Experimental and Theoretical Investigations on Diamond Wire Sawing for a NdFeB Magnet

At a Glance

Metadata	Details
Publication Date	2022-04-22
Journal	Materials
Authors	Jia Liu, Zhenyu Zhang, Shengzuo Wan, Bin Wu, Junyuan Feng
Institutions	Dalian University of Technology, Harbin Engineering University
Citations	14
Analysis	Full AI Review Included

Technical Analysis: Diamond Wire Sawing of NdFeB Magnets

This document analyzes the research findings regarding the diamond wire sawing (DWS) of NdFeB magnets, focusing on the mechanisms of surface formation, vibration, and cutting force. The analysis is framed to highlight how 6CCVD’s advanced MPCVD diamond materials and customization capabilities can support and extend research in high-precision slicing and machining applications.

Executive Summary

Core Challenge: Sintered NdFeB magnets exhibit high brittleness, leading to severe surface roughness (Sa, Ra) and periodic waviness (PV) during standard diamond wire sawing (DWS).
Waviness Mechanism: Periodic waviness (PV) is primarily caused by the low-frequency lateral swing of the diamond wire, which is attributed to guiding wheel installation errors. PV amplitude is positively proportional to the normal cutting force.
Roughness Mechanism: High-frequency wire vibration (observed at 443 Hz) significantly impacts the material removal process, causing rubbing/ploughing grits to induce NdFeB grain loosening and brittle fracture pull-out.
Cutting Force Optimization: Dry cutting resulted in normal cutting forces twice as large and thrusting forces three times as large compared to wet cutting, confirming the critical role of lubrication and chip transport.
Optimal Parameters: Wet cutting at a 300 rpm spindle speed and 0.1 mm/min feed rate provided the best balance, doubling the cutting efficiency compared to 0.05 mm/min while maintaining similar surface roughness (Ra) and waviness (PV).
Material Removal Modes: NdFeB removal involves both conventional cutting/chipping and vibration-induced grain falling off, making vibration control critical for surface quality.

Technical Specifications

The following table summarizes the key experimental parameters and measured results extracted from the research:

Parameter	Value	Unit	Context
Workpiece Material	N48H Sintered NdFeB	N/A	Sample size 30 x 30 x 10 mm
Diamond Wire Diameter	250	µm	Electroplated, #300 grits
Spindle Speed (Low)	200 (1.3)	rpm (m/s)	Cutting speed equivalent
Spindle Speed (High)	300 (2.0)	rpm (m/s)	Cutting speed equivalent
Feed Rate Range	0.05 to 0.3	mm/min	Tested range for Dry and Wet conditions
Optimal Feed Rate (Wet)	0.1	mm/min	Achieved optimal efficiency/quality balance
High-Frequency Vibration	443	Hz	Observed wire vibration frequency
Low-Frequency Swing	2	Hz	Periodic lateral swing frequency
Normal Force (Dry, 0.3 mm/min)	~8	N	Twice the force of wet cutting
Thrusting Force (Dry, 0.3 mm/min)	~0.3	N	Three times the force of wet cutting
Waviness Period (0.05 mm/min)	37	µm	Positively proportional to feed speed
Waviness Period (0.3 mm/min)	225	µm	Positively proportional to feed speed

Key Methodologies

The experimental investigation utilized precise monitoring and advanced surface analysis techniques:

Sawing Equipment: Experiments were conducted on an STX-203 diamond wire saw machine.
Force Monitoring: Normal cutting force (Fn) and thrusting cutting force (Ft) were recorded in real-time using a dynamometer fixed to the cutting platform.
Vibration Monitoring: Lateral displacement of the diamond wire was measured using a laser displacement sensor (200 µm spot size) positioned horizontally.
Wire Specifications: A 250 µm diameter wire electroplated with #300 diamond grits was used.
Cutting Conditions: A matrix of 12 experimental groups was tested, varying:
- Coolant Condition (Dry or ST12 water-based cutting fluid).
- Spindle Speed (200 rpm or 300 rpm).
- Feed Rate (0.05, 0.1, 0.2, 0.3 mm/min).
Surface Analysis: Sawed surfaces were characterized using:
- Zygo Newview 9000 3D optical surface profiler to measure areal roughness (Sa), linear roughness (Ra), and Peak-to-Valley (PV) waviness.
- FEI QUANTA 450 SEM for detailed analysis of surface morphology, fracture pits, and grain loosening mechanisms.

6CCVD Solutions & Capabilities

The research highlights the critical role of diamond tool stability and precision in achieving high-quality surfaces, particularly when processing brittle materials like NdFeB. 6CCVD provides the foundational MPCVD diamond materials necessary to advance DWS technology, whether for optimizing fixed abrasive wires or developing high-precision monitoring components.

Applicable Materials

To replicate or extend this research—especially for high-precision slicing of hard, brittle materials like SiC or Silicon, where surface integrity is paramount—6CCVD recommends the following materials:

Polycrystalline Diamond (PCD) Plates: Ideal for developing next-generation fixed abrasive wire saw tooling or high-stability substrates for mounting samples/sensors. Our PCD plates offer high mechanical stability and are available in large formats (up to 125mm).
Optical Grade Single Crystal Diamond (SCD): Essential for high-power laser windows or optical components used in advanced, non-contact metrology systems (like the laser displacement sensor used in this study) that require extreme thermal stability and transparency.
Boron-Doped Diamond (BDD) Films: Recommended for integrating electrochemical sensors directly into the cutting fluid loop (ST12 water-based fluid) to monitor chip density, chemical breakdown, or lubrication effectiveness in real-time.

Customization Potential

The study identified mechanical instability (lateral wire swing) and friction/chip transport issues as major limitations. 6CCVD’s customization capabilities directly address the need for high-precision tooling and integrated monitoring:

Paper Requirement/Challenge	6CCVD Customization Service	Technical Advantage
High-Precision Tooling/Substrates: Need for stable, large-area components to minimize mechanical error (guiding wheel error).	Custom Dimensions & Thickness: PCD plates up to 125mm diameter and substrates up to 10mm thick.	Provides large, ultra-flat diamond platforms for building highly stable DWS machine components or fixed abrasive wire guides.
Surface Quality (Ra < 1µm): Requirement for minimal post-sawing grinding.	Ultra-Precision Polishing: SCD (Ra < 1nm), Inch-size PCD (Ra < 5nm).	We deliver materials with superior surface finish, reducing subsequent processing time and cost for sensitive applications (e.g., SiC wafer slicing).
Integrated Sensing/Bonding: Need for robust sensor integration (e.g., BDD electrodes, metalized SCD heat sinks).	In-House Metalization: Custom deposition of Au, Pt, Pd, Ti, W, Cu layers.	Enables seamless integration of diamond components into complex DWS systems for real-time force, temperature, or chemical monitoring.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of MPCVD diamond and its application in extreme environments. We can assist researchers and engineers with material selection and design optimization for similar high-precision slicing and machining projects, particularly those involving brittle materials (SiC, sapphire, silicon, or advanced ceramics) where vibration and surface integrity are critical concerns.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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

Original Source

DOI: https://doi.org/10.3390/ma15093034

References

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]