For building bicycle frames from aluminum
MIG (Metal Inert Gas) welding is the best choice.
This is also known as gas-shielded electrical welding. There are also electrical welders that use a spool of
flux-cored wire that don't need inert gas to keep the oxygen away, but they
don't work as smoothly as MIG welding.
Gas welding aluminum is possible, but takes
a lot of skill. While it is not the
recommended way to make aluminum bicycle frames, it is good for other workshop
tasks, such as repairing aluminum tool handles.
The problem with aluminum is that it is a
very good conductor of heat. When
you get the edge to melting temperature, the whole piece is nearly melting
temperature. It is very common to
think you are going to weld an aluminum item, and have the entire thing melt
into a puddle instead. A variation
of that theme is to have a large area of the welded item lose its shape, sagging
under the force of gravity once it reaches welding temperature.
Let's go ahead and fool around with some
1. Find a couple of old handlebar stems,
and prepare them to be welded together. With
a grinder or file, clean the surfaces to bright, shiny, fresh metal.
This removes the invisible outer layer of aluminum oxide.
2. Use a torch tip one size larger than you would for the equivalent thickness of steel. For handlebar stems, this would be a #3 or maybe even a #4 tip. Light the torch with a big, hot, neutral flame.
3. Hold a flux core aluminum welding rod in
your left hand. You can use long
oxy-acetylene welding aluminum rods, or the shorter flux-coated aluminum rods
for electric welding if your welding supplier doesn't carry the gas welding
rods. Assuming you are right-handed, bring the torch flame close to the
right-hand edges of the pieces. Move
the torch in a small pattern. The
idea is to quickly heat up the edges, trying to get them to melting temperature
before the aluminum carries the heat away and melts itself entirely. Keep the
welding rod very near. In fact, you
can rest it on the work pieces, and allow it to melt just a bit first. This little ball of aluminum that will form will melt just a
second before the work pieces themselves. As
soon as the ball melts, you should be able to push the rod against the work
pieces, and you'll have a puddle consisting of the end of your rod, and edges of
the work pieces. Work quickly,
adding rod, and moving to the left as the melting continues.
You might even be able to prod or stir the puddle with the rod as it is
melting into the puddle. If you feel that you are going to lose control, let
everything cool down entirely, then start again.
4. When you are done, let the attached
handlebar stems cool. Flip them
over, and weld again on the other side.
5. Let the stems cool, then wash off the
flux. You should be able to remove
it easily with a wire brush and water. Look at your work.
Do the pieces appear well-attached?
Now, its time for the usual vise and hammer technique.
The stems should not break apart at the welds, but should break nearby if
you have done a good job.
Oxy-Acetylene Welding Main Menu
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