What I learned today: prep is everything (first TIG welds)

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After finishing a few projects with the MIG side of my new Multimatic 200, I decided to try some TIG for the first time ever today. I know, I know, I've seen it said a million times that prep is important for TIG, but it just didn't really sink in until I tried it out today.This is some practice beads on a piece of 1/8" HR, about 6" long. 3/32" tungsten (grey, I believe, whatever that is) and using the autoset on the MM, which I seem to recall was 110 amps, pedal to the floor. The very top bead was done with the metal "cleaned"...that is, wiped down to remove oil and crap, but I didn't remove the mill scale. It went so horribly that I knew my days of being lazy with metal prep were over. I mean, I usually prep at least a little for MIG, trying to get down to bare metal where I can, but if there's a difficult area to grind or I just forgot then so be it.After that first "bead" I sandblasted the whole thing to get off the scale, hit it with the flap wheel to get it shiny, wiped it down with some mineral spirits (didn't have acetone handy), then hit it with the torch for a few seconds to burn off anything the mineral spirits might have left behind. (The first line ended up being ground mostly off). The next bead, second from the top, was a night and day difference. The puddle was so nice and I didn't see anything at all floating around in it. I was sold. Then I tried a few beads with some filler.After a few lines, however, I noticed things going downhill pretty quickly again (5th and 6th beads). I thought it may have been a contaminated tungsten, but even after grinding it down it didn't seem to help. So then I figured maybe the act of welding itself left some contaminants near the weld, so I left a bit more of a gap before doing the next one. This one, the 7th, turned out very nicely again. So I tried some more lines close to that to test my theory, and it seems I may have been right since things went crappy again. Either that or I just contaminated the weld early on in these ones and didn't notice. Or perhaps heat had built up or something and it affected the weld? So, could somebody answer that question for me? Does welding contaminate the area around it, needing it to be prepped again if doing another weld in that area? Or did I just screw something else up?Then I ran out of time and had to go to my day job, so I decided to run two more final beads -- one with filler and one without -- to see if I could get somewhat consistent results on metal I thought to be thoroughly "prepped". Considering they're only my 11th and 12th beads with TIG, I think I did alright, though perhaps you guys can spot some issues that my noob eyes don't see (other than the wandering line and unevenly spaced dimes)? Any and all feedback is welcome.And so the practicing begins...
Reply:You understand what scale is right? It's oxidized steel caused by heat and air. When you heat steel with the tig torch, you can form scale if the material surface isn't shielded by the argon gas. this happens a lot on the back side of pieces that are thin. you grind off the scale, and then re create it with your torch heat. That is one possibility. I see a bit of scale at the edge of the left hand bead 3rd down from the top in the 1st pict.On thin stuff I've seen guys pull mill scale in to the top from the back if they overheat it. It can be fairly common on 1/8". It's possible in your case that's what happened as I don't see a lot of scale in those picts of the top, but I won't be all all surprised if I see that in the picts of the back.As far as the tungsten contaminating the weld. it happens usually when the tungsten gets fouled. With steel, usually you will see a tell tale red dust on the surface that tells me some one dipped the tungsten and fouled it without stopping to grind.Bead on the right pict 1 3rd row down looks fair. All the others need more filler and might possibly be a bit narrow. Things that help us help you. Material thickness ( which you posted), tungsten size ( posted), amps used, filler size ( neither of which I can find).Tig gives you the most control over your weld, so it's very important you learn to control everything that is going on. I tell students to 1st spend 30 minutes playing with the pedal so they learn what it does and they have an understanding of how to use it. After than they shoud set the machine to a fixed amperage, say 100 on 1/8" and then play with just travel speed or torch height to see how those effect the puddle. It's not something they will work with right away ( unless they don't have a pedal and are doing scratch start) but they need to have an understanding of how these things change the puddle so they can understand why they get really nice beads one time, then everything goes to $hit the next. Typically it's because they changed something like travel speed torch height or torch angle and didn't realize it.Right now you want to limit as many variables as possible, and if you change one, you change only one at a time. Consistency is king right now. Keep practicing..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Originally Posted by DSWYou understand what scale is right? It's oxidized steel caused by heat and air. When you heat steel with the tig torch, you can form scale if the material surface isn't shielded by the argon gas.
Reply:Beads on flat plate always look a bit different than actual welds on joints. Width wise I look for something 1/8" to 3/16" max on 1/8" plate. Typically you want a bead the size of the thickness of the plate material. though on smaller stuff, that can be a bit more difficult to accomplish, thus a slight bit wider isn't too bad. Height about 1/16" roughly. I look more at how the toes of the weld meet the plate to tell how "cold" the weld is. I want a nice smooth transition like a mound or small hill, not a really steep transition like a mountain.3/32" filler is doable on 1/8", but can wick out a lot of heat from the puddle if you are borderline. Remember you melt the filler with the puddle, NOT the arc. We typically use 1/16" filler to tig 1/8" at the tech school on steel. It's a bit easier to melt with the puddle. I keep both in the shop depending on what I'm doing. T joints are pretty easy with 3/32", but it can get a bit tough on outside corners if you are running a bit on the cooler side with a rod that big.Amps sounds about right. 125 amps is typical for 1/8" steel. Slightly cooler like you are running and you need to slow your travel speed some to compensate. 110-115 amps is about what I like to have students run if they have no pedal as it allows them to cool things down a bit by speeding up a bit and lets the filler chill the puddle a bit more..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Learn the basics--general amperage per piece, argon coverage, speed, and etc.--and the rest comes with practice and patience. I am a tool welder by trade so I am not familiar with the math involved. Eventually you learn to do things by feel, you just know what amperage, what speed works. You are essentially drawing, sculpting, material on to another material. Your welds look like mine the first time I started. Remember those days! Just keep at it. You will improve.I am what I am. And I do what I do.