Surface Quality of Al2O3 Ceramic and Tool Wear in Diamond Wire Sawing Combined with Oil Film-Assisted Electrochemical Discharge Machining

At a Glance

Metadata	Details
Publication Date	2023-08-07
Journal	Applied Sciences
Authors	Zhixin Jia, Kaiyue Zhang, Jin Wang
Institutions	University of Science and Technology Beijing
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: Oil Film-Assisted ECDM of Al₂O₃ Ceramic

This document analyzes the research on combining diamond wire sawing (DWS) with oil film-assisted Electrochemical Discharge Machining (ECDM) for processing Al₂O₃ ceramic. The findings demonstrate a significant increase in Material Removal Rate (MRR) by leveraging thermal stress-induced spalling, a technique highly relevant to engineers utilizing advanced CVD diamond materials for high-throughput machining applications.

Executive Summary

The integration of spark discharge via oil film-assisted ECDM with traditional DWS provides a critical pathway for improving the efficiency of hard, brittle, and insulating material processing.

Efficiency Gain: The combined DWS/ECDM process achieved a 36% increase in Material Removal Rate (MRR) for Al₂O₃ ceramic, reaching 1.75 mm³/min compared to 1.29 mm³/min for DWS alone.
Mechanism Shift: Material removal is driven by thermal stress and mechanical failure (spalling) induced by spark discharge, rather than melting, successfully avoiding the formation of recast layers and micro-cracks.
Process Stability: The use of an oil film coating on the electrode wire successfully replaced the unstable hydrogen gas film, enabling stable discharge generation necessary for cutting thick (10.0 mm) insulating workpieces.
Surface Quality Trade-off: Increased DC voltage (up to 58 V) facilitated greater spalling and MRR, but resulted in higher surface roughness (Ra up to 1.002 µm) and increased micro-crater density.
Tool Wear Implications: Spark discharges caused micro-craters on the diamond wire matrix (Ni-based) and increased the probability of diamond grit pull-out, highlighting the need for robust diamond tooling and bonding layers.
Electrolyte Composition: A 20% NaCl solution was utilized as the electrolyte, demonstrating that the oil film successfully prevented carbon decomposition or deposition onto the workpiece surface.

Technical Specifications

Parameter	Value	Unit	Context
Workpiece Material	Al₂O₃ Ceramic	N/A	Hardness: 9 Mohs
Al₂O₃ Electrical Resistivity	10¹⁶	Ω cm	Insulating property
Diamond Wire Diameter	0.2 ± 0.01	mm	Tool specification
Workpiece Thickness	10.0	mm	Cut depth
Wire Speed	1400	mm/s	Constant for all tests
Electrolyte (ECDM)	20% NaCl solution	Mass Fraction	Used for conductivity
DC Voltage Range (ECDM)	46 to 58	V	Applied voltage range
Maximum MRR (ECDM Assisted)	1.75	mm³/min	Achieved at 52 V (implied optimal)
Baseline MRR (DWS only)	1.29	mm³/min	Standard diamond wire sawing
Minimum Surface Roughness (Ra)	0.485	µm	Parallel direction, 46 V
Maximum Surface Roughness (Ra)	1.002	µm	Perpendicular direction, 58 V
Recast Layer / Micro-cracks	None	N/A	Material removal by mechanical spalling

Key Methodologies

The experimental setup utilized a modified fast wire EDM machine to integrate the oil film-assisted ECDM process with diamond wire sawing.

Equipment Transformation: A DK7720 fast wire EDM machine was adapted by replacing the molybdenum wire with a diamond wire saw and integrating a specialized discharge circuit and electrolyte supply system.
Oil Film Application: A uniform oil film (guide rail oil, density 0.87-0.89 g/cm³) was coated onto the electrode wire prior to entering the electrolyte. This oil film acts as the primary dielectric layer, ensuring electrical insulation and stable discharge generation, overcoming the instability of the traditional hydrogen gas film.
Electrolyte Selection: A 20% mass fraction NaCl solution was chosen for its non-corrosive properties and high electrical conductivity, serving as the auxiliary electrode medium.
Discharge Generation: A pulse power supply applied DC voltage (46 V to 58 V) between the electrode wire and the auxiliary electrode. Spark discharge occurred when the voltage exceeded the critical breakdown threshold of the oil film.
Material Removal: The high temperature from the spark discharge generated thermal stress, lowering the strength of the Al₂O₃ ceramic and facilitating its removal by the moving diamond wire via spalling (mechanical failure).
Analysis: Surface quality was assessed using a TR100 roughness tester (Ra) and Scanning Electron Microscopy (SEM). Energy Dispersive X-ray Spectroscopy (EDS) confirmed the absence of Nickel (Ni) tool transfer and carbon deposition from the oil film.

6CCVD Solutions & Capabilities

The research highlights the critical role of high-quality diamond tooling and robust bonding matrices in advanced machining processes like ECDM-assisted DWS. 6CCVD is uniquely positioned to supply the foundational CVD diamond materials and customization services required to replicate, optimize, and scale this research.

Applicable Materials

To replicate or extend this research, high-quality, durable CVD diamond materials are essential for tool fabrication and potential workpiece modification:

Polycrystalline Diamond (PCD) Plates: Ideal for fixed abrasive tooling matrices (like the diamond wire used here) due to their superior toughness, high wear resistance, and ability to handle the thermal and mechanical stresses induced by spark discharge and spalling.
- 6CCVD Capability: We supply PCD plates in custom dimensions up to 125 mm and thicknesses from 0.1 µm to 500 µm.
Boron-Doped Diamond (BDD) Substrates: For researchers exploring conductive ceramic processing or optimizing the auxiliary electrode, BDD offers tunable conductivity and extreme chemical stability in aggressive electrolytes (like 20% NaCl).
- 6CCVD Capability: We provide BDD materials for high-performance electrochemical applications.

Customization Potential

The paper identifies tool wear (Ni matrix removal and grit pull-out) as a key challenge. 6CCVD’s in-house engineering capabilities directly address these tooling limitations:

Research Requirement	6CCVD Customization Service	Benefit to Researcher
Robust Tool Bonding (Mitigating Ni matrix wear)	Custom Metalization Services	We offer in-house deposition of Ti, W, Cu, Au, Pt, and Pd layers. Researchers can test novel, high-adhesion conductive matrices to improve grit retention and reduce tool wear under ECDM conditions.
Large-Scale Workpieces (10 mm thickness used)	Custom Substrate Dimensions	We provide SCD and PCD substrates up to 10 mm thick, allowing for large-scale, industrial-relevant experiments and component fabrication.
Surface Finish Optimization (Post-processing)	Precision Polishing Services	While ECDM increases Ra, 6CCVD can provide SCD materials polished to Ra < 1 nm and inch-size PCD polished to Ra < 5 nm for subsequent high-precision finishing steps.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of CVD diamond applications, including advanced machining and electrochemical processes. We offer consultation services to assist researchers in:

Material Selection: Choosing the optimal SCD or PCD grade based on specific thermal, electrical, and mechanical requirements for ECDM/DWS projects.
Process Optimization: Advising on metalization schemes to enhance electrode performance and mitigate tool wear in spark discharge-assisted processes.
Global Logistics: Ensuring reliable, global delivery of custom diamond materials (DDU default, DDP available) to maintain project timelines.

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

View Original Abstract

Diamond wire sawing is one of the most widely used methods of cutting Al2O3 ceramic because it has good machining accuracy and causes less surface damage. However, its material removal rate (MRR) needs to be improved with the increasing demand for Al2O3 ceramic parts. In this paper, spark discharges are generated around the diamond wire based on the electrochemical discharge machining (ECDM) process. An oil film-assisted ECDM process is applied to solve the difficulty of generating spark discharges when the thickness of the workpiece exceeds 5.0 mm due to the difficulty of forming a hydrogen gas film. Experimental results show that the combination of oil film-assisted ECDM and diamond wire sawing improved the MRR of Al2O3 ceramic. Oil film-assisted ECDM may improve the surface quality of machined parts and reduce the wear on diamond wire. Therefore, this research focuses on the surface quality of Al2O3 ceramic and tool wear in diamond wire sawing combined with oil film-assisted ECDM. Surface roughness and topography, recast layer, and elements of the machined surface are analyzed. The tool wear is studied using SEM images of diamond wire. The results provide a valuable basis for application of diamond wire sawing combined with oil film-assisted ECDM.

Tech Support

Original Source

DOI: https://doi.org/10.3390/app13159030

References

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