In resistance spot welding for sheet metals, the electrodes are made with tips of which material to ensure very high electrical and thermal conductivity along with adequate strength?

Introduction / Context:

Resistance spot welding (RSW) joins sheets by passing a high current through a localized contact area clamped between two water-cooled electrodes. Electrode material selection directly affects nugget formation, heat balance, and electrode life.

Given Data / Assumptions:

• Standard industrial RSW of steels and common alloys.
• Need for low electrode resistivity and high thermal conductivity.
• Electrodes are typically water-cooled and shaped at the tip.

Concept / Approach:

Electrodes must conduct large currents with minimal heating and quickly extract heat from the weld zone. Copper and copper alloys (e.g., Cu-Cr-Zr) deliver very high electrical/thermal conductivity plus sufficient hardness when alloyed/heat-treated. Hence, the tips are copper-based.

Step-by-Step Solution:

Verification / Alternative check:

Standards (RWMA classes) list copper alloys for RSW electrodes; stainless steel, aluminium, brass, or titanium do not meet the conductivity requirement.

Why Other Options Are Wrong:

• Stainless steel: poor electrical/thermal conductivity; would overheat.
• Aluminium: better conductivity than steel but too soft and picks up; unsuitable as an electrode tip material.
• Brass: lower conductivity than copper; inferior for high-current duty.
• Titanium: low conductivity; inappropriate for RSW electrodes.

Common Pitfalls:

• Confusing the material being welded with electrode material.
• Ignoring the need for water cooling and alloy-strengthened copper grades.

Final Answer:

copper