Aluminiations(1): Shedding Light on Aluminum Welding Issues
May 1, 2007
For the last 20 years, anyone TIG welding aluminum or other alloys requiring an AC arc knew that a Squarewave™ output provided the best results. Today, though, the best results might come from an inverter-based AC/DC TIG welder that incorporates advanced Squarewave technology. To see if an inverter can improve weld quality, increase travel speed or reduce costs in your operation, read on.
In 1974, Miller Electric invented and patented the Squarewave AC output and balance control function found on their Syncrowave® series of TIG welders. Squarewave technology made the transition through the zero amperage range faster than a regular sine wave, which improved arc starts and created a more stable arc. With balance control, the operator could change the duration of the AC half cycle, adjusting the electrode negative (EN) from 45 to 68%.
Now Miller introduces the next generation of technology with their new AC TIG inverter, which features three advanced Squarewave capabilities. First, it produces incredibly smooth, stable arcs because the Squarewave is driven through the zero point thousands of times faster than a rectifier-based welder. Miller's Dynasty™ DX is so fast that its built-in high-frequency capabilities are used for arc starting only.
Second, inverter-based welders extend EN balance control. The Dynasty DX lets operators fine-tune duration times from 50 to 90%. Making the EN portion of the cycle last longer:
- Achieves greater penetration.
- Narrows the weld bead.
- May increase travel speeds up to 20%.
- May permit using a smaller diameter tungsten to more precisely direct the heat or make a narrower weld bead.
- Reduces the size of the etched zone for improved cosmetics.
Less EN time produces greater cleaning action to remove heavier oxidation, lessens penetration for work on thin materials and widens the bead profile.
Third, inverter-based welders let operators adjust the welding output frequency, from 20 to 250 Hz in the case of the Dynasty DX. Conventional welders have a fixed output of 60 Hz. Lowering the frequency produces a broader arc cone, which widens the weld bead profile and better removes impurities from the surface of the metal. Increasing frequency above 60 Hz produces a tight, focused arc cone. This drives more heat into the weldment for better penetration, and it narrows the weld bead, which helps when welding in corners, on root passes and fillet welds.
Note that when AC TIG welding with an inverter, the operator should treat the tungsten as if the weld were being made in the DC mode: select a 2%-type tungsten (thorium, cerium, etc.) and grind the electrode to a point. Electricity likes to come off a point, which further improves controlling the weld puddle. For example, a skilled welder can make a 1/8 in. fillet weld on 1/8 in. aluminum plate with a pointed electrode.
For more information on the Dynasty DX, AC TIG welding, or a free copy of our White Paper, "New controls for AC TIG welders," call 1-800-4-A-MILLER (1-800-426-4553, ext. 602).
Questions & Answers
Q. I've heard that inverters let me adjust the arc to stay in the electrode negative mode for up to 90% of the AC cycle. Can this really improve my travel speed?
A. Absolutely. You can increase travel speed, get better penetration or both because inverters let you direct about 25% more heat into the weldment in the same amount of time. When welding at 100 amps, an inverter like the Dynasty™ DX essentially gives you 125 amps of welding power.
Q. I don't have much room in the shop, and my incoming power is at capacity. Would an inverter be a good solution?
A. Yes. For example, the Dynasty DX has a footprint of 17 in. x 12.5 in. x 24 in. and weighs only 90 lb. Even better, it draws just 26.3 amps of 230 V three-phase primary power to create a 250 amp Squarewave output. A conventional Squarewave machine, which only accepts single-phase power, draws 92 amps on the primary side.
Q. Why do inverters have an "adjustable output frequency" function?
A. Increasing the output frequency (which conventional machines cannot do) creates a tighter and more focused arc cone, directing the heat into a smaller area. In fact, you can get better penetration and reduce the size of the weld profile. This may let you increase travel speed, use less filler metal and reduce or eliminate pre-heating, pre-weld beveling and post-weld grinding.
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.