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Aluminations (5): Shedding Light on Aluminum Welding Issues

When you control the shape of an AC TIG weld bead, you control profitability. The perfect bead takes less time to weld and looks great without grinding or polishing. This Aluminations explains how balance control and output frequency affect penetration depth, bead width, etched zones - and your bottom line.

An AC/DC TIG inverter fine tunes the weld bead profile by controlling arc cone shape and arc force. Think of an inverter like adding a nozzle to a fire hose; it lets you change the shape and force of the "water" (welding current) from a wide fan to a more focused stream. But instead of turning a nozzle, you adjust balance control and output frequency.

Balance control adjusts the ratio of electrode positive (EP) to electrode negative (EN). During EN, the welding current travels from the tungsten to the work. Increasing EN duration better defines arc cone and directs more heat into the work. This creates deeper penetration, a smaller bead and pulls the etched zone closer to the weld bead. Compared to conventional machines, inverters let you add about 25% more heat into the work in the same amount of time. This increases penetration per amp of welding power.

EP does not create a well-defined arc cone because the electricity wanders slightly while it searches for the path to the tungsten. Adding more EP provides shallower penetration, a wider bead, more cleaning and a bigger etched zone.

Frequency and Fillet Welds

Frequency, or Hz, is the number of times the arc switches between EP and EN in one second. The Dynasty permits adjusting output frequency from 20 to 250 Hz. Conventional TIG machines have a frequency fixed to that of the primary power (e.g., 60 Hz). Frequencies below 60 Hz transfer more energy into the work and create a wider bead with decent penetration - an ideal combination for build-up work or to catch both edges of an outside corner while maintaining travel speed.

Increasing the frequency ("constricting the nozzle") narrows the shape of the arc cone and increases the arc force. This stabilizes the arc, reduces arc wandering and provides excellent directional control over the arc (in fact, it might remind you of the DC arc used on steel). On lap and T-joints, using a higher frequency lets you establish the weld puddle exactly at the root. This can ensure good penetration, control bead width and minimize the etched zone. With a 60 Hz output on fillet welds, the wider arc dances from plate to plate. The puddle starts at the toes of the weld and flows toward the center; on some joints, you're almost compelled to over-weld to ensure penetration at the root.

For a free technical article on how TIG inverter technology helps solve welding challenges, call 1-800-4-A-MILLER (1-800-426-4553) or visit www.MillerWelds.com

Questions & Answers

Q: How can I weld thinner materials or small parts without burning through?
A. Using an inverter, select a pointed tungsten and weld with an output frequency of 80 to 120 Hz. This narrows the arc cone so you can direct the arc right where you want it. You can establish the weld puddle faster and precisely place the filler wire. This helps prevent the burn-through and/or warping that you might experience with a conventional TIG welder and a balled tungsten.

Q: How can I tell if I'm over-welding?
A. Excessive bead width can be one indication. For example, a fillet weld has a triangular shape. Assuming good penetration, the longest "leg" should be no longer than the thinnest plate. When joining 1/8 in. to 1/4 in. plate, you only need a 1/8 in. bead. Any wider and you lose travel speed and waste filler wire and gas; the bead may also require post-weld grinding.

Q: Experience tells me that I need to overweld for good penetration. How can I ensure penetration with a narrow bead?
A. If you've only used a conventional AC TIG machine, the need to over-weld is understandable. You have very limited control over bead shape. For precisely tailoring bead width and penetration ratios, use a TIG inverter like the Dynasty™ 300 DX. It permits increasing output frequency and extending balance control which, respectively, narrows the bead and directs more heat into the weldment for deeper penetration.

View Online Arc Shaping Videos

Frequency, or Hz, is the number of times the AC TIG arc switches between electrode negative and electrode positive in one second. Miller's Dynasty™ 300 DX inverter-based TIG power source permits adjusting output frequency from 20 to 250 Hz. Conventional TIG machines have a frequency fixed to that of the 60 Hz primary power.

Increasing the frequency narrows the shape of the arc cone and increases the arc force. This stabilizes the arc, reduces arc wandering and provides excellent directional control over the arc. On lap and T-joints, using a higher frequency lets you establish the weld puddle exactly at the root (view 200 Hz arc shaping video). This can ensure good penetration, control bead width and minimize the etched zone. With a 60 Hz output on fillet welds, the wider arc dances from plate to plate. The puddle starts at the toes of the weld and flows toward the center (view 60 Hz video). On some joints, you're almost compelled to over-weld to ensure penetration at the root.

Other Aluminations Articles

Issue 1 - See if an inverter-based AC/DC TIG machine that incorporates advanced Squarewave technology can improve your operation.
Issue 2 - How to TIG weld thin aluminum, adjust balance control and determine amperage requirements.
Issue 3 - New push-pull feeder technology improves MIG welding.
Issue 4 - Why you should consider pulsed MIG for your aluminum welding jobs.
Issue 5 - When you control the shape of an AC TIG weld bead, you control profitability.

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