MIG Techniques

[scolliflower]

I was concerned about the welds being cold, so I did a cross section. I cannot tell, what do you all think?

 

[Ed.]

By virtue of the fact that the weld hasn't broken you don't have to worry about your welds being strong enough, just need to work on your technique and travel speed so they look better and make the beads more consistant. If you want to look at the penetration, sand the cut edge down with a fine flap disk and/or some 800 grit wet and dry abrasive paper with water, then wet it with some acid; Nitric, Hydrochloric or other, when it has corroded the surface, you just rince it off, wipe it dry and you should be able to see the penetration.

Cheers

 

[scolliflower]

I did some reading and was reminded that the corner of the T joint must be fused to the root. You can see a pin hole there. Of course these are scrap pieces that I didn't take too much time properly lining them up. But could this be corrected with ensuring the arc is aimed at the corner? Also below are some more recent welds. I keep trying to improve consistency.

 

[Ed.]

Try raising the voltage up a smidge with the same wire speed for the horizontal welds, if your welder is capable of it, try 0.5V a time. Depending on your welder it shouldn't take more than 1.0 to 2.0V for it to make a noticible difference in bead appearance and also slightly flatten down the bead in the process. I don't know if you already do so, but if not, support the torch with the other hand as well, any slight shake or wobble whilst holding the torch will result in uneveness in the bead.

Just out of curiosty, what gas mix are you using and how old is the torch liner? as it could be grabbing the wire intermittantly. There are quite a number of factors that could produce uneveness especially in older machines, another one to consider is whether or not the wire feed rollers are worn and need replacing and if the correct tension is applied to the wire. There are a few consumables that need replacing over time but are often overlooked.

Cheers

 

[Jan]

To my eye those top 2 pics on this page seem to have zero penetration. There's a visible gap where the two parent metals meet which should have been filled by the weld pool during welding. The butt joint looks like the wire has just fused with the edge of the top piece and then arched down to fuse with the lower one, but none of it has run between them. The same seems to have happened with the 'T' joint. A bit more heat and a slightly wider gap between the two pieces being joined might improve that.

 

[scolliflower]

I want to make sure I'm thinking correctly. I turned down my wire speed from the manufacturers recommended setting (from 7 to 5) but kept the voltage the same. I did this because the weld was too large and I was afraid to travel faster due to lack of penetration. I thought a larger weld pool made it harder to get penetration. Would increasing my wire speed increase or decrease penetration?

 

[Lawnmowerboy]

Your cut test pics have no penetration at the root. Some of your newest pics look better but still a little bit cold.

 

[Liquid Metal]

You need to have the two balanced, best thing i can say is to use your ears aswell as your eyes when setting up, aiming for the welder to sound like a sheet of paper being torn with no popping. If you have popping, turn the wire down a little at a time until it stops. If you have an adjustable gas regulator, adjust the gas to around 25cfh, this would be a good starting point. Also another thing which is very important with dip transfer mig welding, is to make sure you have a good electrical connection on your work return lead. Any heat in the clamp after welding is good sign you dont have an ideal connection.

 

[pedrobedro]

I was concerned about the welds being cold, so I did a cross section. I cannot tell, what do you all think?

You can't see the extent of the weld just by cutting the part, you need to polish to a shine and etch with some kind of acid (probably nitric?) to see the penetration.

 

[Ed.]

To my eye those top 2 pics on this page seem to have zero penetration. There's a visible gap where the two parent metals meet which should have been filled by the weld pool during welding. The butt joint looks like the wire has just fused with the edge of the top piece and then arched down to fuse with the lower one, but none of it has run between them. The same seems to have happened with the 'T' joint. A bit more heat and a slightly wider gap between the two pieces being joined might improve that.

Hi Jan, If I understand what you have written correctly, are you are saying that in this T joint, the top plate should have been beveled at the base where it contacts the base plate and the gap filled with weld to fuse the bottom part of it completely to the base plate in order to be a good weld?, ie a full penetration weld, and unless that is done it is not a good weld. If that is the case then I would have to disagree with you on that point. Unless the plans/design calls for a full penetration T joint weld then it is perfectly acceptable to just press the the plates together and weld fillet weld them together.

Here is a reference in case you are interested which explains this: http://www.lincolnelectric.com/en-u...heory/Pages/weld-fusion-weld-penetration.aspx,

As I said earlier, by virtue of the fact that the top plate has been flattened to horizontal and not broken or cracked, that bead would in my book mean that it is a good weld. As long as there is fusion to the root there won't be a problem, without a polish and a acid test you can't tell if that was achieved or not but as it didn't break the weld I would assume it did!

Cheers

Ed.

 

[Jan]

It would depend on the expected peak strain on the joint while in service. If the top plate has been hammered into going flat with just the weld, and not either plate, having distorted I would call that a weak joint which has failed. You can balance on a unicycle after a lot of practice, a bike with less, but for real stability 3 or more wheels are far better. Similarly Beveling or raising the upright metal will allow the puddle run between the two pieces. Alternatively you could weld both sides, but that would still leave a gap in the middle which could easily become the 'root' of a stress fracture. If it was merely a coat hook then the worst that could happen is that your coat would fall on the floor, but if it was an engine mount in a truck ...