Project #6 from Spike : Aluminum Seat Pan Hole blow through repair
I was making an aluminum seat pan yesterday for a project i'm working on, when i made a liitle 'oops'.
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While annealing the seat pan i got a little over-zealous with Oxy-Acetylene torch and blew two holes into the aluminum of my seat pan. The holes are on the other side of the picture, but it shows what i was working on.
Normally, this type of blow-through is not generally considered to be repairable with satisfactory results... the paper thin edges of the holes blow away easily, it's hard to form properly because of the thicker metal where the aluminum retracted around the hole. I have an interesting method for repairing stuff like this, and that is to use a backing metal.
First i formed out my seat pan, i didn't want to fill the hole and risk filling the holes and then having the weld crack or break when working the material ( the hole was in an area that had a very deep draw in the shape). Since this thread isnt' about making the seatpan, but fixing my holes, i'll skip to the fixing bit.
I took a piece of aluminum, one step thinner than original base metal (this is important!). I hammered it around the form, so that it had the same contour, and fit flush to the back of the seatpan where the holes were.
http://i1168.photobucket.com/albums/...15161101_m.jpg
I clamped it in tight with some vise-grips, and then ran the tig torch quickly around the outside of the holes. This retracts the paper-thin metal back to a make a larger hole, but a hole with thicker and usable thickness material around the edge.
To fill the hole, first start welding to the thinner backing metal. Feed the filler metal in for buildup and walk the puddle over to the edge. Now touch your weld filler puddle on the backing material to the edge of the hole *quickly*. Continue the weld around the hole until it's all filled in.
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Both holes filled in.
http://i1168.photobucket.com/albums/...15161120_m.jpg
and while i was there, i had to fill in a crack along the edge, where i went to fast in the draw and put a little stress crack in the material. No big deal. When you fill these cracks, though, it is important to do it correctly. First, walk the torch around the cracked area, and bring the end points of the crack up to welding temperature. This will take the stress and surface tension off of the metal, and keep it from either re-cracking as soon as you're done, or cracking worse and becoming uneven while you are welding it. After that, drop a couple spot welds on the ends of the crack to keep it still, and then weld it up. Even on small cracks, you still need to use all of these steps. To go one step further, i will usually run my weld a little longer than the crack at both ends.
http://i1168.photobucket.com/albums/...15160703_m.jpg
After some handy work with the angle grinder smoothing out the welds, it looks good as new, and still strong to boot.
http://i1168.photobucket.com/albums/...15162413_m.jpg
QUICK NOTE: If you are going to do any more metal work on the repaired area, or the project will be exposed to heat cycles/expansion-contraction, then you will need to take the oxy-acetylene out and re-anneal the heat affected area.
