Subframe repairs

[stay_upright]

I was interested in aluminuim welding with a MIG and my subframe and sub-subframe were both broke.


There is a guide here http://www.mig-welding.co.uk/aluminium-welding.htm

The problem I had was that the frames use relatively thick aluminium and my hobby welder (130A) could not put enough heat into the frame to get the weld to melt into the frame properly so usually the weld sits more on-top of the frame.

I eventually managed a reasonable job and added a plate to the light/number plate frame as the design itself seems very weak so would expect it to break again however it was welded.

For the subframe I built up quite a lot of metal around the joint and filed it down which looks reasonable and flexing the frame by hand it holds up OK so I'll see how it holds up.

I also saw this http://www.youtube.com/watch?v=jijW310xvp4 so have ordered some rods to try out, the only thing I'm wondering now is will a cheap butane/propane/mapp torch be able to heat the joint up enough to enable the rods to melt? I seem to remember some-people on KTM talk using a similar product and being impressed with the results.

 

[rpduc]

Hmmm,
That stuff looks pretty interesting... Must be some kind of special alloy in those rods. As the comment suggested this is not technically welding as the base metal is not molten so there is no penetration. Just like what you got with your MIG. This would more accurately described as soldering. A mapp torch should get it hot enough I'd think. I personally would not trust it in a structural application, but it looks like there would be some other excellent applications, like patching leaky beer cans...

Back to your original problem with the MIG... did you try preheating with a mapp torch before hitting it with the MIG? I would think that preheating to similar temps and then going at it with your MIG would be better than this "solder" approach. I'm no hot shot aluminum welder but it helps a lot to preheat, even with my TIG machine.

 

[stay_upright]

I only pre-heated with either a petrol stove or electric hot air gun (550deg).

 

[GMP]

I've used the HTS-2000 with great success to fix worn and broken shifters and brake pedals. Basically it works as advertised with a little practice. Its much more than soldering, once the rod is molten, it appears to penetrate the base metal, almost seems like it causes the base surface to melt slightly. If you deposit some rod material on the base, and brush it away, you will also remove some base material. The trick it to do a repair in two steps, first "tin" the surfaces, then build them up. I was able to replicate that hammer smash video and its no BS. I would use it for the subfarme, but use a slug of aluminum rod in the tubing for strength. It would also be perfect for fixing a radiator or cracked case, as it works well on oily surfaces, unlike TIG. The filler rod material itself seems a little harder than the base aluminum, from my experience drilling and tapping it. I wouldn't attempt to fix a broken T-clamp or swingarm, but it has its applications and is a good tool.

 

[Eric K]

The aluminum repair rods that melt at a lower temp than the base metal are very similar to brazing. It requires proper preparation - cleaning the Alum oxide coating off the part(s) being repaired.

Use plenty of preheating and get the filler rod flowing smoothly. It is very strong with an adequate fillet.

As a test/practice case, I joined 2 pieces of alum plate together at a right angle angle with a fillet both sides. Then I tried to break the joint. I ended up only bending the plates.

 

[GMP]

Yes, its more like brazing. The pre "tinning" is what cleans the base metal. The rods I bought paid for themselves five times over in rebuilding shifters alone. A few rods and a MAPP torch in your truck could save a riding trip where Quick Steel epoxy won't do.

 

[stay_upright]

Yes this stuff does get the thumbs up - I 'finished' the subframe repair where I welded it with mig along the edges that weren't smooth (most of them), don't know how strong it is yet but from other people's reports it should be very strong - excellent.

Mapp gas is the stuff to use I was happy it was able to heat the subframe enough to braze it which is good considering there is a lot of metal there to carry the heat away.