What Happens When the Welder Stops the GMAW Arc: Essential Guide
At the end of a GMAW weld, releasing the gun trigger does more than turn off the visible arc. The welding machine stops feeding wire, the arc extinguishes, shielding gas may continue briefly, and the molten weld pool begins to solidify.
Understanding what happens when the welder stops the gmaw arc helps explain common end-of-weld defects such as crater cracking, porosity, excessive wire burnback, and an oversized weld bead. The exact sequence depends on the power source, gun settings, and whether the equipment has crater-fill or burnback control.
What happens when the GMAW arc stops?
When the operator releases the trigger or reaches the programmed stop point, the GMAW system normally performs several closely related actions:
- The wire feeder stops advancing electrode wire.
- The arc between the electrode and workpiece goes out.
- The weld pool loses its heat source and begins to cool.
- Shielding gas may continue for a short period through postflow.
- The electrode tip may retract slightly because of burnback control.
These events happen quickly, but they are not always simultaneous. A modern welding power source can use programmed timing to manage wire feed, arc voltage, current, gas flow, and crater filling at the end of the weld.
The wire feed stops
In GMAW, the continuously fed wire electrode is both the electrical conductor and the filler metal. Once the trigger circuit tells the system to stop, the wire feeder stops pushing wire through the gun liner and contact tip.
The final portion of wire can remain hot after feed stops. Depending on the machine’s burnback setting, the power source may keep welding current on for a very short interval so the wire does not freeze into the solidifying weld or remain excessively long outside the contact tip.
The arc extinguishes
The GMAW arc transfers heat from the electrode to the workpiece and melts filler metal and some base metal. When the arc is extinguished, that heat input ends. The liquid weld pool then cools and changes into solid weld metal.
Solidification begins at the cooler edges of the weld pool and progresses toward the center. As the metal contracts, the final area may form a shallow depression called a weld crater. If the crater is deep, abruptly terminated, or contaminated, it can become a weak location in the weld.
Shielding gas may continue
Many GMAW systems provide gas postflow after the arc stops. Postflow keeps shielding gas around the hot electrode tip and the still-hot weld area for a short time. This can reduce oxidation and help protect the final portion of the weld as it cools.
Postflow does not replace correct welding technique. If the gun is pulled away immediately, the gas may not protect the crater effectively. If gas flow is disrupted by a leak, blocked nozzle, incorrect flow rate, or strong air movement, the cooling weld can absorb atmospheric contamination and develop porosity or surface oxidation.
Why the weld crater matters
The crater is the small depression left where the weld pool solidifies at termination. A minor crater is normal, but an abrupt stop can leave a deep or sharply shaped one. That shape concentrates stress and may reduce the effective weld cross-section.
As molten metal cools, it contracts. If the surrounding weld metal has already become rigid, the shrinking final pool can experience tensile stress. In susceptible materials or highly restrained joints, this can contribute to crater cracking.
A crater can also create an appearance problem without being structurally dangerous. For example, a short fillet weld may end with a noticeable divot, while a long bead may show a small depression that is difficult to see until the surface is cleaned and inspected.
Common defects at arc termination
- Crater cracking: A crack forms in the final solidifying weld metal, often because the crater is deep, the stop is abrupt, or shrinkage stress is high.
- Porosity: Gas becomes trapped as the weld pool freezes, commonly because shielding was lost or the final pool was not adequately protected.
- Undercut: The arc removes base metal near the edge of the weld without depositing enough filler to fill the groove.
- Excessive reinforcement: A slow or poorly controlled stop can leave too much filler metal in a small area.
- Burnback: The wire melts back toward the contact tip, especially when wire feed stops before welding current stops or when the burnback time is excessive.
- Long wire stickout: If the wire stops without the proper electrical timing, the remaining electrode may be too long for a clean restart.
Not every end-of-weld defect comes from the stop itself. Joint fit-up, travel speed, wire diameter, shielding gas, contact-tip condition, and machine programming can also affect the result. The termination area should therefore be evaluated along with the rest of the weld.
How crater fill changes the stopping sequence
A welding power source with crater-fill control does not always end the weld in one abrupt step. After the operator releases the trigger, the machine can temporarily reduce voltage and amperage while continuing to feed wire. This places a smaller amount of heat and filler metal into the final portion of the weld.
The purpose is to reduce the crater’s depth and shape the termination more gradually. Some systems use a separate crater-fill time, while others use a programmed slope-down or end parameter. The names and available controls vary by manufacturer.
Crater fill must be matched to the process and joint. Too little crater-fill time may leave a depression or crack-prone termination. Too much filler or too slow a transition can create a bulky end, excessive reinforcement, or unwanted heat input.
Trigger modes
GMAW guns commonly operate in a two-step trigger mode, although equipment may also offer four-step or specialized sequencing.
- Two-step mode: Pulling the trigger starts welding, and releasing it begins the programmed stop sequence.
- Four-step mode: The operator can release the trigger while welding continues, then use another trigger action to begin the stop sequence. This can reduce hand fatigue during longer welds and provide more control over the ending.
Some machines also provide spot, stitch, tack, or timed weld functions. In those modes, the power source may stop automatically after the programmed interval. The underlying result is similar: wire feed and arc energy end, the weld pool solidifies, and the final metal must be protected and shaped correctly.
What the welder should do at the end
The correct stopping motion depends on the joint, position, material, and machine settings. A common technique is to pause briefly at the termination point or use a small controlled motion that allows the crater to fill before the arc disappears. The operator should avoid simply snapping the gun away from the workpiece while a large molten pool remains.
For equipment with crater-fill programming, the operator should use the recommended trigger sequence and let the machine complete its end cycle. For equipment without that feature, a controlled stop may help distribute the final filler metal instead of leaving one deep depression.
The gun should remain positioned over the end of the weld long enough for postflow to protect the hot electrode and weld area. Moving away too quickly can expose the cooling metal to air. The correct distance and postflow duration must follow the machine and welding procedure requirements rather than an assumed universal value.
Restarting after a stop
If the weld must resume, the restart area needs attention. The operator should inspect the termination, remove obvious contamination or excessive metal if required, and restart slightly back from the end when the welding procedure allows it. The arc can then travel over the previous end and tie into the existing weld.
A restart placed directly on a sharp crater may produce poor fusion, an overlap, or a visible lump. A restart that begins too far away may leave an unfused section between the old and new welds. Joint access and the applicable welding procedure determine the correct technique.
Why settings affect the final weld
End-of-weld behavior is controlled by the relationship between wire feed speed, voltage, welding current, burnback, crater fill, and gas timing. These settings are connected, so changing one can alter the appearance and quality of the termination.
- Wire feed speed: Influences deposition and current. A mismatch during the stop cycle can leave too much or too little filler.
- Voltage: Affects arc length and bead shape. An unsuitable end voltage can produce an irregular crater or unstable final arc.
- Burnback time: Controls how long current remains after wire feed stops. Excessive burnback can melt the wire back into the contact tip.
- Crater-fill time and output: Control how much lower-energy welding occurs at the termination.
- Gas postflow: Protects the hot end of the electrode and weld area after arc extinction.
A machine that leaves wire fused to the contact tip may have an unsuitable burnback setting, poor electrical contact, incorrect polarity, or a problem in the wire-feeding system. A crater that repeatedly cracks may indicate a termination technique or procedure problem rather than a simple gas-flow issue.
Safety after the arc stops
The absence of visible arc light does not mean the gun or weld is immediately safe to touch. The electrode tip, contact tip, nozzle, and newly deposited weld metal can remain hot. The weld may also continue to release fumes while it cools.
Keep the gun pointed safely, maintain required personal protective equipment, and avoid touching the workpiece until it has cooled enough for the task. Do not use the nozzle or electrode to move hot material. If inspection or cleaning is necessary, follow the site’s lockout, hot-work, and handling procedures.
Shielding gas can also continue flowing after the arc disappears. The operator should not assume that gas flow has stopped merely because the arc is off. Ventilation remains important, particularly in enclosed or poorly ventilated work areas.
FAQ
Does the wire stop at the same instant
Not necessarily. The welding control may stop wire feed first and maintain current briefly for burnback, or it may use a programmed end sequence. The exact timing depends on the power source and its settings.
Why does the weld crater form when the arc stops?
The arc stops supplying heat and filler metal, so the remaining liquid weld pool solidifies and contracts. That contraction can leave a depression at the termination, especially when the arc is stopped abruptly.
Can stopping the GMAW arc cause a crack?
Yes. A deep, poorly filled crater can develop a crater crack as the final weld metal cools and shrinks. Joint restraint, material, weld size, contamination, and termination technique all influence the risk.
Why does the wire stick to the contact tip after
Wire can stick when burnback is excessive, wire feed stops too early, the contact tip is worn or incorrectly sized, or the welding parameters are unstable. The wire may melt back and fuse inside or against the contact tip.
Should the gun stay over the weld after the arc
Usually, the gun should remain in position long enough for the programmed postflow to shield the hot electrode and termination area. The correct duration and movement depend on the welding equipment and procedure.
What is the best way to prevent an end crater?
Use the machine’s crater-fill or end-slope function when available, follow the qualified welding procedure, and use a controlled stopping motion. Avoid abruptly pulling the gun away from a large molten pool.
Conclusion
When considering what happens when the welder stops the gmaw arc, the essential sequence is clear: wire feed ends, the arc extinguishes, the weld pool solidifies, and shielding gas may continue during postflow. A controlled stop, suitable burnback and crater-fill settings, and proper protection of the cooling weld help prevent crater cracks, porosity, burnback, and poor restarts.
