Electric Discharge Machining (EDM)
Electric Discharge Machining (EDM)
Wire Electric Discharge Machining (WEDM)
0.25 mm brass wire, wire feed of 10 m / min, MMR of 25mm^3/min. For a 5 mm plate and assuming a 0.75 mm cutting slot, linear speed is 6.7 mm / min. If the slow width is 0.5 mm, linear speed is 10 mm / min. (ref link)
A 0.012″ (0.30 mm) wire typically creates a 0.016″ (0.41 mm) kerf. Minimum inside radius is 0.016″ (.016 mm), inside radius for 0.25 mm wire is 0.13 mm. Skim cuts can improve accuracy.
Commercial machines: 0.010″ OD brass wire you can expect a consistent, reliable wire EDM cutting speed of approximately eighteen to twenty inches/hour.
A 20 tooth gear with 1 mm teeth has a path length of 40 mm, requires 6 min and uses 60 m of wire, $0.25-$0.50.
EDM wire ranges in diameter from 0.0008 to 0.013 inch. A wire with a diameter of 0.0008 inch will produce a 0.00044-inch radius in a corner.
EDM wire is sold by the pound and typically comes in an 8-pound spool. Under normal cutting conditions, one spool will last eight to 10 hours of uninterrupted cutting.
Plain brass wire 0.010 inches in diameter is used in more than 80 percent of EDM work. Three types of brass wire exist: hard, half-hard and soft. Soft brass is typically used for cutting tapers because a low tensile strength is needed. This type can bend while cutting at an angle without breaking.
Hard brass is best for both roughing and skimming when higher tensile strength is desired. Hard brass withstands aggressive flushing and enables a high voltage to be applied to the wire without breaking. A faster cutting rate is the result.
Wire with a copper core and a defused zinc outer layer is often referred to as a high-speed wire, or stratified wire. The high electrical conductivity of copper enables doubling the cut speed. However, the price of the wire can be double that of other types. A stratified wire is recommended for roughing cuts. Plain copper wire is now rarely used because it is too soft and is too expensive.
Specifying the tensile strength of EDM wire is also important. Even though the wire does not touch the part during cutting, it is stretched by the machine’s wire drive feed mechanism, which consists of wire tensioner, roller guides, and upper and lower feed contacts (where the electric current is applied). Tension is preloaded onto the wire and can then be increased or decreased to accomplish different cutting techniques. Tensile strength determines the ability of the wire to withstand the tension imposed during cutting. The lower the tensile strength, the easier it is to break.
Wire with less tensile strength will cut angles without breaking. By displacing or offsetting the wire guides in the U-V axis, large tapers and angle cuts of up to 45 degrees can be generated. Wire with more tensile strength can be stretched more tightly when using the U-V axis to closely control the perpendicularity of vertical walls for precise cutting.
For roughing, lower wire tension enables the machine to cut faster without breaking the wire. Skim cuts require higher tension, so slower speeds and less power are applied to achieve maximum surface finish and precision.
Wire cost:
Hard Brass EDM Wire CuZn37 0.25mm 900n/mm 20,400yds, $182.
EDM HARD BRASS WIRE .010 X 6.6 LBS (6800m), $54
Circuit design
Very basic circuit:
1. Full-bridge + capacitor for smoothing.
2. Single MOSFET (Ton, Tperiod) for pulses.
3. Voltage and current sensor feed into control circuit.
4. Controller sends Ton to sequencer. Reads a Run input, V and A sensors. Saves / shows Vave and Aave, sends ‘Open or above max set voltage, advance movement’ or ‘Shorted, or below min set voltage, reverse movement’ signals.
MOSFET driver, MAX15070AAUT+T, $0.61
MODFET, SUP90220E, 200V, >30A – 50A continuous, low gate charge 20-50 nC, fast turn on/off < 50 ns, 3V minimum drive voltage, $2.60 / each. LTspice simulation: 1. 5us peaks in 20us period. Current peaks at 70A, with 25% duty cycle, average 10A – 15A. 2. Minimum input voltage to drive the MOSFET driver, about 65V peak to peak. 3. 
Bridge rectifier: 1kV, 50A (400A peak),TS50P07GD2G-ND, $2.35
add 250 mOhm resistor, PWR221T-30-R250F, 30W TO220, $2.93 to limit current or
SMD PWR163S-25-R200FE 200 mOhm 1% 25W, $3.07
Diode to prevent load ringing: SDUR6060W, 600V 60A TO247AC, $2.25 (expected load ~40A)
BOM:
Ref. Mfg. Part No. Description
C1 capacitor, 4.4mF, 200V
C2 capacitor, 0.33uF, 35V
C3 capacitor, 1nF, 30V
C4 capacitor, 100nF, 30V
U2 LM7805, $1.36
D1 Bridge rectifier: 1kV, 50A (400A peak),TS50P07GD2G-ND, $2.35
D5 DUR6060WT, 600V 60A TO247AC, $2.25
L1 inductor, 100nH, 1.9A pk
M1 MOSFET, SUP90220E, $2.60
R2 resistor, PWR221T-30-R250F, 250 mOhm, 30W TO220, $2.93
R3 resistor, 100 Ohm
R4 resistor, 100k Ohm
R5 resistor, 120 Ohm
R6 resistor, 10 Ohm
U1 MOSFET driver, MAX15070AAUT+T, $0.61
3 MAX15070AAUT+T-ND MAX15070AAUT+T IC MOSFET DRVR TTL SOT23-6 0.61000 $1.83
2 TS50P07GD2G-ND TS50P07G D2G BRIDGE RECT 1PHASE 1KV 50A TS-6P 2.35000 $4.70
2 GBU6D-BPMS-ND RECT BRIDGE GPP 6A 200V GBU 0.94000 $1.88
2 1655-1201-ND SDUR6060W DIODE GEN PURP 600V 60A TO247AC 2.25000 $4.50
1 PWR221T-30-R250F-ND PWR221T-30-R250F RES 0.25 OHM 30W 1% TO220 2.93000 $2.93
2 SUP90220E-GE3-ND SUP90220E-GE3 MOSFET N-CH 200V 64A TO220AB 2.95000 $5.90
2 PA2982.101HL FIXED IND 100NH 62A SMD 0.94000 $1.88
1 595-1754-1-ND SCIH1040HC-1R0M IND SMD 1.00UH 25A 200KHZ 1.05000 $1.05
2 296-44522-1-ND LM7812SX/NOPB IC REG LIN 12V 1.5A DDPAK 1.58000 $3.16
2 620-1794-1-ND ACS730KLCTR-50AB-T 1MHZ BANDWIDTH INTEGRATED, HALL 5.22000 $10.44
Current sensor
1. Based on TS507, following STEVAL-ISQ013V1 design and AN3222 application note.
Rshunt = 1-30 mOhms,
For 50A current, Rshunt = 1 mOhm, Rg = 100 Ohm, Rf = 10k Ohm, Cf = 16 pF
Power through shunt resistor, 4A^2*10mOhms – 50A^2*30mOhms = 0.16W – 2.5W
2. Based on ACS730KLCTR-50AB-T, 65A Hall effect, 40mV/A, 1MHz, $5.20
Full feature circuit:
1. Full-bridge LCsCp resonant converter. Uses a fast full bridge to pump LCsCp.
2. Add an extra MOSFET (Moff) to bleed charge off quickly.
3. Voltage and current sensor feed into control circuit.
4. Sequencer gets programmed by controller. Sends signals to H-bridge for PWM period–Ton of Tperiod. Reads current, if above current max (Amax), shuts off Ton period prematurely and turns on Moff.
5. Controller sends Ton, Tperiod, Amax to sequencer. Reads a Run input, V and A sensors. Saves / shows Vave and Aave, sends ‘Open or above max set voltage, advance movement’ or ‘Shorted, or below min set voltage, reverse movement’ signals.
Water purification
For these reasons, filters with a fineness smaller than 5μm are recommended.
Schuurman et al. developed a patented method for Philips for removing the iron and chromium compounds out of an aqueous solution in ECM. This method consists of the following steps (Schuurman and Faber, 1997; Altena, 2004):
1- Adding an excess of hydrogen peroxide based upon the amount of chromium present to the solution and, if necessary, adapting the acidity of the solution so that the pH value of the solution is ≥ 7;
2- Separating the iron hydroxide formed;
3- Adapting the acidity of the solution so that the pH value of the solution is < 4; 4- Adapting the acidity of the solution so that the pH value of the solution is ≥ 7; 5- Separating the chromium hydroxide formed. Water pump: KEDSUM 550GPH Submersible Pump(2500L/H,40W), 40W, 5 ft lift, $17 The usual range of pressure used is between 0.1 to 0.4 kgf/cm (3-12 ft of lift). Filter: 5 um filter, NW-19 EDM FILTER 150X33X375 mm for Charmilles, AGIE, AMADA, $37. 5 um Pre-Filter A406 Wire EDM Single Column DI System, $20 Water deionization: Deionization Water Filter Replacement – RO DI Mixed Bed Purifier – Inline 2 Pack, 10″x2.5″, $38 References
Prototype machine for micro-EDM
MANUFACTURING OF HIGH QUALITY MINIATURE GEARS BY WIRE ELECTRIC DISCHARGE MACHINING
Fixed parameters: Wire material: brass; Wire diameter: 0.25 mm; Wire tension: 1200 grams, Dielectric: de-ionized water; Dielectric conductivity: 20 μS/cm; Dielectric pressure: 7 kg/cm2
Optimiszed parameters: optimum ranges of voltage (6-8 V), pulse-on time (0.6-0.7 μs), pulse-off time (150-160) and wire feed rate (12.5-14.5 m/min)
RC and pulsed driven EDM plans
Reprap forum discussion of EDM machines, project and circuit
Jon Elson’s Machining Page: A Mini-EDM System
Yahoo EDM forum
Basic EDM Instructable
Final Project: The Garden of EDM
Pulsed circuit design with voltage / current sensing
Hey…What’s the BIG idea? EDM design
Wire EDM for the Home Shop
Sink EDM for the Home Shop
EDM Electrodes Repurposed As Air Bearings
A study on the machining of high-aspect ratio micro-structures using micro-EDM
, pdf
Micro-EDM for Three-Dimensional Cavities – Development of Uniform Wear Method, pdf
Not Your Father’s EDM, hackaday IO, website, github
The Home Built EDM Machine
Electrical Efficiency of EDM Power Supply, pdf
Includes circuit Psplice model.
Performance of a Low Cost Tabletop Die Sinker Electric Discharge Machining [EDM] Unit, pdf
Study on volt-ampere characteristics of spark discharge for transistor resistor pulse power of EDM, pdf
Design, analysis and experimental study of a high-frequency power supply for finish cut of wire-EDM, pdf
Developments in electric power supply configurations for electrical-discharge-machining (EDM), pdf
Research on Highly Efficient EDM Pulse Power Supply and Its Experiments, pdf
A Technical Report on Design of a transistor based pulse generation circuit for Electrical Discharge machine, pdf
Development of Electrical Discharge Machining System for Cutting Single Crystal SiC, pdf
Series–parallel resonant converter for an EDM power supply, pdf
Good circuit description.
Books
Build an EDM – Electrical Discharge Machining – Removing Metal by Spark Erosion by Robert P. Langlois, $18
The EDM How-To Book, by Ben Fleming, pdf
Theses / Dissertations
Digital control of an electro discharge machining (EDM) system. Dissertation by Azli Yahya, pdf
MICRO ELECTRO-DISCHARGE MACHINING: TECHNIQUES AND PROCEDURES FOR MICRO FABRICATION by Christopher James Morgan, pdf
EFFECTS OF MACHINING CHARACTERISTICS ON ELECTRIC DISCHARGE MACHINE USING DIFFERENT ELECTRODE MATERIALS by MOHD KHAIRUL ANUAR BIN MOHD IDRIS, pdf
MONITORING AND CONTROL OF MICRO-HOLE ELECTRICAL DISCHARGE MACHINING by Chen-Chun Kao, pdfro Electrical Discharge Machining: Axis-symmetric component manufacture and surface integrity by Andrew Rees, pdf
Meso – Micro EDM by Maradia, Umang, pdf
An investigation and analysis of Process Parameters for EDM Drilling machine using Taguchi method by Popat, Mitesh A., 2011, pdf
Development of an Electrochemical Micromachining (μECM) machine by Alexandre SPIESER, pdf
Design for EDM
carabiner clip
Costs
tubing 1/4″, 3/8″, $11
hose clamps, $6
brass adapter, $3
tubs, $4
Yosoo 12pcs Plastic Flexible Water Oil Coolant Pipe Hose CNC 1/4″ + Switch, $17
KEDSUM 550GPH Submersible Pump(2500L/H,40W), $14.50
ATmega328P, $7.50
Consumables:
2 gal distilled, $2.50
Flat Wire Stainless Steel 0.001″x 5000ft, $9
PRE-FILTER FOR DI TANK FOR WIRE EDM MACHINE, 5 filters, $20
Nema 17 Stepper Motor 45Ncm(64oz.in) 2A 42x42x40mm 4-wire w/1m Cable & Connector, 3 ea., $22
5Pcs A4988 Stepper Motor Driver, $8.50
ASEK730, 3 PCBs, $27
Basic circuit, 10 PCBs, $15
Parts for very basic circuit and ASEK730 current monitor, $48
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Total $152
z-axis. 10 mm / revolution, 200 steps / revolution = 50 um / step.
Distilled water, fresh, ~0.8-1.5 MOhm / cm
Other projects
Not Your Father’s EDM
Archive for EDM
BAXEDMDIY Wire EDM Machine, youtube
ACS730 – Current Sensor Sensor Evaluation Board
High Voltage Switching With MOSFETs