Welding & Reaming
I have a couple of gear leg weldments that were misdrilled at the factory, i.e, off center,...about 50 holes worth total. Most are 3/16, some are quarter inch. If I try to repair the weldments which I believe are 4130N and maybe thicknesses of .063 or .100, can I get some one to TIG weld the holes undersize so that I can then drill them back up in proper orientation.
I will need to match drill them to a laminated aluminum spar which is approximately an inch thick. I have a number of brass bushings which can protect the aluminum as I drill them back up to a final reaming size.
My fear is that the welded area will be extremely hard to drill through and difficult to ream, as well as not being as structurally sound.
Am I better off just shelling out 5 or 6 hundred dollars to buy new weldments?
I have a Miller 175 Mig but I don't have the consistent skills to weld something like this.
I've been able to re-thread a hold I repaired with a Meg welder. The tap did seem like it was encountering some harder metal. But it worker.
I to have the same kind of question. Is there a mild steel wire for meg welding that can be drilled, milled or turned in a home shop? Seems like there should be.
I'll get back, with the answer.
Last edited by Vern2; 03-31-2010 at 08:58 AM.
Mild weld wire
Yes you can do this. We do it a lot at work. You can get a mild wire for your welder. I would TEST one before before I did them all to make sure your weldment is not made of something that will harden after you weld it.
I would also completely fill the hole because if you leave some of the hole your drill will try to follow the hole.
Another way we do this is to plug the hole with all thread drill and tap the hole larger. Then screw all thread into the hole. Weld the all thread and then drill the new hole into the all thread
Because of the .063 thickness your best bet maybe to weld. Something this thin wouldn't have enough threads for the all thread.
Last edited by Machinist-Guide; 03-31-2010 at 11:38 AM.
Would silver soldering a close-fitting plug in the hole be out of the question? I imagine you'd have a bit less trouble with the steel hardening that way.
Preheat, weld, post heat or bury the weldment in insulating material to slow the quench will help with localized hardening.
Migs weld very clean so inclusions won't be an issue.
Since the material spec is not clear, the only way to find out is to try some.
Thanks everyone for the comments.
The material is 4130 steel, supposedly normalized or half hard. It is a standard material for aircraft metal tube and fabric aircraft. This weldment however is made to hold a heavy spring steel landing gear in place and can get some abuse. Most of the loads will be in shear as the weldment tries to move upward but there is some twisting force as well. Thats why so many bolts, I guess.
The main thing is to get the holes closely drilled so there is no shifting around and/or cracking. However, the bolts are not really close tolerance bolts and are standard AN hardware.
If I can get it to fit, I will see what happens with welding a few holes.
Wouldn't do it.
This is going on an aircraft - do you want to be the one landing on it? Do you want your children flying in the plane with this repaired part? If it was a low stress part I would say "go for it.", but as it is a stressed part in the landing gear I would not want to be responsible for adding stresses to the part by welding on it.
4130 is rather forgiving. It is routinely welded with TiG and Stick. With Stick use 7014 for thin sections, and 7018 for heavier sections. Tig use a 70s wire. 41XX materials are oil hardening, there isn't any problem with the weld or heat affected area.
You will run into other issues and a lot more difficulty welding 4140, 4150 etc. these can be welded, but these do require preheat and post weld heat treating. Otherwise they will be likely to fail in service.
Originally Posted by kf2qd
If I were the one to weld it I would. I am a licensed pilot have been since 1989. I have flown in many home built aircraft, and have even welded new parts for them. Nothing I have welded has ever failed. How do you think they made the "Weldment" to begin with? They "welded" it together. You don't think Boeing, and Northrop Grumman, Cessna, Piper, Airbus and the rest of them don't repair parts???? You better never fly again, the plane is destined to fall out of the sky.
You are talking about common MIG? Regular wire will mill and drill well provided its welded on common mild steel.
Looking at common MIG wires weld yield strength of 70,000 to 80,000 psi. No mild steel MIG filler wires. Deoxidizers and other wire alloys is part of problem. MIG welding puts minimum heat into weld cooling faster than a gas weld or TIG weld so the weld is hard and hard to drill. Grinding heats weld and might temper it a little.
Just had needle gun thread. Vibrating steel can normalize it making it less brittle and relaxing some locked in weld cooling contraction forces.
I have not had any problems machining after MIG welding er 70-s6
Now, if you have tried to machine aluminum after TIG welding, you will find that a momentary tungsten contamination will destroy even a decent carbide end mill given the "right" circumstances!
Many variables for the HAZ ...... sometimes no troubles.
Other times some hardness.
When in dout,
play a rose-bud over the repair.
Watch for a "black-heat" (old-world term)
for the temp range a little beyond the temporing rainbow.
Sanded surface seems colorless, like it's not reflecting or emitting light.
Sustain this for say 30 seconds and back down slowly.
Soft as butter now.
I think what Phil is trying to say is to heat the affected area just above the blue stage to the gray color, just below a low red glow.
Once when I was forging something, the thing slipped out of my tongs. I instinctively reached down and grabbed the piece of metal. It wasn't glowing but it was mighty hot. You smell your skin burning before you feel it. Not fun. Do not do this.
In today's lighting grey might be a good call.
Smithing before overhead electric lighting,
(and even now) temporing should be done in a room
with ambient low-level lighting.
Steel in this temorature range will not be emmitting any glow
and will have passed the range where colors form.
Visually a (black-heat).