OA welding 4130 aircraft frames
Great Topic to applies to more than just airplanes: I Hold an AP, like so many, and OA welding was taught inthe training back in 1970s. Was perhaps my strength area as I had study to be a welding engineer before starting the AP program. In my simple view practice first on good quality mild steel .030 -.040 sheet first. Good quality is material made in the USA that has the free sulfer controlled to a standard.
Start with, butt joints,then advance to tee joints ( fillet welds) lap weld and cornor welds. Must get this down to zero undercut, excellent heat control, bead width, penetration and apperance. Master thin section flat work first, as the tube weld is nothing more than all of these joints in one. . Oh yes, in all positions. Start sitting at a bench, and then move to sitting on the floor and welding under the bench.! Then move to tubing.
As for equipment, very important: Regulators must hold a percise flame as indicated. Very important. As for brands of torches, well that is also fun: I have a Victor Aircraft or J series torch. My friend has a Smiths Aircraft torch. There is not a week that passes the we do not tell each other to trade up and scrap each other's equipment! I learned on a Smith Torch and they are excellent. But I have Victor torch- and it is excellent. Nice to have a choice.
Most important point to consider and maintain is the condition of the torch. Valves must be tight thus maintaining the nutral flame or ever so slightly on the carbon side as clearly indicated. Never - never the other way to an oxygen rich flame. Tips are important: I keep a set of tips just for 4130 tubing work: Tips must be clean, and the flame cone must be maintained. In cluster joints the tips take a beating and must be keep super clean with each weld joint.
Years back sodium filled tips were on the market to help tip cooling, but I have not seen them for years.
Filler material, again must be keep clean, E70s of the highest quality wich is mild steel is what makes it all work. Do not use 4130 rod as that will produce a joint that must be heat treated or normalized and will crack. Big no go here.
Joint fit up: I would say an area that is as important as the weld it self. Joints have to fit, parts have to fit, not to tight thush placing pressure on tubing that will warp when welding heat is applied. Gaps must be avoided. Even fitting joints, pride on how the joints are cut, full strength and thickness must be maintained as the edges of the joint rotated 360 degree from a 100% fillet weld to what on the tips of the tube becomes almost a lap weld.
Joint fit up this is an art to master. Joints must be clean and free from any and all oil before welding. I do not like to grind a finish joint, grind or rough out Ok, but the finial fit is with a file, to prevent transfer of abrasive materials. On this same note, I suggest avoiding any type of blasting the joint before welding. Tubing is best welded clean and certainly free from anything like rust. If you use end mills or hole saws to cut joints avoid the use of sulfer cutting fludids, as they find their way back to the weld joint. Cutting joints with end mills is the best way, but does not always work and certainly hard for field work.
Blasting always gets material in the tubing and during the welding process finds it way to the weld joint. I know there is many great ideas here, and in industrial applications with the correct blast media weld joints can become super clean. But that is a complete new topic with many smart guys out there. Avoid any foreign material added to the weld joint is what I am trying to say.
Grinders, sanders, burrs, lock them up and toss out the keys. Wire brushes must be clean and stainless steel. Keep using fresh brushes, clean as you go on the joints, and just before welding brush and wash with a cleaner to remove oils and oxides, even oils from ones hands can be detected in inspection processes.
Plan your welding sequence to eliminate as many starts and stops as possible. Starts and stops must be mastered, again no undercut but no excesive build up either.
Once welded leave the joint alone: Do not go back and reweld, do not grind and sand to make the weld "look nice" that has to be accomplished as welded. Bad welds, take the entire thing out and start over. Excessive heat zones and reheating a joint must be avoided.
Tubing welding is fun and one can have a great deal of pride in the work. Take your time, plan your work and think about what the application of heat does to the airframe. Support joints, avoid welding on fire bricks or stone, as foreign material transfer to the joints.
TIG welding is another subject - but the same ideas apply. Torch welding is fun, slow but an art that can be mastered. My two cents on the topic. I would like to hear from others as there are many very smart guys out there who practice this each and every day.