September 11, 2007
Q:I'm fabricating toolboxes for pickup trucks using gas metal arc welding (GMAW) and polished aluminum tread plate. The cleaning stripes along each side of the weld are wide and detract from the appearance of the toolbox. Please don't tell me to wire-brush the weld because this stands out even worse. Is there anything I can do to eliminate or minimize the cleaning stripes?
A: Well, you don't want to eliminate the cleaning stripes. You need some arc cleaning from the electrode-positive GMAW arc to remove the oxide from the surface of the aluminum while welding. However, there are some things you can do to minimize their width while still maintaining adequate cleaning.
In general, you want to minimize the width of the weld. I would recommend using 0.035-inch wire on the thin sheet (1⁄8 in. or so) usually used for fabricating toolboxes. Next, you should use a smaller gas nozzle than normal, say, 3⁄8 in. ID. It is important to keep the arc length short so the contact-tip-to-work distance must be no more than 1⁄2 in. Also, try reducing the arc voltage. You still need to stay in spray transfer mode, but you should adjust the arc voltage until the sharp crackle just goes away, and no further. Last, consider turning down the flow rate of the shielding gas to 25 to 30 SCFH. With the smaller gas nozzle, you should be able to do this and still have adequate shielding gas.
Your situation isn't all that uncommon. You don't say what type of power supply you are using, but if you are using a programmable pulsing power supply, I suggest you contact your power supply manufacturer. Some of these power supplies can use pulsed waveforms specifically designed to minimize the cleaning stripes.
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