Problem 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.