Spot Welder Troubleshooting: Causes & Fixes

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Problems on this page:

Weak or cold welds Electrode wear or sticking Expulsion or burn-through Electrodes misaligned Electrode tips overheating Tip dressing not working Wrong weld schedule or controller faults Current shunting through earlier welds Gun force varying or gun slow to close

Weak or cold welds

Hits OEE: Quality

Symptoms: Undersized nuggets, peel failures, low weld strength at checks.

Low current or short weld time

Set current and weld time to the schedule; verify the weld controller.

Poor electrode force or contact

Set force; check the cylinder and tip contact.

Worn electrodes or contamination

Dress or replace electrodes; clean the faying surfaces.

Prevention: Weld-schedule control, force checks, electrode maintenance.

Electrode wear or sticking

Hits OEE: Availability

Symptoms: Electrodes mushroom or stick to the part, marking, frequent dressing.

Excess current or insufficient cooling

Tune current; verify electrode water cooling flow.

Worn or wrong cap

Dress on schedule; use the correct cap alloy and shape.

Contaminated or coated material

Adapt the schedule for coatings; clean surfaces.

Prevention: Cooling-flow checks, tip-dressing schedule, schedule for coatings.

Expulsion or burn-through

Hits OEE: Quality

Symptoms: Weld spatter/expulsion, holes, surface burn, weak joints.

Current too high or time too long

Reduce current/time; tune the schedule.

Insufficient electrode force

Increase and verify force before current.

Poor fit-up or gaps

Improve part fit-up and clamping.

Prevention: Balanced weld schedule, correct force, good fit-up.

Electrodes misaligned

Hits OEE: Quality

Symptoms: Off-centre or oval welds, electrodes skidding, uneven tip wear.

Arm deflection under force

Check arm stiffness and support.

Loose holders or shanks

Tighten and replace worn holders.

Tips dressed at the wrong angle

Check the tip dresser setup.

Prevention: Alignment check with carbon paper or a test coupon at tip changes.

Electrode tips overheating

Hits OEE: Availability

Symptoms: Tips wear fast, tips stick, discoloured caps.

Low cooling water flow

Check water flow at each gun.

Blocked or badly placed water tubes

Clear tubes and set them correctly inside the cap.

Leaks on the return

Fix return leaks.

Prevention: Water flow checks every shift.

Tip dressing not working

Hits OEE: Quality

Symptoms: Tip faces stay worn or uneven after dressing, weld quality drops between dresses.

Worn dresser blades

Replace the blades.

Dressing too seldom

Set dressing frequency from weld results.

Force or alignment wrong while dressing

Check dresser force and gun alignment.

Prevention: Dresser blade changes on a schedule.

Wrong weld schedule or controller faults

Hits OEE: Quality

Symptoms: Welds suddenly weak or strong after a change, controller alarms.

Wrong schedule selected

Check schedule selection against the part.

Secondary circuit resistance rising

Check cables, shunts and connections for wear and looseness.

Transformer fault

Have the transformer tested.

Prevention: Schedule check at every part change and secondary circuit inspection.

Current shunting through earlier welds

Hits OEE: Quality

Symptoms: Later welds in a row are weaker than the first ones.

Welds too close together

Check weld spacing against the part design.

Fixtures conducting current

Insulate fixture contact points.

Poor fit-up

Improve part fit-up.

Prevention: Destructive tests on the last weld of a row, not only the first.

Gun force varying or gun slow to close

Hits OEE: Quality

Symptoms: Weld results vary, the gun closes slowly or unevenly, force alarms.

Low air pressure or a leaking cylinder on pneumatic guns

Check the air supply and reseal the cylinder.

Servo gun force not calibrated

Calibrate the servo gun force as the maker describes.

Worn pivot bearings

Replace worn pivot bearings.

Prevention: Gun force checks on a schedule with a force gauge.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: wave solder machine · reflow oven · welding · laser welding machine

Stop the same fault coming back

Recurring spot welder stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover