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do i need to/how can i make this crappy cast aluminum weld better?

jml74

Plastic
Joined
Oct 18, 2017
I have a cast aluminum camshaft holder from a motorcycle that had an ear on it snap off. The ear holds the rod for the tachometer output, there's a worm gear at one end that meshes with a gear on the cam that spins the rod to register the engine RPMs. It cracked off pretty cleanly, so I just cleaned it up and TIG welded it back up last night; I'm happy with the outside, other than a couple of boogers, but I didn't get penetration all the way through (well, I actually did on one side, but it didn't fuse). I can't really come at it from the other side, it would require so much stickout that I wouldn't have any gas coverage. It feels solid, I banged it on the edge of the table a couple of times and it still held. Is there more that I can/should do? The camshaft holder will be bolted firmly to the head, the ear just floats, so I don't think it will be subject to a lot of stress. This is ~1/8" thickness.

Here's what I ended up with. One of these is blurry and looks like it's got some undercut, but the original casting is rounded right there and I didn't need to go far enough to cover it up. On the last picture you can see the remains of the crack on the inside.

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Its going to fall apart again. You cant have any crack remaining or it will just work its way back through your repair.
I have gotten into far tighter spots than what im seeing in the picture. Get a gas lens.
You *might* want to give it to someone more used to doing cast AL repairs before you try any more on it...
Sorry if that sounds harsh, but as the guy who gets these kind of jobs at work, I wish more people would just stop and give it to me before they did anything more to it... It usually makes it way harder to fix and therefore costs more.
 
First step is to bake it... then v out the crack. Weld both sides and leave a healthy bead at each end, the crack will start from the ends.
 
You can get long and super long gas lenses, there tricky to use, but when you need them you need them.

Other option is to simply cut a 1/8" of material out from one side and do a full penetration weld. My experience with alu penetration is not reliable, its gotta be prepped.
 
Cast needs a slow heat up and a slow cool down. The cast alum isn't as critical on how fast up it down, but it doesn't like rapid.

On your first pass, you should sand it all out and then do a second first pass. This will help remove the deeper contaminats. Alum should be removed mechanically, not with sanding or grinding discs if you wa ts better welds.

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A while ago I was modifying some engine heads for competition cars, and the material wouldn't weld well if you try to go fast, kept bubbling, developing porosity, mentioning this because first pic shows something that looks like porosity, like Bondo suggested, I was going really slow, walking around a bit till I see no bubbling, dab, wait again, then move on, and since castings usually have high Si content, used 4043 rod, didn't hear any complaints about my work, so I guess the mod held up

and if you need to weld deep inside at the bottom of a pocket, you can extend the electrode way more than usual (even without the long reach lenses), and you need to reduce the argon flow somewhat (you need to experiment here to see by how much), argon is heavier than air, and the idea behind low flow it that it doesn't cause turbulence which would otherwise suck in air and cause problems, you sort of flood the pocket with argon and weld in the pool
 
I don’t have a lot of experience with welding but can you braze this instead? I’ve seen that brazed joints can be stronger than the aluminum itself.
 
Grind out the crappy AC weld. Get some pure helium for gas and set the machine to DC (like steel) it will penetrate but if you are not a good tig welder maybe practice on some scrap first. I will warn you it is not like AC with argon.
 
If this landed on my table at work:
I'd clean the living piss out of it with solvents (acetone and 90% rubbing alcohol), a bit of warmth from a mapp/propane torch, then wire brush (hand not powered), and then some more solvents and brushing...
Carbide burr bits work great for removing offending material, as long as you get ones made for aluminium. They have fewer teeth and bigger flutes. They can be a bit grabby and bouncy so hold on tight. The other option is to use a bit of wax on the part and the burr but then you have to do the solvent/brush dance again.
I'd weld the difficult side first with very little if any prep, maybe a skim with the burr to remove the surface.
I'd then take the burr to the "top" side and backgouge into the pass on the back side, weld it out and blend clean if needed.
The machine you're welding it with is the biggest factor. Is it an old transformer or a new inverter.
On the old transformers, I'd try and run the farthest to the negative side as you can while still getting good cleaning. The more cleaning you have the more it's going to ball up and try to roast your tungsten. I'd use 1/8" Brown(zirconium) or Green ground with a slight taper and a 3/32" flat on it before you strike an arc. Just using 3/32 tungsten it might be more inclined to melt when you have the stickout you need to get at the back side.
For an inverter, go around 120 hz frequency, start at 80/20 En/Ep and add more Ep if needed. 1/8 tungsten again, ground to a short taper with a 1/16 flat on it.
For filler wire, 4043/4047 is a good all around guess, with 1100 as a backup. The only casting alloy number I remember for aluminium is 356 which is really close to 6061. https://www.esabna.com/shared/documents/litdownloads/alc-10030c_alcotec_alloy_selection_brochure.pdf That is a chart from ESAB detailing how deep the rabbit hole of "which filler for what" can go...
Me and Al castings never got along very well until we got Dynastys at work. Having control over all of the aspects of an AC welding arc is like switching from DOS to a smartphone...
 








 
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