Cutting of Rock by Wire-Sawing in Vacuum (1st Report)
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-08-04 |
| Journal | Journal of the Japan Society for Precision Engineering |
| Authors | Katsushi Furutani, Shoudai FUKUNAGA, Tatsuaki Okada, Kazuto Saiki, Hiroyuki OHUE |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Challenge Addressed: The research investigates wire-sawing rock (Basalt) in high vacuum (down to 10-5 Pa) for planetary exploration, where liquid coolants cannot be used, leading to severe tool wear and short life.
- Performance Degradation: Cutting efficiency (machined depth) decreased significantly as vacuum pressure increased (higher vacuum), contrasting with atmospheric cutting.
- Adhesion Mechanism: The performance drop is attributed to the adhesion of rock debris (Si, Al) and nickel (Ni) bond material onto the diamond grits and the rock surface. This Ni adhesion causes the diamond grits to slip, inhibiting effective material removal.
- Tool Preference: Non-coated diamond saw wire demonstrated superior cutting depth compared to Ni-coated wire, making it the preferred tool for vacuum processing due to reduced Ni adhesion issues.
- Process Control: Cutting depth was found to be proportional to the cutting load (0.8 N vs. 1.6 N) but was unaffected by wire feeding speed in the tested low range (0.1 to 1.0 m/s), indicating the process operates in a pressure-controlled cutting regime (consistent with Prestonâs equation).
- Wear Analysis: The grinding ratio (material removed per unit tool wear) was lower in high vacuum, suggesting that the abrasive wear is exacerbated by chemical or frictional effects (e.g., potential Ni carbide formation at the interface) rather than pure mechanical abrasion.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Workpiece Material | Basalt | N/A | Analog for lunar/planetary rock. |
| Workpiece Dimensions | 10 x 15 x 15 | mm | Sample size for cutting tests. |
| Saw Wire Diameter | 0.28 | mm | Nominal wire diameter. |
| Abrasive Grain Size | 30 - 40 | ”m | Diamond grit size. |
| Wire Types Tested | Ni-coated, Non-coated | N/A | Comparison of bonding exposure. |
| Wire Feeding Speed (Test Range) | 0.1 to 1.0 | m/s | Tested constant speed range. |
| Cutting Load (Test Range) | 0.8, 1.6 | N | Applied load via lever mechanism. |
| Saw Wire Tension | 2 | N | Constant tension maintained. |
| Ambient Pressure (High Vacuum) | 10-5 | Pa | Lowest pressure tested. |
| Ambient Pressure (Medium Vacuum) | 10-3 | Pa | Intermediate pressure tested. |
| Ambient Pressure (Air) | 105 | Pa | Atmospheric reference. |
| Achieved Surface Roughness (Ra) | 1.1 (Parallel), 3.8 (Perpendicular) | ”m | Roughness achieved using non-coated wire. |
| Cutting Depth (Ni-Coated, 1.6 N, 10-5 Pa) | ~2.5 | mm | Example performance under high vacuum. |
| Cutting Depth (Non-Coated, 1.6 N, 10-5 Pa) | ~4.0 | mm | Example performance under high vacuum. |
Key Methodologies
Section titled âKey Methodologiesâ- Custom Wire Sawing System: A compact wire-sawing machine (270 x 110 x 198 mm) was developed and placed inside a vacuum chamber, driven by an external AC servo motor via a rotary feedthrough.
- Process Control: Cutting load (0.8 N or 1.6 N) was applied using a constant force spring/lever system. Wire tension was maintained at 2 N via torque control on the feeding motor.
- Vacuum Environment: Experiments were conducted at three pressure levels: high vacuum (10-5 Pa), medium vacuum (10-3 Pa), and atmospheric pressure (105 Pa).
- Dressing Requirement: New Ni-coated saw wires required a dressing step (10 reciprocations in air) prior to vacuum testing to remove the surface Ni layer and expose the diamond grits. Without dressing, cutting failed completely in vacuum due to Ni adhesion.
- Performance Measurement: Cutting performance was quantified by measuring the machined depth (T) after 15 reciprocations. The depth was measured at the deepest point of the resulting curved groove.
- Wear Measurement: Wire wear was assessed by measuring the change in wire diameter (ÎD) in the cutting direction using a micrometer, taken at 20 points across both acceleration/deceleration and constant speed sections.
- Surface Characterization: Post-cut surfaces of both the saw wire and the basalt workpiece were analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) to identify adhered materials (Si, Al from rock; Ni from bond).
Commercial Applications
Section titled âCommercial Applicationsâ- Planetary Sample Preparation: Direct application in preparing geological samples (e.g., basalt, regolith) in situ on planetary surfaces (Moon, Mars) for analysis, eliminating the need for heavy, complex liquid coolant systems.
- Space Mechanism Design: Provides critical tribological data on the friction and wear of diamond/nickel tools against silicates in high vacuum, informing the selection and design of moving parts for space exploration hardware.
- Contamination-Sensitive Machining: Relevant for cutting hard, brittle materials (e.g., specialized optics, semiconductor substrates, ceramics) in ultra-clean or vacuum environments where liquid contamination or atmospheric oxidation must be strictly avoided.
- Micro-Sectioning Technology: Enables the creation of high-quality, low-damage thin sections of geological or advanced materials for subsequent high-resolution microscopy (e.g., TEM, optical microscopy) where surface integrity is paramount.
- High-Temperature Vacuum Processing: The findings regarding Ni adhesion and potential Ni3C formation (which occurs above 600 °C but can initiate at lower temperatures) are crucial for designing diamond tools used in high-friction, high-vacuum, or high-temperature industrial processes.
View Original Abstract
In-situ analysis is demanded for the investigation of a larger amount of rock samples in future lunar and planetary explorations. Because coolant cannot be used in vacuum environment, tool life will shorten. It is expected for wire-sawing to keep cutting performance due to successive supply of cutting edges in vacuum. The cutting performance was experimentally investigated under various machining conditions such as a wire feeding speed, cutting load and ambient pressure. Cutting debris adhered around grits on a saw wire in vacuum. In addition, nickel bond of the saw wire was adhered onto a rock surface. Then diamond grits slipped on the rock and cutting amount was decreased with a decrease of the vacuum pressure. The wire feeding speed below 1 m/s did not affect the cutting performance and the cutting depth was increased with an increase of cutting load. Saw wires with exposed grits was compared with a nickel-coated one. The cutting depth with the exposed saw wire was larger than that with the non-coated one. The wear of both the saw wires was almost the same. In addition, amount of grit wear was almost the same both in vacuum and air. The non-coated saw wire was preferable for vacuum use rather than the nickel-coated one.