KEVOS® MAKEOS · Manufacturing
EDM Sinker Plan (Current for the Electrode, Duty Cycle, Roughing and Finishing Time, Electrode Wear and Sizes)
For sinking a cavity by EDM, what current suits the electrode, how long will roughing and finishing take, how many roughing electrodes will wear out, what size must they be, and what does the cavity cost?
Plan for die-sinking EDM of a straight-walled cavity: the roughing current from the electrode face area and your current density against the machine limit, the duty cycle and spark frequency from the on and off times, the volume left for finishing on the walls and floor and the roughing volume, roughing and finishing times from the removal rates for your settings, the end wear of the roughing electrode from its linear wear and the number of roughing electrodes needed to keep each within your limit, the undersize of the roughing and finishing electrodes from the overcut and finishing stock, and the machine and electrode cost, with a check that the finishing stock covers the damaged layer left by roughing.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Cavity | ||
| Electrode face (projected) area | cm² | Area of the electrode face seen along the direction of sinking, which carries the roughing current. |
| Cavity depth | mm | Depth of the cavity to be sunk. |
| Cavity perimeter | mm | Length around the cavity walls, used for the finishing stock on the walls. |
| Finishing stock left on each wall and the floor | mm | Material left on each wall and on the floor by the roughing electrode for the finishing electrode to remove. |
| Roughing | ||
| Current density on the electrode face | A/cm² | Roughing current per unit of electrode face area for graphite or copper electrodes, from the machine maker's guidance. |
| Machine maximum current | A | Largest current the EDM generator can deliver. |
| On time | µs | Time the current is on in each spark cycle. |
| Off time | µs | Time the current is off in each spark cycle, which lets the dielectric clear and recover. |
| Roughing removal rate at these settings | cm³/h | Volume of work removed per hour at your roughing settings, from the machine maker's technology tables or your own records. |
| Roughing electrode end wear as a share of depth cut | % | Loss of electrode length as a share of the depth sunk at the roughing settings, from the maker's tables. |
| Roughing overcut on each side | mm | Gap left on each side between the roughing electrode and the cavity wall. |
| Damaged layer left by roughing (craters and recast) | mm | Depth of craters, recast layer and heat-affected zone left by roughing, which finishing must remove. |
| Largest end wear accepted on one roughing electrode | mm | Most an electrode may wear at its end before it is replaced by a fresh one. |
| Finishing | ||
| Finishing removal rate | cm³/h | Volume removed per hour at your finishing settings. |
| Finishing overcut on each side | mm | Gap left on each side between the finishing electrode and the cavity wall. |
| Cost | ||
| Machine rate | A$/h | Charge-out rate for the EDM machine. |
| Cost of one finished electrode | A$ | Cost to make one electrode, including material and machining. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Cavity
What this means: Electrode face (projected) area
- What it is
- The area of the electrode face seen looking along the direction of sinking, which carries the spark current while roughing.
- Units and format
- Enter a number in cm²: square centimetres. The form accepts 0.000001 cm² to 100000 cm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 cm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The roughing current and the cavity volume rise in proportion.
- Get it right
- Use the area actually engaged in the cut, not the electrode shank or holder.
What this means: Cavity depth
- What it is
- How deep the electrode must sink to form the cavity.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Volume, time and electrode wear all rise with depth.
- Get it right
- Measure from the work surface to the cavity floor on the drawing.
What this means: Cavity perimeter
- What it is
- The length around the cavity walls, used to work out the finishing stock left on the walls.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer perimeter leaves more wall stock for the slow finishing pass.
- Get it right
- Take it from the CAD outline of the cavity at its finished size.
What this means: Finishing stock left on each wall and the floor
- What it is
- The material the roughing electrode leaves on each wall and on the floor for the finishing electrode to remove.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.2 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More stock means more slow finishing time and smaller roughing electrodes.
- Get it right
- Make it slightly more than the depth of the craters and recast left by roughing, and no more.
Roughing
What this means: Current density on the electrode face
- What it is
- The roughing current carried by each square centimetre of electrode face.
- Units and format
- Enter a number in A/cm²: A/cm². The form accepts 0.01 A/cm² to 100 A/cm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 A/cm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The roughing current rises in proportion; too much overheats the work.
- Get it right
- The handbook gives a rule of 50 to 65 A per square inch (about 8 to 10 A/cm²) for graphite and copper; use less for thin or detailed electrodes.
What this means: Machine maximum current
- What it is
- The largest current the EDM generator can deliver to the gap.
- Units and format
- Enter a number in A: amperes. The form accepts 0.000001 A to 10000 A. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 A as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the current pass line.
- Get it right
- Read it from the machine's specification plate or manual.
What this means: On time
- What it is
- The time the current flows in each spark cycle, during which metal is removed.
- Units and format
- Enter a number in µs: µs. The form accepts 0.01 µs to 100000 µs. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 µs as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the duty cycle and lowers the spark frequency.
- Get it right
- Longer on times rough faster but leave deeper craters; take it from the machine's tables.
What this means: Off time
- What it is
- The time the current is off in each spark cycle, while the dielectric clears the debris and recovers.
- Units and format
- Enter a number in µs: µs. The form accepts 0.01 µs to 100000 µs. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 µs as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A shorter off time raises the duty cycle and the spark frequency.
- Get it right
- Shorten it in small steps only while machining stays stable.
What this means: Roughing removal rate at these settings
- What it is
- The volume of work metal removed per hour at your roughing settings and electrode material.
- Units and format
- Enter a number in cm³/h: cm³/h. The form accepts 0.000001 cm³/h to 10000 cm³/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 cm³/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Roughing time falls in proportion as the rate rises.
- Get it right
- Take it from the machine maker's technology tables or from your own records of similar jobs.
What this means: Roughing electrode end wear as a share of depth…
- What it is
- How much the roughing electrode shortens, as a share of the depth it sinks.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More wear means more roughing electrodes for the same depth.
- Get it right
- Take end wear from the maker's tables for the electrode material, polarity and settings.
What this means: Roughing overcut on each side
- What it is
- The gap left on each side between the roughing electrode and the cavity wall after roughing.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.25 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The roughing electrode must be made smaller by this amount on each side.
- Get it right
- Take it from the machine's tables; it grows with current and on time.
What this means: Damaged layer left by roughing (craters and rec…
- What it is
- The depth of craters, recast layer and heat-affected metal that roughing leaves on the surface.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the finishing stock pass line.
- Get it right
- Use the maker's data for your roughing settings or section a test cut.
What this means: Largest end wear accepted on one roughing elect…
- What it is
- The most a roughing electrode may wear at its end before a fresh one takes over.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller allowance calls for more roughing electrodes.
- Get it right
- Set it from the floor accuracy and corner detail the cavity needs.
Finishing
What this means: Finishing removal rate
- What it is
- The volume of work metal removed per hour at your finishing settings.
- Units and format
- Enter a number in cm³/h: cm³/h. The form accepts 0.000001 cm³/h to 10000 cm³/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 cm³/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Finishing time falls in proportion as the rate rises.
- Get it right
- Take it from the maker's tables for the finish you need; it is much lower than the roughing rate.
What this means: Finishing overcut on each side
- What it is
- The gap left on each side between the finishing electrode and the cavity wall.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.05 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets how much smaller than the cavity the finishing electrode is made.
- Get it right
- Take it from the machine's tables for the finishing settings.
Cost
What this means: Machine rate
- What it is
- The hourly charge-out rate for the EDM machine, including the operator share and overheads.
- Units and format
- Enter a number in A$/h: A$/h. The form accepts 0 A$/h to 100000 A$/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90 A$/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The machine cost rises in proportion.
- Get it right
- Use your shop's costing rate for this machine.
What this means: Cost of one finished electrode
- What it is
- The cost of making one electrode, including the graphite or copper and the machining.
- Units and format
- Enter a number in A$: A$. The form accepts 0 A$ to 1000000 A$. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 A$ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each extra roughing electrode adds this to the cost.
- Get it right
- Use your electrode shop's cost for an electrode of this size and detail.
Method and formulas
- Roughing current = current density × electrode face area, against the machine maximum.
- Duty cycle = on time ÷ (on time + off time); spark frequency = 1 ÷ (on time + off time).
- Cavity volume = face area × depth; finishing volume = stock × (perimeter × depth + face area); roughing volume = cavity − finishing volume.
- Times = volume ÷ removal rate for roughing and finishing.
- Roughing end wear = wear share × (depth − stock); roughing electrodes = end wear ÷ the largest accepted wear, rounded up.
- Roughing electrode undersize on each side = overcut + finishing stock; finishing electrode undersize = finishing overcut.
- Cost = total time × machine rate + (roughing electrodes + 1) × electrode cost.
- Example: 48 A on the 6 cm² electrode; roughing takes 1.43 h and finishing 0.42 h, with 2 roughing electrodes, about A$616.5 for the cavity.
Limitations
- A straight-walled cavity of constant section; tapers, ribs and detail need their own electrodes and settings.
- Removal rates, wear and overcut come from your machine's tables for the electrode and work materials; this plan does not predict them.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Plan the electrodes and machine time for an EDM cavity
- Size roughing and finishing electrodes for overcut and finishing stock
- Estimate the cost of a sunk cavity for a quote
Who it is for
- Toolmakers
- Mould and die makers
- Manufacturing engineers
What you get
- Roughing current, duty cycle and spark frequency
- Roughing and finishing volumes and times
- Roughing electrode end wear and number of electrodes
- Electrode undersize for roughing and finishing
- Machine, electrode and total cost
Interpreting the result
- Finishing removes metal far more slowly than roughing, so leave only enough stock to clear the damaged layer.
- Electrode wear is usually the hidden cost: one electrode per wear allowance, plus a finisher.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1394–1399. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Method explained here · Library collection
EDM, micromachining and other non-traditional processes: when cutting tools are not the answer
What it covers: How wire and sinker EDM work, what they can and cannot do, the recast layer, other non-traditional processes such as ECM, etching and ultrasonic machining, and the challenges of very small features.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.