how to weld 4130

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PTAirco

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Sep 20, 2003
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Up to the end of the 1940s almost all aircraft used oxy-acetylene welding for structural tubing. There may have been a few exceptions, but they are rare enough that I haven't heard about it and old aircraft production engineering is a bit of a pet subject of mine.

Bellanca later used MIG welding (50s onwards) and so did many others, including Maule and many kit manufacturers.

There should be no measurable difference in strength between any of the methods, if the welding is done correctly. Tubes will always fail just outside the welded area.

No welder I have known who worked on aircraft would advocate normalising after TIG welding; it just isn't necessary, since the heat is concentrated at the joint and less overall heat gets into the tubing. And the more gradual process of gas welding means it tends to do that by itself, especially if take care to end the weld in a gradual manner, letting the torch play over the whole area until it it has cooled to a red glow.

Personally I am very happy with the gas welding process, but I have never tried TIG. I find a torch is essential to remove the kinks that inevitable form at joints whatever process is used. TIG minimizes these, but does not eliminate them. Some TIG welded fuselage I have seen still exhibit the sticking-out-joint when you sight down a longeron. When I first started welding, I was amazed how much distortion occurs , but even more, at how much you can fix just by repeated heating and cooling and shrinking of tubes. Ity's definitely an art more than a science.
 

TFF

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I think that the should or should not stress relieve is not cut and dry. If you are in a factory with jigs that look like a Transformer and made from 1" steel plates with welders who have been on the job for 20 years, not to worried about it. On a field repair or a 4130 frame made on top of a piece of ply jig where the warping is not contained, I would be hitting all the joints with the torch. That is just my experience with my welding which is just a hobby, but have had to do it at work.
 

wildun

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May 10, 2007
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New Zealand
What happens if someone buys one of these aircraft, trusting the builder that it is safe?

Then a fool just bought an airplane. There is no way to fully protect an ignorant buyer.

Philosophical example: You know a bridge is washed out around a blind corner and someone is headed down that road. You have a duty to warn him but no right to stop him.
In your example, I guess there is no Legal right to stop him of course, but so far as I'm concerned there is a Moral right which would certainly come before any laws or philosophical arguments ! (and this is something which is ingrained in (most) of us).
 

Martti Mattila

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Feb 24, 2021
Messages
96
MIG was proposed over here for the production jig-welding of one popular CRMO framed 2 seater. The Authorities initially rejected the proposal out of hand but the would-be factory persisted and provided various test pieces with cluster joints made using OA flame welding, TIG and MIG.

The TIG was neatest, flame was second and MIG didn't look that great at all.

Without stress relief, which wasn't planned for these fuselages, the flame welded was weakest under shock loading, breaking at the heat affected zone (HAZ), TIG was second and MIG was strongest, surprisingly.

The factory received approval to manufacture using MIG.

Most of the airframes seem to be fine but the type gained a feared reputation because a few of them had weld fractures develop at the strut attach points and I believe there was at least one catastrophic airborne failure.

From what I saw the strut attachments could have been designed much better so that the weld was not solely responsible for holding the struts attached. I think that a retro-fix was approved by adding a strap from side to side.

If I was you I would experiment with the MIG as it is very much quicker than any other means and one of the reasons that factory wanted to use it was to allow much poorer fit-ups at the joints and just pour in more wire to fill the gaps. It seemed to work fine and had superior strength although the welds weren't all that elegant. Very thin wire and low current settings are the order of the day.

The reason for the superior strength seemed to be two-fold. The MIG and poor fit-ups resulted in much larger fillets which in turn provided added support to the members, albeit with a little added weight. And, mindful of the damage that excess heat causes in the HAZ, the welders were told to keep the power low and make welds that were technically 'cold' and had limited penetration. That lack of penetration is what some blamed for the weld failures I mentioned earlier.
One builder here welds with MIG first and after that makes it nice with TIG. Sounds litle disturbing. Had a Avid Flyer in my shop for small repair and that looked MIG work. Not bad looking at all I wonder what was the wall thickneses diameters were awfull small half inch and so. To my acknowlege welding stress that is build in the structure by welding is usually bigger than stress caused by flying. Maybe cutting cormers with that statement.
I was learned to weld O/A when I was 14 and TIG when over forty. So I dont figth against O/A and many of my planes have been build from 1020 mild steel.
How you can be sure with MIG that base material is melted and if the root is not melted than it goes in scale from 1 to 5 to 2. and that is not nice in written testemony. I would like to learn more about this wing strut failure.
 

wktaylor

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Sep 5, 2003
Messages
493
Location
Midwest USA
Hmmmm...

OK with all the talk about cost/quality/strength/individuality/etc...

I'm a bit surprised that no one here ever seems to mention alloy steel tubing and parts [fasteners, etc] that are sold exclusively for race-car structures from specialty shops, claiming high reliability. Perhaps limited sizes/lengths?

Especially some of the alloys such as drawn mild steel and 4130 steel tubing, sheet/plate, bar, etc... and Docol alloy [no endorsement]... for ease of cutting/forming/welding. Materials appear to have quality controls for reliability and relative strength and safety.

Also, I had the privilege of working with a 'master' aerospace quality welder who passed-on many of his hard-earned tips/tricks above/beyond training, and process manuals and the tools-of-the-trade.

Weld-melt surfaces must ALWAYS be cleaned break water quality... typically cleaned to bright metal [surfaces and EDGES]. This also goes for weld filler rod/wire or sheet which must be kept immaculately clean... and wiped-off with fresh cloth... immediately before use.

NOTE. YouTube videos of welder placing 2 materials together with bare hands... which OBVIOUSLY have a chromate or other inorganic surface finish applied... or just contaminated with 'whatever'... and then striking an arc and running beads, drives me INSANE.

The secret value of MIG/TIG fusion welding is the flow of inert gas to suppress all oxygen contamination, guide the arc to the intended point and help control distortion by containing the heat to the immediate weld-puddle.

Inert gas flow 'purge' [prior to welding] directed thru pipes to interior surfaces and back sides and thru joints to be welded, which forces-out oxygen and trace moisture. My 'master' preferred welding parts under a plastic bubble/dome for inert gas atmosphere purge well-before welding... especially for oxygen/moisture sensitive aluminum, magnesium and titanium parts.

ALWAYS know/confirm exactly the alloy(s) and heat treat [HT] of the parts being welded. Duhhhhhhh... makes a difference in fusion/distortion.

Tight fitting parts require less weld-filler which means less melt-heat [smaller HAZ].

Sometimes weld filler may be omitted/minimized in favor of slightly excess-flange for edge 'melt-down' of 100% same metals... or use scrap sheet of the same material for weld-filler.

Use 'tack welds' to set the position of parts and control distortion when running beads.

Use 'copper' chill blocks and inert gas to protect areas where extreme heat is undesirable.

And so-on...

Anyone else have professional hands-on procedures for quality/clean welds in mild-steel and alloy-steel parts [typically 'normalized' HT to a low/stable strength [4130 HT125-KST]????

I hope this all makes sense. Wife is yelling... gotta go walk the dog. bye.
 
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Martti Mattila

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Joined
Feb 24, 2021
Messages
96
Hmmmm...

OK with all the talk about cost/quality/strength/individuality/etc...

I'm a bit surprised that no one here ever seems to mention alloy steel tubing and parts [fasteners, etc] that are sold exclusively for race-car structures from specialty shops, claiming high reliability. Perhaps limited sizes/lengths?

Especially some of the alloys such as drawn mild steel and 4130 steel tubing, sheet/plate, bar, etc... and Docol alloy [no endorsement]... for ease of cutting/forming/welding. Materials appear to have quality controls for reliability and relative strength and safety.

Also, I had the privilege of working with a 'master' aerospace quality welder who passed-on many of his hard-earned tips/tricks above/beyond training, and process manuals and the tools-of-the-trade.

Weld-melt surfaces must ALWAYS be cleaned break water quality... typically cleaned to bright metal [surfaces and EDGES]. This also goes for weld filler rod/wire or sheet which must be kept immaculately clean... and wiped-off with fresh cloth... immediately before use.

NOTE. YouTube videos of welder placing 2 materials together with bare hands... which OBVIOUSLY have a chromate or other inorganic surface finish applied... or just contaminated with 'whatever'... and then striking an arc and running beads, drives me INSANE.

The secret value of MIG/TIG fusion welding is the flow of inert gas to suppress all oxygen contamination, guide the arc to the intended point and help control distortion by containing the heat to the immediate weld-puddle.

Inert gas flow 'purge' [prior to welding] directed thru pipes to interior surfaces and back sides and thru joints to be welded, which forces-out oxygen and trace moisture. My 'master' preferred welding parts under a plastic bubble/dome for inert gas atmosphere purge well-before welding... especially for oxygen/moisture sensitive aluminum, magnesium and titanium parts.

ALWAYS know/confirm exactly the alloy(s) and heat treat [HT] of the parts being welded. Duhhhhhhh... makes a difference in fusion/distortion.

Tight fitting parts require less weld-filler which means less melt-heat [smaller HAZ].

Sometimes weld filler may be omitted/minimized in favor of slightly excess-flange for edge 'melt-down' of 100% same metals... or use scrap sheet of the same material for weld-filler.

Use 'tack welds' to set the position of parts and control distortion when running beads.

Use 'copper' chill blocks and inert gas to protect areas where extreme heat is undesirable.

And so-on...

Anyone else have professional hands-on procedures for quality/clean welds in mild-steel and alloy-steel parts [typically 'normalized' HT to a low/stable strength [4130 HT125-KST]????

I hope this all makes sense. Wife is yelling... gotta go walk the dog. bye.
Not much add to previous. I was taught that cleaning busines in my stailes steel TIG welding training. But some remaks has been arisen by the years. When removing that black surface from 4130 tubing I never make a groswise marks on tubing to propagate stress next to a weld. Always led to wheel or paper make a lenghtwise marks to the pipe surface. Inert gas inside the pipe is must in 316 L, 304, When we build these LPG tankers we use denatured alkohol for cleaning. Certified aircraft welder gave us Exp. gyuis to lessons and he advised us to use bench grinder to make fishmouth fittings. I am suspicious for that what if stone chips impegrate to metal. Aircraft welding is a least worisome work, there is always someone that knows better.
 

dog

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Joined
Dec 29, 2019
Messages
743
should I weld on anything for aviation use my procedure would be simple,cleanliness,carefull
joint preperation,adequate lighting,apropriate jigs
and fixures,correct filler material,proven welding process,and of utmost importance to actualy see
the weld take place and be able to say that the weld puddle was watched and did touch and liquify both edges of the joined pieces in a continious manner,without the inclusion of slag
blow outs,bubbling,sparklering or drooping.
 

trimtab

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Apr 30, 2014
Messages
351
Location
rocky mountains, rocky, usa
What worries me a lot is that I notice that many people on this forum ask about how to weld Hi Tensile tube and many of the people asking seem to be learning to weld from scratch on an aircraft project! - how can this be? at least, how can it be possible to be allowed to get an aircraft in the air, having been built by a novice welder?
This is lunacy, but I did once see a helicopter (which I would never have even considered flying in) which had obviously been constructed by an incompetent welder and it set me thinking, why isn't this practice regulated more?

What happens if someone buys one of these aircraft, trusting the builder that it is safe?
I haven't been involved in flying an aircraft constructed in this way of course but, as a retired engineer I'm keen to find out what the regulations (if any) regarding this dangerous practice actually say.

Hopefully most of the people asking these questions are not really serious about building and just talking.
Surely it should be mandatory for the welder to have at least gained some sort of certificate in welding, (not really a very difficult thing to do) helping to bring down the accident rate from twice what it is for factory built light aircraft?

Although learning all about welding from a book etc is also necessary, it is also an art, it can only be perfected by practice and from the aptitude and ability of the person holding the torch or electrode, not an over enthusiastic novice dreaming that he knows all about it (because he read about it) and starting his project anyway!
As an engineer, you can appreciate that the ultimate judgment is informed by data.

Novice welders build a lot of airframes. Welding is not voodoo, and it doesn't require substantial or rarified skill to execute competent, strong welds. I have an Instron tensile tester, and it shows pretty boring differences most of the time between beautiful welds and ugly ones. It's so boring for 4130 or mild steels that I quit bothering playing with it except for learning to weld aluminum and titanium. The largest issues with steels are usually filler volume and compatibility, porosity, and stress relief.

Like other kids decades ago, I was learning to weld in Jr High, and helped build two super cub style experimentals using gas and stick welding.

The only thing that should inform or support regulation of things like welds in experimental aircraft is safety and outcomes data. And the data just doesn't exist to gesticulate wildly for some sort of larger scrutiny.

Welding steels is pretty easy in terms of achieving adequately strong joints when some details are followed, and when the basic mechanical skills are gained quickly through practice.

Just like flying airplanes, actually.
 

TFF

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Messages
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Location
Memphis, TN
The beauty of 4130 is it was designed to be welded by minimum wage people in dirt floor factories just about 100 years ago. Barely out of the Victorian age. Better preparation is always better, but the safety margin is high as long as one understands the metal has to melt both sides together. It’s really two puddles mixed together. Get that, and one can play perfectionist to the degree they want. At that point it works for everyone.
 

Pops

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USA.
The beauty of 4130 is it was designed to be welded by minimum wage people in dirt floor factories just about 100 years ago. Barely out of the Victorian age. Better preparation is always better, but the safety margin is high as long as one understands the metal has to melt both sides together. It’s really two puddles mixed together. Get that, and one can play perfectionist to the degree they want. At that point it works for everyone.
Well said. You can do a strong weld that may not look like an artist did the welding or try to be the artist.
 
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