OPEN ROOT DOWNHILL MIG (USING STT)

by Jason Becker


Alright guys. Welcome back to another episode of weld.com. Today I'm here again with Man Cub and we're going to be talking about some STT or Service Tension Transfer, really good for thin materials, poor fit ups, large gaps, things of that nature.


So today we've prepped up a three eights plate. I've got a 37 and a half degree bevel. We went ahead and opened it up to about a quarter inch just to kind of show you the range that this process has and what's available to it as far as poor fit ups. So what I'd like to do is on the back end, I want to end up flush to one eighth of weld reinforcement. And today we're going to be using the Lincoln Power Wave. We are running about 150 inches a minute on our wire feed speed. Trim is going to be set to point 98. Now what trim's going to do it's just going to adjust our arc length typically between point five and one point five. So one is about the ideal setting. However, we're going to run this vertical down. So I'm going to set it at point 98. This is going to shorten up my arc length just a little bit and provide me a little bit of a stiffer puddle, so that puddle doesn't get ahead of me while I'm welding. It's a short circuit process, we're going to run 75, 25 gas, about 30 CFH and I think we're ready. Alright Man Cub, so what we're going to do is we're going to start at the top, and we're going to work our way to the bottom. So we're going to run this downhill. Typically you know, everybody always runs uphill. I'm not looking for penetration on this. I want to keep the profile low, flush to eighth inch in the back. You know, so I don't want over penetration. STT is going to help with that. As I'm coming down, I'm going to probably come in perpendicular and drop about 10 to 15 degrees on my travel angle and I want to stay right there at the leading edge of that puddle. Typically with regular short circuit, you know, you end up with a lot of whiskers poking through on the back. STT is going to help alleviate a lot of that. - [Man Cab] Gotcha. - It's got like a, you know, kind of like a voltage sensing, you know, where the peak current is going to hit and it's not going to allow it to overflow. So when you think of STT, it's kind of like a raindrop, you know, you get that surface tension on water. Very similar to that you know. As it penetrates through the back, that's when it's going to cause that electrical short and then it's going to reestablish the arc so we don't blow through the back. - [Man Cub] So we just feather our tacks and so we got to have good tie ins here? - [Instructor] Yeah, we get the tacks feathered. I got a little bit thicker up at the top that way I can initiate the arc there. - [Man Cub] Yeah. - [Instructor] Pull right into there and we should have a good tie in at the top tack. And then as we work our way down the bottom tacks feathered on the top side. So we'll get a good tie in coming back into it. So if you notice on the front and back of the coupons here, we've cleaned up all the middle scale, about a half inch on either side. - [Man Cub] Yeah. - [Instructor] To kind of help alleviate you know, any discontinuities we would have and just try to set up the best possible scenario for our weldment. - [Man Cab] Gotcha. - [Instructor] So as I run this It's going to oscillate side to side a little bit and stay at the leading edge of the puddle. I want about a half inch, I've got three eighth contact tip to work distance. You'll notice that it sounds very similar to a short circuit process 'cause that's you know ultimately what it is, it's a variation of short circuit. Just get right there at the leading edge. We're going to run this about halfway, and then we're going to let Man Cub take over and give it a try. - [Man Cub] Sweet. I'm going to stop right here. Alright, so now we're going to switch sides. Man Cub's going to go ahead and take over, but before he starts welding on it, what I want you to do is feather this tack out. Typically I take an eighth inch wheel and a feather out kind of about three eighths of an inch. Take it down from the biggest part of that weld, almost to the same thickness as that fainting that we have on here. - [Man Cub] Alright. - [Instructor] And then when you restart, just restart on whichever side you're most comfortable with and then bring that back through. - [Man Cub] I'm just moving back and forth like that, right? - [Instructor] Yes sir. - [Man Cub] Stay on that leading edge. - [Instructor] Stay right on the leading edge. - [Man Cub] Alright. - [Instructor] Hey, why is that balling up like that? - [Man Cub] Where at? - [Instructor] The wire piece for the whip circle. - [Man Cub] I don't think so. Yeah, I can feel the wire chattering in here. It's got resistance on it. - Looks like you've got a pretty good tie in here. You know, you said when you were down towards the bottom you were getting resistance and the gun you felt like the wire was balling up a little bit. And then you got some kind of excess batter up in this area. So the most likely culprit of that is the contact tip to work distance. That's a very key element, you want to hold that nice. Three eighths to a half inch contact tip to work distance and then everything will flow in there a little bit smoother for you. Alright, so let's flip it around and check out the route. - Alright. - Now you've got a pretty good restart in here, it's about the area where that was performed. So that tied in good, everything is flush, it looks like that turned out right. We got a little bit of under fill in this area and that's where you ran right into that bottom tack. So one thing we could do to alleviate that is maybe feather that or taper that in a little bit more. - [Man Cub] Yeah. - [Instructor] Where as you're getting close to the bottom there, just kind of rotate that angle your torch down a little bit further and it's going to punch through into the back area for you a little bit better. - [Man Cub] Gotcha. - [Instructor] But that's exactly what we're looking for. So I mean, we have a a quarter inch root opening. There's no excessive penetration. You know, we don't have any whiskers sticking out on the backside. - [Man Cub] Yeah. - [Instructor] So that's kind of the ultimate goal here. That's just a minor discontinuity and we could remedy that quickly. - [Man Cub] Then we could pass a what? A D1.1 code with that, just by fixing, we can fix that on our test and keep going. - [Instructor] No, we couldn't do a D1.1 because short circuit is not pre-qualified. So we'd actually have to write a procedure for this. - [Man Cub] You would have to write the procedure, gotcha. - Make sure you guys subscribe to our channel. Click that like button down below. If you have any questions, leave it in the comment section. Make sure to follow us on Facebook and Instagram. And until next time, make every weld better than your last.