Tips for welding sheet metal
Aluminum sheet metal is lightweight, easy to form and does not rust, which offers manufacturers the option to skip the painting step when producing parts with this material. These benefits make aluminum sheet metal popular in a range of applications, from toolboxes and jon boats to signs and awnings.
But welding this thin material does present some challenges.
Learn about five tips to help control heat input and improve technique to optimize results and reduce rework when MIG welding aluminum sheet metal in a manufacturing operation.
What is sheet metal?
First, it’s important to understand what is meant by the term “sheet metal.” In discussing sheet metal, people are often referring to material that is 1/8-inch thick (.125) or less. Sheet metal comes in a range of thicknesses, and people may have different definitions of what they consider sheet metal to be depending on their application.
For the purposes of this article, the term sheet metal refers to material 1/8-inch thick or less.
Tip 1: Use pulsed MIG welding
The right welding process can help improve results with aluminum sheet metal. Pulsed MIG welding lowers heat input and makes it easier to weld thin materials and minimize burn-through.
Pulsed MIG alternates between a high peak current and a lower background current, lowering the overall amperage. The pulse of peak current propels the molten droplet across the arc and provides the energy to produce good fusion associated with spray transfer, while the low background current allows the weld puddle to cool.
What are some benefits of pulsed MIG welding?
- Operators can run larger diameter wires at currents lower than what it would take to run a non-pulsed process like CV MIG.
- The process provides better control of the bead profile. Dialing in a wider arc cone helps tie-in both sides of a joint or on an outside corner. A narrow arc cone helps focus the arc and provide good fusion at the root of a joint.
- Adjusting arc length (voltage) and wire feed speed for optimum performance helps eliminate excess heat input, over-welding and post-weld grinding.
Tip 2: Choose the best filler metal alloy possible
There are many factors to consider when selecting the best filler metal for welding aluminum sheet metal. These include the base metal alloy, service temperature and environment, formability and more.
The two most common aluminum filler metals are 4043 and 5356. They produce very different results when welding sheet metal. Characteristics of a 4043 filler metal include:
- A lower melting temperature and improved fluidity, due to silicon as its main alloying element.
- Wets out better than a 5356 filler metal.
- Contracts less as the weld cools thanks to the high silicon content since silicon expands as it solidifies.
- Compatible with 3003, 3004, 6061, 6063, 5005, 5050 and 5052 base metals.
- A 4047 filler metal has a slightly lower melting point and has about twice as much silicon as 4043, so welds contract/warp even less.
When pulsed MIG welding material that’s 1/8-inch thick to 16-gauge, a 3/64-inch filler metal can be used provided there is tight fit-up. For even thinner materials, try a .035-inch filler metal. For CV MIG welding on sheet metal, wire diameters of .035 inch are recommended.
A 100% argon shielding gas is the most common in MIG welding aluminum sheet metal.
Tip 3: Take the time for proper fit-up
Proper, tight part fit-up is especially important when welding thin materials. Gaps between the pieces to be welded can contribute to warpage.
Even a small gap can turn into a larger gap if the piece warps — forcing the operator to slow down to fill the larger gap and add unwanted heat into the weld. This can lead to bottlenecks in your line.
Ensure there are no gaps in part fit-up. It’s also recommended to have the edges of the pieces overlap slightly. Use a lap corner part fit-up rather than an outside corner fit-up to reduce the chance for burn-through.
Another option to combat burn-through is to use a copper backing bar when MIG welding sheet metal. Place or clamp a copper bar on the back side of the welded area, which helps dissipate heat faster than atmospheric cooling alone.