Effect of Abrasive Grain Concession on Micromechanical Behavior of Lapping Sapphire by FAP
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-08-16 |
| Journal | Micromachines |
| Authors | Huimin Xu, Jianbin Wang, Yiliang Xu, Qingâan Li, Benchi Jiang |
| Institutions | Anhui Polytechnic University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the micromechanical behavior of single-crystal sapphire lapping using Fixed Abrasive Pads (FAP), focusing on the effect of diamond abrasive grain concession (elastic retreat) within the soft matrix.
- Core Mechanism Modeled: A theoretical model was developed to analyze the elastic retreat ($\delta\rho$) of diamond abrasive grains in the FAP matrix under normal force, demonstrating that concession reduces the effective cutting depth, promoting ductile-mode material removal.
- MD Simulation Results (Micro-Scale): Increasing the abrasive particle radius from 8 A to 12 A significantly increased the peak micro-cutting force (reaching up to 4000 nN) and the steady-state temperature in the Newtonian zone (up to 380 K). Larger particles resulted in a more stable energy system during cutting.
- Material Removal Rate (MRR): Experimental results showed that MRR increased nonlinearly with the increase in diamond abrasive particle size (15 ”m to 65 ”m).
- Surface Quality (Ra): Surface roughness (Ra) increased approximately linearly with abrasive particle size, confirming that larger grains cause deeper residual cutting marks and greater subsurface damage.
- Model Validation: Experimental trends for both MRR and Ra were consistent with theoretical predictions, confirming the feasibility of the theoretical model for selecting optimal lapping process parameters.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Wafer Dimensions (MD) | 90 x 30 x 40 | A | Molecular Dynamics simulation box size |
| Number of Wafer Atoms (MD) | 22,004 | atoms | Single-crystal sapphire (c-plane) |
| Cutting Speed (MD) | 150 | m/s | Simulation velocity |
| Initial Temperature (MD) | 300 | K | Constant temperature zone |
| Time Step (MD) | 1 | fs | Simulation resolution |
| Abrasive Radius (MD) | 8, 10, 12 | A | Diamond grain sizes simulated |
| Cutting Depth (MD) | 5 | A | Fixed micro-cutting depth |
| Peak Micro-Cutting Force (MD) | ~4000 | nN | Observed at 12 A radius (transient state) |
| Steady-State Cutting Force (MD) | 700 to 1250 | nN | Increasing trend with particle size (8 A to 12 A) |
| Max Newtonian Zone Temp (MD) | 380 | K | Observed at 12 A radius |
| Experimental Abrasive Size (FAP) | 15, 25, 35, 45, 55, 65 | ”m | Diamond particle sizes used in FAP |
| Table Rotation Speed (Exp) | 80 | rpm | Grinding parameter |
| Pressure (Exp) | 34.5 | kPa | Grinding parameter |
| Max MRR (Exp) | ~1800 | nm/min | Observed at 65 ”m particle size |
Key Methodologies
Section titled âKey Methodologiesâ- Theoretical Modeling of Concession: Developed a mechanical model to analyze the plastic intrusion of diamond abrasive grains into the sapphire and the elastic retreat ($\delta\rho$) characteristics of the soft FAP matrix, linking normal force (F), particle diameter (D), and matrix elastic modulus (E*) to the effective cutting depth.
- Molecular Dynamics (MD) Simulation:
- Software/Potential: LAMMPS was used with the Matsui potential function, which accurately models the lattice structure and energy of a-Al2O3.
- Workpiece Setup: Single-crystal sapphire (c-plane, 0001 orientation) was modeled, partitioned into Boundary, Constant Temperature (300 K), and Newtonian (processing) zones.
- Tool Setup: A rigid hemispherical diamond abrasive grain was used, simulating micro-cutting at a fixed depth of 5 A and a velocity of 150 m/s.
- Experimental Grinding:
- Material: c-direction (0001) single crystal sapphire slices (50.8 mm diameter).
- Equipment: Intelligent nano-polishing machine system (Nanopoli-100).
- FAP Variation: Hydrophilic fixed abrasive pads containing diamond particles of six different sizes (15 ”m to 65 ”m) were tested.
- Process Control: Grinding parameters were held constant: 80 rpm table speed, 34.5 kPa pressure, and 40 minutes grinding time.
- Characterization: Material Removal Rate (MRR) was calculated based on mass loss. Surface roughness (Ra) and topography were measured using a Nano Map500LS 5.
Commercial Applications
Section titled âCommercial Applicationsâ- LED and Power Electronics Substrates: Sapphire is the primary substrate for GaN-based LEDs and high-power RF devices. Controlling abrasive concession is vital for achieving the ultra-low subsurface damage required for high-yield epitaxy.
- Precision Optics and Windows: Used in aerospace, defense, and high-power laser systems, sapphire optics require extremely high surface quality (low Ra) to minimize scattering and failure under stress.
- Chemical Mechanical Polishing (CMP) Tool Design: The findings on the relationship between abrasive size, force, and material removal rate directly inform the design and optimization of fixed abrasive pads (FAPs) used in industrial polishing processes.
- Wear-Resistant Components: Sapphire is used in high-durability applications (e.g., watch crystals, industrial bearings). This research improves the efficiency and quality control of the final finishing steps for these components.
- Micro-Machining and MEMS: The understanding of ductile-mode removal at the nanoscale, driven by controlled cutting depth (via concession), is crucial for fabricating high-precision sapphire micro-components.
View Original Abstract
Aiming at exploring the material removal mechanism for sapphire using diamond abrasive grains at the microscopic level, this paper modeled and analyzed the microscopic yield behavior of diamond abrasive grains in the FAP grinding process of sapphire. Molecular dynamics were used to simulate the effects of abrasive particle size on the cutting force, potential energy, and temperature in the Newtonian zone during micro-cutting. The effect of different abrasive particle sizes on material removal was analyzed through experiments. The simulation results show that the abrasive particle radius was 12 Ă , the micro-cutting force reached more than 3500 nN, while the cutting force with an abrasive particle radius of 8 Ă only reached 1000 nN. Moreover, the potential energy, cutting force, and temperature in the Newtonian zone between the sapphire crystal atoms also increased. The results showed that the material removal rate saw a nonlinear increasing trend with the increase in particle sizes, while the surface roughness showed an approximately linear increase. Both of them showed a similar trend. The experimental results lay a theoretical basis for the selection of the lapping process parameters in sapphire.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2016 - Process Optimization of Lapping Sapphire Substrate with Fixed Diamond Abrasive Pad
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- 2019 - Subsurface damage and material removal of Al-Si bilayers under high-speed grinding using molecular dynamics (MD) simulation [Crossref]
- 2020 - Effect of Cutting Depth on Mechanical Properties of Single Crystal gamma-TiAl Alloy
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