Projection Welding of Dissimilar Metals — Where Should the Projection Be Made? When two different metals are to be joined by projection welding, on which piece should the projection be formed to balance heat generation and obtain a sound weld?

Introduction / Context:
Projection welding localizes current and force through small raised features (projections). With dissimilar metals, differences in electrical and thermal properties strongly affect heat generation at the faying interface. Proper placement of the projection is essential for consistent nugget formation.

Given Data / Assumptions:

• Dissimilar metals with different electrical conductivities and thermal conductivities.
• Weld quality depends on localized resistance heating at the interface.
• Electrode force and current are appropriately set for projection welding.

Concept / Approach:
Joule heat is I^2 * R * t. High local resistance at the projection concentrates heating. If one workpiece is highly conductive (thus tends to carry current away), forming the projection on that higher conductivity piece increases contact resistance at the raised feature, compensating for its heat-sinking tendency and promoting balanced interfacial heating.

Step-by-Step Solution:
Identify property mismatch: one piece is higher in electrical/thermal conductivity.Goal: maximize interfacial heat where weld nugget must form.Strategy: add projection on the higher conductivity piece to raise local contact resistance.Outcome: heat is focused at the interface, producing a sound nugget.

Verification / Alternative check:
Shop practice and standards recommend placing projections on the better conducting or thicker member to equalize heating.

Why Other Options Are Wrong:
Lower conductivity metal: already has higher resistance; additional projection can overheat that side.Density or melting point alone is not the controlling factor for resistance heating.Thickness-only rule ignores the primary electrical/thermal consideration.

Common Pitfalls:
Assuming projections should always be on the thinner or softer piece; conductivity governs heating effectiveness.

Final Answer:
higher conductivity metal