Resistance-Weld Heating: Current, Contact Resistance and Time Are Paired Inputs

Define the teaching approximation

TWI describes resistance joining through current-generated heating at contacting materials. With explicitly constant resistance and current, electrical energy is I²Rt. Primary reference: TWI technical explanation.

Real contacts can change as surfaces heat and deform. An average resistance label does not automatically justify a constant-resistance calculation across the entire event. Retain the assumed electrical boundary before interpreting its energy.

Calculate a hypothetical energy term

Assume fictional current 1,000 A, resistance 0.00010 Ω and interval 0.020 s. The stated model gives 1,000²×0.00010×0.020 = 2 J. Doubling only current gives 8 J because current is squared.

These are original teaching assumptions, not resistance-welding settings. The computed electrical term does not establish nugget size, complete fusion or how much energy reaches a specific interface. Heat loss and changing contact behavior are outside this simplified model.

Keep contact and timing evidence

Create an event record with current waveform, relevant voltage/contact boundary, force condition and time interval. Preserve which quantity was measured and which was assumed. A waveform integral may be needed when the stated constants do not describe the event.

Ask for joint evidence separately from the heating calculation. This avoids replacing the process assessment with a current number or interpreting unchanged current as proof that contact heating was unchanged across surface or assembly revisions.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: TWI technical explanation