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Mike Armstrong

Well Known Member
I'm very interested in building the RV-12 and have been following these Forums for quite awhile now learning alot along the way. But until the -12 finaly goes into production (which maybe a long time) Ill be tinkering around with another project to pass the time. It's a Warner Aero Sportster that has a steel truss fuselage made of the standard 4130 Chro-Mo tubing. This site has some of the most knowlegeable builders I've come across and of whom's opinions I respect. I have posted this question elsewhere but would like your opinions on the subject also, if you dont mind, thanks.

I have been reading everything about this subject (welding 4130) thats available on the internet and I am more uncertain now than I was when I started out. The apparently hotly debated question is...

Which is 'best' for welding 4130 Chro-Mo? TIG, MIG or Gas?!!!

This question is so common and thoroughly debated to the point of confusion it's almost ridiculous. 'Experts' of each method insist on theirs as the 'only' method to ever use. 'Amatures' new to welding just want to know which method to become proficiant at for the 'best' and 'safest' weld and seem to be often told to use O/A gas first but later start using TIG, instead of just learning to TIG in the first place. 'Old timers' who have welded for a living insist on the tried and true O/A gas yet newer (last 10yrs) welders insist TIG is the bugs ear for 4130 and gas is old school. I have read that long time and trusted aircraft manufactures have been using the 'never use it on 4130' MIG method to weld their airframes for decades without a problem while other manufacturers use MIG 'primarily' and TIG only for 'critical' areas. Well respected organizations and builders among others all have their own seperate and different opinions on the the same subject. Even 'normalizing' or 'stress relieving' the joints aftrerward is debated, some always do, some never have without a problem. It's all VERY confusing.

I plan on building the aircraft that uses the 4130 Chro-Mo for the airframe starting some time next year and I want to start getting proficiant (read- airworthy weld joints) at welding before then. It's my butt I'm risking, so, knowing what metal I'm going to have to weld together I would like to take the right classes (Sportair) and purchase the right equipment and start practicing (along with pounding a thousand rivets till I get that right too).

I know if I just go ahead and sign up for a class whether its TIG, Gas or whatever, by the end of it the instructor will probably convince (brainwash) me and the rest of the class that that method is the 'only' one to use.

Can we come to a general (hopefully specific) consensus as to which method to use to weld 4130 that I and the rest of those new to welding should invest their time and money to start to learn? I dont care which method looks the nicest (its gonna be skinned over anyway) or which method is the easiest to learn (I got plenty of time to learn), or which is cheapest (the price of my life is'nt cheap). I want the safest, strongest, 'best' weld for 4130! Maybe I need to take a poll or something I dont know. I'm about to flip a coin! Thanks


Mike
 
I dont know a **** thing about welding, but a local designer builder of the Meyer 360 and Atlantis single and 2 place 13g competition aerobatic plane, uses 4130 steel tube frame and TIG for all his frames and is considered a guru in metals and welding.

Best,
 
????????

Hi Mike,
I built a Cassutt in the early seventies with oxy/acetylene and at that time Cessna was welding all the Agwagons and Agtrucks with O/A only (the fuselages). Most tube airplane mfg was done with O/A then. I'm not sure whether TIG was even around then but now seems to be the choice since it has such a narrow heat band to prevent crystallization of the joint.

Seems to me that some of the A&P's on this forum would chime in as to what is/isn't acceptable to the FAA and why. (Heck, call the FAA).

I just spoke with an A&P/IA who has both tig and O/A and says that he prefers Oxy since that was what he learned on.....also that the heat is easier to control since a lot of the welding, if not most, is on thin stuff, around .035" to .041".

He said that he wouldn't even consider MIG because of that reason, burning holes in the tubing because it's very difficult, if not impossible, to control the heat with MIG. Also it's difficult to fit the tip in between two tubes in a cluster type joint with an acute angle between the tubes. So now you're down to two options...... :)
Regards,
Regards,
 
I'm not going to pretend to be a welding expert, but I do know some. The bottom line is that gas welding is just the easiest form of welding out there in terms of making an airworthy joint. It's easy to control and it's very difficult to make a decent looking weld with gas that has structural issues.

TIG requires more skill and practice than gas. Not a bad thing. Just the way it is for most people. It can produce very high quality welds, though, if you know what you're doing. TIG welding's fun. It's like welding with a scalpel compared to gas or mig. I'm no good at it.

MIG welding has issues. First, it splatters junk all over the place. Really messy compared to gas and especially TIG. Second, because the filler and electrode are the same thing, it's very easy to make a great looking weld (i.e. nice looking puddle) without ever getting good penetration. It's also fairly difficult to see the puddle. It's pretty crude. You get to find out you screwed up when the weld breaks. Bummer. There's nothing inherently bad about it. You just need to have proper training so you KNOW the weld's proper.

If you do MIG or TIG, you're probably going to need a gas kit anyway to "relax" the joints.

Like anything else, it's all about technique. All three can be used safely and it's kinda' like asking if bucking/shooting is "better" than squeezing a rivet. With the right equipment and techniques, they both squash the rivet adequately.

Personally, I like gas welding because I'm better at it and frankly, I think it's just a lot more fun and "organic" than arc.

just my $.02. YMMV.
 
I'm a gas welder

I can make very nice gas welded joints in 4130...Gas is pretty much self stress relieveing as well....I just play the torch over the freshly welded joint for half a minute to cool it even more slowly.

I have been to the TIG demos and I think they give a perfectly good air worthy joint I just never done any TIG.

Forget Mig, the joints will be brittle and its just the wrong tool for the job....Its really meant for speed...you want CONTROL and you want QUALITY


That means TIG or Gas.

Gas...Advatages

You will use it for just about everything needing some heat
Its very satisfying
Cheaper to get set up
You can braze and silver solder too.

It will only do steel though

TIG....Advantages

Will weld aluminium and SS better than gas, very useful but........Thats about all I can think of

Frank...The gas man!
 
jcoloccia said:
MIG welding has issues. First, it splatters junk all over the place. Really messy compared to gas and especially TIG. Second, because the filler and electrode are the same thing, it's very easy to make a great looking weld (i.e. nice looking puddle) without ever getting good penetration. It's also fairly difficult to see the puddle. It's pretty crude. You get to find out you screwed up when the weld breaks. Bummer. There's nothing inherently bad about it. You just need to have proper training so you KNOW the weld's proper.
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John, sounds like you have confused MIG and stick ARC welding. MIG is just a production version of TIG, and is very clean. But, I don't think it is good for something like a tube frame. TIG is better because you have filler in one hand, and heat in the other (just like gas) so you have more control.

For whoever wants to learn just one kind of welding, that is like learning only one piece on the piano. Learn them all, they are only different in the details anyway.

The comment about TIG being less likely to crystalize the metal doesn't make sense, crystalization comes from the steel being cooled too quickly, as in quenched in water, etc. If anything, it is more likely with TIG since a smaller area is heated, and so the joint will cool more quickly. But, it is not a problem with air cooling.

I have been welding for (censored) years now, and for a cro moly tube frame, TIG is my choice. Nothing wrong with gas, but the TIG process is cleaner, and most who can do either will use TIG.
 
I've been fabbing and welding for 25 years on race cars and aircraft. Gas welding is relatively easy to learn and do good joints on thin material like you'll be working with. It might be old school but it works well.

I use TIG on everything now. It takes more skill to master but you get very nice, strong welds. You will need good equipment to do proper welds on thin material so this is more expensive. Good TIG welds for most people depends on good work orientation so welding upside down without good hand bracing opportunities and a poor view will give even good welders uglier welds. Gas welding allows you to get into joints with very shallow joint intersections where getting the TIG torch in can be difficult.

MIG is really best suited for fast attachment of thick material. Due to it's nature, it is difficult to get good intial penetration at the start of a weld without melting through at the end. Lots of splatter too. Warpage is also much more likely due to the size of the beads laid down. MIG is great for slapping together 2.5 inch 1/8+ wall square tubing, fast but it would not be my choice for welding thin 4130 tubing.

I prefer to use a slightly lower tensile rod like 70S2 for welding 4130 as it more maleable however for max strength ER80 works nicely also.

To stress relieve or not. Well, I can only say that I've seen some disasters happen after a nice piece was fabbed and sent off to be stress relieved only to come back twisted and contorted. Unless the fixture is already stress relieved and also put in the oven bolted to the part, bad things can happen. Proper stress relief and heat treatment of a fuselage structure is impractical for a home builder in most cases.

There is some evidence that gas welding heats up enough of the surrounding joint as to impart less residual stress in the finished part where TIG does this less so.

For engine mounts, I don't stress relieve them. They are welded in the jig and left to air cool. They are straight and remain that way in service and nothing has ever cracked (yet). Getting tight tubing fits (no gaps) is key in keeping warpage to a minimum with TIG so don't get lazy in this area.

Might find these links useful: http://home.hiwaay.net/~langford/sportair/
http://www.netwelding.com/Welding 4130.htm

I'm sure others will disagree with some of this and now you have yet another opinion. :)
 
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Thank you for your opinions and suggestions, I appreciate it. So far it looks like this... MIG if your very experienced, TIG if you like precision looking welds and only if you normalize afterward with that Gas torch you didn't think you would need anymore after dropping all that cash on the TIG or just good 'ol Gas in the first place. Am I close?
 
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TIG more versatile but

Mike Armstrong said:
Thank you for your opinions and suggestions, I appreciate it. So far it looks like this... MIG if your very experienced, TIG if you like precision looking welds and only if you normalize afterward with that Gas torch you didn't think you would need anymore after dropping all that cash on the TIG or just good 'ol Gas in the first place. Am I close?
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TIG actually takes a little more finesse, because you are welding thicker mild steel tubes, either will work. Metal inert gas - uses argon/CO2 75/25 and auto wire feed. Great for volumn work and steel. TIG uses a tungsten electrode and hood with gas, 100% argon. The material is added with a second hand and a welding rod. The fact you need two hands and a little more coordination TIG is harder, but scrap and practice is all that is needed. MIG, pull the trigger and go one hand. With TIG you have the option to weld thinner metals, aluminum and stainless as well as mild steel. Good luck


Ask the experts, Call or check out Lincoln. http://www.lincolnelectric.com/knowledge/
 
I learned to weld back in the early 70's and although I don't do it for a living, or as part of my job as back then,,,I could not imagine myself without a decent welder around the house. For this type of work, I prefer the TIG because of the pin point control of the puddle and heat you have, but like others have said, an old fashioned OC set-up will work just fine. Whatever you feel most comfortable with.
 
We took over a part built and tacked One Design project.

After advice from the designer and major parts supplier, there was only one way forward - TIG.

We sourced a suitcase TIG set that would do AC and DC so we could then do steel and aluminium.

Within a week, we were tacking to a good standard, however we needed a CAA coded welder to do all the final welds. This was easy as all he needed to do was provide test coupons in the material that were analysed and passed.

TIG is easy to learn to a basic standard, it is very versatile and can cope with everything from a .025 stainless firewall up to .250 and above structure.
 
Mike Armstrong said:
Thank you for your opinions and suggestions, I appreciate it. So far it looks like this... MIG if your very experienced, TIG if you like precision looking welds and only if you normalize afterward with that Gas torch you didn't think you would need anymore after dropping all that cash on the TIG or just good 'ol Gas in the first place. Am I close?
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Mike:

You can use gas welding or TIG for aerospace quality welds. I know I'm opening a can of worms when I say this, but it is not necessary to stress relieve TIG welds. When TIG welding, the HAZ (heat affected zone) is much smaller than with gas welding. The highest tensile strength can be obtained from TIG welding 4130, and the welds we be almost as strong as the parent metal. 4130 is about 90,000 psi tensile strength, and will be about 85,000 PSI after TIG welding, about 50,000 to 60,000 after gas welding. The design of many joints used in aircraft construction make this acceptable.

There is nothing wrong with gas oxy fuel welding; is has been used successfully for many decades in aircraft construction. TIG may take a bit more practice, but the quality of the weld is much higher.

Mig welding uses an auto feed of the welding wire. In order to get the filler wire to travel through the torch, it is lubricated. This lubricant pollutes the weld, reducing it's strength. Mig welding is easy; but more control of temperature, filler material and the final quality and appearance of the weld is possible with TIG.

Scott Hetzer gives excellent forums at Oshkosh every year in collaboration Lincoln Electric. Much of this information was published in Sport Aviation in a series of articles several years ago. You can buy recordings of Scott Hetzers forums on welding and metalurgy at Oshkosh (http://www.forums4.us/) and learn all about welding 4130 as you drive to work.
 
Jon Ross has the correct answer. I have been professionally welding 4130 for aircraft exclusively for the past 16 years and have done it using all the discussed methods and the only way to go is #1=TIG, #2=Gas. Attempting to stress relive TIG joints is not recommended or necessary. Why do we use TIG for new production? Stronger, cleaner, faster, and for the operator its cooler and safer, no flame to avoid all day long.

Now hear are a few tips for the aspiring TIG welder. ESAB 65 is the best 70s2 rod we have found and it?s the same out of every box and is the only thing we use, Use a water cooled torch WP20 style and 1/16? 2% (Theroided,, Spelling?) electrode, If you buy a system ready to go it will probably come with a gas tip, bras with holes where the argon comes out around the electrode, throw this tip in the trash and get a gas lens, on the lens the argon comes out through a stack of fine SS screens now you can run your electrode out ?? past the end of the cup, all of a sudden those impossible to reach places are only difficult to reach.

The major problem the hobbyist runs into is figuring out how to weld, yes a collage class can get you started but I hirer welders fresh out of the collage classes and so far cant see how they passed the class. I don?t let this bother me, if there attitude is right then I can teach them to weld, the problem is it takes 6 months to get them going to an ok standard and 6 to 8 years to reach there skill peak, so for the hobbyist getting the results they want is difficult and some times impossible regardless of the method they chose TIG or Gas, the very vocationally skilled will figure it out and the rest will consider getting it ready and bringing in a professional to do the welding, I do this sort of thing for the local builders regularly, often they have there own equipment and I go to them to do the work, when the structure is small they bring it to me, they build it and jig it I just weld it how they want it and charge for my time this keeps there cash out lay low and they get professional quality. Either way the best of luck to you, it?s a great profession and can be a great hobby for those that can figure it out.
 
My brother is a Aircraft welder and owns a Jet engine repair Crogenic flask bussiness and he says the same thing.. He only hires military trained welders.. I don't know much about welding or had to because of my brother but I was going to do a prebuy inspection on a experimental and I had him look at it and he told me to run away from it.. Also he has to do sample welds and send them off to be x rayed every 5 years to be current on the aircraft side.
 
You have to love the diverse information available! I will throw another stone on the fire: In the 1960's era, all of the motor mounts for the Bellancas were MIG welded. I have read about studies of the life of these mounts and weld joint failure was not even an issue. The history in print mentions the reason as "speed of manufacture". TIG and GAS are just too slow apparently for production.

I also think I read once that the Kitfox is a MIG welded airframe.

Sport Aviation did a great article on welding about 1-2 years ago. The interesting point was that in aircraft, by design, even a poor weld tended to be 200 times stronger than necessary. (That is a quote from memory and should be checked.... my memory is fuzzy) the gist of the article was to encourage homebuilders to learn a new process and not fear it.
 
Oh, my God, I'm doing aerobatics on a MIG welded engine mount -how will I survive ............................... :eek:
 
This Forum is definitely one of the best, thanks to all of you.

Chickenlips said:
The interesting point was that in aircraft, by design, even a poor weld tended to be 200 times stronger than necessary. (That is a quote from memory and should be checked.... my memory is fuzzy) the gist of the article was to encourage homebuilders to learn a new process and not fear it.
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Chickenlips (theres gotta be a good story behind that name :D ), somewhere on the net I read a really good article about welding that noted that in all the years of aircraft homebuilding there are very few reported cases of airframe welds failing, most are over engineered beyond the stresses that would cause one to fail.

Though many airfames have been and still are welded using MIG, there are too many negative comments on the web about the homebuilder using it proficiantly. TIG is the 'best' but Gas is more than adaquate for the homebuilder. It looks like there is a learning curve for both TIG or Gas but neither one would take longer to become proficiant at (for a homebuilder) than the amount of time I have to learn before I start my project.

A Sportair class is a must to get started and then it will be many practice welds after that and a final ok by someone 'official' before I start on my own airframe.
 
I started welding using an O/A set up. It is called the Mecco Midget. I like the torch becasue It is very small and light, perfect for thin wall 4130 tube. I was making quality welds in just a week or two after watching the video you can buy from the maker of the torch. I found gas welding easy to learn and relatively cheap to start up with.
 
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