Aluminum Welding

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 aluminum welding:

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.