The nugget of a properly formed spot weld is shaped like:

The nugget of a properly formed spot weld is shaped like:

• A. Circle
• B. Oval
• C. Square
• D. Rectangle

Answer: (B)

In resistance spot welding, the nugget is the fused metal that forms between the sheets under the electrode tips as heat is generated by I^2R losses. The shape of that solidified zone reflects how heat and metal flow are distributed under the clamp. The current path and the constraint of the electrode tips tend to produce more growth along the direction between the tips, and the molten metal flowing under pressure solidifies into a footprint that is elongated rather than perfectly circular. That practical, elongated footprint shows up as an oval shape when you inspect a properly formed nugget. A perfectly circular nugget would require perfectly uniform heating and symmetric metal flow, which is difficult to achieve in real welding; a square or rectangle would indicate more severe nonuniformities, not typical of a well-formed weld.

In resistance spot welding, the nugget is the fused metal that forms between the sheets under the electrode tips as heat is generated by I^2R losses. The shape of that solidified zone reflects how heat and metal flow are distributed under the clamp. The current path and the constraint of the electrode tips tend to produce more growth along the direction between the tips, and the molten metal flowing under pressure solidifies into a footprint that is elongated rather than perfectly circular. That practical, elongated footprint shows up as an oval shape when you inspect a properly formed nugget. A perfectly circular nugget would require perfectly uniform heating and symmetric metal flow, which is difficult to achieve in real welding; a square or rectangle would indicate more severe nonuniformities, not typical of a well-formed weld.