A 4g Mig Welding plate test along with a 3g are used to qualify a welder for all positions.
If you watch the video you probably wont even need to read further but just in case,
Here are some tips for passing an overhead mig welding test....
in my opinion, the 3 main things are stickout, gun angle, and current.
• maintain a short stickout
• maintain as close to 90 degree gun angle as you can
• dont be afraid to crank up the heat.
• Grind or file a 1/16” land on the beveled plates
• Gap the pieces 3/32” ( a bit tighter than for 3g)
• Make the tack welds big enough so that they hold the gap when you start the weld on a tack
• For 3/8” plate, 3 passes works best for me. Its hard to fit 4 without making the cover too high.
• For the root pass on a 4g mig test, I like a slight drag angle…but 90 degrees works too.
• For the second pass as well as the cover pass, I try to keep the torch at 90 degrees or a slight push angle.
• All passes in this video were welded at 19 volts and around 220-250 ipm wire speed.
• This joint could probably be welded successfully using anywhere from 18 to 20 volts depending on fitup.
• A wider gap or less land requires lower heat.
• A tighter gap and or heavier land needs more heat.
• The cover pass goes in a lot better if the joint is slightly below flush
• Let cool to where the plate is still very warm but not hot for the cover pass.
4g mig overhead settings using a Millermatic 250
• 0.035” er70s6 wire
• 25 cfh of 75/25 argon/co2
• Voltage =19
• Wire speed=220-250
( to determine wire speed, I pulled the gun trigger, counted to 6 seconds measured to nearest whole inch and added a zero because a millermatic 250 reads out some meaningless number and not inches per minute….for those with a millermatic 250 it was set on about 32 on high range)