Design guidelines for resistance spot welding The minimum recommended pitch (center-to-center spacing) between two adjacent spot welds should not be less than which multiple of the weld diameter d?

Introduction / Context:
In resistance spot welding, proper layout of welds prevents weakening due to overlapping heat-affected zones, avoids sheet distortion, and ensures current flows efficiently through each weld. A key layout parameter is the minimum pitch (spacing) between consecutive spots.

Given Data / Assumptions:

• Weld diameter is d (approximate nugget diameter used for layout).
• Thin sheet metal joints in lap configuration are considered.
• Standard fabrication practice is assumed (typical steels, automotive or appliance sheets).

Concept / Approach:
If spots are placed too closely, heat-affected zones overlap, causing sheet weakening and expulsion, and the second weld may draw current preferentially, degrading consistency. A commonly used rule of thumb is that the pitch should be at least 3 d to 4 d for thin sheets so that each nugget forms independently with adequate cooling and load-carrying area between welds.

Step-by-Step Solution:
Identify the controlling variable: weld diameter d sets heat and load scale.Apply the rule of thumb: minimum pitch ≈ 3 d (often 3 d to 4 d in practice).Select the closest minimum from the options: 3 d.Therefore, the correct answer is 3 d.

Verification / Alternative check:
Process sheets and welding handbooks provide typical pitch values in the 3 d–6 d range depending on material thickness and service loads; minimums smaller than ~3 d risk nugget interaction.

Why Other Options Are Wrong:
d and 1.5 d are too small and promote excessive thermal overlap; 6 d or 10 d may be conservative and increase part weight/cost without added benefit unless loads require it.

Common Pitfalls:
Confusing edge distance with pitch; both have guidelines (edge distance often ≥ 2 d), but they address different layout constraints.

Final Answer:
3 d