Wedling 4130 CroMO

AZmiik

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Ok I hear people saying that 4130 was designed to normalize when gas welded and that there is a large amount of stress built up in the HAZ when welded with TIG. So my question is why not gas weld it. Its cheaper not quite as fast but aircraft people have been doing it for a long time with few problems. As a welding major with a strong interest in off road fab work i am just really curious.

Mike
 

1992f150

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I have wondered the same thing; I think most people dont know how. There are some minor reasons I could think of. When you first light the torch the acetylene soot floats up in the air and lands on everything. The flame tail reaches out and can burn stuff not in the weld area. The acetylene can explode if the regulator is cranked up too high. The worst part is definately the heat on your face when you gas weld.

Azusa: shame of the foothills
 

ntsqd

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Have a look at the penetration models for the two types of welding. I think you'll find that GTAW (TIG) results in better penetration than Oxy-Fuel. A two edged sword, the better penetration results in a consistantly better weld, but the much more concentrated heat required to do so results in the undesirable loss of Ductility until normalized.
Then there is the cosmetic factor. GTAW beads are commonly much nicer to look at. At one time I could put down an Oxy-Fuel bead that looked very much like a slightly too wide GTAW bead but no longer. Takes a lot of practise and time to do that.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 

1992f150

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if you use a small root gap and keyhole weld the tubing, you get more than enough penetration. The filler rod flows thru onto the inside of the pipe.

Azusa: shame of the foothills
 

singlehanded

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Now what are the disadvantages of mig on 4130 compared to tig. Obviosly tig looks better and takes like 3x as long. Curios my engine cage is 4130 and was migged. If you use the right wire somwhere around 80,000 tensile strength, will it be as strong as if you tigged it. I have a mig and was wondering for future projects?

local
 

partybarge_pilot

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Yes you can mig cro-mo with the right wire. Can't remeber the exact alloy right now but I'll look at it the next time I'm in the shop. It took about two weeks to special order for imperial and was about 30% more than a normal roll. A must if you want to heat treat ( which I strongly recomend ). I use the mig on insides of things that can't be seen and tig the outsides. I know, cheater, cheater.........
 

singlehanded

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I not to familiar with what or how you heat treat it. Is it the wire that already comes heat treated? Or do you hae to send it out or something explain?

local
 

partybarge_pilot

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Yes, you have to send out the finished piece. Also no enclosed pockets, vent holes for everything. A fixture to keep it from warping isn't a bad idea either. Wire is in the anealed state but becomes work hardend when welded. Heat treating normalizes that differance between the weld and material. Plus making it much stronger, up to 50%. Most heattreaters have a minimum of 75$ up to 75# if they have a run going.
 

singlehanded

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So if I was building a chromoly cage for my prerunner and wanted it to be heat treated. A. would I build the entire cage and take it to be heat treated before the final welds were done to connect it to the frame(which obviously wouldnt be heat treated.). Or B. send the whole truck to be heat treated with cage attached.

local
 

partybarge_pilot

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C, niether. Your still sticking it on a mild steel frame. Go all cro-mo or no cro-mo. For a prerunner with a frame, cro-mo is a waste of time and money in the cage. But that's just My opinion, If you've got the money to spend and it gives you a hard on, go for it!
 

Kritter

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Cages or space frames are not commonly (I've never heard of anybody doing it, but I have never done research on it) heat treated due to their size and irregularity (reads very expensive). Triangulation is used to compensate for not heat treating the structure. If I was building a race vehicle I would def. use chromoly, you save A LOT of weight since you are not only using thinner tubing, you are using a smaller diameter.

Excerpt from SCORE rule book
"4130 is recommended for all types of roll cage construction"

Kris
<A target="_blank" HREF=http://www.dmsrace.com>www.dmsrace.com</A>
"Jesus loves you, everybody else thinks you're an A-hole"
 

partybarge_pilot

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The original TT frame started by Jim Mckinze for Mike Jacobson was a monque sheet design that was heat treated. Unfortunantly the penchy heat treaters dropped it and tweaked the whole affair beyond repair. Back to the old " will give you three times the cost of the heat treat!". #2's still on the jig table and in limbo....... If you have the money it's the way to go........
 

ntsqd

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Most Drag Race chassis builders fall back on localized Normalization, i.e. heat it with a Rosebud to the approximate temperature and let it slow cool in still air. Can't say whether dez fabricators do this or not. The quality of that type of Normalization is entirely dependent on the experience of the guy doing the work. Then again, finding a heat treater that can take a 300" long structure is a trick. Paying for it would also be a trick.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 

1992f150

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One more thing, originally tig was developed for aircraft industry because of its ability to cleanly weld on a variety of metals. Steel, stainless, brass, copper, aluminum, magnesium, etc... Apparently you can even weld composites with it, like graphite etc... No other process can really do that.

Azusa: shame of the foothills
 

Steve_Sourapas

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We used this technique on many of my older race cars and at the time if it was done correctly it really worked especially on single seat cars in the cage area.My roof cage area would crack every race til we used this technique then no more cracks.

BEERMAN
 

AZmiik

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So from what it sounds like is that know one really knows why no one oxy fuels any more. I am not really sure that slightly better penetration is better than brittleness. When you think about it the most penetration you can is about.095 on CroMo, which can be done pretty easy. It think that maybe the whole industry is kinda in a wow that was TIGed mode. With the time issue I think that it would take as long to TIG and then normalize with a rose bud as it would to just oxy fuel it in the first place.

Mike
 

ntsqd

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I can vouch for welding copper with and w/o silicone bronze filler. It's a trick, but once you get it figured out it's not too hard.

One other thing that may have caused the switch to GTAW welding of 4130 is the weld purity issue. Critical aircraft parts are welded with a trailing cup. This allows the weld and HAZ to cool further while still covered by the shield gas. This would be hard to do with Oxy-fuel. The by-products of the Oxy-fuel combustion are bound to have an effect on the metalurgy of any metal at a temp above the critical temp. GTAW only effects the crystalline structure of this metal, it doesn't add minute amounts of other elements (like Carbon) as is at least possible with Oxy-fuel.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 

partybarge_pilot

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Aircraft are even moving away from TIG. Hello friction stir welding. This method would just be a little hard to do on tubing.....
 

YotaWhoopRunner

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I was told that gas welding is not as strong as tig since the grains in the metal will be melted when you gas weld. So once your piece has cooled down, it has lost its strength since there are no more grains inside the metal to hold itself together. I don't know to what degree it will be weakened though.
 
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