Basics for TIG Welding Aluminum As we strive to meet the demands of increasingly fast-paced industries, our focus on productivity can often overshadow some of the basic techniques necessary for our weldingapplication. Unknowingly, we may come to rely too much on technology to solve our problems and keep products moving out the door. Unfortunately, when we forget the basics, our equipment (no matter how advanced) can easily fall short of the job. Following is a discussion of good TIG welding practices for aluminum applications. These basics are applicable regardless of whetheryou use a conventional AC power source or power sources with squarewave or advanced squarewave capabilities. Knowing the basics of TIG welding aluminum is important no matter how advanced the equipment you use. Clean Aluminum is Good Aluminum Cleaning aluminum before TIG welding is essential to avoid contaminates, which can lead to lack of fusion, inclusions or porosity. Most TIG power sources provide good cleaning action during the EP (electrode positive) portion of the weld cycle, however, you should never rely solely on this cleaning action to do the job for you. Instead, first wipe the base metal with a cloth to remove dirt, oil or grease. This procedure, though outwardly simplistic, is absolutely necessary. Equally important is removing the oxides that naturally form on the aluminum. This procedure can be done mechanically, by using a scraping tool or a stainless steel wirebrush, or chemically, by applying an acidic solution designated for aluminum oxide removal. If you choose to remove the oxides mechanically, remember to designate the scraping tool or wire brush for that purpose only—using these tools for multiple jobs could cause contaminants to be introduced to the aluminum. Using a power brush is not recommended as it can also re-embed contaminants into themetal. Finally, if you are considering using the chemical method to remove oxides, consult your local welding distributor for the best product options. To prevent the drawing of contaminants from the backside of a joint, remember to clean both sides of the aluminum. Also be certain thatyou are using clean filler rods, as they too can contain dirt and/or oxides—clean the rods using a clean or new Scotch Bright ™ pad dedicated to the purpose. The Basics Remembering the following basics about shielding gases and tungsten can help you avoid problems when TIG welding aluminum. Gases: Pure argon offers the advantage of being more cost effective than helium and is a good, all-purpose gas that produces a focused, concentrated arc. Adding helium to your argon mixture can provide greater penetration when welding aluminum over 3/8-inch thick. It also increases your arc voltage from 13 to 18 volts (the range for argon) up to a range of 22 to 25 volts, thus increasing your overall power for a given amperage setting. For the infrequent welding of heavier aluminum, adding helium to gain voltage can be helpful; however, if you weld thicker aluminum on a regular basis, you should invest in a larger power supply. Finally, adding 3 to 5% percentage of helium can also stabilize your arc on low-end applications. To avoid contamination when TIG welding aluminum, clean both sides of the joint with a stainless steel brush designated solely for that purpose. Generally, pure helium is used for TIGwelding aluminum only in specialized applications or for DC aluminum welding. Helium is much more expense and requires good welding skills and exceptional cleanliness. Gas Flow: Bear in mind that setting your gas flow too high can lead to problems, including but not limited to porosity and/or pin holes. When using argon and/or an argon/helium mixture, set your gas flow between 5to 20 CFH (cubic feet per hour) for flatposition aluminum welding and at approximately 20 CFH for all other welding positions. When welding overhead, vertical or horizontal the addition of helium can also be beneficial because it is lighter that air and will float upward to protect the weld. Use approximately one second of pre-flow prior to welding aluminum and use one second of post-flow for every 15 amps with which you have been welding. Both pre- and post-flow help prevent tungsten and weld puddle contamination. Tungsten Style and Diameter: If you are using a conventional AC or squarewave power source, balled pure tungsten works well on aluminum applications that are above 100 amps. For example, 3/32 tungsten can be used up to 180 ampswithout problems. You can also use pointed zirconiated tungsten for 100-plus amp applications, but at even higher amperages than pure tungsten (a 3/32 zirconiated tungsten can be used up to 210 amps). For applications below 100 amps on thinner gauge aluminum (.005 to.093 inches), it is best to use 2% tungsten, ceriated or thoriated. Sharpening these tungstens to a point helps prevent distortion by better focusing the arc and also givesyou better control. If you are using anadvanced squarewave power source,a pointed 2% ceriated tungsten provides an especially focused arc and allows for the use of a smaller diameter for even greater arc control. Note: Thorium is radioactive; therefore, you must always follow manufacture’s warnings, instructions and the MSDS (Material Safety Data Sheet) for its use. Tungsten Extension: Regardless of the type of tungsten you use to TIG weld aluminum, remember that the tungsten should extend no more than the distance that equals the inside diameter (ID) of the nozzle. For example, a number eight nozzle is ½-inch across, so your electrode extension should not exceed ½ inch. Following this basic rule increases your visibility of the weld puddle andtungsten and reduces the possibility of touching the tungsten to the weld puddle. It also provides better weld puddle control. Other Considerations Also consider factors such as equipment, joint preparation and arc starting during the process of TIG welding aluminum. Equipment: Conventional AC sine wave, conventional square wave andadvanced square wave power sources are all acceptable for aluminum TIG welding, but you will need basic operator controls including: pre flow, post flow and high frequency arc starting capabilities. Your power supply should also be large enough to handle the amperage requirements of your application. Achieving quality TIG welds on aluminum, like the one shown here, is a matter of both skill and good welding practices. An air-cooled TIG torch will work well for aluminum applications under 200 amps or for fieldwork, but you should consider using water-cooled torch for welding above 200 amps or where torch size matters for comfort or limited access joints.
Posted on: Thu, 22 Aug 2013 23:31:10 +0000
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