Adjust the discharge settings of die-sinking electrical discharge machining (EDM) and see how fast the process removes metal. Changing the peak discharge current, pulse on/off time and discharge voltage updates the duty cycle, pulse energy, material removal rate and surface roughness in real time, so you can feel the trade-off between machining speed and surface finish.
Parameters
Peak discharge current I
A
Peak current flowing during one discharge
Pulse on-time t_on
µs
Time the discharge lasts within one cycle
Pulse off-time t_off
µs
Rest interval for debris flushing and insulation recovery
Discharge voltage V
V
Gap voltage during the discharge
Results
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Duty cycle
—
Energy per pulse (J)
—
Discharge frequency (Hz)
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Average discharge power (W)
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Material removal rate MRR (mm³/min)
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Surface roughness Ra (estimate) (µm)
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EDM in action — sparks and craters
Submerged in dielectric fluid, sparks jump the tiny gap between the shaped electrode and the workpiece, cutting microscopic craters into the surface. Molten metal debris is flushed away by the flowing dielectric.
Material removal rate MRR vs peak discharge current I
The duty cycle is the fraction of time the spark is on, and the pulse energy E_pulse is the energy each spark delivers (t_on converted to seconds). The material removal rate MRR is proportional to the discharge current I and the duty cycle. Raising the current and duty cycle speeds up removal, but coarsens the surface finish because each crater grows larger.
What is Electrical Discharge Machining (EDM)?
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I heard EDM cuts metal with sparks, like little bolts of lightning. Is that real? It doesn't use a cutting tool at all?
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It's real. EDM stands for Electrical Discharge Machining, and there is no cutting edge anywhere. What it does is simple: you take the shaped "electrode" and the "workpiece", submerge them both in a dielectric fluid (an insulating liquid), and bring them very close together. Apply a voltage, and thousands of times per second a tiny electrical spark jumps the gap. Each spark is many thousands of degrees hot — it melts and vaporises a microscopic crater of metal. Repeat that at a furious rate and you carve out the shape.
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Cutting with sparks... so it can machine really hard metal too?
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That's the most remarkable part of EDM. The only thing touching the workpiece is the spark — there is zero pressing force, no cutting force at all. So it does not care how hard the material is. Fully hardened tool steel, tungsten carbide, heat-resistant superalloys — materials that defeat milling cutters and drills — EDM machines them just as easily as soft metal. And it reaches places a rotating tool never can: sharp internal corners, deep narrow slots, intricate die cavities. That is why mould makers cannot do without it.
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That all sounds great. Doesn't it have a weakness?
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It does — in one word, speed. Try raising the "peak discharge current" with the slider on the left. The material removal rate MRR climbs and machining gets faster. But notice the "surface roughness Ra" gets worse at the same time. That is the fundamental trade-off of EDM. A larger current or on-time means each spark digs a bigger crater. Bigger craters remove metal faster, but they leave a rougher surface.
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So speed and finish can't both be good. How do machinists deal with that on the shop floor?
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They do it in two stages. First, with a high current and long on-time, they cut the shape quickly — that is "roughing". Then they progressively reduce the current and on-time to smooth the surface — that is "finishing". Rough to save time, finish to make the surface clean — knowing how to switch between them is the real skill of EDM. The off-time matters too: cut it too short and debris stops being flushed away, the spark degenerates into a continuous arc, and both electrode and workpiece get burned. Balancing speed against stability is the machinist's job.
Frequently Asked Questions
This tool uses an empirical model for steel: MRR = Km·I·duty. Km is the material removal constant (about 6.0 mm³/(min·A) for steel), I is the peak discharge current and duty is the duty cycle t_on/(t_on+t_off). MRR is proportional to both the discharge current and the duty cycle. For I=20 A, t_on=100 µs and t_off=50 µs, duty=0.667 and MRR=6.0·20·0.667 ≈ 80 mm³/min. The real removal rate also depends on dielectric contamination, electrode material and flushing, so treat this tool as a trend estimate.
The duty cycle is duty = t_on/(t_on+t_off), the fraction of each cycle during which the spark is on. Raising the duty cycle (shortening the off-time) increases the average discharge power and the material removal rate, so machining gets faster. But the pulse off-time is the rest interval the dielectric fluid needs to flush away the metal debris from the discharge and recover its insulation. Cut it too short and debris is not removed, the process collapses into a continuous arc (abnormal discharge), and both the electrode and the workpiece are burned. The off-time is chosen to balance speed against process stability.
EDM removes metal one tiny crater at a time, one crater per spark. Increasing the discharge current and the pulse on-time raises the discharge energy per pulse, so each crater becomes larger and deeper. Larger craters mean faster machining (higher MRR), but they also leave a coarser surface, so the surface roughness Ra gets worse. This tool estimates roughness with the empirical model Ra = 0.85·(I·t_on)^0.33. That is why, in practice, you machine quickly with a high current and long on-time for roughing, then progressively reduce the current and on-time for the smooth finishing passes.
The defining strength of EDM is that the electrode never touches the workpiece and there is no cutting force, so it machines metal regardless of hardness. It excels at hard-to-cut materials such as fully hardened tool steel, tungsten carbide and heat-resistant superalloys that wear down milling cutters and drills. It also produces sharp internal corners, deep narrow slots and intricate die cavities that no rotating tool can reach. Because EDM is slower than conventional cutting, it is most valuable for dies, fixtures and prototype parts that are hard, complex and produced in small quantities.
Real-World Applications
Die and press-tool manufacturing: The mould and die industry is where EDM shines. Plastic injection-mould cavities, press-tool punch dies and die-casting dies all require complex shapes cut into hardened tool steel. Die-sinking EDM transfers the shape of a copper or graphite electrode directly into the workpiece, reaching deep rib slots and sharp corners that milling cannot. The standard flow is to rough out the form first, then smooth the surface to a near-mirror finish with finishing passes.
Machining hard-to-cut materials and carbide: Tungsten carbide, heat-resistant superalloys (such as Inconel) and titanium alloys quickly wear down milling cutters and drills because of their hardness and toughness. Since EDM is indifferent to workpiece hardness, it machines these difficult materials reliably. It is also applied to cooling holes in aero-engine parts and turbine blades.
Precision machining of fine holes and complex profiles: Wire EDM uses a thin metal wire as the electrode to cut intricate contours like a scroll saw — profiles of gears, cams and blanking dies. Small-hole EDM produces the micro-holes of fuel-injection nozzles. It can machine inward-pointing acute corners and very narrow slots that are physically impossible for a rotating tool.
Pre-study of machining conditions and education: A simple calculation like this tool shows in advance how the material removal rate and surface roughness move when you change the discharge current and on/off time. It helps you get a first read before settling on roughing and finishing conditions, and serves as teaching material for understanding EDM principles — a way to build intuition before condition-setting on the real machine.
Common Misconceptions and Pitfalls
The biggest misconception is that "the higher the current and on-time, the faster you can machine". It is true that the material removal rate rises with the discharge current and the duty cycle, but not without limit. Push the current or on-time too high and the energy each discharge delivers becomes excessive, so electrode wear shoots up. If the electrode that defines the shape is itself eroded, you do not get the form you wanted. The workpiece surface also ends up with a thick recast (white) layer and micro-cracks, harming downstream processes and fatigue strength. Do not chase speed alone — decide the conditions with electrode wear and surface quality in view.
Next, the assumption that "the pulse off-time is wasted idle time, so shorter is better". The off-time is time when no machining happens, so shortening it raises the duty cycle and speeds up the process. But the off-time is essential for the dielectric fluid to flush the debris (molten metal particles and carbon) out of the gap and recover its insulation. Trim the off-time too far and debris accumulates, leading to a "continuous arc" (abnormal discharge) where sparks fire repeatedly at the same spot. When that happens, both the electrode and the workpiece burn locally, the machined surface degrades, and in the worst case machining stops altogether. Securing enough off-time, together with good flushing conditions, is essential.
Finally, the misconception that "the numbers from this tool are the machining speed of the real machine". The material removal rate and surface roughness here are estimates from empirical models assuming steel. The real MRR and roughness depend on the workpiece material and thermal properties, the electrode material (copper, graphite, copper-tungsten), the polarity, the type and contamination of the dielectric, the quality of flushing, the machined area, the servo control of the discharge and much more. This tool is an educational aid for understanding trends and physics — "raising the current increases removal and roughens the surface", "shortening the off-time raises the duty cycle". Always confirm real-machine conditions with the machine maker's condition tables and trial cuts.
How to Use
Set Peak Current (curNum) between 5–500 A using the curRange slider to control spark intensity and crater depth.
Adjust Pulse-On Time (onNum) in microseconds (typically 1–200 µs) to control single-pulse energy and material ejection volume.
Set Pulse-Off Time (offNum) in microseconds (typically 5–500 µs) to allow dielectric fluid recovery between discharges.
Define Open Circuit Voltage (voltNum) between 40–300 V to establish the gap breakdown threshold.
Observe real-time outputs: duty cycle percentage, energy per pulse in joules, discharge frequency in Hz, average power in watts, MRR in mm³/min, and surface roughness Ra estimate in micrometers.
Worked Example
For roughing a hardened tool steel die (60 HRC) using EDM: Set peak current to 200 A, pulse-on time to 100 µs, pulse-off time to 80 µs, and voltage to 200 V. Duty cycle = 100/(100+80) = 55.6%. Energy per pulse ≈ 0.2 × 200 × 100×10⁻⁶ = 4 J. At discharge frequency of 5 kHz, average power reaches ~20 kW and MRR approximately 45 mm³/min with Ra surface finish around 3.2 µm—acceptable for pre-finishing operations.
Practical Notes
Increase pulse-on time for faster MRR on graphite electrodes, but expect Ra > 5 µm; reduce to 50 µs for finishing steel molds with Ra < 1.6 µm.
Higher duty cycle (short pulse-off) risks flushing problems and unstable gap in tight cavities; maintain 40–60% for precision die-sinking with small electrodes.
Peak current above 300 A generates excessive heat on tungsten-copper electrodes, causing rapid wear; use servo-controlled voltage to maintain 20–50 µm gap stability.
Carbon electrodes tolerate 150 A continuously; copper electrodes require active flushing above 200 A to prevent arcing and surface oxidation defects.