TIG Welding a Fuselage-Insight needed

[Aaron Novak]

Hey Guys,
Havent forgotten about you, I have just been out of town. I am currently putting together an article on this subject, from both engineering and practical perspectives. One thing I would like to point out, is that a vast majority of the articles on the internet about weldiung 4130 with tig are written with the intention of selling a welding process, and typically by automovie motorsports persons ( this is important ). They also tend to have little or no engineering test data behind them. Tensile testing is whats mostly talked about since its cheap and easy to perform, however in most cases pointless. A correctly designed weldment in our tubing sizes will never fail in the weld, even with the weakest welding filler ( RG-45 ), it will always fail in the HAZ reguardless of welding process and with similiar strengths. Whats this mean, the correctly designed joint in 3/4" .035 welded with RG-45 and a torch will have the same strength as if it were welded with ER120S series and a the gtaw process. Go up to 3/8 plate and things change a bit, and high strength fillers and electric welding have an advantage. So since strangth is not the issue....what is? Fatigue. Look back at incident reports and some 98% appear to be all fatigue failures. So the auto racing industrys products (cars) tend to use heavier material, typically have a very low useful life, and so they tend to use Gtaw, high strength fillers with little or no reguard for fatigue as they typically destroy a vehicle before the fatigue life of a weldment is surpassed. This is why one should be very careful is chising where to get information from. The auto racing world, while using the same alloys, has a completely different set of operating and lifecycle conditions than aviation. So what about fatigue, well thats the article I am writing.......

[Jon Johnson]

First off, you are much braver than I posting pictures! I am not a professional welder, but I weld all my own boat, house, car and plane projects.
The first photo shows pits on the left side. Might have touched the tungsten. These may cause stress cracks. I have had weld results like yours and have had them crack as soon as they cool!
The second photo shows a pit where you might have shut off while the pool was molten. Can you taper off on the peddle until the pool hardens? It also shows some discoloration. Do you have your machine set up for post gas flow? Keep the torch on the weld after you stop. Gotta protect the weld until it has cooled enough.
The third photo looks a little ugly. Where you covering up a gap or hole? I like to fit things up with no gaps. Much easier to weld that way.
The fourth photo looks pretty good. Make sure you carry the weld on the quadrant past the end of the weld on the next finished quadrant. Just don't need to add filler on the overlap.
Great suggestions in the other replies, so I won't repeat them.
Here are a couple of more. I like to rest the cup on one or both tubes to keep it steady otherwise my poor hand to eye would make a real mess.
Polish the weld sites and clean all oil and fingerprints. Us a new wire brush or wheel and don't use it for anything else (contamination).
Can you set your machine for pulse? I find it does better for thin materials. I like a faster pulse, around 200 per second.
Do you have a really good helmet? I started with a cheap auto-dark and it kept flashing me when I was welding hard to reach places. Not enough sensors. I bought a nice Miller helmet and love it. Make sure to set the dark so you can see well.
I don't know if your welds are safe or not. But you are pretty close to doing a very nice job. It should not take you long to get results you are proud of. If it was my plane, I would weld all the cut-offs together for practice. Maybe build some deck furniture or something out of it. TIG welding really is a lot of fun, so the practice should be enjoyable.

[highflyer]

I am just a bit curious. Why do we want to do all this TIG welding on 4130 anyway? It welds very nicely with gas which is easier to use than TIG. You need the gas anyway to normalize the area after you are done so you don't crack next to the weld next week. :-) A couple of gas bottles on a "lifetime" lease and a good Smith torch with a fair selection of tips is relatively inexpensive and does a beautiful job on clusters, etc. Gas also works well for aluminum welding for fairings and stuff after we bump them out on a sack and stake with a hammer.

[Eric Marsh]

That fourth picture looks pretty good. I do notice a bit of a gap where the piece in the upper right hand corner of the photo is fit. How are you doing your pipe fitting? The reason I ask is that it's a skill I would like to develop and so far my results have been poor.

[Chad Jensen]

I am just a bit curious. Why do we want to do all this TIG welding on 4130 anyway? It welds very nicely with gas which is easier to use than TIG. You need the gas anyway to normalize the area after you are done so you don't crack next to the weld next week. :-) A couple of gas bottles on a "lifetime" lease and a good Smith torch with a fair selection of tips is relatively inexpensive and does a beautiful job on clusters, etc. Gas also works well for aluminum welding for fairings and stuff after we bump them out on a sack and stake with a hammer.

This is a matter of personal preference here, and I would argue (well, not argue but mention) that TIG is easier. I've done both, and much prefer TIG over gas. Most people do not normalize after TIG welding unless they are in a cold shop where it will cool rapidly.

Gas is cheaper by a huge margin, and it does a fine job. It just comes down to preference I suppose.

[Mike Switzer]

Besides the equipment being expensive, you will need a fairly good sized dedicated 220v circuit, so make sure the electric service to your shop can handle it before buying the equipment.

[Chad Jensen]

Besides the equipment being expensive, you will need a fairly good sized dedicated 220v circuit, so make sure the electric service to your shop can handle it before buying the equipment.

Excellent point Mike...

[Jim Hann]

Besides the equipment being expensive, you will need a fairly good sized dedicated 220v circuit, so make sure the electric service to your shop can handle it before buying the equipment.

Excellent point Mike...

Okay, that answers it for me for now. Not economically feasible to upgrade my house wiring/service for 220V to the garage. If/when we move I know what will be on my list!!!

[Mike Switzer]

My buddies tig requires a 40 amp 220v circuit - some of them need 60 amps. There are still a lot of older houses around that only have 60 amp service to the house. I've got 400 amp service, one 200 amp box for the office/apartment, another 200 amp box in the shop, but if I need something tig welded it is still easier to just haul it to my buddies shop & have him do it.

[Tom Downey]

I have a ATA in welding tech. with certification for nukie boiler plate and pipe in all positions, and own a Miller Econo TIG setup in my garage running off the dryer style plug on a home 50 amp service. I see nothing wrong with the welds pictured here that practice in how far to move the puddle, and how much rod to add to each dip. wouldn't cure. practice, practice.practice makes perfect.

As far as gas over TIG, makes no matter, use what you are good at.

this is the unit I have they can be bought for way less than a grand used
http://www.gts-welco.com/gts-welco.aspx?pcid=340&ptid=1