Troubleshooting Guide for
Gas Metal Arc Welding - GMAW (MIG)




Possible Cause

Corrective Measures

Poor arc ignition Control circuit Replace defective part if necessary
Gas not turned on Check gas cylinder valve
Gas depleted Replace cylinder
Wrong polarity Check polarity for DCEP (Electrode must be +, the work -). Check ground
Poor connection Readjust control circuit
Burn-backs and arc-length fluctuations Improper drive rolls Check for correct size and type
Insufficient drive roll pressure Increase pressure
Excessive drive roll pressure Decrease pressure
Wire feed too slow Increase wire feed speed
Contact tube plugged Clean, replace contact tube
Arcing in contact tube Clean, replace contact tube
Power circuit fluctuations Check line voltage
Wrong polarity Check polarity for DCEP (Electrode must be +, the work -)
Gun overheating Replace with higher amp gun (all guns having current ratings above 200 amps should be water cooled)
Conduit liner dirty or worn Check for water leaks causing gun to overheat. Check for filter on the water inlet line to prevent clogging and overheating of the gun. Replace liner.
Porosity Gas entrapped due to turbulence in weld pool Adjust parameters
Gas entrapped due to excessive current Reduce current and/or travel speed
Oil or other contaminants on filler wire Avoid contamination by storing wire, covered, in clean, dry area. Do not open wire package until ready for use. Keep spool on welder covered. Do not use wire that has been open for any length of time. If a new spool seems oxidized or dirty, remove two or three outer layers and use remainder only if it is clean. Change to clean high quality wire.
Oily drive rolls Clean rolls with solvent
Oily, dirty liner Replace with new liner
Wet shielding gas Check dewpoint of gas. Reject cylinders about -40°F dewpoint.
Water leaks in gun Repair guns overheated due to water failure
Oily base metal Clean plate with solvent and clean with stainless steel wire brush
Spatter particles ahead of weld Adjust parameters to minimize spatter
Cooling rate of weld too rapid Use higher current and/or slower travel. Consider preheat if necessary.
Drive roll slip Increase pressure on rolls. Change size and type of rolls if necessary.
Excessive bending of guide liner Change position of MIG unit to minimize bending of cable
Dirty welds Inadequate gas shielding Hold gas cup closer to work. Increase gas flow. Adjust gun angle. Check gun and cables for air or water leaks. Shield arc from drafts. Center contact tube in gas cup. Replace gas cup if damaged.
Dirty filler wire (see "Porosity")
Dirty base metal (see "Porosity")
Hot short cracking Improper filler wire Check filler metal for compatibility with base metal
Faulty joint design Check root opening, root face dimensions, included angle
Faulty fixturing Reduce the stress level by changing the restraining fixtures for the design of the part where possible
Travel speed too slow Use a higher welding speed
Improper technique Change angle of gun to improve deposition
Crater cracks Leaving crater open at end of weld Quickly reverse direction of travel and "seal" the crater; or peed rate of travel approaching end of weld, reducing size of weld pool as arc is broken; or use runoff tabs at the end of weld.
Incomplete penetration Faulty joint design Check root opening, root face dimensions, included angle
Welding speed too rapid Slow travel speed
Welding current too low Increase welding current
Arc length too long Shorten arc length
Improper welding angle Change gun angle
Incomplete fusion Faulty joint preparation Check root opening, root face, dimensions, included angle
Arc length too long Shorten arc length
Dirty joint Clean chemically and/or mechanically with clean stainless steel wire brush
Welding cables overheating Cables too small Check current requirements. Replace.
Cable connections loose Check, tighten
Cables too long Check current carrying capacity
Inadequate cooling of the in-out water cables Check water flow rate. Check for possible leaks.