Experimental and Theoretical Investigations on Diamond Wire Sawing for a NdFeB Magnet
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-04-22 |
| Journal | Materials |
| Authors | Jia Liu, Zhenyu Zhang, Shengzuo Wan, Bin Wu, Junyuan Feng |
| Institutions | China Academy of Space Technology, Dalian University of Technology |
| Citations | 14 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study experimentally and theoretically investigated the surface formation mechanisms during the diamond wire sawing (DWS) of sintered NdFeB magnets, focusing on minimizing periodic waviness and surface roughness.
- Waviness Mechanism Identified: Periodic waviness (PV) on the sawed surface is primarily caused by the periodic lateral swing of the diamond wire. This swing is linked to the wireâs reciprocating motion and exacerbated by guiding wheel installation errors.
- Force-Waviness Correlation: The peak-to-valley (PV) value of the surface waviness was found to be positively proportional to the normal cutting force (Fn).
- Vibration-Roughness Link: High-frequency wire vibration significantly impacts surface roughness (Ra). Vibration impact from rubbing/ploughing grits causes the NdFeB grain structure to loosen off and pull out, leading to more brittle fractures, especially at very low feed rates (0.05 mm/min).
- Coolant Effect: Dry cutting resulted in significantly higher cutting forces (Fn was 2x, Ft was 3x higher) and deeper fracture zones compared to wet cutting due to poor lubrication and chip transportation.
- Optimal Condition: Wet cutting at a feed rate of 0.1 mm/min was determined to be the most effective condition, providing a balance between high material removal efficiency and acceptable surface quality (low Ra and PV).
- Vibration Suppression: Vibration amplitude is suppressed when the wire bow deflection is very large (high Fn, e.g., dry cutting at 0.3 mm/min) but increases heavily when the wire bow deflection is too small (low Fn, e.g., wet cutting at 0.05 mm/min).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sample Material | N48H NdFeB | - | Sintered permanent magnet |
| Sample Dimensions | 30 x 30 x 10 | mm | Workpiece size |
| Wire Diameter | 250 | ”m | Electroplated diamond wire |
| Abrasive Grit Size | #300 | - | Diamond abrasive specification |
| Cutting Fluid | ST12 | Water-based | Wet cutting condition |
| Spindle Speeds | 200 and 300 | rpm | Corresponds to 1.3 and 2.0 m/s cutting speed |
| Feed Rate Range (f) | 0.05 to 0.3 | mm/min | Experimental variable |
| Dry vs Wet Fn Ratio | 2:1 | - | Normal force comparison at 0.3 mm/min feed rate |
| Dry vs Wet Ft Ratio | 3:1 | - | Thrusting force comparison at 0.3 mm/min feed rate |
| High-Frequency Vibration | 443 | Hz | Typical wire vibration frequency |
| Low-Frequency Swing | 2 | Hz | Corresponds to wire reciprocating motion |
| Waviness Period (f=0.05 mm/min) | 37 | ”m | Measured periodic mark length |
| Waviness Period (f=0.3 mm/min) | 225 | ”m | Measured periodic mark length |
Key Methodologies
Section titled âKey MethodologiesâThe experimental investigation utilized a comprehensive setup to monitor forces, wire motion, and resulting surface quality under various conditions.
- Sawing Setup: Experiments were conducted on an STX-203 diamond wire saw machine using a N48H NdFeB magnet sample.
- Force Measurement: A dynamometer was used to continuously record the normal cutting force (Fn) and the thrusting cutting force (Ft) during the sawing process.
- Wire Motion Monitoring: A laser displacement sensor (200 ”m spot size) was positioned to capture the horizontal (lateral) displacement signal of the diamond wire during cutting.
- Signal Processing: The raw lateral displacement data was analyzed in the frequency domain and separated into two components using filters:
- High-frequency component (vibration, ~443 Hz).
- Low-frequency component (periodic swing, ~2 Hz), corresponding to the wireâs reciprocating motion.
- Surface Metrology: A Zygo Newview 9000 3D optical surface profiler was used to quantify surface quality:
- Areal surface roughness (Sa).
- Peak-to-valley (PV) value perpendicular to the saw mark (waviness).
- Roughness along the saw mark (Ra).
- Microstructural Inspection: An FEI QUANTA 450 SEM was employed to observe the surface morphology, identify fracture pits, and analyze material removal mechanisms (ductile marks vs. grain pull-out).
- Specific Cutting Force Calculation: The specific cutting force (Fn/Cdg, where C is grit density and dg is average removal depth per grit) was calculated to provide insight into cutting efficiency and energy loss across different parameters.
Commercial Applications
Section titled âCommercial ApplicationsâNdFeB magnets are critical components in high-performance magnetic systems, making efficient and high-quality slicing essential for manufacturing.
- Electric Vehicles (EVs): NdFeB magnets are fundamental components in high-efficiency traction motors, where precise slicing minimizes material waste and preparation time.
- Wind Power Generation: Used in permanent magnet synchronous generators (PMSGs) for wind turbines, requiring large volumes of high-quality magnet slices.
- Aerospace and Defense: Used in high-performance actuators and specialized motors, aligning with the context of the sample provider (Beijing Spacecrafts Manufacturing Factory).
- Industrial Automation: High-efficiency industrial motors and robotics rely on NdFeB magnets for compact, powerful designs.
- Consumer Electronics: Applications include high-end audio equipment (speakers/headphones) and magnetic storage devices (hard drives).
View Original Abstract
The normal processing of sintered NdFeB magnets, used in many applied fields, involves diamond wire sawing. Due to the fact of its relatively lower hardness and high brittleness, the surface roughness and periodic waviness of the sawed surface have become a serious problem, but the surface formation mechanism is still unknown. In this work, a diamond wire sawing experiment with a NdFeB magnet was conducted while both the cutting force and the diamond wire lateral displacement were monitored. The vibration, the lateral swing of the wire and the cutting force were thoroughly analyzed. After the experiment, the surface morphology was carefully inspected under both a white light interferometer and SEM. It was discovered that the lateral swing of the diamond wire was the main cause of the periodic waviness on the surface, the PV of which was positively proportional to the normal cutting force. The surface morphology and surface roughness along the saw mark revealed that the vibration impact of ploughing/rubbing grits can induce the NdFeB grain to loosen off and cause more brittle fractures when the feed rate was 0.05 mm/min under wet cutting.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2020 - Formation Mechanism of Wire Bow and Its Influence on Diamond Wire Saw Process and Wire Cutting Capability [Crossref]
- 2015 - Investigation into Influence of Feed Speed on Surface Roughness in Wire Sawing [Crossref]
- 2014 - High-Speed Slicing of SiC Ingot by High-Speed Multi Wire Saw [Crossref]
- 2011 - Investigation of Long Waviness Induced by the Wire Saw Process [Crossref]
- 2019 - Wire Vibration Modeling and Experimental Analysis for Wire Saw Machining [Crossref]
- 2017 - Effect of Wire Vibration on the Materials Loss in Sapphire Slicing with the Fixed Diamond Wire [Crossref]
- 2015 - Experimental Investigation on the Machining Characteristics of Single-Crystal SiC Sawing with the Fixed Diamond Wire [Crossref]
- 2014 - Error Analysis of Natural Vibration Characteristic of the Diamond Wire Saw
- 2015 - Analysis of Wire Vibration in Wire Electric Discharge Machining Process
- 2014 - Experimental Study of Surface Generation and Force Modeling in Micro-Grinding of Single Crystal Silicon Considering Crystallographic Effects [Crossref]