---
title: "EDM principle and ECM metal removal rate"
subject: "Manufacturing and Production Processes"
chapter: 8
key: "semester_4/manufacturing_and_production_processes:edm-ecm-principle-mrr-numerical"
source: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/edm-ecm-principle-mrr-numerical
site: BCT Engineering
---

# EDM principle and ECM metal removal rate

Manufacturing and Production Processes · Chapter 8: Material Removal Processes: “Abrasive and Non-Traditional”

- Asked in: year not given, 4+4 marks
- Video: [ELECTRIC DISCHARGE MACHINING PROCESS (Animation): How electric discharge maching works](https://www.youtube.com/watch?v=kh4DSOtef4k) — ADTW Study
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/edm-ecm-principle-mrr-numerical
- Whole chapter: https://www.bctengineer.com/md/semester_4/manufacturing_and_production_processes/chapter-8

## Question

(a) Explain the working principle of electrical discharge machining (EDM) with a sketch. State its advantages and limitations. (b) Explain the principle of electrochemical machining (ECM). In ECM of pure iron (atomic weight 55.85, valency 2, density 7.86 g/cm$^3$) a current of 1000 A is used with a current efficiency of 90 percent. Calculate the volumetric material removal rate and the tool feed rate if the cross-sectional area of the machined cavity is 400 mm$^2$.

## Short answer

EDM uses pulsed spark between tool and workpiece in dielectric fluid, melting/vaporising material. ECM is anodic dissolution in electrolyte, governed by Faraday's law. For pure iron, MRR = 33.1 mm³/s (1.99 cm³/min) and feed rate = 4.97 mm/min for a 400 mm² cavity.

## Answer

#### (a) EDM

In **EDM**, the work and the shaped tool (electrode) are both immersed in a dielectric fluid (kerosene, transformer oil or deionised water) and kept a small gap apart (0.01-0.5 mm). A pulsed DC supply produces spark discharges across the gap; each spark generates a temperature of 8000-12000 degree C in a tiny spot, melting and vaporising a small crater in the work. The dielectric flushes out the debris and re-insulates the gap. A servo system keeps the gap constant as the tool advances, and the tool shape is reproduced in the work.

```text
   +---- pulse generator ----+
   |                         |
 tool (+/-)   spark gap    work (-/+)
   |__ dielectric fluid + flushing __|
          servo feed (down)
```

**Advantages:** machines any electrically conductive material regardless of hardness (hardened steel, carbide); produces complex cavities, dies and small deep holes; no cutting force and no burr; good accuracy.

**Limitations:** only conductive materials; slow metal removal; tool wear and a recast (heat-affected) layer; high power consumption; very sharp inside corners are not possible.

#### (b) ECM

In **ECM**, the work is the anode and the tool is the cathode. A low-voltage (10-20 V), high-current DC (current density about 20-200 A/cm$^2$, total current up to several thousand amperes) flows through a fast-flowing electrolyte (NaCl or NaNO$_3$ solution) in a gap of about 0.1-0.5 mm. The work metal dissolves according to **Faraday's law**, and the electrolyte carries the hydroxide sludge away. The tool does not wear.

By Faraday's laws, the mass removed per second is

$$
\dot{m} = \frac{\eta\,I\,A_w}{z\,F}
$$

Volumetric rate:

$$
\dot{V} = \frac{\eta\,I\,A_w}{z\,F\,\rho}
$$

with $A_w = 55.85$ g/mol, $z = 2$, $F = 96\,485$ C/mol, $\rho = 7.86$ g/cm$^3$, $\eta = 0.9$, $I = 1000$ A.

$$
\dot{V} = \frac{0.9\times1000\times55.85}{2\times96\,485\times7.86} = 0.0331\ \text{cm}^3/\text{s} = 33.1\ \text{mm}^3/\text{s}
$$

This equals $33.1\times60 = 1988\ \text{mm}^3/\text{min}$ (about 2.0 cm$^3$/min).

Tool feed rate for the cavity cross-section of 400 mm$^2$:

$$
v = \frac{\dot{V}}{A} = \frac{33.1}{400} = 0.0828\ \text{mm/s} = 4.97\ \text{mm/min}
$$

**Answer:** volumetric removal rate $= 33.1$ mm$^3$/s (1.99 cm$^3$/min); feed rate $= 4.97$ mm/min.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does EDM remove metal?
   A. The tool cuts by rotation in a dielectric
   B. Pulsed sparks across a gap in a dielectric melt and vaporise tiny craters
   C. Metal dissolves ions in electrolyte
   D. A steady arc melts the work
   Answer: B. Each spark reaches about 8000-12000 deg C; the dielectric flushes debris. (Key point: EDM principle)

2. Which is a limitation of EDM?
   A. It cannot machine hardened steel
   B. It produces cutting forces and burrs
   C. Only electrically conductive materials can be machined
   D. It cannot make complex cavities
   Answer: C. EDM works regardless of hardness but needs conductive work. (Key point: EDM limitation)

3. In ECM, which electrode is the work and what happens to the tool?
   A. Work is the cathode and tool wears
   B. Work is the anode and the tool wears quickly
   C. Work is melted by sparks
   D. Work is the anode and dissolves by Faraday's law; tool is the cathode and is not worn
   Answer: D. Metal ions dissolve from the anode in electrolyte flow. (Key point: ECM principle)

4. What is the volumetric removal rate in the iron problem?
   A. About 33.1 mm^3/s from eta I A_w/(z F rho)
   B. About 331 mm^3/s
   C. About 3.3 mm^3/s
   D. About 66 mm^3/s using z = 1
   Answer: A. 0.9 x 1000 x 55.85/(2 x 96485 x 7.86) = 0.0331 cm^3/s. (Key point: ECM removal rate)

## Related in Manufacturing and Production Processes

- [Hot and cold working; temperature and strain rate](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Ahot-cold-working-friction-strain-rate) — Manufacturing and Production Processes, chapter 5
- [Milling, shaper and drilling machine operations](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Amilling-shaper-drilling-machines-operations) — Manufacturing and Production Processes, chapter 7

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