4130 welding

4130 wire is readily available for TIG welding in 2 - 3' lengths. I've never seen a spool of 4130 for MIG welding. A major issue may be the control of penetration with a spool gun in the confined spaces of aviation welding (like an engine mount). MIG welding was really designed for production work; lots of welding with no need to stop and look for a new piece of welding rod.  I'm not saying it isn't possible, I'd stick with TIG welding.

Dave

Roll cages, etc, are often mig welded; this is one of those hotly controversial topics, right up there with which filler metal to use.  In the WW2 era, 4130 was oxy/actylene welded with one advantage of this being the preheat and more gradual colling incurred with gas welding versus a technique like mig.

If I were going to mig weld 4130, I'd definitely use post heat to stress relieve the HAZ (heat affected zone).

Here are some posts elsewhere that may be helpful:

http://en.allexperts.com/q/Welding-3487/2009/3/chrome-moly-welding.htm

http://weldingweb.com/archive/index.php/t-1006.html

Jay Smith

This is one of those questions where if you ask enough people you will eventually find the answer you are looking for.  Gas welding is perhaps the most forgiving.  I like it because when welding a fuselage you don't have to deal with being able to operate a foot pedal or work around in a big clunky helmet between tubes. 

 I do like to use TIG when I have parts in a fixture on a welding table and I can get braced up to hold a steady hand.  Being steady is crucial with TIG.  TIG is also pretty, but with practice a good gas weld is hard to tell from a TIG weld once painted.

MIG welding is a process I don't even consider.  It can be done.   I will tell you that some early Glastar fuselage cages were MIG welded and there was a failure of some sort due to the weld process and as a result there are no longer any MIG units in their facility

For welding 4130, you need to use either 4130 filler wire per AMS6457 OR 6130 filler metal per AMS6461 or AMS6462.  Use 6130 if you want post welding heat treat properties. 

As for MIG vs Gas vs TIG, these are so process and welder qualification dependent.  Either process can be used with these alloys but some are easier to develop the skill necessary for good welding.  TIG is probably the easiest to control and learn.  MIG will likely be the hardest to get good welds due to the wire feed being another variable that will likely give headaches.

Below is an article from the American Welding Society-Welding Journal written by a guy with way greater credentials than mine on this subject.  I'll defer to him.  Here's a teaser lifted from the article that may entice some to read it (GMAW is mig, by the way if this new terminology): 

"There is a misconception in the race car and street rod circles that GMA welding is not usable for critical welds. In fact, the GMAW process is used extensively in industry to make very high-quality, critical welds in items such as submarine hulls. Submarine hulls are made from high-strength steel and are predominantly welded with the GMAW process."

We hope our birdies won't hit the ground hard enough to test our welds but these race cars guys EXPECT to slam into things at high rates of speed; their methods/opinions are of interest to me.  Here is the link: 

http://www.aws.org/wj/apr03/AWfeature.html

The selection of filler material actually may be more important then the process (assuming a competent welder).   If a lower carbon filler is used, the dilution of the weld pool with the higher carbon tube material will lower the strength of the weld but that can be "designed around"  to a degree as the author of the article above mentions.

The same author referenced above who wrote in the American Welding Society about process and filler also wrote this which is pertinent to the discussion regarding TIG (sorry for the crazy spacing, couldn't get it to paste without it!).

(material sourced from   http://www.netwelding.com/Welding%204130.htm

OTHER PROBLEMS ENCOUNTERED

In addition to the filler metal selection issues mentioned, some additional cautions should be followed.  Many fabricators use TIG welding and make very small, concave fillet welds.  There seems to be a feeling that the smaller the better.  This raises several concerns.  First there is little filler metal used to make these very small welds.  Therefore the weld consists mostly of the high (by welding standards) carbon from the 4130 base material. This can cause cracking since there is no preheat or postweld heat treatment being used.  Also cooling rates for these small welds, especially when using TIG, can be quite high.  Therefore one suggestion I had made in the article (removed from this abstract) was that  some stainless steels filler materials could be used.  This is also mentioned on a number of Internet sites.  However with these small fillet welds there is only a small amount of stainless filler in the deposit and possibly a significant amount of the high carbon base material.  This combination can lead to a crack sensitive deposit.  It is suggested stainless filler metals not be used for welding 4130. 

Making an analysis of the resulting weld chemistry for varying amounts of filler metal dilution creates a scary scenario at low amounts of  any stainless filler alloy.  When I discussed the use of stainless filler metal making these small fillets in 4130 tubing with a friend who is an acknowledged "worldwide stainless welding expert," he cringed!  As he said, the suggestion that 312 stainless filler be used is based on at least 40 to 50% filler metal diluted in the high carbon material.  If you make almost an autogenous TIG weld (no filler metal) and add just 20% of even 312 stainless you get a Martensitic  deposit.  You do not obtain the desired microstructure on which folks base their recommendation for a particular stainless alloy rod being acceptable.  I have had race car fabricators say they like to use stainless filler because it makes the weld stand out and look good on unpainted frames they sell!  Not a good reason since it could also contain cracks!

CHECK WELD QUALITY

It is very important to check weld quality and understand the types of defects that could be encountered.  Check your weld procedures and keep them consistent.  You should make some sample welds and bend them to destruction to assure failure occurs only after considerable bending has taken place.  Look for porosity or cracks that may have been present in the weld.  It would be a wise investment to hire the services of an American Welding Society (AWS) Certified Welding Inspector (CWI).  There are some 20,000 registered.  In fact many of them are members of the  50,000 member AWS.  They can advise on procedures and what to check for such as small undercuts at the weld toe of fillet welds that can lead to premature failure.

Consistently following the proper weld procedures and knowing how to check for possible weld problems is of major importance.

Closing Suggestion
When welding 4130 chrome moly in the normalized condition, AWS ER70S-2 filler metal, with its low carbon content is the proper choice. Make sufficiently large fillets and make them flat, not concave. If the part is to be heat-treated after welding, then a filler metal matching the 4130 chemistry should be employed. This requires preheat and special precautions to avoid cracking. 

Be sure to employ the skills of a qualified welder who has experience welding this material.  Also inspection of the final welds by an Certified Welding Inspector (Certified by The American Welding Society) is highly recommended.

I concur with this statement 100%.  The welding specialists and metallurgists I've talked to agree that one should not use 4130 filler rod when welding a 4130 aircraft structure.  The recommended filler is ER70S-2.

Remember that literally thousands of homebuilts have been welded using RG-45 filler.  While this results in a technically "weaker" weld (45,000 psi tensile strength as compared to 70,000 psi) time has proven that these welds are more than strong enough.  Using ER70S-2 filler and proper technique will reward you with a weld that is more than adequate to the task.

I agree Joe.  I tend to use RG-45 with O/A (Gas) and ER-70S with TIG.  There are some high tech wire products out there, but the tubing will tear out before the weld fails with these.

I have seen a number of TIG weld failures and almost all were due to lac of filler material.

I agree Neil.  I do the same.  Works great!

Cheers!

Joe

While ER-70S is an OK rod to use with TIG there is a better rod that is better suited for 4130 tubing. It is the ER80S-D2. It has a post weld strength of over 85KSI which is closer to the 90KSI of 4130. It also does not have to have any post weld heat treatment to reach this strength. I am not referring to post weld stress relieving with a gas torch after welding.

Cessna requires this welding rod to be used on the C208 (Carivan) rudder bar repair.

Also please go to http://www.tigdepot.net/ and do your own research. There you can meet Mister TIG. There are also alot of technical articles about welding. Also if you have a question you want to ask a real expert ( not me!) you can and Wyatt will respond. Wyatt also taught some of the early Sport Air Workshops. I don't know the man personally, but I admire his efforts to educate welders and freely share his knowledge.

"With over 30 years experience, Wyatt Swaim is known throughout the world as the leading expert in the TIG Welding Industry.
Wyatt founded Hi-Tech Welding Services Inc. in 1986, developing a complete production facility geared towards providing the highest level of welding, R&D, welding engineering, and metallurgy to high technology industries. This facility includes TIG, Plasma and Electron Beam Welding, as well as Non-Destructive Testing, X-Ray and Penetrant Inspection."

I hope this information helps in the safe construction and repair of all aircraft. I am not trying to offend anyone by disagreeing with a welding rod selection.

Good Luck!

Swaid (fixnflyr)

I have used both RG-45 and ER70s-2 rod with a torch. While both make very strong welds the ER70-2 gets more like pudding when hot and does not flow out as nice as the RG-45. I have tried to destroy both welds in a vice and have not been able to make them fail.

Dave Conrad

I attended an open house at the American Champion factory in Rochester WI. a few years back. I believe they stated that they MIG welded their fuselages.

You might want to talk to the folks at Maule Air on this subject.  They have been MIG welding their frames for years with no problems.  You would want to talk to Davie Maule or their engineer, if they still have one.  I understand they are at a very low point right now.

Lewbloms

A properly welded MIG (GMAW) joint will be more than acceptable for an aircraft fuselage. However, amateur builders need to think about more than just the strength of a properly welded joint. MIG welding's primary advantage over TIG (GTAW) or oxyacetylene "gas" (OFW) welding is speed. From a production standpoint, speed makes MIG the preferred welding process for manufacturers. Speed isn't as important to homebuilders compared to price and ease of attaining and maintaining proficiency.

MIG equipment is more expensive than gas welding but about half the price of TIG. From a cost standpoint, MIG sounds like a reasonable option, and it's probably the easiest method to learn for welding thick, flat material (just pull the trigger and go!). But for a fuselage, you need to weld thin wall tubing, and this is probably the most difficult use of the MIG process. Even experienced, professional MIG welders have difficulty the first time they attempt to MIG weld thin wall tubing.

For builders learning to weld so they can build their fuselages, learning and maintaining TIG or gas welding proficiency is far easier than with MIG. With TIG & gas, you will know you have a safe, strong weld.

I didn't read all the post's but

 I am welding my  amatuer built plane together with mig..,.preheat joints to 300F prior to welding,..make sure joints are as tight  and clean as possible,..wrap joint after welding  to cool slow ..picture weld joint like a clock   4 oclock to 8 oclock ..8 oclock to 12 oclock and 12 to 4,.do the bottom section first ..and if at all possible,.. make sure that you do not to leave a dimple at the end of any weld in any phase ..mig, tig , flame,.etc...the dimple will be the first place to crack..try to over lap the weld if possible but watch the edges when you do ,..if you get what looks like a dark red almost black line around the puddle at the overlap  ..it's a cold weld ..meaning no penetration,..a good weld ,,the glow will run out on both pieces,,..if it is a cold weld ..grind it out ..doing your best not to grind too deep into your work,..knock off the high points with a small grinder then hand file the rest down to the top of the tubes your joining, flash heat again ,..flash heating is bringing it to temp without holding the flame dirrectly on the joint  making it red hot,.when you re weld it ,..it will come back to red  hot...

   if you cut into the tubing while grinding ,,you  could have a great looking second weld ,..but only paper thin tube around the joint,..same if you clean up after a weld with a grinder ..do your best not to hit the tubing that has no weld on it,..and use as fine a grinding disc as you can ..coarse grinding disc's cut really fast.

  I am not current ,..but was certified in all phases of welding ...

I have heard of guys mig welding fuselages for years. I know ER70S-2 is available on a spool. Soooo what diameter would one use. I read that .023 works quite well with the Hobart Handler 140 which is a 115 volt welder that I have. The problem with 115 volt mig welders is that they are notorious for cold lap if the wire is too large. However, this shouldn't be a problem on fuse tubing.

Jim

  I would think for thin wall tubing .023 would be the best bet. 

 http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp

Good page for TIG info. My son uses ER80S-D-2 and gets very good results on 035 to 062 wall 4130.

Some interesting items on this site:

http://www.weldingtipsandtricks.com/welding-4130.html

Rod