EDM Pulse Generator Line Discharge Without Impedance Matching
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Solution Overview
Problem
Existing EDM pulse generators are unsuitable for medium-machining accuracy due to issues like impedance mismatch, high electrode wear, inefficient energy transfer, and thermal deformation, which hinder precise machining between rough-machining and fine-machining.
Innovation Solution
A method and apparatus for generating machining pulses by charging a line via a voltage source and discharging it directly via a diode without impedance matching, incorporating parasitic elements to achieve high-efficiency, monopolar pulses with increased current amplitude and reduced delay, suitable for medium-machining applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If impedance matching is used with terminal resistors and coaxial cables, then energy transfer efficiency is improved, but the system becomes sensitive to stray inductance and capacitance causing reflections and bipolar pulses
Solution Approach 1:
The patent removes the impedance matching resistors from the circuit. Instead of using terminal resistors ZA and ZB for impedance matching, the invention directly connects the coaxial cables to the spark gap, eliminating the source of reflections and bipolar pulse formation while maintaining energy transfer efficiency through direct discharge.
Solution Approach 2:
The patent inverts the conventional approach by not matching impedance but deliberately using impedance mismatch. The coaxial cables are designed with specific impedance (50Ω or 75Ω) that does not match the spark gap impedance, but this mismatch is compensated by the distributed capacitance of the cables themselves, transforming the harmful reflection into a useful energy storage mechanism.
2Stress or pressure
If charged coaxial cables are used to generate high voltage pulses, then pulse amplitude is improved, but DC voltage is applied to the working gap causing sparkout when the spark gap is too large
Solution Approach 1:
The patent employs periodic pulsed discharge instead of continuous DC voltage. The coaxial cables are charged to high voltage and then discharged in controlled pulses through the spark gap. The periodic nature of the discharge, combined with the distributed capacitance of the cables, ensures that voltage is applied only during the discharge phase, preventing continuous DC stress that would cause sparkout.
Solution Approach 2:
The patent changes the temporal characteristics of voltage application from continuous DC to pulsed AC. By controlling the charging and discharging cycles of the coaxial cables, the system applies high voltage only during the necessary discharge intervals, transforming the harmful continuous DC stress into beneficial periodic pulses that eliminate sparkout while maintaining high voltage amplitude.
3Device complexity
If terminal resistors are used for charging and discharging coaxial cables, then pulse generation is simplified, but power loss is very high (e.g., 100 kW at 100 A and 10Ω cable impedance)
Solution Approach 1:
The patent removes the terminal resistors ZA and ZB from the circuit entirely. Instead of using resistive discharge through terminal resistors, the invention uses the inherent distributed capacitance of the coaxial cables themselves as the energy storage element, eliminating the need for external resistors and the associated I²R power losses.
Solution Approach 2:
The patent uses the distributed capacitance of the coaxial cables as an intermediary energy storage element. Rather than directly discharging through resistors, the cable capacitance stores energy and releases it in controlled pulses, acting as a mediator between the voltage source and the spark gap, thereby eliminating resistive power loss while maintaining circuit simplicity.
4Duration of action of moving object
If coaxial cables are used for medium-length pulses, then pulse duration control is improved, but the cables must be accommodated on the machine which is unpractical for longer pulses
Solution Approach 1:
The patent makes the pulse duration dynamically adjustable by changing the physical length of the coaxial cables. Instead of using fixed-length cables with electronic control circuits, the invention allows direct adjustment of cable length to achieve different pulse durations, transforming a static system into a dynamically adaptable one that is both simple and effective.
Solution Approach 2:
The patent changes the physical parameter of cable length to control pulse duration. By varying the length of the coaxial cables, the system directly adjusts the time constant of the RC circuit formed by the cable capacitance and the spark gap resistance, providing a simple and effective method for pulse duration control without complex electronics or accommodation issues.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables faster, more accurate, and less material-damaging EDM processes, capable of machining hard and high-melting materials with improved surface finish and reduced thermal stress, suitable for medium-machining range with surface roughness between 0.15 μm to 0.8 μm.
Implementation Method 1
charging the line via a first charging circuit by a voltage source
Implementation Method 2
discharging the line after ignition of the spark gap directly via a diode
Implementation Method 3
after ignition of the spark gap
Data Source
AI summary
An apparatus and a method of generating machining pulses for electrical discharge machining by discharge of at least one line applying a voltage to a working gap formed between a machining electrode and a workpiece, including the steps of: charging the line via a first charging circuit by a voltage source, discharging the line after ignition of the spark gap directly via a diode, without impedance matching, at the working gap, and recharging the line after a predefined pulse-off time.