Ending a MIG weld

It is a good idea so snip off the end of your wire before every start. It helps with bad starts. As you weld a bead the heat builds. When you start your bead it is relatively cold so start your welds at the thing edge that you likely would burn through if it was at the end of your weld. another tactic is to start at the thin edge and weld in about half an inch. Start your weld at the other end and meet your short little tack at the end. You have already figured out another ploy. By filling your crater afterwards. with a bit of planning you can come to the end of your weld, release the trigger then pull the trigger just as the red disappears and fill the crater. Randy

"Randy Zimmerman" wrote: (clip) As you weld a bead the heat builds. (clip) This is a related question. My MIG welder has four heat positions. For most of what I do, the highest position works best, but it is sometimes a little too hot, especially after the "heat builds" as you say. Yet, the number 3 position is to cold. Is there anything wrong with interrupting the weld, and then restarting it as the crater cools, as a way of keeping from burning through?

Rapid stop starts with bare wire mig is commonly done on thin material. You don't necessarily get the best weld but you avoid melting through. If you stop start too much with flux core there is the risk of slag inclusions when you start up on top of cold slag. To avoid melt though you also can speed up or do a rapid forward back motion to elongate your puddle spreading the heat over a larger area. With wire feed you also can increase your stick out. This automatically reduces your amperage slightly. Remember though that with increased stickout the shielding gas may not provide enough protection. I have used inch and a half stickout down in a corner where the shielding gas is trapped. The gap is filled then a cover pass is put over to hide the sin.... Hoping Ernie doesn't spot it when he inspects :')))) Randy

Some machines have "stitch mode" for this sort of thing. My old Dan-Mig does, and I use stitch mode pretty regularly to prevent burn through on really thin stuff.

Gunner

Liberals - Cosmopolitan critics, men who are the friends of every country save their own. Benjamin Disraeli

hi all

Following on from Randy's comment about stick-out. If you increase stick-out you also increase Ohmic (electrical resistance) heating of the wire. So when it gets to the arc, it melts-off more easily. So even if the current didn't fall, there can't be as much arc energy if some energy has goin in ohmic heating... With a constant voltage power supply, whihc MIG's are, there is a current reduction as resistance goes up... So with increased stick-out: for two reasons you are not arcing as energetically (reduced current and more of that reduced electrical energy used up as ohmic heating); while you are still deposting metal at teh same rate (wire feed speed is fixed) - and metal is coming off the wire as a liquid due to ohmic preheating before the arc and the arc is still doing some melting of the base metal.

Damn', that's not a very neat explanation. Anyway, from what I've observed repairing motorcycle exhausts with a lot of corrosion and thinning, if you think you are on thin metal, pull away to more stick-out and you are deposting metal with very little melting action on the sheet metal.

Anti-patent idea declaration - if could have a nozzle which can move in and out, perhaps under the control of a switch on the torch, you could pull more stick-out at will, pullnig the torch back in pace to the nozzle trying to come forward, so still be delivering shielding gas to shroud the weld. Sorry - over-active imagination...

Richard Smith

When I am at the end of a weld bead with a MIG machine, I was taught to fold the weld back on itself slightly to fill the crater that forms at the end of the weldment. It's just a very slight reversal of direction back up the bead at the end to fill the crater while your still running the original bead. That has always worked for me.

Try snipping off the end of the electrode wire after each weld bead. This ensures that there is a fresh, un oxidized end of the electrode wire. Also you might want to reduce your stick out to start your bead, just a bit, and set your stick out appropriately while welding.

Hope this was of some help James Walsh Jr. Jigsaw Custom Fabricating

All,

Thanks for the tips. These are the things they don't write about in the books or instruction manuals.