Grain flash temperatures in diamond wire sawing of silicon
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-06-11 |
| Journal | The International Journal of Advanced Manufacturing Technology |
| Authors | Uygar Pala, Stefan SĂŒssmaier, Konrad Wegener |
| Institutions | ETH Zurich, Inspire |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research focuses on measuring and modeling the highly dynamic flash temperatures generated during the diamond wire sawing of single-crystal silicon (sc-Si), a critical factor influencing tool wear and wafer quality.
- Novel Setup: A new experimental setup was designed to conduct high-speed, long-contact single-grain scratching tests, accurately emulating the kinematics of industrial diamond wire sawing.
- Temperature Measurement: Flash temperatures exceeding 1500 K (up to 2000 K) were successfully measured at the diamond grain tip using a two-color fiber optic pyrometer in dry cutting conditions.
- Thermal Modeling: A flash temperature model, based on heat conduction principles (Archard/Jaeger), was developed to predict temperatures based on cutting speed, grain geometry, and penetration depth.
- Material Removal Mode Influence: The study confirmed that the material removal mode significantly affects temperature. Ductile removal (low penetration depth) results in higher flash temperatures due to increased thermal energy dissipation.
- Model Validation & Correction: The analytical model underestimated the measured temperatures by a factor of 4.5, primarily due to simplified assumptions regarding the contact area geometry and the heat sink effect of the bonding material.
- Engineering Impact: The validated temperature model provides essential input for advanced kinematic process models, enabling accurate prediction of diamond wear and optimization of the wire sawing process for superior wafer quality.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Measured Flash Temperature (Tf) | >1500 (up to 2000) | K | Observed during dry cutting conditions. |
| Cutting Speed (vc) | 10 | m/s | Speed used for single-grain scratch tests. |
| Single Grain Contact Length | 40 | mm | Length of one scratch pass. |
| Total Contact Distance (per grain) | 0.8 | m | Average total distance scratched by one grain. |
| Grain Protrusion Decrease (Wear) | 0.5-1.5 | ”m | Observed wear over the course of the experiment. |
| Workpiece Material | Monocrystalline Si (sc-Si) | N/A | Commercial solar-grade material. |
| Si Density (ÏÏ) | 2329 | kg/m3 | At 300 K. |
| Si Thermal Conductivity (kÏ) | 156 | W/mK | At 300 K. |
| Diamond Thermal Conductivity (kg) | 2000-2100 | W/mK | At 300 K. |
| Workpiece Surface Roughness (Rz) | 0.49-0.52 | ”m | Maximum profile height before scratching. |
| Empirical Model Correction Factor | 4.5 | N/A | Factor applied to simulated Tf to compensate for model simplifications. |
Key Methodologies
Section titled âKey Methodologiesâ- Experimental Setup: Scratch tests were conducted on a Fehlmann Versa 825 5-axis milling machine. The heavy sc-Si workpiece was rotated at high speed, while the tool (diamond wire segment fixed on an aluminum pin) was stationary on a force measurement platform.
- Tool Isolation: A single diamond grain was isolated on the pin tip from a commercial electroplated diamond wire to ensure precise measurement of individual grain interaction.
- Kinematics Emulation: The setup emulated wire sawing kinematics, with the grain moving over the cutting path at a constant velocity (vc = 10 m/s) and advancing onto the surface via vertical (vfz) and radial (vfr) feed rates.
- Force and Temperature Measurement: A Kistler MiniDyn 3-component force dynamometer measured cutting forces (Fc). A Fire-3 two-color fiber optic pyrometer measured the highly dynamic flash temperatures (Tf) at the grain tip. Experiments were conducted without coolant.
- Geometry and Penetration Depth: Grain geometry and workpiece surface were measured using an Alicona Infinite Focus G4 microscope (IFM). Penetration depth (hcu) was estimated from the residual scratch depth due to the slightly irregular concave shape of the workpiece surface.
- Flash Temperature Modeling: A steady-state heat flow model was developed based on Archard, Carslaw, and Jaeger principles. The model calculates the total heat rate (qt) generated by the tangential cutting force (Fc) and relative sliding velocity (vrel), distributing it between the grain (qg) and the workpiece (qw) using the Peclet number (Pe).
- Model Refinement: The simulated flash temperatures were adjusted using an empirically determined constant factor (4.5) to account for deviations caused by simplified assumptions, such as assuming a rectangular contact area and treating the bonding material as a constant temperature heat sink.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings and validated model are directly relevant to industries relying on precision slicing and machining of hard, brittle materials:
- Photovoltaic Wafer Production: Directly supports the optimization of diamond wire sawing, the dominant method for slicing single-crystal silicon ingots for solar cells, by minimizing thermal damage and improving wafer yield.
- Semiconductor Manufacturing: Applicable to the slicing and processing of advanced semiconductor materials (e.g., Si, SiC, GaN) where subsurface damage control and high wafer strength are critical.
- Advanced Abrasive Tool Development: Provides fundamental data for developing next-generation electroplated diamond wires and grinding tools with enhanced wear resistance and thermal stability.
- Precision Machining: Relevant for high-speed grinding and cutting processes involving hard and brittle engineering ceramics and sapphire, where understanding the transition between ductile and brittle removal regimes is essential for surface quality.
- Tribology and Wear Modeling: The experimental data on flash temperatures in high-speed sliding contacts is valuable for improving general tribological models used in predicting tool life and material degradation under extreme thermal loads.
View Original Abstract
Abstract Diamond wire sawing has obtained 90% of the single-crystal silicon-based photovoltaic market, mainly for its high production efficiency, high wafer quality, and low tool wear. The diamond wire wear is strongly influenced by the temperatures in the grain-workpiece contact zone; and yet, research studies on experimental investigations and modeling are currently lacking. In this direction, a temperature model is developed for the evaluation of the flash temperatures at the grain tip with respect to the grain penetration depth. An experimental single-grain scratch test setup is designed to validate the model that can emulate the long contact lengths as in the wire sawing process, at high speeds. Furthermore, the influence of brittle and ductile material removal modes on cutting zone temperatures is evaluated.