It looks like you’d better get ready to pay up. It is possible to encounter arc blow when welding aluminum. We usually think of arc blow occurring with magnetic materials such as carbon steels. In this case, the steel can be magnetized in many ways. For instance, the steel can be magnetized when you machine it with a magnetic chuck. Additionally, the flowing welding current can induce magnetic fields in the steel. To attack arc blow problems in steel, you often can change the location where the ground cable is attached to the piece and/or change the direction of welding.
Arc blow in aluminum welding is somewhat different, but the end result is the same. You’re right: aluminum alloys are nonmagnetic and can’t be made to become magnetic. So where does the arc blow come from?
Let’s assume you’re using a steel fixture to hold the pieces of aluminum you’re welding. It’s possible that part or all of the fixture has become magnetic over time. Welding currents, especially high welding currents, can cause this to happen.
Now you load the aluminum pieces into the fixture and begin to weld. Suddenly the weld deflects sharply due to arc blow. Why? Arc welding uses a flowing current, and any flowing current produces a magnetic field. If another magnetic field is present in the area—for instance, from your magnetized fixture—the two magnetic fields will interact and deflect the arc, sometimes strongly.
It’s actually fairly common for robotic welding fixtures or other automated welding fixtures, such as a weld seamer, to become magnetic over time. So how do you know if this is your problem? First, purchase a small gaussmeter, which measures magnetic field strength. These commonly are used in magnetic particle testing. A number of sources for gaussmeters can be found on the Internet.
Scan the weld area with the meter. Any magnetic field over 20 gauss will cause some arc blow (by comparison, the Earth’s field is about 0.5 gauss). By the time the field strength reaches 50 gauss, welding will be very difficult.
Now that you know your fixture is magnetic, what can you do? Deguassing is part art, part science. It’s not impossible to do it yourself, but it can be difficult. Several companies specialize in degaussing, which you also can find on the Internet.
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