Published In The March 2013 Issue Of Cycle Source
Article By: Will Ramsey – Faith Forgotten Choppers – www.faithforgottenchoppers.com
There is some debate as to the best method of welding aluminum sheet metal (under .090”). The two methods most commonly used to weld aluminum are gas welding (Oxy- Acetylene) and TIG welding with AC current. Although the TIG process was invented in the ‘40s, gas welding aluminum remained the primary method used for fuel tank construction in the aircraft industry until the mid-nineties. Both methods have advantages and disadvantages. However, the increased weld density found in aluminum gas welds makes a strong case for it being the best choice when welding an aluminum chopper fuel tank. A porous weld on an aluminum fuel tank, mounted to a hardtail chopper that actually gets ridden, is begging for a disaster down the road. It is no secret that conventional aluminum TIG welds are very susceptible to porosity. Without a $4000-$8000 inverter power source and a $2000- $3000 argon purification system, the weld density and ductility of the conventional aluminum TIG weld will struggle to match that of a gas torch and a good flux. The following tech article illustrates the steps involved in welding 3003 aluminum panels using 1100 alloy welding rod with an oxy-acetylene gas torch.
Once the panels are formed and fitted, it’s time to prep the aluminum panels to be welded.
Aluminum is very susceptible to contamination. Proper preparation is necessary to obtain a strong dense weld bead. The aluminum is first wiped clean using a solvent such as acetone or isopropyl alcohol. Then the edge should be scrubbed with a clean stainless steel brush.
The panels can be tacked together using either the gas torch or the TIG welder. I often use the TIG for tacking simply because it is faster for me.
Aim to fit panels fully shaped and tight enough for fusion tack welds only. This allows for a consistent weld with a balanced “heat affected zone,” resulting in less distortion. Filling large gaps with welding rod is not ideal.
The powdered aluminum flux is mixed with clean water to a thin paste consistency. The mixture should be held in a ceramic or plastic bowl to avoid contamination.
Brand new welding rods have remnants of lubricants used to form the rod size. All welding rods must be cleaned with a solvent to avoid contamination.
Flux is applied to the weld seam and the welding rod.
Protective eyewear–specifically designed for aluminum welding- -must be used to protect your eyes from the orange sodium flare produced by the welding flux.
The seam is welded using just enough filler rod to avoid undercutting the aluminum. Excessive rod makes the metal finishing process more difficult. Practice makes perfect!
Aluminum flux is corrosive and must be completely removed after welding. Remaining flux is best removed with hot water and a stainless steel brush or Scotch- Brite pad.
Unlike a TIG weld, a good gas weld will lay flat making the metal finishing process very easy.
The back side of the seam shows excellent weld penetration and again the bead lays down flat and can easily be hammered smooth.
Aluminum gas welds are ductile and can be planished flat and smooth with little or no grinding. Planishing the weld restores strength and a uniform surface to the weld seam.
Finally, the weld seam is simply block sanded with 240 grit sandpaper to finalize the surface finish.