How to Check Arc Starts and Stops in Robotic Welding: End Porosity, Craters and Restarts After Arc Loss

Checking arc starts and stops in robotic welding requires a combined review of workpiece condition, torch position, gas and wire timing, and power-source programs. After arc loss, also confirm the interruption point, quality disposition and approved repair welding method; simply having the robot finish the path is insufficient.

When the middle of a robotic weld looks consistent but porosity appears at the start, a pronounced depression remains at the end, or the restart location repeatedly shows abnormalities after arc loss, increasing current across the entire weld is not an appropriate sole response. Arc initiation, steady welding, termination and restart are separate stages with different conditions.

This article covers robotic gas metal arc welding applications such as MIG/MAG. To check starts and stops, put the actual coordination of the welding power source, robot motion, gas supply and wire feeding on the same timeline, and validate it against the approved welding procedure specification (WPS), equipment instructions and quality plan.

1. Define the affected area first: start, end or interrupted joint

Record the abnormal location by weld number and distinguish three cases: the start segment after a normal start, the termination segment at a normal finish, and the restart joint after an alarm or manual interruption. These can look similar, but their treatment logic must not be interchanged.

For porosity at the start, check shielding conditions and workpiece cleanliness; for a crater, check end filling and the termination sequence. Repeated arc-start failures also require checking power-source feedback, the wire end and wire feeding condition. Do not attribute every end abnormality to inaccurate robot positioning.

Keep alarms, program versions, and workpiece and consumable batch records, and inspect adjacent weld segments. If cracks, lack of fusion or other conditions outside the requirements are suspected, quality personnel should first define the inspection and disposition scope before deciding how production can continue.

2. Check the actual position and shielding gas conditions before starting

Check the weld start area for oil, moisture, rust or coatings that affect welding, and confirm that fit-up gaps, tack welds and joint condition meet the procedure requirements. A correct programmed start point does not mean the actual seam is in the same position on every workpiece.

Check torch orientation, contact-tip-to-work distance and wire extension against the approved procedure. After replacing torch components or a collision, also check the tool and position using the equipment procedure. Do not arbitrarily lengthen wire extension to compensate for an unexplained positioning error.

Shielding gas must reach the weld area when needed. Long hoses, leaking connections, blocked nozzles or external air currents can make programmed gas timing differ from actual shielding conditions. Check gas delivery and timing at the nozzle using the equipment method; do not prescribe one preflow time for every station or substitute continually increasing gas flow for inspection.

3. Align start signals, wire condition and motion feedback

Authorized personnel should check the arc-start command, power-source ready status, arc-established or fault feedback, and the conditions for the robot to enter welding motion. Signal names and meanings depend on the particular system; a command being issued does not mean that a stable arc has already formed.

Inspect the wire end and consumables before starting as required by the manufacturer. An end ball, burnback sticking, contact-tip wear or wire feeding resistance can affect the next start. The actual wire-end treatment must suit the procedure, wire and equipment functions.

Compare whether the fault occurs only at particular robot orientations, after long travel or after a spool change. Trials should cover the actual working envelope, with complete records of both failures and successes, rather than verification at just one convenient test-weld position.

4. Include the auxiliary wire feeder in dynamic start/stop validation

TitanWeld has introduced an auxiliary wire feeder as part of its system integration offering. For projects with long wire paths or frequent orientation changes, its role can be assessed together with the layout. The specific configuration must, however, be confirmed in the project proposal; this does not establish that all models use the same wire feeding arrangement.

Validating an auxiliary wire feeder requires more than checking smooth continuous feeding. Observe how its start response, stopping, burnback and subsequent arc starts coordinate with the main feeding mechanism and power source. If the system has a wire retract function, also check its compatibility and actual action according to the instructions; do not assume every auxiliary feeder supports identical controls.

An auxiliary wire feeder cannot replace correct gas shielding, a reliable welding current circuit or a suitable termination procedure. System interfaces can be reviewed further using this site's complete robotic welding system.

5. Check end filling when stopping, not just arc extinction

At a normal finish, check crater-fill or current-transition programs that the power source supports and the procedure approves, and confirm coordination between robot motion, wire stopping, burnback and postflow. Functions differ between power sources and welding modes; timing values from another system cannot simply be copied.

A pronounced crater, insufficient end filling and crater cracks are different acceptance items. An unfavorable crater shape may increase solidification cracking risk, but a photograph alone cannot establish or exclude cracking. After a visual abnormality is found, inspect it under the applicable requirements. Do not cover the problem with unapproved repeated spot welds.

6. Confirm the joint after arc loss, then perform the approved restart

Record the weld position where the arc was lost, the cause and the last valid weld segment. Before restarting, eliminate the fault, inspect joint cleanliness and surface condition, and address unacceptable weld segments, joint geometry and necessary temperature conditions according to the procedure. Moving the robot back a short distance alone does not establish that the overlap will fuse naturally.

First-piece reinspection can separately record the appearance and required inspection results for the start segment, steady segment, termination segment and restart joint, while retaining the program version, timing settings and disposition records. A return to normal arc sound cannot replace weld acceptance.

Provide joint drawings, the WPS, power-source and wire feeding configurations, abnormal locations and alarm records through the TitanWeld robotic welding project review to discuss start/stop interfaces and auxiliary wire feeder integration validation. Improvement results must be based on actual welding trials and acceptance.