTC). Several approaches have been adopted for monitoring cutting temperature, including thin film thermocouples and infrared thermography. Although these are good solutions, they can be costly and become impractical for certain finishing cutting operations, tool geometries such as rotary tools, as well as during material removal in intricate spaces. In the scope of this study, diamond/WC-Co substrates were coated with BDD by hot filament chemical vapor deposition (HFCVD). Scanning electron microscopy, Raman spectroscopy, and the van der Pauw method were used for morphological, structural, and electrical characterization, respectively. The thermal response of the thin diamond thermistors was characterized in the temperature interval of 20-400 °C. Compared to state-of-the-art temperature monitoring solutions, this is a one-step approach that improves the wear properties and heat dissipation of carbide tools while providing real-time and in-situ temperature monitoring.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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