5 Ways to Improve Your MIG Welding Operation and Reduce Rework on Sheet Metal
October 23, 2019
Learn how to control heat input and improve technique when welding aluminum sheet metal to reduce distortion and burn-through.
Improve results on aluminum 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, so operators must take care to avoid warpage, distortion and burn-through.
Learn more 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. But be aware that 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. For example, pulsed MIG welding lowers the heat input and makes it easier to weld thin materials and minimize burn-through.
The pulsed MIG welding process alternates between a high peak current and a lower background current, which lowers 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.
Pulsed MIG also allows operators to run a larger diameter wire at currents that are lower than what it would take to run a non-pulsed process, such as CV MIG. In addition, it provides the ability to better control the bead profile. A wider arc cone can help tie-in both sides of a joint or on an outside corner, where a narrow arc cone helps focus the arc and provide good fusion at the root of a joint. Adjusting the 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 — such as base metal alloy, service temperature, the environment, formability and more — when selecting the best filler metal for welding aluminum sheet metal. The two most common aluminum filler metals are 4043 and 5356, and they produce very different results when it comes to welding sheet metal.
A 4043 filler metal has silicon as its main alloying element, which lowers its melting temperature and improves its fluidity, helping it wet out better than a 5356 filler metal. Silicon is also an element that expands as it solidifies, so filler metals that have high silicon content will contract less as the weld cools. A 4047 filler metal has a slightly lower melting point and has about twice as much silicon compared to 4043, so the welds contract/warp even less.
Common base metals that would be compatible with 4043 and 4047 filler metals are 3003, 3004, 6061, 6063, 5005, 5050 and 5052. When pulsed MIG welding material that is 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 to .030 inch are recommended.
A 100% argon shielding gas is the most common gas in MIG welding applications with aluminum sheet metal and is readily available.
Tip 3: Take the time for proper fit-up
Proper, tight part fit-up is especially important when welding thin materials, like sheet metal. Gaps between the pieces to be welded can contribute to problems with 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.
In addition to ensuring there are no gaps in part fit-up, it’s recommended to have the edges of the pieces overlap slightly. Using a lap corner part fit-up rather than an outside corner offers less chance for burn-through.
Another option to combat issues with burn-through is to use a copper backing bar when MIG welding sheet metal. This involves placing or clamping a copper bar on the back side of the welded area, which helps dissipate heat faster than atmospheric cooling alone.
Tip 4: Keep travel speeds high
Another factor that helps minimize burn-through, warpage and distortion on sheet metal is keeping a fast travel speed and a small bead during welding. Using a slower travel speed means dwelling longer in an area, causing heat to build up.
Operators should always use stringer beads (not weave) and use the fastest travel speed possible to maintain a good bead profile. Backstepping techniques should be avoided, as they slow travel speeds, increasing heat input and distortion. Pulsed MIG welding is recommended because it provides the ability for a fast travel speed, especially compared to other welding processes that may be used to weld aluminum sheet metal.
Tip 5: Use weld bead sequences
Bead sequences can be greatly affected by the part geometry and fixturing in use. Using weld bead sequences, such as intermittent welds, rather than a constant weld bead, can help offset distortion and warping.
When possible, weld beads in any low heat sinking areas first, to minimize burn-through. Also, it can help to spread the weld sequence around the part to reduce the localized heating in one area. Another option is to make short welds in one direction, starting the next weld behind the beginning of the previous bead. This helps reduce heat buildup while still allowing operators to weld in one direction.
Avoid common problems with sheet metal
MIG welding aluminum sheet metal leaves little room for error. Taking steps to reduce the heat input, keeping travel speeds high, and ensuring there are no gaps in part fit-up can help reduce the risk of burn-through, warpage and distortion. This helps manufacturing operations reduce rework and costs for optimized productivity.