Electro-chemical machining (ECM): What is the typical inter-electrode gap maintained between tool and work?

Introduction / Context:
Electro-chemical machining removes material by anodic dissolution, with the workpiece as anode and the tool as cathode in a flowing electrolyte. Maintaining a proper inter-electrode gap is vital for stable current density, accurate shape replication, and removal of reaction products (sludge and gas).

Given Data / Assumptions:

• Typical aqueous electrolyte (e.g., NaCl, NaNO3) with high flow rate.
• Moderate current densities and standard tool feed controls.
• Production ECM, not micro-ECM or macro-roughing extremes.

Concept / Approach:
Practical ECM gaps are small to achieve good accuracy yet large enough to prevent arcing and ensure debris flushing. A commonly cited nominal gap is about 0.25 mm for many setups. Larger gaps reduce accuracy and voltage efficiency; smaller gaps risk shorting and clogging without very precise control and high flushing velocity.

Step-by-Step Solution:

Verification / Alternative check:
Process handbooks list 0.2–0.5 mm as common; 0.25 mm is a frequently used nominal value in general-purpose ECM tooling.

Why Other Options Are Wrong:

• 0.10 mm: possible in specialized micro-ECM, but risky in general practice.
• 0.40–0.75 mm: workable but tends to reduce accuracy and efficiency.
• 1.50 mm: excessively large for normal ECM, leading to poor control.

Common Pitfalls:
Ignoring electrolyte cleanliness and flow; forgetting that gap varies dynamically with feed and voltage; using too small a gap causing shorts.

Final Answer:
0.25 mm