Experimental investigation and thermal modeling on electro discharge drilling of PCD

At a Glance

Metadata	Details
Publication Date	2015-01-01
Journal	Lincoln (University of Nebraska)
Authors	Farnaz Nourbakhsh
Analysis	Full AI Review Included

Technical Documentation & Analysis: ED-Drilling of Polycrystalline Diamond (PCD)

This technical analysis evaluates the research concerning the Electro Discharge Drilling (ED-Drilling) and thermal modeling of Polycrystalline Diamond (PCD). This documentation highlights the demanding requirements of machining ultra-hard PCD and positions 6CCVD’s capabilities as the premier solution provider for high-performance PCD material used in advanced manufacturing processes.

Executive Summary

Application Focus: The study investigates the optimization of Material Removal Rate (MRR) for Polycrystalline Diamond (PCD) using high-speed Electro Discharge Drilling (ED-Drilling), a non-traditional machining method essential for ultra-hard materials.
Performance Drivers: Statistical analysis (ANOVA and Taguchi DOE) confirmed that Voltage, Pulse Current, and Spindle Speed (electrode rotation) are the most significant process parameters governing MRR.
Thermal Control: Finite Element Method (FEM) simulation using ANSYS identified pulse current as the major influencing factor in thermal analysis, directly governing the plasma channel size, temperature distribution, and subsequent material removal.
Productivity Enhancement: MRR was significantly improved by increasing voltage and pulse current, which enhances discharge energy, and by utilizing single-channel (tube) electrodes to improve dielectric fluid flushing efficiency.
Crater Geometry Insight: Thermal modeling predicted a single-spark crater geometry characterized by a greater dimension in radius (32 µm) than depth (22 µm), suggesting that heat loss effects lead to shallow crater formation.
Material Necessity: The research validates EDM as the most effective, low-cost, and flexible technique for fabricating intricate holes and features in high-performance PCD tool blanks.

Technical Specifications

Extracted physical properties of the Polycrystalline Diamond (PCD) workpiece and key process parameters used in the experimental and numerical analysis.

Parameter	Value	Unit	Context
Workpiece Material	Polycrystalline Diamond (PCD)	N/A	Sintered diamond layer (0.5 to 0.7 µm) on cemented carbide.
PCD Density (ρ)	4300	kg/m³	Property used in FEM thermal modeling.
PCD Thermal Conductivity (k)	400	W/m·K	Property used in FEM thermal modeling.
PCD Specific Heat (C_p)	512	J/kg·K	Property used in FEM thermal modeling.
Tested Voltage Levels (V)	40, 50	V	Found to be a significant parameter maximizing MRR.
Tested Pulse Current (I)	8, 13, 18	A	The major influencing parameter in thermal analysis.
Tested Pulse On-Time (t_on)	20, 30, 40	µs	Variables tested in L18 DOE.
Constant Pulse Off-Time (t_off)	30	µs	Held constant during optimization experiments.
Electrode Configuration	Solid & Single Channel (Tube)	N/A	Copper; Outer diameter 1.4 mm. Inner tube diameter 0.38 mm.
Max Recorded MRR (Single Channel)	2.973	mm³/min	Achieved under optimal conditions (50V, 18A).
Plasma Heat Input (P)	15	%	Assumed percentage of heat transferred to the PCD workpiece.
Single Spark Crater Dimensions	32 (Radius) vs. 22 (Depth)	µm	Modeled geometry favoring radial material removal.

Key Methodologies

The experimental and numerical approaches focused on optimizing cutting speed (MRR) by correlating electrical discharge parameters and thermal modeling results for PCD.

Workpiece Selection: Commercial Polycrystalline Diamond (PCD) blanks consisting of a diamond layer bonded to a cemented carbide substrate were used.
Machining Platform: Experiments were conducted using a standard ED-Drilling Hole Popper machine suitable for small hole EDM applications.
Dielectric and Flushing: De-ionized water was employed as the dielectric fluid, utilizing high-pressure flushing, a critical mechanism for debris removal and cooling in ED-Drilling.
Electrode System: Two types of copper electrodes (1.4 mm diameter) were tested: solid and single-channel (tube). The rotation of the electrode was employed to improve flushing efficacy.
Experimental Design: A Taguchi L18 Standard Orthogonal Array (DOE) was implemented to systematically investigate the effect of five process parameters at two or three distinct levels (Voltage, Spindle Speed, Pulse On-Time, Pulse Current, and Gap Size).
Performance Analysis: Material Removal Rate (MRR) was analyzed using the “Larger the Better” Signal-to-Noise (S/N) ratio methodology to identify optimal parameter settings that maximize cutting speed.
Thermal Modeling (FEM): A two-dimensional, axi-symmetric transient thermal model was developed using ANSYS finite element software (APDL 15.0). The model used a Gaussian heat flux distribution to simulate single spark discharge and predict temperature profiles and heat distribution along the radius and depth of the workpiece.

6CCVD Solutions & Capabilities

6CCVD provides the specialized MPCVD diamond materials and precision services necessary to replicate, control, and extend the high-precision ED-Drilling and Micro-EDM research presented in this paper.

Research Requirement / Challenge	6CCVD Solutions & Capabilities	Engineering Advantage for Our Customers
Material Sourcing & Consistency: Need for high-quality PCD suitable for demanding thermal machining applications (EDM).	Advanced MPCVD PCD Wafers: We supply Polycrystalline Diamond (PCD) sheets up to 125 mm diameter, offering superior purity and uniformity compared to traditional sintered blanks.	Predictable Machinability: High-quality MPCVD PCD ensures predictable thermal and electrical properties, essential for stable and repeatable EDM processes at high current/voltage levels.
Crater/Feature Precision: EDM machining creates shallow craters (32 µm radius, 22 µm depth); minimizing the Heat Affected Zone (HAZ) is critical.	Custom Thickness & Polishing: We offer SCD and PCD material in precise thicknesses (0.1 µm - 500 µm) and provide ultra-low roughness polishing (Ra < 5 nm for inch-size PCD).	Enhanced Surface Integrity: Starting with highly polished, thin diamond films allows researchers to maximize precision and minimize structural damage and residual stresses below the surface.
Thermal Modeling Input: Simulation requires precise material properties and controlled geometry.	Custom Substrates and Dimensions: We offer PCD attached to high-quality substrates (up to 10 mm) or free-standing films. Our custom dimensions accommodate unique experimental setups like those requiring specific electrode guides or high-pressure flushing systems.	Direct Model Integration: Access to custom-grown diamond materials with verified, specific thermal and electrical properties facilitates the development of more accurate FEM models like those conducted using ANSYS.
Electrode Wear Management: Testing requires efficient flushing mechanisms (e.g., tube electrodes) to manage material removal and electrode wear.	In-House Metalization Services: We offer custom metalization options (Au, Pt, Pd, Ti, W, Cu) on diamond surfaces. This capability can be leveraged for advanced electrode research or integrated workpiece contacts for specialized EDM setups.	Optimized Tooling/Workpiece Interfaces: Metalized layers can improve electrical contact or assist in flushing mechanisms, enabling novel electrode designs for complex ED-Drilling geometries.

Engineering Support

6CCVD’s in-house PhD-level engineering team specializes in the thermal, electrical, and mechanical properties of MPCVD diamond. We are prepared to assist researchers and engineers in selecting the optimal PCD or SCD grade—and appropriate dimensional specifications—required to maximize Material Removal Rate and geometric precision for similar Electro Discharge Drilling projects.

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

View Original Abstract

This study presents an experimental investigation and finite element simulation of Electro Discharge Drilling (ED-Drilling) of Polycrystalline Diamond (PCD). PCD has many outstanding properties including uniformly high hardness, high wear resistance and strong corrosion which are the main causes of widely using PCD. While PCD has many advantages and an important role in industrial applications, its high level of hardness and wear resistance cause this material to be difficult to form and machine by using traditional machining methods. EDM as a nontraditional machining process is an effective method among other non-traditional methods for PCDs due to its low cost and flexibility. The objective of this study is to investigate the effect of five process parameters including voltage, spindle speed, pulse on-time, pulse current and gap size on cutting speed on Material Removal Rate. A Taguchi L18 design of experiment (DOE) has been applied to optimize the number of trivals in order to save time and raw material. All experimental trials have been conducted using ED-Drilling Hole Popper machine. EDM process is a complicated process and it is very difficult to understand the mechanism which involves electrodynamics, thermodynamic and hydrodynamic. Hence to understand the process and to identify the effects of various process parameters, it is essential to model the process using a numerical method for analyzing and solving the ED-Drilling of PCD process. ANSYS (Computer simulation tool) finite element simulation has been applied to calculate the temperature distribution on the workpiece. The effect of current and pulse on-time in EDDrilling process on heat distribution along the radius and depth of the workpiece has been obtained. In experimental study, it is found that voltage, pulse current and spindle speed have the significant impact on MRR. By increasing these parameters, MRR was improved. Also in numerical simulation, by investigating the effects of pulse current and on-time, the results showed that current is the major influencing parameter in thermal analysis which is in an agreement with experimental result.\nAdvisor: Kamlakar Rajurkar

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Original Source

DOI: None