How EDM burn time is estimated
Sinker EDM time comes down to the volume you have to erode divided by the machine removal rate. This calculator multiplies the electrode projected area by the burn depth to get the volume, then applies time (hr) = volume (in³) ÷ MRR (in³/hr). The utilization figure divides that result so the estimate also covers flush stops, retracts and in-process gauging rather than pure spark time.
MRR is by far the most variable input. Electrode material (copper or graphite), peak amperage, on-time and flushing condition can swing it by more than an order of magnitude: a heavy roughing setting may run well above 1 in³/hr while a fine finishing orbit drops to a small fraction of that. Pull the numbers from the machine builder tech table and run each stage separately instead of using one blended rate.
Volumetric electrode wear is what sizes your spare electrodes and the extra length you leave on each one. Remember that the result is spark time only — setup, electrode changes, tool-length gauging and the switch from roughing to finishing all sit on top of it when you build a real quote or schedule.
Frequently asked questions
Not accurately. Roughing removes most of the volume quickly while finishing removes a thin allowance slowly, so split the volume and MRR by stage and add the times together.
With good flushing and reliable unattended running, 85 to 95% is realistic. Deep ribs or poor flushing that cause frequent arcing and retracts are closer to 60 to 80%.