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There was a huge welding TIG/OA debate on the old Yahoo group. Once the science was put out people began to understand there is another way to weld up thin wall 4130 that is acceptable. Attitudes began to change towards TIG welding. Once you’re there...and have a good understanding of how martinsite crystals are formed, the artesian aspect or learning the art of welding can begin. This thread is a little short on science...study up on the topics. Heat treating to normalized condition is something that will never happen unless you have access to a heat treating oven. Welding a cluster properly to an annealed condition is your goal. If you believe you can weld up fuselage in a cold drafty shop... go back and read how martinsite crystals are born.......and how they can kill you.
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Id buy my wife a new oxy welding set and a nice stool for the garage, if she were interested.......
we can all live in hope..
PeterComment
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Wag-Aero will sell you a box of assorted 4130 cutoffs cheap.Comment
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For those looking for welding practice material, the assortment of drops I purchased had a lot of fairly heavy wall tubing(including a couple solids over 1" in diameter) that wasn't really good for practice(though it was useful for making bushings and other items during the build).
It would be better to buy a couple pieces of 1/2 or 5/8 tubing with .035 wall thickness to get the most practice material/$. -
That's a good idea. The "assorted box of 4130" I picked up from Wicks on sale was pretty thick wall stuff, too. Ditto for the stuff provided at SportAir Workshops, if you're so inclined to take one of those courses.
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Yep.Originally posted by Mark Moyle View Post
IMO, a significant factor is that most of us are amateur welders. TIG welding can make beautiful clean welds and can be faster than OA welding. It is also really easy to inadvertently allow martensite to form because of the intense localized heating. OA welding is a bit more challenging to get a prefect looking weld but because of the much larger heat affected zone you have to be pretty sloppy to get any embrittlement of the welded area. OA is much more tolerant of welder error which a major reason why I think it is the right method for us amateur welders. MIG is even more susceptible to embrittlement which is why it requires a very specific and controlled technique.
I mig welded my seats together and haven't died yet
Quick but funny story: Back in college a group of my peers elected to compete in a bicycle design competition; most of the designs were actually tricycles. This group decided to use 4130 for the structure. After drawing it up in Solidworks and performing all kinds of CAD analysis they started building it. They tacked the frame together and completely assembled everything before taking it back apart for finish welding and powder coating. They had the frame welded (mig) then coated and it looked great. After reassembling the bike they took it out on a test ride around campus. The frame snapped at the heat affected zone of some welds in the rear A-frame structure.Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.Comment
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I have spent some of my engineer career dealing with welds, and weld inspection. For those of you interested in learning to weld I would recommend either the gas or TIG courses taught by the SportAir Academy. The Oshkosh forums are really a bad place to experience welding in a controlled environment and my assessment is that few of the TIG guys in the booth are actually involved in welding thin wall tubing. It is possible to make a bad weld with any process. With gas welding a poorly adjusted torch can either remove or inject carbon in the weld zone resulting in either a too soft or too brittle weld. The reason TIG has basically displaced gas in industrial settings is because of the controlled quality of the weld. Nothing like ARGON to keep the weld zone clean. For that reason TIG is always specified for mission critical welds in the aerospace industry. Pictured here DSC_1414.JPG is a TIG weld that you can produce with a little bit of practice. Not saying OXY is bad as long as one carefully controls the flame. A cosmetically beautiful weld may not be a strong weld. The only way to really know is to X-ray or destructively test.Comment
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In the 70's I had the distinct challenge of selling and supporting some very early MIG equipment. At that time, SMAW (stick) was prevalent in production shops. I hate to stereotype, but it’s been my experience that welders (everywhere) are reluctant to embrace change. It was just so much faster and lower cost per pound of weld metal, the evolution was inevitable.
Mr Lathrop has an excellent memory. Early MIG equipment was unbelievably difficult to maintain and not intuitive to adjust. I used to be fairly competent in the common processes and can’t even imagine trying to weld thin wall 4130 tubing with those archaic MIG systems. Eventually the guns improved, reducing some of the pushback. Wires improved, power sources and feeders were made more user friendly and gas blends were explored. Now, stick electrodes are relegated to field installation and maintenance/repair applications.
In the late 90’s, Lincoln and Miller began experimenting with pulsed MIG. I’m not talking about pulsing that you can see, but pulsing wave forms that controlled the size and frequency of the droplets coming off the wire, crossing the arc into the puddle. For a while, we could sell you a programmable wave form MIG power source. That was probably not a good thing, though. Done right, Pulsed MIG rivaled the appearance and quality of TIG welds. Done wrong, it was a mess. Now the Pulsed systems have pre-determined programs. These modern MIG systems are certainly capable of welding 4130 tubing, when operated by competent individuals. Let me stress that a competent individual, working with quality equipment, utilizing proper consumables, could weld a fine aircraft fuselage with MIG equipment. Harbor Freight equipment is fine to fix your bar-b-que grill, but don’t strike an arc on any aircraft components with it.
Oxy / Acetylene welding is much like stick welding in production facilities. TIG has replaced it in precision, high quality environments. Artists (jewelers, glass artists) and some very specialized processes still use Acetylene, but it’s days in industry are numbered. I’ve been to large facilities that forbid contractors to even bring Acetylene on their property, because of safety issues. I’m not even going to start with the ecological problems surrounding Acetylene production, but that’s another conversation.
There are countless 4130 structures that have been welded with OxyAcetylene and are performing perfectly. I’ll suggest that the TIG process is replacing Acetylene torches in most production environments. If one is comfortable and competent with an Acetylene torch it would be foolish to suggest that he/she couldn’t fabricate an airplane with that torch. At the same time, it would be foolish to suggest that one is likely to build a sub-standard aircraft if it were TIG welded. It’s all about familiarity and your comfort level.
I haven’t touched on heat input, stress build up from welding or microcrystalline structures resulting from those welds. No matter the process, the structure might require preheat and/or post weld heat treatment. No matter the process, the goal is to bring the weldment up to temp as uniformly as possible, maintain uniform heat while welding and allow the weldment to cool at a controlled rate as a homogenous component. That part of the process is where the question of competence comes up.
Welding discussions frequently touch on 'absolute truths' and absolutes. One process is 'absolutely better' and another process 'is absolutely unsuitable'. Reading those absolutes, I'm reminded of the countless times I was told that "those wire welders would never replace the Lincoln 5P!" The only welding discussions leave me queasy, is when an individual wants to learn to weld, so that he/she can weld up an airplane. I’m sure it’s been done, but that’s an awful lot to learn, to bet your life on it!
Bill
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On the topic of welding inspection:
If you do some checking in your area, there are commercial inspection companies that have portable NDT (non-destructive testing) equipment that can be brought to your airplane and they can inspect each weld cluster, etc. I priced a company here in my area (Wichita, KS) about a year ago at $500-600 bucks for a fuselage. They do this testing with ultrasound or X-ray and can give a report for each cluster giving the thickness and potential voids/inclusions. I have to find the places website, but this is one that is similar: http://www.coderxray.com/
So if you're concerned about your welds, or want to "trust but verify"...check into it.
Andy
1423BComment
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Oh the weld debate. I’ll just trust the old reliable way and use my meco midget. The OA process has built alot of airframes so I’ll trust in that and save the tig welding for aluminum, like the fuel tanks! Just my 2 cents worth.Comment
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Does anyone know how Bob built the fuel tanks on the original bearhawk prototype....
did he mig tig or oxy weld those?Last edited by way_up_north; 06-01-2019, 07:08 AM.Comment
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My bet is that they were brazed. I say that because of the type of joints and because the tank is riveted. Brazing would minimize the distortion.Originally posted by way_up_north View Post
When I first started building race cars ( early 1970's), we used aluminum fuel tanks. Back then I gas welded the tanks. I think that a gas welded tank would be the best way to go. But as Bob designed the tanks, I did not think that gas welding would work. I changed the joints on my tanks, mains and aux. tanks so that all the seams were butt welds. I formed all the edges to be welded so there was a 45 degree bend and 3/8 inch of material from the bends to the welded joints. I feel that this change reduced the distortion that one would encounter with a lap joint. It may be that rivets on the lap joints help reduce the distortion. I don't know because I did not make my tanks per the plans. I also TIG welded my tanks because that is what I am best doing.
The guys who gas weld tanks (oil tanks) frequently use Ox and Hydrogen to weld aluminum. The big advantage of gas welding is that the inside of the weld frequently looks just as good as the outside. They use the same process to do body work where they woll form the welded parts.Comment
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Bob has a friend TIG weld his fuel tanks. MarkComment
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Im going to throw in my 2 Cents. I think the biggest problem here is the fact that 4130 is a high carbon content alloy. a such--- it is sensitive to how fast it heats and cools.
Just like a tool steel -- if it cools too fast---- the area gets hard. Then there is now a transition area between the very hard weld area and the areas near by that did not get as hot.
When you gas weld- the heat is diffuse and takes time to get hot--- and you intentionally back off slowly at the end of the bead-- to make sure the cooling is slow-- which makes
sure the weld area does not harden any further from too fast cooling. This is why some think oxy is best. Cant say they are incorrect.
Tig is a little more focused and localized heat---- and idealy you linger a bit at the end of the bead for the same reasons. But it is not generally so fast as to cause hardening.
Mig is kind of the other extreme----- it is EASY to lay down a great looking mig bead where the underside of the bead isn't even wetted to the base metal. But that isn't the main problem.
I think the biggest problem with it is the fact that it starts and then - most importantly--- ends very abruptly in time. That kind of ensures a quick cooling scenario. To do it safely---
I think you would have to torch pre-heat the area--- do the MIG weld-- while the area is at an elevated temp---- so the weld is done before the area is cooled off.
This is nothing peculiar to MIG---- when you have to TIG weld a thick part--- you may have to pre-heat with a big torch--- because the thick wall of the work will suck the heat away and
let the bead area cool too quickly--- so later when the weld is stressed - the brittle bead just fractures away where the very hot area met the colder area that never got hot.
I cant really understand you MIG welding would be any advantage when you have to pre- and post- heat the area anyway. If Im going to do THAT----- I will just go ahead and gas weld it to start with. (unless you people don't have the skills to gas weld it to start with...… Than you Mark--- your guys do GREAT looking gas welds---)
Or just TIG it -- which takes less skill than gas and is cleaner overall. But gas is great if you are good at it. Just look at airframe from the 1930 on up to 1950's. Their gas welds are
works of art.
My worry is that by welding a tab on a longeron with MIG---- with no pre or post heating--- you have made a very hard spot in the tube--- great place for a crack to start later on. They will
tend to start in a local hard spot long before they would have elsewhere where the tubing is still normalized ( unhardened-) It makes a sharp discontinuity in the hardness.
The higher the carbon content of the steel -- the more intense this effect is. With low carbon steel -- it all most isn't a problem at all. With something like O-1 tool steel---(lots of carbon)
after hardening--- if it is NOT annealed some (tempered) to reverse some of the hardening--- you can drop it on the floor and it will just break like glass. Many beginning
knife makers find that out the hard way.....
So I don't know why even American champion would WANT to use MIG.--- even if they did it properly---- seems unproductive at best.
Im not quite a professional welder-- but I do weld regularly as part of my work. Been a machinist and done some toolmaking here and there. Prototyper now....
I think if the unknown welder had done gas weld it would have been fine -- even if it was so bad it had to be ground off and done over. At least the tubing would not be harmed.
as far as having the welds NDT tested---- I don't think that would do any good. These tests can only find air bubbles, voids and internal defects in new welds-- or cracks in old ones.
They do not tell you that the area is brittle. perhaps a hardness tester could be used---- but that may but be practical here. Possibly the areas could be torch annealed after the fact---
but I suspect that needs to be done during the weld--- not after-- once the metal is all ready hard.
T
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My eyes were opened about the welding debate when a buddy and I made some samples to break at the local community college. My OA weld broke slowly, tearing. His snapped right at the HAZ edge. Our calculated strength of an unwelded piece of the same tube was in the range of 5k pounds. As I recall, mine broke at 5800, his over 7000. Our publishing of that test has fallen by the wayside. I need to check in with him to come up with a plan.Last edited by jaredyates; 06-23-2019, 05:01 AM.Comment
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I am going to go with BDflies post about 5 posts above. I am not a professional welder, with a little work, I might work my way up to novice. But I do have a reasonable knowledge of metallurgy.
I think the welding process doesn't matter. I think the welding process, plus how the weld is heat treated, annealed, etc, is what matters.
I think you could screw up an OA 4130 weld. I think you could Mig weld a 4130 fuselage, and with proper heat treating, have a great result.
I am getting there with Tig with .035 4130. Not there yet. After that I want to learn to OA weld.Comment
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From my point of view, "EAA Welding" (as I call it) focuses on process and technique with little emphasis on metallurgy. People learn an exciting "new" process and leave OSH much like I left A&P school - feeling like an expert. In some of the above posts, there is mention of preheat, post heat, and actual weld heat. I suspect that people see heating base metals as a form of stress relief, but the facts - as determined by metallurgists through testing - are contained in the metallurgic standards found in SAE, AWS, ASTM, NIST, and ASM publications. And the fact is that 4130 steel heat treatment for stress relief is only 12% effective under the most ideal conditions. And the process of heat treatment for stress relief (avoiding use of specific terminology like "normalizing", "annealing", "tempering", etc.), if performed IAW the published standards, involves heating in a controlled atmosphere where the cooling ("quench") can be slowed down - not just throwing your neutral flame on it for several seconds and then letting it cool.
Next, if you reread every word in this thread, there is no mention of hydrogen embrittlement. Relax, the same standards I referenced above stipulate that 4130 "generally" does not require a hydrogen embrittlement bake. But if, for instance, you were working with 300M or one of the DPS steels, you would have a 4 hour window in which you MUST do the embrittlement bake following any plating or welding operation or you will likely be in for the surprise of your life! The "bottomline" here is that understanding the metallurgy involved in your welding and using appropriate process and technique based upon that understanding is vitally important to weld integrity.Comment
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