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Humping is the repeating ridge-and-valley pattern that can form in a high-speed MIG weld. Instead of producing a smooth bead, the arc leaves a series of lumps, often with narrow sections between them. This is usually a process problem rather than a defect in the welder itself. The common causes are excessive travel speed, too much wire deposition for the available heat, an unstable arc, or poor fit-up.
Humping is most common when welding fillet joints in the horizontal or flat position, especially with short-circuit or spray-transfer MIG. It can reduce throat size, trap slag or porosity between ridges, and make a weld fail visual inspection. The fix is usually a combination of slower travel, corrected voltage and wire-feed speed, and a steadier gun position.
Why high-speed MIG welds hump
As travel speed increases, the arc moves away from the hottest part of the weld pool before the pool has time to flatten. Surface tension then pulls the liquid metal into a ridge. The arc catches up, adds more metal and heat, and the cycle repeats. The result is a regular series of humps.
Humping can also occur when wire-feed speed is high but voltage is too low. The machine deposits more wire than the arc can spread into the joint. Excessive inductance, an incorrect shielding-gas flow rate, wind, or a long and inconsistent stickout can make the arc less stable and exaggerate the pattern.
Do not confuse normal weld ripples with humping. Normal ripples are shallow and evenly blended into the toes. Humping produces sharp peaks, deep valleys, poor toe wetting, or a bead that appears to sit on top of the joint.
The first adjustments to make
Start by reducing travel speed slightly—often 10 to 20 percent is enough. Do not simply stop moving and pile in more metal. The goal is to give the existing weld pool time to spread while maintaining a consistent pace. Watch the leading edge of the pool, not just the bright arc. A stable pool should stay approximately the same size from start to finish.
If slowing down does not work, reduce wire-feed speed in small steps. On a constant-voltage MIG machine, wire-feed speed primarily controls amperage and deposition rate, while voltage controls arc length and fluidity. A wire-feed reduction of roughly 5 to 10 percent is a reasonable test. If the bead becomes narrow or the arc starts stubbing, you have gone too far.
When the bead is tall and rope-like, increase voltage slightly—typically 0.5 to 1.5 volts at a time—while keeping wire speed constant. More voltage can flatten the bead and improve wetting, but too much creates excessive spatter, undercut, and a long, wandering arc. Make one change at a time and test on scrap of the same thickness.
Settings and gun technique
Use the wire and transfer mode recommended for the material thickness. Spray transfer can produce a smooth, fast weld, but it requires enough voltage, amperage and shielding gas. Trying to force spray-like travel speeds with a short-circuit setup commonly produces humping or lack of fusion. Pulsed MIG can control heat and deposition better, but it costs more and still requires correct parameter selection.
| Symptom | Likely cause | Useful first correction |
|---|---|---|
| Regular tall ridges at high travel speed | Travel speed too high for the heat available | Slow 10–20 percent or increase heat slightly |
| Rope-like bead with poor toe wetting | Wire speed too high or voltage too low | Reduce wire speed 5–10 percent; then fine-tune voltage |
| Wide, flat bead with undercut | Voltage or travel speed too high | Reduce voltage or slow the travel only if fusion remains sound |
| Erratic arc and heavy spatter | Wrong polarity, stickout, gas flow or contaminated wire | Check setup, clean the joint and stabilize stickout |
Keep contact-tip-to-work distance consistent. For short-circuit MIG, about 3/8 inch is a useful starting point; spray or flux-cored setups may call for more. A long stickout reduces arc energy and can make the weld bead cold and convex. A short stickout increases amperage and may make the arc harsh.
Use a work angle of about 45 degrees in a fillet joint and a travel angle of roughly 5 to 15 degrees. A slight drag angle is generally easier to control than a steep push angle when trying to eliminate humping. Keep the nozzle close enough to see the pool clearly, but do not weave broadly. A straight stringer is usually the most reliable high-speed technique.
Check fit-up and shielding
A large or inconsistent gap forces the welder to fill changing joint volume, which can make the bead alternate between cold and overloaded. Keep joint gaps consistent and avoid trying to bridge a gap that is too wide for the material thickness. Tack the parts securely so heat does not pull the joint open during the weld.
Set gas flow according to the nozzle and shop conditions. Around 20 to 30 cubic feet per hour is common for indoor MIG, but excessive flow can create turbulence and draw air into the shield. Drafts from fans or open doors can do the same. If porosity appears along with humping, inspect the regulator, hose, diffuser, nozzle and gas supply before changing welding parameters.
Clean mill scale, oil, paint and rust from the joint. Contamination destabilizes the arc and can make a correct setting look incorrect. For steel, a clean surface and a typical argon-carbon-dioxide mix are often more important than buying a premium machine. Use quality ER70S-6 MIG wire when welding clean or lightly scaled mild steel.
When equipment changes are worthwhile
Most humping problems do not justify replacing a welder. A sound 180- to 250-amp machine with usable voltage and wire-speed controls can produce smooth beads if the joint, wire and gas are correct. A basic MIG gas flow meter can be more useful than a more expensive gun because it confirms whether shielding gas is actually reaching the nozzle.
Consider a spool gun only for aluminum or when feeding soft wire through a long conventional gun is unreliable. Consider pulsed MIG when production speed, thin-to-thick transitions or controlled heat input justify the cost. For occasional repair work, slowing down and dialing in the machine is usually the cheaper and better solution.
Verify the corrected weld
After each adjustment, make a test weld at least 4 to 6 inches long. Inspect both toes for smooth fusion, look for undercut and check that the bead is consistent rather than merely flatter. If practical, cut and etch a sample or break a test coupon to check penetration. A bead that looks attractive but lacks fusion is not a successful repair.
Once the settings work, record wire size, gas, voltage, wire speed, stickout and travel direction. Repeating those conditions prevents the humping problem from returning when the next production joint is welded.