i made a bumper for my truck with one of our mig welders at work and i had the amps set at about 115. I then primered with a paint bomb. i got the truck home and went to put the plates on it and i saw that my welds were sepaating and i could see dow in the weld some and it was already rusting afte 2 days. what did i do wrong? Should i make another pass with the arc? i did 2 passes with the mig. i made this bumper in to sections, i made the bumber main tubes one week and then this week i did the license plate holder and a place for a d ring and its the second set of welds thats cracking. whats up? i had the gas on and the welder was set the same as far as i can tell.whats up? thanks

 

What type and size of rod are you using? Some types, especially 7018, can crack if improperly stored. Also, if you are running 3/32 wire, that's too hot, and if you are running 1/8" wire, that is too cold. If you just dragged it, rather than weaving, there's a good chance you didn't get good penetration, or a lack of fusion between the two beads. Send me some photos of the welds, both the intact ones and the cracked ones, if you can get some.

 

I would say it is a penetration issue. Wirefeed can be deceptive, as the weld can look good, but just actually be laying on the surface. Arc welding can look good, but once you chip the slag, it doesn't look as good sometimes. When welding, you can see the colr changes, right after stopping. The heat glow should be smooth and continuous, no lines in the color.

 

im not sure in standard but it was .035 wire that we run on it. ill try to get some pictures of it, but the truck isnt here right now, so it will be later tonight. how do i post pics? thanks for the responses

 

115 amps w/ .035 wire is not enough heat. you MAY be able to play with the wire speed to make it work better but I would go with more amps or smaller wire. Greg

 

sorry but cant get pics tonight, trucks gone. i think im just gonna run a third pass with the arc and lotsa amps. figure i can just refuse all the metal thats already there. what amp. is good for a .035 wire on heavy metal? thanks for the replys

 

Be sure to grind the old weld down so as to get a better penetrating weld.

 

Thats what happens when you use a Mono machine you have no penetration the weld is laying ontop of the steel like a bead of silicone thats why we call mig welders mono machines. If the steel you were using wasn't absolutly clean along with the proper shielding gas etc the weld isn't going to stick.

I started welding when I was 15 I learned on nothing but stick no wire feed welders used in our shop its all stick. From 3/32s to 5/32s then Jet rod up to 7/32s and larger then again our welders are 3phase 400 amp DC one AC machine is a 600 amp it will burn a rail road spike it will also bite you if you wet.

Anyhow the problem you have is there isn't enough penetration you need to do as the others said grind the old weld out and reweld it. I can't tell how todo it with wire feed because I refuse to use a wire feed machine.

You can weld the brackets with 7018 1/8 I don't know how thick your plates are but you can chamfer the edge abit to get more penetration. I usually weld on the hot side I do get abit more splatter but thats what a angle grinder is for. I would rather have good penetration then good looks you can always put a cap pass over your root weld anyhow. If you were real fussy you can weld a root pass with 6011 then go over top with 7018.

When I was taught welding I was taught by old guys that only used stick they said you need to learn how to weld with stick first they said any monkey can weld with a mig welder. I don't know how many pounds of rod I burnt never did keep track I don't weld anymore only on my own stuff I can't hack it staring at a bright light and electricity running through my body.

Good Luck

 

What kinda metal thickness are we talking about..1/4 inch with one pass at 100 amps sould be about the lowest you could go. 150 would be about right with .035 also it depends on your torch angle and method. I've been mig welding for years and never had a weld crack or break. Make sure of what wire you are using. Are you sure someone didn't throw some different wire in there.

 

it also sounds like some disimular metal corrosion. the two different metals wont weld together right and then you have a bad weld. could be the wrong type of wire for the metal your welding also. what kinda of metal are you welding and what kinda metal is the wire you welded with? just a thought.

 

Hey Kenworth, I like welding bridging on bar joists in the winter. Wet gloves, wet butt. So when you put in a new rod you ground it in through your hand and out through your guy parts. Nice. Anyhow, If what you're welding is real heavy a little pre/post heating with a torch could help. Don't know much about migs, have only used'em once or twice. I know the metal has to be real clean though.

 

I've read some truth and some myth in this thread. There really isn't enough information given to make a conclusive determination of what the problem is.

We don't know how (or if) he cleaned the weld area.
We don't know what filler metal he used.
We don't know what weld prep (bevel,etc) he used.
We don't know if he ground the weld down after welding.
We don't know the material thickness.

With more info, we'd have a better chance of helping.
Odds are, it's not a preheat problem, since that's usually only going to be a problem on metals about 1.5" thick and up. It's likely not a problem with cleaning, or the weld would have cracked to begin with. The metal does NOT have to be perfectly clean to weld, but it is reccomended.

The cracking referred to with the 7018's being stored improperly:
This will be the case with any low hydrogen electrodes. What happens is if they have moisture in them, it will burn the H20, releasing Hydrogen. This hydrogen can sometimes not have time to get out of the weld (floats up) and will get stuck in there as the weld solidifies...resulting in porosity. Cracking can also be caused by cold starts, when the hydrogen is not allowed to escape before the weld solidifies.

Penetration MAY be an issue, especially if there was no bevel made prior to welding, and the weld was ground flush afterwards. Basically, you could have welded on top of the metal, then ground it off....leaving very little enjoined metal.

 

when i welded it i had the metal very clean. the metal was 1/4 inch piping. im not sure on what the type of wire was used in the mig. i talked to one of our pipe welders and he just pointed me to a box of rods and said to use them to rerun it after i ground it off. ill have to ask him what rods they were. the joint did have a bevel to it when i welded it and i didnt grind the it off until i went to reweld it so i can eliminate grinding off the whole weld. so far since i redid it, its holding up really well. thanks for all the info.
chrono

 

As I've heard on many jobs.. "If it were easy, they'd have women and children doing it."

Although I am not going to bash people, there is a touch of reality in the previous posts. Reading over this reminded me of a recent job I worked at a plant that's making the big tanker trucks for the military to take over to Iraq. One of the "welders" was welding a rear bumper on the rear frame assembly. I commented about some problems with the weld and his comment was, "It's just a bumper."

My reply, "Yeah, just a bumper. If the driver hits a landmine and the bumper comes off, it won't disable the truck and the driver will continue on, hopefully to safety....but what about the truck that's following him? Maybe it will be your cousin or neighbor driving that one."

I know you're just welding a bumper, but it can still be a big deal. You may damage it on a stump in the woods or something, then it can slowly rust from the inside, then something can make it fall off while driving. So what I'm saying is that lives WILL depend on your welds. You may want to practice up some more, try bending your stuff, like in an actual certification test, and make sure you find the reason why your welds are cracking now. You MUST find the problem to ensure that it's not a problem with all the welds you did on the bumper.

I'd tell you to take it to a qualified welder, but I don't think that would happen...so just find the problem and remember that safety is the most important feature that any welder can put in his work. If it's not safe, it's not done.

 

I'm pretty amazed that someone who has had classes in welding says that he ran a MIG welder at 115 Amps and used RODS in that same MIG welder that someone pointed toward .

To begin with, MIG welders are constant voltage machines, not constant current. There is no Current setting on a MIG welder.

Secondly, you don't use rods in a MIG welder, you use a roll of wire.

I'm sorry to be the one to get picky here, but what I'm hearing just doesn't add up. You have gotten some really good suggestions in this thread. People here want to help, we're not here to bash your welding skills, but you need to give the right information so you can get the right answers.

Best of luck,
Doc