Micromachining of polycrystalline CVD diamond-coated cutting tool with femtosecond laser
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | Journal of Advanced Mechanical Design Systems and Manufacturing |
| Authors | Xiaoxu Liu, Kohei Natsume, Satoru Maegawa, Fumihiro ITOIGAWA |
| Institutions | Nagoya Institute of Technology |
| Citations | 14 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research successfully implemented femtosecond (fs) laser Pulse Laser Grinding (PLG) to sharpen polycrystalline Chemical Vapor Deposit (CVD) diamond-coated cutting tools, mitigating the thermal damage associated with conventional nanosecond (ns) laser processing.
- Core Value Proposition: fs-PLG achieves a high-quality, sharp tool edge while effectively suppressing negative microstructural changes (graphitization) caused by thermal impact.
- Edge Sharpening: The tool edge roundness was successfully reduced from 20 ”m (as-deposited) to approximately 1 ”m radius of curvature, comparable to ns laser results.
- Microstructure Integrity: Raman spectroscopy confirmed that fs-PLG processing resulted in almost no negative change to the diamond crystal quality, unlike ns-PLG which showed tendencies toward graphitization (G band increase).
- Optimal Processing Conditions: The most suitable fs-PLG parameters identified were 7 W laser power, 60 mm/s scanning speed, and a 20° processing angle.
- Surface Quality: Under optimal conditions, fs-PLG reduced the surface roughness (Ra) by half compared to the as-deposited surface, achieving 0.045 ”m.
- Energy Efficiency Trade-off: Despite requiring a higher total input energy (approximately 2.5 times higher at 20° angle) than ns-PLG, the fs laserâs âcoldâ ablation mechanism ensures superior material quality preservation.
- Future Direction: Further improvements in efficiency and smoothness are suggested by using an fs laser in the ultraviolet range (higher absorption rate) with a lower repetition rate.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Tool Material | Polycrystalline CVD Diamond | Coating Thickness: 20 ”m | Coated on cemented carbide (CVDD tool) |
| Initial Edge Roundness | 20 | ”m | Before PLG processing |
| Final Edge Roundness (fs-PLG) | ~1 | ”m | Achieved under optimal conditions |
| Optimal fs Laser Power | 7 | W | Specimen No. 1 |
| Optimal fs Scanning Speed | 60 | mm/s | Specimen No. 1 |
| Optimal fs Processing Angle (Ξ) | 20 | ° | Achieved processing removal of ~10° |
| fs Pulse Width | 700 | fs | Ultra-short pulse fiber-based laser |
| fs Wavelength | 1045 | nm | Infrared range |
| fs Repetition Rate | 100 | kHz | High repetition rate |
| fs Focused Spot Diameter | ~50 | ”m | - |
| fs Pulse Fluence | 3.6 | J/cm2 | Per pulse |
| fs Input Energy Fluence (One-way scan) | 297.2 | J/cm2 | - |
| ns Comparison Pulse Width | 7 | ns | Nd:YAG laser |
| ns Comparison Wavelength | 355 | nm | Ultraviolet range |
| ns Pulse Fluence | 40.8 | J/cm2 | Per pulse |
| Final Roughness (fs-PLG, Ra) | 0.045 | ”m | Optimal fs condition |
| Final Roughness (ns-PLG, Ra) | 0.024 | ”m | Nanosecond comparison condition |
| Raman Diamond Peak | 1330 | cm-1 | As-deposited CVD diamond |
| Raman G Band Peak | 1560 | cm-1 | Related to sp2 bond stretching mode |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized Pulse Laser Grinding (PLG), a non-contact processing method, to shape the CVD diamond tool edge.
- Laser Setup: An ultra-short pulse fiber-based femtosecond laser (700 fs pulse width, 1045 nm wavelength, 100 kHz repetition rate) was focused using a lens (100 mm focal length) to create a focused spot diameter of approximately 50 ”m.
- PLG Kinematics: The focused laser beam repeatedly scanned the tool edge at a small processing angle (Ξ) to gradually grind the diamond coating via ablation.
- Scanning Recipe:
- The number of scans was fixed at 30 (reciprocating).
- The tool was fed horizontally towards the laser beam in steps.
- The feed step was 2 ”m, repeated 5 times.
- Optimal fs Condition (Specimen No. 1): Processing was conducted at 7 W power, 60 mm/s scanning speed, and a 20° processing angle.
- Nanosecond Comparison (Specimen No. 6): Conventional PLG used a Nd:YAG nanosecond laser (7 ns pulse width, 355 nm wavelength, 3 W power, 30 mm/s speed, 4.5° angle) to achieve a smooth surface for benchmarking.
- Geometric Evaluation: Edge sharpness and straightness were evaluated using Scanning Electron Microscopy (SEM). Processed angle (Ξ) and roughness (Ra) were measured using laser microscopy.
- Microstructural Evaluation: Raman spectroscopy (532 nm exciting wavelength) was used to detect changes in the processed surface, specifically monitoring the G band (sp2 amorphous carbon/graphitization) and the diamond peak (crystallinity).
Commercial Applications
Section titled âCommercial ApplicationsâThe successful application of fs-PLG for sharpening CVD diamond tools opens avenues for manufacturing high-performance cutting inserts used in demanding industrial environments.
- High-Performance Machining: Manufacturing ultra-sharp CVD diamond micro-tools for high-precision turning and milling of extremely hard materials (e.g., hardened steel, ceramics, composites) where edge integrity is paramount.
- Tool Life Enhancement: Utilizing the positive surface modification effect (improved crystallinity/hardness) observed under certain low-fluence fs-PLG conditions to create tools with superior wear resistance compared to thermally damaged ns-PLG tools.
- Micro-Tool Fabrication: Producing micro-tools with edge radii approaching 1 ”m, suitable for micro-milling applications requiring nanometric surface roughness on components like polymethyl methacrylate (PMMA).
- Athermal Processing: Applying fs laser ablation techniques to other thermally sensitive hard materials (e.g., DLC, PCBN) where suppressing graphitization or phase change is critical for maintaining mechanical properties.
- Grinding-Less Manufacturing: Integrating fs-PLG into automated production lines to achieve final tool geometry and surface quality without requiring subsequent, costly, and inefficient mechanical grinding steps.
View Original Abstract
To enhance the cutting performance of chemical vapor deposit (CVD) diamond-coated tool, a short pulse laser grinding technique is applied. However, the thermal impact of a nanosecond laser damages the diamond crystallinity of the processed surface. To reduce this thermal impact, a femtosecond laser is innovatively used in this study to conduct the pulse laser grinding (PLG) of a CVD diamond-coated cutting tool, to achieve a sharpened tool edge with high quality. Furthermore, the CVD diamond tool edges processed by femtosecond and nanosecond lasers are compared based on sharpness, smoothness, and microstructure changes. The results show that a sufficient laser fluence higher than the threshold and a reduction in the pulse overlapping rate of the laser fluence of the femtosecond laser PLG could ensure a better tool edge shaping. A laser power of 7 W, processing angle of 20°, and scanning speed of 60 mm/s with roughness reduced to approximately half, are the suitable processing conditions of the femtosecond laser. From the observation of a scanning electron microscope, the tool edge processed by femtosecond laser PLG has a relatively sharp edge, with a radius of curvature around 1 Όm, similar to that of a nanosecond laser. The further magnified images reveal a distinct processed surface characteristic. The nanosecond laser-processed surface has obvious longitudinal machining marks while that of the femtosecond laser has ablated debris. Moreover, the surface microstructure change of CVD diamond by femtosecond and nanosecond laser PLG are compared using Raman spectroscopy, further confirming that femtosecond laser could successfully suppress unfavorable structural effects in CVD diamond. Based on the results, femtosecond laser has a great potential for processing higher-quality CVD diamond tool edges.