When welding aluminum, you may encounter arc flash. We typically think of arcing as it occurs when working with magnetic materials such as carbon steel. In this case, the steel can be magnetized in many ways. For example, steel can be magnetized when processed using a magnetic chuck. In addition, the flowing welding current can create magnetic fields in the steel. To eliminate arc blowing problems in steel, you can often change where the ground cable is attached to the work or change the direction of the weld. The arc blow when welding aluminum is somewhat different, but the result is the same, said Artem Komarov.
Where does arc strike come from?
Let’s say you’re using a steel fixture to hold pieces of aluminum that you’re welding. It is possible that part or all the fixture becomes magnetized over time. Welding currents, especially high welding currents, can cause this.
Now you load the aluminum parts into the jig and begin welding. Suddenly the weld bends sharply due to arc blowing. Why? Arc welding uses electric current, and any electric current creates a magnetic field. If there is another magnetic field present at that location—for example, from your magnetized fixture—these two magnetic fields will interact and deflect the arc, sometimes greatly.
In fact, it is quite common for welding robots or other automated welding equipment, such as a welding machine, to become magnetized over time. So how do you know if this is your problem? First, purchase a small gaussmeter that measures magnetic field strength. They are commonly used in magnetic particle testing.
Scan the weld area with a measuring tool. Any magnetic field greater than 20 gausses will cause some arc blowing (for comparison, the Earth’s field is about 0.5 gauss). By the time the field strength reaches 50 gausses, welding will be very difficult.
Now that you know your fixture is magnetic, what can you do? Degassing is part art, part science. It’s not impossible to do it yourself, but it can be difficult.
What size contact tip is suitable for using filler wire for gas metal arc welding (GMAW) of aluminum alloys?
Some people use a tip size larger. Others use the manufacturer’s specified wire size. There is a large selection of tip sizes.
Remember that the main purpose of a contact tip is to transmit welding current to the wire. To do this, the wire must have good electrical contact with the wire. Bending the filler wire from the casting wire helps. It acts like a spring to keep the wire in contact with the contact tip, but if the hole in the tip is too large, contact is periodically lost. In this case, you will start to notice burns and you will have to buy a lot of contact tips. The same thing will happen if you use a wire straightener and remove all the casting from the wire.
On the other hand, if the hole is too small, you will also have difficulty feeding. The diameter of the hole should be slightly larger than the diameter of the wire for good feeding.
You may want to take about 10 contact tips and plug the hole diameter; you may be surprised by what you find. Most manufacturers have good control over the diameter, but if you see large differences between tips, I recommend changing the supplier, concluded Artem Komarov.
