Resistance spot welding — electrode tip sizing For resistance spot welding of sheet metal, the recommended electrode tip face diameter d is taken approximately as which multiple of the sheet thickness t?

Introduction / Context:
Electrode tip face diameter in resistance spot welding must be sized to deliver the required current density and contact area to form a sound nugget without causing excessive indentation or expulsion. Simple thumb rules relate the tip diameter to the sheet thickness for rapid shop-floor selection.

Given Data / Assumptions:

• Single-sheet thickness t (mm) for lap joints in typical steels.
• Standard copper alloy electrodes with flat or slightly domed tips.
• Empirical rule-of-thumb sizing for general-purpose work.

Concept / Approach:
Too small a tip face concentrates current excessively, risking expulsion and deep indentation; too large a tip spreads current, making nugget formation difficult and increasing heat input. A commonly cited practical rule is to take the tip face diameter d around 6 t for thin to moderate sheet gauges, balancing current density and contact resistance to produce a proper weld nugget.

Step-by-Step Solution:
Define requirement: choose d to achieve adequate nugget with minimal indentation.Apply rule-of-thumb: d ≈ 6 * t for general sheet thicknesses.Check reasonableness: as t increases, larger d maintains appropriate current density.Therefore, the recommended approximation from the options is 6 t.

Verification / Alternative check:
Process charts from welding practice often give ranges; some references relate nugget diameter to 5 * sqrt(t) and select tip size accordingly. The 6 t rule serves as a simple, conservative guideline where detailed charts are unavailable.

Why Other Options Are Wrong:
t and 1.5 t produce very small contact areas causing overheating/expulsion; 3 t may suit very thin sheets but is generally small; 0.5 t is clearly inadequate.

Common Pitfalls:
Confusing nugget diameter rules with electrode face diameter; although related, they are not identical and are chosen to achieve stable heat generation and nugget growth.

Final Answer:
6 t