Hey guys
Looking cor advice on my 3G gas metal with backing plate issues.
I am running at 19 and 220 with no visable issues other than a lack of root fusion and a lack second pass to root fusion. This is an inconcistent problem that comes and goes every 2nd or 3rd test plate.
I was trying to run a verticle stringer for my root but it seems to just not cut the mustard. I'm going to try Jodi's upside down V and the triangle techniques tomorrow and see how they work out but I could use any other ideas you guys have.
Here is a shot of todays last plate that split on the root side on both root bends.
Thanks
Jeff
Last edited by Mrkil on Tue Apr 02, 2013 10:26 pm, edited 1 time in total.
Did you also have a macro done of your weld with the backup plate?
For a starter, it is important to have a fit-up that does not leave space between the base metal plates and the backup plate.
In addition, when utilizing a backing plate, it usually requires more root gap between the two base metal plates, than we using an open butt joint (without backing plate).
Having the backup plate, you have the advantage of utilizing more heat, than you would with an open butt joint.
This is the exact test we use at work. When I did it, i was allowed a 6mm gap, this allowed me to get arc manipulation so as to burn into fresh metal. Turn it up bit because you wont burn through . As alexa said, make sure there is no gap between the backing plate and the parent metal, grind both shiny clean and make the root run a sort of zig zag motion that hits the clean sharp edges of the bevel. If you are allowed to grind, the face appearance of this root run is irrelevant . just grind the shit out of it down to square across the face. Other runs, put them in like a series series of )))))))))) heading up wards of course. the wire speed can be turned down abit, to allow the voltage to burn it in. The movement must still hit fresh steel every time. This is where your lack of fusion is coming from. On the final run, have it about a mm under and you can turn the wire up a little to help avoid undercut.
Weldin Mike 27's comment concerning the marginal preparation of the weld just prior to the cap pass is a great gift for anyone learning how to weld in all positions.
That small extra, of leaving a mm ledge on the sides of the welds, will make a tremendous difference of the appearance of the cover pass. If your filler passes are planned well, you will be able to do it without grinding. If not, simply grind the last filler pass, and that cap will be a beaut.
I would add to the other great advice, that if, as you said, this problem bites you only occasionally, that your technique (skill) has exceeded the heat you are welding with, and a slight increase may be in order. Say 19.5-20V, and an appropriate increase in wire speed/current. Try a small step up, and see if your problem occurs less frequently.
It happens to many... You find a setting that works for you, and then your skills exceed the setting. It's hard to make yourself change from what worked before.
Hey guys thanks for all of the advice, it's really appreciated.
Just to clarify some things, it is actually a 3gf joint. 30 on one side and a 90 on the other. We are not permitted to grind test plates at all.
I started the day by doing some t joints vertical to see what is giving me penetration and what isn't. After snapping them I could see how far each weld was getting in the corners.
The solution seems to have been upping the volts to 22 and the feed up to match. I managed to do some real nice work and had to cracks in the coupons.
I was also asked to do some display plates for the welding dept. cabinet.
They had me do 1 of each poition flux core plates and gas metal as well. Unfortunately my overhead mig is aweful. So I passed on that for now.
Keep in mind that MIG welding is very fast compared to stick welding. So fast, that it is not possible to ensure good bevel fusion by relying just on the naked eye. So after finding your rough mix of voltage and amperage (feed) that is working for you, it is helpful to fine tune that voltage once again. Slowly increase your voltage until it is excessive (too much), then taper the voltage back just enough to be within range. It will leave you at the upper end of the voltage range for that amperage (feed), and helps with better wall fusion.
