Why do i keep getting pieces that have weldment fused onto only half of the weld. Is this the way lack of penetration manifests itself with the small 120 volt mig units? When I bust my practice pieces apart there are bits of weld attached to one side but appears to be zero fusion where it broke off. The beads also seem to be very high off the pieces. Is the heated area in 120 volt mig welds just too small to do anything but an ultra thin bead on thicker angles and such? What I dont get is why I can get a solidly fused bead to lay on one immensely thick piece, but can't fuse two together. Would it in theory work if the joints were exactly fitted and touching each other, and the bead was placed exactly in the center of that contact point. Is the small wire welder capable in theory of welding .25", but not in practice? Wow, lots of stupid questions. I better stop! Thanks to anyone who tries to give me accurate answers.
What you are experiencing is a typical problem with MIG welding when in the dip transfer mode. To get away from this you need to try and deposit in the spray transfer mode. This is not always very practical with a small capacity power source.
Obviously, you can improve your results with good technique and the correct gas for the application. If nothing else, make sure that when you are welding, the electrode dips into the weld pool on the leading edge. If it dips in, in the middle of the weld pool, you will invariably get lack of fusion.
Regarding the issue that it is only fusing on one side, may I suggest that if you break the specimen, it will always break on the weakest area. Just because the other side of the joint appears to be sound does not mean that it is. If you were to section the weld, and etch it, you would quite possibly find that there is not that great a deal of fusion on the other surface either.
Regards
Niekie Jooste
When I get lack of fusion what is happening? Is the wire simply melting in one large pool then spreading out over the unheated base piece? Perhaps I need concentrate on smaller weld beads and somewhat faster movement with the lowest possilbe wire speed? I'm completely new to welding, but it sounds almost like the bad practice of melting the solder with the gun and letting it drip onto the workpiece while soldering. Is this bascially what happens?
Take a look at this other string posted earlier at this site, I think it might help.
http://www.aws.org/cgi-bin/mwf/topic_show.pl?id=2224
I like your solder analogy, it applies pretty well sometimes.
G Roberts
Bzzz,
You need more current than I think you can get out of your 120 V unit to achieve spray. A few days ago there wasw a post, something about spray, which will have all spray parameters you need to find out if it's attainable with your rig and wire.
The diameter and designation of wire you use, machine settings, polarity and gas you are using are information needed to help solve any problem like you describe. Weld position and pushing the arc or dragging it also makes a difference.
Quarter inch is a bit heavy and may tend to rapidly age your equipment, pushing the limit of it's duty cycle if it is as small as I fear it may be... I bet it does a great job on thin # sheet, though.
Good luck
D
At the risk of being redundant, let's make sure you're doing the basics...
First make sure your two pieces are tacked together good on both ends and your ground lead is firmly attached to the material. This will help the pieces fuse together by reducing arc-blow, which could prevent your bead from fusing to one of the pieces due to reverse magnetism.
Next, crank your machine up almost all the way. (If it blows through the metal, turn it down a little at a time until it does'nt) Trying to weld too cold reduces fusion and makes your bead pile up high on the plate.
Next make sure your shielding gas is set around 30 cfm.
Then as your welding the seam, try weaving a little from one piece to the other in a zig-zag motion. This will help make sure the weld fuses with both pieces, just don't over do it. The bead should be no more than 1/2" wide.
If you want to make your bead penetrate all the way through the plate, prepare at least one of the pieces with a bevel before you tack them together.
If you still have trouble, you'll have to give us a little more information like what machine, wire, gas, metal, and joint design you're using.
Let us know how it turns out!
Tim
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