I've been practicing welding the last few days and the first day my friend was coaching me. I was practicing on an exhaust joint and made a remark about a certain spot on the "lower" piece (the pipe that slid into the slightly larger pipe) not getting good penetration. I asked him how he could tell from the outside, but he didn't really answer. So, how can you tell from looking at the outside if it has good penetration. Right now, it reminds me of buying fruit, I know what the outside looks like, but don't know how to check the inside.
[ QUOTE ] So, how can you tell from looking at the outside if it has good penetration [/ QUOTE ] To start,the edges should be washed in smoothly with no undercuts. If your weld is sitting on the surface like a Snot Ball,then you don't have enough penetration.
The weld should not look like a worm sitting on top of the piece, But you should NOT have any undercut either, you can also get an idea from the "heat effected area" around the weld. Weld something similar and then cut it in half (across the weld) and check the weld out. LUKESTER
Depending on the thickness you should be able to see evidence on the back side of the weld. Try welding a couple pieces of scrap together, put them in a vise and give it the bend test. If you don't have a good weld you will know right away. TZ
I have to say I have no idea what "washed in" or "undercut" means. I'm guessing that being that this is just exhaust and mainly for sealing purposes, and that there is a section of flex in there, I'm probably all set with what I've done so far. I'll start doing some tests on scrap this weekend. This is fast becoming my favorite tool.
well for one u can tell a good weld just from the sound it should sound like becon frying on a open grill over fire . 2 u shold have a nice moltent puddle followng u the hole time listn for imperfectinons.3 if u can see the back side u will vissaly see if its a good weld try some tacs on sheet metal and u will see the penatration.4not to sound like a ass to drive my car ,i couldent tell u how far to depress the accelartoto matain a certin speed ,its the samewith mig welders u can come close to your initial settings trial and error is what u need to get it rightso pick a reasonabal setting on your welders chart.pratice on some scrape the same of what u are going to weld until u can determan the right settings5 u can check by color around the welfmild steels melting point is between 2400-2700 dreegs /f\it should be dazzling white i medium light not in the sun.5 ill tell u to get some scrap and go ahead and burn through it itll give u a feel for tempature and visually a good looking weld can be a bad weld like migs have less penatration and less clean up so just pratic u will be able to tell wit some pratic live your life by the law and i wont live life at all
Deyo, Think of a caulk gun. If you lay down a bead with the tip away from the surface, you'll get a round "worm" of caulk laying on the surface. If you hold the tip against the crack your caulking, it'll push into the crack and spread or "wash in" to the surrounding surface. If you push the tip to far into the crack, the caulk will all push out the other side and you'll see the original edges of the crack above the caulk (undercut). Your weld should look look like part of the original surface. The edges of the weld should be the same height as the metal surface and should slightly flow into the original metal (wash in). If your set too hot or move too slow, you'll sink the weld too far into the gap and you'll see the original edges above the weld. If your set too cold or move to quickly your weld won't penetrate. If your shielding is wrong (gas or flux) you'll get a lot of sputter and your weld will look sloppy and won't penetrate right. Your weld should look like a caulk bead when the tip has been pressed lightly against the surface. Even height with the surrounding surface and a slight, even, rippling. Mark
On the exhaust you mentioned or sheetmetal your bead will[should] be penetrated to where it is showing about as much on both sided of this thinner metal- on a thicker peice you should have blueing on both sides and around perimeter-to show the heat applied. a sharp rap[not that street music shit] with a hammer will test the weld/ a poor one may just fall off!
While you are practicing, turn up the heat until you start to blow through. Getting the feeling for too much heat will be a big help. Try filling the holes when you blow through. Getting the touch for each extreme will make it easier to get the right heat for the material, location and type of joint you are working on. A good welder can carry more heat and move quicker than a novice. You have to develop the "feel".
The first time we tried welding on this same pipe (pieces taken off of another fairly new exhaust) I didn't have the bottle of Argon/CO2 yet, so we were using flux core, .030. Even on the lowest setting it was no match, we might as well have had a plasma cutter, it just blew right through the shit. I'm loving this gas thing.
I think UnklIan nailed it. If it looks like a rabbit took a crap, that aint good. You should get some scrap pieces, weld them up and then cut them apart across the weld. You'll learn alot about how best to set up the welder. I've been welding for 6 or 7 years or so and I've still got alot to learn. Worked with AntiChrysler on some stuff today and learned quite a bit. He's ugly, but very talented.
The idea to weld similar size scrap and then cross-section it is a good idea. Here is how to make that cross-section even more effective. After the saw cut, grind it down successively finer until you reach about 600 or even better 1200 grit sandpaper. At this level you should be able to really see you weld. To make the weld show up, you can etch it in dilute acid (like 2-3% nitric is great). Just swab the surface for a few seconds and you will see the weld and heat affected zones show up real nice. The finer grit you have it before etching the better the results. You can get the 2-3% hydrochloric acid solution by diluting swimming pool acid, commonly called muriatic, which I think is about 20% hydorchloric. Nitric is better, but harder to find in a cheap commercial source. Gas shielded MIG is the only way to go as you found out. If you really want to learn to weld proper technique and learning what is happening, sign up for a course at your local junior college. Or maybe they have an adult education program through your local scholl district. Your local welding shop may even offer classes. Either way you will get instruction that will make you a better welder. Welding is not just science but also has an art elemnt involved: the skill of the welder plays a significant role. You can have perfect machine set-up and still make shitty welds if you don;t use good technique.
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