Weld Quality

Aeronut said:

Also, I was using 1/16“ 70S-2 filler rod, a 1/16“ 2% ceriated tungsten, #12 pyrex cup with gas lens, stick out of about 3/4 gas cup diameter, and an on/off trigger on the torch. Although I can use my foot pedal on pieces like this the intent is to practice with the same setup I‘ll be using on the fuselage. I‘m also not using pulsing. I played around with it and thought it did offer value but the constant „flashing“ kept my eyes from being able to focus. I‘m talking the pulse flashing not flashing caused by contamination.

Someone brought up fit. I don‘t have any before pics but using my tube notcher I was able to get a reasonably tight fit up. A gap wasn‘t really present.

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If it passes a destructive hammer test I am sure it’s going to do the job it needs to. Welding is like painting in the sense that it takes time to develop the skills to really be consistently proficient. The picture from Crash Jr shows what a skilled welder with good equipment will produce. If you don’t do this routinely you just can’t expect those kind of results. Keep welding, learn with every pass and have fun.


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Back in the day, (the 1970’s)(sheesh...) when I started teaching myself how to weld airframes, TIG was illegal to use on airframes, (or so I thought, anyway...I’ve been unable to locate any printed evidence of this since) because of microcracks which formed along the edge of the heat affected zone, causing weld failures under bending loads. Since, I have read (somewhere) that that problem goes away if the work is preheated before TIG application. Anyone have any light to shed on this?

From what I‘ve read, heat treating isn‘t needed for anything thinner than 0.120“ assuming a starting temperature of the material in the ball park of no less than 70ish degree F. I‘ve played around with hitting the piece with a MAPP torch getting it up to 350F before working it. I can make an argument from an engineering perspective that you shouldn‘t have a dramatic temp gradient along the piece and allow it to cool slowly. However the annealing temp of 4130 is north of 1500F so I wouldn‘t be surprised if a lot of people are woefully under this temp when heat treating implying that at least anecdotally it‘s affect are more myth than fact on thin walled 4130. But that‘s only my opinion.

I am assuming you mean “pre heating” when you say “heat treating”....??

So I was taught that pre-heat was only really beneficial on high carbon steel. When I read some of the threads it seems folks think it might help with 4130. Am I missing something, and would someone please help educate me. I am a little slow mind you...

Fobjob, that‘s my mistake. I‘m conflating pre-heating with heat treating. From what I understand pre-heating is done to prevent a significant temperature gradient and the associated excessive stress ultimately resulting in cracks. Heat treating is done to relieve (relax) stress in the material.

Kid Durango, my knowledge of these process is drawn largely from being an engineer. If there‘s anything I‘ve learned when it comes to heat and metals is that a lot of it is tribal knowledge and established best practices from experience which I‘m sure can be justified using engineering. That being said, I‘ll defer to those with the most experience to answer your question.

Wailing on a welded piece with a big hammer is a feel good test, its not scientific. Standard practices will yield good results. There have been many airframes expertly welded long before some of the current gadgets came on the market. Since you can't build a tube fuselage without an ox/acet rig you can gain some control experience jumping back and forth on your test pieces. Run some beads with ox/acet in addition to practicing with Tig. Get working on 035 wall, if you keep practicing on thicker material you'll slow your skill progress. Your photo is about what my first welds looked like 41 years ago, I went about six months before I started charging for tig welding. I had previous experience with the gas torch. Any welding experience counts.

Thanks, Cub Junkie! I was planning on sticking with the TIG setup exclusively for now. I want to focus on one thing at a time.

Guys kick Cubs around all over the rudder pedals but complain about manipulating a foot amperage control. Lol!

Welds look good! A pointer for chromoly welding, as it doesn’t want to “wet out” or run down into the root of the weld as easily as some other materials, I am conscious of how I grind or clean the base metal in relation to the direction of the scores or scuffs. I try not to leave the marks perpendicular to the direction of the weld as sometimes I see it kinda hanging up the smooth advance of the pool, particularly on the cooler outer edges of the puddle. Maybe over critical but anything helps on tight joints and uncomfortable props and positions to just keep that puddle moving.


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I can in no way say I am an expert at welding, only been doing it 51 years, 45 of that Tig welding. I find it interesting the mention of a 1/16 electrode used with the thinner tubes used in aircraft. It is rare for me to run an electrode that large. I find a 1mm electrode my common use size, this is usable for .028 through .065 wall tube. I grind to a long needle point. There are times when doing allot of .028 or welding thin sheet a .020 electrode is more comfortable to get a good stable arc. By thin sheet I mean .009 to .025 or materials such as stainless or Ti that need very little heat. The electrode must come up to temperature to run clean.

Your choice on gas lens or straight cup, each weld has it's different need. I use the smallest I can get a stable flow with. You do not need nor want allot of flow since you are prone to get turbulence at the puddle, the turbulence can draw in the atmosphere which is not a good thing.

Filler rod, rare that it would ever be a larger Dia than material thickness.

Just my opinion from someone who has earned a lifelong living sitting at a welding table.

Charlie, I appreciate this type of knowledge from experience. I‘m developing practices now so it‘s a great time to experiment with some of your points. One thing, in my inexperienced mind I feel that having a bit more filler than material thickness would be advantageous. Why would that not be true?

I'm not sure it's a universal rule that the filler rod is thinner than the metal you're welding. 1/16" (.065) rod is very commonly used to weld .035 wall tubing in a fuselage. Not saying it's right or wrong, just don't think it makes much difference when the weld is that small. Smaller rod just means you need to feed more in faster than a larger rod.

CharlieN said:

. You do not need nor want allot of flow since you are prone to get turbulence at the puddle, the turbulence can draw in the atmosphere which is not a good thing.
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Yup learned too much argon can be worse than not enough.


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Crash said:

If you have that much of an issue you should probably call instead of airing it out online.

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Believe me I did....

I can post copies of the exchanges if that would make you happier?


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Filler rod diameter is not a "given rule". It is a developed desire. The rod diameter has to do with more than one function, one is to cool the weld puddle, if one puts allot of heat in, then the parent material needs quicker cooling so one develops a style where they want a thicker filler. The larger wire has value if the joint fitment is not perfect. More common than not.But a small filler can be stitched along each edge to fill a gap with far less heat introduced.
One will find it to be common the use of the larger filler can be part of the reason the backside of a weld is far less than smooth. Obviously more reasons than just filler material size, more to style and overall technique.

If a style is developed using the smallest electrode possible one can direct the heat to just where it is needed, as in one side of the joint more than the other while the filler then directs the flow of material within the puddle.

I personally would vary rarely use 1/16 filler on .035 material. I have .045 and smaller filler for that. My fuselage I am building is mostly welded with .032 filler. I have areas with tubing as thick as .095 wall at high load regions as well as wing mounts machined fro ½" plate. Some of these I utilized 1/16 filler but no heavier.

Granted I have decades working a torch but I am also on the other end of the skills, my right hand, for me this being the torch hand, I have little to no use of my thumb and only two usable fingers. Left hand is pretty good still. And the eyes, I was bless with being a hawk eye, still have 15/20 with good glasses on. But those glasses do not go into the shop and are not really cut for close work.
I still weld pretty well but I am no longer a grade A welder. Those days are a distant memory and show up when welding .016 and thinner material.

CharlieN, thank you! I'm going to try to find some 0.045" filler rod. Do you have a preference for ER70S-2 vs ER80S-2?

Yes, 70. You want to keep the welded joint as ductile as possible. You may want to get some .035 as well since you will want some in the future, the shipping can cost more than the material.

What torch are you working with? And I presume a foot control, you had mentioned 49A and 15 cu ft flow.

The thinner the tube you want to vary the current as needed, partly one needs to trail off the arc to slowly cool the puddle, this reduces/prevents the crater. I use small cups on a #20 water cool torch, that would be a #9 if aircooled. If aircooled there are super flexible cables. These are a must have for this work.

I'm using a PTA17 air cooled torch with a trigger for the finger. I have a foot pedal but I've been practicing out of position and using both hands. I believe that foot pedal will limit my skill progression. To prevent cratering in the future I'm going to play with backing the torch up at the end so as to not overheat the final point.

In the long run you will be happier with the #9 torch when working in the tight V between tubes, and Lincoln has a very flexible cable that makes torch manipulation much more comfortable.
I would truly recommend working with the pedal, the act of lifting the torch breaks the envelope of shielding gas as well as letting the puddle collapse. Letting the atmosphere to get onto the molten puddle creates scrap metal. The argon shield needs to surround the weld puddle from the time the metal starts to melt and till the puddle cools below until no portion is molten. The grey dry look of your sample weld is not a weld that would pass any inspection, keep that shield gas on the weld area, that is what post flow is for.
When I close out of a weld I back the arc down to a minimum allowing the puddle and electrode to cool and only then do you shut off the arc while keeping the torch in position to keep the shield gas coverage over the heat affected zone. If you let the electrode cool to fast or allow the atmosphere get to it when hot it is prone to become brittle, that brittle electrode can snap off and drop into the puddle, you will not like that.

Thank you, Charlie! I'll take this into consideration on future welds.

I have used .035 mig wire er70, I am definitely better with oxy/acetylene than tig. For me welding thin sheet tabs ont to tubes is the most challenging for me. Tim

Couple things. One 4130 if TIG welded...weld the entire cluster. TIG induces heat quickly. A hot fast bead may look pretty but it’s not acceptable unless the cluster has been preheated. The primary reason is the problem cause by rapid cooling. Enough heat needs to be conducted into and away from the bead to prevent the formation of martinsite crystals at the very edge of a TIG bead. The tubing needs to cool slowly in still air greater than 70 degrees. The tubing will crack at the edge of the bead if you allow martinsite crystals to form....heating and cooling is critical to a good TIG weld.
Paul Minelga has posted YouTube videos of the destructive testing done at UAA in Anchorage... covers gas welding and TIG welded joints...both fast pretty beads and clusters welded slowly to induce enough heat into the cluster.

CharleN posted his method of sharpening the tungsten to to grid to a fine point. I’ll do that when I’m welding a very small part wherein I’m taking my sweet time creating a narrow bead using the smallest diameter filler wire I have on hand...

For everything else on a fuselage I sharpen to a point, then square off the tip of the tungsten. Small flat area on the tip creates a small ball of plasma...the more I dull the point of the tungsten the larger the ball of plasma at the tungsten tip. With that I use the TIG torch like a gas torch...take my sweet time creating the puddle, make sure I can see the parent metal melt and use larger diameter filler wire to regulate cooling of the puddle...Your weld have edges which means the parent metal wasn’t hot enough...some of your bead may not have blended with the parent metal...you’ll want the edge of the bead to smooth and not leave an undercut.
Here’s an example of a bead laid on to cold...
Poor welds wrecked this airplane....



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Great points, Mark. Thank you!

Yes good points, I did not want to go into the many ways to shape an electrode. The Tig torch can easily preheat and post heat the work area. The weld material does not know how it is being heated, welded and cooled. That is all operators skill. And yes, there are many beautiful rows of dimes that are not the best structurally performed weld.

What I can not fathom are those that Mig weld 4130, no preheat and probably no post treatment. I do own two Mig machines along with my three tag machines. Nether of the Mig welders have many hours on them. My Syncrowave and the Thermal Dynamics Tig machines do though. The Lincoln Tig is all but unused.

And yet look at the Stinson....at least part of it was arc welded....and looks like it, but I've yet to hear of a failure.
John

Having flown MIG welded airframes for the last 32 years, I still totally agree with CharlieN. The best I can come up with, is that MIG welding an airframe, while not as good as gas or TIG, seems to be, "good enough." There are a lot of kitplanes out there with a lot of fleet hours now, MIG welded. The only cracks I've had in my current S-7S, have been after massive impacts, (chipped tooth, bent seat frame, trashed gear, etc.) and yes the cracks were right outside the welds. Even more surprising is welding over the cracks, and now a couple thousand hours later, the repairs are holding! I can see how a REAL welder would scoff at a MIG welded structure, and I have no idea how the various kit company owners decided MIG was good enough, probably a cost benefit analysis I suppose, but my S-7S has as many hours now as my BC-12D did when I bought it, so good enough means just that I suppose: not the best it could be, but it seems to get the job done.

Great thread, good info, I need to learn to TIG! I MIG well enough to never have had any thing break on me, I would call myself a adequate amateur, who at least knows enough to design things to make up for his lack of real welding expertise, like these two big solar racks I fabbed up for a guy with a Tesla about 6 years ago. It's that thin wall 4130 that scares me!

I think the first I heard about arc welded fuselages was Fleet in the later 20s, the airframe was welded up in two sections, then moved outdoors to mate the two sections together since they did not have a large enough shop to build one piece weldments. I have not looked into what material was used in them, probably 1020. That might have been a different company as well.

I think it was the Kitfox was the first modern application of MIG welding that I am aware of, and he was using high school students as a laborforce. Granted my introduction to GMAW was in 1972 when a high school instructor took me to a Miller dealer for a introduction lesson on a new MIG machine. You varied the current by plugging a cable into different holes. This was at a time I was into my second year doing weld repairs on rusty Pipers after school. I never took to ARC or MIG till more recent years.

I've always read that Maule was the first to certify MIG.

From what I remember, Stinson was the first to stick weld fuselages, but that could have been just a rumor. Tim

Citabria/Decathlon welded with mig but their structure uses thicker walled tubing which makes it a little easier I guess................... I still use gas if I repair one.