keeping the arc going on thin sheet

Date 07-31-2002 04:19

When mig welding thin sheet I have trouble keeping the arc going. I need to move along at a good clip to prevent burn-through. My regulator is a preset cheapo type. Would the correct thing be to increase shielding gas flow ,(if I could), when arc travel speed is high? I know if flow rate gets too high it can spread out and draw in air, thus reducing the shielding efffect. I was thinking that at a high arc travel rate the gas would not have the chance to bounce off the work and draw air into the weld area. Is this a reasonable hypothesis or am I totally wrong. On the other hand, if you used to little at a fast arc travel , the gas would not have the chance to envelope the area before the weld occurred. Are any of my guesses even close to correct? It's frustrating because the welds are just great when the arc keeps going, but once it starts to sputter that whole area turns to crap. Burn through hasn't really been a problem with the welds. I'm doing some 20 gauge steel. Basically backyard project stuff. Plan on doing up some maple syrup finishing pans before next spring. I don't want to trash the expensive 304 stainless sheet and 308 .024 wire.

By kam

Date 07-31-2002 12:33

Do you lose your arc only when traveling at high speeds? With alittle more info I might be able to help you. What are you weld parameters...volts, wire feed speed or amps, type of gas, ect... Could be caused by several things. Check tips, wire guides & liner for wear and replace if needed. What brand of equipment are you using.

Just a few ideas.

kam

By bzzzzzzzzzz (**)

Date 07-31-2002 15:36

sears craftsman 80 amp welder with 75/25 gas. only two settings-high and low. gas regulator is preset supposedly for 20 cu.ft./hr. tips are quite new. liner is probably old but I did take it out and clean it and blow it dry with air. I clean the steel to shiny before welding. As for wire speed- I set as follows: Turn it up to max. strike arc. slowly turn it down until it has a smooth buzz sound. weld. The range from sputter and burning back to buzzng smoothly,. to hissing and back to sputtering is not much movement on the dial. Could this mean that the drive system is not especially precise in the machine? I set drive rolls and brake both as light as possible to achieve ther purpose. Also, all the talk is of a "frying bacon sound". When I tune wire speed I get two distinct sounds while it maintains arc. First is a kind of "zipping buzz noise" then a hissing sound. The zip sound seems to weld the best. Is this the "fryiing bacon" sound?

By overthehill (*)

Date 08-01-2002 04:14

Your doing good bzzzzzz. You want that smooth buzz sound. The gas and cfh are fine. You may just be traveling too fast for the amount of power that little machine has. You say that machine only has two settings. Is that voltage settings? Are you running on the high setting? Are you maintaining a 1/4 to 3/8 wire extension (from contact tip to metal)? That's kind of important. Having more wire stick out reduces the amperage necessary to burn off the wire, cooling down the weld. The only other thing would be to try and slow down a little. Welding downhill on thin guage works pretty well, cause your welding away from the heat. You can also push the weld and carry the arc back on the puddle a little. The molten metal acts sort of like a heat sink, limiting penetration, which is what you want to do on 20 gauge.

By Goose

Date 08-01-2002 15:29

I do a good deal of sheetmetal welding at a body shop doing restorations.

One trick you need to use is to stitch weld about 1/2" to 1" at a time, then stop, and move to another area (I also keep a wet rag close by to cool the welds and keep heat from warping the panels). You need to move around and perform short beads to keep from warping the thin sheetmetal. Also, the short beads limit heat input which helps keep from burning holes.

Your amperage/voltage setting may be alittle hot, but we keep our shop welder set hot on purpose...this allows the machine to be able to burn through zinc & galvanize coatings on new metal and rust/paint on areas where you just can't get in there to grind everything real clean. It takes a light touch on thin sheetmetal, so if it looks like your starting to burn though, let off the trigger fast. Your finger needs to be able to start and stop the arc quickly to control heat input with thin sheetmetal. If you try to lay a long bead on 20 ga., you will run the risk of blowing a hole.

By bzzzzzzzzzz (**)

Date 08-01-2002 15:37

Is it still possible to get watertight welds with stop/go method such as this? That is what I need for this project. I do stitch it intermitently before I attempt the whole bead. Usually grinding the stitches smooth to where they barely hold the pieces together. Then I weld the entire seam. Tried to slow the travel down somwhat the last time and it seems to keep the arc going much better. Probably just need lots and lots of practice. Burn through has not been too much of problem.

By overthehill (*)

Date 08-02-2002 04:24

What Goose is doing, welding on galvanized or painted metal, is extremely difficult, no doubt about it. Welding on clean shiny new metal is a lot easier. Can you get watertight welds with a lot of starts and stops? Maybe. The problem is cold starts. Sewing it up like your doing, then grinding it off, and making another pass works good, just takes a lot of time. What your doing is getting rid of the edges, which like to melt away. Just keep practicing. Crank the voltage on that little machine wide open and tune the wire. Watch the puddle. You have to move fast enough to keep from burning through, but not so fast that you leave the puddle behind. On some practice metal, try slowing down till it burns through. Watch what it looks like. The idea is to move just a little faster than that, kind of right on the edge of total disaster.