Projection welding — placing projections for unequal thickness joints When projection welding two sheets of unequal thickness, on which sheet should the projections be formed to obtain consistent heat concentration and collapse?

Introduction / Context:
Projection welding localises current and force at small raised points, creating repeatable nuggets while allowing multiple welds in one squeeze. For dissimilar sheet thicknesses, projection placement determines current density, heat balance, and mechanical collapse of the projection.

Given Data / Assumptions:

• Two low-carbon steel sheets with different thicknesses are to be joined.
• Standard dome or truncated cone projections are available.
• Objective is reliable fusion at the interface without burn-through of the thin sheet.

Concept / Approach:
Projections are generally formed on the thicker sheet. The thicker sheet provides structural support for the projection during squeeze, maintains geometry, and reduces the risk of overheating or expulsion in the thin sheet. As current concentrates at the small contact area of the projection tip, heat is generated at the interface; the projection collapses plastically, forging the joint. Putting the projection on the thin sheet raises the risk of local overheating and burn-through before adequate forging pressure is attained.

Step-by-Step Solution:
Identify goal: concentrate heat at interface while preventing thin-sheet burn-through.Choose projection location to maximise robustness: on the thicker sheet.Result: stable collapse and balanced heat input yield sound nuggets.

Verification / Alternative check:
OEM welding practice standards and projection nut applications consistently place projections on the thicker member or on the fastener (nut), which is thicker than the sheet.

Why Other Options Are Wrong:

• Thinner sheet: prone to overheating and expulsion.
• Either/both: not optimal for heat balance and tooling economy.
• Interlayer only: used for special fasteners, not typical sheet-to-sheet joints.

Common Pitfalls:
Assuming electrical resistance of the thin sheet automatically places heat there; projection geometry intentionally controls resistance and pressure at the interface.

Final Answer:
thicker