Your welds look pretty good. They just have to work--that's it--no winning a beauty contest.
Try a 1/16" tungsten ( purchased 1/16"x7" 2% Thoriated tungsten today at my local welding store when getting argon. They didn't have 1/16" 2% Lanthanated tungsten but, I ordered it from amazon when I got home, should be here this weekend. I'll use the 1/16" Thoriated for now, I'll wear a respirator when grinding the tip, otherwise my wife will be pissed if I come into the house, glowing....LOL ) and
use any small MIG carbon steel wire you have. I think you might like that on 19 or 20 gauge ( will use that tomorrow and will post an update with pictures )
The quality of your weld only has to meet/exceed how you intend to use it. @ wore-out welder has given some good advice about motion--
the more uniform rhythm you can be the faster you can weld with the least amount of heat input. As you already know, and I know Pugsy and Wornoutwelder already knows, one of my complaints has been too much heat build up, especially from mid point of my welds, to the end of my welds due to not having a foot pedal to control amps. What you, Pugsy and Wornoutwelder already know, is heat can be controlled without foot pedal amps, simply by speeding up and adding filler. I figured that out after you told me quench cools the weld. That method/procedure is what advanced my learning curve this week. It was a major hurdle for me. Now I have to get my rhythm so I'm not too slow adding filler (cold weld) or not adding enough filler ( hot weld ) You want to sequence weld deposits to act in your favor and keep in mind the concept of "fixing" a weld start in the highest restraint place then work towards "free points" alternating deposits outward in sequence via symmetry from your first fixed point if possible.
Don't weld into a corner if you can avoid it--start there and work back out and try to end a weld on a weld (understood)
"Walking the cup" makes a huge difference. Your heat lines are a way wide in comparison to the automatic machine sample below. That's as close to a robotic weld as you're going to get and that could be regarded as perhaps the most idealized set of welding parameters. That was done in a six segment program I wrote for the programable power source at about 130-145 amps and using a 3/32" tungsten except for the last segment where the weld slows down and tails out. I changed pulsing frequency and width duration time over the course of the segments in my favor-but kept travel speed constant after it punched through on starting. That tube sample is double the thickness of your sheet metal one--about the same length of weld and likely way more amperage you than you used and the heat lines are less than a 3/16" or so into the base metal. The ones on the ends of the tube are from the hot cut-off saw--I was too lazy to use the bandsaw to cut it down so I could photograph the inside. It's all about uniformity and symmetry in the weld deposit punching thru and solidifying as you move forward in synchrony. Such ideas can be applied to manual welding--to help offset the usual problems. But the act of welding and how to use it is a whole other matter. You have to be able to determine what end result you want--welding is just one part of problem in metal joining. You have to be able to access how to remedy the negative issues welding can leave. Sometimes it creates more than it solves and then its sorting it out backwards. Dry Ice is often a way out.
I do some automatic tig work on 2" OD tubing both carbon and stainless at about 0.130" wall or thereabouts. Essentially you square the ends of the tubes to within 0.005" square--butt them together tight in the welding head and press the machine button attached to a power source for a automatic deposit not using any filler metal. It's called an autogenous weld. And in this case--the weld starts and ends on itself.
The sample in my hand was x-rayed and is flawless internally and externally. I cut it down from it's 1' sample length to take some pictures of the inside surface. The external weld surface is flush with the tube's outside or proud by a few thousandths--it is not concave--it is flat or slightly reinforced. The inside has root penetration all the way around. Looks as good on the inside as out. The weld didn't "shrink"--it "expanded" and gained volume with no addition of filler metal. The tube wall remains constant in thickness all the way down the welded sample length--What happened? The overall length of the 1' length of sample contracted in overall length because it was free to do so with no restraining forces. This only was this way because the weld started and stopped on itself--that length was fixed unable to change in circumference length.
Look at your sheet metal welded sample, free to move around on your support when you welded it. If you started welding at one end and ended at the other--even though they are tacked together--the end where you stopped welding is likely no longer straight across-it is a bit shorter when you check for square with the long edges with a combination square. You may also find the width in the very center is less across the welded piece than when you started. That's what feeds your thickening of the weld and its increase in volume--regardless of if you used filler metal. When something thickens and gains volume--something else moves and contracts. If there are restraining forces beyond that which is elastic--than something stretches and thins. It's often nowhere near the weld. In my business-- it can be 50' away. Planishing isn't always the answer when the elastic limit of a metal is exceeded.
( I'm still processing your last four paragraphs. Don't want to speak about something I'm not sure about in my mind yet )
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