Experimental Analysis of Ductile Cutting Regime in Face Milling of Sintered Silicon Carbide
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-03-24 |
| Journal | Materials |
| Authors | Marvin Groeb, Lorenz HagelĂŒken, Johann Groeb, Wolfgang Ensinger |
| Institutions | Facility for Antiproton and Ion Research, Ăcole Polytechnique FĂ©dĂ©rale de Lausanne |
| Citations | 4 |
| Analysis | Full AI Review Included |
Experimental Analysis of Ductile Cutting Regime in Face Milling of Sintered Silicon Carbide
Section titled âExperimental Analysis of Ductile Cutting Regime in Face Milling of Sintered Silicon CarbideâExecutive Summary
Section titled âExecutive Summaryâ- High-Productivity Finishing: The study successfully achieved a ductile cutting regime in face milling of sintered SiC using a geometrically defined PCD cutting edge, offering a high-productivity alternative to traditional Single Point Diamond Turning (SPDT) or grinding.
- Critical Transition Depth: The brittle-to-ductile transition was confirmed to occur below a critical median chip thickness (Hm) of approximately 55 nm, validated through ramped scratch tests.
- Superior Surface Quality: The ductile cutting regime produced highly reflective surfaces with an areal surface roughness (Sa) between 0.1 and 0.2 ”m (below 100 nm in a competitive time frame), significantly improving the surface bearing parameter (Smr) below Hm = 80 nm.
- Minimal Sub-Surface Damage (SSD): Scanning Acoustic Microscopy (SAM) showed a drastically reduced amount of SSD in ductile-milled samples compared to brittle-milled or conventionally ground samples, confirming the effectiveness of the ductile removal mode.
- Material Integrity Maintained: Raman spectroscopy and Grazing Incidence X-ray Diffraction (GIXRD) confirmed that the SiC retained its original 6H crystallographic structure with no detectable amorphization, suggesting the high-pressure phase transformation is metastable and reverses upon decompression.
- Process Monitoring Potential: Acoustic Emission (AE) signals showed a strong correlation with the surface bearing parameter (Smr), indicating potential for in-process optimization and real-time detection of cutting regime changes or tool failure.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Type | Sintered 6H SiC | Polycrystalline | Composition: >97 weight % SiC |
| Material Hardness | 22 | GPa | Youngâs modulus: 400 GPa |
| Fracture Toughness | 3.00 | MPa m1/2 | Sintered SiC property |
| Machine Type | Kern Micro HD | CNC | High-precision, hydrostatic drives |
| Max Spindle Speed | 42,000 | min-1 | Fischer HSK 40 interface |
| Tooling Material | PCD | 2 mm diameter | Bull nose endmill (R 0.05 mm) |
| Axial Depth of Cut (DOC) | 0.1 | mm | Standard depth for experiment series 1-3 |
| Radial Engagement (WOC) | 0.1 | mm | Constant for experiment series 1-3 |
| Critical Chip Thickness (Hm) | 55 | nm | Brittle-to-Ductile Transition (Ramped Scratch Test) |
| Achieved Roughness (Sa) | 0.1 to 0.2 | ”m | Ductile Cutting Regime |
| Highest Cutting Speed Tested | 262.5 | m/min | Experiment Series 1 |
| SSD Detection Depth | 90 to 120 | ”m | SAM analysis depth |
| Raman TO Mode Position | 788.1 | cm-1 | Reference 6H-SiC |
| Raman LO Mode Position | 969.5 | cm-1 | Reference 6H-SiC |
| GIXRD Structure | 6H | Polytype | Confirmed in all milled samples |
Key Methodologies
Section titled âKey MethodologiesâThe experiments were conducted on a high-precision Kern Micro HD CNC machine, focusing on controlling the median chip thickness (Hm) and cutting speed.
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Machine and Tool Preparation:
- The machine utilized hydrostatic microgap drives and linear motors, achieving sub-micrometer positioning accuracy.
- A 2 mm PCD bull nose endmill was used for finishing operations.
- Thermal stability was ensured by a 300 s spindle warm-up and 10 min workpiece tempering with flood coolant (Oelheld SintoGrind TC-X 1500).
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Milling Experiment Series:
- Series 1 (Varying Cutting Speed): Feedrate was fixed at 150 mm/min, while cutting speed varied from 50.0 to 262.5 m/min. This inversely varied Hm from 281 nm down to 54 nm.
- Series 2 (Varying Feedrate): Cutting speed was fixed at 187.5 m/min, while feedrate varied from 45 to 403 mm/min. This varied Hm from 22 nm to 201 nm.
- Series 3 (Orthogonal Matrix): Explored the interaction between cutting speed (100 to 200 m/min) and Hm (67 nm to 268 nm).
- Fixed Parameters: Axial DOC (0.1 mm) and radial engagement (0.1 mm) were kept constant across the first three series.
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Brittle-to-Ductile Transition Determination:
- Scratch Test: The PCD tool was ramped into the SiC surface at a shallow angle (0.002°).
- Critical Depth Measurement: CLSM analysis of the resulting scratch marks determined the transition depth from brittle failure (granular tear-outs) to ductile material removal (smooth cut).
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Surface and Sub-Surface Characterization:
- Surface Topography: Confocal Laser Scanning Microscopy (CLSM) was used for quantitative measurement of ISO 25178 parameters (Sa, Sq, Smr).
- Qualitative Analysis: Scanning Electron Microscopy (SEM) was used to visualize surface morphology (brittle breakouts vs. smooth, inter-crystalline cuts).
- Sub-Surface Damage (SSD): Scanning Acoustic Microscopy (SAM) was performed at 80 kHz and 400 kHz to image defects below the surface layer, confirming minimal SSD in ductile-milled samples.
- Crystallographic Analysis: Raman Laser Spectroscopy (RLS) and Grazing Incidence X-ray Diffraction (GIXRD) were used to check for phase transformations, amorphization, and residual stress.
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In-Process Monitoring:
- Acoustic Emission (AE) signals were recorded during cutting and analyzed using FFT to derive the Power Spectral Density (PSD) sum, which showed a correlation with the surface bearing parameter (Smr).
Commercial Applications
Section titled âCommercial ApplicationsâThe successful achievement of a ductile cutting regime in SiC milling opens up high-productivity finishing options for several critical engineering sectors:
- Semiconductor and Electronics:
- High-precision machining of SiC wafers and components used in high-power electronics and microelectromechanical systems (MEMS), where surface integrity and minimal SSD are paramount.
- Aerospace and Optics:
- Fabrication of lightweight, high-stiffness SiC mirrors and optical components requiring nanometric surface finishes without the form errors associated with lapping or grinding.
- Medical and Chemical Engineering:
- Production of chemically inert and high-hardness SiC parts for demanding environments, such as chemical processing equipment or medical implants.
- Advanced Energy Systems:
- Machining of SiC components for next-generation fusion reactors, where low activation and high thermal stability are required.
- Manufacturing Optimization:
- Implementation of high-speed milling as a final finishing step, replacing slower, more costly ultra-precision processes like SPDT, thereby reducing overall manufacturing time and cost for brittle ceramic parts.
View Original Abstract
In this study, sintered silicon carbide is machined on a high-precision milling machine with a high-speed spindle, closed-loop linear drives and friction-free micro gap hydrostatics. A series of experiments was undertaken varying the relevant process parameters such as feedrate, cutting speed and chip thickness. For this, the milled surfaces are characterized in a process via an acoustic emission sensor. The milled surfaces were analyzed via confocal laser scanning microscopy and the ISO 25178 areal surface quality parameters such as Sa, Sq and Smr are determined. Moreover, scanning electron microscopy was used to qualitatively characterize the surfaces, but also to identify sub-surface damages such as grooves, breakouts and pitting. Raman laser spectroscopy is used to identify possible amorphization and changes to crystal structure. We used grazing incidence XRD to analyze the crystallographic structure and scanning acoustic microscopy to analyze sub-surface damages. A polycrystalline diamond tool was able to produce superior surfaces compared to diamond grinding with an areal surface roughness Sa of below 100 nm in a very competitive time frame. The finished surface exhibits a high gloss and reflectance. It can be seen that chip thickness and cutting speed have a major influence on the resulting surface quality. The undamaged surface in combination with a small median chip thickness is indicative of a ductile cutting regime.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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