Sheet metal can be the most troublesome material to weld as it’s a lot thinner than other materials. They’re prone to warping and burn-through due to high heat. And flux core is notorious for requiring more heat due to its tubular transfer, which increases the risk of burn-through.
How can you weld such material with these factors at play? You see, even professional welders find it hard to weld sheet metal.
Whether you end up with a scrap weld or a perfect-looking project, the answer comes down to the approach you use.
In this article, we’re going to explain the best ways to weld sheet metal with flux core so that even novice welders and DIYers can succeed on their first try.
Choosing the appropriate flux core for sheet metal
Always conscientiously choose the diameter of flux-cored wire you’re going to use, as well as the thickness of the sheet metal.
We recommend using a wire with the most compact diameter possible. The reason is simple. Smaller wires have a lower melting point, so less heat is required. More importantly, you can have more control over your welding project thanks to the lower deposition rate of smaller wires.
For new and DIY welders, deposition rate refers to the amount of wire converted into weld metal in a one-hour time frame of welding.
The I-CAR finds it appropriate to use 0.023-inch diameter wire when repairing autos, primarily composed of sheet metal. And a 0.030-inch wire like the Forney flux-cored welding wire is suitable for welding materials that are 18 gauge thick or 4.175 millimeters.
Gauge refers to the sheet metal thickness measurement. It’s not the standard of measurement for this material, but you will often hear or read it when you start searching about sheet metals. So learning about it will help a bit with your sheet metal welding project.
But if you want to choose the appropriate flux-cored wire quickly, you can use welding calculators to provide you an approximate diameter of the flux core you should use based on the thickness of the sheet metal you’re welding. One such web application is Miller Electric Manufacturing’s welding calculator.
How to weld sheet metal with flux core
We’ve now got the essential part of welding sheet metal with flux core covered. It’s time to deep dive into the steps.
Prepare your workpiece
Always start with cleaning your sheet metal, whether you’re working on new or used sheet metal. Doing so will help remove any contaminants that can negatively react with the weld and result in an ugly fabrication line.
Use a wire brush to scrub any debris from the workpiece. A grinder with a wire wheel is a better choice if the sheet metal has rust, paint, and oxides that can drastically reduce the quality of the weld.
To do the cleaning, secure the sheet metal on a workbench or a table with a C-clamp and start grinding the contaminants away.
Set up the metal
Make sure that you keep the metal pieces from going loose to avoid doubling your work.
Set up the sheet metal to the exact position you have in mind. Doing so will ensure that you will be able to weld the metal without any hitches. For small projects, guiding it with your hand may be enough.
Home repair shop owners can use portable jigs like the 3-Axis Set Screw to pin sheet metals together.
Adjust the welder to the proper settings
When you’re done setting everything up, it’s time to jump into welding.
Turn on your welder and adjust it to the appropriate settings. The following are three crucial welder settings or controls you should properly set up:
· Heat range
· Wire Feed Speed
· Gas Flow Rate/Gas Type or Mixture (for gas-shielded flux-cored wire)
For the heat range, keep it on or between Low-1 up to High-2. The wire speed should be between 7 to 9, depending on the thickness of the sheet metal. The thinner the metal, the lower these numbers are. The opposite holds for thicker metals.
If you’re using a gas-shielded flux-cored wire, regulate the gas to avoid the electric arc from heating more than necessary. Adjust the percentage of argon or helium accordingly to prevent the heat level from surging up.
Lastly, don’t forget to change the machine’s polarity from electrode negative (EN) to electrode positive (EP).
Weld the sheet metals
There are two techniques to weld sheet metals. It’s either by tack-welding or bead welding.
Depending on the project you are working on, tack-welding may be enough to hold the workpieces together.
To tack-weld, layer several tack welds on the sheet metal workpieces, preferably on the corners first. Tack-welding the metal first will allow you to hold and align each workpiece before the full-blown welding.
You don’t need to be particular with the size of tack welds. But essentially, you should consider the thickness and complexity of the sheet metals you’re welding.
For reference, tack welding is simply the process of conjoining certain parts of the workpieces to avoid the warping of the sheet metals due to the heat.
If your project needs to be more steadily connected, continue the welding processes with bead welding. Fill in the gaps in the workpieces until you cover every seam with beads.
Position the torch at a 10-degree angle, and run it on the workpiece at a consistent pace. Avoid speeding up or slowing down while welding to keep the weld fluid.
Remove spatter and slag
You’re going to experience some splatter when you weld sheet metal. But you can chip the slag away with a chipping hammer and wire brush.
If applicable, you can also grind the finished product on a speed bench grinder until each corner is seamless without holes and cracks. Weld the portions with visible holes and repeat the process from there on out.
To sum up everything
The age-old mantra “everything is unique” may seem cliche, but dismissing this statement can mean trouble, especially when you’re trying to weld sheet metal with flux core.
When welding sheet metal using flux core, everything can be a bit messy. Aside from splattering, there’s also the risk of warping, melt-through, and even holes. And they can all double the work you put in. How tedious would that be?
Luckily, you can minimize, if not prevent, some of them from happening.
Avoid whipping or wiping the wire and or rod with the puddle as this will create inconsistent results. Also, do not weave the torch because you risk overheating your piece, resulting in warping and burn-through.
Instead, run the torch continuously from the time it touches the sheet metal until you finish welding. Maintain a straight line and at a pace that will give a good bead profile.
To prevent burn-through, we suggest using the push technique in MIG welding. In this welding technique, you push the weld pool forward while welding, disabling deep heat penetration into sheet steel.
The result? The melted steel does not overflow to the other side of the sheet metal, which is the result we want.
And that’s how you weld a sheet metal with flux core.
