Fundamental Study on Electrode Performance of Diamond Composite for EDM
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | International Journal of Electrical Machining |
| Authors | Shun-ichiro Tsuetani, Koki Yoshida, Akira Okada |
| Institutions | Okayama University |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigated the feasibility and performance of metal-diamond composite materials (Cu-Dia and Ag-Dia) as electrodes for Electrical Discharge Machining (EDM), aiming to leverage their high thermal conductivity and low thermal expansion.
- Initial Performance Failure: Standard diamond composites exhibited poor performance (high wear, low material removal rate) compared to pure copper due to extremely high surface roughness leading to unstable discharge states.
- Wear Mechanism Identified: Under high discharge current, the metal matrix (Cu or Ag) is preferentially removed, exposing the insulated diamond grains. The intense plasma heat (~10,000 K) causes the exposed diamond surfaces to graphitize/carbonize, making them conductive.
- Discharge Instability: The exposure of conductive, protruding diamond grains creates a highly undulating surface, leading to discharge concentration, short circuits, and intermittent machining, significantly degrading performance.
- Optimization Strategy: To prevent significant diamond exposure, testing was shifted to conditions involving small discharge areas and low discharge currents (Condition II: 3 A, 10 mm2 area).
- Key Achievement (Practicability): Under optimized low-wear conditions, the average electrode wear ratio (Δ) of the Cu-Dia composite was measured to be lower than that of pure copper. Analysis confirmed that only the copper matrix was removed, leaving the diamond grains intact.
- Conclusion: Cu-Dia composite is a practical electrode material for high-precision EDM applications characterized by small discharge areas, provided conditions are managed to prevent significant diamond grain exposure.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Thermal Conductivity (Cu-Dia) | 380 | W/(mK) | High thermal dissipation capability. |
| Thermal Conductivity (Ag-Dia) | 580 | W/(mK) | Highest conductivity among tested composites. |
| Thermal Conductivity (Pure Cu) | 398 | W/(mK) | Reference material. |
| Linear Thermal Expansion (Cu-Dia) | 8.4 | 10-6/K | Low expansion, beneficial for thermal stability. |
| Diamond Grain Content (Cu-Dia) | 60 | vol.% | Composition of the copper-diamond composite. |
| Average Diamond Grain Size | < 200 | ”m | Size of insulated diamond grains used in composites. |
| Cu-pack Layer Thickness | ~200 | ”m | Thickness of the thin copper surface layer. |
| Discharge Current (Condition I) | 15 | A | High current test (10x10 mm2 area). |
| Discharge Current (Condition II) | 3 | A | Optimized low current test (2x5 mm2 area). |
| Pulse Duration (Condition I) | 3 | ”s | Short pulse duration. |
| Pulse Duration (Condition II) | 16 | ”s | Longer pulse duration for low wear test. |
| Open Circuit Voltage (V) | 90 | V | Applied voltage for all tests. |
| Plasma Temperature | ~10,000 | K | Temperature sufficient to induce diamond graphitization. |
| Cu-Dia Wear Ratio (Condition II) | ~1.5 | % | Lower than pure Cu (~2%) under small area conditions. |
| Raman Shift (Graphite Peak) | ~1580 | cm-1 | Characteristic peak observed on EDMed diamond grains. |
Key Methodologies
Section titled âKey Methodologiesâ- Electrode Material Preparation: Diamond composites (Cu-Dia, Ag-Dia) were manufactured by sintering metal powder (Cu or Ag) with insulated diamond grains (< 200 ”m) under pressing.
- Surface Modification (Cu-pack): A specialized Cu-pack electrode was prepared by pressing a thin copper plate (~200 ”m thick) onto the Cu-Dia surface to achieve low initial surface roughness (1.6 ”mRz) and prevent initial diamond exposure.
- EDM Setup: Experiments were conducted using a Sodick AP3L die-sinking electrical discharge machine. The workpiece material was alloy tool steel SKD11, machined in working oil.
- Testing Conditions: Two distinct EDM regimes were employed, both using cathode polarity for the electrode in Condition I (high current/wide area) and anode polarity in Condition II (low current/small area) to establish low-wear baseline performance.
- Performance Metrics: Electrode wear ratio (Δ) was calculated based on weight subtraction. Due to the composite nature, error bars were used to represent the range between the removal of only the metal matrix (lower value) and the removal of only the diamond grain ( upper value).
- Discharge Waveform Analysis: Single and multiple discharge current and voltage waveforms were monitored to assess discharge stability, particularly when diamond grains became exposed.
- Surface Characterization: EDMed electrode and workpiece surfaces were analyzed using optical microscopy and height maps to correlate surface undulation with discharge concentration areas.
- Chemical Composition Analysis: Laser Raman microscopy was used on the exposed diamond grains before and after EDM to confirm the change in composition from insulated diamond to conductive carbon (graphite).
Commercial Applications
Section titled âCommercial Applicationsâ- High-Precision Die and Mold Machining: Utilizing the low electrode wear ratio of Cu-Dia under small discharge conditions for creating intricate features and high-tolerance cavities, minimizing electrode replacement costs.
- Micro-EDM and Fine Feature Generation: The materialâs superior performance in small discharge areas (2x5 mm2) makes it highly suitable for micro-machining applications where minimizing electrode wear is paramount for dimensional accuracy.
- Machining of Hard/Brittle Materials: As EDM is the preferred method for machining materials regardless of hardness, the improved stability and reduced wear offered by Cu-Dia benefit the processing of advanced alloys and ceramics.
- Extended Electrode Life: By ensuring that only the copper matrix is preferentially removed while the hard diamond grains remain intact, the Cu-Dia composite offers potential for significantly longer electrode life compared to pure copper in optimized regimes.
- Thermal Management Integration: Leveraging the high thermal conductivity of the base composite material, this technology is relevant for manufacturing components (like heat sinks) that require both high thermal performance and precise machining.
View Original Abstract
Diamond composites which are made of diamond grains and metals has high thermal conductivity and low coefficient of linear thermal expansion. Therefore, a possibility of diamond composite as electrode for EDM was highly expected. In this study, tool electrode performances of copper-diamond (Cu-Dia) composite and silver-diamond (Ag-Dia) composite in EDM die-sinking were experimentally investigated. The results show that the metal around the diamond grains in the electrode is preferentially removed during EDM under large discharge current condition, which causes the diamond grains to expose on the electrode surface. Consequently, the undulation of electrode surface increases and the discharging state becomes unstable. In order to exert maximum effect of high thermal conductivity of diamond grains and prevent its sign ificant exposure, EDM performance was investigated under the conditions with small discharge current and small discharge area. As a result, the electrode wear ratio of Cu-Dia became lower than that of pure copper. Therefore, Cu-Dia composite has a possibility as an electrode for EDM with small discharge area.