I'm interested in fabricating an Ultralight fuselage out of 4130 and I was looking for information on welding this material. I'm unfamiliar with welding chomemoly and since my life depends on it, I'm interested in doing it right. Any info on this matter is greatly appreciated.
Dean,
Rather than giving instructions I choose to offer some advice. As you rightly surmise, your life depends on those joints being airworthy. Chrome Molly has in common with Titanium the blessing of easy weldability; however if proper preparation and technique are not followed, welds in these sensitive materials while appearing to be good under visual inspection may actually be embrittled and at risk of failure in service.
If you are not an expert GTA welder, experienced with thin wall tubing and even if you are, you would be wise to approach the welding instructor at your local Jr. college or technical school. By demonstrating your experience you may be allowed to challenge beginners material and get the specific training you need. Many JCs still allow advanced students to bring in projects, a method of instruction which would be ideal for you.
Lawrence Bower
Welding Instructor
United Airlines
I don’t know which thickness is your material. You must use 150C preheat for thicknesses up to 13mm. Use E10018-D2 electrode. Use clean gloves. Before use, Bake electrodes for 2 hour at 350C; then hold them at 150C. Welded joint must be heat treated immediately after welding. If immediate heat treating is not practical, heat welded joint from preheat temperature to 300C and hold it for one hour; then let it cool to room temperature.
We build NHRA dragsters and do a lot of fabricating for the race car industry in general. A lot of our work is done with lighter weight (.058" wall) 4130N tubing. We have also supplied this tubing to some local homebuilt aircraft customers.
Our procedures for welding are fairly basic and are common in our industry. Fit-ups have to be very tight (<.020" gap) and the material must be cleaned - we sand or wire brush. We use a Miller SynchroWave and an old Lincoln 300. The small Weldcraft Crafter series torches are very nice for this delicate work. We run straight argon and use an uncoated (no copper) ER70S-2 rod.
There is some debate in filler rod selection with some people using a 4130 rod and others using a mild steel rod. Our theory (right or wrong-but it works) is that we would like a little less tensile strength in the joint to eliminate cracking when the chassis flexes. We have had great results with this method for many years.
Preheat is not necessary due to the fact that the materials are way less than 1/4" thick and we do not do any kind of a post heat or stress relief.
Probably the best advice I can give you is to buy a couple of books that are really practical for what you and I are doing and then spend a lot of time practicing. TIG welding on small diameter, thin wall tubing takes a lot of practice and skill. I've had a lot of veteran welders apply for work that had not and could not master this skill.
The books I would strongly recommend are:
Welders Handbook (Finch, Monroe) published by HP Books
Performance Welding (Finch) published by Motorbooks International
These books are written by people with extensive aircraft backgrounds and have been adapted slightly for the race car market so they should be a great help to you. They're a bargain at $20-$30 each and I think both are available from Motorbooks Int. in Wisconsin. They have a good website also.
Hope this helps and if you have any more questions let me know!
Thank you ALL for your responses to my inquiry on welding 4130. Its nice to see so many people offering there experience with this material. I really appreciate the recommendations on literature as well. I'm always looking for more reference material to add to my collection. I've heard of many home builders using gas welding to accomplish this task due to the thin wall thickness mentioned and because of economic reasons as well. This method was also favored due to many recommendations of normalizing the weld after it is made, even with TIG. Of course, its cheaper to just buy a torch outfit rather than that AND a TIG set-up.
I'm curious though, what was your personal experience with NOT normalizing the welds. I mean, what led you to not perform this seemingly important operation. From what I understand and have read so far, even with using a mild steel filler rod, the weld produced in a thin wall tube rapidly cools by radiation due to lack of material thickness and the rapid cooling near the edge of the weld acts as a quench line and causes a narrow hardened region to be created along side the weld. I'm told that this area can easily crack unless it is normalized. I've also heard of people having problems with distortion of the welded frame due to PWHT with a torch. Anyone's thoughts on this?
What I would suggest is that to best understand the benefits of PWHT on thinwall 4130 is to do some destructive testing of your own. Take some 3" lengths of tube in a size you are interested in and weld up a bunch of T's using a variety of types of welding (gas, TIG, MIG) with a variety of normalizing techniques, then put them in a vice with a big bar on one leg and see how much strain it can take and what mechanism of failure occurs. Try and be uniform in the amount of stress you apply to make a fair comparison. Let us know what you find. Scott.
Dean,
I am not a welding engineer but base what we do on our own experiences and what we gleam from those who are doing similar work. In our industry (race cars) PWHT hasn't been frequently used in the 15 years that I've been around it. I have seen very few failures and the ones I have seen have usually been more attributable to fatigue of the tubing than to a heat zone resulting from welding. The heat input from a skilled TIG welder is very little and I feel this helps to control the effects on the base materials. You also have quite a large area covered when you weld two peices of tubing together in a "T" and even more area at lesser included angles. If we have a problem it is usually where a small (but highly loaded) bracket is welded to the wall of a tube.
Grab a handbook and look at the specs for heat treating this material in regards to time, temp, atmosphere, etc and then explain to me how someone can duplicate this with a torch. Personally I would be more afraid of driving (or flying) a chassis that someone had taken a torch to trying to normalize the welded joints. I suppose that ideally a chassis could be properly heat treated or stress relieved after welding but I know we don't have a heat treat oven that large and I doubt many people do. We have considered the vibratory stress relief machines and I think some of the sprint car builders are using them.
Just my 2 cents but I hope it helps!
By -
Date 12-06-2001 18:53
In the industry in which I am active, (petro-chemical) we would both pre-heat and PWHT this type of material. I do however know that in the light aircraft industry they often do not PWHT these materials for a very practical reason.
You can only practically PWHT the entire weldment after completing the welding, but this will more often than not lead to distortion and even possible sagging of the members due to the very thin nature of the materials and the high temperatures used during PWHT.
The solution is then to give a suitable pre-heat, and no PWHT. This you can only do if your frame is very carefully designed to place the welded joints in low stressed areas.
If I was you, I would approach a company that manufactures light aircraft and ask one of their welding engineers for advice. As long as you are not competition to them, they should help.
Regards
Niekie
Being in the airframe welding business I will agree with the very sound advice given by HPMTM and only add that the skill level requirement keeps going up as the wall thickness goes down and I would suspect that an ultralight airframe will be mostly .035" wall or less. Good luck, Scott.
Thin wall < 1/8" (0.125"/3.2mm) 4130 Chromoly can be very successfully welded with ER 70S2 or S6 without preheat or postheat weld treatment. Use 0.023"/0.6mm, 0.030"/0.8mm, 0.035"/0.9mm, 0.045"/1.2mm or maximum 0.0625" - 1/16"/1.6mm diameter bare or copper coated GMAW wire.
Use small diameter (0.020"/0.5mm, 0.040"/1.0mm, 0.0625"/1.6mm)2% Thoriated or Ceriated Tungsten electrodes. Sharpen these tungstens chemically with sodium nitrate or use a "tungsten grinder" (very difficult to hand sharpen).
Use the low amperages recommended for the tungsten diameters.
Gas lenses work great!
Use a back purge, and "cleanliness is next to godliness"!
NO ARC STRIKES/ARC BURNS OUTSIDE OF THE WELD JOINT!! Make work connections (ground) so there is no arc burn/strike outside the weld joint!
Dear D.F.:
The response by 357 is the best you can get without paying for it. The welding may also be performed satisfactorily without gas lenses (another subject...), but the welds do look much cleaner when they are used properly (nice and shiny).
The as-welded condition for these welds potentially may be acceptable for your application. In my early welding years I fabricated parts (key structural components) for Ultralites and helicopters with the same material and thicknesses using GTAW without any PWHT. The only ones that I know of that failed were due to operator error.
I can only recommend one thing in addition to 357's accurate technical response: Verify your welding parameters (thorough fusion, soundness, weld size, desired mechanical properties, etc.) through some sort of mechanical or NDT method.
If you don't, it will give you something to think about on the way down...
