TIG Welding Aluminum
The TIG (Tungsten Inert Gas) arc welding process is used for welding the thinner sections of aluminum and aluminum alloys. There are several precautions that should be mentioned with respect to using this process.
Alternating current is recommended for general-purpose work since it provides the half-cycle of cleaning action. Table 7-22 provides welding procedure schedules for using the process on different thicknesses to produce different welds. AC welding, usually with high frequency, is widely used with manual and automatic applications. Procedures should be followed closely and special attention given to the type of tungsten electrode, size of welding nozzle, gas type, and gas flow rates. When manual welding, the arc length should be kept short and equal to the diameter of the electrode. The tungsten electrode should not protrude too far beyond the end of the nozzle. The tungsten electrode should be kept clean. If it does accidentally touch the molten metal, it must be redressed.
Welding power sources designed for the gas tungsten arc welding process should be used. The newer equipment provides for programming, pre-and post-flow of shielding gas, and pulsing.
For automatic or machine welding, direct current electrode negative (straight polarity) can be used. Cleaning must be extremely efficient, since there is no cathodic bombardment to assist. When dc electrode negative is used, extremely deep penetration and high speeds can be obtained. Table 7-23 lists welding procedure schedules for dc electrode negative welding.
The shielding gases for* TIG Welding Aluminum* are argon, helium, or a mixture of the two. Argon is used at a lower flow rate. Helium increases penetration, but a higher flow rate is required. When filler wire is used, it must be clean. Oxide not removed from the filler wire may include moisture that will produce polarity in the weld deposit.
TIG Welding Aluminum Joint Design
The joint designs shown in figure 7-11 are applicable to the gas tungsten-arc welding process with minor exceptions. Inexperienced welders who cannot maintain a very short arc may require a wider edge preparation, included angle, or joint spacing. Joints may be fused with this process without the addition of filler metal if the base metal alloy also makes a satisfactory filler alloy. Edge and corner welds are rapidly made without addition of filler metal and have a good appearance, but a very close fit is essential.
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