Welding of 5 mm thick plate with GMAW

Date 02-17-2017 06:43

Dear Experts,

Recently I came across a client specification asking to qualify a single pass fillet welds by single pass per side butt welds only. I tried in a 5 mm thick plate with 1.2 mm wire(since I have to use the same wire dia. in actual production) in 2G position.

Electrode- ER 70S-6.
Current 165-190 A. Voltage 18-20 V.
Joint design - square groove.
Travel Speed- 300 mm/min.
Welding Sequence- One Pass on one side and the other pass on the opposite side after backgrinding.

I was able to fuse the material properly without any surface defects. But in RT weld shows porosity.

Can anybody suggest the right parameters for getting sound welds ?

By jwright650 (*****)

Date 02-17-2017 11:11

For ER70S-6: Material will need to be clean, no mill scale or rust...Obviously no oils or coatings. Solid wire does not deal well with anything on the material. ER70S-3 tolerates those even less than the S-6 wire.
Is FCAW a choice?

By TimGary (****)

Date 02-17-2017 12:48

Ensure square groove faces are clean, shiny metal with no contaminates.
Clean all contaminates, including mill scale from the plate surfaces, at least 12 mm away from the plate edges to be welded.
Shielding gas of at least 75% and max of 90% argon, remainder CO2.
Shielding gas flow of 35 - 40 CFH.
12 - 19 mm diameter nozzle.
12 mm max electrical stickout.
Pulling technique travel angle of about 15 deg, and 90 deg work angle.
Minimize oscillation.
When grinding the back side, open the cut to a V-shape about 4 - 6 mm wide at the surface, not a deep narrow U shape.
Back gouge grind depth is to clean, sound metal, penetrating into the root from the first pass, leaving no areas of lack of fusion or original root face behind.
Ensure all contaminates, including grinding dust, are cleaned from the back gouge before welding the back side.
Ensure there is no shielding gas leakage from connections, hose, weld gun and the back side of the nozzle.

Experienced welders who are familiar with making welds acceptable to RT know how to read a weld puddle, in so that potential defects like porosity and lack of fusion can be seen developing in the molten puddle while welding, and know when to stop and remove potential defects prior to continuing.

Tim

By welderbrent (*****)

Date 02-17-2017 15:34

John and Tim are right on the money.

My only observation would be to leave a slight opening between the two plates prior to the first pass especially since you are working with about a 3/16" thickness and .045 wire (sorry, I have trouble keeping metrics straight in my head). Around 1/16 to 3/32 max. Get some extra penetration so you have plenty of material to backgrind into.

Since you are working with Short Arc, make sure you keep the voltage down a bit to get your nice crisp crackling sound from the arc.

While you can use up to a 90% Argon mix, I prefer 75-80% for these kinds of jobs. 90% works great for some things and especially if you are going back and forth between Short Arc and Spray Transfer, but if concentrating on the Short Arc, keep the percentage on the lower side.

He Is In Control, Have a Great Day, Brent

By 803056

Date 02-18-2017 15:38

I'm with Brent on this one. A slight root opening will help the welder stay on the joint while back gouging the second side. Make sure the welder back gouges deep enough to get down to sound metal. All too often the welder will leave remnants of root intact with the belief they will "burn it out." Rarely are they successful, especially with GMAW-S. There is often a void, incomplete fusion, at the root of the V-groove. Make sure the back gouge is deep enough to completely remove any incomplete fusion in the weld root.

CO2 will improve the arc characteristics when using short circuiting transfer. Too much argon "pushes" the tendency to produce an unstable arc.

With regards to the back gouge, make sure it is wide enough. I prefer a back gouge to be twice as wide as it is deep for thin materials and then per the details of a prequalified U-groove for thicker materials.

Best regards - Al