The short video above shows a proven technique for getting penetration into the root of a vertical uphill 3f lap joint using short circuit mig
(gmaw-s).
The technique works because it keeps the arc on the leading edge of the weld puddle while maintaining a relatively short stickout aka "contact tip to work distance (CTWD).
Welding with short circuit mig downhill is likely to get lack of fusion for anything thicker than 3/16".
Open butt root passes are an exception due to the beveled edges, gap, and little to zero land or root face.
This example shown in the video is 1/4" thickness and even though settings were much lower than those recommended on the machine chart, it was still a bit hot.
...the wire speed could have been lowered by 10% to around 250 for less crowning of the bead while still penetrating into the root.
19 volts 280 imp.030”er70s6
WELD PROCESS = GMAW, SHORT CIRCUIT MIG, GAS METAL ARC WELDING
METAL TYPE = CARBON STEEL, COLD ROLLED STEEL, AISI 1010
THICKNESS = 1/4"
WELD TYPE = Fillet weld
JOINT TYPE = LAP JOINT
POSITION = 3f vertical uphill
VOLTS = 19 volts
WIRE SPEED = 280 IPM
WIRE SIZE = .030"
POLARITY = DCEP
GAS FLOW = 20-25 CFH C25 GAS
CTWD = 3/8”-1/2"
FILLER METAL = ER70S6
ADDITIONAL SETTINGS =
TIPS:A relatively short stickout aka contact to work distance CTWD of 3/8” to 1/2" makes a big difference.
The technique shown is simple series of upside down V motion.This technique sweeps the arc across the front leading edge of the puddle and helps ensure penetration.
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