Comparative Study of Ultrasonic Vibration-Assisted Die-Sinking Micro-Electrical Discharge Machining on Polycrystalline Diamond and Titanium

At a Glance

Metadata	Details
Publication Date	2024-03-25
Journal	Micromachines
Authors	Cheng Guo, Longhui Luo, Zhiqiang Liang, Hao Li, Xiawen Wang
Institutions	Shenzhen University, Beijing Institute of Technology
Citations	1
Analysis	Full AI Review Included

Executive Summary

This study compares the effects of Ultrasonic Vibration (UV) assistance on die-sinking micro-Electrical Discharge Machining (µEDM) for Polycrystalline Diamond (PCD) and Pure Titanium (TA2).

PCD Machining Promotion: At a low open-circuit voltage (100 V), UV significantly promotes PCD µEDM, increasing the Material Removal Rate (MRR) by 3 to 5 times (maximum MRR: 0.0022 mm³/min).
PCD Machining Inhibition: At a high open-circuit voltage (200 V), UV generally inhibits the process, as the vibration disrupts the already stable inter-electrode gap achieved under high-energy conditions.
TA2 Machining Promotion: UV consistently promotes TA2 µEDM at both 100 V and 200 V, effectively mitigating the material’s poor thermal conductivity issues.
Mechanistic Difference (PCD): UV-induced cavitation improves the discharge gap environment, accelerating the removal of graphite and cobalt debris, which otherwise cause secondary discharges.
Mechanistic Difference (TA2): UV acts primarily to break the electrical arc, which is prone to forming due to TA2’s low thermal conductivity, thereby accelerating heat transfer and stabilizing the process.
Electrode Wear: UV assistance significantly increases electrode wear when machining PCD, particularly under low-energy conditions (e.g., 30 µm wear vs. 10 µm unassisted wear at 100 V, 1.5 nF, 12 Ω).
Guidance: Optimal UV amplitude must be adjusted based on material, discharge energy, and machining depth to maximize efficiency and stability.

Technical Specifications

Parameter	Value	Unit	Context
Workpiece 1	Polycrystalline Diamond (PCD)	Material	C (diamond) and Co (binder)
Workpiece 2	Pure Titanium (TA2)	Material	Low thermal conductivity, high toughness
Tool Electrode	W70Cu30	Alloy	Tungsten-Copper
Electrode Tip Thickness	100	µm	Sheet tool electrode geometry
Ultrasonic Frequency	21,714	Hz	Fixed operating frequency
Ultrasonic Amplitude	2 to 3	µm	Range, varies with impedance
Open-Circuit Voltage (V_e)	100, 200	V	RC power supply parameter
Discharge Capacitance (C)	1.5, 4.7, 10, 22	nF	RC power supply parameter
Discharge Resistance (R)	12, 20, 50, 100	Ω	RC power supply parameter
Max MRR (PCD @ 100 V, UV)	0.0022	mm³/min	Achieved at 22 nF, 20 Ω
Electrode Wear (PCD @ 100 V, 12 Ω, 1.5 nF, UV)	45	µm	High wear rate observed with UV assistance
Electrode Wear (TA2)	3 to 10	µm	Generally less than PCD due to lower hardness
Effective Discharge Count (PCD @ 100 V, 10 nF, 12 Ω)	100	count/40 ms	With UV (promotional effect)
Effective Discharge Count (PCD @ 100 V, 10 nF, 100 Ω)	200	count/40 ms	With UV (inhibitory effect compared to 360 unassisted)

Key Methodologies

The study utilized a die-sinking micro-EDM setup assisted by vertical ultrasonic vibration, employing an RC power supply circuit.

Setup Configuration: The experimental setup integrated an RC power supply, ultrasonic control unit, and an EDM workstation. The ultrasonic tool holder was mounted on a vertical platform (Z-axis).
Dielectric Environment: Spark oil was used as the dielectric, fully immersing the workpiece throughout the process.
Vibration Application: Ultrasonic vibration (21,714 Hz, 2-3 µm amplitude) was applied vertically to the tool electrode.
Parameter Variation: Experiments were conducted across two open-circuit voltages (100 V, 200 V) and four capacitance levels (1.5 nF to 22 nF) combined with four resistance levels (12 Ω to 100 Ω).
Material Preparation: PCD and TA2 samples (10 mm x 10 mm x 2 mm) were mechanically polished and ultrasonically cleaned prior to testing.
Data Acquisition: Performance was evaluated by measuring Material Removal Rate (MRR), analyzing discharge waveforms (voltage V_c vs. time), tracking Z-axis displacement trajectories, and observing groove profiles and effective discharge counts.
Surface Analysis: Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to characterize the materials and analyze machined surface craters.

Commercial Applications

This research directly supports the advanced manufacturing of intricate micro-structures in industries requiring high precision and the processing of extremely hard or difficult-to-machine materials.

Industry/Field	Relevance to UV-Assisted µEDM
Aerospace & Defense	Machining of complex, high-precision titanium alloy (TA2) components (e.g., engine turbine parts, structural elements) where thermal damage and arcing must be minimized.
Tool Manufacturing	Fabrication of intricate geometries and micro-features on Polycrystalline Diamond (PCD) cutting tools and wear-resistant components, leveraging the high hardness of PCD.
Medical Devices	Production of micro-scale implants and surgical instruments from biocompatible titanium alloys, requiring high surface quality and precise dimensions.
Micro-Electromechanical Systems (MEMS)	Creating high-aspect-ratio micro-holes and cavities in hard materials where traditional milling is impossible, benefiting from enhanced debris evacuation via cavitation.
Die and Mold Making	Manufacturing micro-molds and dies from hard materials, utilizing the die-sinking method for high efficiency without complex electrode compensation.

View Original Abstract

Die-sinking micro-electrical discharge machining (micro-EDM) is a potential method used to fabricate intricate structures without complex electrode motion planning and compensation. However, machining efficiency and poor discharge states are still bottlenecks. This study conducted a comparative investigation into the impact of ultrasonic vibration on die-sinking micro-EDM of polycrystalline diamond (PCD) and pure titanium (TA2). By adjusting discharge parameters, this study systematically evaluated the influence of ultrasonic vibration on these two materials based on discharge waveforms, motion trajectories, effective discharge counts and groove profiles. At an open-circuit voltage of 100 V, ultrasonic vibration promotes die-sinking micro-EDM of PCD. However, when the open-circuit voltage increases to 200 V, ultrasonic vibration exhibits inhibitory effects in general. Conversely, for TA2, ultrasonic vibration shows a promoting effect at both voltages, indicating the differences of ultrasonic vibration-assisted die-sinking micro-EDM on PCD and TA2. For PCD, ultrasonic cavitation improves the discharge gap environment, accelerating the removal of discharge debris. For TA2, due to its poor thermal conductivity, ultrasonic cavitation acts to break the arc, accelerating heat transfer. These research findings provide guidance for ultrasonic vibration-assisted die-sinking micro-EDM in industrial applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi15040434

References

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2021 - Multi-Variable Optimization in Die-Sinking EDM Process of Aisi420 Stainless Steel [Crossref]
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