When one projection on a welding nut collapses before the others, check contact and force distribution before increasing weld current. A projection welding nut needs its projections to contact the sheet evenly enough to develop a balanced weld. If the nut sits at an angle, the sheet moves under pressure, or one projection carries most of the load, additional heat can make the imbalance worse.

The most useful starting point is to separate a mechanical seating problem from a problem that develops during current flow. Check how the assembly behaves under the approved electrode force with welding current disabled, then compare that condition with a welded sample. This helps narrow the investigation without repeatedly changing a working weld schedule.

Identify what “uneven collapse” looks like

A tilted nut, unequal remaining projection heights, and an irregular weld footprint can indicate different problems. Before adjusting the machine, keep several defective samples and mark their orientation relative to the fixture. Record which projection appears overcollapsed, which remains high, and where any expulsion occurs.

Look for a repeatable pattern:

• The same machine-side projection collapses first: electrode alignment, uneven support, or fixture loading deserves attention.
• The defect follows a particular projection when the nut is rotated: projection geometry or damage to the nut becomes more likely.
• The pattern changes randomly: inconsistent feeding, contamination, sheet position, or variable seating may be involved.
• The problem develops as production continues: electrode wear, pickup, cooling, or changing machine temperature may contribute.

Where the part and fixture permit, rotate an unwelded nut for a controlled trial while keeping the sheet and tooling orientation unchanged. This is a diagnostic comparison, not a production change. Avoid drawing conclusions from one sample, especially if the defect is intermittent.

Also distinguish collapse from weld formation. A flattened projection does not prove that a sound weld formed beneath it. Mechanical crushing can produce a convincing appearance with inadequate bonding.

Check seating under force before applying current

Follow the machine’s approved setup procedure, disable welding current, and keep hands clear of the electrodes and fixture. Use the specified production force to check seating. Isolate the equipment before reaching into tooling or removing components for inspection.

The nut should locate without rocking, and the sheet should remain supported as the electrodes close. If the nut tilts before current flows, electrical adjustments will not correct the underlying contact problem.

Check for burrs around the sheet hole, distortion from previous forming operations, trapped debris, and a nut sitting partly on a locator shoulder. A burr can lift one side just enough to concentrate load on the opposite projection. Thin sheet can also deflect over a gap in the lower support, changing contact as force builds.

Inspect the locating pin carefully. Its purpose is to position the nut and protect alignment; it should not unintentionally carry the welding load or hold the nut away from the sheet. Check for bending, wear, spatter buildup, incorrect protrusion, and binding between the pin and nut bore.

Contact impressions can help reveal uneven loading when made through an approved setup method. Remove any marking material before welding. Do not leave paper, film, or other checking materials in the joint during a live weld.

Make sure the electrodes deliver balanced pressure

Electrode faces must load the assembly in the intended direction. A worn or angled upper electrode can press one side of the nut first, while an uneven lower electrode can tilt the sheet beneath an otherwise correctly positioned nut.

Inspect both working faces for pitting, mushrooming, embedded particles, and material pickup. Check their alignment under load, because tooling that appears parallel while open may move as the welding head closes. Loose holders, worn guides, and excessive electrode extension can contribute to this movement.

Dress or replace electrodes according to the established tooling specification. Freehand correction that changes the working face or support geometry may create another source of uneven loading. After maintenance, recheck alignment and seating before evaluating weld quality.

The force setting also needs closer attention than a regulator reading alone provides. Friction, sticking guides, mechanical interference, or a poorly responding actuator can prevent the intended force from reaching the joint consistently.

During welding, the head must continue moving as the projections soften and collapse. If that follow-up movement is restricted, contact pressure can become unstable. The result may include local overheating, expulsion, or incomplete bonding even though the initial squeeze appeared satisfactory.

Inspect the nut and sheet as a matched joint

Compare unused nuts from the affected batch with a known acceptable sample. Look for differences in projection height, shape, position, and damage. A taller projection may take the initial load and current before the others establish effective contact. A damaged or partly flattened projection may behave differently even when its remaining height looks acceptable.

Use the component drawing and appropriate inspection equipment where dimensions matter. Visual inspection is useful for screening obvious damage, but it cannot establish that a projection pattern meets its dimensional requirements.

Confirm that the installed fastener is the specified weld nut. A general fastening product such as ISO8675 Hex Thin Nuts should not be treated as an interchangeable projection-welding component simply because its thread fits. The joint depends on the designated projection geometry and welding suitability.

Inspect the sheet alongside the nut. Changes in thickness, material, coating, hole condition, or local flatness can change both electrical heating and mechanical support. A nut that welds consistently to a flat coupon may behave differently near a bend or on an unsupported panel.

Check cleanliness at the intended weld interface and electrode contact surfaces. Oil, scale, coating buildup, and other residues can make contact resistance inconsistent. Use the cleaning method specified for the material; unplanned coating removal changes the joint condition and can affect corrosion protection.

Use the weld schedule to resolve the remaining imbalance

Once the parts seat correctly and the tooling applies force consistently, review the schedule against the approved process. Avoid changing current, force, and time together. A controlled adjustment should answer a specific question and produce samples that can be compared with the previous condition.

Squeeze time: has the assembly settled before current starts?

Current should begin after the electrodes have seated the parts and established the required force. If energization starts while the nut or sheet is still moving, the first contacting projection may receive disproportionate heating.

Increasing squeeze time can help when the existing interval is insufficient for seating. It will not correct a bent pin, a rocking nut, or unstable machine motion. Those faults remain even if the cycle waits longer.

Force: is it supporting stable contact?

Too little force can allow unstable contact and local expulsion. Excessive force can mechanically deform projections before useful heating develops and change the contact area enough to alter heat generation.

For that reason, “more force” is not a universal correction for uneven collapse. Establish the actual force at the electrodes and compare it with the qualified setting for the nut and sheet combination.

Current and weld time: when does the imbalance develop?

If the assembly seats evenly but one location expels metal early, the initial heating may be too aggressive for that contact condition. Increasing current can intensify the problem. If projections remain largely intact and joint testing shows insufficient bonding, heat input may be inadequate, but poor current delivery or unintended current paths can produce similar symptoms.

Review current and duration together within the permitted process range. A longer, lower-current weld is not automatically equivalent to a shorter, higher-current weld because contact area and resistance change as the projections collapse.

Where a qualified schedule uses current ramps or multiple pulses, check that those functions are operating as intended. They should not be added casually to compensate for unresolved mechanical faults.

Hold time: maintain support after heating

Keep the specified electrode force applied through the hold period so the joint remains supported as it cools. Releasing too early can disturb a newly formed weld. Extending hold time, however, cannot repair uneven contact or missing bonds created during current flow.

Investigate current paths when mechanics look correct

A nearby completed weld, conductive fixture contact, or unintended contact through a locator can divert some current away from the intended interface. This becomes particularly relevant when the defect appears only at certain positions or changes with welding sequence.

Check fixture clearances and the condition of any insulation required by the tooling design. Inspect electrode holders and electrical connections for looseness, deterioration, or signs of overheating using the machine’s maintenance procedures. Electrical maintenance belongs with personnel qualified for that work.

If the machine provides current, force, or displacement monitoring, compare defective cycles with accepted cycles from the same setup. An unusual displacement trace can help identify early collapse or unstable movement, while a current trace can reveal delivery changes. These signals support diagnosis; they do not prove that every projection formed an acceptable weld.

Verify the correction through weld quality

After correcting the suspected cause, produce trial parts under representative conditions. Check nut seating, tilt, expulsion, sheet indentation, and thread condition. Then perform the destructive or mechanical checks required by the part’s control plan, such as an applicable push-out, torque, peel, or sectioning method.

The acceptance criteria must come from the joint specification. A nut can resist a particular loading direction while still having uneven bonding around its projections, so choose checks that address the actual failure risk. Where sectioning or fracture examination is specified, inspect the individual projection locations rather than judging only the overall attachment.

Keep the distinction between appearance and performance clear. Equal-looking collapse is a useful process indicator, but it is not a substitute for the required weld assessment. Likewise, a neat surface does not establish adequate strength.

Check repeatability across consecutive cycles and representative production conditions. If the original fault appeared after the machine warmed up or when a new nut batch entered production, include that condition in the verification. A correction demonstrated only on a cold machine may leave the original trigger unresolved.

Build the restart decision around the identified cause

A useful troubleshooting record connects the defect to a specific observation: the nut tilted during squeeze, the lower support allowed sheet movement, a projection varied with the fastener batch, or the current began before force stabilized. Record the correction and the inspection results that support restarting production.

If several variables were changed during fault finding, establish which settings and tooling conditions form the approved restart setup. Leaving undocumented adjustments in place makes the next recurrence harder to diagnose.

When uneven collapse returns, begin with the defect’s orientation and the current-disabled seating check. Those observations quickly establish whether to investigate the nut, fixture, force delivery, or heating sequence—and keep weld-current changes tied to evidence.