Starting a mig weld?

[loply]

Hi folks,

Been doing quite a big of mig welding on 3mm thick mild steel box section lately using my Clarke 130amp mig welder with Argon/CO2 and 0.6mm wire.

I'm having a problem with getting a good result - I can weld very neatly with good penetration after a few centimeters, but when I first start the weld it struggles to make a pool and I get a tall, bulbous weld which hasn't really penetrated.

Because this is box section I can't weld all around it in one, so the end result is that on each side I've got 50% good weld and 50% dodgy stuff where it hadn't heated enough yet.

If I hold the torch on one spot to try to get the pool going, or don't move it enough, it just ends up with a bigger blob.

I'm welding on full power and the welds are definitely good once I can get the pool going.

Any tips on how to work around this?

Cheers,
Rich

[DHACK666]

Try slowing the wire feed down.

But I have not used that small of wire after I used the first roll. I switch over to .030 inch or about .8 mm.

I run a Lincoln weld pak 100 120 volt. 3 mm is only 1/8 thick. I don't run it at max output for 1/8 but I have always used .030 wire.
My gas is set to 18-20 , (I think that it's L/min)

[J Tiers]

Wire speed SHOULD set the current.... and so the welding heat. That wire may be too thin.

If the filler material is piling up, there isn't enough heat to get into the base metal, it is cooling off too fast and freezing in lumps that stick up. More heat should get it started faster.

Some welders have a bad calibration on the voltage dial, you might try adjusting that. A bit higher should give more heat, subject to wire thickness.

I may not know much, but so far it seems quite a bit better to have too much heat than too little.... you can nearly always move faster....

That 0.6mm wire is thinnish...... 0.023 inch while 3mm material is , in imperial, 0.120 inch. You might do better with thicker wire, which will also raise the current and delivered heat. We welded that thickness in class with 0.035"/ 0.9mm wire, and it started fine.

[strokersix]

Be sure to clip off the wire sticking out of the gun before each weld. Possibly allows a split second extra shielding gas flow before the wire touches? Not sure why this helps but it seems to for me.

You could preheat the parts. A minute or two with a propane torch would probably be enough.

May not be practical but I have placed an extra piece of material in front of the deisired weld. Start your bead on this material and by the time you get to where you want the good weld the pool will be established. Of course you then need to break off the sacrificial starting piece after welding. I've done this with stick welding but not with MIG. Application was nickle rod repair of cast iron where I wanted to make sure the arc was established and good bead going before I reached the part I was trying to fix.

[BMW Rider]

Its an inherent problem with a MIG welder to have a cold start on the weld. Some higher end machines are designed to minimize it, but without preheating, it's hard to eliminate. The smaller/cheaper home machines like your's are often really bad for it and hard to overcome the problem. I used to have a Clarke unit too, and could never get really nice welds consistantly with it. My Miller 211 is much better at minimizing the problem. If the welds are super critical, you may not be able to get a satifactory job with a MIG at all.

Of course, its important to ensure your setting up the joint properly for the weld too. Not sure if you're doing butt welds or fillet welds, but leaving a slight gap in the joint will allow better penetration. If the two pieces are tight together, the lack of penetration on the cold start will be much worse. It might also help to use a stiching technique.

[Forestgnome]

Mine is computer controlled and provides different start settings. I think with your machine a preheat would be the best solution. It doesn't take much, a propane torch would do.

[loply]

I have a propane blow torch, how much should I be preheating? Are we talking 10-20 seconds worth, or until the work glows?

Most of my welds are 90 degree intersections between once piece of box section and another.

Thanks for the tips so far.

[strokersix]

I would heat until you start to see some oxide color, say 450F. Probably does not need to be quite that hot to be effective but that's a good place to start.

[Fasttrack]

Its an inherent problem with a MIG welder to have a cold start on the weld. Some higher end machines are designed to minimize it, but without preheating, it's hard to eliminate. The smaller/cheaper home machines like your's are often really bad for it and hard to overcome the problem.

Yep. Short of buying a new machine, there is not often much you can do. Like JT said, the current is determined by wire speed, so increasing the wire speed will increase penetration as weld current increases. Changing wire diameter may also help. The larger the diameter the wire, the better the penetration but the faster the fill, meaning you may not have time to burn in your bead before you're forced to move on or let the puddle spill.

If the welds are super critical, you may not be able to get a satifactory job with a MIG at all.

Lest any newbs be misled like I once was, this is not entirely true. MIG welding can be effectively utilized if both the machine and the joint are setup correctly. For some reason, in automotive circles, there is a misconception that TIG welding is the end-all be-all of welding and is the only process suitable for "critical" welds. Sometimes, the extra control and precision offered by TIG welders is needed, but MIG, SMAW and TIG can all be used on critical welds.


Regarding preheat - until oxidization colors show is a good place to shoot for but it isn't super critical if all you are concerned with is avoiding the cold start.


<EDIT> I used to have a 110 volt stick welder and it was susceptible to cold starts, as well. It had very low open circuit voltage. I then moved up to a Syncrowave 350LX ... can't remember what the max OCV but it was capable of 65 volts when set for 200 amps. Even the old cracker box I used pegged out around 40.

[mark61]

Use a start/run on tab of metal to get the weld up to temp. Place a piece of steel next to where you want to start the weld. Begin the weld on that tab then move on to area you want to weld. Break off tab when done. You can "jump" or "skip" the weld across where the 2 meet.

mark61